Dr Valérie Attali
email: valerie.attali@aphp.fr

Marie-Françoise Vecchierini

Jean-Marc Collet

Marie -Pia D'ortho

Frederic Goutorbe

Jean-Baptiste Kerbrat

Damien Leger

Florent Lavergne

Christelle Monaca

Pierre-Jean Monteyrol

Laurent Morin

Eric Mullens

Bernard Pigearias

Francis Martin

Fabienne Tordjman

Hauria Khemliche

Lionel Lerousseau

Jean- Claude Meurice

Efficacy and tolerability of a custom-made Narval mandibular repositioning device for the treatment of obstructive sleep apnea: ORCADES study 2-year follow-up data

ABSTRACT

Objective/Background: Mandibular repositioning device (MRD) therapy is an alternative to continuous positive airway pressure (CPAP). The ORCADES study is assessing the long-term efficacy and tolerability of MRD therapy in OSAS; 2-year follow-up data are presented.

Patients/Methods: OSAS patients who refused or were noncompliant with CPAP were fitted with a custom-made computer-aided design/computer-aided manufacturing (CAD/CAM) biblock MRD (ResMed, Narval CC™); mandibular advancement was individually titrated.

Sleep and respiratory parameters were determined at baseline, 3-6 months and 2 years. The primary endpoint was treatment success (percentage of patients achieving a 50% reduction in the apnoea-hypopnoea index [AHI]).

Results: Of 315 enrolled patients, 237 remained on MRD treatment at 2 years and 197 had follow-up data. Treatment success rate at 2 years was 67%; AHI <5/h, <10/h and <15/h was achieved in 30%, 56% and 72% of patients, respectively. On multivariate analysis, 50%

decrease in AHI at 3-6 months and absence of nocturia at 3-6 months were significant predictors of MRD treatment continuation. Adverse events were generally mild and the majority occurred in the first year of treatment.

Conclusions: Two years' treatment with an MRD was effective and well tolerated in patients with mild to severe OSAS who refused or were intolerant of CPAP.

Introduction

Obstructive sleep apnoea syndrome (OSAS) is characterised by recurrent obstructions of upper airways during sleep, which result in sleep fragmentation and intermittent hypoxia [START_REF] Levy | Obstructive sleep apnoea syndrome[END_REF].

Moderate to severe OSAS is associated with cardiovascular, metabolic and cognitive comorbidities, and sleepiness-related accidents [START_REF] Campos-Rodriguez | Cardiovascular mortality in women with obstructive sleep apnea with or without continuous positive airway pressure treatment: a cohort study[END_REF][START_REF] Heinzer | Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study[END_REF][START_REF] Jordan | Adult obstructive sleep apnoea[END_REF]. Continuous positive airway pressure (CPAP) remains the gold standard treatment for OSAS [START_REF] Barbe | Effect of continuous positive airway pressure on the incidence of hypertension and cardiovascular events in nonsleepy patients with obstructive sleep apnea: a randomized controlled trial[END_REF]. CPAP therapy reduces the apnoea-hypopnoea index (AHI), improves symptoms and quality of life, reduces the risk of motor vehicle crashes [START_REF] Tregear | Continuous positive airway pressure reduces risk of motor vehicle crash among drivers with obstructive sleep apnea: systematic review and meta-analysis[END_REF], and potentially reduces cardiovascular events and mortality [START_REF] Drager | Sleep Apnea and Cardiovascular Disease: Lessons From Recent Trials and Need for Team Science[END_REF][START_REF] Sanchez-De-La-Torre | Obstructive sleep apnoea and cardiovascular disease[END_REF][START_REF] Marin | Association between treated and untreated obstructive sleep apnea and risk of hypertension[END_REF]. However, as many as 30-50% of patients prescribed CPAP are non-compliant with therapy over the long term [START_REF] Meurice | Predictive factors of long-term compliance with nasal continuous positive airway pressure treatment in sleep apnea syndrome[END_REF][START_REF] Weaver | Adherence to continuous positive airway pressure therapy: the challenge to effective treatment[END_REF][START_REF] Wolkove | Long-term compliance with continuous positive airway pressure in patients with obstructive sleep apnea[END_REF].

A mandibular repositioning device (MRD) is recommended as the first alternative to CPAP [START_REF] Marklund | Update on Oral Appliance Therapy for OSA[END_REF] in patients requiring treatment for OSAS. The MRD prevents recurrent obstruction of the upper airways during sleep by maintaining the mandible in a forward position to enlarge [START_REF] Chan | The effect of mandibular advancement on upper airway structure in obstructive sleep apnoea[END_REF] and maintain an open airway [START_REF] Kato | Dose-dependent effects of mandibular advancement on pharyngeal mechanics and nocturnal oxygenation in patients with sleep-disordered breathing[END_REF], and significantly reduces the AHI [START_REF] Vecchierini | A custom-made mandibular repositioning device for obstructive sleep apnoea-hypopnoea syndrome: the ORCADES study[END_REF]. Although MRD therapy is not as effective as CPAP in controlling the occurrence of obstructive events [START_REF] Sharples | Meta-analysis of randomised controlled trials of oral mandibular advancement devices and continuous positive airway pressure for obstructive sleep apnoea-hypopnoea[END_REF],

this is counterbalanced by better adherence to treatment [START_REF] Almeida | Patient preferences and experiences of CPAP and oral appliances for the treatment of obstructive sleep apnea: a qualitative analysis[END_REF]. Therefore, improvement in symptoms and quality of life after up to 12 months are similar with MRD therapy and CPAP [START_REF] Aarab | Long-term follow-up of a randomized controlled trial of oral appliance therapy in obstructive sleep apnea[END_REF]. However, there is a lack of data on the longer term effects of second-line MRD therapy in patients with OSAS.

The multicentre, prospective ORCADES study was designed to investigate the long-term effects of MRD therapy in OSA patients non-compliant with or intolerant of CPAP with follow-up for 5 years. The first analysis of data after 6 months of follow-up showed a significant reduction in AHI and symptoms during MRD therapy, which was well tolerated [START_REF] Vecchierini | A custom-made mandibular repositioning device for obstructive sleep apnoea-hypopnoea syndrome: the ORCADES study[END_REF]. Patients were treated either with a custom-made computer-aided design/computer-aided manufacturing (CAD/CAM) bi-block MRD (ResMed, Narval CC™; 84% of patients) or a non-CAD/CAM MRD device (ResMed, Narval™). Early evaluation suggested that the CAD/CAM device, which allows more accurate adjustment of the vertical opening, was superior to the non-CAD/CAM MRD [START_REF] Vecchierini | A custom-made mandibular repositioning device for obstructive sleep apnoea-hypopnoea syndrome: the ORCADES study[END_REF]. Therefore, this 2-year follow-up of the ORCADES trial focusses on patients with OSAS treated with the CAD/CAM MRD.

Methods

Study design

ORCADES was a single-arm prospective observational study that was conducted at 28 centres in France (NCT01326143). Full details of the study design have been reported

previously [START_REF] Vecchierini | A custom-made mandibular repositioning device for obstructive sleep apnoea-hypopnoea syndrome: the ORCADES study[END_REF]. The study protocol was approved by the relevant ethics committees, and all procedures were conducted in accordance with the Declaration of Helsinki principles. All patients received detailed information and gave written informed consent to participate.

Patients

Adult patients (age ≥18 years) with OSAS (AHI >30/h, or AHI <30/h with excessive daytime sleepiness and/or an Epworth Sleepiness Scale [ESS] score >10) who refused or were noncompliant with CPAP (device usage <3 h/night) and had not previously received MRD treatment were screened by a sleep specialist. Only those without any contraindications to MRD treatment, as confirmed by a dental sleep specialist, were included. Patient should not presented dental, periodontal or articular contraindications. A patient completely edentulous or presenting partial toothless (less than 3 teeth (or implants) by hemi-arch including the canine at the maxillary level, or presenting less than 4 teeth (or implants) by hemi-arch including the canine at the mandibular level was not enrolled in the study.

MRD titration and follow-up

Patients included in this analysis were treated with a custom-made CAD/CAM MRD device (ResMed, Narval CC™). The device was fitted by a dental specialist; initial mandibular advancement that was adjusted over a 15-mm range (the maximal advancement allowed with MRD depending of the connecting rod size) at subsequent titration visits, to achieve the best balance between clinical efficacy and tolerability. The first evaluation took place 4-6 months after treatment initiation [START_REF] Vecchierini | A custom-made mandibular repositioning device for obstructive sleep apnoea-hypopnoea syndrome: the ORCADES study[END_REF], then patients were re-evaluated at the 2-year follow-up visit.

