Ectopic PLAG1 induces muscular dystrophy in the mouse.

Even though various genetic mutations have been identified in muscular dystrophies (MD), there is still a need to understand the biology of MD in the absence of known mutations. Here we reported a new mouse model of MD driven by ectopic expression of PLAG1. This gene encodes a developmentally regulated transcription factor known to be expressed in developing skeletal muscle, and implicated as an oncogene in certain cancers including rhabdomyosarcoma (RMS), an aggressive soft tissue sarcoma composed of myoblast-like cells. By breeding loxP-STOP-loxP-PLAG1 (LSL-PLAG1) mice into the MCK-Cre line, we achieved ectopic PLAG1 expression in cardiac and skeletal muscle. The Cre/PLAG1 mice died before 6 weeks of age with evidence of cardiomyopathy significantly limiting left ventricle fractional shortening. Histology of skeletal muscle revealed dystrophic features, including myofiber necrosis, fiber size variation, frequent centralized nuclei, fatty infiltration, and fibrosis, all of which mimic human MD pathology. QRT-PCR and Western blot revealed modestly decreased Dmd mRNA and dystrophin protein in the dystrophic muscle, and immunofluorescence staining showed decreased dystrophin along the cell membrane. Repression of Dmd by ectopic PLAG1 was confirmed in dystrophic skeletal muscle and various cell culture models. In vitro studies showed that excess IGF2 expression, a transcriptional target of PLAG1, phenocopied PLAG1-mediated down-regulation of dystrophin. In summary, we developed a new mouse model of a lethal MD due to ectopic expression of PLAG1 in heart and skeletal muscle. Our data support the potential contribution of excess IGF2 in this model. Further studying these mice may provide new insights into the pathogenesis of MD and perhaps lead to new treatment strategies.

Intrathecal Onasemnogene Abeparvovec for Sitting, Nonambulatory Patients with Spinal Muscular Atrophy: Phase I Ascending-Dose Study (STRONG).

BACKGROUND: Spinal muscular atrophy (SMA) is a neuromuscular disorder arising from biallelic non-functional survival motor neuron 1 (SMN1) genes with variable copies of partially functional SMN2 gene. Intrathecal onasemnogene abeparvovec administration, at fixed, low doses, may enable treatment of heavier patients ineligible for weight-based intravenous dosing. OBJECTIVE: STRONG (NCT03381729) assessed the safety/tolerability and efficacy of intrathecal onasemnogene abeparvovec for sitting, nonambulatory SMA patients. METHODS: Sitting, nonambulatory SMA patients (biallelic SMN1 loss, three SMN2 copies, aged 6-<60 months) received a single dose of intrathecal onasemnogene abeparvovec. Patients were enrolled sequentially into one of three (low, medium, and high) dose cohorts and stratified into two groups by age at dosing: younger (6-<24 months) and older (24-<60 months). Primary endpoints included safety/tolerability, independent standing ≥3 seconds (younger group), and change in Hammersmith Functional Motor Scale Expanded (HFMSE) from baseline (older group) compared with historic controls. RESULTS: Thirty-two patients were enrolled and completed the study (medium dose, n = 25). All patients had one or more treatment-emergent adverse events, with one serious and related to treatment (transaminase elevations). No deaths were reported. One of 13 patients (7.7%) in the younger group treated with the medium dose achieved independent standing. At Month 12 for the older group receiving the medium dose, change from baseline in HFMSE was significantly improved compared with the SMA historic control population (P < 0.01). CONCLUSIONS: Intrathecal onasemnogene abeparvovec was safe and well-tolerated. Older patients treated with the medium dose demonstrated increases in HFMSE score greater than commonly observed in natural history.

Response to treatment in pediatric ocular myasthenia gravis.

INTRODUCTION: Juvenile myasthenia gravis (JMG), a pediatric autoimmune neuromuscular junction disorder, includes generalized (GMG), and ocular (OMG) variants. We sought to determine whether differences existed between OMG and GMG children regarding demographics or treatment response. METHODS: We performed retrospective analysis of 60 children with JMG seen between 1990 and 2018. Osserman scores were used to define OMG and GMG. The myasthenia scale of Millichap and Dodge was used to assess treatment responses. RESULTS: There were no differences between GMG and OMG regarding time interval from disease onset to prednisone initiation (P = .42), or treatment response according to Millichap and Dodge (P = .12). Compared with GMG, OMG children showed younger age of disease onset and better outcomes after treatment. No OMG patients progressed to generalized disease during the follow-up period. DISCUSSION: Compared with GMG, OMG patients had earlier disease onset and improved outcomes after treatment.

Congenital muscular dystrophies and congenital myopathies.

