Directly inherited partial trisomy of chromosome 6p identified in a fatherand daughter by chromosome microdissection

Cytogenetic analysis of a 4 year old girl with developmental delay and dysm orphic features showed extra chromosomal material of unknown origin on 20p (46,XX,add(20) (p13)). Familial chromosome studies showed direct inheritanc e of add(20)(p13) from the father, who had a similar, albeit milder, phenot ype. Fibroblast chromosome studies of the father showed no karyotype mosaic ism. The additional material could not be identified on the basis of the G banding pattern owing to its small size and ambiguous banding pattern. Chro mosome microdissection of the unknown material was performed, the DNA was a mplified and labelled using degenerate oligonucleotide primed polymerase ch ain reaction (DOP-PCR) and reverse painted to the proband's cells to show t he karyotype 46,XX, der(20)t(6;20) (p23;p13), conferring partial trisomy 6p and presumed partial monosomy for 20p. Chromosome microdissection has made possible the first reported case of directly inherited partial trisomy 6p.