J. Dastgir

Severe congenital RYR1-associated myopathy: The expanding clinicopathologic and genetic spectrum

Objective: To report a series of 11 patients on the severe end of the spectrum of ryanodine receptor 1 (RYR1) gene–related myopathy, in order to expand the clinical, histologic, and genetic heterogeneity associated with this group of patients. Methods: Eleven patients evaluated in the neonatal period with severe neonatal-onset RYR1-associated myopathy confirmed by genetic testing were ascertained. Clinical features, molecular testing results, muscle imaging, and muscle histology are reviewed. Results: Clinical features associated with the severe neonatal presentation of RYR1-associated myopathy included decreased fetal movement, hypotonia, poor feeding, respiratory involvement, arthrogryposis, and ophthalmoplegia in 3 patients, and femur fractures or hip dislocation at birth. Four patients had dominant RYR1 mutations, and 7 had recessive RYR1 mutations. One patient had a cleft palate, and another a congenital rigid spine phenotype—findings not previously described in the literature in patients with early-onset RYR1 mutations. Six patients who underwent muscle ultrasound showed relative sparing of the rectus femoris muscle. Histologically, all patients with dominant mutations had classic central cores on muscle biopsy. Patients with recessive mutations showed great histologic heterogeneity, including fibrosis, variation in fiber size, skewed fiber typing, very small fibers, and nuclear internalization with or without ill-defined cores. Conclusions: This series confirms and expands the clinical and histologic variability associated with severe congenital RYR1-associated myopathy. Both dominant and recessive mutations of the RYR1 gene can result in a severe neonatal-onset phenotype, but more clinical and histologic heterogeneity has been seen in those with recessive RYR1 gene mutations. Central cores are not obligatory histologic features in recessive RYR1 mutations. Sparing of the rectus femoris muscle on imaging should prompt evaluation for RYR1-associated myopathy in the appropriate clinical context.

Novel mutations widen the phenotypic spectrum of slow skeletal/β-cardiac myosin (MYH7) distal myopathy.

Laing early onset distal myopathy and myosin storage myopathy are caused by mutations of slow skeletal/β‐cardiac myosin heavy chain encoded by the gene MYH7, as is a common form of familial hypertrophic/dilated cardiomyopathy. The mechanisms by which different phenotypes are produced by mutations in MYH7, even in the same region of the gene, are not known. To explore the clinical spectrum and pathobiology, we screened the MYH7 gene in 88 patients from 21 previously unpublished families presenting with distal or generalized skeletal muscle weakness, with or without cardiac involvement. Twelve novel mutations have been identified in thirteen families. In one of these families, the father of the proband was found to be a mosaic for the MYH7 mutation. In eight cases, de novo mutation appeared to have occurred, which was proven in four. The presenting complaint was footdrop, sometimes leading to delayed walking or tripping, in members of 17 families (81%), with other presentations including cardiomyopathy in infancy, generalized floppiness, and scoliosis. Cardiac involvement as well as skeletal muscle weakness was identified in nine of 21 families. Spinal involvement such as scoliosis or rigidity was identified in 12 (57%). This report widens the clinical and pathological phenotypes, and the genetics of MYH7 mutations leading to skeletal muscle diseases.

Ataluren in patients with nonsense mutation Duchenne muscular dystrophy (ACT DMD): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial

