Disorders of mitochondrial beta-oxidation: prenatal and early postnatal diagnosis and their relevance to Reye's syndrome and sudden infant death.

There are still many problems with the diagnosis and classification of inherited disorders of mitochondrial beta-oxidation. At present only the acyl-CoA dehydrogenase step of the beta-oxidation spiral has been explored in any detail and a large number of patients have disorders that cannot be properly characterized. beta-Oxidation defects may present in a wide variety of ways, the most dramatic being acute encephalopathy with hepatic involvement (atypical Reye's syndrome) or 'sudden' death. Investigations may include urinary and plasma organic acids, metabolic stress tests and assays of overall metabolic pathways or of specific enzymes in cultured fibroblasts, lymphocytes, or other material. Early postnatal diagnosis presents particular difficulties but in medium-chain acyl-CoA dehydrogenase deficiency the diagnosis may be apparent from careful examination of urine. There is as yet little general experience in prenatal diagnosis of this group of disorders except for glutaric aciduria type II. Single prenatal diagnoses of medium-chain acyl-CoA dehydrogenase deficiency and of an incompletely characterized defect of medium-chain fatty acid oxidation have been performed.