Defects of mitochondrial beta-oxidation: a growing group of disorders

Two disorders of fatty acid metabolism were described in 1973. Since then, at least 22 different inborn errors of metabolism affecting beta-oxidation in skeletal muscle and other tissues have been identified. Neurological findings are prominent in many of these, including hypotonia, myopathy (often with lipid storage), and peripheral neuropathy. Recurrent rhabdomyolysis and hypoglycemia are frequent clinical problems. In many cases, a correct diagnosis will only be made if these disorders are specifically considered and appropriate tests are obtained, since screening tests which detect other inborn errors of metabolism are often normal in patients with beta-oxidation defects under many circumstances. Clinical symptoms, diagnostic testing, and issues of newborn screening for this important group of disorders are discussed.