Study of RYR1 gene analysis in a unique myopathy characterized as congenital fiber type disproportion associated with myofibrillar disorganization and altered internal nuclei

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Mutations in the gene encoding skeletal muscle ryanodine receptor (RYR1) have been implicated in various forms of neuromuscular diseases including congenital myopathy. There is a broad range of clinical and pathological features. We detected 7 unrelated Japanese patients with compound heterozygous RYR1 mutations showing a unique muscle pathology characterized as congenital fiber type disproportion associated with myofibrillar disorganization and altered internal nuclei. Clinically, all patients showed axial and proximal dominant muscle weakness of variable severity from neonatal period, and often required respiratory supports. Muscle weakness was stable or rather improved during childhood. In addition, some patients revealed ptosis and/or opthalmoparesis. All patients had a compound heterozygous mutations including nonsense mutation, splicing mutation or deletion in the central portion of RYR1.