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.

The clinical spectrum of the congenital myasthenic syndrome resulting from COL13A1 mutations.

Next generation sequencing techniques were recently used to show mutations in COL13A1 cause synaptic basal lamina-associated congenital myasthenic syndrome type 19. Animal studies showed COL13A1, a synaptic extracellular-matrix protein, is involved in the formation and maintenance of the neuromuscular synapse that appears independent of the Agrin-LRP4-MuSK-DOK7 acetylcholine receptor clustering pathway. Here, we report the phenotypic spectrum of 16 patients from 11 kinships harbouring homozygous or heteroallelic mutations in COL13A1. Clinical presentation was mostly at birth with hypotonia and breathing and feeding difficulties often requiring ventilation and artificial feeding. Respiratory crisis related to recurrent apnoeas, sometimes triggered by chest infections, were common early in life but resolved over time. The predominant pattern of muscle weakness included bilateral ptosis (non-fatigable in adulthood), myopathic facies and marked axial weakness, especially of neck flexion, while limb muscles were less involved. Other features included facial dysmorphism, skeletal abnormalities and mild learning difficulties. All patients tested had results consistent with abnormal neuromuscular transmission. Muscle biopsies were within normal limits or showed non-specific changes. Muscle MRI and serum creatine kinase levels were normal. In keeping with COL13A1 mutations affecting both synaptic structure and presynaptic function, treatment with 3,4-diaminopyridine and salbutamol resulted in motor and respiratory function improvement. In non-treated cases, disease severity and muscle strength improved gradually over time and several adults recovered normal muscle strength in the limbs. In summary, patients with COL13A1 mutations present mostly with severe early-onset myasthenic syndrome with feeding and breathing difficulties. Axial weakness is greater than limb weakness. Disease course improves gradually over time, which could be consistent with the less prominent role of COL13A1 once the neuromuscular junction is mature. This report emphasizes the role of collagens at the human muscle endplate and should facilitate the recognition of this disorder, which can benefit from pharmacological treatment.

Congenital Myasthenic Syndrome Type 19 Is Caused by Mutations in COL13A1, Encoding the Atypical Non-fibrillar Collagen Type XIII α1 Chain.

The neuromuscular junction (NMJ) consists of a tripartite synapse with a presynaptic nerve terminal, Schwann cells that ensheathe the terminal bouton, and a highly specialized postsynaptic membrane. Synaptic structural integrity is crucial for efficient signal transmission. Congenital myasthenic syndromes (CMSs) are a heterogeneous group of inherited disorders that result from impaired neuromuscular transmission, caused by mutations in genes encoding proteins that are involved in synaptic transmission and in forming and maintaining the structural integrity of NMJs. To identify further causes of CMSs, we performed whole-exome sequencing (WES) in families without an identified mutation in known CMS-associated genes. In two families affected by a previously undefined CMS, we identified homozygous loss-of-function mutations in COL13A1, which encodes the alpha chain of an atypical non-fibrillar collagen with a single transmembrane domain. COL13A1 localized to the human muscle motor endplate. Using CRISPR-Cas9 genome editing, modeling of the COL13A1 c.1171delG (p.Leu392Sfs(∗)71) frameshift mutation in the C2C12 cell line reduced acetylcholine receptor (AChR) clustering during myotube differentiation. This highlights the crucial role of collagen XIII in the formation and maintenance of the NMJ. Our results therefore delineate a myasthenic disorder that is caused by loss-of-function mutations in COL13A1, encoding a protein involved in organization of the NMJ, and emphasize the importance of appropriate symptomatic treatment for these individuals.

Muscle magnetic resonance imaging in congenital myasthenic syndromes.

