Mosaic Turner syndrome: cytogenetics versus FISH

Twenty‐two cases with Turner syndrome features were subjected to standard cytogenetic techniques using giemsa trypsin (GTG‐) banding then fluorescence in situ hybridization (FISH) using a specific whole‐X chromosome painting probe, Quint‐Essential Y‐specific DNA probe (AMELY) for Yp11.2, alpha‐satellite (DYZ3) probe and X/Y cocktail‐alpha satellite probe (ONCOR) for confirmation of the initial diagnosis and comparison of the two techniques. Eight cases (36%) showed the same karyotype results by both techniques [5 cases: 45,X/46,XX, 2 cases: 45,X/46,X,i(Xq) and one case with a triple cell line 45,X/46,XX/47,XXX]. In the other 14 cases (64%) the FISH technique has identified a third cell line in 7 cases (32%), delineated the origin of the marker in 5 cases (23%) to be derivative X and clarified the deletion of the Yp11.2 region in 2 cases (9%) with the 45,X/46,XY karyotype. The application of FISH has highlighted the differences between the initial diagnosis based on the standard cytogenetic technique and the final diagnosis determined by the application of DNA probes specific for the X and Y chromosomes. FISH proved useful in detection of the low frequency cell lines which need analysis of a large number of metaphase spreads by GTG‐banding, helped in identifying the nature and the origin of the unknown markers which has an important implication in the development of gonadal tumours and delineated the deletion of the Yp11.2 region in the 45,X/46,XY Turner patients.