Differential inclusion of NEB exons 143 and 144 provides insight into NEB-related myopathy variant interpretation and disease manifestation.

Biallelic pathogenic variants in the gene encoding nebulin (NEB) are a known cause of congenital myopathy. We present two individuals with congenital myopathy and compound heterozygous variants (NM_001271208.2: c.2079C>A; p.(Cys693Ter) and c.21522+3A>G ) in NEB. Transcriptomic sequencing on patient muscle revealed that the extended splice variant c.21522+3A>G causes exon 144 skipping. Nebulin isoforms containing exon 144 are known to be mutually exclusive with isoforms containing exon 143, and these isoforms are differentially expressed during development and in adult skeletal muscles. Patients MRIs were compared to the known pattern of relative abundance of these two isoforms in muscle. We propose that the pattern of muscle involvement in these patients better fits the distribution of exon 144-containing isoforms in muscle than with previously published MRI findings in NEB-related disease due to other variants. To our knowledge this is the first report hypothesizing disease pathogenesis through the alteration of isoform distributions in muscle.

The recurrent deep intronic pseudoexon-inducing variant COL6A1 c.930+189C>T results in a consistently severe phenotype of COL6-related dystrophy: Towards clinical trial readiness for splice-modulating therapy.

Collagen VI-related dystrophies (COL6-RDs) manifest with a spectrum of clinical phenotypes, ranging from Ullrich congenital muscular dystrophy (UCMD), presenting with prominent congenital symptoms and characterised by progressive muscle weakness, joint contractures and respiratory insufficiency, to Bethlem muscular dystrophy, with milder symptoms typically recognised later and at times resembling a limb girdle muscular dystrophy, and intermediate phenotypes falling between UCMD and Bethlem muscular dystrophy. Despite clinical and immunohistochemical features highly suggestive of COL6-RD, some patients had remained without an identified causative variant in COL6A1, COL6A2 or COL6A3. With combined muscle RNA-sequencing and whole-genome sequencing we uncovered a recurrent, de novo deep intronic variant in intron 11 of COL6A1 (c.930+189C>T) that leads to a dominantly acting in-frame pseudoexon insertion. We subsequently identified and have characterised an international cohort of forty-four patients with this COL6A1 intron 11 causative variant, one of the most common recurrent causative variants in the collagen VI genes. Patients manifest a consistently severe phenotype characterised by a paucity of early symptoms followed by an accelerated progression to a severe form of UCMD, except for one patient with somatic mosaicism for this COL6A1 intron 11 variant who manifests a milder phenotype consistent with Bethlem muscular dystrophy. Characterisation of this individual provides a robust validation for the development of our pseudoexon skipping therapy. We have previously shown that splice-modulating antisense oligomers applied in vitro effectively decreased the abundance of the mutant pseudoexon-containing COL6A1 transcripts to levels comparable to the in vivo scenario of the somatic mosaicism shown here, indicating that this therapeutic approach carries significant translational promise for ameliorating the severe form of UCMD caused by this common recurrent COL6A1 causative variant to a Bethlem muscular dystrophy phenotype.

Biallelic CRELD1 variants cause a multisystem syndrome, including neurodevelopmental phenotypes, cardiac dysrhythmias, and frequent infections.

PURPOSE: We sought to delineate a multisystem disorder caused by recessive cysteine-rich with epidermal growth factor-like domains 1 (CRELD1) gene variants. METHODS: The impact of CRELD1 variants was characterized through an international collaboration utilizing next-generation DNA sequencing, gene knockdown, and protein overexpression in Xenopus tropicalis, and in vitro analysis of patient immune cells. RESULTS: Biallelic variants in CRELD1 were found in 18 participants from 14 families. Affected individuals displayed an array of phenotypes involving developmental delay, early-onset epilepsy, and hypotonia, with about half demonstrating cardiac arrhythmias and some experiencing recurrent infections. Most harbored a frameshift in trans with a missense allele, with 1 recurrent variant, p.(Cys192Tyr), identified in 10 families. X tropicalis tadpoles with creld1 knockdown displayed developmental defects along with increased susceptibility to induced seizures compared with controls. Additionally, human CRELD1 harboring missense variants from affected individuals had reduced protein function, indicated by a diminished ability to induce craniofacial defects when overexpressed in X tropicalis. Finally, baseline analyses of peripheral blood mononuclear cells showed similar proportions of immune cell subtypes in patients compared with healthy donors. CONCLUSION: This patient cohort, combined with experimental data, provide evidence of a multisystem clinical syndrome mediated by recessive variants in CRELD1.

Association of Initial Maximal Motor Ability With Long-term Functional Outcome in Patients With COL6-Related Dystrophies.

