Can a modified ketogenic diet be a nutritional strategy for patients with McArdle disease? Results from a randomized, single-blind, placebo-controlled, cross-over study.

BACKGROUND: McArdle disease is caused by myophosphorylase deficiency leading to blocked glycogenolysis in skeletal muscle. Consequently, individuals with McArdle disease have intolerance to physical activity, muscle fatigue, and pain. These symptoms vary according to the availability of alternative fuels for muscle contraction. In theory, a modified ketogenic diet (mKD) can provide alternative fuels in the form of ketone bodies and potentially boost fat oxidation. METHODS: This randomized, single-blind, placebo-controlled, cross-over study aimed to investigate if a mKD improves exercise capacity in individuals with McArdle disease. Participants were randomized to follow a mKD (75-80% fat, 15% protein, 5-10% carbohydrates) or placebo diet (PD) first for three weeks, followed by a wash-out period, and then the opposite diet. The primary outcome was change in heart rate during constant-load cycling. Secondary outcomes included change in plasma metabolites, perceived exertion, indirect calorimetry measures, maximal exercise capacity, and patient-reported outcomes. RESULTS: Fifteen out of 20 patients with genetically verified McArdle disease completed all study visits, and 14 were included in the data analyses. We found that the mKD induced a metabolic shift towards increased fat oxidation (∼60% increase), and a 19-fold increase in plasma ß-hydroxybutyrate (p < 0.05). The mKD did not improve heart rate responses during constant-load cycling but did improve patient-reported outcomes and maximal exercise capacity (∼20% increase) compared to the PD. CONCLUSION: The mKD did not alleviate all McArdle disease-related symptoms but did induce some positive changes. To date, no satisfactory treatment options exist other than exercise training. To that end, a mKD can be a possible nutritional strategy for some individuals with McArdle disease who are motivated to undertake a restrictive diet. CLINICAL TRIAL REGISTRATION: clinical trials.gov: NCT04044508.

Long-term Natural History of Pediatric Dominant and Recessive RYR1-Related Myopathy.

BACKGROUND AND OBJECTIVES: RYR1-related myopathies are the most common congenital myopathies, but long-term natural history data are still scarce. We aim to describe the natural history of dominant and recessive RYR1-related myopathies. METHODS: A cross-sectional and longitudinal retrospective data analysis of pediatric cases with RYR1-related myopathies seen between 1992-2019 in 2 large UK centers. Patients were identified, and data were collected from individual medical records. RESULTS: Sixty-nine patients were included in the study, 63 in both cross-sectional and longitudinal studies and 6 in the cross-sectional analysis only. Onset ranged from birth to 7 years. Twenty-nine patients had an autosomal dominant RYR1-related myopathy, 31 recessive, 6 de novo dominant, and 3 uncertain inheritance. Median age at the first and last appointment was 4.0 and 10.8 years, respectively. Fifteen% of patients older than 2 years never walked (5 recessive, 4 de novo dominant, and 1 dominant patient) and 7% lost ambulation during follow-up. Scoliosis and spinal rigidity were present in 30% and 17% of patients, respectively. Respiratory involvement was observed in 22% of patients, and 12% needed ventilatory support from a median age of 7 years. Feeding difficulties were present in 30% of patients, and 57% of those needed gastrostomy or tube feeding. There were no anesthetic-induced malignant hyperthermia episodes reported in this cohort. We observed a higher prevalence of prenatal/neonatal features in recessive patients, in particular hypotonia and respiratory difficulties. Clinical presentation, respiratory outcomes, and feeding outcomes were consistently more severe at presentation and in the recessive group. Conversely, longitudinal analysis suggested a less progressive course for motor and respiratory function in recessive patients. Annual change in forced vital capacity was -0.2%/year in recessive vs -1.4%/year in dominant patients. DISCUSSION: This clinical study provides long-term data on disease progression in RYR1-related myopathies that may inform management and provide essential milestones for future therapeutic interventions.

A systematic review and qualitative synthesis of the experiences of parents of individuals living with Duchenne muscular dystrophy.