MRD replacement during the study was performed based on routine clinical practice.

Endpoints

The primary endpoint was the treatment success rate, defined as the percentage of patients achieving a 50% reduction in AHI at the 2-year follow-up visit. Absolute change in AHI from baseline to 2-year follow-up, and from baseline to 3-6 months and 2 years was also determined. The percentage of patients achieving an AHI below three cut-off values (<5/h, <10/h and 15/h) was calculated, overall and in patient subgroups based on OSAS severity at baseline (mild: AHI 5/h to ≤15/h; moderate: AHI 15/h to ≤30/h; severe: AHI >30/h).

Additional nocturnal respiratory endpoints were the oxygen desaturation index (ODI; average number of desaturation episodes per hour, with desaturation defined as a ≥3% decrease in oxygen saturation [SpO2] from the average value), the lowest SpO2 (nadir SpO2), and total time with SpO2 <90%. In patients who underwent PSG, total sleep time, sleep latency, percentage of slow wave and rapid eye movement (REM) sleep, micro-arousal index and intra-sleep wakefulness were determined. Clinical efficacy, tolerability and device usage were determined as described below.

Clinical evaluation

Clinical evaluation at the 2-year follow-up included the same endpoints as the 3-to 6-month follow-up [START_REF] Vecchierini | A custom-made mandibular repositioning device for obstructive sleep apnoea-hypopnoea syndrome: the ORCADES study[END_REF]. Briefly, somnolence was evaluated using the ESS, and snoring, nocturia, libido disorders and nocturnal mouth breathing were self-reported (yes/no). Patients were asked to rate their sleep quality, state on waking and morning headache on non-graduated 10 cm visual analogue scales (VAS), from "very bad" to "excellent" for sleep quality and state on waking, and from "absence of pain" to "maximal pain" for morning headache. Quality of life was evaluated using the Quebec Sleep Questionnaire (QSQ) [START_REF] Lacasse | A new standardised and self-administered quality of life questionnaire specific to obstructive sleep apnoea[END_REF] and a Pichot fatigue scale questionnaire was administered [START_REF] Pichot | Brief self-evaluation questionnaire for depressive, asthenic and anxious dimensions[END_REF]. Data on MRD-related side effects and their severity were determined by sleep and dental sleep physicians. Self-reported MRD compliance (hours per night; nights per week) was assessed.

Sleep studies

Evaluation of the AHI was based on ventilatory polygraphy (PG) or polysomnography (PSG).

The same test was used in the same patient at baseline, 3-6 months and 2 years. PSG/PG recordings were manually scored according to the American Academy of Sleep Medicine (AASM) guidelines [START_REF]Sleep-related breathing disorders in adults: recommendations for syndrome definition and measurement techniques in clinical research. The Report of an American Academy of Sleep Medicine Task Force[END_REF]. Obstructive apnoea was defined as a ≥10-s cessation of airflow on the pressure nasal cannula, with or without association with an oro-nasal thermal sensor.

Hypopnoea was defined as a ≥50% reduction in airflow, or a <50% airflow reduction on the nasal pressure cannula accompanied by a ≥3% decrease in arterial oxyhaemoglobin saturation (SpO2) recorded using finger pulse oximetry or an arousal.

Statistical analysis

The intention-to-treat (ITT) population for this analysis included all patients using a CAD/CAM MRD device. Values are presented as median and interquartile range (IQR) for quantitative variables, and number and percentage for qualitative variables. Quantitative changes from baseline to the 2-year follow-up visit were compared using unpaired or paired Student's t-test or the Wilcoxon-Mann-Whitney nonparametric test depending on normality of distribution and group comparison. Qualitative changes were described using frequency distribution and compared using Fisher's exact test or Chi-squared test. Change over time in AHI, 3% ODI, time with SpO2 <90%, ESS score, symptoms (snoring, nocturia, libido disorders, nocturnal mouth breathing), QSQ global and sub-scores, and Pichot questionnaire results was determined using a repeated measures ANOVA; if significant this was followed by a Tuckey's test to compare visits two by two. Comparisons between patient subgroups based on baseline OSAS severity, gender and body mass index (BMI) were assessed using the Student's t-test, ANOVA or Wilcoxon-Mann-Whitney test. Two logistic models were created and backward stepwise regression analysis was used to determine independent factors associated with continuation of treatment until the 2-year follow-up in the ITT population (first model) and achievement of AHI <10/h at 2-year follow-up in patients with available 2year AHI data (model 2). For both models, variables with a p-value <0.10 in univariate analysis were entered in the stepwise logistic regressions, and variables with a p-value <0.05 were retained in the final multivariate models. Statistical analyses were performed using SAS version 9.

Results

Population

A total of 540 patients were screened, 165 patients were excluded and 315 were treated with a CAD/CAM MRD (Figure 1). The majority of patients were male (76%), 20% were obese and 51% had previously been treated with CPAP (Table 1). The number [IQR] of initial MRD titrations was of 2.0 [1.0, 3.0], and final mandibular advancement was 7.0 [6.0; 8.0] mm. The 2-year follow-up visit was completed for 197 of the 237 patients who remained on treatment, with a median follow-up of 24 [25; 28] months; the 2-year follow-up visit was pending for the remaining 40 patients. Median changes from baseline in weight (0 [-3; 2] kg), BMI (0.28 [-0.73; 0.99] kg/m 2 ), neck circumference (0 [-1; 1] cm) and waist circumference (0 [-2; 4] cm)

were not statistically significant and only seven patients needed to have their MRD replaced before the 2-year follow-up visit.

Withdrawals

A total of 78 patients (25%) were withdrawn before the 2-year follow-up visit, mainly due to side effects (30 patients), or lack of efficacy (21 patients) (Figure 1). The overall proportion of withdrawals did not vary by baseline OSAS severity and gender, but the rate of withdrawal due to adverse events was higher in females than in males (65% vs 32%; p=0.0098).

Withdrawal occurred more frequently in obese versus non-obese patients (40% vs 21%; p=0.0024) and obese patients were withdrawn more often for lack of efficacy than non-obese patients (44% vs 19%; p=0.0195). The majority of withdrawals (83%) occurred within the first 6 months of MRD therapy (Figure 2).

Sleep study data

AHI data were available for 191 patients (132 underwent PG and 59 had PSG). A 50% reduction in the AHI was achieved in 67% of participants. The proportion of patients achieving an AHI of <15/h, <10/h and <5/h was 72%, 56% and 30%, respectively (Figure 3). After 2 years, the reduction in AHI from baseline was -15 [-23; -7]/h (-64 [-83; -42]%). AHI, 3% ODI, time with SpO2< 90% and nadir SpO2 values decreased significantly from baseline to 2-year follow-up (Table 2). In the 59 patients with 2-year PSG data, the change from baseline in median sleep latency was -5 [-24; 2] minutes (p=0.0014) and in micro-arousal index was -8 [-13; 1]/h (p=0.0001). No changes in the percentage of slow wave and REM sleep were observed.

Symptoms and quality of life

Device usage

At the 2-year follow-up, median [IQR] MRD usage was 7 [7; 7] nights/week and 7 [6; 8] hours/night; 95% of patients used their MRD for 4 hours/night on 4 nights/week, and 85% for 4 hours/night on 7 days/week. Device usage was similar across patient subgroups based on OSA severity, gender or BMI.

Predictive factors

A number of factors were significant predictors of either treatment continuation or AHI <10/h at 2 years in the univariate analysis (Table 3). Only two variables remained significant predictors of treatment continuation in the multivariate analysis: a 50% decrease in AHI at 3-6 months' follow-up and the absence of nocturia at 3-6 months' follow-up (Figure 5). There were also two significant predictors of AHI <10/h at the 2-year follow-up: smaller initial AI and the absence of previous CPAP treatment (Figure 5).

Tolerability

At least one adverse event was reported by 59% of patients. The most common event was TMJ disorder (Table 4). Of the 509 adverse events recorded by the 2-year follow-up, 137 (27%) were reported in the first 6 months of therapy and 64 (13%) were reported in the first year. Only 13% of all events were classified as severe (Table 4). 30 patients withdrawn the study for side effects before the 2 year evaluation, as follow: dental pain (7 pts), TMJ disorder

Discussion

Two-year follow-up data from the multicentre, prospective ORCADES study showed that MRD therapy remained effective and well-tolerated in patients with mild to severe OSAS who refused, were intolerant of, or non-compliant with CPAP.

