Skin pigment anomalies and mosaicism for a double autosomal trisomy (48,XX,+18,+20).

We present a patient with profound mental retardation, epilepsy, facial dysmorphism and multiple skin hyper- and depigmentation areas. Karyotype in white blood cells was normal female, whereas in cultured skin fibroblasts originating from a depigmentated area, mosaic 48,XX,+18,+20 was found. Molecular analyses using polymorphic microsatellites showed a different origin of both additional chromosomes: maternal for the chromosome 20, paternal for chromosome 18. This, together with a mosaic state is consistent with a double postzygotic error in chromosome segregation possibly occurring in a single cell division.