The role of methionine in ethylmalonic encephalopathy with petechiae.

BACKGROUND Among patients with ethylmalonic aciduria, a subgroup with encephalopathy, petechial skin lesions, and often death in infancy is distinct from those with short-chain acyl-coenzyme A dehydrogenase deficiency or multiple acyl-coenzyme A dehydrogenase deficiency. The nature of the molecular defect in this subgroup is unknown, and the source of the ethylmalonic acid has been unclear. OBJECTIVE To determine whether the administration of candidate amino acids increased the excretion of ethylmalonic acid. DESIGN Examination of patterns of organic acids excreted in the urine before and following loading doses of isoleucine and methionine. SETTING General clinical research center. PATIENT An infant with ethylmalonic aciduria, global developmental delay, acrocyanosis, and intermittent showers of petechiae. MAIN OUTCOME MEASURE Excretion of ethylmalonic acid in the urine. RESULTS Loading with methionine increased the excretion of ethylmalonic acid, whereas loading with isoleucine did not. Restriction of the dietary intake of methionine decreased ethylmalonic acid excretion. CONCLUSION In ethylmalonic acid encephalopathy with petechiae, methionine is a precursor of ethylmalonic acid.