Arthur Gavotto1

Vincent Dubard

Martina Avesani

Helena Huguet

Marie-Christine Pico

Hamouda Abassi

Sophie Guillaumont1

Gregoire De

La Villeon

Stephanie Haouy

Nicolas Sirvent

Anne Sirvent

Alexandre Theron

Anne Requirand

Stefan Matecki

Pascal Amedro
email: pascal.amedro@chu-bordeaux.fr

Impaired aerobic capacity in adolescents and young adults after treatment for cancer or non-malignant haematological disease

Keywords:

IMPACT:

• In childhood cancer survivors, aerobic capacity is five times more impaired than in healthy subjects.

• This impairment mostly reflects early onset of physical deconditioning.

• No evidence of heart failure was observed in this population.

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PURPOSE:

Childhood cancer survivors are at increased risk for cardiovascular disease. Maximal oxygen uptake (VO 2max ) is a major determinant of cardiovascular morbidity. The aim of this study was to compare aerobic capacity, measured by cardiopulmonary exercise test (CPET), of adolescents and young adults in remission with that of healthy controls and to identify the predictors of aerobic capacity in this population.

METHOD:

This is a controlled cross-sectional study.

RESULTS:

A total of 477 subjects (77 in remission and 400 controls), aged from 6 to 25 years, were included, with a mean delay between end of treatment and CPET of 2.9 ± 2.3 years in the remission group. In this group, the mean VO 2max was significantly lower than in controls (37.3 ± 7.6 vs. 43.3 ± 13.1 mL/kg/min, P < 0.01, respectively), without any clinical or echocardiographic evidence of heart failure. The VAT was significantly lower in the remission group (26.9 ± 6.0 mL/kg/min vs. 31.0 ± 9.9 mL/kg/min, P < 0.01, respectively). A lower VO 2max was associated with female sex, older age, higher BMI, radiotherapy, and hematopoietic stem cell transplantation.

CONCLUSION:

Impaired aerobic capacity had a higher prevalence in adolescents and young adults in cancer remission. This impairment was primarily related to physical deconditioning and not to heart failure.

INTRODUCTION

Cancer affects around 1 in 4000 children and is the leading cause of death in children over one year of age, with 6000 deaths per year in Europe, according to the International Agency for Research on Cancer. However, thanks to the dissemination of multimodal therapeutic strategies to paediatric oncology, the 5-year remission rates currently exceed 85%.1 As a result, it is nowadays more about 'living rather than surviving' after childhood cancer. Therefore, improving the quality of life after childhood cancer must now consider, from paediatric age, the reduction in morbidity. Indeed, childhood cancer survivors remain at high risk for obesity,2 diabetes mellitus,3 and cardiovascular disease as adults.4-6 Furthermore, some anticancer therapies are cardiotoxic, such as radiotherapy or chemotherapy using anthracyclines, resulting in a 5% incidence of heart failure related to dilated or restrictive cardiomyopathy in adulthood.7-9 Young patients with non-malignant haematological disease requiring a hematopoietic stem cell transplantation are also affected by cardiovascular complications. Overall, the mortality from cardiovascular disease in adults after childhood cancer would be seven times higher than that of the general population.10 Nevertheless; early predictors of cardiovascular morbidity in childhood cancer survivors have not been clearly identified. Recent studies have suggested using aerobic capacity to promote physical activity and induce a preventive action for long-term adverse health outcomes in childhood cancer survivors .11,12 In adult cancer, aerobic capacity has shown a strong, graded, and inverse association with total cancer mortality.13 Moreover, in the general population, the maximum oxygen uptake (VO 2max) is a strong surrogate of physical capacity, which stands as a major and independent predictor of cardiovascular risk.14 In many paediatric chronic diseases, impaired physical capacity assessed by cardiopulmonary exercise test (CPET), correlates with lower health-related quality of life scores, and may indicate early onset of physical deconditioning, such as in congenital heart disease, cystic fibrosis, or kidney disease. [START_REF] Amedro | Correlation between cardio-pulmonary exercise test variables and health-related quality of life among children with congenital heart diseases[END_REF][START_REF] Amedro | Cardiopulmonary fitness in children with congenital heart diseases versus healthy children[END_REF][START_REF] Klijn | Longitudinal determinants of peak aerobic performance in children with cystic fibrosis[END_REF][START_REF] Goldstein | Physical fitness in children with end-stage renal disease[END_REF] Despite previous studies reporting the feasibility and interest of aerobic capacity assessment in cancer surveillance, routine CPET in clinical practice has not been widely disseminated in the paediatric population.19,20 Moreover, the level of aerobic capacity in adolescents and young adults after childhood cancer survivors has been scarcely reported.21,22 Thus, we planned to compare the aerobic capacity of a cohort of adolescents and young adults treated for cancer or transplanted for non-malignant haematological diseases during childhood, to that of age-and sex-matched healthy controls. In this specific population, we also intended to identify the predictors of the aerobic capacity.

METHODS

Study design and patient population

This cross-sectional controlled study was carried out from November 2010 to November 2020 in a tertiary care paediatric centre (Montpellier University Hospital, France).

Adolescents and young adults aged 6-25 years were screened during a regular outpatient visit in one of the participating centres. Two groups were identified: adolescents and young adults in complete remission after treatment for cancer or transplanted for non-malignant haematological disease during young age (i.e., the 'remission group'), and the control subjects. Subjects from both groups were enrolled during the same period.

(1) The 'remission group' consisted of patients treated for paediatric cancer by chemotherapy, radiotherapy and/or hematopoietic graft, as well as patients with non-malignant paediatric haematological disease requiring a hematopoietic stem cells transplantation (before the age of 25 years). To be eligible for the study, all patients from this group needed to be in complete remission at the time CPET was performed. Patients with the following medical conditions were screened from our CPET database: haematological malignancies (acute lymphoblastic or myeloblastic leukaemia and Hodgkin or non-Hodgkin lymphoma), solid tumours, and nonmalignant haematological diseases treated with a hematopoietic stem cells transplantation (Wiskott-Aldrich syndrome, thalassemia, and medullar aplasia). The following patient characteristics were collected from electronic health records: age at diagnosis, type of treatment (chemotherapy, radiotherapy, corticosteroids, autologous or allogeneic hematopoietic stem cell transplantation), and overall length of hospital stay.

The following clinical data were systematically collected when the CPET was performed: sex, age, weight, height, body mass index (BMI), heart failure functional class (NYHA), and echocardiographic assessment of left ventricle ejection fraction (LVEF).

(2) The control group consisted of children referred for a non-severe functional symptom linked to exercise (murmur, palpitation, or dyspnoea) or for a medical sports certificate. As in our similar controlled CPET studies, these subjects were classified into the control group only after a completely normal check-up, including physical examination, electrocardiogram, echocardiography, and spirometry.16,23,24

CPET procedure

The CPET laboratory used the following equipment: paediatric face masks (Hans Rudolph, Shawnee, KS), a calibrated gas analyser (Quark CPET, Cosmed Srl, Pavonna di Albano, Italy), breath-to-breath measurement software (Windows 7-10, Omnia, Cosmed), 12-lead ECG equipment (Norav, Medical, Mainz-Kastel, Germany) and pulse oxymeter (Nonin Medical Inc, Plymouth, MN), and a manual sphygmomanometer with adapted paediatric cuffs. Spirometry using a common gas device (Oxycon Pro, Jaeger, Erich Jaeger GmbH, Hoechberg, Germany).

A spirometry was systematically performed before the exercise test. From the flow volume curve, forced expiratory volume in 1 s (FEV1), forced ventilatory capacity (FVC) and Tiffeneau index (FEV1/FVC) were recorded and expressed as Z-scores using the reference spirometry equations. [START_REF] Quanjer | Multi-ethnic reference values for spirometry for the 3-95-yr age range: the global lung function 2012 equations[END_REF] The CPET paediatric cycle ergometer protocol oversaw a homogeneous incremental overall duration between 8 and 12 min: a 1-min rest; a 3-min warm-up (10-20 watts) in increments of 10, 15, or 20 watts each minute; a pedalling rate of 60-80 revolutions per minute; a 3-min active recovery (20 watts); and a 2-min rest. [START_REF] Amedro | Cardiopulmonary fitness in children with congenital heart diseases versus healthy children[END_REF][START_REF] Gavotto | Oxygen uptake efficiency slope: a reliable surrogate parameter for exercise capacity in healthy and cardiac children?[END_REF][START_REF] Gavotto | The V ̇e/V ̇co2 slope: a useful tool to evaluate the physiological status of children with congenital heart disease[END_REF] In this study, the level of aerobic capacity was determined by the VO2max and the ventilatory anaerobic threshold (VAT). VO 2max and VAT values were normalised in a percentage of the predicted VO2max using normal values from Wasserman and Cooper. [START_REF] Cooper | Aerobic parameters of exercise as a function of body size during growth in children[END_REF] The CPET was considered as maximal when two out of the following four criteria were reached: respiratory exchange ratio (RER=VCO 2 /VO 2 ) ≥1.1, maximum heart rate >80% of maximal age predicted heart rate, limit of the child's tolerance despite verbal encouragement, and plateau of VO 2 (VO 2max ) despite the increasing exercise intensity.16 When the VO2max did not reach a plateau, the peak VO 2 (VO 2peak ) was informed, as usual in paediatrics.27,28 A VO 2max < 80% of predicted values indicated impaired aerobic capacity. [START_REF] Blais | A systematic review of reference values in pediatric cardiopulmonary exercise testing[END_REF] The VAT was measured using the V-slope method.30 A VAT < 55% of predicted VO2max values was in favour of physical deconditioning. [START_REF] Amedro | Cardiopulmonary fitness in children with congenital heart diseases versus healthy children[END_REF][START_REF] Stephens | Exercise testing in pediatrics[END_REF] The ventilatory efficiency (VE/VCO 2 slope), i.e., a submaximal CPET surrogate of heart failure severity, was calculated from breath-by-breath data and determined using linear regression of minute ventilation (VE) and CO 2 production (VCO 2 ) obtained during incremental exercise. [START_REF] Paolillo | Heart failure prognosis over time: how the prognostic role of oxygen consumption and ventilatory efficiency during exercise has changed in the last 20 years[END_REF] The VE/VCO 2 slope was measured from the beginning of incremental exercise (after the warm-up period) to maximum exercise. [START_REF] Amedro | Cardiopulmonary fitness in children with congenital heart diseases versus healthy children[END_REF][START_REF] Gavotto | The V ̇e/V ̇co2 slope: a useful tool to evaluate the physiological status of children with congenital heart disease[END_REF] The oxygen uptake efficiency slope (OUES), i.e., a submaximal CPET surrogate of aerobic fitness, was derived from the logarithmic relation between VO2 and VE during incremental exercise, reflecting oxygen transport response to muscular oxygen consumption's increase. The OUES being influenced by anthropometric variables, we used the weight-normalised OUES kg value. [START_REF] Gavotto | Oxygen uptake efficiency slope: a reliable surrogate parameter for exercise capacity in healthy and cardiac children?[END_REF] From the Fick equation, the oxygen pulse (O2 pulse), i.e., the ratio between VO 2 and heart rate, was measured as an indicator of the systolic volume (SV), and, indirectly, of the left ventricular performance. The following CPET respiratory variables at maximal exercise were also collected: partial pressure of end tidal CO 2 (PetCO 2 ), tidal volume (Vt), breathing reserve (BR) and respiratory rate (RR).

