Skin pigmentary anomalies and mosaicism for an acentric marker chromosome originating from 3q

We report on a 22 year old man with hyperpigmentation distributed along the lines of Blaschko in whom cytogenetic analysis showed mosaicism for an unu sual supernumerary marker chromosome. The patient was of normal intelligenc e and was not dysmorphic. The marker was present in 30% of his lymphocytes and in 6% of his skin fibroblasts fi om a dark area, while fibroblasts from a light area showed a normal karyotype, 46,XY. We have identified the orig in of the marker using fluorescence in situ hybridisation (FISH) with whole chromosome painting probes and YAC specific clones. The marker was found t o consist of duplicated chromosome material from the distal part of chromos ome 3q and was interpreted as inv dup(3)(qter-->q27.1::q27.1-->qter). Hence , this marker did not include any known centromeric region and no alpha sat ellite DNA could be detected at the site of the primary constriction. The p atient was therefore tetrasomic for 3q27-q29 in the cells containing the ma rker chromosome. We postulate that, in our case, pigmentary anomalies may r esult directly from the gain of specific pigmentation genes localised on ch romosome 3q.