A SIMPLE, STRAIGHTFORWARD ASSAY FOR LONG-CHAIN 3-HYDROXYACYL-COA DEHYDROGENASE BASED ON THE USE OF N-ETHYLMALEIMIDE - POTENTIAL FOR PRENATAL AND POSTNATAL DIAGNOSIS

In recent years an increasing number of inherited diseases in man have been identified in which there is an impairment in mitochondrial fatty acid beta-oxidation. This includes long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, first identified in 1989 (Wanders et al 1989) and now described in the literature in at least twelve additional patients. Identification of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency in patients suspected to suffer from this enzyme defect is usually done in cultured skin fibroblasts. Correct diagnosis of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency is hampered by the fact that the short-chain enzyme is also reactive with long-chain substrates, which explains the relatively high levels of residual activity in fibroblasts from long-chain 3-hydroxyacyl-CoA dehydrogenase-deficient patients, amounting to 25% of control values (see e.g. Wanders et al 1990). Residual activities are even higher in leukocytes from these patients, amounting to 50-60% of control levels (Wanders and IJlst, 1992), owing to the fact that leukocytes contain only little long-chain 3-hydroxyacyl-CoA dehydrogenase activity compared to the activity of the short-chain enzyme. We now report that N-ethylmaleimide (NEM) inhibits the long-chain enzyme but not the short-chain enzyme. This novel finding allows accurate determination of long-chain 3-hydroxyacyl-CoA dehydrogenase activity, which is of great importance for correct pre- and postnatal diagnosis in leukocytes and chorionic villi (fibroblasts), respectively.