Cardiac manifestations of congenital fiber-type disproportion myopathy

Cardiac involvement has not been a reported feature of congenital fiber-typ e disproportion myopathy. We describe two children, aged 13 years and 1 yea r, respectively, who presented with serious cardiac symptomatology in conju nction with congenital fiber-type disproportion. One child developed dilate d cardiomyopathy and medically intractable congestive heart failure necessi tating cardiac transplantation at the age of 13 years. The second (unrelate d) child developed atrial fibrillation with rapid atrioventricular conducti on requiring treatment with digoxin. Skeletal muscle biopsy findings in bot h children showed congenital fiber-type disproportion with no evidence of a structural, dystrophic, or metabolic myopathy Adenosine triphosphatase (AT Pase) reacted sections showed type I hypotrophy with a predominance of type I fibers, confirmed by histogram analysis. Examination of the heart from p atient 1 at the time of transplantation confirmed dilated cardiomyopathy wi th hypertrophic myocardiocytes. Although cardiomyopathy is commonly associa ted with other childhood myopathies, to our knowledge it has not been a fea ture in reported cases of congenital fiber-type disproportion. We recommend close cardiac assessment, with annual electrocardiograms, of children with congenital fiber-type disproportion.