Non-compliance with CPAP is an important concern in OSAS management [START_REF] Weaver | Adherence to continuous positive airway pressure therapy: the challenge to effective treatment[END_REF]. MRD therapy is recommended as a potential first-line treatment option for mild to moderate OSA patients without cardiovascular comorbidities, but guidelines also acknowledge that an MRD provides a non-surgical second-line treatment option and is better than no treatment for adult patients intolerant of CPAP or who prefer alternate therapy [START_REF] Ramar | Clinical Practice Guideline for the Treatment of Obstructive Sleep Apnea and Snoring with Oral Appliance Therapy: An Update for 2015[END_REF]. Several studies have investigated the long-term effects of MRD in OSAS, but mainly included only a small number of mild to moderate OSAS patients [START_REF] Fransson | Effects of a mandibular protruding device on the sleep of patients with obstructive sleep apnea and snoring problems: a 2-year follow-up[END_REF][START_REF] Gong | Long-term therapeutic efficacy of oral appliances in treatment of obstructive sleep apnea-hypopnea syndrome[END_REF][START_REF] Marklund | Long-term efficacy of an oral appliance in early treated patients with obstructive sleep apnea[END_REF][START_REF] Rose | Therapeutic efficacy of an oral appliance in the treatment of obstructive sleep apnea: a 2-year follow-up[END_REF][START_REF] Eriksson | A prospective 10-year follow-up polygraphic study of patients treated with a mandibular protruding device[END_REF][START_REF] Gauthier | Mandibular advancement appliances remain effective in lowering respiratory disturbance index for 2.5-4.5 years[END_REF]. Larger comparative [START_REF] Aarab | Long-term follow-up of a randomized controlled trial of oral appliance therapy in obstructive sleep apnea[END_REF][START_REF] Doff | Oral appliance versus continuous positive airway pressure in obstructive sleep apnea syndrome: a 2-year follow-up[END_REF][START_REF] Walker-Engstrom | 4-year follow-up of treatment with dental appliance or uvulopalatopharyngoplasty in patients with obstructive sleep apnea: a randomized study[END_REF][START_REF] Ghazal | A randomized prospective long-term study of two oral appliances for sleep apnoea treatment[END_REF] or noncomparative [START_REF] Fransson | Effects of a mandibular protruding device on the sleep of patients with obstructive sleep apnea and snoring problems: a 2-year follow-up[END_REF][START_REF] Marklund | Long-term efficacy of an oral appliance in early treated patients with obstructive sleep apnea[END_REF][START_REF] Gupta | The long-term effects of mandibular advancement splint on cardiovascular fitness and psychomotor performance in patients with mild to moderate obstructive sleep apnea: a prospective study[END_REF][START_REF] Marklund | Mandibular advancement device in patients with obstructive sleep apnea : long-term effects on apnea and sleep[END_REF] trials evaluated an MRD as first-line therapy, but only one reported long-term data in CPAP-intolerant patients [START_REF] Anandam | Cardiovascular mortality in obstructive sleep apnoea treated with continuous positive airway pressure or oral appliance: an observational study[END_REF].

The purpose of the 5-year ORCADES study is to provide long-term evaluation of MRD as second-line treatment of OSAS in patients with a range of disease severity. The large number of patients included (n=315) and continuing treatment at 2 years (n=237), the selection of a homogeneous population intolerant of or refusing CPAP, and the high proportion of individuals with severe disease are important strengths of this study. In addition, particular attention was payed to adapting the study design to follow the most recent guidelines on MRD treatment [START_REF] Ramar | Clinical Practice Guideline for the Treatment of Obstructive Sleep Apnea and Snoring with Oral Appliance Therapy: An Update for 2015[END_REF]. Sleep and dental maxillofacial specialists were both involved to ensure selection of the right patients and to exclude those with contraindications for MRD therapy.

The CAD/CAM MRD was a custom-made titratable device and a titration period was included to achieve mandibular propulsion that maximised resolution of symptoms, tolerability and AHI reduction before patients entered the long-term follow-up. In addition, this 2-year interim analysis provided important information to improve understanding of therapy withdrawal and adverse event rate evolution over time at a time point in therapy where patients should, in theory, renew their MRD.

As well as these strengths, the study also has a number of limitations. The most important is the observational, registry-based design, without random allocation to treatment. However, patient management in this setting is representative of routine clinical practice and our findings are similar to those of another observational cohort study [START_REF] Attali | Predictors of long-term effectiveness to mandibular repositioning device treatment in obstructive sleep apnea patients after 1000 days[END_REF]. The findings are therefore likely to have good external validity. Seventy-eight patients withdrew from our study before the 2-year assessment and 40 were still awaiting assessment. This left a total of 191 patients (60% of the ITT population) who had an AHI evaluation at 2 years, something that could influence the study results and their interpretation. The reduction in patient numbers over time highlights the difficulty in maintaining adherence to chronic therapy and retaining patients in a clinical pathway, even when therapy is reimbursed. Such difficulties have been described previously [START_REF] Attali | Predictors of long-term effectiveness to mandibular repositioning device treatment in obstructive sleep apnea patients after 1000 days[END_REF][START_REF] Iglay | Metaanalysis of studies examining medication adherence, persistence, and discontinuation of oral antihyperglycemic agents in type 2 diabetes[END_REF] and were taken into account in our multivariate model analysis of treatment continuation, where non-analysed patients were considered as treatment failures. It is also important to acknowledge that two different types of patients were enrolled in the study: those intolerant of CPAP therapy and those who refused CPAP. This could have influenced the study findings, as indicated in the univariate analysis on treatment success (AHI <10/h). More research is needed to differentiate and identify specific traits of these two populations. Another study limitation to mention is that two types of sleep test (PG and PSG) were used in the study to evaluate respiratory events, however each patient was evaluated with the same sleep test all along the study which limits discrepancy.

In our study, we defined the rate of treatment success as a 50% reduction in AHI because it is an endpoint that has been widely used in non-CPAP surgical intervention and MRD studies [START_REF] Walker-Engstrom | 4-year follow-up of treatment with dental appliance or uvulopalatopharyngoplasty in patients with obstructive sleep apnea: a randomized study[END_REF][START_REF] Bettega | Obstructive sleep apnea syndrome. fifty-one consecutive patients treated by maxillofacial surgery[END_REF][START_REF] Lee | A Comparison of Different Success Definitions in Non-Continuous Positive Airway Pressure Treatment for Obstructive Sleep Apnea Using Cardiopulmonary Coupling[END_REF], thus allowing easy comparison of findings, and is suited to evaluating MRD efficacy related to quality of sleep [START_REF] Lee | A Comparison of Different Success Definitions in Non-Continuous Positive Airway Pressure Treatment for Obstructive Sleep Apnea Using Cardiopulmonary Coupling[END_REF]. The treatment success rate in this analysis (67%), without any difference between OSAS severity subgroups, is consistent with previous longterm studies [START_REF] Marklund | Update on Oral Appliance Therapy for OSA[END_REF]. To improve sensitivity and clinical relevance, we also performed analyses using three different residual AHI thresholds (<15/h, <10/h and <5/h). Residual AHI <10/h is commonly related to long-term control of symptoms [START_REF] Wee | Comparison of success criteria based on long-term symptoms and new-onset hypertension in mandibular advancement device treatment for obstructive sleep apnoea: observational cohort study[END_REF], and was observed in 56% of patients. In our study, 72% of patients had an AHI <15/h, which has been associated with a reduction in the risk of new-onset hypertension [START_REF] Wee | Comparison of success criteria based on long-term symptoms and new-onset hypertension in mandibular advancement device treatment for obstructive sleep apnoea: observational cohort study[END_REF]. The AHI findings were consistent with the maintenance of good OSAS symptom control, good sleep quality and good quality of life, including all domains of the QSQ. In the subgroup of patients with severe OSAS at baseline, the proportion of patients achieving an AHI <10/h and <15/h was 37% and 53%, respectively, suggesting that long-term MRD treatment is a good alternative to CPAP for some of these patients. An AHI <5/h is often used to evaluate CPAP efficacy [START_REF] Marin | Long-term cardiovascular outcomes in men with obstructive sleep apnoea-hypopnoea with or without treatment with continuous positive airway pressure: an observational study[END_REF], and was achieved by 30% of patients during MRD therapy. However, this threshold may not be as appropriate for MRD evaluation based on the findings of relevant MRD studies [START_REF] Wee | Comparison of success criteria based on long-term symptoms and new-onset hypertension in mandibular advancement device treatment for obstructive sleep apnoea: observational cohort study[END_REF][START_REF] Ravesloot | Reliable calculation of the efficacy of non-surgical and surgical treatment of obstructive sleep apnea revisited[END_REF]. Although the AHI <5/h cut-off was determined to define OSAS based on historical cohorts [START_REF] Bixler | Prevalence of sleep-disordered breathing in women: effects of gender[END_REF][START_REF] Duran | Obstructive sleep apnea-hypopnea and related clinical features in a population-based sample of subjects aged 30 to 70 yr[END_REF][START_REF] Young | The occurrence of sleepdisordered breathing among middle-aged adults[END_REF], recent data suggest that the prevalence of sleep-disordered breathing in the general population based on an AHI >5/h would be 84% in men and 61% in women [START_REF] Heinzer | Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study[END_REF]. It was suggested that the higher apparent prevalence of sleep-disordered breathing in recent versus historical studies might be explained by the increased sensitivity of current recording techniques and scoring criteria. In addition, revision of the AHI criteria for definition of OSAS may be appropriate based on recent findings of a lack of association between mild OSAS and cardiac morbidity [START_REF] Campos-Rodriguez | Cardiovascular mortality in women with obstructive sleep apnea with or without continuous positive airway pressure treatment: a cohort study[END_REF][START_REF] Heinzer | Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study[END_REF].