INTRODUCTION: In this study we investigated muscle magnetic resonance imaging in congenital myasthenic syndromes (CMS). METHODS: Twenty-six patients with 9 CMS subtypes and 10 controls were imaged. T1-weighted (T1w) and short-tau inversion recovery (STIR) 3-Tesla MRI images obtained at thigh and calf levels were scored for severity. RESULTS: Overall mean the T1w score was increased in GFPT1 and DPAGT1 CMS. T1w scans of the AChR-deficiency, COLQ, and CHAT subjects were indistinguishable from controls. STIR images from CMS patients did not differ significantly from those of controls. Mean T1w score correlated with age in the CMS cohort. CONCLUSIONS: MRI appearances ranged from normal to marked abnormality. T1w images seem to be especially abnormal in some CMS caused by mutations of proteins involved in the glycosylation pathway. A non-selective pattern of fat infiltration or a normal-appearing scan in the setting of significant clinical weakness should suggest CMS as a potential diagnosis. Muscle MRI could play a role in differentiating CMS subtypes. Muscle Nerve 54: 211-219, 2016.

A severe congenital myasthenic syndrome with "dropped head" caused by novel MUSK mutations.

INTRODUCTION: Congenital myasthenic syndromes are rare. Mutations in MUSK were first described in 2004. Thirteen patients have been reported to date, mostly with a relatively mild course. The molecular diagnosis has implications for choice of treatment and genetic counseling. METHODS: Clinical course and electrophysiological, pathological, and genetic findings were assessed. RESULTS: We describe the case of a boy with prenatal onset and severe respiratory symptoms with a persisting need for ventilation. The patient had severe bulbar symptoms, marked axial weakness causing a "dropped head," and some facial and proximal weakness. Ophthalmoparesis developed during the first year of life. Salbutamol led to improvement, 3,4-diaminopyridine had a modest effect, but pyridostigmine produced deterioration. Two novel mutations in MUSK were found by whole exome sequencing. CONCLUSIONS: We expand the phenotype of congenital myasthenic syndromes with MUSK mutations, describing a more severe clinical course with prenatal onset. Predominant bulbar and respiratory weakness with facial and axial weakness and ophthalmoparesis are diagnostic clues.

The spectrum of mutations that underlie the neuromuscular junction synaptopathy in DOK7 congenital myasthenic syndrome.

Congenital myasthenic syndromes (CMS) are a group of inherited diseases that affect synaptic transmission at the neuromuscular junction and result in fatiguable muscle weakness. A subgroup of CMS patients have a recessively inherited limb-girdle pattern of weakness caused by mutations in DOK7. DOK7 encodes DOK7, an adaptor protein that is expressed in the skeletal muscle and heart and that is essential for the development and maintenance of the neuromuscular junction. We have screened the DOK7 gene for mutations by polymerase chain reaction amplification and bi-directional sequencing of exonic and promoter regions and performed acetylcholine receptor (AChR) clustering assays and used exon trapping to determine the pathogenicity of detected variants. Approximately 18% of genetically diagnosed CMSs in the UK have mutations in DOK7, with mutations in this gene identified in more than 60 kinships to date. Thirty-four different pathogenic mutations were identified as well as 27 variants likely to be non-pathogenic. An exon 7 frameshift duplication c.1124_1127dupTGCC is commonly found in at least one allele. We analyse the effect of the common frameshift c.1124_1127dupTGCC and show that 10/11 suspected missense mutations have a deleterious effect on AChR clustering. We identify for the first time homozygous or compound heterozygous mutations that are localized 5' to exon 7. In addition, three silent variants in the N-terminal half of DOK7 are predicted to alter the splicing of the DOK7 RNA transcript. The DOK7 gene is highly polymorphic, and within these many variants, we define a spectrum of mutations that can underlie DOK7 CMS that will inform in managing this disorder.

Myasthenia in pregnancy: best practice guidelines from a U.K. multispecialty working group.

A national U.K. workshop to discuss practical clinical management issues related to pregnancy in women with myasthenia gravis was held in May 2011. The purpose was to develop recommendations to guide general neurologists and obstetricians and facilitate best practice before, during and after pregnancy. The main conclusions were (1) planning should be instituted well in advance of any potential pregnancy to allow time for myasthenic status and drug optimisation; (2) multidisciplinary liaison through the involvement of relevant specialists should occur throughout pregnancy, during delivery and in the neonatal period; (3) provided that their myasthenia is under good control before pregnancy, the majority of women can be reassured that it will remain stable throughout pregnancy and the postpartum months; (4) spontaneous vaginal delivery should be the aim and actively encouraged; (5) those with severe myasthenic weakness need careful, multidisciplinary management with prompt access to specialist advice and facilities; (6) newborn babies born to myasthenic mothers are at risk of transient myasthenic weakness, even if the mother's myasthenia is well-controlled, and should have rapid access to neonatal high-dependency support.

