Autosomal dominant in cis D4Z4 repeat array duplication alleles in facioscapulohumeral dystrophy.

Facioscapulohumeral dystrophy (FSHD) has a unique genetic aetiology resulting in partial chromatin relaxation of the D4Z4 macrosatellite repeat array on 4qter. This D4Z4 chromatin relaxation facilitates inappropriate expression of the transcription factor DUX4 in skeletal muscle. DUX4 is encoded by a retrogene that is embedded within the distal region of the D4Z4 repeat array. In the European population, the D4Z4 repeat array is usually organized in a single array that ranges between 8 and 100 units. D4Z4 chromatin relaxation and DUX4 derepression in FSHD is most often caused by repeat array contraction to 1-10 units (FSHD1) or by a digenic mechanism requiring pathogenic variants in a D4Z4 chromatin repressor like SMCHD1, combined with a repeat array between 8 and 20 units (FSHD2). With a prevalence of 1.5% in the European population, in cis duplications of the D4Z4 repeat array, where two adjacent D4Z4 arrays are interrupted by a spacer sequence, are relatively common but their relationship to FSHD is not well understood. In cis duplication alleles were shown to be pathogenic in FSHD2 patients; however, there is inconsistent evidence for the necessity of an SMCHD1 mutation for disease development. To explore the pathogenic nature of these alleles we compared in cis duplication alleles in FSHD patients with or without pathogenic SMCHD1 variant. For both groups we showed duplication-allele-specific DUX4 expression. We studied these alleles in detail using pulsed-field gel electrophoresis-based Southern blotting and molecular combing, emphasizing the challenges in the characterization of these rearrangements. Nanopore sequencing was instrumental to study the composition and methylation of the duplicated D4Z4 repeat arrays and to identify the breakpoints and the spacer sequence between the arrays. By comparing the composition of the D4Z4 repeat array of in cis duplication alleles in both groups, we found that specific combinations of proximal and distal repeat array sizes determine their pathogenicity. Supported by our algorithm to predict pathogenicity, diagnostic laboratories should now be furnished to accurately interpret these in cis D4Z4 repeat array duplications, alleles that can easily be missed in routine settings.

High-resolution breakpoint junction mapping of proximally extended D4Z4 deletions in FSHD1 reveals evidence for a founder effect.

Facioscapulohumeral muscular dystrophy (FSHD) is an inherited myopathy clinically characterized by weakness in the facial, shoulder girdle and upper a muscles. FSHD is caused by chromatin relaxation of the D4Z4 macrosatellite repeat, mostly by a repeat contraction, facilitating ectopic expression of DUX4 in skeletal muscle. Genetic diagnosis for FSHD is generally based on the sizing and haplotyping of the D4Z4 repeat on chromosome 4 by Southern blotting (SB), molecular combing or single-molecule optical mapping, which is usually straight forward but can be complicated by atypical rearrangements of the D4Z4 repeat. One of these rearrangements is a D4Z4 proximally extended deletion (DPED) allele, where not only the D4Z4 repeat is partially deleted, but also sequences immediately proximal to the repeat are lost, which can impede accurate diagnosis in all genetic methods. Previously, we identified several DPED alleles in FSHD and estimated the size of the proximal deletions by a complex pulsed-field gel electrophoresis and SB strategy. Here, using the next-generation sequencing, we have defined the breakpoint junctions of these DPED alleles at the base pair resolution in 12 FSHD families and 4 control individuals facilitating a PCR-based diagnosis of these DPED alleles. Our resultsshow that half of the DPED alleles are derivates of an ancient founder allele. For some DPED alleles, we found that genetic elements are deleted such as DUX4c, FRG2, DBE-T and myogenic enhancers necessitating re-evaluation of their role in FSHD pathogenesis.

Best practice guidelines on genetic diagnostics of facioscapulohumeral muscular dystrophy: Update of the 2012 guidelines.

