Interchromosomal duplication for the short arm of chromosome no. 9: report of three cases due to a familial translocation t(9; 11) and one case with a de novo 47, XX, +9p karyotype.

Four cases of the 9p duplication syndrome are described. Three affected sibs resulted from a maternal t(9;11) translocation and have a duplication of the segment 9p13 leads to 9pter. They have the typical facies, hands and other features of the syndrome but are relatively mildly retarded. The fourth case has a de novo duplication of the short arm of chromosome 9. Her features are also typical although she is more retarded, particularly in expressive speech, than the other three individuals and had club feet. These observations further confirm the distinctive clinical features of this type of duplication, and support previous suggestions that the severity is roughly correlated with the length of the duplicated segment.