Benign hereditary chorea related to NKX2.1: expansion of the genotypic and phenotypic spectrum.

AIM: Benign hereditary chorea is a dominantly inherited, childhood-onset hyperkinetic movement disorder characterized by non-progressive chorea and variable degrees of thyroid and respiratory involvement. Loss-of-function mutations in NKX2.1, a gene vital to the normal development and function of the brain, lungs, and thyroid, have been identified in a number of individuals. METHOD: Clinical data from individuals with benign hereditary chorea identified through paediatric neurology services were collected in a standardized format. The NKX2.1 gene was analysed by Sanger sequencing, multiplex ligation-dependent probe amplification, and microarray analysis. RESULTS: Six of our cohort were female and four male, median age at assessment was 8 years 6 months (range 1 y 6 mo-18 y). We identified 10 probands with NKX2.1 mutations; nine of these mutations are novel (including two whole-gene deletions) and one has been previously reported. Of the 10 individuals, eight presented with muscle hypotonia and four had evidence of hypothyroidism or respiratory involvement. Only three out of the 10 individuals had the full triad of 'brain-lung-thyroid syndrome' symptoms. Additional clinical characteristics occurring in individual participants included growth hormone deficiency, pes cavus, kyphosis, duplex kidney, and obsessive-compulsive disorder. INTERPRETATION: Our data suggest that the neurological phenotype is prominent in this condition and that many patients with benign hereditary chorea do not have the classic triad of brain-lung-thyroid syndrome. The extended phenotype may include obsessive-compulsive disorder and skeletal abnormalities.

Long-term benefits and adverse effects of intermittent versus daily glucocorticoids in boys with Duchenne muscular dystrophy.

OBJECTIVE: To assess the current use of glucocorticoids (GCs) in Duchenne muscular dystrophy in the UK, and compare the benefits and the adverse events of daily versus intermittent prednisolone regimens. DESIGN: A prospective longitudinal observational study across 17 neuromuscular centres in the UK of 360 boys aged 3-15 years with confirmed Duchenne muscular dystrophy who were treated with daily or intermittent (10 days on/10 days off) prednisolone for a mean duration of treatment of 4 years. RESULTS: The median loss of ambulation was 12 years in intermittent and 14.5 years in daily treatment; the HR for intermittent treatment was 1.57 (95% CI 0.87 to 2.82). A fitted multilevel model comparing the intermittent and daily regiments for the NorthStar Ambulatory Assessment demonstrated a divergence after 7 years of age, with boys on an intermittent regimen declining faster (p<0.001). Moderate to severe side effects were more commonly reported and observed in the daily regimen, including Cushingoid features, adverse behavioural events and hypertension. Body mass index mean z score was higher in the daily regimen (1.99, 95% CI 1.79 to 2.19) than in the intermittent regimen (1.51, 95% CI 1.27 to 1.75). Height restriction was more severe in the daily regimen (mean z score -1.77, 95% CI -1.79 to -2.19) than in the intermittent regimen (mean z score -0.70, 95% CI -0.90 to -0.49). CONCLUSIONS: Our study provides a framework for providing information to patients with Duchenne muscular dystrophy and their families when introducing GC therapy. The study also highlights the importance of collecting longitudinal natural history data on patients treated according to standardised protocols, and clearly identifies the benefits and the side-effect profile of two treatment regimens, which will help with informed choices and implementation of targeted surveillance.

Congenital myasthenic syndromes: a retrospective natural history study of respiratory outcomes in a single centre.