In our study, MRD therapy was associated with relatively consistent control of the AHI over time. However, there was a slight increase in the median AHI at the two-year follow-up in the absence of weight gain [START_REF] Eriksson | A prospective 10-year follow-up polygraphic study of patients treated with a mandibular protruding device[END_REF] and irrespective of OSAS severity (Figure 3). Only seven patients had an MRD replacement before the 2-year follow-up, and it is possible that the slight increase in AHI could simply be due to a worn device even though long-term increases in the AHI over a median follow-up of 16.6 years have been reported in a small group of patients using an optimally titrated MRD in the absence of weight change [START_REF] Marklund | Long-term efficacy of an oral appliance in early treated patients with obstructive sleep apnea[END_REF]. It is important to note that increasing age and bite changes over time could influence long-term assessments of MRD effectiveness [START_REF] Marklund | Update on Oral Appliance Therapy for OSA[END_REF]. These factors will be taken into account for the 5-year follow-up of the ORCADES study.

Baseline AI and absence of previous CPAP treatment were independent predictors of a complete response to MRD treatment (AHI <10/h). Baseline AI and others factors such as gender or positional OSAS have previously been reported to be related to MRD efficacy [START_REF] Vecchierini | A custom-made mandibular repositioning device for obstructive sleep apnoea-hypopnoea syndrome: the ORCADES study[END_REF][START_REF] Marklund | Mandibular advancement devices in 630 men and women with obstructive sleep apnea and snoring: tolerability and predictors of treatment success[END_REF][START_REF] Sutherland | Oral Appliance Treatment Response and Polysomnographic Phenotypes of Obstructive Sleep Apnea[END_REF]. Conversely, the absence of previous CPAP treatment has not previously been associated with long-term AHI reduction on MRD to the best of our knowledge, although it was predictive of MRD treatment continuation in one observational study [START_REF] Attali | Predictors of long-term effectiveness to mandibular repositioning device treatment in obstructive sleep apnea patients after 1000 days[END_REF]. This suggests that patients intolerant of CPAP may be at greater risk of not having a long-term response to MRD therapy. However, even if treatment may be slightly less efficient over the long-term, use of an MRD could help retain these vulnerable patients in the care network. This was supported by our observation that some patients accepted a return to CPAP therapy after MRD treatment cessation. Absence of nocturia and a 50% reduction in AHI at short-term follow-up were independent predictors of long-term MRD therapy continuation; of these, relapse of nocturia has previously been associated with MRD treatment cessation [START_REF] Attali | Predictors of long-term effectiveness to mandibular repositioning device treatment in obstructive sleep apnea patients after 1000 days[END_REF].

The CAD/CAM MRD used in this study was well tolerated. The majority of adverse events were of mild intensity, most were observed within the first 6 months of treatment, and the majority of withdrawals (83%) occurred within 6 months of MRD therapy initiation. Taken together with the predictors of therapy continuation found in our study, this highlights the importance of optimal early control of AHI and symptoms and early identification and management of adverse events for achievement and maintenance of MRD efficacy and compliance.

This second interim analysis of the 5-year ORCADES study showed that 2 years of MRD therapy was effective and well-tolerated in patients with mild to severe OSAS who refused or were intolerant of CPAP. Long-term maintenance of a complete response to MRD therapy was significantly more likely in patients who refused CPAP compared with those who were intolerant or noncompliant with CPAP.

Acknowledgements: Editing assistance was provided by Nicola Ryan, independent medical writer, funded by ResMed.

Study funding and role of the funding source:

The ORCADES study was funded by ResMed (France). The Executive Steering Committee defined the study design and is responsible for the clinical and scientific conduct of the study and publication of the results. C.R.O. Clinact (France) mandated by ResMed performed the collection, quality control, management and analysis of the data. The Executive Steering Committee had full access to all of the data and takes responsibility for the integrity and accuracy of the data analysis.

TABLES

A

  total of 81% of patients had an ESS score <10 at the 2-year follow-up. The ESS score decreased from 11 [8; 15] at baseline to 7 [5; 10] at 3-6 months and 7 [4; 9] at 2 years (p<0.0001); reductions were similar across OSAS severity subgroups. The QSQ global score increased from 144.0 [111.0; 173.0] at baseline to 180.5 [153.0; 201.0] at 3-6 months and 191.5 [94.0; 205.0] at 2 years (p<0.001), and the Pichot score decreased from 14.0 [7.0; 20.0] at baseline to 7.0 [3.0; 14.0] at 3-6 months and 6.0 [3.0; 11.0] at 2 years (p<0.001). Changes over time in symptoms and QSQ subscores are shown in Figure 4.

( 7

 7 pts), gingival pain (5 pts), occlusion change (2 pts), tooth loosening (1 pt), mouth pain (1 pt), discomfort (1 pt), mouth dryness (1 pt), nausea (1 pt), suspected allergy (1 pt) and other reasons (3 pts).

FiguresFIGURE 1

 1 Figures

FIGURE 2 FIGURE 3

 23 FIGURE 2 Proportion of patients continuing mandibular repositioning device therapy over

FIGURE 4

 4 FIGURE 4 Proportion of patients with different symptoms and Epworth Sleepiness Scale

FIGURE 5

 5 FIGURE 5 Forest plot of multivariate analysis showing predictors of apnoea-hypopnoea

TABLE 1

 1 Demographic, respiratory and clinical data at baseline for the intention-to-treat population

	Baseline characteristics

TABLE 2

 2 Change in sleep and respiratory parameters over time during MRD therapy.

	(n=191)	Baseline	3-6 months	2 years
	AHI, /h	26 [18; 35]	6 [3; 11]*	8 [4; 16]*
	3% ODI, /h	17 [9; 29]	5 [2; 12]*	8 [3; 15]*
	Time with SpO2 <90%, %	7 [1; 22]	0 [1; 9]**	0 [1; 9]**
	Nadir SpO2, %	84 [87; 94]	87 [90; 95]*	87 [89; 96]*
	Values are median [interquartile range].
	AHI, apnoea-hypopnoea index; ODI, oxygen desaturation index; SpO2, oxygen saturation.
	*p<0.0001 vs baseline; **p<0.0004 vs baseline.

TABLE 3 :

 3 Univariate analysis of predictive factors based on continuation of treatment after two years and achievement of reduction of an apnoea-hypopnoea index AHI of <10/h at the 2-year follow-up

	Variable

MRD, mandibular repositioning device; TMJ, temporo-mandibular joint.