PURPOSE: Some parents of children with DMD find their role challenging, affecting quality of life. To inform support methods, we aimed to understand the lived experiences of parents and how these interact with disease progression. MATERIALS AND METHODS: PRISMA informed protocol development. Qualitative and mixed methods studies were included. Four databases were searched and study quality was assessed using a standardised measure. Extracted data were analysed using thematic synthesis. RESULTS: 26 studies were included, comprising 362 parents. Seven descriptive themes were apparent: "Diagnostic Experiences", "Coping with the Caregiver Role", "Illness Trajectory and Associated Interventions", "Family Communication", "Network of Support", "Navigating Systems" and "Transition Experiences". Four analytical themes were then derived: "The Cyclical Nature of Grief", "Lifelong Expert in the Needs and Experiences of an Individual with DMD", "Navigating Deviation from Typical Life Course" and "Uncertainty as Ever Present". CONCLUSION: The extant evidence suggests that the experience of parenting a child with DMD is often characterised by: a cycle of grief that begins at diagnosis, which runs parallel to the development of expertise in caregiving; within this parents notice deviations from their child's and their own expected life course and adjust to the emotions and uncertainty that this can bring.IMPLICATIONS FOR REHABILITATIONProfessionals should be cognisant to the complex grief process associated with DMD, which occurs from diagnosis onwards.There should be continued support for parents following bereavement.Peer support groups may also offer parents ways to maintain well-being.The necessity for parents to function effectively within an uncertain context that induces challenging emotions suggests a role for psychological therapies.

Specialist multidisciplinary input maximises rare disease diagnoses from whole genome sequencing.

Diagnostic whole genome sequencing (WGS) is increasingly used in rare diseases. However, standard, semi-automated WGS analysis may overlook diagnoses in complex disorders. Here, we show that specialist multidisciplinary analysis of WGS, following an initial 'no primary findings' (NPF) report, improves diagnostic rates and alters management. We undertook WGS in 102 adults with diagnostically challenging primary mitochondrial disease phenotypes. NPF cases were reviewed by a genomic medicine team, thus enabling bespoke informatic approaches, co-ordinated phenotypic validation, and functional work. We enhanced the diagnostic rate from 16.7% to 31.4%, with management implications for all new diagnoses, and detected strong candidate disease-causing variants in a further 3.9% of patients. This approach presents a standardised model of care that supports mainstream clinicians and enhances diagnostic equity for complex disorders, thereby facilitating access to the potential benefits of genomic healthcare. This research was made possible through access to the data and findings generated by the 100,000 Genomes Project: http://www.genomicsengland.co.uk .

Cardiac Manifestations of Myotonic Dystrophy in a Pediatric Cohort.

Myotonic dystrophy type 1 (DM1) is the most prevalent inherited neuromuscular dystrophy in adults. It is a multisystem disease with cardiac manifestations. Whilst these are well-defined in adults, there are scarce published data in the pediatric population. This study aimed to investigate the yield and progression of cardiac disease in pediatric DM1 patients, focusing on congenital DM1 (cDM1). Methods: A retrospective observational study of all pediatric DM1 patients referred to our center (December 2000-November 2020) was conducted. Patients were classified into DM1 forms according to age of symptom onset and disease severity. Patients underwent clinical and cardiac evaluation with 12-lead ECG, transthoracic echocardiography and 24-h ECG Holter monitoring. Results: 67 DM1 pediatric patients were included: 56 (83.6%) cDM1 and 11 (16.4%) non-cDM1. Median follow-up time of cDM1 patients was 8.0 [3.25-11.0] years. 49 (87.5%) cDM1 patients had baseline 12-lead ECG and 44 (78.6%) had a follow-up 12-lead-ECG, with a median follow-up time from diagnosis to baseline ECG of 2.8 [1.0-8.5] years and to follow-up ECG of 10.9 [5.7-14.2] years. Overall, 43 (87.8%) presented ECG abnormalities, most commonly in the form of asymptomatic conduction disease (n = 23, 46.9%), of which 21 (42.9%) had first degree atrioventricular block (1st AVB). There was an increase of prevalence from baseline to follow-up ECG in low QRS voltage (16.7%), poor R wave progression (13.9%), abnormal repolarisation (11.9%) and 1st AVB (7.6%). one patient (1.8%) underwent pacemaker implantation for syncope in the context of progressive conduction disease. No patients developed left ventricular systolic dysfunction. 4 (7.1%) cDM1 patients died during follow up, including three who died suddenly with no clear cause of death. Conclusions: This study is the first to analyse the prevalence and progression of ECG abnormalities in cDM1 pediatric patients. The high prevalence of abnormal findings, progressive changes and number of potentially associated events (1 pacemaker implantation and 3 unexplained sudden deaths) stresses the importance of systematic and continued cardiac evaluation of these patients.

