FISH CHARACTERIZATION OF SMALL SUPERNUMERARY MARKER CHROMOSOMES IN 2 PRADER-WILLI PATIENTS

A small supernumerary chromosome was observed in two Prader-Willi synd rome (PWS) patients, The clinical diagnosis of PWS was confirmed by th e ascertainment of the deletion of region 15q11-13 in one case and uni parental disomy (UPD) of the same region in the other, The markers wer e negative for dystamycinA/DAPI banding, did not contain NOR-positive satellites, and had an appearance consistent with a very small ring ch romosome, Fluorescent in situ hybridization (FISH) analysis with the ' 'all human centromere'' probe indicated the presence of centromeric se quences in both markers, Chromosomal in situ suppression hybridization with chromosome specific libraries demonstrated that the small marker s in the deleted and UPD patient originated from chromosome 15 and X, respectively, To the best of our knowledge these are the only PWS pati ents reported with a supernumerary marker chromosome other than inv du p(15) characterized by FISH. (C) 1997 Wiley-Liss, Inc.