Mosaic supernumerary ring chromosome 19 identified by comparative genomic hybridisation.

We report the use of comparative genomic hybridisation (CGH) to define the origin of a supernumerary ring chromosome which conventional cytogenetic banding and fluorescence in situ hybridisation (FISH) methods had failed to identify. Targeted FISH using whole chromosome 19 library arm and site specific probes then confirmed the CGH results. This study shows the feasibility of using CGH for the identification of supernumerary marker chromosomes, even in fewer than 50% of cells, where no clinical or cytogenetic clues are present.