A further inv dup/del 9p de novo rearrangement. Reappraisal of 25 instances

• We describe an inv dup/del 9p de novo chromosome and compile 24 similar cases.
• The imbalances' size falls within the observed ranges in 20 previous patients.
• der(9) chromosomes likely arise from a U-type reunion between sister chromatids.
• These der(9) mostly arise prezygotically from the paternal or maternal homolog.

Over 20 patients with an inv dup/del 9p de novo rearrangement have been described. We report on a similar der(9) found in a mildly affected girl and summarize the cytogenetic findings in 25 patients. The patient's G-banded karyotype was 46,XX,add(9)(p23) de novo with the extra segment being interpreted as a 9p23 → p13 inverted duplication. FISH assays revealed that the rearranged chromosome was entirely painted by a WCP probe, lacked 9p subtelomeric repeats, and had two BAC RP11-795C14 (mapping at 9p13) signals, one proximal and one terminal. aCGH using a 4x180K Microarray Kit from Agilent confirmed a terminal deletion of ~ 12.5 Mb in 9p24.3p23 (204,193-12,455,192)x1 and an immediately adjacent duplication of ~ 21.3 Mb involving 9p13.3p23 (12,490,471-33,777,844)x3. The inverted duplication disclosed by the BAC probe and the absence of an intercalary single copy region between both imbalances, are consistent with an intrachromosomal U-type reunion. Moreover, the imbalances' size falls within the observed ranges in 20 previous patients. The rea(9) was always de novo (n = 23 parental couples) and involved either the paternal (3 cases) or the maternal (2 cases) homolog.