Construction of a 3.7-Mb physical map within human chromosome 20p12 ordering 18 markers in the Alagille syndrome locus.

Alagille syndrome (AGS, MIM 118450) is associated with human chromosome band 20p12. To study this region, we constructed a 3.7-Mb physical map using 36 YACs isolated from the CEPH YAC library with three sequence-tagged sites (STS): D20S503, D20S41, and D20S188. New STSs were obtained from 6 isolated YAC end-fragments. Eighteen markers were ordered on the contig as follows:20ptel-D20S177-D20S175-D20S509- D20S5/D20S503-D20S506-D20S162-D20S504- D20S505-D20S507-D20S188-(D20S6-D20S27- D20S189)-D20S186-D20S41-D20S61-D20S492- D20S508-20pcen. A restriction map with the enzymes AscI, MluI, NotI, SacII, and SfiI was generated, revealing seven putative CpG islands. We established a YAC contig that spans the AGS region and thus will be valuable for cloning candidate genes and searching for DNA polymorphisms segregating with this syndrome.