Congenital myopathy-1B caused by a homozygous RYR1 variant: A case report

Congenital myopathies are a group of clinically and genetically diverse neuromuscular diseases that often present with stable and/or slowly progressive trunk and proximal weakness. Genetic analysis can help diagnose each congenital myopathy more accurately. Although an increasing number of other causative genes have been reported, ryanodine receptor 1 (RYR1)-related myopathy is the most common cause. Herein, we report the clinical presentation of a patient with congenital myopathy-1B (multiminicore disease) that was caused by a c.115 G>A homozygous variant of RYR1. The patient had normal cognitive abilities but was developmentally delayed and unable to walk. Electromyography revealed myogenic changes. The c.115G>A variant located in the second exon of RYR1 was found to be homozygous in the congenital neuromuscular gene panel. The patient’s parents and sister both carried the heterozygous variant. Clinical differences between family members with the homozygous and heterozygous variants of RYR1 highlight the correlation between the genotype and phenotype.