Thibault Béziers

La Fosse

Massimo Tisi

Erwan Bousse

Jean-Marie Mottu

Gerson

Towards platform specific energy estimation for executable domain-specific modeling languages

Towards platform specific energy estimation for executable domain-specific modeling languages Thibault Béziers la Fosse * , Massimo Tisi * , Erwan Bousse † , Jean-Marie Mottu † * , Gerson Sunyé † LS2N, UMR CNRS 6004, * IMT Atlantique, † Université de Nantes {firstname.lastname}@ls2n.fr Abstract-Energy consumption is becoming a major subject when designing, developing and running programs. Most developers code and run their applications in an energy oblivious manner, mostly because of a lack of energy-related knowledge about their system. This problem also exists in the realm of executable domain-specific modeling languages, where end-users create models conforming to a given meta-model and execute them with little knowledge about their operational semantic and related energy consumption. In this work, we propose a domainspecific language for decorating meta-models of executable languages with platform-specific energy estimation formulas. We also extend the GEMOC execution engine to dynamically perform energy estimations on any executable model conforming to the decorated meta-model. The energy estimation model defined can then be easily adapted to other models and platforms, without requiring any measurement tooling or knowledge from the enduser.

Index Terms-Model-Driven Engineering, xDSMLs, Energy Estimation

I. INTRODUCTION

In 2007, Jed Scaramella stated that in the realm of datacenters, for each $1.00 spent on new hardware, an additional $0.50 is spent on power and cooling [START_REF] Scaramella | Solutions for the datacenter's thermal challenges[END_REF]. This same year, the estimated greenhouse emissions from the IT sector represented about 2% of the total human activity [START_REF] Webb | Enabling the low carbon economy in the information age[END_REF]. Several studies show that this amount keeps on growing, and is expected to grow even more in the future: up to 23% of the global greenhouse emissions of human activities, and as much as 51% of the global electricity in the worst-case scenarios [START_REF] Andrae | On global electricity usage of communication technology: trends to 2030[END_REF].

Even if several hardware optimizations successfully manage to reduce the energy consumption of computers [START_REF] Rotem | Power-management architecture of the intel microarchitecture code-named sandy bridge[END_REF], [START_REF] Herbert | Analysis of dynamic voltage/frequency scaling in chip-multiprocessors[END_REF], [START_REF] Wu | Clock-gating and its application to low power design of sequential circuits[END_REF], a considerable amount of this energy is due to the software executed on it [START_REF] Brown | Toward energy-efficient computing[END_REF], [START_REF] Saxe | Power-efficient software[END_REF]. Implementing energyefficient applications should be the main focus for developers. Nevertheless, studies show that the majority of them do not consider energy efficiency when developing or do not know enough about the energy consumption of their programs for doing more efficient design choices [START_REF] Pang | What do programmers know about software energy consumption[END_REF], [START_REF] Pinto | Mining questions about software energy consumption[END_REF]. Having feedbacks about the energy consumption of their programs would help towards that purpose. However, deploying energy measurement tools is complex, and often requires knowledge about systems, software analysis, or hardware properties [START_REF] Noureddine | A review of energy measurement approaches[END_REF], [START_REF] Ahmed | Software energy measurement at different levels of granularity[END_REF]. This is especially true in the realm of executable domainspecific modeling languages (xDSMLs), where end-users do not necessarily know, or consider, the implementation of the operational semantics of their language. To help end-users improve the energy efficiency of the executable models they design, we propose in this paper a generic approach for estimating the energy consumption of their execution. This approach does not require any measurement tooling from the end-user, nor any knowledge about energy consumption, and can provide estimations about the energy consumption of any executed model, on the platform for which it has been designed.

Our contributions towards that purpose are the following: (1) A domain-specific language (DSL) for specifying energyestimation formulas. This DSL can be attached to any xDSML in the GEMOC language workbench and can be used for estimating the energy consumption of all the executable models conforming to this meta-model, and for a specific platform. This DSL is meant to be used by qualified DSL engineers, or energy measurement specialists with knowledge of the xDMSL. (2) An extension of the GEMOC modeling workbench to estimate the energy consumption of running models using the modeled energy-estimation formulas. This work is the first step towards a fully generic, automated, and validated approach for estimating the energy consumption of any interpreted DSL.

This paper is organized as follow: Section II presents related work about energy estimation and measurement, Section III presents our approach for modeling and evaluating energy estimation formulas, Section IV discusses the approach, and Section V concludes the paper and proposes some future work.

II. RELATED WORK

In this section, we present some related work on energy estimation and measurements. We group this work according to the measurement level to which the approach is applied. Power meters. Power-meters are external devices, usually plugged to the power supply of the computers they monitor [START_REF] Zhang | Accurate online power estimation and automatic battery behavior based power model generation for smartphones[END_REF], [START_REF] Hirst | Watts up? pro ac power meter for automated energy recording[END_REF], [START_REF] Hindle | Greenminer: A hardware based mining software repositories software energy consumption framework[END_REF]. Their main benefit is that they do not require any modification of the hardware, nor the software, to measure the power consumed by the system. Nonetheless, the metrics obtained are coarse-grained: they include the entire system's power consumption and require heavier analysis than the remaining of the approaches. They measure power at a fixed frequency: from 1 Hz 1 to 500 kHz, on an external device. This implies cumbersome and error-prone analysis, to correlate running programs with the measured power consumptions. Specialized systems for energy monitoring. Specialized systems are designed and deployed to enable fine-grained energy measurements. The most popular ones are Atom LEAP [START_REF] Singh | The atom leap platform for energyefficient embedded computing[END_REF] and Spartan FPGA [START_REF] Sahin | Initial explorations on design pattern energy usage[END_REF]. Such systems embed multiple sensors, plugged to several parts of the system (e.g., CPU, disks, RAM), and can perform fine-grained measurements at high frequencies. The main drawback of such systems is that they require extremely specific tooling and operating system, and hence are not easily accessible to most developers and xDSMLs end-users. Application level monitoring tools. Several software and middleware applications or libraries can be queried at the software level to measure or estimate the energy consumption of a given application. Their main benefits are that they do not require any hardware tweaking, can be used on popular exploitation systems, and are accurate as they can measure the energy consumption of a given running process. The most used ones are RAPL, an Intel feature easily accessible on Unix-based system [START_REF] David | Rapl: memory power estimation and capping[END_REF]; JRAPL, a Java library enabling highlevel access to RAPL [START_REF] Liu | Data-oriented characterization of application-level energy optimization[END_REF]; and POWERAPI, a middleware solution providing process-level power estimations at custom frequencies [START_REF] Bourdon | Powerapi: A software library to monitor the energy consumed at the process-level[END_REF]. The main drawback of this approach is that using these applications during the software development lifecycle requires knowledge about dynamic analysis, and applying it in the realm of xDSMLs requires tweaking the operational semantics of the language, or the execution engine. Furthermore, the values measured might be inaccurate and influenced by the state of the system, making the approach complicated to use for developers and xDSMLs end-users. Model-level monitoring.

Little work has been done in the realm of xDSMLs for enabling energy-aware design and modeling. Luca Berardinelli et. al., propose an extension of the Agilla Modeling Language (AML) with an instruction triggering energy measurements of nodes in Wireless Sensors Network (WSN) [START_REF] Berardinelli | Energy consumption analysis and design of energyaware wsn agents in fuml[END_REF]. The energy measured is then used for predicting and optimizing the design of the WSN, towards a better energy-awareness. This approach is platform-specific as it requires a WSN running a specialized exploitation system and only focuses on AML.

Compared to the related work, our approach is meant to be used regardless of the operating system, does not require any hardware device, does not require any knowledge about dynamic analysis from the end-user, and can be used on any xDSMLs designed with the GEMOC language workbench.

