Centric fission of chromosome 9 in a boy with trisomy 9p

A centric fission of chromosome 9 was found in a boy with trisomy 9p resulting from a de novo del (9p) and a 9p isochromosome. The patient presented with clinical findings similar to those described in previously reported cases of trisomy 9p. The cytogenetic evaluation and the molecular analysis using fluorescence in situ hybridization (FISH) with specific alphoid probe for chromosome 9 showed a karyotype of 47,XY,+del(9)(q10),+i(9p). We suggest that the mechanism leading to this situation is unusual.