GENETIC-LINKAGE MAPPING OF HSD3B1 AND HSD3B2 ENCODING HUMAN TYPE-I AND TYPE-II 3-BETA-HYDROXYSTEROID DEHYDROGENASE/DELTA-5-DELTA-4-ISOMERASE CLOSE TO D1S514 AND THE CENTROMERIC D1Z5 LOCUS

The enzyme 3 beta-hydroxysteroid dehydrogenase/ Delta(5)-Delta(4)-isomerase (3 beta-HSD) catalyses an essential step in the biosynthesis of all steroid hormones. Consequently, classical 3 beta-HSD deficiency is responsible for a severe form of congenital adrenal hyperplasia. The HSD3B1 and HSD3B2 genes encoding the types I and II 3 beta-HSD isoenzymes, respectively, have been previously assigned by in situ hybridization to the chromosome 1p13.1 region. To determine the physical distance between these two genes, NotI and SacII digests of genomic DNA were resolved by pulse-field gel electrophoresis and hybridized with type I and type II 3 beta-HSD cDNAs used as probes. The detection of a single band under low stringency conditions indicates that HSD3B1 and HSD3B2 are located within an approximately 0.29 megabase SacII DNA fragment. We constructed a high resolution genetic map of the region flanking the polymorphic HSD3B1 and HSD3B2 genes including ten Genethon markers and the two NIH/CEPH markers AMY2B and D1Z5. The HSD3B1A and HSD3B2A markers were mapped relative to other reference markers through eight CEPH reference families. The order of polymorphic genes and markers is: pter-[AMY2B-D1S239]-D1S457-D1S502-D1S250-D1S252-[HSD3B1A-HSD3B2A-D1S514]-[D1Z5-D1S342]-D1S305-D1S303-D1S484-qter. The D1S514 marker was thus closely linked to HSD3B1A (theta < 0.001; lod = 14.13) and HSD3B2 (theta = 0.008; lod = 35.36). The HSD3B loci are located 1-2 cM of the centromeric marker D1Z5.