Chromosome painting using FISH (fluorescence in situ hybridization) with chromosome-6-specific library demonstrates the origin of a de novo 6q+ marker chromosome.

We report the application of chromosome painting using FISH (fluorescence) in situ hybridization) to demonstrate the origin of a de novo 6q+ marker chromosome. A girl with a mental retardation/multiple malformation syndrome was shown to have the karyotype 46,XX, 6q+. Banding analysis could not determine the origin of the extra chromosomal material. Using FISH with a chromosome-6-specific library we showed that the marker chromosome was completely painted, indicating an origin from chromosome 6. The child's phenotype was compared with previously reported cases with partial chromosome 6 trisomy. A clinically recognized syndrome emerged, although she apparently also demonstrated novel features.