Primary carnitine deficiency (Plasma Membrane Carnitine Transport Defect) is the only genetic defect in which carnitine deficiency is the cause, rather than the consequence of impaired fatty acid oxidation. Patients present with progressive cardiomyopathy at 2-4 years of age with or without skeletal muscle weakness. Infants may have fasting hypoketotic hypoglycemia. The defect is in the plasma membrane sodium dependent carnitine transporter present in the heart, muscle and kidney. This transporter maintains the intracellular carnitine 20 to 50 times higher than plasma concentrations. Patients have extremely reduced carnitine levels in plasma and muscle (1-2% of normal). It is an autosomal recessive disorder and heterozygote parents have plasma levels of carnitine approximately 50% of normal. The fasting urinary organic acid profile may show a hypoketotic dicarboxylic aciduria if hepatic fatty acid oxidation is impaired. The defect in carnitine transport can be demonstrated in vitro by assay of carnitine uptake using cultured fibroblasts or lymphoblasts. Treatment consists of oral carnitine (50-100 mg/kg/day) in pharmacologic doses and it corrects the cardiomyopathy & muscle weakness.