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 cytogenetic 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 appeared 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 telomere-telomere fusion without loss of genetic material. Thus it was imperative to use the latest molecular cytogenetic techniques for evaluation of this ring chromosome. It is believed that the ring chromosome retained specific telomeric sequences unique to 16q and that there was no loss of genetic material during the ring formation. Apparently, either a 16p telomere-16q telomere fusion or a fusion between the 16q telomere and a distal segment of the 16p13 band may explain the mechanism of ring formation. In either case, loss of genetic material is assumed to be negligible. A more descriptive karyotype of the proband was determined to be: 46,XY,r(16)(::pter or ::p13.3-->qter::)/46,XY. The fluorescent in-situ hybridization technique using various DNA probes provided this finer characterization.