Respiratory problems are a major cause of morbidity and mortality in patients with congenital myasthenic syndromes, a rare heterogeneous group of neuromuscular disorders caused by genetic defects impacting the structure and function of the neuromuscular junction. Recurrent, life-threatening episodic apnoea in early infancy and childhood and progressive respiratory failure requiring ventilation are features of certain genotypes of congenital myasthenic syndromes. Robb et al. published empirical guidance on respiratory management of the congenital myasthenic syndromes, but other than this workshop report, there are little published longitudinal natural history data on respiratory outcomes of these disorders. We report a retrospective, single-centre study on respiratory outcomes in a cohort of 40 well characterized genetically confirmed cases of congenital myasthenic syndromes, including 10 distinct subtypes (DOK7, COLQ, RAPSN, CHAT, CHRNA1, CHRNG, COL13A1, CHRNE, CHRNE fast channel syndrome and CHRNA1 slow channel syndrome), with many followed up over 20 years in our centre. A quantitative and longitudinal analysis of key spirometry and sleep study parameters, as well as a description of historical hospital admissions for respiratory decompensation, provides a snapshot of the respiratory trajectory of congenital myasthenic syndrome patients based on genotype.

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.

Clinical and genetic findings in a large cohort of patients with ryanodine receptor 1 gene-associated myopathies.

Ryanodine receptor 1 (RYR1) mutations are a common cause of congenital myopathies associated with both dominant and recessive inheritance. Histopathological findings frequently feature central cores or multi-minicores, more rarely, type 1 predominance/uniformity, fiber-type disproportion, increased internal nucleation, and fatty and connective tissue. We describe 71 families, 35 associated with dominant RYR1 mutations and 36 with recessive inheritance. Five of the dominant mutations and 35 of the 55 recessive mutations have not been previously reported. Dominant mutations, typically missense, were frequently located in recognized mutational hotspot regions, while recessive mutations were distributed throughout the entire coding sequence. Recessive mutations included nonsense and splice mutations expected to result in reduced RyR1 protein. There was wide clinical variability. As a group, dominant mutations were associated with milder phenotypes; patients with recessive inheritance had earlier onset, more weakness, and functional limitations. Extraocular and bulbar muscle involvement was almost exclusively observed in the recessive group. In conclusion, our study reports a large number of novel RYR1 mutations and indicates that recessive variants are at least as frequent as the dominant ones. Assigning pathogenicity to novel mutations is often difficult, and interpretation of genetic results in the context of clinical, histological, and muscle magnetic resonance imaging findings is essential.

TUBA1A mutations cause wide spectrum lissencephaly (smooth brain) and suggest that multiple neuronal migration pathways converge on alpha tubulins.

We previously showed that mutations in LIS1 and DCX account for approximately 85% of patients with the classic form of lissencephaly (LIS). Some rare forms of LIS are associated with a disproportionately small cerebellum, referred to as lissencephaly with cerebellar hypoplasia (LCH). Tubulin alpha1A (TUBA1A), encoding a critical structural subunit of microtubules, has recently been implicated in LIS. Here, we screen the largest cohort of unexplained LIS patients examined to date to determine: (i) the frequency of TUBA1A mutations in patients with lissencephaly, (ii) the spectrum of phenotypes associated with TUBA1A mutations and (iii) the functional consequences of different TUBA1A mutations on microtubule function. We identified novel and recurrent TUBA1A mutations in approximately 1% of children with classic LIS and in approximately 30% of children with LCH, making this the first major gene associated with the rare LCH phenotype. We also unexpectedly found a TUBA1A mutation in one child with agenesis of the corpus callosum and cerebellar hypoplasia without LIS. Thus, our data demonstrate a wider spectrum of phenotypes than previously reported and allow us to propose new recommendations for clinical testing. We also provide cellular and structural data suggesting that LIS-associated mutations of TUBA1A operate via diverse mechanisms that include disruption of binding sites for microtubule-associated proteins (MAPs).

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.

The use of rituximab in myasthenia gravis and Lambert-Eaton myasthenic syndrome.