The gold standard for facioscapulohumeral muscular dystrophy (FSHD) genetic diagnostic procedures was published in 2012. With the increasing complexity of the genetics of FSHD1 and 2, the increase of genetic testing centers, and the start of clinical trials for FSHD, it is crucial to provide an update on our knowledge of the genetic features of the FSHD loci and renew the international consensus on the molecular testing recommendations. To this end, members of the FSHD European Trial Network summarized the evidence presented during the 2022 ENMC meeting on Genetic diagnosis, clinical outcome measures, and biomarkers. The working group additionally invited genetic and clinical experts from the USA, India, Japan, Australia, South-Africa, and Brazil to provide a global perspective. Six virtual meetings were organized to reach consensus on the minimal requirements for genetic confirmation of FSHD1 and FSHD2. Here, we present the clinical and genetic features of FSHD, specific features of FSHD1 and FSHD2, pros and cons of established and new technologies (Southern blot in combination with either linear or pulsed-field gel electrophoresis, molecular combing, optical genome mapping, FSHD2 methylation analysis and FSHD2 genotyping), the possibilities and challenges of prenatal testing, including pre-implantation genetic testing, and the minimal requirements and recommendations for genetic confirmation of FSHD1 and FSHD2. This consensus is expected to contribute to current clinical management and trial-readiness for FSHD.

Nerve enlargement in patients with Noonan syndrome: A retrospective cohort study.

Noonan syndrome (NS) is an autosomal dominant condition characterized by facial dysmorphism, congenital heart disease, development delay, growth retardation and lymphatic disease. It is caused by germline pathogenic variants in genes encoding proteins in the Ras/mitogen-activated protein kinase signaling pathway. Nerve enlargement is not generally considered as a feature of NS, although some cases have been reported. High-resolution nerve ultrasound enables detailed anatomical assessment of peripheral nerves and can show enlarged nerves. This retrospective cohort study aims to describe the sonographic findings of patients with NS performed during a 1-year time period. Data on the degree of enlargement, the relation to increasing age, pain in extremities, genotype on the gene level and clinical features were collected. Twenty-nine of 93 patients visiting the NS Center of Expertise of the Radboud University Medical Center Nijmegen underwent high-resolution ultrasound. In 24 patients (83%) nerve enlargement was found. Most of them experienced pain. We observed a weak correlation with increasing age and the degree of nerve enlargement but no association with pain, genotype at the gene level or clinical features. This study shows that patients with NS have a high predisposition for sonographic nerve enlargement and that the majority experience pain.

The other face of facioscapulohumeral muscular dystrophy: Exploring orofacial weakness using muscle ultrasound.

INTRODUCTION/AIMS: One of the most distinct clinical features of facioscapulohumeral muscular dystrophy (FSHD) is facial weakness. It leads to diminished facial expression and functional impairments. Despite its clinical relevance, little else is known about orofacial muscle involvement. We therefore evaluated orofacial muscle involvement in a sizeable cohort of FSHD participants with muscle ultrasound. METHODS: Muscle ultrasound images of the following orofacial muscles were scored visually and quantitatively: depressor anguli oris (DAO), orbicularis oris (OO), buccinator, temporalis, masseter, digastric, zygomaticus major and minor bilaterally, and the geniohyoid. Reliability analyses of both visual and quantitative evaluations were performed. Ultrasound results were correlated with other measures: the FSHD clinical score, facial weakness score, and facial function scale. RESULTS: We included 107 FSHD participants (male 54%; age 52 ± 14 years), of whom 92% showed signs of facial weakness. The reliability of visual ultrasound analysis varied widely (κ 0.0-1.0). Quantitative ultrasound reliability was high (intraclass correlation analysis ≥ 0.96). The DAO, buccinator, OO, temporalis, and zygomaticus minor muscles were affected most often (15%-39%). The digastric, geniohyoid, zygomaticus major, and masseter muscles were least often affected (<5%). The ultrasound compound score correlated weakly to moderately with other outcome measures used (ρ = 0.3-0.7). DISCUSSION: This study adds to the understanding of orofacial weakness in FSHD, confirming the involvement of the muscles of facial expression in FSHD using ultrasound. We showed that orofacial muscle ultrasound is feasible and reliable when quantitatively assessed. Future studies should evaluate orofacial muscle ultrasound longitudinally, alongside clinical and patient-reported facial weakness outcome measures, to assess their potential as outcome measures.

A 5-year natural history study in LAMA2-related muscular dystrophy and SELENON-related myopathy: the Extended LAST STRONG study.

