Fluorescent in situ hybridization (FISH) using X and Y chromosome-specific alpha-satellite DNA probes hybridizing to loci DXZ1 and DYZ3 was performed to identify the origin of ring/marker chromosomes in 6 patients with Ullrich-Turner syndrome (UTS). All patients had a mosaic karyotype, 5 with 45,X/46,X,r(?) and one with 45,X/46,X,mar. We demonstrated that the marker/ring chromosome in each of these 6 patients originated from the X. A timely knowledge of the X or Y origin of ring and marker chromosomes can be crucial in genetic counseling and medical management since the presence of Y chromosome material in phenotypic females is known to increase the risk for developing gonadoblastoma.
