Central core myopathy with RYR1 mutation masks 5q spinal muscular atrophy.

We report the case of a male who presented in infancy with motor delay and muscle weakness. Typical muscle biopsy features and heterozygous RYR1 mutation confirmed a diagnosis of central core disease. Family studies showed this to be a de-novo mutation. Some years later, his two older teenage brothers presented with proximal muscle weakness. Neurophysiology, muscle biopsy and DNA studies confirmed spinal muscular atrophy. Subsequent genetic studies in the index case also confirmed homozygous deletions of exon 7 and 8 in the SMN gene. Review of the original muscle biopsy showed classical features of central core disease with no evidence to suggest denervation, such that the diagnosis of spinal muscular atrophy could not have been suspected in the absence of the family history.