BACKGROUND: SELENON-related myopathy (SELENON-RM) is a rare congenital myopathy characterized by slowly progressive axial muscle weakness, rigidity of the spine, scoliosis, and respiratory insufficiency. Laminin-a2-related muscular dystrophy (LAMA2-MD) has a similar clinical phenotype, which ranges from severe, early-onset congenital muscular dystrophy type 1A (MDC1A) to milder forms presenting as childhood- or adult-onset limb-girdle type muscular dystrophy. The first 1.5-year natural history follow-up showed that 90% of the patients had low bone quality, respiratory impairments were found in all SELENON-RM and most of the LAMA2-MD patients, and many had cardiac risk factors. However, further extensive knowledge on long-term natural history data, and clinical and functional outcome measures is needed to reach trial readiness. Therefore, we extended the natural history study with 3- and 5-year follow-up visits (Extended LAST STRONG). METHODS: The Extended LAST STRONG is a long-term natural history study in Dutch-speaking patients of all ages diagnosed with genetically confirmed SELENON-RM or LAMA2-MD, starting in September 2023. Patients visit our hospital twice over a period of 2 years to complete a 5-year follow up from the initial LAST-STRONG study. At both visits, they undergo standardized neurological examination, hand-held dynamometry (age ≥ 5 years), functional measurements, muscle ultrasound, respiratory assessments (spirometry, maximal inspiratory and expiratory pressure, sniff nasal inspiratory pressure; age ≥ 5 years), Dual-energy X-ray absorptiometry (DEXA-)scan (age ≥ 2 years), X-ray of the left hand (age ≤ 17 years), lower extremity MRI (age ≥ 10 years), accelerometry for 8 days (age ≥ 2 years), and questionnaires (patient report and/or parent proxy; age ≥ 2 years). All examinations are adapted to the patient's age and functional abilities. Disease progression between all subsequent visits and relationships between outcome measures will be assessed. DISCUSSION: This study will provide valuable insights into the 5-year natural history of patients with SELENON-RM and LAMA2-MD and contribute to further selecting relevant and sensitive to change clinical and functional outcome measures. Furthermore, this data will help optimize natural history data collection in clinical care and help develop clinical care guidelines. TRIAL REGISTRATION: This study protocol including the patient information and consent forms has been approved by medical ethical reviewing committee ('METC Oost-Nederland'; https://www.ccmo.nl/metcs/erkende-metcs/metc-oost-nederland , file number: 2023-16401). It is registered at ClinicalTrials.gov (NCT06132750; study registration date: 2023-10-05; study first passed date: 2023-11-15).

Myopathic manifestations across the adult lifespan of patients with malignant hyperthermia susceptibility: a narrative review.

Malignant hyperthermia susceptibility (MHS) designates individuals at risk of developing a hypermetabolic reaction triggered by halogenated anaesthetics or the depolarising neuromuscular blocking agent suxamethonium. Over the past few decades, beyond the operating theatre, myopathic manifestations impacting daily life are increasingly recognised as a prevalent phenomenon in MHS patients. At the request of the European Malignant Hyperthermia Group, we reviewed the literature and gathered the opinion of experts to define MHS-related myopathy as a distinct phenotype expressed across the adult lifespan of MHS patients unrelated to anaesthetic exposure; this serves to raise awareness about non-anaesthetic manifestations, potential therapies, and management of MHS-related myopathy. We focused on the clinical presentation, biochemical and histopathological findings, and the impact on patient well-being. The spectrum of symptoms of MHS-related myopathy encompasses muscle cramps, stiffness, myalgias, rhabdomyolysis, and weakness, with a wide age range of onset mainly during adulthood. Histopathological analysis can reveal nonspecific abnormalities suggestive of RYR1 involvement, while metabolic profiling reflects altered energy metabolism in MHS muscle. Myopathic manifestations can significantly impact patient quality of life and lead to functional limitations and socio-economic burden. While currently available therapies can provide symptomatic relief, there is a need for further research into targeted treatments addressing the underlying pathophysiology. Counselling early after establishing the MHS diagnosis, followed by multidisciplinary management involving various medical specialties, is crucial to optimise patient care.

Future Directions for Respiratory Muscle Training in Neuromuscular Disorders: A Scoping Review.

BACKGROUND: Respiratory muscle training (RMT) aims to improve inspiratory and/or expiratory muscle function in neuromuscular disorders (NMDs). A comprehensive overview of the available literature is lacking. This scoping review explores methodological characteristics, (adverse) effects, and adherence of RMT studies in NMDs. Moreover, it identifies limitations and research gaps in the literature and provides future research directions. SUMMARY: Eligible studies were identified using MEDLINE, Embase, Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials databases. Three reviewers independently selected articles. Inclusion criteria were English language, original research articles on RMT using a device, patients with an NMD, and pulmonary function tests or respiratory muscle strength as outcome measures. We included NMDs with slow, intermediate and fast progression. Exclusion criteria were critically ill patients, weaning from mechanical ventilation, other neurological disorders, and RMT combined with non-respiratory interventions. One reviewer extracted the data on patients' characteristics, methodological characteristics, results of outcome measures, adverse events, and patient adherence. Forty-five studies were identified. We found a large diversity in study designs and training protocols. The effects of RMT on respiratory muscle strength and/or endurance are variable. Patient adherence was high and no serious adverse events were reported. KEY MESSAGES: The diversity in studies across the available literature precludes definitive conclusions regarding the effects of RMT on respiratory muscle function and clinically relevant outcomes in NMDs. Therefore, well-powered and -designed studies that focus on clinically relevant outcomes and assess whether RMT can improve or offset deterioration of respiratory muscle weakness in NMDs are needed.

