An overview of beta-oxidation disorders.

Fatty acids (FAs) are components of cell membrane, enzymes, and hormones and are one of the most important energy sources for many organisms. There are several types of fatty-acid oxidative degradation processes in the cell, namely alpha-, beta-, and omega-oxidation, which take place in specialized cellular structures: mitochondria and peroxisomes. The best-known pathway is beta-oxidation taking place in the matrix of mitochondria. It is responsible for the degradation of straight-chain FAs. The pathway of beta-oxidation of fatty acids is comprised of at least 25 enzymes and specific transport proteins. Deficiencies in 18 of them have been demonstrated to cause disease in humans. These diseases show a wide variety of symptoms, which can be expressed at random, one at a time, or in sets, characteristic of the individual rather than the metabolic character of the disease. Disorders of beta-oxidation are believed to cause about 1-3% of unexplained sudden infant deaths (SIDS). Acute fatty liver of pregnancy (AFLP) and the syndrome of hemolysis, elevated liver enzymes, and low platelets (HELLP syndrome), which have significant neonatal and maternal morbidity and mortality, have also been associated with beta-oxidation deficiency in fetuses. This review summarizes recent observations on disorders associated with fatty-acid oxidation: deficiencies of beta-oxidation enzymes, namely VLCAD, TFP and LCHAD, MCAD, MCKAT, M/SCHAD, and SCAD, and deficiencies of the enzymes TCP I, CT, and CPT II of the carnitine cycle.