Bi-allelic loss-of-function OBSCN variants predispose individuals to severe recurrent rhabdomyolysis.

Rhabdomyolysis is the acute breakdown of skeletal myofibres in response to an initiating factor, most commonly toxins and over exertion. A variety of genetic disorders predispose to rhabdomyolysis through different pathogenic mechanisms, particularly in patients with recurrent episodes. However, most cases remain without a genetic diagnosis. Here we present six patients who presented with severe and recurrent rhabdomyolysis, usually with onset in the teenage years; other features included a history of myalgia and muscle cramps. We identified 10 bi-allelic loss-of-function variants in the gene encoding obscurin (OBSCN) predisposing individuals to recurrent rhabdomyolysis. We show reduced expression of OBSCN and loss of obscurin protein in patient muscle. Obscurin is proposed to be involved in sarcoplasmic reticulum function and Ca2+ handling. Patient cultured myoblasts appear more susceptible to starvation as evidenced by a greater decreased in sarcoplasmic reticulum Ca2+ content compared to control myoblasts. This likely reflects a lower efficiency when pumping Ca2+ back into the sarcoplasmic reticulum and/or a decrease in Ca2+ sarcoplasmic reticulum storage ability when metabolism is diminished. OSBCN variants have previously been associated with cardiomyopathies. None of the patients presented with a cardiomyopathy and cardiac examinations were normal in all cases in which cardiac function was assessed. There was also no history of cardiomyopathy in first degree relatives, in particular in any of the carrier parents. This cohort is relatively young, thus follow-up studies and the identification of additional cases with bi-allelic null OBSCN variants will further delineate OBSCN-related disease and the clinical course of disease.

Genotype-related respiratory progression in Duchenne muscular dystrophy-A multicenter international study.

INTRODUCTION/AIMS: Mutations amenable to skipping of specific exons have been associated with different motor progression in Duchenne muscular dystrophy (DMD). Less is known about their association with long-term respiratory function. In this study we investigated the features of respiratory progression in four DMD genotypes relevant in ongoing exon-skipping therapeutic strategies. METHODS: This was a retrospective longitudinal study including DMD children followed by the UK NorthStar Network and international AFM Network centers (May 2003 to October 2020). We included boys amenable to skip exons 44, 45, 51, or 53, who were older than 5 years of age and ambulant at first recorded visit. Subjects who were corticosteroid-naive or enrolled in interventional clinical trials were excluded. The progression of respiratory function (absolute forced vital capacity [FVC] and calculated as percent predicted [FVC%]) was compared across the four subgroups (skip44, skip45, skip51, skip53). RESULTS: We included 142 boys in the study. Mean (standard deviation) age at first visit was 8.6 (2.5) years. Median follow-up was 3 (range, 0.3-8.3) years. In skip45 and skip51, FVC% declined linearly from the first recorded visit. From the age of 9 years, FVC% declined linearly in all genotypes. Skip44 had the slowest (2.7%/year) and skip51 the fastest (5.9%/year) annual FVC% decline. The absolute FVC increased progressively in skip44, skip45, and skip51. In skip53, FVC started declining from 14 years of age. DISCUSSION: The progression of respiratory dysfunction follows different patterns for specific genotype categories. This information is valuable for prognosis and for the evaluation of exon-skipping therapies.