Repeated oral sucrose dosing after the second wind is unnecessary in patients with McArdle disease: Results from a randomized, placebo-controlled, double-blind, cross-over study.

It is well-established that oral sucrose ingested shortly before exercise improves early exercise tolerance in individuals with McArdle disease. This is by supplying blood-borne glucose for muscle metabolism to compensate for the blocked glycogenolysis. The present study investigated if individuals with McArdle disease could benefit further from repeated sucrose ingestion during prolonged exercise. In this double-blind, placebo-controlled, cross-over study, the participants were randomized to ingest either sucrose or placebo first and subsequently the opposite on two separate days. The participants ingested the drink 10 min before and thrice (after 10, 25, and 40 min) during a 60-min submaximal exercise test on a cycle ergometer. The primary outcome was exercise capacity as indicated by heart rate (HR) and perceived exertion (PE) responses to exercise. Secondary outcomes included changes in blood metabolites, insulin and carbohydrate, and fatty acid oxidation rates during exercise. Nine participants with McArdle disease were included in the study. We confirmed improvement of exercise capacity with oral sucrose vs. placebo during early exercise (pre-second wind) indicated by lower peak HR and PE (p < 0.02). We found no further beneficial effect with repeated sucrose versus placebo ingestion during prolonged exercise, as indicated by no difference in HR or PE post-second wind (p > 0.05). Glucose, lactate, insulin, and carbohydrate oxidation rates increased, and fatty acid oxidation decreased with sucrose versus placebo (p ≤ 0.0002). We can conclude that repeated sucrose ingestion is not recommended during prolonged exercise. This finding can prevent excessive caloric intake and reduce the risk of obesity and insulin resistance.

Withdrawal of intravenous immunoglobulin in chronic inflammatory demyelinating polyradiculoneuropathy.

Intravenous immunoglobulins are an efficacious treatment for chronic inflammatory demyelinating polyradiculoneuropathy. Biomarkers for disease activity are lacking, making the need for ongoing treatment difficult to assess, leading to potential overtreatment and high health-care costs. Our objective was to determine whether intravenous immunoglobulin withdrawal is non-inferior to continuing intravenous immunoglobulin treatment and to determine how often patients are overtreated. We performed a randomized, double-blind, intravenous immunoglobulin-controlled non-inferiority trial in seven centres in the Netherlands (Trial registration: ISRCTN 13637698; www.isrctn.com/ISRCTN13637698). Adults with clinically stable chronic inflammatory demyelinating polyradiculoneuropathy using intravenous immunoglobulin maintenance treatment for at least 6 months were included. Patients received either intravenous immunoglobulin withdrawal (placebo) as investigational treatment or continuation of intravenous immunoglobulin treatment (control). The primary outcome was the mean change in logit scores from baseline to 24-week follow-up on the patient-reported Inflammatory Rasch-Overall Disability Scale. The non-inferiority margin was predefined as between-group difference in mean change scores of -0.65. Patients who deteriorated could reach a relapse end point according to predefined criteria. Patients with a relapse end point after intravenous immunoglobulin withdrawal entered a restabilization phase. All patients from the withdrawal group who remained stable were included in an open-label extension phase of 52 weeks. We included 60 patients, of whom 29 were randomized to intravenous immunoglobulin withdrawal and 31 to continuation of treatment. The mean age was 58 years (SD 14.7) and 67% was male. The between-group difference in mean change Inflammatory Rasch-Overall Disability Scale scores was -0.47 (95% CI -1.24 to 0.31), indicating that non-inferiority of intravenous immunoglobulin withdrawal could not be established. In the intravenous immunoglobulin withdrawal group, 41% remained stable for 24 weeks, compared to 58% in the intravenous immunoglobulin continuation group (-17%; 95% CI -39 to 8). Of the intravenous immunoglobulin withdrawal group, 28% remained stable at the end of the extension phase. Of the patients in the restabilization phase, 94% restabilized within 12 weeks. In conclusion, it remains inconclusive whether intravenous immunoglobulin withdrawal is non-inferior compared to continuing treatment, partly due to larger than expected confidence intervals leading to an underpowered study. Despite these limitations, a considerable proportion of patients could stop treatment and almost all patients who relapsed were restabilized quickly. Unexpectedly, a high proportion of intravenous immunoglobulin-treated patients experienced a relapse end point, emphasizing the need for more objective measures for disease activity in future trials, as the patient-reported outcome measures might not have been able to identify true relapses reliably. Overall, this study suggests that withdrawal attempts are safe and should be performed regularly in clinically stable patients.

