Analysis of nucleolar organizing regions in parents of trisomic spontaneous abortions.

Nucleolar organizing region (NOR) variants of parents of karyotyped spontaneous abortions were examined to test the hypothesis that double NORs are important in the genesis of acrocentric trisomies. We were unable to detect any significant difference in the frequency or types of NOR variants between parents of acrocentric trisomies and parents of other types of spontaneous abortions, nor did we identify a double NOR in either group. Thus, it seems unlikely that double NORs are of major significance in the etiology of acrocentric trisomies.