FISH studies of the sperm of fathers of paternally derived cases of trisomy 21: no evidence for an increase in aneuploidy

Paternal nondisjunction accounts for approximately 5% of cases of trisomy 2 1. To test the hypothesis that, in some such cases, the fathers might be pr edisposed to meiotic nondisjunction, we utilized fluorescence in situ hybri dization (FISH) to screen for aneuploidy in sperm. We analyzed sperm sample s from ten males with a trisomy 21 offspring of paternal origin. Among thes e individuals, the overall frequency of disomy 21 was 0.15%, comparable to estimates of disomy 21 in the general male population. Furthermore, none of the ten fathers of trisomy 21 individuals had significantly elevated level s of disomic sperm. Thus, our results provide no evidence that the occurren ce of a trisomy 21 conceptus of paternal origin imparts an increased risk o f trisomy in subsequent pregnancies.