Molecular Genetic Diagnosis of a Bethlem Myopathy Family with an Autosomal-Dominant COL6A1 Mutation, as Evidenced by Exome Sequencing

BACKGROUND We describe herein the application of whole exome sequencing (WES) for the molecular genetic diagnosis of a large Korean family with dominantly inherited myopathy. CASE REPORT The affected individuals presented with slowly progressive proximal weakness and ankle contracture. They were initially diagnosed with limb-girdle muscular dystrophy (LGMD) based on clinical and pathologic features. However, WES and subsequent capillary sequencing identified a pathogenic splicing-site mutation (c.1056+1G>A) in COL6A1, which was previously reported to be an underlying cause of Bethlem myopathy. After identification of the genetic cause of the disease, careful neurologic examination revealed subtle contracture of the interphalangeal joint in the affected members, which is a characteristic sign of Bethlem myopathy. Therefore, we revised the original diagnosis from LGMD to Bethlem myopathy. CONCLUSIONS This is the first report of identification of COL6A1-mediated Bethlem myopathy in Korea, and indicates the utility of WES for the diagnosis of muscular dystrophy.