Multi-locus (ML)-FISH is a reliable tool for nondisjunction studies in human oocytes.
In the present study, we developed a fluorescence in situ hybridization (FISH) strategy, which allows a reliable determination of the chromatid number of specific chromosomes in mature human oocytes. 168 unfertilized oocytes were analyzed by dual-color FISH with two direct-labeled locus-specific DNA probes for chromosome 13 and 21. To exclude FISH failures, metaphases with abnormal signal patterns were reanalyzed by multi-locus-FISH (ML-FISH) for chromosome 13 and 21. Following dual-color FISH, abnormal signal patterns were detected in 21 out of 108 metaphases (19.4%). 17 of these metaphases were reanalyzed by ML-FISH. In contrast to the first FISH, seven metaphases showed normal signal patterns after rehybridization, whereas ten metaphases remained abnormal. Out of these real aneuploid metaphases, five showed gain or loss of a single signal (= chromatid), two showed missing double signals (= chromosome) and three showed both. In conclusion, locus-specific FISH probes facilitate differentiation between first meiotic nondisjunction of whole chromosomes and prematurely divided chromatids. Moreover, simultaneous hybridization with a second locus-specific probe on the same chromatid (ML-FISH) helps to differentiate between FISH failures and real meiotic division errors and therefore, allows a more reliable analysis of aneuploidies in human oocytes.
Eckel
H
H
Clinic for Reproductive Medicine and Gynecological Endocrinology, Magdeburg, Germany. Heike.Eckel@Medizin.Uni-Magdeburg.de
Kleinstein
J
J
Wieacker
P
P
Stumm
M
M
D000328:Adult; D000782:Aneuploidy; D002842:Chromatids / Q000648:ultrastructure; D002882:Chromosomes, Human, Pair 13 / Q000648:ultrastructure; D002891:Chromosomes, Human, Pair 21 / Q000648:ultrastructure; D003116:Color; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods*; D008677:Metaphase; D009630:Nondisjunction, Genetic; D009865:Oocytes / Q000648:ultrastructure*