Ethylmalonic encephalopathy: application of improved biochemical and molecular diagnostic approaches

Ethylmalonic encephalopathy (EE, OMIM # 602473) is an autosomal recessive metabolic disorder of infancy affecting the brain, the gastrointestinal tract and peripheral vessels. It is caused by a defect in the ETHE1 gene product, which was recently shown to be part of a metabolic pathway devoted to sulphide detoxification. We report the application of improved biochemical and molecular approaches to the diagnosis of three cases of EE from two unrelated Cypriot families. The children presented all the typical biochemical hallmarks of the disease including elevated lactate and butyrylcarnitine in blood and elevated urinary excretion of ethylmalonic acid, 2-methylsuccinate, isobutyrylglycine and isovalerylglycine. We also detected an elevated level of thiosulphate in urine, which we propose as an additional biochemical marker of the disease. The proband of the first family was shown to be a compound heterozygote for a missense mutation in exon 5, L185R, and a deletion of exon 4. The deletion was identified using quantitative real-time polymerase chain reaction (qRT-PCR). Using the same technique, the proband of the second family was found to be homozygous for the exon 4 deletion. A prenatal diagnosis was performed for the second family using qRT-PCR, thus establishing the usefulness of RT-PCR in prenatal diagnosis.