Statistical analysis

The study population was described with means and standard deviations (SD) for quantitative variables, and with numbers and percentages for qualitative ones. The continuous variables distributions were tested using the Shapiro-Wilk test. Quantitative variables were compared using Student's t-test when the distribution was Gaussian and with the Mann-Whitney test, otherwise. For qualitative variables, groups were compared using the χ2 test or Fisher's exact test.

For the remission group, age-and sex-matched control comparisons were performed. For a given case, all the controls with the same sex and age (exact year of age) were matched. The case with his (or her) matched controls was considered as a cluster. Therefore, to compare CPET parameters between the two groups, mixed models were performed in which the clusters were introduced as a random effect and BMI as a fixed effect.

A multiple linear regression was used to identify the explanatory factors for VO 2max and VAT in the remission group. All clinically relevant variables were proposed. The best method to select variables was determined using leave-one-out cross-validation (LOO). Finally, a forward selection based on the corrected Akaike Information Criterion was applied. No collinearity between variables was detected with variance inflation factors. The normality of residues in the final model was tested using the Shapiro-Wilk test.

The statistical significance was set at 0.05 and analyses were performed using the software SAS Enterprise Guide, version 7.13 (SAS Institute, Cary, NC).

Formal aspects

The study was conducted in compliance with the Good Clinical Practices protocol and Declaration of Helsinki principles. It was approved by the institutional review board of Montpellier university hospital (IRB-MTP-2020-02-202000335) and registered on ClinicalTrials.gov (NCT04815447). Informed consent was obtained from all parents or legal guardians.

RESULTS

Population

During the 10-year study period, 477 patients were included, of which 77 in the remission group and 400 in the control group. No patient or legal guardian refused to participate. Adolescents and young adults in the remission group had a higher BMI than healthy matched controls (19.7 ± 4.0 vs. 18.3 ± 2.8 kg/m2, P < 0.01, respectively) and were also older (14.8 ± 4.9 vs. 11.5 ± 2.5 years, P < 0.01, respectively).

In the remission group, the median age at diagnosis was 10.3 [0-23] years and the mean delay between end of treatment and CPET assessment was 2.9 ± 2.3 years. By order of frequency, the patients referred to the CPET laboratory and enrolled in the study were affected by the following medical conditions: haematological malignancies (78%), non-malignant haematological diseases (16%) such as Wiskott-Aldrich syndrome, primitive medullar aplasia, or thalassemia, and solid tumours (6%). Hematopoietic stem cell transplantation was performed in 52 (68%) patients, with one (N=43) or two (N=9) transplantations, either allogeneic (N=53) or autologous (N=8). A total of 32 (42%) patients had previously undergone radiotherapy, with total body irradiation for 21 (27%) subjects. In terms of drug treatments, most patients received corticosteroids (60%) and anthracyclines (82%). Overall, the median length of hospital stay was 103 [0-495] days. All patients had a normal cardiac function as assessed by the NYHA functional class and LVEF (Table 1).

CPET results

No CPET-related adverse events were observed. Both groups were similar in terms of Tiffeneau ratio, peak heart rate, and percentage of peak heart rate. In the remission group, the FEV1, FVC, and maximum load were lower than in healthy matched subjects, and the RER was higher. In the control group, the mean VO 2max was normal (43.3 ± 13.1 mL/kg/min), representing 105.2 ± 19.5% of the predicted values (Table 2).

In the remission group, the mean level of VO2max was good, overall (37.3 ± 7.6 mL/kg/min), and in percent-predicts (89.7 ± 16.4%), but was significantly lower than that of healthy controls, with a magnitude of the difference of 6 mL/kg/min (P < 0.01) (Fig. 1a and Table 2). The proportion of subjects with an impaired VO 2max was 5.4 times more important in the remission group than in matched healthy controls (38% vs. 7%, P < 0.01, respectively). No significant VO 2max difference was observed between non-malignant and malignant cancers (88.1 ± 17.0 mL/kg/min vs 84.6 ± 23.7 mL/kg/min, P = 0.31, respectively).

The VAT was significantly lower in the remission group, overall (26.9 ± 6.0 mL/kg/min vs. 31.0 ± 9.9 mL/kg/min, P < 0.01, respectively) and in percent-predicts (64.9 ± 13.6% vs. 75.8 ± 18.4%, P < 0.01) (Fig. 1b and Table 2). The proportion of patients with a decreased VAT was five times more important in the remission group than in matched healthy controls (35% vs. 7%, P < 0.01).

Moreover, in the remission group, the OUES and the oxygen pulse were significantly lower and the VE/VCO 2 slope was significantly higher, than in healthy subjects (Table 2).

No significant difference was observed for the other ventilatory = parameters at maximum exercise (PetCO 2 , Vt, BR, and RR).

Predictors of VO 2max and VAT in the remission group (Table 3)

In both univariate and multivariate analyses, a lower VO 2max in the remission group was associated with female sex, higher BMI, and previous treatment with radiotherapy (regardless the site) or hematopoietic stem cells transplantation. The final multivariate model explained 47% of the VO 2max variability in the remission group.

In both univariate and the multivariate analyses, a lower VAT in the remission group was associated with female sex, older age, higher BMI, and previous treatment with hematopoietic stem cell transplantation. The final multivariate model explained 43% of the VAT variability in the remission group.

DISCUSSION

This controlled cross-sectional study on 477 subjects showed that aerobic capacity was decreased in adolescents and young adults treated for cancer or non-malignant haematological disease during childhood, in comparison with healthy matched controls and despite the absence of any clinical or echocardiographic evidence of heart failure. Moreover, the decrease in physical capacity was associated with female sex, higher BMI, and previous treatment with radiotherapy or hematopoietic stem cell transplantation.

The physical aerobic capacity in the examined population was overall good, with mean VO 2max values reaching nearly 90% of the predicted values. This level of VO 2max and the absence of any heart failure reflect good cardiopulmonary fitness in the young population in remission. This result seems to be in contrast with few data previously published.22,33-36 However, factors such as the short distance from the end of cancer therapy,33,34 the inclusion of older population samples,34 or the use of different techniques to assess exercise capacity35 might have influenced those results. Nevertheless, the magnitude of the difference in VO 2max in our cohort was clinically relevant, being 6 mL/kg/min lower in the remission group in comparison with healthy matched controls. Of note, in the general population, a VO 2max decrease superior to 3.5 mL/kg/min (1-MET) is a predictor of all-cause mortality and cardiovascular events in healthy men and women.14 Moreover, nearly 40% of the young patients in remission enrolled in this study had an impaired VO 2max , which is higher than our previous results in paediatric asthma (24%)37 and congenital heart disease (25%). [START_REF] Amedro | Cardiopulmonary fitness in children with congenital heart diseases versus healthy children[END_REF] This result represents a strong alert, considering that childhood cancer survivors are at high risk for premature cardiovascular disease.10 Indeed, a recent review on impairments of cardiopulmonary fitness level in previous childhood cancer reported poor levels of physical capacity in this population, despite limited number of high-quality studies on this subject. [START_REF] Yildiz Kabak | Short and longterm impairments of cardiopulmonary fitness level in previous childhood cancer cases: a systematic review[END_REF] Lastly, this study found significant differences in VAT, suggesting an early entry of young childhood cancer survivors into the vicious circle of muscular deconditioning. Despite good overall values, the VAT was decreased in the remission group by 4.1 mL/kg/min, and this magnitude of discrepancy is close to the 4.6 mL/kg/min difference previously reported. [START_REF] Sato | Cardiorespiratory exercise capacity and its relation to a new Doppler index in children previously treated with anthracycline[END_REF] Moreover, the proportion of patients with abnormal VAT (37%) was similar to the one of patients with abnormal VO 2max (38%). This deconditioning is probably multifactorial, involving the lack of physical activity in the paediatric population,39 the change in body composition during the first year of chemotherapy,40 with fatty mass increase and muscle mass decrease, as well as the alteration of aerobic muscular fibbers by corticosteroids. [START_REF] Hoffman | Deficits in physical function among young childhood cancer survivors[END_REF] The VAT is a submaximal CPET parameter which reflects muscular conditioning and provides additional value to VO 2max in cancer survivors. [START_REF] Schneider | Exercise intensity prescription in cancer survivors: ventilatory and lactate thresholds are useful submaximal alternatives to VO2peak[END_REF] The VAT commonly strongly correlates to VO 2max 16 and, in our study, the predictors of VAT and VO 2max were interestingly almost the same. While sex, age and therapies received are unmodifiable factors, preventive actions such as cardiac rehabilitation programmes can help in controlling BMI43 and avoiding overweight/ obesity which, in turn, is responsible for scarce physical activity. [START_REF] Schindera | Physical fitness and modifiable cardiovascular disease risk factors in survivors of childhood cancer: a report from the SURfit study[END_REF] Overall, the decreased exercise capacity was most apparent in decreased workload and decreased oxygen pulse with no change in peak heart rate and comparable efforts as measured by peak RER. Moreover, the severity of decreased exercise tolerance in this study seemed limited, and at a level where most patients would not be aware of it daily. Further studies remain necessary to precisely determine why childhood cancer survivors have a deconditioning over the treatment and recovery period, and subclinical consequences of therapy (such as chest radiation and anthracyclines) on cardiac performance.45,46 Our results seem to support both systematic evaluation of long-term cancer survivors and systematic fitness or rehabilitation programmes, which have the potential to shift the long-term trajectory of exercise capacity.43

Study limitation

In this cross-sectional observational study, the paediatric oncologists may have referred the most severe patients for CPET assessment, and further prospective studies are necessary to determine the aerobic capacity in larger and more heterogeneous cohorts. Moreover, this study did not precisely identify the mechanisms behind the decline in physical capacity (cardiotoxicity, type of cancer, level of physical activity, muscle function, etc.) in childhood cancer survivors.

The control group was recruited at the hospital and may not be considered as healthy as if they were recruited from the general population.

Physical capacity has been estimated by CPET parameters, but data on muscular function (handgrip), physical activity (fitness tracker) or patient-reported outcomes (health-related quality of life) have not been collected.

CONCLUSION

Adolescents and young adults treated for oncologic or nonmalignant disease by chemotherapy, radiotherapy, and/or hematopoietic stem cell transplantation, have lower aerobic capacity compared to matched controls. Female sex, older age, higher BMI, radiotherapy, and hematopoietic stem cell transplantation are associated with a lower VO 2max . The absence of any evidence of heart failure in this population and the association with a low VAT suggest that physical deconditioning plays an important role in determining this impairment. The early screening of aerobic capacity could improve supportive care in addressing patients with impaired cardiopulmonary fitness to cardiac rehabilitation programs.

