ISOLATION AND MAPPING OF DISCRETE DXS101 LOCI IN XQ22 NEAR THE X-LINKED AGAMMAGLOBULINEMIA GENE LOCUS

The X-linked agammaglobulinaemia (XLA) gene locus has previously been mapped to Xq22 in genetic linkage studies, The DXS101 locus has shown no recombinations with XLA in the ten informative meioses investigated so far. The DXS101 sequence, recognised by the cX52.5 plasmid, is mod erately repeated in Xq22. We have isolated cosmids which contain this sequence; two copies of which have been found to lie near DXS178 and X LA, and a third copy which lies near the PLP gene, distal to these loc i. We have used the cosmids to generate probes which should be of use for RFLP analysis, and thus in both prenatal diagnosis and carrier tes ting for XLA, and in constructing a genetic map of this re-ion. These probes will also be used to complement the genetic map in the construc tion of a complete physical map of Xq22.