Use of whole genome sequencing to determine genetic basis of suspected mitochondrial disorders: cohort study.

OBJECTIVE: To determine whether whole genome sequencing can be used to define the molecular basis of suspected mitochondrial disease. DESIGN: Cohort study. SETTING: National Health Service, England, including secondary and tertiary care. PARTICIPANTS: 345 patients with suspected mitochondrial disorders recruited to the 100 000 Genomes Project in England between 2015 and 2018. INTERVENTION: Short read whole genome sequencing was performed. Nuclear variants were prioritised on the basis of gene panels chosen according to phenotypes, ClinVar pathogenic/likely pathogenic variants, and the top 10 prioritised variants from Exomiser. Mitochondrial DNA variants were called using an in-house pipeline and compared with a list of pathogenic variants. Copy number variants and short tandem repeats for 13 neurological disorders were also analysed. American College of Medical Genetics guidelines were followed for classification of variants. MAIN OUTCOME MEASURE: Definite or probable genetic diagnosis. RESULTS: A definite or probable genetic diagnosis was identified in 98/319 (31%) families, with an additional 6 (2%) possible diagnoses. Fourteen of the diagnoses (4% of the 319 families) explained only part of the clinical features. A total of 95 different genes were implicated. Of 104 families given a diagnosis, 39 (38%) had a mitochondrial diagnosis and 65 (63%) had a non-mitochondrial diagnosis. CONCLUSION: Whole genome sequencing is a useful diagnostic test in patients with suspected mitochondrial disorders, yielding a diagnosis in a further 31% after exclusion of common causes. Most diagnoses were non-mitochondrial disorders and included developmental disorders with intellectual disability, epileptic encephalopathies, other metabolic disorders, cardiomyopathies, and leukodystrophies. These would have been missed if a targeted approach was taken, and some have specific treatments.

Phenotype and genotype of 197 British patients with McArdle disease: An observational single-centre study.

McArdle disease is caused by recessive mutations in PYGM gene. The condition is considered to cause a "pure" muscle phenotype with symptoms including exercise intolerance, inability to perform isometric activities, contracture, and acute rhabdomyolysis leading to acute renal failure. This is a retrospective observational study aiming to describe phenotypic and genotypic features of a large cohort of patients with McArdle disease between 2011 and 2019. Data relating to genotype and phenotype, including frequency of rhabdomyolysis, fixed muscle weakness, gout and comorbidities, inclusive of retinal disease (pattern retinal dystrophy) and thyroid disease, were collected. Data from 197 patients are presented. Seven previously unpublished PYGM mutations are described. Exercise intolerance (100%) and episodic rhabdomyolysis (75.6%) were the most common symptoms. Fixed muscle weakness was present in 82 (41.6%) subjects. Unexpectedly, ptosis was observed in 28 patients (14.2%). Hyperuricaemia was a common finding present in 88 subjects (44.7%), complicated by gout in 25% of cases. Thyroid dysfunction was described in 30 subjects (15.2%), and in 3 cases, papillary thyroid cancer was observed. Pattern retinal dystrophy was detected in 15 out of the 41 subjects that underwent an ophthalmic assessment (36.6%). In addition to fixed muscle weakness, ptosis was a relatively common finding. Surprisingly, dysfunction of thyroid and retinal abnormalities were relatively frequent comorbidities. Further studies are needed to better clarify this association, although our finding may have important implication for patient management.

The phenotypic and genotypic features of a Scottish cohort with McArdle disease.

This retrospective study evaluated the phenotypic and genotypic features of 14 patients with McArdle disease attending the West of Scotland adult muscle clinic. Although all patients experienced exercise-induced cramps, exercise intolerance and hyperCKaemia, only 71% (n = 10) experienced the second wind phenomenon, rhabdomyolysis and/or myoglobinuria. We observed a high rate of fixed muscle weakness (50%; n = 7), coronary artery disease (36%; n = 5), and psychological comorbidity (50%; n = 7). Although 79% had symptom onset in the first decade of life, the mean age at presentation and at genetic diagnosis was 43.8 years and 47.7 years, respectively. 93% had at least one copy of the common PYGM pathogenic variant, c.148C > T, p.(Arg50*), with 50% (n = 7) of the cohort being homozygous. Our cohort highlights the phenotypic variability seen in McArdle disease and underscores the potential for late-onset presentations. It emphasises the need for improved awareness and recognition of this condition amongst neurologists, rheumatologists and general physicians. A history of exercise intolerance and second wind phenomenon may not always be volunteered by the patient, underscoring the need to ask specific questions in clinic to extrapolate the relevant symptoms in this patient cohort.