DATA AVAILABILITY

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

AUTHOR CONTRIBUTIONS

Study conception and

COMPETING INTERESTS

The authors declare no competing interests.

ADDITIONAL INFORMATION

Correspondence and requests for materials should be addressed to Pascal Amedro.


Kevin W Southern

Carlo Castellani

Elise Lammertyn

Alan Smyth

Donald Vandevanter

Silke Van Koningsbruggen-Rietschel

Jürg Barben

Amanda Bevan

Edwin Brokaar

Sarah Collins

Amanda Bevani

Gary J Connett

Thomas W V Daniels

Jane Davies

Dimitri Declercq

Silvia Gartnerp

Andrea Gramegnaq

Naomi Hamiltonr

Jenny Hauser

Nataliya Kashirskaya

Laurence Kessler

Jacqueline Lowdon

Halyna Makukh

Clémence Martin

Lisa Morrison

Dilip Nazareth

Jacquelien Noordhoek Aa

Ciaran O'neill Bb

Elizabeth Owen

Helen Oxley Dd

Karen S Raraigh Ee

Caroline Raynal Ff

Karen Robinson

Jobst Roehmel

Carsten Schwarz

Isabelle Sermet Jj

Michal Shteinberg Kk

Ian Sinha Ll

Constance Takawira

Peter Van Mourik

Marieke Verkleij

Michael D Waller Oo

Alistair Duff

Standards of care for CFTR variant-specific therapy (including

Keywords: CFTR, Cystic fibrosis transmembrane conductance regulator; VST, Variant-specific therapy Cystic fibrosis CFTR Variant-specific therapy CFTR modulators Guidelines

Introduction

Background

The European Cystic Fibrosis Society (ECFS) defines standards of care for cystic fibrosis (CF). The last update [START_REF] Castellani | ECFS best practice guidelines: the 2018 revision[END_REF] , whilst comprehensive, did not include standards for the provision of variant-specific therapy (VST) that has emerged over the past decade and rep-resents a significant treatment for many people with CF (pwCF). CF is a result of disease-causing variants affecting the CF Trans-membrane Conductance Regulator ( CFTR ) gene. VST for CF is a new class of drug, of which CFTR modulators are the first agents li-cenced to treat the basic defect. A VST is a systemic agent, generally taken orally, that corrects the molecular defect arising from the pathogenic CFTR gene variant. These agents are distinct from genetic therapies (DNA, RNA) or therapies that treat the clinical sequelae of CFTR disease (e.g., antibiotics, dornase alfa). VST results in greater CFTR quantity and/or function. Several different terms are used to describe VST, to some degree reflecting the mechanism of action ( Table 1 ). In this paper we provide evidence-based guidance for pwCF and their healthcare workers regarding variant-specific therapy. We consider the different challenges of these therapies and provide statements to guide pwCF, CF teams and policymakers ( Table 2 ).

Methods

This guidance was completed without support or funding from the pharmaceutical industry. Conflicts of interest of contributors are described completely and the process was undertaken with transparency (Supplementary Table 1).

A core author group (KS, CC, EL, AS, DV, SvK) was selected by the ECFS Standards of Care Committee, who defined the outline of the paper. Three to four contributing authors were selected by the ECFS Standards of Care Committee and invited to write each section. Their contributions were reviewed internally by the core author group and the ECFS Board. The process was undertaken in partnership with the CF Cochrane Review Group and systematic reviews were prioritized when available to inform the guidance (see www.cochrane.org/ for detailed methodology). Sections were reviewed internally by the core group and changes incorporated. The section authors also generated statements ( Table 2 ) which were reviewed by a wider group of stakeholders using a modified Delphi methodology [START_REF] Munck | Cystic Fibrosis Screen Positive, Inconclusive Diagnosis (CFSPID): a new designation and management recommendations for infants with an inconclusive diagnosis following newborn screening[END_REF] . Contributors from a range of back-grounds were asked to review statements and state if they agreed or disagreed (yes/no/cannot answer). If they disagreed, they were asked to explain why and provide an alternative version. Consensus was achieved when 80% of contributors agreed with a statement (respondents who ticked "cannot answer" were not included in the calculation, as stakeholders commented a "cannot answer" response was not the same as a "disagree"). This threshold of 80% agreement has been used in previous Delphi exercises in CF [START_REF] Munck | Cystic Fibrosis Screen Positive, Inconclusive Diagnosis (CFSPID): a new designation and management recommendations for infants with an inconclusive diagnosis following newborn screening[END_REF]. All comments on statements were reviewed by the core panel, even if agreement was achieved.

In total, 32 statements were generated by the contributing author group and were reviewed by the Delphi consultation between January and February 2022 (65 respondents from 24 countries, see list in Supplementary Table 2). Respondents were physicians (46.2%), other healthcare professionals (26.2%), scientists (12.3%), pwCF and their families (10.8%) and patient organization representatives (4.6%). An acceptable ( > 80%) agreement was achieved for all statements in the first round of consultation. Two statements were removed, despite achieving agreement. One statement (on the theme of adherence) was removed because it was repetitive, and one (on the theme of exercise) was removed due to comments and a lack of supporting evidence. After round 1 of the Delphi consultation, several statements were edited for clarity without changing the meaning (Supplementary Table 3).

Disease causing variants of the CFTR gene and standards for CFTR gene testing

Karen Raraigh, Nataliya Kashirskaya, Caroline Raynal, Halyna Makukh

Definitions and nomenclature

It is important that the names given to gene abnormalities are precise and accurate. The Human Genome Variation Society (HGVS) sets standards to describe genetic changes in all genes [START_REF] Den Dunnen | HGVS recommendations for the description of sequence variants: 2016 update[END_REF] . The term "mutation" is no longer recommended, as it assumes a disease state and has a somewhat negative connotation. Instead, the term "variant" is preferred. Variants are classified as disease-causing (pathogenic), non-disease-causing (benign), or of uncertain significance [3 , 4 ]. Variants should be described at the DNA level using HGVS nomenclature (e.g., c.1652G > A); although protein (e.g., p.Gly551Asp) and legacy (e.g., G551D) names are also widely recognized. In this paper, we describe variants by their HGVS name initially, then use the legacy name.

CFTR disease-causing variants that lead to a CF phenotype [START_REF] Castellani | ECFS best practice guidelines: the 2018 revision[END_REF] impair quantity and/or function of CFTR, when found in trans with a known CF-causing variant, according to a validated CFTR gene database (such as CFTR2 [START_REF] Us Cf Foundation | The Clinical and Functional TRanslation of CFTR (CFTR2)[END_REF] and CFTR-France [START_REF] Claustres | CFTR-France, a national relational patient database for sharing genetic and phenotypic data associated with rare CFTR variants[END_REF] ) (Statements 1 and 2, Table 2 ). Depending on the related phenotype observed [START_REF] Castellani | Consensus on the use and interpretation of cystic fibrosis mutation analysis in clinical practice[END_REF] , these variants are classified as CF-causing variants that consistently cause CF [6 , 8 ], or variants of varying clinical consequences (VVCC) that result in either 1) no disease, 2) CF in some individuals, or 3) a CFTR-related disorder (CFTR-RD) [ 6 , 8 , 9 ].

Variants with a lack of consistent data to determine if they are pathogenic or benign are classified as variants of uncertain significance (VUS) (Statement 3, Table 2 ).

Standards for CFTR gene testing

A DNA panel of common CF-causing variants are typically assessed for first level testing. Ideally, the variants included should reflect the person's ancestry [START_REF] Dequeker | Best practice guidelines for molecular genetic diagnosis of cystic fibrosis and CFTR-related disorders-updated European recommendations[END_REF] . More extensive second level testing includes analysis of CFTR coding sequences, intronic flanking regions, and deep-intronic regions where disease-causing variants have been described [START_REF] Highsmith | A novel mutation in the cystic fibrosis gene in patients with pulmonary disease but normal sweat chloride concentrations[END_REF][START_REF] Chillon | A novel donor splice site in intron 11 of the CFTR gene, created by mutation 1811 + 1.6kbA->G, produces a new exon: high frequency in Spanish cystic fibrosis chromosomes and association with severe phenotype[END_REF][START_REF] Faa | Characterizatio of a disease-associated mutation affecting a putative splicing regulatory element in intron 6b of the cystic fibrosis transmembrane conductance regulator (CFTR) gene[END_REF][START_REF] Costantino | A novel donor splice site characterized by CFTR mRNA analysis induces a new pseudo-exon in CF patients[END_REF][START_REF] Bergougnoux | Functional characterization and phenotypic spectrum of three recurrent disease-causing deep intronic variants of the CFTR gene[END_REF].

The diagnosis of CF is confirmed by a positive newborn screening result (i.e., elevated immunoreactive trypsinogen [IRT]) or when a person has clinical features of CF plus sweat chloride > 59 mmol/L and/or two disease-causing variants identified in trans (i.e., on opposite alleles) [START_REF] Castellani | ECFS best practice guidelines: the 2018 revision[END_REF] . However, in the context of CF symptoms, laboratory features, or abnormal CFTR bioassays, the absence of two disease-causing variants does not rule out CF. Further sequencing of the entire CFTR gene [ 16 , 17 ] or transcript analysis on nasal epithelial cells [START_REF] Costa | A recurrent deep-intronic splicing CF mutation emphasizes the importance of mRNA studies in clinical practice[END_REF] should be performed to search for additional disease-causing variants. It is also recommended to search for complex alleles (i.e., two or more CFTR variants associated in cis on the same allele) in those whose genotype does not correlate with expected phenotype and in people bearing variants known to be involved in complex alleles that may impact on the effectiveness of VST [ 17 , 19 , 20 ].

Molecular consequences and functional classes of variants

Variants have different molecular consequences, depending on type and location in the CFTR gene [START_REF] Bareil | CFTR gene variants, epidemiology and molecular pathology[END_REF] , and have traditionally been classified by functional impact from Class I to VI [ 22 , 23 ]. Though generally useful, this system does not capture nuances that may impact response to VST. Recent proposals for more ac-curate classification group variants by the effect on CFTR quantity or function (Fig. 1) [START_REF] Foil | The increasing challenge of genetic counseling for cystic fibrosis[END_REF] , or divide Class I variants into those amenable to read-through therapies (i.e., nonsense) and those un-likely to be corrected by small molecules (no mRNA production; i.e., frameshifts, large deletions/duplications) [START_REF] Boeck | Progress in therapies for cystic fibrosis[END_REF] .

