Nucleolus organizer region heteromorphism in patients with Down syndrome and their parents.

ABSTRACT

The study aimed to evaluate the role of nucleolus organizer region (NOR) heteromorphism as an etiological factor for parental nondisjunction in Down syndrome by comparing 25 patients affected by Down syndrome, and their parents with a control group of 80 non-affected Egyptians. All parents had normal karyotypes. The average modal number per parent of Ag-positive NORs was significantly higher in parents than controls. A significant difference in the size of the double-NOR variants (dNORs) was found. The mean maternal and paternal ages were significantly lower, with a significant increase in spontaneous abortions, for dNOR(+) couples compared with dNOR(-) couples.