Autosomal recessive sudden unexpected death in children probably caused by a cardiomyopathy associated with myopathy

The propositus, who died suddenly at the age of 22 months, was investigated because of an unusual myopathy. Family history revealed two sisters and four cousins who had also died suddenly and unexpectedly. The finding of asymmetric septal hypertrophy by echocardiography in the propositus suggested that the cause of the sudden death in the relatives was an undetected cardiomyopathy accompanying a mild and often subclinical myopathy. The affected children were in two sibships and both sets of parents were first cousins. The mother of one sibship was the sister of the father of the other. It is suggested that a gene causes a mild autosomal recessive myopathy with cardiomyopathy that is often undiagnosed and usually ends in sudden unexpected death in the second year of life. The same gene may manifest on echocardiogram in some heterozygotes as asymmetric septal hypertrophy.