Pathogenicity of rare variants and VUS may be investigated by groups with well-established protocols by evaluating in vivo CFTR function using intestinal current measurement [START_REF] Derichs | Intestinal current measurement for diagnostic classification of patients with questionable cystic fibrosis: validation and reference data[END_REF] or nasal potential difference [START_REF] Rowe | Nasal potential difference measurements to assess CFTR ion channel activity[END_REF] , ex vivo organoid forskolin-induced swelling (FIS) [START_REF] Boj | Forskolininduced swelling in intestinal organoids: an in vitro assay for assessing drug response in cystic fibrosis patients[END_REF] , or variant testing in a heterologous cell system in vitro [START_REF] Sosnay | Defining the disease liability of variants in the cystic fibrosis transmembrane conductance regulator gene[END_REF] . Notably, the potential impact of any variant on CFTR splicing -which may compromise CFTR modulator efficacy -must be considered prior to functional evaluation to avoid misinterpretation of results [29 , 30]. It is possible that developments in the field may identify agents that address splicing defects.

A list of CFTR variants and eligibility for VST is included in the appendix (Supplementary Table 4). It should be acknowledged that some of the licensed variants included in this list are characterized as non-CF causing (i.e., causing a CFTR-RD or non-disease causing) [5 , 6] and others are known or suspected to affect splicing or have characteristics that may decrease the expected clinical benefit of VST [ 29 , 30 ]. A clear diagnosis of CF is a pre-requisite to prescription of these agents. This issue is further discussed in Section 12 .

3. Who is eligible for variant-specific therapy?

Kevin W Southern, Karen Robinson, Alan Smyth and Ian Sinha

Emerging CFTR modulator therapies for pwCF have been li-censed for specific variants of the CFTR gene, based on data from clinical trials and in vitro testing. This variant-focused approach to licensing may oversimplify a complex situation since many CF-causing variants are not easily characterized and their response to VST may be unpredictable. This has led to the concept of "theratyping" to chart individual clinical response to VST, regardless of CFTR variant. This approach offers therapeutic options to pwCF with rare variants [START_REF] Crawford | Theratyping in cystic fibrosis[END_REF] (see Section 11 ). The evidence for VST in pre-school children is reviewed in Section 4 .

The first VST licensed was the "potentiator" ivacaftor in 2012, initially for pwCF with at least one c.1652G > A variant (legacy name: G551D). The evidence base for the use of this therapy in pwCF older than 6 years of age is strong, with a good safety profile [START_REF] Skilton | Potentiators (specific therapies for class III and IV mutations) for cystic fibrosis[END_REF] . Ivacaftor is now licensed for infants with CF aged 4 months and older (see detail in Section 4 ). G551D is a class III or "gating" variant, with CFTR protein correctly located in the cell membrane but non-functioning. Ivacaftor addresses the gating defect, enabling some salt transport.

Ivacaftor has subsequently been approved for other less-common variants with a similar molecular pathobiological characterization based on in vitro laboratory evidence or in vivo clinical trial data (Supplementary Table 4).

The most common CF-causing variant is c.1521_1523delCTT (legacy name: F508del) [START_REF] Southern | Corrector therapies (with or without potentiators) for people with cystic fibrosis with class II CFTR gene variants (most commonly F508del)[END_REF]. The first VST to be licensed for this variant was a combination of lumacaftor (initially termed a corrector) and ivacaftor. There is good evidence that lumacaftor-ivacaftor treatment results in improved respiratory function in pwCF with two F508del variants, albeit with a lower magnitude of improvement than was observed with ivacaftor treatment amongst pwCF and the G551D variant [START_REF] Southern | Corrector therapies (with or without potentiators) for people with cystic fibrosis with class II CFTR gene variants (most commonly F508del)[END_REF]. Lumacaftor-ivacaftor has a reasonable safety profile but is associated with transient respiratory symptoms and a small but clinically significant rise in blood pressure in adults. Another dual therapy, tezacaftor-ivacaftor, has similar efficacy but a better safety profile [START_REF] Southern | Corrector therapies (with or without potentiators) for people with cystic fibrosis with class II CFTR gene variants (most commonly F508del)[END_REF]. Both dual therapies were licensed for pwCF with two F508del variants. Tezacaftor-ivacaftor has since been approved for certain combinations of F508del and another variant (Supplementary Table 4).

The addition of elexacaftor to tezacaftor-ivacaftor resulted in further improvement in clinical outcomes for pwCF with two F508del variants already established on dual therapy, as well as pwCF with one F508del variant who were modulator naïve [START_REF] Middleton | Elexacaftor-tezacaftor-ivacaftor for cystic fibrosis with a single Phe508del Allele[END_REF][START_REF] Heijerman | Efficacy and safety of the elexacaftor plus tezacaftor plus ivacaftor combination regimen in people with cystic fibrosis homozygous for the F508del mutation: a double-blind, randomized, phase 3 trial[END_REF][START_REF] Nichols | Clinical effectiveness of elexacaftor/tezacaftor/ivacaftor in people with cystic fibrosis: a clinical trial[END_REF] . The impact on modulator-naïve pwCF was particularly notable, with rapid improvements in all outcomes measured, including a disease-specific quality of life measure. Elexacaftor-tezacaftor-ivacaftor, often called triple therapy, is associated with a reasonable safety profile, and no rise in blood pressure was reported in the initial trial [START_REF] Southern | Corrector therapies (with or without potentiators) for people with cystic fibrosis with class II CFTR gene variants (most commonly F508del)[END_REF] Subsequent studies of elexacaftor-tezacaftor-ivacaftor in 6-11-year-olds confirmed the safety profile reported in adults and provided evidence of efficacy, leading to an extension of the licence to this age group [START_REF] Zemanick | A phase 3 open-label study of elexacaftor/tezacaftor/ivacaftor in children 6 through 11 years of age with cystic fibrosis and at least one F508del Allele[END_REF] .

A frequently asked question is whether it is appropriate to transfer patients established on effective monotherapy or dual therapy onto triple therapy? A study of adult pwCF with F508del and another variant responsive to either ivacaftor alone or tezacaftor-ivacaftor demonstrated significant further improvement in outcomes when they commenced triple therapy [36 , 38]. This supports the rationale that all pwCF, aged 6 years and older, who have one or two F508del variants should have access to daily elexacaftor-tezacaftorivacaftor therapy (Statement 4, Table 2).

PwCF carrying non-F508del CFTR gene variants should be con-sidered for modulator therapy if in vitro or clinical trial data support potential responsiveness to any of the therapeutic op-tions: mono (ivacaftor), dual (tezacaftor-ivacaftor or lumacaftor-ivacaftor) or triple modulator therapy (elexacaftor-tezacaftor-ivacaftor) (Statement 5, Table 2 ) (Supplementary Table 4). Several CFTR gene variants are non-responsive to current modulator therapy (see Section 11 ) and there is no currently approved effective VST for pwCF have premature truncation codon variants (e.g. non-sense) or other large deletions or duplications [START_REF] Aslam | Ataluren and similar compounds (specific therapies for premature termination codon class I mutations) for cystic fibrosis[END_REF] .

Modulator therapy for pre-school children with CF

Isabelle Sermet, Jane C Davies and Silvia Gartner

CFTR modulator therapies, in particular ivacaftor and elexacaftor-tezacaftor-ivacaftor, have significantly impacted the course of CF in older children and will likely improve their survival. Most infants and young children with CF still await trials to confirm eligibility for these treatments. In Europe, ivacaftor is licensed for children with CF aged 4 months and older, with at least one of 10 CFTR variants (Statement 6, Table 2 ) (Supplementary Table 4). Lumacaftor-ivacaftor is licensed for 2-5-year-olds who are homozygous for F508del (Supplementary Table 4).

Ivacaftor led to significant improvements in sweat chloride, growth and in some cases pancreatic function biomarkers (in-creased faecal elastase-1, decreased serum trypsinogen) in clinical trials in pre-school children [START_REF] Davies | Safety, pharmacokinetics, and pharmacodynamics of ivacaftor in patients aged 2-5 years with cystic fibrosis and a CFTR gating mutation (KIWI): an open-label, single-arm study[END_REF][START_REF] Rosenfeld | Ivacaftor treatment of cystic fibrosis in children aged 12 to < 24 months and with a CFTR gating mutation (ARRIVAL): a phase 3 single-arm study[END_REF][START_REF] Davies | Ivacaftor in infants aged 4 to < 12 months with cystic fibrosis and a gating mutation. results of a two-part phase 3 clinical trial[END_REF] . These improvements appeared within weeks and were maintained during the open-label extension for > 2 years [START_REF] Rosenfeld | An open-label extension study of ivacaftor in children with CF and a CFTR gating mutation initiating treatment at age 2-5years (KLIMB)[END_REF]. Measurement of respiratory function based on multiple breath washout also demonstrated significant improvement in lung clearance index (LCI) [START_REF] Ratjen | Changes in lung clearance index in preschool-aged patients with cystic fibrosis treated with ivacaftor (goal): a clinical trial[END_REF] . This is encouraging because elevated LCI, which measures the inhomogenity of lung ventilation, is an indicator of progression of CF air-way disease later in life [ 45 , 46 ]. An ongoing open-label trial is currently assessing the safety, pharmacokinetics, and pharmacodynamics of ivacaftor in infants with CF aged < 4 months (clinicaltrials.gov NCT02725567).

Lumacaftor-ivacaftor also led to better growth and reduced sweat chloride in children aged 2-5 years (Statement 7, Table 2). Treatment effects were smaller than those seen with ivacaftor but were maintained long term [START_REF] Mcnamara | Safety, pharmacokinetics, and pharmacodynamics of Lumacaftor and ivacaftor combination therapy in children aged 2-5 years with cystic fibrosis homozygous for F508del-CFTR: an open-label phase 3 study[END_REF][START_REF] Hoppe | Long-term safety of Lumacaftor-ivacaftor in children aged 2-5 years with cystic fibrosis homozygous for the F508del-CFTR mutation: a multicentre, phase 3, open-label, extension study[END_REF]. There were no significant improvements in LCI [START_REF] Mcnamara | Safety, pharmacokinetics, and pharmacodynamics of Lumacaftor and ivacaftor combination therapy in children aged 2-5 years with cystic fibrosis homozygous for F508del-CFTR: an open-label phase 3 study[END_REF].

Both therapies are formulated as granules for younger children, are well tolerated and have pharmacokinetic profiles similar to those in older children. Moderate alanine transaminase elevations were reported in some infants, which did not increase with longer treatment duration [ 40-43 , 47-49 ]. This supports more frequent tests of liver function early in treatment. Preclinical studies showed cataracts in juvenile rats, and cases of noncongenital lens opacities have been reported in paediatric patients on ivacaftor. Although other risk factors were sometimes present, possible causation cannot be excluded. Therefore, baseline and follow-up ophthalmological examinations are recommended in children with CF treated with therapies containing ivacaftor (Statement 8, Table 2).