OBJECTIVE: To accurately categorize the phenotypes of individuals with collagen VI-related dystrophies (COL6-RDs) during the first years of life to predict long-term motor function and pulmonary function, to provide phenotype-specific anticipatory care, and to improve clinical trial readiness. METHODS: This retrospective, multicenter, international study analyzed the relationship of long-term motor and pulmonary function with the initial maximal motor ability achieved in individuals with COL6-RD. RESULTS: We studied 119 patients with COL6-RD from Spain (n = 54) and the United States (n = 65). The early maximal motor milestones of ability to rise from the floor unassisted and ability to climb 4 steps without holding onto a railing demonstrated reliability in distinguishing between 3 COL6-RD phenotypic subgroups: (1) Ullrich congenital muscular dystrophy, (2) intermediate COL6-RD, and (3) Bethlem myopathy. Long-term motor function and pulmonary function are strongly correlated with the maximal motor ability achieved during the first years of life. Maximal motor capacity can predict other disease-relevant events such as the age at loss of ambulation and the need for the initiation of nocturnal noninvasive ventilation. CONCLUSION: This work proposes a prospective phenotypic classification for COL6-RDs that will enable an accurate prediction of a patient's COL6-RD phenotype during the first years of life. The ability to establish a patient's COL6-RD phenotypic classification early will enable a more accurate prognosis of future motor and pulmonary function, thus improving anticipatory clinical care, and it will be instrumental in aiding the design of future clinical trials by allowing early stratification of trial cohorts.

Hypoglycemia in patients with congenital muscle disease.

BACKGROUND: Only a few small studies have previously reported episodes of hypoglycemia in children with neuromuscular diseases; however, there has been no broader investigation into the occurrence of hypoglycemia in children with congenital muscle disease (CMD). METHODS: Pediatric patients enrolled in the CMD International Registry (CMDIR) with a history of hypoglycemia were included in this retrospective review. Hypoglycemic episodes and associated clinical and biochemical characteristics were characterized. RESULTS: Ten patients with CMD (5 with LAMA2-related muscular dystrophy) reported at least one episode of hypoglycemia beginning at an average age of 3.5 years. Predominant symptoms included altered mental status and nausea/vomiting, and laboratory studies demonstrated metabolic acidosis and ketonuria, consistent with ketotic hypoglycemia. CONCLUSION: Patients with CMD may have an increased risk of hypoglycemia during fasting, illness, or stress due to their relatively low muscle mass and hence, paucity of gluconeogenic substrate. Clinicians should therefore maintain a high index of suspicion for hypoglycemia in this high-risk patient population and caregivers should routinely be trained to recognize and treat hypoglycemia.

Congenital Titinopathy: Comprehensive characterization and pathogenic insights.

OBJECTIVE: Comprehensive clinical characterization of congenital titinopathy to facilitate diagnosis and management of this important emerging disorder. METHODS: Using massively parallel sequencing we identified 30 patients from 27 families with 2 pathogenic nonsense, frameshift and/or splice site TTN mutations in trans. We then undertook a detailed analysis of the clinical, histopathological and imaging features of these patients. RESULTS: All patients had prenatal or early onset hypotonia and/or congenital contractures. None had ophthalmoplegia. Scoliosis and respiratory insufficiency typically developed early and progressed rapidly, whereas limb weakness was often slowly progressive, and usually did not prevent independent walking. Cardiac involvement was present in 46% of patients. Relatives of 2 patients had dilated cardiomyopathy. Creatine kinase levels were normal to moderately elevated. Increased fiber size variation, internalized nuclei and cores were common histopathological abnormalities. Cap-like regions, whorled or ring fibers, and mitochondrial accumulations were also observed. Muscle magnetic resonance imaging showed gluteal, hamstring and calf muscle involvement. Western blot analysis showed a near-normal sized titin protein in all samples. The presence of 2 mutations predicted to impact both N2BA and N2B cardiac isoforms appeared to be associated with greatest risk of cardiac involvement. One-third of patients had 1 mutation predicted to impact exons present in fetal skeletal muscle, but not included within the mature skeletal muscle isoform transcript. This strongly suggests developmental isoforms are involved in the pathogenesis of this congenital/early onset disorder. INTERPRETATION: This detailed clinical reference dataset will greatly facilitate diagnostic confirmation and management of patients, and has provided important insights into disease pathogenesis. Ann Neurol 2018;83:1105-1124.

Electrical impedance myography in individuals with collagen 6 and laminin α-2 congenital muscular dystrophy: a cross-sectional and 2-year analysis.

