Fatty acid oxidation disorders

Abstract

Fatty acid oxidation disorders (FAODs) are inborn errors of metabolism due to disruption of either mitochondrial β-oxidation or the fatty acid transport using the carnitine transport pathway. The presentation of a FAOD will depend upon the specific disorder, but common elements may be seen, and ultimately require a similar treatment. Initial presentations of the FAODs in the neonatal period with severe symptoms include cardiomyopathy, while during infancy and childhood liver dysfunction and hypoketotic hypoglycemia are common. Episodic rhabdomyolysis is frequently the initial presentation during or after adolescence; although, these symptoms may develop at any age for most of the FAODs The treatment of all FAOD's include avoidance of fasting, aggressive treatment during illness, and supplementation of carnitine, if necessary. The long-chain FAODs differ by requiring a fat-restricted diet and supplementation of medium chain triglyceride oil and often docosahexaenoic acid (DHA)-an essential fatty acid, crucial for brain, visual, and immune functions and prevention of fat soluble vitamin deficiencies. The FAOD are a group of autosomal recessive disorders associated with significant morbidity and mortality, but early diagnosis on newborn screening (NBS) and early initiation of treatment are improving outcomes. There is a need for clinical studies including randomized, controlled, therapeutic trials to continue to evaluate current understanding and to implement future therapies.

Keywords: Fatty acid oxidation disorders (FAODs); carnitine; hypoketotic hypoglycemia; mitochondrial β-oxidation; trifunctional protein.

Figure 1

Overview of Mitochondrial Fatty Acid Oxidation Metabolism. Dark Green line, mitochondrial outer membrane (Mito OM); light green line, mitochondrial inner membrane (Mito IM); gold line, plasma membrane (PM). FAOD are shown in the red star shapes with associated enzyme defect. AC, Acyl-CoA; ACS, acyl-CoA synthase; CoA, coenzyme A; FA, fatty acids; MC, medium chain; LC, Long Chain; TFP, tri-functional protein complex; C I, complex I of ETC; CT, carnitine transporter defect; CPT1a, Carnitine palmitoyltransferase I; CPT2, carnitine palmitoyltransferase II; CACT, carnitine acylcarnitine translocase; LCHAD, long-chain 3-hydroxy acyl-CoA dehydrogenase; VLCAD, very long chain acyl-CoA dehydrogenase; MCAD, medium-chain acyl-CoA dehydrogenase; SCAD, short-chain acyl-CoA dehydrogenase; MAD, multiple acyl-CoA dehydrogenases; HAD, 3-hydroxyacyl-CoA dehydrogenase.