PURPOSE OF REVIEW: The purpose of this review is to provide information regarding the diagnosis and natural history of some very rare disorders: congenital muscular dystrophies and congenital myopathies. Patients with these conditions share characteristics such as early onset of weakness and severe hypotonia. Other organs such as the brain, eyes, and skin may be involved. Diagnosis depends largely on recognition of phenotype, muscle biopsy, and mutation analysis. RECENT FINDINGS: More than 30 genes have been associated with these diseases, most of which have only been recognized in the past decade. Increasing availability of DNA analysis has been important in decreasing delay in diagnosis. SUMMARY: Patients with congenital muscular dystrophy or congenital myopathy are at high risk of complications including restrictive lung disease, orthopedic deformities, seizures, cardiomyopathy, and malignant hyperthermia. Life expectancy varies with the severity of complications. Having an accurate and specific diagnosis allows the neurologist to carry out anticipatory guidance and appropriate monitoring. New hope exists for experimental treatments for congenital muscular dystrophy and congenital myopathy as our understanding of pathogenesis evolves.

Recessive truncating titin gene, TTN, mutations presenting as centronuclear myopathy.

OBJECTIVE: To identify causative genes for centronuclear myopathies (CNM), a heterogeneous group of rare inherited muscle disorders that often present in infancy or early life with weakness and hypotonia, using next-generation sequencing of whole exomes and genomes. METHODS: Whole-exome or -genome sequencing was performed in a cohort of 29 unrelated patients with clinicopathologic diagnoses of CNM or related myopathy depleted for cases with mutations of MTM1, DNM2, and BIN1. Immunofluorescence analyses on muscle biopsies, splicing assays, and gel electrophoresis of patient muscle proteins were performed to determine the molecular consequences of mutations of interest. RESULTS: Autosomal recessive compound heterozygous truncating mutations of the titin gene, TTN, were identified in 5 individuals. Biochemical analyses demonstrated increased titin degradation and truncated titin proteins in patient muscles, establishing the impact of the mutations. CONCLUSIONS: Our study identifies truncating TTN mutations as a cause of congenital myopathy that is reported as CNM. Unlike the classic CNM genes that are all involved in excitation-contraction coupling at the triad, TTN encodes the giant sarcomeric protein titin, which forms a myofibrillar backbone for the components of the contractile machinery. This study expands the phenotypic spectrum associated with TTN mutations and indicates that TTN mutation analysis should be considered in cases of possible CNM without mutations in the classic CNM genes.

Dystrophinopathy in girls with limb girdle muscular dystrophy phenotype.

OBJECTIVES: Limb girdle muscular dystrophy (LGMD) is a diverse group of myopathic disorders characterized by proximal muscle weakness and hyperCKemia. Mutations encoding sarcoglycans and numerous other proteins have been shown to be responsible for most cases. We report a series of girls with a negative family history for boys with Duchenne muscular dystrophy, demonstrating an LGMD phenotype associated with dystrophinopathy. METHODS: A retrospective chart review of all girls presenting with the LGMD phenotype to our clinic between January 2001 and September 2007 was conducted. Patients 18 years old or younger with dystrophinopathy proven by muscle biopsy and/or gene mutations and a negative family history for affected boys were included in the review. RESULTS: Five patients, 4 to 10 years of age at presentation, were included in the series. Four had an LGMD phenotype at presentation. All five patients had hyperCKemia, all five patients had gene mutations, and four patients had muscle biopsy consistent with dystrophinopathy. CONCLUSION: Dystrophinopathy is an important cause of LGMD phenotype in girls and should be considered in the differential diagnosis.

Novel subtype of congenital generalized lipodystrophy associated with muscular weakness and cervical spine instability.

Congenital generalized lipodystrophy (CGL) is a rare autosomal recessive disorder characterized by extreme paucity of adipose tissue from birth, and early onset of metabolic complications related to insulin resistance. Mutations in three genes, 1-acylglycerol 3-phosphate-O-acyltransferase 2 (AGPAT2), Berardinelli Seip Congenital Lipodystrophy 2 (BSCL2), and Caveolin-1 (CAV1) are associated with the three subtypes of this disorder, CGL1, CGL2 and CGL3, respectively. We report two siblings of Hispanic origin who displayed characteristic features of CGL such as generalized loss of subcutaneous fat from birth, acanthosis nigricans, acromegaloid habitus, umbilical prominence, hepatosplenomegaly, hypoleptinemia, dyslipidemia, and insulin resistance. However, no disease causing variants were detected in the DNA sequence of AGPAT2, BSCL2 or CAV1 genes. Further, whole body magnetic resonance imaging (MRI) in the two siblings revealed marked loss of subcutaneous, intraabdominal and intrathoracic fat like in other patients with CGL, but preservation of bone marrow fat which is invariably lost in all patients with CGL1 and CGL2, but not in the patient reported with CGL3. They also had generalized muscle weakness during infancy and early childhood associated with a nearly fivefold increase in serum creatine kinase (CK) levels, but with normal muscle biopsy and electrophysiologic studies. Both patients were also found to have atlantoaxial dislocation requiring surgical intervention. Thus, this pedigree represents a novel subtype of CGL characterized by generalized loss of body fat but with preservation of bone marrow fat, congenital muscular weakness and cervical spine instability. The genetic basis of this novel subtype remains to be determined.