Long-term outcomes for females with early-onset dystrophinopathy.

AIM: To study long-term disease course for females with early-onset dystrophinopathy, including common (female) symptoms, challenges in social participation, the need for care, and current healthcare management to support guideline development. METHOD: Twelve females with early-onset dystrophinopathy were followed for a median period of more than 17 years (range 1-36). RESULTS: One patient died owing to end-stage cardiac failure. Cardiac abnormalities were observed in three of the remaining 11 participants. Respiratory function was reduced in seven of 10 participants. Fatigue, myalgia, lower back pain, and arthralgia were reported in more than six of the participants. Functional status varied from exercise intolerance to wheelchair dependency. Most or all of the 10 participants reported restrictions in participation in work (n = 10), household duties (n = 10), sports (n = 9), and education (n = 8). Only a few participants received followed-up pulmonary (n = 2) or rehabilitation (n = 3) care. INTERPRETATION: Females with early-onset dystrophinopathy experience a wide range of impairments, comorbidities, limitations in activities, and restrictions in social participation. The whole spectrum should be acknowledged in the healthcare setting. Neuromuscular and cardiac follow-up are indispensable. Additional respiratory assessment and rehabilitation care are expected to improve health status and support daily activities and participation. WHAT THIS PAPER ADDS: No standard diagnostic procedures seem to exist for female patients suspected for dystrophinopathy. Female participants with early-onset dystrophinopathy experienced a broad scope of burdening symptoms, such as fatigue, myalgia, lower back pain, and arthralgia. None of participants worked full time, all felt restricted in paid work, and most felt restricted in education. Most participants showed decreased lung function, while only one was symptomatic. Availability of rehabilitation care may improve support for daily activities and participation for females with early-onset dystrophinopathy.

Oral Dantrolene for Myopathic Symptoms in Malignant Hyperthermia-Susceptible Patients: A 25-Year Retrospective Cohort Study of Adverse Effects and Tolerability.

BACKGROUND: Patients susceptible to malignant hyperthermia (MH) may experience disabling manifestations of an unspecified myopathy outside the context of anesthesia, including myalgia, fatigue, or episodic rhabdomyolysis. Clinical observations suggest that oral dantrolene may relief myopathic symptoms in MH-susceptible (MHS) patients. However, high-dose oral dantrolene has been associated with severe hepatotoxicity. METHODS: In a retrospective database review (1994-2018), we investigated a cohort of patients who were diagnosed as MHS by a positive caffeine-halothane contracture test (CHCT), had myopathic manifestations, and received oral dantrolene. Our aim was to investigate the occurrence of serious adverse effects and the adherence to oral dantrolene therapy. We also explored factors associated with self-reported clinical improvement, considering as nonresponders patients with intolerable adverse effects or who reported no improvement 8 weeks after starting treatment. RESULTS: Among 476 MHS patients with positive CHCT, 193 had muscle symptoms, 164 started oral dantrolene, 27 refused treatment, and 2 were excluded due to abnormal liver function before starting therapy. There were no serious adverse effects reported. Forty-six of 164 patients (28%; 95% confidence interval [CI], 22%-35%) experienced mild to moderate adverse effects. Twenty-two patients (22/164, 13%; 95% CI, 9%-19%) discontinued treatment, among which 16 due to adverse effects and 6 due to lack of improvement. One hundred forty-two patients (87%; 95% CI, 80%-90%) adhered to therapy and reported improvement of myalgia (n = 78), fatigue (n = 32), or rhabdomyolysis/hiperCKemia (n = 32). The proportion of responders was larger among patients with MH history than among those referred due to a clinical myopathy with nonpertinent anesthetic history (97% vs 79%, respectively; 95% CI of the difference, 8.5-28; P < .001). Patients with a sarcoplasmic reticulum Ca2+ release channel ryanodine receptor gene ( RYR1 ) variant had higher odds of responding to dantrolene treatment (OR, 6.4; 95% CI, 1.3-30.9; P = .013). Dantrolene median dose was 50 (25-400) and 200 (25-400) mg·day -1 in responders and nonresponders, respectively. CONCLUSIONS: We found that oral dantrolene produced no serious adverse effects within the reported dose range, and was well tolerated by most MH-susceptible patients presenting myopathic symptoms. Our study provides dosing and adverse effect data as a basis for further randomized controlled clinical trials to determine the efficacy of oral dantrolene for symptomatic relief in MHS-related myopathies.

