FINE MAPPING OF THE HUMAN SCIDX1 LOCUS AT XQ12-13.1

Previous linkage analysis of families with X-linked severe combined im munodeficiency (SCIDX1) mapped this locus to a large region encompassi ng about 10 to 20 cM at Xq12-21. We have analyzed in SCIDX1 families t he segregation of 7 highly polymorphic microsatellites repeats localiz ed to this region, including a new polymorphic microsatellite at the D XS135 locus described in this study, to refine the mapping of this dis ease locus. The observations of genetic recombinants within the previo usly defined SCIDX1-region allow us to establish new flanking markers at the DXS135 and DXS227 loci, which significantly reduce the region h arboring the SCIDX1 locus to a distance estimated between 3 to 5 cM. T he existence of multiple, highly polymorphic markers in the refined SC IDX1 region will greatly improve the accuracy of carrier detection and prenatal diagnosis for SCIDX1.