Frequent occurrence of translocations of the short arm of chromosome 15 to other D-group chromosomes.

The presence of DA/DAPI (distamycin A/4,6-diamino-2-phenyl-indole) heteromorphism on the short arm of human acrocentric chromosomes was investigated in 127 individuals. In 7 cases, a DA/DAPI signal was observed on an acrocentric chromosome other than 15. Subsequently, in situ hybridization (ISH) with a pericentromeric probe specific for chromosome 15 was carried out. In all 7 cases, three ISH signals were present in every metaphase, i.e., on both chromosomes 15 and on the third DA/DAPI-fluorescence-positive acrocentric chromosome (a chromosome 13 or 14), indicating that a chromosome 15 short arm was also present on these chromosomes. Therefore, we conclude that translocations of short arm sequences from chromosome 15 onto other D-group chromosomes occur frequently. Moreover, it appears that DA/DAPI staining remains specific for the short arm of chromosome 15, despite a number of recent papers suggesting otherwise.