X-MICROCHROMOSOME WITH ADDITIONAL CHROMOSOME-ANOMALIES FOUND IN ULLRICH-TURNER SYNDROME

Using standard cytogenetic methods coupled with molecular techniques, the following karyotype mos 45,X/46,XXq+/46,X+mar (X)/47,XXq+,+-mar(X) , was identified in a patient with Ullrich-Turner syndrome (UTS). High -resolution banding (n = 650) of the metaphase chromosomes yielded a b reakpoint at q28 on the Xq+ rearranged chromosome. FISH was used to de termine the presence of Y-containing DNA in the Xq+ and the mar(X) chr omosomes. The following molecular probes were used: DYZ1, DYZ3, and sp ectrum orange WCP Y. The lack of specific hybridization of these probe s was interpreted as a low risk of gonadoblastoma in this patient. Usi ng X-chromosome- and centromere-specific probes, FISH demonstrated the presence of hybridizing material on rearranged chromosomes, the Xq+ w e determined that mar(X). Finally, mar(X) and Xq+ chromosomes containe d telomeres in the absence of any interstitial telomeric hybridizing m aterial. A micro-X chromosome is present in this UTS patient. Delineat ion of events leading toward the mechanisms responsible for the multip le DNA rearrangements required to generate the micro-X and Xq+ chromos omes awaits future studies. (C) 1995 Wiley-Liss, Inc.