AIM: To assess the treatment effects of rituximab in a population of patients with myasthenia gravis and Lambert-Eaton myasthenic syndrome. METHODS: Data on all treated patients in the UK were collected from referring physicians, with full case ascertainment and follow-up. RESULTS: Since 2004, 10 patients with generalised myasthenia gravis (three of whom were positive for muscle-specific tyrosine kinase (MuSK) antibodies) and two patients with Lambert-Eaton myasthenic syndrome (LEMS) were treated with rituximab. Using the Myasthenia Gravis Foundation America postintervention status, three patients (25%) achieved remission, and a further five (42%) improved clinically over an 18-month period. Only one patient developed worsening symptoms. The probability of achieving remission was unrelated to the duration of neurological symptoms prior to treatment. All LEMS and MuSK antibody patients improved following rituximab treatment. CONCLUSION: In a relatively large, unselected group of patients with myasthenia gravis and LEMS, rituximab treatment resulted in a significant clinical improvement in two-thirds of cases. As a selective, B cell targeted therapy, rituximab should be considered as a treatment option for patients with either myasthenia gravis or LEMS for whom standard immunosuppressive treatments have been unsuccessful.

Paediatric myasthenia gravis: Prognostic factors for drug free remission.

Our aim was to identify clinical outcomes, serological features and possible prognostic indicators of paediatric myasthenia gravis (MG). We collected 74 MG patients with disease onset before the age of 16 years (73% pre-pubertal onset defined as ≤10 years), seen regularly at two UK specialist centres, over a period of 11 years. The cohort was multi-ethnic, with a high number of non-Caucasians (52%). Ocular presentation was seen in 38 (51%) and only 8 (21%) of these generalised. Fifty-two (70%) patients had antibodies to the acetylcholine receptor (AChR) measured by radioimmunoprecipitation, 10 (14%) had antibodies only to clustered AChRs detected by a cell based assay, 3 (4%) had muscle-specific kinase and one (1%) low-density lipoprotein receptor-related protein 4 antibody. Only 8 (11%) had no detectable antibodies. Seventeen patients attained drug free remission (Kaplan Meyer survival curve estimates 25% by 7 years). Several factors were associated with a higher likelihood of free remission: onset age ≤10 years, Asian and Caucasian races, lack of AChR antibodies on RIA, and normal repetitive nerve stimulation at diagnosis. However, in a multifactorial regression analysis, the antibody status was the only significant predictor for drug free remission, with 60% of patients with antibodies only to clustered AChR achieving this outcome. Complete drug free remission is not uncommon in paediatric MG and several factors appear to influence this outcome with antibody status being the most important. These factors can be easily evaluated at diagnosis, and may help to determine whose patients are likely to require more intensive treatments.

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.

Brain involvement in muscular dystrophies with defective dystroglycan glycosylation.

OBJECTIVE: To assess the range and severity of brain involvement, as assessed by magnetic resonance imaging, in 27 patients with mutations in POMT1 (4), POMT2 (9), POMGnT1 (7), Fukutin (4), or LARGE (3), responsible for muscular dystrophies with abnormal glycosylation of dystroglycan (dystroglycanopathies). METHODS: Blinded review of magnetic resonance imaging brain scans from 27 patients with mutations in 1 of these 5 genes. RESULTS: Brain magnetic resonance images were normal in 3 of 27 patients; in another 5, only nonspecific abnormalities (ventricular dilatation, periventricular white matter abnormalities, or both) were seen. The remaining 19 patients had a spectrum of structural defects, ranging from complete lissencephaly in patients with Walker-Warburg syndrome to isolated cerebellar involvement. Cerebellar cysts and/or dysplasia and hypoplasia were the predominant features in four patients. Polymicrogyria (11/27) was more severe in the frontoparietal regions in 6, and had an occipitofrontal gradient in 2. Pontine clefts, with an unusual appearance to the corticospinal tracts, were seen in five patients with a muscle-eye-brain-like phenotype, three patients with POMGnT1, one with LARGE, and one with POMT2 mutations. Prominent cerebellar cysts were always seen with POMGnT1 mutations, but rarely seen in POMT1 and POMT2. Brainstem and pontine abnormalities were common in patients with POMT2, POMGnT1, and LARGE mutations. INTERPRETATION: Our results expand the spectrum of brain involvement associated with mutations in LARGE, POMGnT1, POMT1, and POMT2. Pontine clefts were visible in some dystroglycanopathy patients. Infratentorial structures were often affected in isolation, highlighting their susceptibility to involvement in these conditions.

