IDENTIFICATION OF SUPERNUMERARY DER(20) CHROMOSOMES BY FISH IN 3 PATIENTS

Small supernumerary marker chromosomes of 3 patients were characterize d at the molecular cytogenetic level, Two ring chromosomes and one met acentric marker were shown to be distamycinA/DAPI-negative and did not possess satellite regions after conventional banding techniques. Fluo rescence in situ hybridization (FISH) was performed and in all 3 cases the supernumerary markers were shown to be derived from chromosome 20 , Phenotypes are described and discussed with respect to karyotypes, T wo of the patients are developmentally and/or phenotypically normal. T he first patient has a ring chromosome, containing a small amount of e uchromatic material; the second patient is the carrier of a small, met acentric and most probably heterochromatic marker, Patient 3 has physi cal anomalies, including a congenital heart defect and delayed motor d evelopment, but is intellectually almost normal. His marker chromosome is a ring containing a small amount of euchromatic material. (C) 1997 Wiley-Liss, Inc.