Elexacaftor-tezacaftor-ivacaftor is in phase 3 trials for children with CF aged 2-5 years, with results expected at the end of 2022 (clinicaltrials.gov NCT04537793). In summary, data from younger children have largely mirrored those from older populations, although the more limited base-line disease means that measuring efficacy is more challenging. CF organ disease progression in infants is largely irreversible which highlights the need to begin VST as early as possible. It is un-known whether treatment of infants could prevent various aspects of CF, such as structural lung disease, chronic infection, hepatobiliary disease, pancreatic/intestinal dysfunction and glucose intolerance [START_REF] Ferkol | Prevention of cystic fibrosis: the beginning of the end?[END_REF]. This has only been shown in the animal model to date [START_REF] Sun | In utero and postnatal VX-770 administration rescues multiorgan disease in a ferret model of cystic fibrosis[END_REF] . The goal should be to determine the safety and effectiveness of early life initiation in order to provide VST following neonatal screening, to potentially slow down disease evolution considerably.

Monitoring the introduction and maintenance of variant-specific therapy (CFTR modulators)

Gary J Connett, Amanda Bevan, Edwin Brokaar

Before starting CFTR modulator therapy, families and individuals with CF should discuss with the CF team the reasons for which treatment is being considered. There should also be discussion, backed up with written information, about when and how to take the medication (Statement 9, Table 2). There should be opportunities to address any emerging concerns or uncertainties about medication use as part of routine and annual assessments. A drug history, cross-checked with prescribing information about potential drug interactions, must be obtained before starting treatment (Statement 10, Table 2) and should also enquire about the use of complementary and alternative medicines. St. John's wort (Hypericum perforatum) for example, is an herbal remedy used for anxiety and depression and a strong CYP3A inducer that might de-crease modulator efficacy. Drugs that inhibit CYP3A-mediated drug catabolism, including some used regularly in CF care such as antifungal azoles and the macrolide antibiotics erythromycin and clarithromycin, can result in significant increases in modulator expo-sure and modulator dose should be adjusted accordingly. Dose adjustments should also be considered for patients with severe liver disease according to the Child-Pugh Score for assessing the correct dose reduction.

Blood pressure measurements and liver function tests, in addition to standard care, should be obtained at baseline, then every 3 months for the first year of treatment and at least annually there-after (Statement 11, Table 2). More frequent liver function monitoring should be considered in those with significant underlying liver disease.

Transaminitis (raised liver enzymes) is reported in up to 25% of patients established on CFTR modulator therapy. Elevations are usually transient and mild, but in 2% to 5% of cases are above 3 times the upper limit of normal (ULN) [START_REF]NIH Cystic fibrosis agents. Livertox: clinical and research information on drug-induced liver injury[END_REF]. Current prescribing guidance suggests that with bilirubin levels > 2 x ULN with transaminases > 3 x ULN, or if transaminase levels > 5 x ULN, dosing should be interrupted until levels return to normal. The risks of restarting treatment on long-term liver function should be assessed on a case-by-case basis and the decision to restart taken working in partnership with the patient and their family, taking into account objective measures of effectiveness. Acute cholecystitis is a rare possible side effect of treatment [START_REF] Safirstein | Biliary disease and cholecystectomy after initiation of elexacaftor/ivacaftor/tezacaftor in adults with cystic fibrosis[END_REF], probably because of the effects of increased bile flow on stones and biliary sludge.

Respiratory side effects such as chest tightness and dyspnoea have been reported, especially after introduction of Lumacaftor-ivacaftor treatment and in adults with more severe lung disease [START_REF] Dagenais | Real-world safety of CFTR modulators in the treatment of cystic fibrosis: a systematic review[END_REF]. These adverse effects are less problematic with other modulator combinations, but it is advisable to initiate treatment after optimising other aspects of care including routine respiratory treatments.

Increased sputum production can occur shortly after initiating treatment and patients should be warned about this phenomenon. This transient phenomenon is sometimes referred to as 'the purge' and is discussed in the airway clearance section (Section 6).

Other side effects include gastrointestinal symptoms, headache, and rash, which are often transient or resolve after dose reduction or interruption. Rash might occur more commonly in those taking hormonal contraceptives. Muscle pain (myositis) can also occur and be associated with raised creatinine kinase (CK) levels. Monitoring should be considered if the patient is taking other medicines, such as statins, which can also increase CK levels [START_REF] Valiyil | Drug-related myopathies of which the clinician should be aware[END_REF].

Rarer side effects reported include menstrual irregularities, testicular pain, and sinus pain. Such events are usually transient, but unsettling for pwCF.

Whilst quality of life measures suggest significant improvements in wellbeing for most patients receiving modulator therapy, there have also been reports of mental health, neurocognitive and neuropsychiatric events. Careful consideration is required to assess whether these events are pharmacologically derived, or due to changes in life circumstances as a result of modulator use (de-scribed in Section 9).

Monitoring response to VST by standard clinical measures can inform dosing regimens. Measuring LCI might be informative in pwCF with normal spirometry (i.e., a forced expiratory volume in one second [FEV 1] above 90% of predicted) [START_REF] Davies | A phase 3, double-blind, parallel-group study to evaluate the efficacy and safety of tezacaftor in combination with ivacaftor in participants 6 through 11 years of age with cystic fibrosis homozygous for F508del or heterozygous for the F508del-CFTR mutation and a residual function mutation[END_REF] . Repeat sweat testing provides evidence of a treatment effect on CFTR activity but does not predict clinical response [START_REF] Sermet-Gaudelus | Sweat chloride testing and Nasal Potential Difference (NPD) are primary outcome parameters in treatment with Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) modulators[END_REF].

The continued effectiveness of modulators depends on maintaining high levels of adherence to these therapies. CF services should routinely access pharmacy dispensing data as part of adherence monitoring (Statement 12, Table 2). The benefit of with-drawing concomitant treatments, such as mucoactive agents is being evaluated in a number of trials including CF STORM (EudraCT-2020-005864-77) and CF SIMPLIFY (Clinicaltrials.gov identifier NCT04378153). Monitoring and supporting adherence to such treatments, when clinically indicated, remains important.

As with all new therapies, the safe use of modulator treatment and recognition of rare side effects depends upon responsible clinicians providing regular follow-up and reporting all potentially related adverse reactions to their relevant medicine regulatory authorities.

Managing airway clearance during introduction of variant-specific therapy

Lisa Morrison, Jenny Hauser, Naomi Hamilton

VST has been shown to increase airway surface liquid, ciliary beat frequency, mucociliary transport, and reduce mucus viscosity [START_REF] Birket | Combination therapy with cystic fibrosis transmembrane conductance regulator modulators augment the airway functional microanatomy[END_REF]. It is important that the healthcare team reflects carefully on airway clearance techniques to determine their role, effectiveness, and optimal prescription for pwCF established on VST (Statement 13, Table 2).

Some individuals experience a period of "sputum purging" following VST commencement [START_REF]Kaftrio: turning around the lives of patients with cystic fibrosis[END_REF]. We recommend a review of optimal airway clearance techniques, prior to commencing VST. Outpatient review or an inpatient stay may be considered by the healthcare team and the pwCF, before and during this purge phase, with appropriate symptom treatment. Transient adverse effects have been reported on commencement of VST in some pwCF, including chest tightness, inability to tolerate increase in airway secretions, an initial decline in FEV, haemoptysis or decreased oxy-gen levels [54. This may reflect significant disease, and increased physiotherapy support will be required for these individuals.

Comments posted by pwCF on social media suggest that a purge can be immediate and profound, although on occasion less apparent (Fig. 2). PwCF established on dual CFTR modulator therapy who then switch to triple therapy may also experience a purge and should have adequate physiotherapy support as needed.

There is no evidence to support discontinuation of physiotherapy management for pwCF on established VST. However, pwCF regularly experience reduced airway secretions and improved respiratory symptoms. An individualized approach to rationalizing therapies could therefore ease the relative burden of care whilst upholding optimal health outcomes. This should be done in partnership with the pwCF, their physiotherapist and health-care team. Maintaining routine airway clearance techniques will ensure that pwCF continue to achieve optimal benefit from VST. It is important that pwCF are proactive in their airway clearance management and remain receptive to their individual symptoms. In some cases, it may be appropriate to consider alternative approaches to maintaining respiratory health, including exercise as an adjunct to airway clearance particularly in those individuals with stable respiratory health. Whilst exercise is important for all pwCF, there is no evidence to support it replacing formal airway clearance techniques. Clinical trials are needed to answer this frequently asked question and modulator therapy has thrown this into sharper perspective.

In addition to the impact on the lungs, pwCF on VST have re-ported improvements in chronic rhinosinusitis symptoms. These include improvements in CT scan appearances (relating to sinus architecture) and patientreported outcomes, specifically rhinorrhoea, postnasal drip, thick nasal discharge, and fatigue [ 60 , 61 ].

Managing glucose intolerance following the introduction of variant-specific therapy

Sarah Collins, Dilip Nazareth, Laurence Kessler

Effect of CFTR modulators on CFRD

Cystic fibrosis-related diabetes (CFRD) is a common complication, present in over 50% of adult pwCF [START_REF] Moran | Cystic fibrosisrelated diabetes: current trends in prevalence, incidence, and mortality[END_REF] . CFRD is associated with poorer clinical outcomes, including accelerated pulmonary function decline and excess morbidity [START_REF] Bell | The future of cystic fibrosis care: a global perspective[END_REF]. The aetiology is likely multi-factorial secondary to pancreatic damage, resulting in alpha and beta cell loss and dysfunction, manifested as a decreased first-phase insulin secretion.

CFTR modulator therapy has been shown to impact glucose handling. Ivacaftor has a significant beneficial effect on glycaemia [START_REF] Christian | Sustained glycemic control with ivacaftor in cystic fibrosis-related diabetes[END_REF][START_REF] Tsabari | CFTR potentiator therapy ameliorates impaired insulin secretion in CF patients with a gating mutation[END_REF][START_REF] Volkova | Disease progression in patients with cystic fibrosis treated with ivacaftor: data from national US and UK registries[END_REF][START_REF] Hayes D Jr | Resolution of cystic fibrosis-related diabetes with ivacaftor therapy[END_REF] and the combinations of ivacaftor and Lumacaftor or tezacaftor have also shown a small benefit in glucose handling [START_REF] Thomassen | Effect of Lumacaftor/ivacaftor on glucose metabolism and insulin secretion in Phe508del homozygous cystic fibrosis patients[END_REF][START_REF] Flume | Ivacaftor in subjects with cystic fibrosis who are homozygous for the F508del-CFTR mutation[END_REF][START_REF] Wainwright | Lumacaftor-ivacaftor in patients with cystic fibrosis homozygous for Phe508del CFTR[END_REF][START_REF] Li | Continuous glucose monitoring in youth with cystic fibrosis treated with Lumacaftorivacaftor[END_REF]. Elexacaftor-tezacaftor-ivacaftor has been shown to improve continuous glucose monitoring (CGM) markers of glycaemia in pwCF with and without known CFRD [START_REF] Scully | The effect of elexacaftor/tezacaftor/ivacaftor (ETI) on glycemia in adults wit cystic fibrosis[END_REF] . Hence, it is important to monitor glucose handling in pwCF established on VST.

