Paediatrics: Disorders of fatty acid oxidation

Disorders of fatty acid oxidation

Disorders of fatty acid metabolism may be due to deficiency in the acyl dehydrogenase enzyme complex, deficiency in carnitine, or a defect in the carnitine transport process.

•   Clinical presentation is with acute encephalopathy with recurrent vomiting, lethargy, drowsiness, and seizures. Hypoglycaemia is usually observed, as well as hepatomegaly and hyperammonaemia.

•   Episodes of acute encephalopathy are precipitated by periods of prolonged fasting or by intercurrent illness associated with poor feeding.

·  Presentation is usually in the first 2yrs of life.

•   Diagnosis depends on a high index of suspicion. A positive family history or a history of previous acute metabolic crisis during trivial intercurrent illness may be present.

•   Diagnosis of a specific disorder of fatty acid metabolism is established by demonstrating characteristic abnormalities in urinary organic acid excretion and in plasma acyl carnitine profiles. Abnormalities may not be present when child is well. Molecular genetic testing is also available for some disorders.

•   Treatment successfully managed by avoidance of prolonged fasting, high carbohydrate diet, and carnitine supplements. During intercurrent illness, administration of high carbohydrate diet is required.

Medium chain acyl-CoA dehydrogenase deficiency (MCAD)

This is the commonest fatty acid oxidation disorder (1/13 000 births) and is due to mutations in the MCAD gene (1p31). Clinical presentation may vary from asymptomatic to fulminant. Newborn screening programs, uti-lizing neonatal blood spot collection methods, are now in place in many countries for the early detection and management of this condition.