FISH mapping of the sex-reversal region on human chromosome 9p in two XY females and in primates

Accumulating evidence suggests that haploinsufficiency of a dosage-sensitiv e gene(s) in human chromosome 9p24.3 is responsible for the failure of test icular development and feminisation in XY patients with monosomy for 9p. We have used molecular cytogenetic methods to characterise the sex-reversing 9p deletions in two XY females. Fluorescence in situ hybridisation (FISH) w ith YACs from the critical 9p region containing an evolutionarily conserved sex-determining gene, DMRT1, is a very fast and reliable assay for patient screening. Comparative YAC mapping on great ape and Old and New World monk ey chromosomes demonstrated that the critical region was moved from an inte rstitial position on the ancestral primate chromosome to a very subtelomeri c position in chimpanzee and humans by a pericentric inversion(s). Patholog ical 9p rearrangements may be the consequence of an evolutionary chromosome breakpoint in close proximity to the sex-reversal region.