Usefulness of fluorescence in situ hybridization for the diagnosis of turner mosaic fetuses with small ring X chromosomes

Objective: To emphasize the usefulness of fluorescence in situ hybridizatio n (FISH) techniques on uncultured amniocytes for the diagnosis of abnormal mosaic karyotypes. Methods: In the course of three prenatal diagnoses, spec ific fluorescent probes, coding, respectively, for chromosomes X, Y, 18, 13 , and 21, were applied on amniocyte preparations directly after amniocentes is. At least 50 nuclei were counted in each case. Parallel to the FISH proc edure, cell cultures were set up in order to obtain karyotypes. FISH and cy togenetic results were then compared. Results: In each case, FISH showed an abnormal mosaic chromosomal constitution, 45,X/ 46,XX, which was related t o the existence of tiny ring X chromosomes in karyotypes. Conclusion: Becau se very small ring X chromosomes can escape identification when standard cy togenetic techniques are used alone, we show that misdiagnosis can be avoid ed when FISH is performed beforehand. Copyright (C) 2000 S. Karger AG, Base l.