Screening for CFRD

The significance of early glucose abnormalities in pwCF remains controversial [START_REF] Chan | Continuous glucose monitoring in cystic fibrosis-Benefits, limitations, and opportunities[END_REF], however, weight and lung function decline have been shown to precede a diagnosis of CFRD [START_REF] Lanng | Influence of the development of diabetes mellitus on clinical status in patients with cystic fibrosis[END_REF]. A prospective 4-year study reported the degree of glucose intolerance to be a strong determinant of future lung function decline in pwCF [START_REF] Milla | Trends in pulmonary function in patients with cystic fibrosis correlate with the degree of glucose intolerance at baseline[END_REF], justifying early screening.

Guidelines propose definitions of glucose tolerance abnormalities in pwCF based on 2-hour blood glucose levels following oral glucose tolerance testing (OGTT). This should be performed annually in adults. From the age of 10 years onwards, children with CF should be screened annually for glucose tolerance abnormalities [START_REF] Moran | ISPAD Clinical Practice Consensus Guidelines 2018: management of cystic fibrosis-related diabetes in children and adolescents[END_REF]. Several studies report the usefulness of determining 1-hour (T 1) blood glucose levels following OGTT, enabling earlier hyper-glycaemia to be detected [START_REF] Brodsky | Elevation of 1-hour plasma glucose during oral glucose tolerance testing is associated with worse pulmonary function in cystic fibrosis[END_REF]. T 1 hyperglycaemia is correlated with hyperglycaemia detected by continuous glucose monitoring (CGM) [START_REF] Elidottir | Abnormal glucose tolerance and lung function in children with cystic fibrosis. Comparing oral glucose tolerance test and continuous glucose monitoring[END_REF].

There is increasing evidence of the use of CGM in CF and several studies report links between CGM abnormalities and clinical deterioration [START_REF] Chan | Continuous glucose monitoring in cystic fibrosis-a practical guide[END_REF][START_REF] Chan | Continuous glucose monitoring abnormalities in cystic fibrosis youth correlate with pulmonary function decline[END_REF].

In the era of modulator therapy, it remains to be determined whether an OGTT is the most appropriate test. Attention should be paid to tests assessing dynamic glucose handling over time.

Management of CFRD

While changes in glucose handling have been observed with CFTR modulator therapy, the impact upon CFRD management is not fully established. Glucose levels should be closely monitored, and treatment modified, as required. Similarly, nutritional status should be closely monitored [START_REF] Petersen | Effect of elexacaftortezacaftorivacaftor on body weight and metabolic parameters in adults with cystic fibrosis[END_REF], with appropriate dietary modifications recommended where applicable (Statement 14, Table 2 ). Improvements in survival will result in people living with CFRD for longer. Therefore, close ongoing monitoring of diabetes-related complications is important, especially for microvascular disease.

Monitoring and supporting nutritional issues during variantspecific therapy

Jacqueline Lowdon, Elizabeth Owen, Dimitri DeClerq

Nutritional status and monitoring

In addition to improving respiratory outcomes, clinical trials have demonstrated significant nutritional impact, although precise mechanisms remain unclear. More significant effects on anthropometric parameters have been seen for pwCF on ivacaftor or elexacaftor-tezacaftor-ivacaftor than for those on dual CFTR modulator therapy [START_REF] Bailey | Effect of CFTR modulators on anthropometric parameters in individuals with cystic fibrosis: an evidence analysis center systematic review[END_REF] . Improvements in weight, height and BMI were reported as secondary or exploratory outcomes in the randomized controlled trials (RCTs) underpinning approval of CFTR modulators. PwCF with one or two G551D variants in phase 3 trials of ivacaftor had sustained increases in weight and BMI [START_REF] Skilton | Potentiators (specific therapies for class III and IV mutations) for cystic fibrosis[END_REF] . PwCF with one or two F508del variants aged ≥12 years on elexacaftor-tezacaftorivacaftor had significant increases in weight and BMI [START_REF] Bailey | Effect of CFTR modulators on anthropometric parameters in individuals with cystic fibrosis: an evidence analysis center systematic review[END_REF]. Real-world studies of pwCF treated with ivacaftor also found consistent increases in weight and BMI [START_REF] Duckers | Realworld outcomes of ivacaftor treatment in people with cystic fibrosis: a systematic review[END_REF]. Data on linear growth and body composition is limited for elexacaftor-tezacaftor-ivacaftor. Longitudinal data is needed to establish whether the effects of elexacaftor-tezacaftor-ivacaftor on anthropometric status are sustained beyond 48 weeks, and to assess the effects on body composition.

Dietary and nutritional issues

Changes reported in nutritional status may be multifactorial. In pwCF with G551D taking ivacaftor, there have been reports of decreased energy expenditure, increased small intestine pH and decreased gut inflammation [START_REF] Davies | Safety, pharmacokinetics, and pharmacodynamics of ivacaftor in patients aged 2-5 years with cystic fibrosis and a CFTR gating mutation (KIWI): an open-label, single-arm study[END_REF][START_REF] Stallings | Energy balance and mechanisms of weight gain with ivacaftor treatment of cystic fibrosis gating mutations[END_REF][START_REF] Gelfond | Impact of CFTR modulation on intestinal pH, motility, and clinical outcomes in patients with cystic fibrosis and the G551D mutation[END_REF]. Data from clinical trials and real-world studies of pwCF are needed to determine the long-term effects and the physiological mechanisms with differ-ent modulators. As evidence is lacking regarding macronutrient requirements, it is recommended that current practice continues to assess energy requirements individually, depending on age and clinical status (Statements 15-16, Table 2) [START_REF] Bailey | Effect of CFTR modulators on anthropometric parameters in individuals with cystic fibrosis: an evidence analysis center systematic review[END_REF][START_REF] Burgel | Reallife safety and effectiveness of Lumacaftor-ivacaftor in patients with cystic fibrosis[END_REF]. If there are concerning trends in weight/BMI/body composition, the focus should shift from a diet of quantity to a diet of quality.

Working closely with their dietitian and CF team supports pwCF to maintain a healthy weight/BMI/body composition and a high quality, balanced diet. Emerging data suggest vitamin levels can be affected by CFTR modulator therapy and longer-term data are required to quantify the impact on need for vitamin supplementation [START_REF] Burgel | Reallife safety and effectiveness of Lumacaftor-ivacaftor in patients with cystic fibrosis[END_REF][START_REF] Sommerburg | CFTR modulator therapy with Lumacaftor/ivacaftor alters plasma concentrations of lipid-soluble vitamins A and E in patients with cystic fibrosis[END_REF]. Similarly the need for salt supplementation on VST should be monitored closely, as per the usual practice of the CF service.

Early initiation of ivacaftor may mitigate existing pancreatic damage and prevent or delay further damage in young children with CF [START_REF] Davies | Safety, pharmacokinetics, and pharmacodynamics of ivacaftor in patients aged 2-5 years with cystic fibrosis and a CFTR gating mutation (KIWI): an open-label, single-arm study[END_REF][START_REF] Rosenfeld | Ivacaftor treatment of cystic fibrosis in children aged 12 to < 24 months and with a CFTR gating mutation (ARRIVAL): a phase 3 single-arm study[END_REF][START_REF] Rosenfeld | An open-label extension study of ivacaftor in children with CF and a CFTR gating mutation initiating treatment at age 2-5years (KLIMB)[END_REF]. Further research characterizing the impact of VST on children is paramount, especially the role of faecal elastase measurement for monitoring pancreatic function. At present, there is no evidence to warrant reducing or stopping pancreatic enzyme replacement therapy (PERT) upon commencement of VST although this is an important question for pwCF.

Identifying and managing psychological issues during the introduction of variant-specific therapy

Helen Oxley, Alistair Duff, Marieke Verkleij

VST can have positive psychological benefits as well as physical ones [START_REF] Martin | Patient perspectives following initiation of elexacaftor-tezacaftor-ivacaftor in people with cystic fibrosis and advanced lung disease[END_REF]. However, there can also be adverse indirect psychological impact for pwCF and caregivers, who report adjustment issues. Feeding and eating are known issues for pwCF and managing changes in weight and eating behaviors associated with VST will remain challenging. The wider CF team needs to be aware of, and sympathetic to, patients having complex feelings about the future and the past that can be difficult to verbalise (Statement 17, Table 2) [START_REF]Emotional and social impact of Kaftrio[END_REF]. CF psychologists should guide the team on the amount of support required and be involved in delivering highly specialized help for adjustment problems, behavior change and psychological well-being. All team members must be patient and give patients every opportunity to air their feelings, without judgement. These reactions have mostly been reported in adults, however children and young people with CF are now transitioning onto VST and need further careful psychological consideration as do all those who are as yet ineligible for, or unable to start VST.

Worsening of depression and anxiety symptoms including suicidal ideation and suicide attempts requiring hospitalization have been reported by some pwCF who have commenced VST [START_REF] Talwalkar | Cystic fibrosis transmembrane regulator modulators: implications for the management of depression and anxiety in cystic fibrosis[END_REF][START_REF] Tindell | Trikafta and psychopathology in cystic fibrosis: a case report[END_REF][START_REF] Mckinzie | Worsening anxiety and depression after initiation of Lumacaftor/ivacaftor combination therapy in adolescent females with cystic fibrosis[END_REF]. Signals for mental health and neurocognitive adverse events have been reported with the four currently available CFTR modulator therapies [START_REF] Dagenais | Real-world safety of CFTR modulators in the treatment of cystic fibrosis: a systematic review[END_REF], as well as reports of "mental fogginess" [START_REF] Heo | Mental status changes during elexacaftor/tezacaftor /ivacaftor therapy[END_REF] . PwCF are known to have 2-3 times the risk of developing elevated symptoms of depression and anxiety than the general population [START_REF] Quittner | Prevalence of depression and anxiety in patients with cystic fibrosis and parent caregivers: results of The International Depression Epidemiological Study across nine countries[END_REF]. Depression and anxiety are in turn associated with negative health outcomes, worse treatment adherence and greater healthcare utilization [START_REF] Quittner | Prevalence of depression and anxiety in patients with cystic fibrosis and parent caregivers: results of The International Depression Epidemiological Study across nine countries[END_REF][START_REF] Ploessl | Prevalence of depression and antidepressant therapy use in a pediatric cystic fibrosis population[END_REF][START_REF] Smith | Depressive symptoms in children with cystic fibrosis and parents and its effects on adherence to airway clearance[END_REF][START_REF] Verkleij | Implementing the International Committee on Mental Health in Cystic Fibrosis (ICMH) guidelines: screening accuracy and referral-treatment pathways[END_REF][START_REF] Quittner | International Committee on Mental Health in Cystic Fibrosis: Cystic Fibrosis Foundation and European Cystic Fibrosis Society consensus statements for screening and treating depression and anxiety[END_REF][START_REF] Snell | Depression, illness severity, and healthcare utilization in cystic fibrosis[END_REF][START_REF] Schechter | Decreased survival in cystic fibrosis patients with a positive screen for depression[END_REF]. Therefore, pwCF and parent-caregivers should be screened in accordance with established CF mental health guide-lines and treatment recommendations [START_REF] Quittner | International Committee on Mental Health in Cystic Fibrosis: Cystic Fibrosis Foundation and European Cystic Fibrosis Society consensus statements for screening and treating depression and anxiety[END_REF], prior to, and during, VST but no later than 3 months after commencement (Statement 18, Table 2 ).