III. APPROACH

This section presents our approach for specifying generic energy estimations and dynamically evaluating them. An implementation is available on GitHub 2 . Figure 1 proposes an overview of the approach and its three actors implied in it: the DSL Engineer, who knows the meta-programming approach and can design an executable meta-model with its operational semantic, the end-user who knows the executable meta-model (or a DSL), creates executable models conforming to it and runs them using the execution engine, and finally the Energy Estimation (EE) Specialist, who knows the EE meta-model, the operational semantics of the execution meta-model, and the platform on which the models are executed. Whereas the DSL engineer and end-user actors are rather common in the realm of xDSMLs [START_REF] Bousse | Omniscient debugging for executable dsls[END_REF], the (EE) specialist is a novelty. She has enough knowledge about energy estimation and measurement to specify generic estimations and associate them with the xDSML. Energy estimation meta-model. Figure 2 depicts the metamodel we propose for specifying energy calculations. The Platform entity is the root element of the meta-model and refers to a specific system. It contains Variables and Estimations. The former defines valued entities that are either defined once for the platform (i.e., Global) or once for each instance conforming to the targeted entity (i.e., Local). Variables can be used for defining local counters, or system attributes, according to the needs of the EE Specialist. The latter defines the formulas used for estimating the energy consumed by the executable model. These formulas are defined as OCL queries and return Double values. Each estimation refers to a Target entity, which is either a MetaClass in the execution metamodel, or an Operation in its operational semantic. Dynamic estimation. To perform dynamic energy estimation for executable models, we extended the existing GEMOC modeling workbench [START_REF] Bousse | Execution framework of the gemoc studio (tool demo)[END_REF], to accept EE models as additional input for the model execution. Furthermore, an execution listener is added to the execution engine. This execution listener is called every time a Step annotated operation [START_REF] Bousse | Omniscient debugging for executable dsls[END_REF] is executed in the operational semantics of the xDSML. There, a simple check is performed, verifying if any estimation in the EE model targets either the running operation, or a meta-class the running object is an instance of.

If an estimation targeting the running entity exists, its contained OCL Query is executed on that entity. Our current approach returns a double value, corresponding to an estimation of the energy consumed by the execution of that entity. This value can be then used for providing a graphical representation of the energy consumption of the model or stored for any future usage. Existing work on quantity specifications could be applied here, to return other types of energy estimations, such as probability distributions or measurement uncertainty [START_REF] Burgueño | Specifying quantities in software models[END_REF].

Example of an energy estimation. To illustrate our approach, we propose a simple use-case, where a DSL Engineer designs a Petri Net meta-model and an EE Specialist defines an EE model for a specific platform (a laptop running on Ubuntu 18.04, with an Intel Core i5-7200U), as shown in Figure 3.

This EE model associates an EE formula to the fire() operation defined in the operational semantics of the Petri Net meta-model. This formula, defined in OCL, estimates the energy consumption of fire() according to the number of inputs and outputs of the Transition. A variable is defined in the EE model and used in this estimation. This variable is the Thermal Design Power (tdp) of the CPU, a system attribute used for estimating the power consumption [START_REF] John | Computer architecture: a quantitative approach[END_REF], [START_REF] Bourdon | Powerapi: A software library to monitor the energy consumed at the process-level[END_REF]. The execution engine replaces this variable by its value in the OCL

IV. DISCUSSION

In this section, we discuss the accuracy of our approach for defining energy estimation formulas, how EE specialists can define them, and the interest of dynamic analysis.

Estimation accuracy.

First of all, the accuracy of the estimation calculated depends on the formula specified by the EE specialist. To evaluate the accuracy of such formula, measurements with specialized tools should be performed on the running model and compared with the estimation. We consider a formula to be accurate if, with enough model executions, the energy estimation calculated converges towards the average energy consumptions measured. This can be defined as:

E(p) ≈ 1 n n-1 x=0 m x (p)
where E(p) is the estimated energy consumption of entity p, m i (p) is the i-nth measure of the energy consumption of p, and n the number of measurements to perform until the values obtained are stable. Defining energy estimation formulas. The EE specialists have to define accurate energy estimation formulas to attach to the meta-elements of an execution meta-model. To define such formulas, the specialist needs several executable models conforming to the execution meta-model, to cover the majority of the execution scenarios. Multiple measured model executions have to be performed to obtain accurate energy measurements. EE formulas can then be defined by performing a thorough study of the operational semantics of the xDSML, and analyzing the energy measurements obtained.

This approach is similar to eCalc, where the energy consumption of each byte-code instructions (execution metaelements) in the language is measured, to estimate the energy consumption of all programs (executable models) compiling to bytecode [START_REF] Hao | Estimating android applications' cpu energy usage via bytecode profiling[END_REF]. Static vs. Dynamic energy estimation. Our current approach focuses on a dynamic analysis: the estimations are performed at runtime, and directly on the running entities. However, considering the Petri Net used as an example in Figure 4, the same energy estimation could have been performed statically. Performing a dynamic analysis ensures that the estimated entities are really executed. A static analysis would be either less precise (e.g., providing EE of nonexecuted entities) or slower (e.g., considering all the possible execution scenarios) [START_REF] Michael | Static and dynamic analysis: Synergy and duality[END_REF]. Nonetheless, statically estimating the energy consumption of the executable models at design time could effectively help end-user taking more energy-efficient decisions when designing the executable models. We will consider this in future work.

Finally, our current EE meta-model cannot estimate some specific xDSMLs accurately. This includes model executions depending on external inputs or events and non-deterministic operational semantics. In a nutshell, all the executable models where the execution duration (and, de facto, energy consumption), cannot be estimated at the xDSML level. Future work will also focus on those cases.

V. CONCLUSION AND FUTURE WORK

This paper is the first step towards a generic approach for estimating the energy consumption of any executable model. We propose a meta-model for specifying energy estimation, along with an extension of the GEMOC modeling workbench enabling the dynamic energy estimation of executable models. Our future work will empirically evaluate our approach by comparing the energy estimations of several executable models, on multiple platforms, to energy measurements obtained with specialized tooling. Furthermore, a dedicated language will be proposed to specify the measurements. Finally, more research will be performed to automatize the generation of EE formulas.

Fig. 1 .

 1 Fig. 1. Overview of the approach.

1 Fig. 2 .

 12 Fig. 2. Energy estimation meta-model.

Fig. 3 .

 3 Fig. 3. Petri net xDSML with an EE model.

Fig. 4 .

 4 Fig. 4. Petri net model conforming to the execution meta-model.


MD David Gómez-Andrés

Jordi Diaz-Manera

MD Aida Alejaldre

MD PhD Irene Pulido-Valdeolivas

MD PhD Laura González-Mera

MD Montse Olivé

Juan José Vilchez

MD PhD Adolfo López De Munain

MD PhD Carmen Paradas

MD PhD Nuria Muelas

MD Jordi Díaz-Manera

MD PhD Juan José Vilchez

MD Ángel Sánchez-Montáñez

MD Alicia Alonso-Jimenez

Marta Gómez

MD García De La Banda

MD Ivana Dabaj

PhD Gisèle Bonne

MD Francina Munell

MD Robert Y Carlier

MD PhD Susana Quijano-Roy

David Gómez
email: david_gomez@vhebron.net

Muscle imaging in laminopathies: Synthesis study identifies meaningful muscles for follow-up

Keywords: LMNA, imaging, magnetic resonance, biomarker, machine learning, laminopathy

Introduction

Muscle imaging has been increasingly recognized in the last decade as a valuable tool to facilitate the differential diagnosis in patients with hereditary muscular disorders. However, series are still small, and the relationships of imaging phenotypes with clinical data such as length of disease course, severity and age of onset require further study. It would be desirable to develop tools allowing analysis of integrated data from different series and enhancing the study of relationships between imaging and clinical data.

LMNA related muscular dystrophies (LMNA-RD) are a spectrum of muscular dystrophies due to mutations in the gene coding for Lamins A and C. Different forms have been described depending on age of onset and clinical presentation, and seem to constitute a continuum of phenotypes [START_REF] Maggi | Skeletal Muscle Laminopathies: A Review of Clinical and Molecular Features[END_REF] . There is a congenital form (L-CMD) [START_REF] Quijano-Roy | De novo LMNA mutations cause a new form of congenital muscular dystrophy[END_REF] , an Emery-Dreifuss muscular dystrophy (EDMD) phenotype [START_REF] Bonne | Emery-Dreifuss muscular dystrophy, laminopathies, and other nuclear envelopathies[END_REF] and a form of limb girdle muscular dystrophy (LGMD1B) [START_REF] Muchir | Identification of mutations in the gene encoding lamins A/C in autosomal dominant limb girdle muscular dystrophy with atrioventricular conduction disturbances (LGMD1B)[END_REF][START_REF] Van Der Kooi | Genetic localization of a newly recognized autosomal dominant limbgirdle muscular dystrophy with cardiac involvement (LGMD1B) to chromosome 1q11-21[END_REF] .

