Maple syrup urine disease (MSUD) is caused by the deficiency of the mitochondrial branched-chain α-keto acid dehydrogenase complex. The multienzyme complex is a macromolecule (Mr 4 × 106) consisting of at least six distinct subunits. In this study, the human E1β gene (BCKDHB) has been localized to human chromosome 6 by hybrid somatic cell analysis, and regionally assigned to chromosome bands 6p21-22 by in situ hybridization. The E2 gene (DBT), which was previously localized to chromosome 1, is regionally assigned to the chromosome band 1p31 also by in situ hybridization. Localization of the E1β gene to chromosome 6p21-22 assigns another major human disease locus to a region that contains several important genes, including the major histocompatability complex, tumor necrosis factor, and heat-shock protein HSP70. Mapping of the E1β and the E2 genes may provide information for the linkage analysis of MSUD families with mutations in these two loci.
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