Genetic analysis of mosaicism in 53 women with Turner syndrome.

Mosaicism involving the sex chromosomes is a common finding in women with Turner syndrome (TS). It is especially important to detect Y-chromosomal material, since this is a risk factor for the development of gonadoblastoma. Recent studies have also indicated that the frequency of 45,X cells may be used to predict prognosis. As part of an ongoing multi-disciplinary study, we have examined the extent of Y-chromosomal material and sex chromosomal mosaicism and its tissue specificity in 53 women with TS. The results of lymphocyte karyotyping were compared with the use of interphase X/Y fluorescence in situ hybridisation (FISH) analysis of lymphocytes and buccal mucosal cells. As could be expected, an extended FISH analysis detected more Y-chromosomal material than karyotyping (in 15% vs. 11% of the women, respectively) and also detected more X-chromosomal mosaicism among the TS women (in 70% vs. 45 % of the women, respectively). In half of the women, tissue-specific differences between lymphocytes and buccal mucosal cells were found. Based on these results, we suggest the use of X/Y interphase FISH as a complement to karyotyping in order to obtain a more complete knowledge of the chromosome constitution of each individual with TS.