Dietary L-tyrosine supplementation in nemaline myopathy.

Nemaline myopathy is defined by the presence of nemaline bodies, or rods, on muscle biopsy. Facial and bulbar weakness in nemaline myopathy cause chewing and swallowing difficulties, recurrent aspiration, and poor control of oral secretions. This article discusses 5 patients (4 infants and 1 adolescent) with nemaline myopathy who received dietary supplementation with L-tyrosine (250 to 3000 mg/day). All 4 infants were reported to have an initial decrease in sialorrhoea and an increase in energy levels. The adolescent showed improved strength and exercise tolerance. No adverse effects of treatment were observed. Dietary tyrosine supplementation may improve bulbar function, activity levels, and exercise tolerance in nemaline myopathy.

Congenital bone fractures in spinal muscular atrophy: functional role for SMN protein in bone remodeling.

Spinal muscular atrophy is the second most common fatal childhood disorder. Core clinical features include muscle weakness caused by degenerating lower motor neurons and a high incidence of bone fractures and hypercalcemia. Fractures further compromise quality of life by progression of joint contractures or additional loss of motor function. Recent observations suggest that bone disease in spinal muscular atrophy may not be attributed entirely to lower motor neuron degeneration. The presence of the spinal muscular atrophy disease-determining survival motor neuron gene (SMN), SMN expression, and differential splicing in bone-resorbing osteoclasts was recently discovered. Its ubiquitous expression and the differential expression of splice variants suggest that SMN has specific roles in bone cell function. SMN protein also interacts with osteoclast stimulatory factor. Mouse models of human spinal muscular atrophy disease suggest a potential role of SMN protein in skeletal development. Dual energy x-ray absorptiometry analysis demonstrated a substantial decrease in total bone area and poorly developed caudal vertebra in the mouse model. These mice also had pelvic bone fractures. Studies delineating SMN signaling mechanisms and gene transcription in a cell-specific manner will provide important molecular insights into the pathogenesis of bone disease in children with spinal muscular atrophy. Moreover, understanding bone remodeling in spinal muscular atrophy may lead to novel therapeutic approaches to enhance skeletal health and quality of life. This article reviews the skeletal complications associated with spinal muscular atrophy and describes a functional role for SMN protein in osteoclast development and bone resorption activity.

Heterogeneity of nemaline myopathy cases with skeletal muscle alpha-actin gene mutations.

Nemaline myopathy (NM) is the most common of several congenital myopathies that present with skeletal muscle weakness and hypotonia. It is clinically heterogeneous and the diagnosis is confirmed by identification of nemaline bodies in affected muscles. The skeletal muscle alpha-actin gene (ACTA1) is one of five genes for thin filament proteins identified so far as responsible for different forms of NM. We have screened the ACTA1 gene in a cohort of 109 unrelated patients with NM. Here, we describe clinical and pathological features associated with 29 ACTA1 mutations found in 38 individuals from 28 families. Although ACTA1 mutations cause a remarkably heterogeneous range of phenotypes, they were preferentially associated with severe clinical presentations (p < 0.0001). Most pathogenic ACTA1 mutations were missense changes with two instances of single base pair deletions. Most patients with ACTA1 mutations had no prior family history of neuromuscular disease (24/28). One severe case, caused by compound heterozygous recessive ACTA1 mutations, demonstrated increased alpha-cardiac actin expression, suggesting that cardiac actin might partially compensate for ACTA1 abnormalities in the fetal/neonatal period. This cohort also includes the first instance of an ACTA1 mutation manifesting with adult-onset disease and two pedigrees exhibiting potential incomplete penetrance. Overall, ACTA1 mutations are a common cause of NM, accounting for more than half of severe cases and 26% of all NM cases in this series.

Postoperative malnutrition in Duchenne muscular dystrophy.

Dysphagia and aspiration seem to be rare in Duchenne muscular dystrophy, but cachexia can be associated with early death. Commonly, weight loss can be attributed to inadequate caloric intake caused by loss of ability to self-feed and/or fatigue. Our objective was to determine whether scoliosis repair is associated with malnutrition. A retrospective chart review was undertaken of patients with Duchenne muscular dystrophy, including those who underwent operative repair of scoliosis. We identified nine boys who lost > 5% body weight within 12 months of surgery. Eight patients who gained weight after surgery and eight patients of comparable age who had no surgery served as control subjects. All patients had no change in biceps strength after surgery, but those who lost weight were unable to self-feed. We found that weight loss after surgery was associated with loss of self-feeding. We conclude that pre- and postoperative management of patients with Duchenne muscular dystrophy should include feeding evaluation and determination of postural changes.