Chromosome 10q-linked FSHD identifies DUX4 as principal disease gene.

BACKGROUND: Facioscapulohumeral dystrophy (FSHD) is an inherited muscular dystrophy clinically characterised by muscle weakness starting with the facial and upper extremity muscles. A disease model has been developed that postulates that failure in somatic repression of the transcription factor DUX4 embedded in the D4Z4 repeat on chromosome 4q causes FSHD. However, due to the position of the D4Z4 repeat close to the telomere and the complex genetic and epigenetic aetiology of FSHD, there is ongoing debate about the transcriptional deregulation of closely linked genes and their involvement in FSHD. METHOD: Detailed genetic characterisation and gene expression analysis of patients with clinically confirmed FSHD and control individuals. RESULTS: Identification of two FSHD families in which the disease is caused by repeat contraction and DUX4 expression from chromosome 10 due to a de novo D4Z4 repeat exchange between chromosomes 4 and 10. We show that the genetic lesion causal to FSHD in these families is physically separated from other candidate genes on chromosome 4. We demonstrate that muscle cell cultures from affected family members exhibit the characteristic molecular features of FSHD, including DUX4 and DUX4 target gene expression, without showing evidence for transcriptional deregulation of other chromosome 4-specific candidate genes. CONCLUSION: This study shows that in rare situations, FSHD can occur on chromosome 10 due to an interchromosomal rearrangement with the FSHD locus on chromosome 4q. These findings provide further evidence that DUX4 derepression is the dominant disease pathway for FSHD. Hence, therapeutic strategies should focus on DUX4 as the primary target.

Clinical and molecular features of 66 patients with musculocontractural Ehlers-Danlos syndrome caused by pathogenic variants in CHST14 (mcEDS-CHST14).

BACKGROUND: Musculocontractural Ehlers-Danlos syndrome is caused by biallelic loss-of-function variants in CHST14 (mcEDS-CHST14) or DSE (mcEDS-DSE). Although 48 patients in 33 families with mcEDS-CHST14 have been reported, the spectrum of pathogenic variants, accurate prevalence of various manifestations and detailed natural history have not been systematically investigated. METHODS: We collected detailed and comprehensive clinical and molecular information regarding previously reported and newly identified patients with mcEDS-CHST14 through international collaborations. RESULTS: Sixty-six patients in 48 families (33 males/females; 0-59 years), including 18 newly reported patients, were evaluated. Japanese was the predominant ethnicity (27 families), associated with three recurrent variants. No apparent genotype-phenotype correlation was noted. Specific craniofacial (large fontanelle with delayed closure, downslanting palpebral fissures and hypertelorism), skeletal (characteristic finger morphologies, joint hypermobility, multiple congenital contractures, progressive talipes deformities and recurrent joint dislocation), cutaneous (hyperextensibility, fine/acrogeria-like/wrinkling palmar creases and bruisability) and ocular (refractive errors) features were observed in most patients (>90%). Large subcutaneous haematomas, constipation, cryptorchidism, hypotonia and motor developmental delay were also common (>80%). Median ages at the initial episode of dislocation or large subcutaneous haematoma were both 6 years. Nine patients died; their median age was 12 years. Several features, including joint and skin characteristics (hypermobility/extensibility and fragility), were significantly more frequent in patients with mcEDS-CHST14 than in eight reported patients with mcEDS-DSE. CONCLUSION: This first international collaborative study of mcEDS-CHST14 demonstrated that the subtype represents a multisystem disorder with unique set of clinical phenotypes consisting of multiple malformations and progressive fragility-related manifestations; these require lifelong, multidisciplinary healthcare approaches.

In Vitro Skeletal Muscle Model of PGM1 Deficiency Reveals Altered Energy Homeostasis.

