FISH characterization of dynamic mosaicism involving an inv dup(15) in a patient with mental retardation

We report on a man with mental retardation and a complex karyotype with cel ls containing up to three morphologically distinct supernumerary marker chr omosomes (SMCs) in most metaphases. Fluorescence in situ hybridization stud ies using chromosome 15-specific probes characterised the presence of seven SMCs all derived from chromosome 15. The results suggest that the patient originally had a large inv dup(15) containing two copies of the Prader-Will i/Angelman critical region which became mitotically unstable, and by a proc ess of dynamic mosaicism various morphologically distinct SMCs arose. (C) 2 001 Wiley-Liss, Inc.