X microchromosome with additional chromosome anomalies found in Ullrich‐Turner syndrome

Abstract

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 breakpoint at q28 on the Xq+ rearranged chromosome. FISH was used to determine the presence of Y-containing DNA in the Xq+ and the mar(X) chromosomes. The following molecular probes were used: DYZ1, DYZ3, and spectrum orange WCP Y. The lack of specific hybridization of these probes was interpreted as a low risk of gonadoblastoma in this patient. Using X-chromosome- and centromere-specific probes, FISH demonstrated the presence of hybridizing material on both rearranged chromosomes, the Xq+ and mar(X). Finally, we determined that the mar(X) and Xq+ chromosomes contained telomeres in the absence of any interstitial telomeric hybridizing material. A micro-X chromosome is present in this UTS patient. Delineation of events leading toward the mechanisms responsible for the multiple DNA rearrangements required to generate the micro-X and Xq+ chromosomes awaits future studies.

Evidence that skewed X inactivation is not needed for the phenotypic expression of Aicardi syndrome

“…However, cases have been reported in which a segment of the X chromosome inappropriately escapes the usual X-inactivation process. They have significant mental retardation and severe congenital malformation (Callen et al 1995;Cole et al 1994;Duncan et al 1993;Jani et al 1995;Kushnick et al 1987;Lindgren et al 1992;Migeon et al 1994;Wolff et al 1994;Wydner et al 1995). In 122 cases of balanced X autosome translocation in females , the derivative X was the active one in all cells analyzed in 77% of the cases.…”

Characterization and clinical implications of marker chromosomes identified at prenatal diagnosis

“…It is well documented that de®cient transcription of the XIST gene in females with small ring X chromosome is associated with severe phenotypes (Migeon et al, 1993(Migeon et al, , 1994Wydner et al, 1995). Therefore, determining the presence or absence of the XIST gene on small ring X chromosomes is of signi®cant value in predicting their phenotypic consequences.…”