BACKGROUND Duchenne muscular dystrophy (DMD) is a severe, progressive, and rare neuromuscular, X-linked recessive disease. Dystrophin deficiency is the underlying cause of disease; therefore, mutation-specific therapies aimed at restoring dystrophin protein production are being explored. We aimed to assess the efficacy and safety of ataluren in ambulatory boys with nonsense mutation DMD. METHODS We did this multicentre, randomised, double-blind, placebo-controlled, phase 3 trial at 54 sites in 18 countries located in North America, Europe, the Asia-Pacific region, and Latin America. Boys aged 7-16 years with nonsense mutation DMD and a baseline 6-minute walk distance (6MWD) of 150 m or more and 80% or less of the predicted normal value for age and height were randomly assigned (1:1), via permuted block randomisation (block size of four) using an interactive voice-response or web-response system, to receive ataluren orally three times daily (40 mg/kg per day) or matching placebo. Randomisation was stratified by age (<9 years vs ≥9 years), duration of previous corticosteroid use (6 months to <12 months vs ≥12 months), and baseline 6MWD (<350 m vs ≥350 m). Patients, parents and caregivers, investigational site personnel, PTC Therapeutics employees, and all other study personnel were masked to group allocation until after database lock. The primary endpoint was change in 6MWD from baseline to week 48. We additionally did a prespecified subgroup analysis of the primary endpoint, based on baseline 6MWD, which is reflective of anticipated rates of disease progression over 1 year. The primary analysis was by intention to treat. This study is registered with ClinicalTrials.gov, number NCT01826487. FINDINGS Between March 26, 2013, and Aug 26, 2014, we randomly assigned 230 patients to receive ataluren (n=115) or placebo (n=115); 228 patients comprised the intention-to-treat population. The least-squares mean change in 6MWD from baseline to week 48 was -47·7 m (SE 9·3) for ataluren-treated patients and -60·7 m (9·3) for placebo-treated patients (difference 13·0 m [SE 10·4], 95% CI -7·4 to 33·4; p=0·213). The least-squares mean change for ataluren versus placebo in the prespecified subgroups was -7·7 m (SE 24·1, 95% CI -54·9 to 39·5; p=0·749) in the group with a 6MWD of less than 300 m, 42·9 m (15·9, 11·8-74·0; p=0·007) in the group with a 6MWD of 300 m or more to less than 400 m, and -9·5 m (17·2, -43·2 to 24·2; p=0·580) in the group with a 6MWD of 400 m or more. Ataluren was generally well tolerated and most treatment-emergent adverse events were mild to moderate in severity. Eight (3%) patients (n=4 per group) reported serious adverse events; all except one event in the placebo group (abnormal hepatic function deemed possibly related to treatment) were deemed unrelated to treatment. INTERPRETATION Change in 6MWD did not differ significantly between patients in the ataluren group and those in the placebo group, neither in the intention-to-treat population nor in the prespecified subgroups with a baseline 6MWD of less than 300 m or 400 m or more. However, we recorded a significant effect of ataluren in the prespecified subgroup of patients with a baseline 6MWD of 300 m or more to less than 400 m. Baseline 6MWD values within this range were associated with a more predictable rate of decline over 1 year; this finding has implications for the design of future DMD trials with the 6-minute walk test as the endpoint. FUNDING PTC Therapeutics.

Position of Glycine Substitutions in the Triple Helix of COL6A1, COL6A2, and COL6A3 is Correlated with Severity and Mode of Inheritance in Collagen VI Myopathies

Glycine substitutions in the conserved Gly‐X‐Y motif in the triple helical (TH) domain of collagen VI are the most commonly identified mutations in the collagen VI myopathies including Ullrich congenital muscular dystrophy, Bethlem myopathy, and intermediate (INT) phenotypes. We describe clinical and genetic characteristics of 97 individuals with glycine substitutions in the TH domain of COL6A1, COL6A2, or COL6A3 and add a review of 97 published cases, for a total of 194 cases. Clinical findings include severe, INT, and mild phenotypes even from patients with identical mutations. INT phenotypes were most common, accounting for almost half of patients, emphasizing the importance of INT phenotypes to the overall phenotypic spectrum. Glycine substitutions in the TH domain are heavily clustered in a short segment N‐terminal to the 17th Gly‐X‐Y triplet, where they are acting as dominants. The most severe cases are clustered in an even smaller region including Gly‐X‐Y triplets 10–15, accounting for only 5% of the TH domain. Our findings suggest that clustering of glycine substitutions in the N‐terminal region of collagen VI is not based on features of the primary sequence. We hypothesize that this region may represent a functional domain within the triple helix.

Clinical, Pathologic, and Mutational Spectrum of Dystroglycanopathy Caused by LARGE Mutations

Dystroglycanopathies are a subtype of congenital muscular dystrophy of varying severity that can affect the brain and eyes, ranging from Walker-Warburg syndrome with severe brain malformation to milder congenital muscular dystrophy presentations with affected or normal cognition and later onset. Mutations in dystroglycanopathy genes affect a specific glycoepitope on α-dystroglycan; of the 14 genes implicated to date, LARGE encodes the glycosyltransferase that adds the final xylose and glucuronic acid, allowing α-dystroglycan to bind ligands, including laminin 211 and neurexin. Only 11 patients with LARGE mutations have been reported. We report the clinical, neuroimaging, and genetic features of 4 additional patients. We confirm that gross deletions and rearrangements are important mutational mechanisms for LARGE. The brain abnormalities overshadowed the initially mild muscle phenotype in all 4 patients. We present the first comprehensive postnatal neuropathology of the brain, spinal cord, and eyes of a patient with a homozygous LARGE mutation at Cys443. In this patient, polymicrogyria was the predominant cortical malformation; densely festooned polymicrogyria were overlaid by a continuous agyric surface. In view of the severity of these abnormalities, Cys443 may be a functionally important residue in the LARGE protein, whereas the mutation p.Glu509Lys of Patient 1 in this study may confer a milder phenotype. Overall, these results expand the clinical and genetic spectrum of dystroglycanopathy.

Mosaicism for dominant collagen 6 mutations as a cause for intrafamilial phenotypic variability.