Phosphoglucomutase 1 (PGM1) is a key enzyme for the regulation of energy metabolism from glycogen and glycolysis, as it catalyzes the interconversion of glucose 1-phosphate and glucose 6-phosphate. PGM1 deficiency is an autosomal recessive disorder characterized by a highly heterogenous clinical spectrum, including hypoglycemia, cleft palate, liver dysfunction, growth delay, exercise intolerance, and dilated cardiomyopathy. Abnormal protein glycosylation has been observed in this disease. Oral supplementation with D-galactose efficiently restores protein glycosylation by replenishing the lacking pool of UDP-galactose, and rescues some symptoms, such as hypoglycemia, hepatopathy, and growth delay. However, D-galactose effects on skeletal muscle and heart symptoms remain unclear. In this study, we established an in vitro muscle model for PGM1 deficiency to investigate the role of PGM1 and the effect of D-galactose on nucleotide sugars and energy metabolism. Genome-editing of C2C12 myoblasts via CRISPR/Cas9 resulted in Pgm1 (mouse homologue of human PGM1, according to updated nomenclature) knockout clones, which showed impaired maturation to myotubes. No difference was found for steady-state levels of nucleotide sugars, while dynamic flux analysis based on 13C6-galactose suggested a block in the use of galactose for energy production in knockout myoblasts. Subsequent analyses revealed a lower basal respiration and mitochondrial ATP production capacity in the knockout myoblasts and myotubes, which were not restored by D-galactose. In conclusion, an in vitro mouse muscle cell model has been established to study the muscle-specific metabolic mechanisms in PGM1 deficiency, which suggested that galactose was unable to restore the reduced energy production capacity.

Muscle cramps and contractures: causes and treatment.

Muscle cramps are painful, sudden, involuntary muscle contractions that are generally self-limiting. They are often part of the spectrum of normal human physiology and can be associated with a wide range of acquired and inherited causes. Cramps are only infrequently due to progressive systemic or neuromuscular diseases. Contractures can mimic cramps and are defined as shortenings of the muscle resulting in an inability of the muscle to relax normally, and are generally myogenic. General practitioners and neurologists frequently encounter patients with muscle cramps but more rarely those with contractures. The main questions for clinicians are: (1) Is this a muscle cramp, a contracture or a mimic? (2) Are the cramps exercise induced, idiopathic or symptomatic? (3) What is/are the presumed cause(s) of symptomatic muscle cramps or contractures? (4) What should be the diagnostic approach? and (5) How should we advise and treat patients with muscle cramps or contractures? We consider these questions and present a practical approach to muscle cramps and contractures, including their causes, pathophysiology and treatment options.

KBTBD13 is a novel cardiomyopathy gene.

KBTBD13 variants cause nemaline myopathy type 6 (NEM6). The majority of NEM6 patients harbors the Dutch founder variant, c.1222C>T, p.Arg408Cys (KBTBD13 p.R408C). Although KBTBD13 is expressed in cardiac muscle, cardiac involvement in NEM6 is unknown. Here, we constructed pedigrees of three families with the KBTBD13 p.R408C variant. In 65 evaluated patients, 12% presented with left ventricle dilatation, 29% with left ventricular ejection fraction< 50%, 8% with atrial fibrillation, 9% with ventricular tachycardia, and 20% with repolarization abnormalities. Five patients received an implantable cardioverter defibrillator, three cases of sudden cardiac death were reported. Linkage analysis confirmed cosegregation of the KBTBD13 p.R408C variant with the cardiac phenotype. Mouse studies revealed that (1) mice harboring the Kbtbd13 p.R408C variant display mild diastolic dysfunction; (2) Kbtbd13-deficient mice have systolic dysfunction. Hence, (1) KBTBD13 is associated with cardiac dysfunction and cardiomyopathy; (2) KBTBD13 should be added to the cardiomyopathy gene panel; (3) NEM6 patients should be referred to the cardiologist.

Facioscapulohumeral muscular dystrophy-Reproductive counseling, pregnancy, and delivery in a complex multigenetic disease.

Reproductive counseling in facioscapulohumeral muscular dystrophy (FSHD) can be challenging due to the complexity of its underlying genetic mechanisms and due to incomplete penetrance of the disease. Full understanding of the genetic causes and potential inheritance patterns of both distinct FSHD types is essential: FSHD1 is an autosomal dominantly inherited repeat disorder, whereas FSHD2 is a digenic disorder. This has become even more relevant now that prenatal diagnosis and preimplantation genetic diagnosis options are available for FSHD1. Pregnancy and delivery outcomes in FSHD are usually favorable, but clinicians should be aware of the risks. We aim to provide clinicians with case-based strategies for reproductive counseling in FSHD, as well as recommendations for pregnancy and delivery.