Several studies have been published with descriptions of signal abnormalities using T1-TSE sequences on magnetic resonance imaging (MRI) or computerized tomography (CT) scans [START_REF] Pasqualin | Congenital muscular dystrophy with dropped head linked to the LMNA gene in a Brazilian cohort[END_REF][START_REF] Deconinck | Differentiating Emery-Dreifuss muscular dystrophy and collagen VI-related myopathies using a specific CT scanner pattern[END_REF][START_REF] Carboni | Muscle imaging analogies in a cohort of patients with different clinical phenotypes caused by LMNA gene mutations[END_REF][START_REF] Mercuri | Muscle magnetic resonance imaging involvement in muscular dystrophies with rigidity of the spine[END_REF][10] . More recently, two systematic analyses of muscle MRI have described the differences of fibroadipose infiltration in the muscle of LMNA-RD patients, one using whole body MRI in children with the congenital form [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF] and the other using MRI and CT scans of lower limbs in adults with later onset forms -EDMD and LGMD1B [START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF] . Patterns of fatty infiltration have been systematically described. However, the course of fibroadipose substitution in different muscles during the course of the disease and the correspondence with the spectrum of different presentations had not been carefully studied.

This article is protected by copyright. All rights reserved.

Accepted Article

Our objectives are 1) to demonstrate that the use of systematic muscle fatty infiltration scoring in imaging studies and their representation of results in heatmaps allows the collection of data from different series and the performance of synthesis studies (studies that pool data from various sources) based on individual data; 2) to detect, which muscles, if any, are differentially affected according to age at onset and which muscles, if any, are affected more as a result of disease duration in LMNA-related muscle disorders using previous published data.

11,12

Methods

Collection of data:

From published heatmaps, [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF][START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF] we collected fatty infiltration scores from 21 lower limb muscles that were imaged in both studies: gluteus maximus, gluteus medius, gluteus minimus, vastus lateralis, vastus medialis, vastus intermedius, rectus femoris, sartorius, gracilis, semimembranosus, semitendinosus, short head of biceps femoris, long head of biceps femoris, tibialis anterior, tibialis posterior, peroneus, extensor digitorum longus, flexor digitorum longus, soleus, medial head of gastrocnemius and lateral head of gastrocnemius. Gómez-Andrés et al. [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF] scored the iliacus and psoas muscles independently whereas Díaz-Manera et al. [START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF] scored the iliopsoas in combination. To solve this, we calculated the median score of iliacus and psoas from Gómez-Andrés et al. [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF] We also calculated the median score of the adductor brevis, longus and magnus to have an equivalent to the global scoring of adductor muscles performed by Díaz-Manera et al. [START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF] In general, the values of individual muscles within these two muscle groups in the work of Gómez-Andrés et al. [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF] were very similar. We collected age of onset and calculated the time of disease duration from the onset until imaging was performed in each subject. We used data from the 8 early-onset patients of Gómez-Andrés et al. [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF] and 26 patients from Díaz-Manera et al. [START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF] (9 EDMD, 12 LGMD and 5 presymptomatic patients, in which disease duration was represented as a negative value. Ten patients were evaluated by means of lower limb CT imaging and 16 patients using lower limb MRI). Clinical features of the patients are shown in supplementary table 1. Research ethics committees approved both studies and informed consent was obtained from the research subjects or their guardians to perform MRI and analyzing the results.

Preparation of data: Muscle imaging scoring was performed using different scales in the two studies. Díaz-Manera et al. [START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF] used a modified Mercuri scale that quantifies muscle fatty infiltration from normal (0) to end-stage (4). Gómez-Andrés et al. [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF] used a modification of Lamminen scale 13 that assesses fatty infiltration from normal (1) to complete fatty substitution (4). We proposed and applied a system of equivalencies between these two scales (see supplementary table 2). In order to estimate the impact of using this proposed system, one researcher (IPV) scored the pediatric cohort with the Mercuri scale used in the adult cohort. Agreement was high or complete in every muscle (see supplementary figure 1).

Machine learning approach: Random forests were used to model the relationship between the pattern of muscle infiltration and disease onset and disease duration.

Random forests are computer algorithms that make predictions about one parameter (output) based on multiple parameters (inputs) after a training period [START_REF] Strobl | An introduction to recursive partitioning: rationale, application, and characteristics of classification and regression trees, bagging, and random forests[END_REF][START_REF] Breiman | Random Forests[END_REF] . In this case, we trained two random forests: one was developed to predict disease onset and the other to predict disease duration. Both random This article is protected by copyright. All rights reserved.

Accepted Article

forests used the same inputs: the scoring of muscle infiltration for the selected muscles. Random forests were considered the most appropriate tool because they are able to deal with situations with a large number of predicting variables and a low number of patients and they are good in processing ordinal data. As random forests are based on classification and regression trees, they make their predictions by means of splitting the database. So, it is possible to include data in which the numerical values are not exact but are present in one extreme of the distribution. This was important in our case because we needed represent negative but unknown values of disease duration in pre-symptomatic patients and negative but unknown values of disease onset in patients with prenatal onset.

Disease duration in pre-symptomatic patients was represented by minus 5 years and prenatal onset, by minus 0.25 years. For disease onset, pre-symptomatic patients were excluded. Moreover, they provide measures of "importance" which are quantifications of the relevance of each input parameter in the prediction. We used package "randomforestSRC" [START_REF] Ishwaran | Random Forests for Survival, Regression, and Classification (RF-SRC)[END_REF] in R software to train random forests with variable selection using minimal depth methodology [START_REF] Ishwaran | High-Dimensional Variable Selection for Survival Data[END_REF] . The goodness of fit of each model (how accurate the random forest was in its predictions) was assessed by Spearman's rho correlation coefficient between actual output parameter and the out-of-the-bag prediction made by random forest. These relationships were also represented by means of scatter plots. We used Breiman-Cutler permutation variable importance to detect muscles in which infiltration is related with the two outputs (disease duration and disease onset). We represented relationships between important infiltrations and the outputs by means of boxplots.

Results

The goodness of fit of the model for disease duration is acceptable (Spearman's rho = 0.612, figure 1A) while in the case of disease onset, it was very low (Spearman's rho = 0.005, figure 1B). This means that the pattern of muscle infiltration in lower limbs changes with the progression of the disease, but there are no significant differences in the global pattern of muscle infiltration according to the different ages at onset. The most relevant muscles to predict disease duration for the random forests were semitendinosus, long head of biceps femoris, gluteus medius and semimembranosus (figure 1C). The rest of evaluated muscles were not selected as relevant by the variable selection algorithm. The relationships between disease duration and infiltration in each muscle could be either linear (meaning in this case that the higher the score of infiltration, the longer the disease duration along the whole spectrum of disease progression) or non-linear (meaning in this case that the relationship is only important for a part of the spectrum of disease progression). Semitendinosus infiltration (figure 2A) is related with disease duration in a non-linear manner. A non-infiltrated semitendinosus is markedly related with short time of disease duration (less than 10 years). Patients with disease longer than 20 years can have variable semitendinosus infiltration, but some degree of infiltration is likely to be present. Infiltration of long head of biceps (figure 2B) is linearly related with disease duration. Patients with less than 10 years of duration show no or mild infiltration in long head of biceps while patients with disease duration longer than 30 years show moderate to severe infiltration. 2C) is also linearly related: the more infiltrated gluteus medius is, the longer the disease duration tend to be in the patient.

Gluteus medius infiltration (figure

This article is protected by copyright. All rights reserved.

Accepted Article

Semimembranosus infiltration (figure 2D) shows a non-linear relationship with disease duration. Only the patients with longer duration (more than 25 years) show a consistently severe infiltration whereas patients with shorter times of disease duration tend to have less infiltration, but infiltration is not progressively related with disease duration for a duration of 10-20 years. Other muscles such as gluteus maximum and minimus, vastus intermedius and medialis, lateral gastrocnemius and tibialis posterior are also related with disease duration, but their importance is lower. Supplementary figure 2 show the relationships between infiltration scoring of these muscle and disease duration.

While global pattern of muscle infiltration is not related with age of onset, there are some muscles that could be detected as different according to the age of onset (figure 1D). For instance, adductor muscles tend to be severely infiltrated in earlyonset patients while preserved in late-onset patients, and semitendinosus is only severely infiltrated in some early-onset patients (supplementary figure 3).

Discussion

Muscle imaging is gaining popularity as an approach to direct genetic studies for patients with suspicion of a hereditary muscle disorders because muscle changes rarely occur randomly but they often follow a specific pattern that is different from one mutated protein to other one [START_REF] Fischer | Recent developments in muscle imaging of neuromuscular disorders[END_REF] . The description of this pattern had usually been qualitative, based on subjective criteria that were difficult to quantify and replicate. The extended systematic use of semi-quantitative scores to describe the degree of muscle fatty infiltration in the different imaging techniques improved information gathering and sharing, which improved the description of specific muscle profiles for different hereditary muscle disorders [START_REF] Fischer | Neuromuscular Imaging[END_REF] . In addition to This article is protected by copyright. All rights reserved.