INTRODUCTION: Electrical impedance myography (EIM) is a noninvasive electrophysiological technique that characterizes muscle properties through bioimpedance. We compared EIM measurements to function, strength, and disease severity in a population with congenital muscular dystrophy (CMD). METHODS: Forty-one patients with CMD, either collagen 6 related disorders (COL6-RD; n = 21) or laminin α-2-related disorders (LAMA2-RD; n = 20), and 21 healthy pediatric controls underwent 2 yearly EIM exams. In the CMD cohorts, EIM was compared with functional and strength measurements. RESULTS: Both CMD cohorts exhibited change over time and had correlation with disease severity. The 50-kHZ phase correlated well with function and strength in the COL6-RD cohort but not in the LAMA2-RD cohort. DISCUSSION: EIM is a potentially useful measure in clinical studies with CMD because of its sensitivity to change over a 1-year period and correlation with disease severity. For COL6-RD, there were also functional and strength correlations. Muscle Nerve 57: 54-60, 2018.

Cytoplasmic body pathology in severe ACTA1-related myopathy in the absence of typical nemaline rods.

Mutations in ACTA1 cause a group of myopathies with expanding clinical and histopathological heterogeneity. We describe three patients with severe ACTA1-related myopathy who have muscle fiber cytoplasmic bodies but no classic nemaline rods. Patient 1 is a five-year-old boy who presented at birth with severe weakness and respiratory failure, requiring mechanical ventilation. Whole exome sequencing identified a heterozygous c.282C>A (p.Asn94Lys) ACTA1 mutation. Patients 2 and 3 were twin boys with hypotonia, severe weakness, and respiratory insufficiency at birth requiring mechanical ventilation. Both died at 6 months of age. The same heterozygous c.282C>A (p.Asn94Lys) ACTA1 mutation was identified by whole exome sequencing. We conclude that clinically severe ACTA1-related myopathy can present with muscle morphological findings suggestive of cytoplasmic body myopathy in the absence of definite nemaline rods. The Asn94Lys mutation in skeletal muscle sarcomeric α-actin may be linked to this histological appearance. These novel ACTA1 cases also illustrate the successful application of whole exome sequencing in directly arriving at a candidate genetic diagnosis in patients with unexpected phenotypic and histologic features for a known neuromuscular gene.

P4HA1 mutations cause a unique congenital disorder of connective tissue involving tendon, bone, muscle and the eye.

Collagen prolyl 4-hydroxylases (C-P4Hs) play a central role in the formation and stabilization of the triple helical domain of collagens. P4HA1 encodes the catalytic α(I) subunit of the main C-P4H isoenzyme (C-P4H-I). We now report human bi-allelic P4HA1 mutations in a family with a congenital-onset disorder of connective tissue, manifesting as early-onset joint hypermobility, joint contractures, muscle weakness and bone dysplasia as well as high myopia, with evidence of clinical improvement of motor function over time in the surviving patient. Similar to P4ha1 null mice, which die prenatally, the muscle tissue from P1 and P2 was found to have reduced collagen IV immunoreactivity at the muscle basement membrane. Patients were compound heterozygous for frameshift and splice site mutations leading to reduced, but not absent, P4HA1 protein level and C-P4H activity in dermal fibroblasts compared to age-matched control samples. Differential scanning calorimetry revealed reduced thermal stability of collagen in patient-derived dermal fibroblasts versus age-matched control samples. Mutations affecting the family of C-P4Hs, and in particular C-P4H-I, should be considered in patients presenting with congenital connective tissue/myopathy overlap disorders with joint hypermobility, contractures, mild skeletal dysplasia and high myopia.

Upper extremity outcome measures for collagen VI-related myopathy and LAMA2-related muscular dystrophy.

Congenital muscular dystrophy (CMD) comprises a rare group of genetic muscle diseases that present at birth or early during infancy. Two common subtypes of CMD are collagen VI-related muscular dystrophy (COL6-RD) and laminin alpha 2-related dystrophy (LAMA2-RD). Traditional outcome measures in CMD include gross motor and mobility assessments, yet significant motor declines underscore the need for valid upper extremity motor assessments as a clinical endpoint. This study validated a battery of upper extremity measures in these two CMD subtypes for future clinical trials. For this cross-sectional study, 42 participants were assessed over the same 2-5 day period at the National Institutes of Health Clinical Center. All upper extremity measures were correlated with the Motor Function Measure 32 (MFM32). The battery of upper extremity assessments included the Jebsen Taylor Hand Function Test, Quality of Upper Extremity Skills Test (QUEST), hand held dynamometry, goniometry, and MyoSet Tools. Spearman Rho was used for correlations to the MFM32. Pearson was performed to correlate the Jebsen, QUEST, hand-held dynamometry, goniometry and the MyoSet Tools. Correlations were considered significant at the 0.01 level (2-tailed). Significant correlations were found between both the MFM32 and MFM Dimension 3 only (Distal Motor function) and the Jebsen, QUEST, MyoGrip and MyoPinch, elbow flexion/extension ROM and myometry. Additional correlations between the assessments are reported. The Jebsen, the Grasp and Dissociated Movements domains of the QUEST, the MyoGrip and the MyoPinch tools, as well as elbow ROM and myometry were determined to be valid and feasible in this population, provided variation in test items, and assessed a range of difficulty in CMD. To move forward, it will be of utmost importance to determine whether these upper extremity measures are reproducible and sensitive to change over time.

