Occurrence of a Tyr393→Asn (Y393N) mutation in the E1α gene of the branched-chain α-keto acid dehydrogenase complex in maple syrup urine disease patients from a mennonite population

Maple syrup urine disease (MSUD) is caused by a deficiency in the mitochondrial branched-chain α-keto acid dehydrogenase complex. The incidence of MSUD in the Philadelphia Mennonites is 1/176 births resulting from consanguinity. In this study, we amplified cDNAs for the decarboxylase E1α subunit of the branched-chain α-keto acid dehydrogenase complex from a classical MSUD patient and from an obligatory heterozygote of a Mennonite family by the PCR. Sequencing of the amplified cDNAs disclosed at codon 393 of the mature E1α polypeptide a base substitution changing a tyrosine (encoded by TAC) to an asparagine residue (encoded by AAC), which is designated Y393N. A segment of the E1α gene containing the 5′ portion of exon 9 was amplified. Probing of the amplified genomic DNA with allele-specific oligonucleotide probes showed that the mutation in the E1α gene was homozygous in six Mennonites affected with classical MSUD and was present in heterozygous carriers. The identification of the MSUD mutation in the Philadelphia Mennonites will facilitate diagnosis and carrier detection for this population.