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 hybridization (FISH) techniques on uncultured amniocytes for the diagnosis of abnormal mosaic karyotypes.
Methods: In the course of three prenatal diagnoses, specific fluorescent probes, coding, respectively, for chromosomes X, Y, 18, 13, and 21, were applied on amniocyte preparations directly after amniocentesis. At least 50 nuclei were counted in each case. Parallel to the FISH procedure, cell cultures were set up in order to obtain karyotypes. FISH and cytogenetic results were then compared.
Results: In each case, FISH showed an abnormal mosaic chromosomal constitution, 45,X/46,XX, which was related to the existence of tiny ring X chromosomes in karyotypes.
Conclusion: Because very small ring X chromosomes can escape identification when standard cytogenetic techniques are used alone, we show that misdiagnosis can be avoided when FISH is performed beforehand.
(Copyright 2000 S. Karger AG, Basel.)