Sex differentiation and development are complex processes reflecting the precise spatiotemporal expression of specific genes and interactions among gene products. In some instances, peripheral blood karyotype diverges from anticipated findings based on phenotypic features. Ascertaining for chromosomal mosaicism aids the shared decision-making discussions with families and other health care providers. We have investigated for sex chromosome mosaicism in 13 patients by using fluorescence in-situ hybridization (FISH) on cells obtained from urine samples (5/13), cord blood (1/13), and uncultured peripheral blood (6/13). We compared cultured peripheral blood sample results to FISH results.
Twelve of thirteen patients had female phenotype. FISH analysis on uncultured peripheral blood cells identified 45,X cell line in 5 patients with normal 46,XX karyotype on cultured blood cells. In 2 patients, the percentage of mosaicism was higher from the FISH analysis on uncultured cells than cultured peripheral blood cells. One phenotypically female patient with 46,XY cell line on cultured peripheral blood cells had absence of SRY in 64.2% of uncultured urine cells indicating loss of Y chromosome or deletion of SRY gene among urine cells. Two phenotypic female patients with 46,XY karyotype had a 45,X cell line. One phenotypically male patient with 45,X karyotype on NIPT was found to have three other cell lines with the derivative Y chromosome markers in uncultured cord blood and urine cells. FISH testing resolved the sex chromosomal complement that was discrepant with the results of peripheral blood analysis.
Genetically abnormal cell lines dwindle and fail to survive in cell culture which contributes to underrepresentation of mosaicism in cultured cells. Therefore FISH studies on the uncultured cells are essential to establish a definitive diagnosis. Mosaicism is not always uniform throughout the body; somatic mutations can result in tissue specific mosaicism. These variations may contribute to the disparity in phenotype-genotype correlations among children with DSD and may impact clinical management. In our study, results obtained from urine samples appeared to better represent the percentage of mosaicism in gonadal tissues. Thus, this noninvasive method with direct genetic analysis of urinary epithelial cells may be helpful because urinary tract cells share similar embryonic origins with gonads.
19 Sep 2019 - 21 Sep 2019