In order to reveal if there is an effect on the genesis of meiotic‐ or early zygotic non‐disjunctions, data related to 1598 Down syndrome patients from 1578 families studied in five different genetic centers in Turkey are reported. Parental consanguinity and the inbreeding coefficient were found to be lower among patients of 21‐trisomics than in parents without Down offspring. It was concluded that available information does not support the presence of a “non‐disjunction gene” in man.

No abstract