Interstitial deletion of chromosome 4, del(4)(q12q21.1), in a mentally retarded boy with a piebald trait, due to maternal insertion, ins(8;4).

A 17-year-old boy who was diagnosed with "Waardenburg syndrome" showed moderate growth and mental retardation. Chromosome analysis showed an apparent interstitial deletion 4q12q21.1. The mother had a direct insertion of the deleted segment into a chromosome 8. The rearrangement was confirmed to be nonreciprocal and an insertion by in situ hybridization using whole chromosome 4 and 8 painting probes. The mother's karyotype is 46,XX,ins(8;4)(q21.2;q12q21.1); that of the propositus is 46,XY, der(4)ins(8;4)(q21.2;q12q21.1)mat. This is the first report of an inherited proximal 4q deletion.