Muscle carnitine deficiency and fatal cardiomyopathy.

A 23-month-old boy with progressive muscle weakness and severe cardiomyopathy was found to have oil red O positive vacuoles predominantly in type 1 muscle fibers. Serum carnitine was normal, but muscle carnitine content was decreased. Both parents were clinically normal, but the muscle carnitine level was low in the father. Despite oral treatment with carnitine, the condition progressed and was fatal. At autopsy, cardiac muscle showed borderline low carnitine content and numerous mitochondria, but no lipid accumulation.