Primary carnitine deficiency is attributable to impaired cellular carnitine transport and is associated with cardiomyopathy or myopathy. Oral carnitine supplements, L-carnitine 100 mg per kilogram per day in divided doses, may effectively reverse symptoms even when only a modes (but apparently critical) increase in cellular carnitine level can be achieved.

Secondary carnitine deficiency is more common and occurs as a consequence of metabolic defects involving the oxidation of organic acids, especially beta-oxidation defects at the level of medium-, long-, or short-chain acyl coenzyme A (acyl CoA) dehydrogenases. The majority of reported cases have involved infants or children who exhibit systemic symptoms of aketotic hypoglycemia (owing to the coexisting metabolic defect in liver) and episodes resembling Reye's syndrome, with or without symptoms of muscle weakness or fatigability. Metabolic crises are triggered by the mobilization of fatty acids in response to fasting or infection, leading to the accumulation of toxic levels of organic acids behind the metabolic block. Pregnancy may also be a risk factor in precipitating metabolic crises. Carnitine depletion occurs through the action of carnitine acyl transferases, which convert accumulated acyl CoA esters to acylcarnitines, which diffuse from the cell and are excreted by the kidney. Treatment - designed to prevent or reduce fatty acid mobilization - consists of a high-carbohydrate, low-fat (less than 20 percent of dietary calories) diet and frequent feedings. L-Carnitine replacement, 100 mg per kilogram per dayin divided doses, counters carnitine depletion, promotes the formation of relatively nontoxic acyl carnitines from more toxic acyl CoA esters, and may increase the ratio of free to esterified CoA.