20-Mb duplication of chromosome 9p in a girl with minimal physical findings and normal IQ: narrowing of the 9p duplication critical region to 6 Mb.

We studied the case of a girl with a partial 9p duplication, dup(9)(p22.1 --> p13.1). Molecular cytogenetics studies defined the chromosome 9 rearrangement as a direct duplication of 20 Mb from D9S1213 to D9S52. Microsatellite analysis demonstrated the presence of a double dosage of the paternal alleles and demonstrated that the duplication occurred between sister chromatids. The patient's phenotype was almost normal, with a few minor anomalies (dolichocephaly, crowded teeth, high arched palate) and normal IQ. The breakpoint's location in this patient and previously reported cases suggest that the critical region for the 9p duplication syndrome lies within a 6-Mb portion of chromosome 9p22 between markers D9S267 and D9S1213.