Accepted Article

systematic scoring, multivariate descriptive techniques have been incorporated to improve the pattern identification and representation [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF][START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF][START_REF] Fischer | Recent developments in muscle imaging of neuromuscular disorders[END_REF][START_REF] Hankiewicz | Whole-body muscle magnetic resonance imaging in SEPN1-related myopathy shows a homogeneous and recognizable pattern[END_REF][START_REF] Garibaldi | Muscle MRI in neutral lipid storage disease (NLSD)[END_REF][START_REF] Figueroa-Bonaparte | Muscle MRI Findings in Childhood/Adult Onset Pompe Disease Correlate with Muscle Function[END_REF] .

One of the best studied myopathies on muscle imaging is the group of muscle skeletal laminopathies or LMNA-RD. Several studies have described a consistent pattern [START_REF] Pasqualin | Congenital muscular dystrophy with dropped head linked to the LMNA gene in a Brazilian cohort[END_REF][START_REF] Carboni | Muscle imaging analogies in a cohort of patients with different clinical phenotypes caused by LMNA gene mutations[END_REF]10 , including two systematic analyses which were recently published on the congenital and adult forms. While the congenital series studied signal abnormalities using T1-TSE sequences on whole body MRI [START_REF] Gomez-Andres | Pediatric laminopathies: Whole-body magnetic resonance imaging fingerprint and comparison with Sepn1 myopathy[END_REF] , the adult multicenter study in LMNA-related EDMD and LGMD1B collected data from muscle MRI and CT scans, all limited to the lower limbs [START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF] .These studies found that LMNA-related muscle dystrophies show a characteristic pattern of muscle infiltration.

The present study shows, by the integration of data included in the two systematic studies using machine-learning techniques, that the pattern of involvement changes with the progression of the disease, but not with the age of onset. These results have several implications. They strengthen the clinical impression of a continuum of phenotypes in the same myopathy rather than different muscle diseases due to a same gene defect. On the other hand, the analysis identifies several muscles that are most clearly related to the progression of the myopathy (semitendinosus, long head of biceps, gluteus medius and semimembranosus muscles), meaning that they are strong candidates for future studies looking for biomarkers to be monitored by muscle quantitative MRI techniques. Our findings also support that including time of disease in muscle MRI interpretation could be important guide genetic studies. For example, if duration of disease is long, , a LMNA-related muscle disorder is unlikely if infiltration is lacking in the semitendinosus, semimembranosus, long head of biceps femoris or gluteus medius. In contrast, these muscles are expected to be spared or only mildly This article is protected by copyright. All rights reserved.

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infiltrated in patients with shorter disease duration. When machine learning is implemented for differential diagnosis in muscle MRI, disease duration may be also relevant to include as this may increase the diagnostic performance of the algorithm.

The lack of relationship with the type of LMNA-RD (form of onset) should be interpreted with caution. Clinical observations strongly suggest that data from cervical, periscapular and upper limb regions is very relevant in the distinction between the phenotypes with different age of onset (congenital vs later onset), but unfortunately this data is not yet available in EDMD and LGMD. In the lower limbs, the only muscles involved at a variable degree are adductor muscles and semitendinosus. These findings, especially those affecting the semitendinosus muscle, may also be due to the longer disease in some patients with earlier onset.

We believe that looking for targets for quantitative MRI by means of strategies of (re-)analyzing semiquantitative scoring is important because focusing on a limited number of muscles selected as candidates by these strategies could accelerate, simplify and reduce the cost of the time-consuming phase of image processing in quantitative MRI studies. Moreover, there may be some muscles that could be overlooked if a non-targeted approach is performed. For instance, the muscles that seem to be more related in our study have not been considered in previous quantitative studies for other muscle diseases [START_REF] Diaz-Manera | Muscle imaging in muscle dystrophies produced by mutations in the EMD and LMNA genes[END_REF][START_REF] Willcocks | Multicenter prospective longitudinal study of magnetic resonance biomarkers in a large duchenne muscular dystrophy cohort[END_REF][START_REF] Willis | Quantitative muscle MRI as an assessment tool for monitoring disease progression in LGMD2I: a multicentre longitudinal study[END_REF] . However, this approach should be undertaken with caution for optimizing longitudinal quantitative MRI studies because the conclusions about the relationships of disease duration with muscle fatty infiltration are based on the assumption that cross-sectional data represent the longitudinal evolution of the disorder. Moreover, the pace of progression in fatty infiltration may be not uniform between patients and a crosssectional design does not permit evaluation of this.

We showed that relationships between the course of the disease and the progression of signal abnormalities can be non-linear. A non-linear relationship between disease duration and signal abnormality in some muscles implies that in these muscles, the pace of progression for fibroadipose infiltration is not homogeneous throughout the disease course. We speculate that the differing rates of fatty infiltration over time in some muscles may represent different pathogenic mechanisms or secondary changes due to disuse atrophy as a result of loss of mobility. This result is also particularly interesting if studies in LMNA-RD are designed using muscle MRI parameters as biomarkers. For instance, the semitendinosus seems to be resistant to infiltration in the early years of the disease, but shows a faster rate of infiltration 5-10 years into the disease course.

Based on this, we could propose fatty infiltration of the semitendinosus as a good candidate biomarker for patients with a disease duration of 10-20 years, but a potentially poor biomarker for monitoring patients with LMNA-RD early in the disease course (no significant infiltration before 10 years of disease duration) and in very advanced cases (variably infiltrated). An alternative explanation for nonlinear relationships could be that the ordinal scale to assess fibroadipose infiltration does not reflect accurate proportional increases (e.g. the increase in fatty infiltration between 1 and 2 may be not the same as the increase between 2 and 3) in some muscles.

Understanding the progression pattern in muscle degeneration in muscle dystrophies is also important for guiding future studies to better understand the underlying pathophysiologic mechanisms in each disease. At a given point in the This article is protected by copyright. All rights reserved.

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disease course, pathologic mechanisms may vary between muscles. For a given muscle, pathologic mechanisms may vary according to the point in the disease course. Knowing the pace of progression of the disease could allow to interpret findings in future studies or to improve the targeting of muscle biopsy in patients.

Another contribution of this study is its methodological proposal. Due to the spread of systematic scoring and heatmap representation in muscle imaging, we expect increasing amounts of imaging data from individual patients. Synthesis and further analysis of these data are critical to hasten our understanding of imaging phenotypes in myopathies, and in producing hypotheses that could be confirmed with additional longitudinal and/or quantitative studies. In particular, these kinds of studies will permit the evaluation of the individual rates of progression and help to identify factors (e.g. functional status, age at onset, mutation type or others) that may influence it [START_REF] Rooney | Statistical modeling of 5-year longitudinal data from a large cohort of Duchenne muscular dystrophy (DMD) subjects: an interim look at temporal characteristics of disease progression from the ImagingDMD study[END_REF] .

Although synthesis studies seems to be attractive approaches to combining data from different sources, they also have limitations [START_REF] Cooper | Hypotheses and problems in research synthesis[END_REF] . In muscle MRI and in this particular study, the most important limitations derive from the use of several scoring techniques and the different selection of muscles. This highlights the need for guidelines and consensus in scoring. To overcome this limitation we incorporated random forests, a data mining techniques that compensates for this.

We believe that the incorporation of new data mining techniques such as random forests could lead to improved differential diagnoses, and an improved understanding of the variability within diseases [START_REF] Obermeyer | Predicting the Future -Big Data, Machine Learning, and Clinical Medicine[END_REF] . This article is protected by copyright. All rights reserved.

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Figure 1 .

 1 Figure 1. Upper row: Scatterplot of the prediction (y-axis) against the actual value

Figure 2 .

 2 Figure 2. Relationships between disease duration and scoring of infiltration in the

Acknowledgement: This work was performed under the support of COST Action Programme BM1304.

LIST OF ABBREVIATION

CT: Computerized tomography EDMD: Emery-Dreifuss muscular dystrophy L-CMD: LMNA-related congenital form LGMD1B: limb girdle muscular dystrophy 1B LMNA-RD: LMNA-related muscular dystrophies MRI: Magnetic resonance imaging.