Molecular mechanisms and phenotypic variation in RYR1-related congenital myopathies.

Dominant mutations in the skeletal muscle ryanodine receptor (RYR1) gene are well-recognized causes of both malignant hyperthermia susceptibility (MHS) and central core disease (CCD). More recently, recessive RYR1 mutations have been described in few congenital myopathy patients with variable pathology, including multi-minicores. Although a clinical overlap between patients with dominant and recessive RYR1 mutations exists, in most cases with recessive mutations the pattern of muscle weakness is remarkably different from that observed in dominant CCD. In order to characterize the spectrum of congenital myopathies associated with RYR1 mutations, we have investigated a cohort of 44 patients from 28 families with clinical and/or histopathological features suggestive of RYR1 involvement. We have identified 25 RYR1 mutations, 9 of them novel, including 12 dominant and 13 recessive mutations. With only one exception, dominant mutations were associated with a CCD phenotype, prominent cores and predominantly occurred in the RYR1 C-terminal exons 101 and 102. In contrast, the 13 recessive RYR1 mutations were distributed evenly along the entire RYR1 gene and were associated with a wide range of clinico-pathological phenotypes. Protein expression studies in nine cases suggested a correlation between specific mutations, RyR1 protein levels and resulting phenotype: in particular, whilst patients with dominant or recessive mutations associated with typical CCD phenotypes appeared to have normal RyR1 expression, individuals with more generalized weakness, multi-minicores and external ophthalmoplegia had a pronounced depletion of the RyR1 protein. The phenomenon of protein depletion was observed in some patients compound heterozygous for recessive mutations at the genomic level and silenced another allele in skeletal muscle, providing additional information on the mechanism of disease in these patients. Our data represent the most extensive study of RYR1-related myopathies and indicate complex genotype-phenotype correlations associated with mutations differentially affecting assembly and function of the RyR1 calcium release channel.

Refining genotype phenotype correlations in muscular dystrophies with defective glycosylation of dystroglycan.

Muscular dystrophies with reduced glycosylation of alpha-dystroglycan (alpha-DG), commonly referred to as dystroglycanopathies, are a heterogeneous group of autosomal recessive conditions which include a wide spectrum of clinical severity. Reported phenotypes range from severe congenital onset Walker-Warburg syndrome (WWS) with severe structural brain and eye involvement, to relatively mild adult onset limb girdle muscular dystrophy (LGMD). Specific clinical syndromes were originally described in association with mutations in any one of six demonstrated or putative glycosyltransferases. Work performed on patients with mutations in the FKRP gene has identified that the spectrum of phenotypes due to mutations in this gene is much wider than originally assumed. To further define the mutation frequency and phenotypes associated with mutations in the other five genes, we studied a large cohort of patients with evidence of a dystroglycanopathy. Exclusion of mutations in FKRP was a prerequisite for participation in this study. Ninety-two probands were screened for mutations in POMT1, POMT2, POMGnT1, fukutin and LARGE. Homozygous and compound heterozygous mutations were detected in a total of 31 probands (34 individuals from 31 families); 37 different mutations were identified, of which 32 were novel. Mutations in POMT2 were the most prevalent in our cohort with nine cases, followed by POMT1 with eight cases, POMGnT1 with seven cases, fukutin with six cases and LARGE with only a single case. All patients with POMT1 and POMT2 mutations had evidence of either structural or functional central nervous system involvement including four patients with mental retardation and a LGMD phenotype. In contrast mutations in fukutin and POMGnT1 were detected in four patients with LGMD and no evidence of brain involvement. The majority of patients (six out of nine) with mutations in POMT2 had a Muscle-Eye-Brain (MEB)-like condition. In addition we identified a mutation in the gene LARGE in a patient with WWS. Our data expands the clinical phenotypes associated with POMT1, POMT2, POMGnT1, fukutin and LARGE mutations. Mutations in these five glycosyltransferase genes were detected in 34% of patients indicating that, after the exclusion of FKRP, the majority of patients with a dystroglycanopathy harbour mutations in novel genes.