Referral Indications for Malignant Hyperthermia Susceptibility Diagnostics in Patients without Adverse Anesthetic Events in the Era of Next-generation Sequencing.

BACKGROUND: The introduction of next-generation sequencing into the diagnosis of neuromuscular disorders has resulted in an increased number of newly identified RYR1 variants. The hypothesis was that there is an increased referral of patients to malignant hyperthermia units without a personal/family history of adverse anesthetic events suspected to be malignant hyperthermia. This retrospective multicenter cohort study evaluates patient referral indications and outcomes for those without a history of an adverse anesthetic event. METHODS: Patients referred between 2010 and 2019 to the malignant hyperthermia units in Antwerp, Belgium; Lund, Sweden; Nijmegen, The Netherlands; and Toronto, Ontario, Canada were included. Previously tested patients and relatives of previously tested patients were excluded. Data collection included demographics, referral details, muscle contracture, and genetic testing results including Rare Exome Variant Ensemble Learner scores. Referral indications were categorized into those with a personal/family history of adverse anesthetic event and other indications including exertional and/or recurrent rhabdomyolysis, RYR1 variant(s) detected in diagnostic testing in the neuromuscular clinic without a specific diagnosis (in a family member), diagnosed RYR1-related myopathy (in a family member), idiopathically elevated resting creatine kinase values, exertional heat stroke, and other. RESULTS: A total of 520 medical records were included, with the three most frequent referral indications as follows: personal history of an adverse anesthetic event (211 of 520; 40.6%), family history of an adverse anesthetic event (115 of 520; 22.1%), and exertional and/or recurrent rhabdomyolysis (46 of 520; 8.8%). The proportion of patients referred without a personal/family history of an adverse anesthetic event increased to 43.6% (133 of 305) between 2015 and 2019 compared to 28.4% (61 of 215) in 2010 to 2014 (P < 0.001). Patients with a personal/family history of an adverse anesthetic event were more frequently diagnosed as malignant hyperthermia-susceptible (133 of 220; 60.5%) than those without (47 of 120; 39.2%; P < 0.001). Due to missing data, 180 medical records were excluded. CONCLUSIONS: The proportion of patients referred to malignant hyperthermia units without a personal/family history of an adverse anesthetic event has increased, with 39.2% (47 of 120) diagnosed as malignant hyperthermia-susceptible.

No effect of oral ketone ester supplementation on exercise capacity in patients with McArdle disease and healthy controls: A randomized placebo-controlled cross-over study.

Patients with glycogen storage disease type V (GSDV), also known as McArdle disease, have blocked glycogen breakdown due to myophosphorylase deficiency, leading to exercise intolerance, muscle pain, and risk of muscle damage. Blood-derived ketone bodies (KBs) constitute an alternative energy source that could fuel the muscle independent of glycogenolysis. However, except for long-time fasting or ketogenic dieting, KBs are present in low quantities. This led us to explore the effects of a drink containing exogenously produced KBs in the form of D-ß-hydroxybutyrate esters (KE) on exercise capacity and metabolism in patients with GSDV. Eight GSDV patients and four healthy controls (HC) were included in this placebo-controlled, cross-over study where subjects were randomized to receive a KE drink with 395 mgKE/kg or placebo drink on two separate days 25 min before a submaximal cycle exercise test. The primary outcome was exercise capacity as indicated by heart rate response (HR) to exercise. Secondary outcomes included perceived exertion (PE) and measures of KB, carbohydrate, and fat metabolism during exercise. In GSDV, the KE drink vs. placebo increased plasma KBs and KB oxidation (p ≤ 0.0001) but did not improve exercise capacity as judged from HR (p = 0.120) and PE (p = 0.109). In addition, the KE drink lowered plasma glucose, free fatty acids, and lowered lipolytic rate and glucose rate of appearance compared with placebo. Similar results were found in the HC group. The present study indicates that an increase in KB oxidation by oral KE supplementation does not improve exercise capacity in GSDV possibly because of KB-induced inhibition of lipolysis and liver glucose output. Thus, oral KE supplementation alone cannot be recommended as a treatment option for patients with GSDV.