FISH analysis helps identify low-level mosaicism in Ullrich-Turner syndrome patients

Abstract

Purpose: To search for X or Y chromosome mosaicism in 45,X individuals using fluorescent in situ hybridization (FISH). Methods: From our series of 53 Ullrich-Turner syndrome patients, we used interphase FISH to evaluate the 19 who had an apparently nonmosaic 45,X karyotype with G-banding. Results: Of those 19 patients, mosaicism was detected in seven (37%), five patients had an XX line, one had a monocentric isochromosome X, and one had The incidence of Ullrich-Turner syndrome (UTS) is approximately one in 3000 newborn girls and is associated with an apparently nonmosaic 45,X karyotype in many of these patients. 1 Fewer than 15% of UTS patients appear to have mosaicism with a 46,XY cell population or a Y chromosome rearrangement, and 30 -50% are mosaic with a second X or a structurally abnormal X. Up to 18% of patients have a small marker chromosome in some cells, the origin of which can be identified by FISH or other methods. 2 The mosaic status of the remaining UTS patients remains uncertain but of clinical interest because if they do have cells with a Y chromosome, they may have an increased risk of gonadoblastoma. The American College of Medical Genetics recommends cytogenetic analysis of 30 metaphase cells in cases studied to rule out sex chromosome mosaicism. 3 This analysis can identify 10% mosaicism with a confidence level of 95%, but a more sensitive level of detection would require costly analysis of many more metaphase cells. PCR-based assays can be used to identify low-level mosaicism but has limitations 4 -7 including a high rate of falsepositive results with nested PCR. 8,9 In this study, we report the results of karyotype and FISH analysis in 53 patients with monosomy X or monosomy X mosaicism. MATERIALS AND METHODSBetween January 1997 and August 2003, we studied 53 samples submitted for karyotype analysis based on phenotypic features suggestive of UTS in which the karyotype results included a 45,X cell line. We excluded females suspected of having UTS who had a nonmosaic 46,XX karyotype. Several blood samples were sent to confirm a prenatal diagnosis of UTS were included.G-banded metaphase analysis from PHA-stimulated lymphocyte cultures was performed. A minimum of 30 metaphase cells was analyzed in cases with a nonmosaic 45,X karyotype, or a minimum of 20 metaphase cells when mosaicism was identified by the 20th cell.FISH testing was performed on all 19 cases with an apparently nonmosaic 45,X karyotype. Using centromere probes for the X (DXZ1) and Y chromosomes (DYZ3) (Vysis, Inc., Downer's Grove, IL), a minimum of 200 interphase cells were scored. A male control was hybridized concurrently with each sample and the intensity of the Y signal was used to discriminate between a true "Y" signal and an artifact signal. If the initial analysis was equivocal (one cell with both X and Y signals), an additional 300 cells were analyzed. Cases demonstrating one XX signal (of 200 cells) or one XY signal (of Ͼ 500 cells) were considered nonmosaic, whereas those with Ͼ 1% XX cells were identified as true mosa...

Detection of low level sex chromosome mosaicism in Ullrich–Turner syndrome patients

“…Combining results of our current study and those of a previously published study [Wiktor and Van Dyke, 2004], we report results of FISH analysis on 69 UTS patients including 41 females with a non-mosaic 45,X karyotype. Our original publication identified seven patients with mosaicism but the validation for that study was not a complete as the current study.…”

Small Supernumerary Marker Chromosomes (sSMC) in Patients with a 45,X/46,X,+mar Karyotype – 17 New Cases and a Review of the Literature

“…Surprisingly, there is a third possibility -two sSMC T (0.4%) that were not derived from one of the gonosomes, but from an autosome are reported in the literature. Wiktor and Van Dyke [2004] report on one case in which the sSMC T did not stain with centromeric probes for the X or Y chromosome, and Gray et al [2001] identified an sSMC T derived from chromosome 20. Thus, this third subgroup might be an underestimated entity among sSMC T cases.…”

A case report of successful pregnancy in a patient with pure 46,XY gonadal dysgenesis

“…The American College of Medical Genetics recommends cytogenetic analysis of 30 metaphase cells, which will identify at least 10% mosaicism with 95% confidence (14). However, when there is reason to suspect lower level mosaicism, as in patients with short stature, more thorough evaluation by fluorescence in situ hybridization (FISH) should be performed to achieve greater sensitivity for detection of an occult mosaic 45,X cell line (15,16). In the patient reported here, FISH was not performed, based on the patient's classic presentation, height, surgical findings, and karyotype.…”