Findings of limb-girdle muscular dystrophy R7 telethonin-related patients from a Chinese neuromuscular center

Two distinct phenotypes and a novel mutation in limb-girdle muscular dystrophy R7 telethonin-related patients from Thai neuromuscular center

Limb-girdle muscular dystrophy R7 telethonin-related (LGMDR7) is a rare autosomal recessive disorder caused by TCAP gene mutations. This study described the phenotypic spectrum, genetic characteristics, and muscle magnetic resonance imaging (MRI) findings of patients with LGMDR7. Five patients from three unrelated families with TCAP mutations were retrospectively identified at the Neuromuscular Center at King Chulalongkorn Memorial Hospital. Demographic, clinical, laboratory, and muscle MRI data were collected and analyzed. We observed a mild phenotype associated with asymptomatic/paucisymptomatic hyperCKemia in one family and a classic limb-girdle muscular dystrophy phenotype in two unrelated patients. The novel deletion variant c.136_137del was identified in a compound heterozygous state with c.26_33dup in a family with a mild phenotype. Muscle MRI of four patients revealed consistent sparing of the sartorius muscle in all patients. This study expands the clinical and genetic spectrum of LGMDR7 by demonstrating an asymptomatic/paucisymptomatic hyperCKemia phenotype and identifying the novel c.136_137del variant. The muscle MRI findings highlight a characteristic pattern in which the sartorius muscle is consistently uninvolved. These findings contribute to a better understanding of the disease and assist in developing future diagnostic strategies for affected individuals, specifically by using clinical profiles in conjunction with the characteristics of muscle MRI.

Calcitriol increases MBNL1 expression and alleviates myotonic dystrophy phenotypes in HSALR mouse models

BACKGROUND

Myotonic dystrophy type 1 (DM1), one of the most common forms of adult-onset muscular dystrophy, is caused by abnormally expanded CTG repeats in the 3' untranslated region of the DMPK gene. The CUG repeats transcribed from the expanded CTG repeats sequestrate a splicing factor, MBNL1, causing the clinical symptoms in DM1. Nowadays, only symptomatic treatments are available for DM1, and no rational therapy is available. Recently, upregulation of MBNL1 expression has been found to be one of the promising therapies for DM1.

METHODS

All experiments were conducted in the C2C12 myoblasts and HSA^LR mice, a DM1 mouse model. Real-time PCR and western blot were used to detect the mRNA and protein level, respectively. The rotarod exercise, grip strength and hanging time were used to evaluate the muscle strength of mice.

RESULTS

In this study, we demonstrated that calcitriol, an active form of vitamin D3, increased MBNL1 in C2C12 mouse myoblasts as well as in HSA^LR mice model for DM1. In HSA^LR mice model, calcitriol improved muscle strength, and corrected aberrant splicing in skeletal muscle. Besides, calcitriol reduced the number of central nuclei, and improved muscle histopathology in HSA^LR mice. In addition, we identified that calcitriol upregulated MBNL1 expression via activating the promoter of Mbnl1 in C2C12 myogenic cells.

CONCLUSION

Our study suggests that calcitriol is a potential pharmacological strategy for DM1 that enhances MBNL1 expression.

Expanding the clinicopathological-genetic spectrum of glycogen storage disease type IXd by a Chinese neuromuscular center

Background

Glycogen storage disease (GSDs) is characterized by abnormally inherited glycogen metabolism. GSD IXd, which is caused by mutations in the PHKA1 gene, is an X-linked rare disease with mild myopathic symptoms. To date, only 13 patients with GSD IXd have been reported. In this study, we aimed to expand the clinicopathological-genetic spectrum of GSD IXd at a neuromuscular center in China.

Methods

Data on patients diagnosed with GSD IXd at our neuromuscular center were collected retrospectively. Clinical features, electrophysiology, muscle pathology, and genetic information were analyzed.

Results

Between 2015 and 2021, three patients were diagnosed with GSD IXd based on clinical manifestations, pathological findings, and genetic testing. One patient presented with mitochondrial myopathy. All patients exhibited muscle weakness and elevated levels of creatine kinase. Electromyography-detected myopathic changes were found in two patients, whereas one patient refused to undergo this examination. Pathological examinations in all patients revealed subsarcolemmal accumulation of glycogen under PAS staining. All patients had mutations in the PHKA1 gene and the patient with mitochondrial myopathy also had a mutation in the MT-TL1 gene.

Conclusion

Our study expands the clinicogenotype and phenotype of GSD IXd in a Chinese population. Our study also expands the known mutation spectrum for GSD IXd, contributing to a better characterization and understanding of this ultrarare neuromuscular disorder.

Clinicopathological-genetic features of congenital myasthenic syndrome from a Chinese neuromuscular centre

Congenital myasthenic syndrome (CMS) encompasses a heterogeneous group of inherited disorders affecting nerve transmission across the neuromuscular junction. The aim of this study was to characterize the clinical, physiological, pathohistological and genetic features of nine unrelated Chinese patients with CMS from a single neuromuscular centre. A total of nine patients aged from neonates to 34 years were enrolled who exhibited initial symptoms. Physical examinations revealed that all patients exhibited muscle weakness. Muscle biopsies demonstrated multiple myopathological changes, including increased fibre size variation, myofibrillar network disarray, necrosis, myofiber grouping, regeneration, fibre atrophy and angular fibres. Genetic testing revealed six different mutated genes, including AGRN (2/9), CHRNE (1/9), GFPT1 (1/9), GMPPB (1/9), PLEC (3/9) and SCN4A (1/9). In addition, patients exhibited differential responses to pharmacological treatment. Prompt utilization of genetic testing will identify novel variants and expand our understanding of the phenotype of this rare syndrome. Our findings contribute to the clinical, pathohistological and genetic spectrum of congenital myasthenic syndrome in China.