Early studies reported sub-optimal adherence to VST, but more recent data shows 89% and 83% adherence at 6 and 12 months respectively [START_REF] Olivereau | Adherence to Lumacaftor-ivacaftor therapy in patients with cystic fibrosis in France[END_REF]. This is thought to result from high costs, good communication, knowledge and monitoring, and optimistic perspectives from the media and patient associations. When first prescribed VST, patients may consider that they will adhere to such effective therapy, but good intentions do not always lead to lasting behavior change. Evidence-based strategies for improving and maintaining optimal adherence remain relevant. Understanding barriers to, and facilitators of, adherence remains important as the landscape shifts. The CF team can improve their ability to sup-port pwCF through this journey by practising patientcentred communication skills such as active listening, expressing empathy, and recognising unique challenges. For pwCF who have not yet commenced VST, it remains essential to focus on optimal adherence to traditional therapies to remain as well as possible. Often obscured are feelings of pressure and responsibility and some patients fear judgement over their struggles to adhere whilst others find it difficult to acknowledge the consequences of their sub-optimal adherence as they pursue a "normal" daily life.

Fertility and breast feeding

Andrea Gramegna, Connie Takawira, Michal Shteinberg

Women with CF have increased rates of subfertility due to multifactorial causes, including endocrine as well as barrier abnormalities [START_REF] Shteinberg | Failure to conceive in women with CF is associated with pancreatic insufficiency and advancing age[END_REF][START_REF] Shteinberg | fertility and pregnancy in cystic fibrosis[END_REF].

A rise in pregnancy rates has been reported following ivacaftor therapy [START_REF] Esan | Pregnancy rates and outcomes in women with cystic fibrosis in the UK: comparisons with the general population before and after the introduction of disease-modifying treatment, 2003-17[END_REF] . More recently, unintentional pregnancies have been recorded within weeks of commencing elexacaftor-tezacaftor-ivacaftor [START_REF] Esan | Pregnancy rates and outcomes in women with cystic fibrosis in the UK: comparisons with the general population before and after the introduction of disease-modifying treatment, 2003-17[END_REF][START_REF] O'connor | Elexacafator/tezacaftor/ivacaftor resolves subfertility in females with CF: a two center case series[END_REF][START_REF] Kendle | Cystic fibrosis transmembrane conductance regulator modulators during pregnancy: a case series[END_REF][START_REF]Clinical Considerations: fertility and CFTR Modulators[END_REF].

Women with CF report under-utilizing contraception, and unintentional pregnancies are a recognized issue [108,[START_REF] Godfrey | Contraceptive use among women with cystic fibrosis: a pilot study linking reproductive health questions to the Cystic Fibrosis Foundation National Patient Registry[END_REF].

Prior to commencing VST, women should be counselled about the risk of unintentional pregnancy (Statement 19, Table 2). Contraceptive use should be reviewed and, if necessary, modified to address potential drug interactions.

In men with CF, complete bilateral absence of vas deferens (CBAVD) causes infertility [START_REF] Gaillard | Normal vas deferens in fetuses with cystic fibrosis[END_REF]. Animal model work suggests that exposure to VST in utero may correct this abnormality. This possibility should be considered in male CF infants, born to CF mothers on VST, as transplacental drug transfer is possible [START_REF] Sun | In utero and postnatal VX-770 administration rescues multiorgan disease in a ferret model of cystic fibrosis[END_REF].

The use of VST during pregnancy

Data regarding safety of VST during pregnancy is limited. With-holding VST during or before pregnancy is an option but has been associated with clinical deterioration in pregnant and non-pregnant women [START_REF] Trimble | Ivacaftor withdrawal syndrome in cystic fibrosis patients with the G551D mutation[END_REF][START_REF] Nash | Outcomes of pregnancy in women with cystic fibrosis (CF) taking CFTR modulators-an international survey[END_REF][START_REF] Taylor-Cousar | Maternal and fetal outcomes following elexacaftortezacaftorivacaftor use during pregnancy and lactation[END_REF] . Available animal and human data have not identified teratogenicity, but the components of VST have all been demonstrated to cross the placenta in animals [START_REF]Kaftrio Summary of Product Characteristics[END_REF]. This transplacental transfer had minor effects on pregnancy outcomes at normal human doses and has not been associated with toxicity to foetal chromosomes or organogenesis [START_REF] Nash | Outcomes of pregnancy in women with cystic fibrosis (CF) taking CFTR modulators-an international survey[END_REF]. Two case series report data on pregnancy and VST. Nash et al. describe 64 pregnancies exposed to ivacaftor, Lumacaftor-ivacaftor or tezacaftor-ivacaftor and Taylor-Cousar et al. describe 45 pregnancies exposed to elexacaftor-tezacaftor-ivacaftor [START_REF] Nash | Outcomes of pregnancy in women with cystic fibrosis (CF) taking CFTR modulators-an international survey[END_REF][START_REF] Taylor-Cousar | Maternal and fetal outcomes following elexacaftortezacaftorivacaftor use during pregnancy and lactation[END_REF]. Data from these case series suggest miscarriage rates similar to those of the general population and no related complications in infants following in utero exposure [START_REF] Nash | Outcomes of pregnancy in women with cystic fibrosis (CF) taking CFTR modulators-an international survey[END_REF][START_REF] Taylor-Cousar | Maternal and fetal outcomes following elexacaftortezacaftorivacaftor use during pregnancy and lactation[END_REF]. The decision to continue or withhold VST during pregnancy should be made between the CF team and the woman with CF, considering the risks for the mother and the baby (Statement 20, Table 2). Babies with CF exposed to modulator therapy in utero may have a reduced serum IRT and this may lead to a false negative newborn screening result.

Breast feeding

Data on the safety of VST in breastfeeding remain lacking. The product characteristics of elexacaftortezacaftor-ivacaftor report all three components to be present in breastmilk in animal studies with no adverse effects reported at equivalent human doses. One case report detected measurable levels of Lumacaftor and ivacaftor in the breastmilk of a breastfeeding mother with CF on this dual therapy [115]. Transient elevations in liver enzymes and bilirubin in the non-CF infant were reported [115]. In a further survey, no adverse effects were reported in 26 infants exposed to elexacaftor-tezacaftor-ivacaftor during breastfeeding, although eye examination was only undertaken in two of these infants [START_REF] Taylor-Cousar | Maternal and fetal outcomes following elexacaftortezacaftorivacaftor use during pregnancy and lactation[END_REF].

The decision as to whether to breastfeed while on VST should be taken after discussion between the CF team and the mother, with review of all available information (Statement 21, Table 2). For breastfeeding mothers on VST, monitoring of the infant (eye examination and liver function) should be considered.

Standards for patients with non-responsive CFTR gene variants

Peter van Mourik, Michael D. Waller, Jobst Roehmel

Approximately 10-20% of pwCF worldwide carry CF genotypes that render them ineligible for CFTR modulator therapies, including those with nonsense (premature stop) variants where clinical benefit from novel read-through agents has not been demonstrated [START_REF] Kerem | Ataluren for the treatment of nonsense-mutation cystic fibrosis: a randomized, doubleblind, placebo-controlled phase 3 trial[END_REF][START_REF] Guo | Worldwide rates of diagnosis and effective treatment for cystic fibrosis[END_REF]. Ancestral and geographical variations in the prevalence of non-responsive CFTR variants lead to varying proportions of pwCF with genotypes eligible for modulator therapies. This can lead to inequitable treatment opportunities [START_REF] Mcgarry | Cystic fibrosis patients of minority race and ethnicity less likely eligible for CFTR modulators based on CFTR genotype[END_REF][START_REF] Boeck | The relative frequency of CFTR mutation classes in European patients with cystic fibrosis[END_REF]. Marketing authorization often restricts the use of currently licensed modulators for unapproved CFTR variants, with clinical trial and efficacy data lacking for other, mostly rare, CFTR variants. Ex vivo CFTR function measurements can potentially determine the function of rare CFTR variants and assess possible responsiveness to approved modulator therapies [START_REF] Silva | Personalized medicine based on nasal epithelial cells: comparative studies with rectal biopsies and intestinal organoids[END_REF]. However, this approach is not routinely available in clinical practice.

Recent studies report that improvements in ex vivo biomarkers of CFTR function such as intestinal organoids and nasal epithelial cells correlate with improvements in outcomes such as increased FEV 1 and decreased sweat chloride concentration [START_REF] Silva | Personalized medicine based on nasal epithelial cells: comparative studies with rectal biopsies and intestinal organoids[END_REF][START_REF] Berkers | Rectal organoids enable personalized treatment of cystic fibrosis[END_REF][START_REF] Ramalho | Correction of CFTR function in intestinal organoids to guide treatment of cystic fibrosis[END_REF][START_REF] Dekkers | Characterizing responses to CFTR-modulating drugs using rectal organoids derived from subjects with cystic fibrosis[END_REF][START_REF] Muilwijk | Prediction of real-world long-term outcomes of people with CF homozygous for the F508del mutation treated with CFTR modulators[END_REF][START_REF] Anderson | CFTR function and clinical response to modulators parallel nasal epithelial organoid swelling[END_REF][START_REF] Sette | Theratyping cystic fibrosis in vitro in ALI culture and organoid models generated from patient-derived nasal epithelial conditionally reprogrammed stem cells[END_REF]. When ex vivo studies suggest that a CFTR variant may have some response to a specific therapy, then a clinical n-of-1 trial of that therapy is warranted [START_REF] Magaret | Expanding access to CFTR modulators for rare mutations: the utility of n-of-1 trials[END_REF] with clear endpoints of improvement in respiratory function and quality of life measures (Statement 22, Table 2).

In the absence of available VST, it is essential that pwCF continue to receive high quality care delivered by a specialist CF multi-disciplinary team at a specialist or accredited CF centre (Statement 23, Table 2) [START_REF] Mahadeva | Clinical outcome in relation to care in centers specializing in cystic fibrosis: cross sectional study[END_REF] .

Maintaining high quality care is imperative for all pwCF in the era of VST.

Experimental therapeutics in development and in clinical trials offer new possibilities to correct the underlying CF defect or dis-ease sequelae. This may improve treatment options for all pwCF, especially those who have had limited benefit from commercially available CFTR modulators. Healthcare providers should remain up to date regarding current and future clinical studies. PwCF should be informed about eligible research studies and be actively encouraged to participate ( https://apps.cff.org/trials/pipeline ) (Statement 24, Table 2 ).