Collagen 6‐related dystrophies and myopathies (COL6‐RD) are a group of disorders that form a wide phenotypic spectrum, ranging from severe Ullrich congenital muscular dystrophy, intermediate phenotypes, to the milder Bethlem myopathy. Both inter‐ and intrafamilial variable expressivity are commonly observed. We present clinical, immunohistochemical, and genetic data on four COL6‐RD families with marked intergenerational phenotypic heterogeneity. This variable expression seemingly masquerades as anticipation is due to parental mosaicism for a dominant mutation, with subsequent full inheritance and penetrance of the mutation in the heterozygous offspring. We also present an additional fifth simplex patient identified as a mosaic carrier. Parental mosaicism was confirmed in the four families through quantitative analysis of the ratio of mutant versus wild‐type allele (COL6A1, COL6A2, and COL6A3) in genomic DNA from various tissues, including blood, dermal fibroblasts, and saliva. Consistent with somatic mosaicism, parental samples had lower ratios of mutant versus wild‐type allele compared with the fully heterozygote offspring. However, there was notable variability of the mutant allele levels between tissues tested, ranging from 16% (saliva) to 43% (fibroblasts) in one mosaic father. This is the first report demonstrating mosaicism as a cause of intrafamilial/intergenerational variability of COL6‐RD, and suggests that sporadic and parental mosaicism may be more common than previously suspected.

Common Data Elements for Muscle Biopsy Reporting

CONTEXT There is no current standard among myopathologists for reporting muscle biopsy findings. The National Institute of Neurological Disorders and Stroke has recently launched a common data element (CDE) project to standardize neuromuscular data collected in clinical reports and to facilitate their use in research. OBJECTIVE To develop a more-uniform, prospective reporting tool for muscle biopsies, incorporating the elements identified by the CDE project, in an effort to improve reporting and educational resources. DESIGN The variation in current biopsy reporting practice was evaluated through a study of 51 muscle biopsy reports from self-reported diagnoses of genetically confirmed or undiagnosed muscle disease from the Congenital Muscle Disease International Registry. Two reviewers independently extracted data from deidentified reports and entered them into the revised CDE format to identify what was missing and whether or not information provided on the revised CDE report (complete/incomplete) could be successfully interpreted by a neuropathologist. RESULTS Analysis of the data highlighted showed (1) inconsistent reporting of key clinical features from referring physicians, and (2) considerable variability in the reporting of pertinent positive and negative histologic findings by pathologists. CONCLUSIONS We propose a format for muscle-biopsy reporting that includes the elements in the CDE checklist and a brief narrative comment that interprets the data in support of a final interpretation. Such a format standardizes cataloging of pathologic findings across the spectrum of muscle diseases and serves emerging clinical care and research needs with the expansion of genetic-testing therapeutic trials.

Intrafamilial variability in GMPPB-associated dystroglycanopathy: Broadening of the phenotype

Dystroglycanopathies are characterized by deficient O-mannosyl glycosylation of α-dystroglycan (αDG) and represent an expanding genetically, biochemically, and clinically heterogeneous group of muscular dystrophies. Currently, there are 18 known genes leading to forms of α-dystroglycan–related dystrophy (αDG-RD), ranging in severity from a Walker-Warburg phenotype with severe brain malformations and hypotonia to milder childhood- or adult-onset limb-girdle muscular dystrophy (LGMD) phenotypes with or without intellectual disability.1,2

Identification of a novel nemaline myopathy-Causing mutation in the troponin T1 (TNNT1) gene: A case outside of the old order amish

Introduction: Nemaline myopathy (NM) is a congenital neuromuscular disorder often characterized by hypotonia, facial weakness, skeletal muscle weakness, and the presence of rods on muscle biopsy. A rare form of nemaline myopathy known as Amish Nemaline Myopathy has only been seen in a genetically isolated cohort of Old Order Amish patients who may additionally present with tremors in the first 2–3 months of life. Methods: We describe an Hispanic male diagnosed with nemaline myopathy histopathologically and subsequently confirmed by next generation gene sequencing. Results: Direct sequencing revealed that he is homozygous for a pathogenic nonsense variant c.323C>G (p.S108X) in exon 9 of the TNNT1 gene. Conclusions: This report describes a novel pathogenic variant in the TNNT1 gene and represents a nemaline myopathy‐causing variant in the TNNT1 gene outside of the Old Order Amish and Dutch ancestry. Muscle Nerve 51:767–772, 2015

TPM3 deletions cause a hypercontractile congenital muscle stiffness phenotype

Mutations in TPM3, encoding Tpm3.12, cause a clinically and histopathologically diverse group of myopathies characterized by muscle weakness. We report two patients with novel de novo Tpm3.12 single glutamic acid deletions at positions ΔE218 and ΔE224, resulting in a significant hypercontractile phenotype with congenital muscle stiffness, rather than weakness, and respiratory failure in one patient.