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

      Ismail, S.R.; Mokhtar, M.M.; Kotb, S.M.; Nazmy, N.A. (‏1999)‏
      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 ...