12. The use of variant-specific therapies outside licence indications (for example, post-transplant or for patients with a CFTR-RD, CFSPID designation etc.)

Thomas Daniels, Carsten Schwarz, Carlo Castellani

PwCF and solid organ transplantation

VST has been shown to significantly improve several aspects of CF, however clinical trials of VST did not include pwCF who had been recipients of solid organ transplants (SOT). In Europe for example, elexacaftortezacaftor-ivacaftor is not recommended for use in transplanted pwCF, whereas the FDA label does not advise against use in the transplanted population.

In liver-transplanted pwCF, healthcare teams must consider the risk for liver toxicity and significant interactions with medications commonly used after liver transplant. VST side effects (such as raised transaminases) and interactions should be monitored. Decisions about starting VST should be made on a caseby-case basis and after careful consideration by the CF team and the transplant team, in partnership with the patient (Statement 25, Table 2). In most cases, the significant benefits in terms of pulmonary function and exacerbation rate will be considered to outweigh the risk of possible side effects. A recent report from the US patient registry reported indications and outcomes for 94 pwCF who had started elexacaftor-tezacaftorivacaftor after lung transplantation (median duration, 4.6 years) [START_REF] Ramos | Use of elexacaftor/tezacaftor/ivacaftor among cystic fibrosis lung transplant recipients[END_REF]. A significant number (42%) stopped elexacaftor-tezacaftor-ivacaftor due to side effects (median, 56 days after starting).

In lung-transplanted pwCF, it may be considered that the trans-planted lung has no CFTR dysfunction (although a donor may be a CF carrier), therefore any abnormality of the transplanted lung should not ordinarily be considered an indication for VST. It could be considered for use in exceptional circumstances when there is evidence of significant extrapulmonary CF disease despite maxi-mal medical therapy. One such extrapulmonary manifestation is chronic rhinosinusitis (CRS) which causes very unpleasant symptoms and reduces quality of life. Elexacaftor-tezacaftor-ivacaftor has been shown to improve CRS symptoms (as measured using the Sino-Nasal Outcome Tool and the Respiratory Domain of the CFQ-R) [START_REF] Dimango | Effect of highly effective modulator treatment on sinonasal symptoms in cystic fibrosis[END_REF]. CRS has been associated with increased risk for Chronic Lung Allograft Dysfunction (CLAD). It remains controversial whether aggressive treatment of CRS after lung transplant reduces the risk of developing CLAD [START_REF] Verleden | Chronic lung allograft dysfunction: definition, diagnostic criteria, and approaches to treatment-a consensus report from the Pulmonary Council of the ISHLT[END_REF][START_REF] Vital | Impact of sinus surgery on pseudomonal airway colonization, bronchiolitis obliterans syndrome and survival in cystic fibrosis lung transplant recipients[END_REF]. However, in selected post-lung transplant patients where CRS persists despite maximal med-ical therapy, a trial of VST should be considered and monitored accordingly. Another extrapulmonary manifestation of CF which may warrant consideration of VST is malnutrition. In lung-transplanted pwCF, BMI < 20 kg/m 2 and > 28 kg/m 2 has been associated with worse survival in a registry study, with the greatest effects seen at the extremes of BMI [START_REF] Fernandez | Association of body mass index with lung transplantation survival in the United States following implementation of the lung allocation score[END_REF]. VST has a positive effect on nutritional status for pwCF without SOT [START_REF] Middleton | Elexacaftor-tezacaftor-ivacaftor for cystic fibrosis with a single Phe508del Allele[END_REF]. Consideration of the use of VST to improve nutrition in malnourished lung transplant recipients when other standard methods of nutritional support have failed is recommended, with the associated caveats and monitoring listed above.

VST is associated with improvements in glycaemic control [START_REF] Scully | The effect of elexacaftor/tezacaftor/ivacaftor (ETI) on glycemia in adults wit cystic fibrosis[END_REF] and better glycaemic control is generally associated with better health outcomes [START_REF] Benhalima | The importance of glycemic control: how low should we go with HbA1c? Start early, go safe, go low[END_REF]. Preliminary data from a US registry study suggests elexacaftortezacaftor-ivacaftor in post-lung trans-plant recipients also improves glycaemic control in this group [START_REF] Ramos | Use of elexacaftor/tezacaftor/ivacaftor among cystic fibrosis lung transplant recipients[END_REF].

Intestinal manifestations for extrapulmonary CF are often under-appreciated but have a major impact on quality of life [START_REF] Rowbotham | The top 10 research priorities in cystic fibrosis developed by a partnership between people with CF and healthcare providers[END_REF]. These problems frequently persist after lung transplantation [START_REF] Gilljam | GI complications after lung transplantation in patients with cystic fibrosis[END_REF]. The effects of VST on gastrointestinal manifestations of CF in pre-transplant recipients is less well established, with effects failing to reach statistical significance in clinical trials [START_REF] Fajac | Nonrespiratory health-related quality of life in people with cystic fibrosis receiving elexacaftor/tezacaftor/ivacaftor[END_REF]. However, given the marked effect on QoL of gastrointestinal symptoms and their persistence after lung transplantation, it would be reasonable to consider a trial of VST in those for whom all other treatment op-tions have failed.

If a trial of elexacaftor-tezacaftor-ivacaftor is considered, it is worth noting the potential interaction between E-T-I and calcineurin inhibitors (especially tacrolimus) reported by Ramos and colleagues [START_REF] Ramos | Use of elexacaftor/tezacaftor/ivacaftor among cystic fibrosis lung transplant recipients[END_REF] . In a subset of 55 subjects not taking azole antifungal medication, 30 required a dose change of tacrolimus (7% required an increased dose, 47% a decreased dose, and 38% required no dose change). This experience reinforces the importance of careful monitoring of tacrolimus levels.

CFTR related disorders (CFTR-RD) and CF screen positive, inconclusive diagnosis (CFSPID)

CFTR-RD are clinical conditions associated with CFTR dysfunction that do not fulfil the diagnostic criteria for CF [START_REF] Bombieri | Recommendations for the classification of diseases as CFTR-related disorders[END_REF]. Their phenotype is usually mono-organ, and their genotype includes at least one variant with a level of residual CFTR function greater than typical CF {Sermet, unpublished #1465}. Hypothetically, CFTR modulators might be beneficial, depending on the CFTR gene variants associated with CFTR-RD. However, no recommendation can be made until 1) clear indications on CFTR-RD standards of diagnosis and care are made available to the medical community, 2) in vivo and ex vivo evidence of CFTR rescue in CFTR-RD variants are documented, and 3) VST clinical trials are undertaken in these populations and improved outcomes demonstrated (Statement 26, Table 2).

Infants with an unclear diagnosis following a positive CF new-born screening result are given the designation "CF Screening Positive, Inconclusive Diagnosis"(CFSPID) [START_REF] Barben | Updated guidance on the management of children with cystic fibrosis transmembrane conductance regulator-related metabolic syndrome/cystic fibrosis screen positive, inconclusive diagnosis (CRMS/CFSPID)[END_REF]. These infants are healthy and most remain healthy with no sequelae of the neonatal testing. Some children may receive a diagnosis of CF as they grow or develop clinical manifestations consistent with CFTR-RD. Children with a CFSPID designation who convert to a CF diagnosis should be considered for VST, if they have an eligible genotype (Statement 27, Table 2).

Assessment of cost-effectiveness and the ethics of access

Ciaran O'Neill, Jürg Barben, Clemence Martin

Various governments use cost-effectiveness analyses to assess the relative value for money of novel therapies compared to other uses of healthcare resources. Industry undertakes such analyses -often alongside clinical trials-which they present as part of a business case to evaluation boards (such as NICE in the UK), who advise government. This often forms part of the negotiation around the price at which a drug may be adopted for reimbursement in a publicly funded system (Statement 28, Table 2).

Cost-effectiveness analysis is intended to provide a rigorous and transparent process by which evidence can be generated and in-formed decisions made. However, increasingly, where the cost-effectiveness ratio breaches accepted thresholds for approval, decisions around the price at which drugs are approved for reimbursement are made behind closed doors. This enables access at a price below that listed without compromising the manufacturer's ability to negotiate with other potential purchasers. From the perspective of an individual country this model may allow them to access novel therapies at below list price. From the perspective of industry, it may allow them to act more effectively as a discriminating monopoly to maximize their profits and invest in further research and development. From the perspective of the user of these therapies it may afford access to life changing therapies that would not otherwise be available.

There are, however, risks and ethical considerations associated with this approach. Within one country, reimbursing therapy that breaches accepted norms for cost-effectiveness effectively gives preferential access to healthcare resources to one patient group over others in society. This may be facilitated by advocacy groups who can readily present patients who would benefit from the new therapy, while policy makers struggle to present to the public those patients who lose because their care can no longer be purchased. A further issue is that not all profits are reinvested in R&D and that the exercise of monopoly power and secrecy around pricing may serve to deter competition in this market.

Pricing of new medicines usually begins in the US as this is the largest market. After FDA approval in terms of safety and efficacy, the company sets a price they consider appropriate. Competition is then limited by patent law which can be extended in the case of rare and orphan diseases. The US price sets a benchmark that may influence price negotiations in other jurisdictions. Patents are neither bad nor good. They can benefit or harm a society and its economy. But they only make sense if the overall benefit for the general public outweighs the harm. This is the only way to politically justify states granting a monopoly to individuals or companies, who can turn it into a business free of competition (Statement 29, Table 2).

The considerable benefits of VST have been somewhat diminished by global inequities in access. Cost is undoubtedly a factor, and the field should reflect on how future developments can benefit all eligible pwCF, regardless of their circumstance or location (Statement 30, Table 2 ) [ 138 , 139 ].

Conclusion

VST represents a paradigm shift for the management of pwCF with eligible CFTR gene variants. CFTR modulators are the first agents to clearly show that correcting the underlying molecular defect is possible, and that this results in profound and significant improvement in clinical outcomes. As with most novel therapies, introduction of these agents has been complex, and this remains an emerging area. This paper provides clear evidence-based and pragmatic guidance for pwCF and their CF teams.

Acknowledgments

The authors thank Fiona Dunlevy, who provided editorial sup-port and coordinated the Delphi consultation. We also thank the ECFS board who supported the project. We thank the team at the CF Cochrane Review Group for support throughout this project. We also thank the ECFS board and CF Europe for their contribution.

Author credit

The core committee (KWS, CC, AD, AS, SvKR, DvD, EL) established the framework for the exercise and identified experts to produce each section (highlighted in the paper). All members of the faculty contributed to the delphi process and had oversight of the final paper. Fiona Dunlevy provided overall administrative sup-port and medical writing skills to produce a consistent document. Conflict of interest statements are fully recorded in supplemental materials.