Clinical varieties of carnitine and carnitine palmitoyltransferase deficiency

Several clinical entities are associated with disorders of fatty acid oxidation or transfer across the inner mitochondrial membrane. Over 40 cases of the primary carnitine deficiency syndrome have been reported to date and various subtypes have been characterized. This represents a large clinical spectrum. The deficiency of carnitine in muscle is at the basis of a syndrome characterized by muscle weakness and lipid storage myopathy. The systemic form of carnitine deficiency is more generalized and includes recurrent episodes of hepatic encephalopathy as well as lipid storage in muscle, liver and heart. In one subtype, hypoglycemia upon fasting and cardiomyopathy are found. There are also several causes of secondary carnitine deficiency states which are either acquired or associated with inborn errors of metabolism (organic acidurias, defects of acyl-CoA dehydrogenases). Clinically, Carnitine palmitoyltransferase (CPT) deficiency is a rather homogeneous syndrome presenting with recurrent episodes of myoglobinuria provoked by fasting or prolonged exercise. The only exception is an infantile variety associated with severe hypoglycemia and hepatic CPT deficiency. Using malonyl-CoA, a specific inhibitor of CPT-I, we had suggestions in five adult patients with myoglobinuria that CPT-II is lacking in muscle, liver and platelets while CPT-I is above the control level. The enzyme abnormality seems partial and limited to CPT-II or to its binding to the inner mitochondrial membrane.