A linkage map of microsatellite markers on the human X chromosome.

The efficiency of mapping and diagnosis of X-linked disorders by linkage depends upon the existence of a high-density genetic map of polymerase chain reaction (PCR)-based markers. DXS1120, DXS1122, DXS1123, DXS1124, DXS1125, DXS1126, and DXS1153 were randomly isolated from a flow-sorted lambda bacteriophage library of the human X chromosome. The CCN (N = A or G) repeat within the androgen receptor was also found to be polymorphic and primers were designed for genotyping the CCN polymorphism in addition to the AGC polymorphism. The above markers, together with microsatellite polymorphisms at DXS237 (GMGX9), 5'DYS-II and 3'DYS MS (within the dystrophin locus), DXS538 (XL27B), PGK1P1, DXS300 (VK29AC), DXS294 (VK17AC), and DXS102 (cX38.1AC), were genotyped in the 40 CEPH reference families. One marker, DXS1153, was found to include cryptic alleles that amplify only in homozygotes and hemizygotes but not heterozygotes. A PCR-based linkage map was constructed using all of the above markers plus PCR-based markers from the CEPH database and those PCR-based markers previously typed in our laboratory: ALAS2, DXS292 (VK14AC), DXS297 (VK23AC), FRAXAC1, and FRAXAC2. The genetic map of the X chromosome incorporates 62 PCR-based marker loci, integrates the Weissenbach markers, and extends from XG near Xpter to DXS52 near Xqter, a distance of 236 cM.