Novel De Novo Mutations in KIF1A as a Cause of Hereditary Spastic Paraplegia With Progressive Central Nervous System Involvement.

Hereditary spastic paraplegias are a clinically and genetically heterogeneous group of disorders characterized by lower extremity spasticity and weakness. Recently, the first de novo mutations in KIF1A were identified in patients with an early-onset severe form of complicated hereditary spastic paraplegia. We report two additional patients with novel de novo mutations in KIF1A, hereby expanding the genetic spectrum of KIF1A-related hereditary spastic paraplegia. Both children presented with spastic paraplegia and additional findings of optic nerve atrophy, structural brain abnormalities, peripheral neuropathy, cognitive/language impairment, and never achieved ambulation. In particular, we highlight the progressive nature of cerebellar involvement as captured on sequential magnetic resonance images (MRIs), thus linking the neurodegenerative and spastic paraplegia phenotypes. Exome sequencing in patient 1 and patient 2 identified novel heterozygous missense mutations in KIF1A at c.902G>A (p.R307Q) and c.595G>A (p.G199 R), respectively. Therefore, our report contributes to expanding the genotypic and phenotypic spectrum of hereditary spastic paraplegia caused by mutations in KIF1A.

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.

English cross-cultural translation and validation of the neuromuscular score: a system for motor function classification in patients with neuromuscular diseases.

OBJECTIVE: To develop and validate an English version of the Neuromuscular (NM)-Score, a classification for patients with NM diseases in each of the 3 motor function domains: D1, standing and transfers; D2, axial and proximal motor function; and D3, distal motor function. DESIGN: Validation survey. SETTING: Patients seen at a medical research center between June and September 2013. PARTICIPANTS: Consecutive patients (N=42) aged 5 to 19 years with a confirmed or suspected diagnosis of congenital muscular dystrophy. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: An English version of the NM-Score was developed by a 9-person expert panel that assessed its content validity and semantic equivalence. Its concurrent validity was tested against criterion standards (Brooke Scale, Motor Function Measure [MFM], activity limitations for patients with upper and/or lower limb impairments [ACTIVLIM], Jebsen Test, and myometry measurements). Informant agreement between patient/caregiver (P/C)-reported and medical doctor (MD)-reported NM scores was measured by weighted kappa. RESULTS: Significant correlation coefficients were found between NM scores and criterion standards. The highest correlations were found between NM-score D1 and MFM score D1 (ρ=-.944, P<.0001), ACTIVLIM (ρ=-.895, P<.0001), and hip abduction strength by myometry (ρ=-.811, P<.0001). Informant agreement between P/C-reported and MD-reported NM scores was high for D1 (κ=.801; 95% confidence interval [CI], .701-.914) but moderate for D2 (κ=.592; 95% CI, .412-.773) and D3 (κ=.485; 95% CI, .290-.680). Correlation coefficients between the NM scores and the criterion standards did not significantly differ between P/C-reported and MD-reported NM scores. CONCLUSIONS: Patients and physicians completed the English NM-Score easily and accurately. The English version is a reliable and valid instrument that can be used in clinical practice and research to describe the functional abilities of patients with NM diseases.

'Double trouble': diagnostic challenges in Duchenne muscular dystrophy in patients with an additional hereditary skeletal dysplasia.

Duchenne muscular dystrophy (DMD) is caused by mutations in Dystrophin and affects 1 in 3600-6000 males. It is characterized by progressive weakness leading to loss of ambulation, respiratory insufficiency, cardiomyopathy, and scoliosis. We describe the unusual phenotype of 3 patients with skeletal dysplasias in whom an additional diagnosis of DMD was later established. Two unrelated boys presented with osteogenesis imperfecta due to point mutations in COL1A1 and were both subsequently found to have a 1 bp frameshift deletion in the Dystrophin gene at age 3 and age 15 years, respectively. The third patient had a diagnosis of pseudoachondroplasia caused by a mutation in the COMP gene and was found to have a deletion of exons 48-50 in Dystrophin at age 9. We discuss the atypical presentation caused by the concomitant presence of 2 conditions affecting the musculoskeletal system, emphasizing aspects that may confound the presentation of a well-characterized disease like DMD. Additional series of patients with DMD and a secondary inherited condition are necessary to establish the natural history in this "double trouble" population. The recognition and accurate diagnosis of patients with two independent genetic disease processes is essential for management, prognosis, genetic risk assessment, and discussion regarding potential therapeutic interventions.