DELINEATION OF A RING CHROMOSOME-16 BY THE FISH-TECHNIQUE - A CASE-REPORT WITH REVIEW

We report on a new case with ring chromosome 16. Initially, the cytoge netic findings with GTG-banding revealed a 46,XY,r( 16)(::p13.3-->q24: :)/46,XY karyotype. This is the first case of r(16) co-existing with a normal cell line with minimal clinical consequences. The ring appeare d to be monocentric and stable. A ring chromosome can result in a loss of varied segments of one or both chromosome arms or may involve telo mere-telomere fusion without loss of genetic material. Thus it was imp erative to use the latest molecular cytogenetic techniques for evaluat ion of this ring chromosome. It is believed that the ring chromosome r etained specific telomeric sequences unique to 16q and that there was no loss of genetic material during the ring formation. Apparently, eit her a 16p telomere-16q telomere fusion or a fusion between the 16q tel omere and a distal segment of the 16p13 band may explain the mechanism of ring formation. In either case, loss of genetic material is assume d to be negligible. A more descriptive karyotype of the proband was de termined to be: 46,XY,r(16)(::pter or ::p13.3-->qter::)/46,XY. The flu orescent in-situ hybridization technique using various DNA probes prov ided this finer characterization.