A T-to-A substitution in the E1 alpha subunit gene of the branched-chain alpha-ketoacid dehydrogenase complex in two cell lines derived from Menonite maple syrup urine disease patients.

We cloned and sequenced cDNAs of the E1 alpha and E1 beta subunits of the branched chain alpha-ketoacid dehydrogenase complex (BCKDH) in two cell lines derived from two different Menonite MSUD patients (GM 1655, GM 1099). A T-to-A substitution which generates an asparagine in place of a tyrosine at amino acid 394 of the mature E1 alpha subunit was present in both alleles in these two cell lines, whereas cDNAs of the E1 beta subunit in these cell lines were identical to that of normal human lymphoid cell line and that of the clone from a human placenta cDNA library. It is suggested that the Menonite MSUD is caused by the missense mutation of the E1 alpha subunit of the BCKDH complex.