Reference values for the 12 minute walk test in McArdle patients.

The maximum distance achieved on a modified 12 min walk test (12MWT) is a well-established measure in McArdle disease glycogen storage disease type V (GSDV). Age, height, body mass and gender are known predictors of walking distance in other patient groups. Reference values to correct for these predictors are necessary for comparisons between individuals. To date, there has not been a systematic investigation of these predictors in the 12MWT in GSDV. This study explores the contribution of these predictors on distance achieved in GSDV. Data, included maximum distance walked, age, gender, height and body mass, was collected from 103 GSDV patients who underwent 12MWT between 2011 and 2017. Analysis showed a significant correlation between distance achieved and height, age, body mass and gender. Multiple linear regression analysis revealed a model accounting for 29.7% of variance (R = 0.545, R2 0.297, adjusted R2 0.269). Gender was not significant after height, age and body mass were entered into the regression analysis. This is the first study to report the contribution of non-disease related factors on distance achieved on the 12MWT in the GSDV population. The reference values generated will allow for improved monitoring and assessment of GSDV patients in clinical and research settings.

First presentation of LPIN1 acute rhabdomyolysis in adolescence and adulthood.

LPIN1 mutations are a known common cause of autosomal recessive, recurrent and life-threatening acute rhabdomyolysis of childhood-onset. The first episode of rhabdomyolysis usually happens in nearly all cases before the age of 5 and death is observed in 1/3 of patients. Here we present two cases of acute rhabdomyolysis with a milder phenotype caused by LPIN1 mutation presenting in adolescence (11 years old) and adulthood (40 years old) after Parvovirus infection and metabolic stress, respectively. In our opinion, the mutation types, epigenetic factors, the environment exposition to triggers or the existence of proteins with a similar structure of LPIN1, may have a role in modulating the onset of rhabdomyolysis. LPIN1 should be included on a panel of genes analysed in the investigation of adult individuals with rhabdomyolysis. Metabolic and viral stressors should be included in the list of possible rhabdomyolysis precipitant.

Cardiorespiratory Progression Over 5 Years and Role of Corticosteroids in Duchenne Muscular Dystrophy: A Single-Site Retrospective Longitudinal Study.

BACKGROUND: Corticosteroids (CSs) have prolonged survival and respiratory function in boys with Duchenne muscular dystrophy (DMD) when compared with CSs-naïve boys. RESEARCH QUESTION: The differential impact of frequently used CSs and their regimens on long-term (> 5 years) cardiorespiratory progression in children with DMD is unknown. STUDY DESIGN AND METHODS: This was a retrospective longitudinal study including children with DMD followed at Dubowitz Neuromuscular Centre, Great Ormond Street Hospital London, England, from May 2000 to June 2017. Patients enrolled in any interventional clinical trials were excluded. We collected patients' anthropometrics and respiratory (FVC, FVC % predicted and absolute FVC, and noninvasive ventilation requirement [NIV]) and cardiac (left ventricular shortening function [LVFS%]) function. CSs-naïve patients had never received CSs. Patients who were treated with CSs took either deflazacort or prednisolone, daily or intermittently (10 days on/10 days off) for > 1 month. Average longitudinal models were fitted for yearly respiratory (FVC % predicted) and cardiac (LVFS%) progression. A time-to-event analysis to FVC % predicted < 50%, NIV start, and cardiomyopathy (LVFS% < 28%) was performed in CS-treated (daily and intermittent) vs CS-naïve patients. RESULTS: There were 270 patients, with a mean age at baseline of 6.2 ± 2.3 years. The median follow-up time was 5.6 ± 3.5 years. At baseline, 263 patients were ambulant. Sixty-six patients were treated with CSs daily, 182 patients underwent CSs intermittent > 60% treatment, and 22 were CS-naïve patients. Yearly FVC % predicted declined similarly from 9 years (5.9% and 6.9% per year, respectively; P = .27) in the CSs-daily and CSs-intermittent groups. The CSs-daily group declined from a higher FVC % predicted than the CSs-intermittent group (P < .05), and both reached FVC % predicted < 50% and NIV requirement at a similar age, > 2 years later than the CS-naïve group. LVFS% declined by 0.53% per year in the CSs-treated group irrespective of the CSs regimen, significantly slower (P < .01) than the CSs-naïve group progressing by 1.17% per year. The age at cardiomyopathy was 16.6 years in the CSs-treated group (P < .05) irrespective of regimen and 13.9 years in the CSs-naïve group. INTERPRETATION: CSs irrespective of the regimen significantly improved respiratory function and delayed NIV requirement and cardiomyopathy.

