Down's syndrome in Kuwait: Recurrent familial trisomy 21 in sibs

Objective: To study the families with recurrent trisomy 21 in sibs, and to understand the increased risk of recurrence in some selected Families. The importance of parental mosaicism as a cause for non-disjunction or the possibility of genetic predisposition to nondisjunction is addressed. Methods: Three young unrelated Kuwaiti families each confirmed to have 3 sibs with regular trisomy 21 were investigated. Detailed chromosome analysis of the peripheral blood culture in Down's syndrome children and their parents was carried out. At least 100 cells in each of the cases were scored to exclude low grade mosaicism. Results: Regular trisomy 21 was confirmed in all the sibs in the three families. Mosaicism was not detected in parents. However, gonadal tissue mosaicism could not be excluded, as it is not practical to study the gonadal biopsy in the parents. Conclusion: Though parental mosaicism (gonadal, more often maternal), has been reported in familial recurrent trisomy 21 cases, no mosaicism could be confirmed in our study. Our finding suggests that the possibility of a genetic predisposition to non-disjunction parental mosaicism should be considered in counselling families having sibs with trisomy 21.