Encephalopathy and fatal myopathy in two siblings. Their association with partial deficiency of muscle carnitine.

Two brothers had intermittent episodes of muscle weakness, lethargy, hyperammonemia, rhabdomyolysis, and elevated activities of creatine phosphokinase (CPK), lactic dehydrogenase, and SGOT in serum associated with low muscle carnitine but normal serum carnitine concentrations. These siblings represent a "mixed" form of carnitine deficiency with the elements of both systemic and myopathic carnitine deficiency. The older sibling died suddenly after a 24-hour fast. The younger boy has received carnitine for three years. During this period, serum CPK activity has remained elevated and increased further during illnesses, but no clinical symptoms of encephalopathy or myopathy have appeared.