Ectopic NORs on human chromosomes 4qter and 8q11: rare chromosomal variants detected in two families

Two different NOR bearing non-acrocentric chromosomes were detected during prenatal diagnosis performed on two probands because of advanced maternal a ge. In the first case, a chromosome 4 carried a NOR in the telomeric region of the long arm (4qs), while in the second case a NOR was inserted into ch romosome 8q11. Family analysis showed the variant chromosomes to be transmi tted through at least three generations in each family. There were no repor ts of reproductive problems or phenotypic effects in the carriers of these chromosomes, indicating the benign character of the aberrant chromosomes. I n order to characterise the chromosomal variants more precisely, various di fferential banding techniques were applied.