Cytogenetic analysis by chromosome painting.

Chromosome painting is a term used to describe the direct visualisation using in situ hybridisation of specific chromosomes in metaphase spreads and in interphase nuclei. Chromosome painting, coupled with fluorescence in situ hybridisation (FISH), is now used routinely to enhance the identification of chromosomal rearrangements, the assignment of breakpoints, and the determination of the origin of extra chromosomal material. Amplification of small numbers of flow-sorted chromosomes by the polymerase chain reaction allows labelled chromosome paints to be generated in a matter of days. These technologies have enabled the development of reverse chromosome painting, in which the paint is produced from sorted aberrant chromosomes and hybridised back onto normal metaphase spreads to identify directly the composition of the aberrant chromosome. Reverse chromosome painting is able to identify not only the chromosomal origin of marker chromosomes but also the regions and breakpoints involved. In some cases, such as interstitial translocations and complex marker chromosomes, the combination of conventional (forward) chromosome painting and reverse chromosome painting combine to provide a definitive analysis of the rearrangement. With the availability of chromosome paints and painting kits from a variety of commercial sources, multicolour chromosome painting has now become a routine method of analysis in the clinical cytogenetic laboratory.