Improving specialised care for neuromuscular patients reduces the frequency of preventable emergency hospital admissions.

Two retrospective audits were undertaken across several hospitals to understand the frequency and preventability of emergency admissions in people with neuromuscular disease (NMD). Following audit 1 (A1), a number of preventable themes emerged on the basis of which recommendations were made to improve quality and co-ordination of care and a network approach was developed to improve awareness and education amongst patients and non-expert professionals. Audit 2 (A2) was undertaken to determine the effect of these measures. The central NHS IT database identified emergency NMD admissions. Case notes were reviewed and audited against pre-agreed criteria. A1 included 576 admissions (395 patients) A2 included 361 admissions (314 patients). Preventable admissions (where an NMD was known) accounted for 63% in A1 and 33% in A2, with more patients followed up at a specialised neuromuscular centre in A2. There were fewer re-admissions in A2 (12%) compared with A1 (25%) and lower mortality (A1: 4.5%, A2: 0.3%). A2 showed a significant rise in patients admitted under the care of neuroscience during the acute admission and fewer preventable ITU admissions. These audits demonstrate a significant impact for both patient care and potential for financial savings following the implementation of recommendations made after A1.

Expanding the molecular and phenotypic spectrum of truncating MT-ATP6 mutations.

OBJECTIVE: To describe the clinical and functional consequences of 1 novel and 1 previously reported truncating MT-ATP6 mutation. METHODS: Three unrelated probands with mitochondrial encephalomyopathy harboring truncating MT-ATP6 mutations are reported. Transmitochondrial cybrid cell studies were used to confirm pathogenicity of 1 novel variant, and the effects of all 3 mutations on ATPase 6 and complex V structure and function were investigated. RESULTS: Patient 1 presented with adult-onset cerebellar ataxia, chronic kidney disease, and diabetes, whereas patient 2 had myoclonic epilepsy and cerebellar ataxia; both harbored the novel m.8782G>A; p.(Gly86*) mutation. Patient 3 exhibited cognitive decline, with posterior white matter abnormalities on brain MRI, and severely impaired renal function requiring transplantation. The m.8618dup; p.(Thr33Hisfs*32) mutation, previously associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa, was identified. All 3 probands demonstrated a broad range of heteroplasmy across different tissue types. Blue-native gel electrophoresis of cultured fibroblasts and skeletal muscle tissue confirmed multiple bands, suggestive of impaired complex V assembly. Microscale oxygraphy showed reduced basal respiration and adenosine triphosphate synthesis, while reactive oxygen species generation was increased. Transmitochondrial cybrid cell lines studies confirmed the deleterious effects of the novel m.8782 G>A; p.(Gly86*) mutation. CONCLUSIONS: We expand the clinical and molecular spectrum of MT-ATP6-related mitochondrial disorders to include leukodystrophy, renal disease, and myoclonic epilepsy with cerebellar ataxia. Truncating MT-ATP6 mutations may exhibit highly variable mutant levels across different tissue types, an important consideration during genetic counseling.