Homozygous MYH7 R1820W mutation results in recessive myosin storage myopathy: scapuloperoneal and respiratory weakness with dilated cardiomyopathy.

Myosin storage myopathy (MSM) is a protein aggregate myopathy caused by the accumulation of myosin in muscle fibres and results from MYH7 mutation. Although MYH7 mutation is also an established cause of variable cardiomyopathy with or without skeletal myopathy, cardiomyopathy with MSM is a rare combination. Here, we update the clinical findings in the two brothers that we previously reported as having recessively inherited MSM characterized by scapuloperoneal distribution of weakness and typical hyaline-like bodies in type 1 muscle fibres. One of the patients, weak from childhood but not severely symptomatic until 28 years of age, had an unusual combination of MSM, severe dilated cardiomyopathy, and respiratory impairment at the age of 44 years. We identified homozygous missense mutation c.5458C>T (p.R1820W) in exon 37 in these patients as the second recessive MYH7 mutation reported to date.