Monosomy 9pter and trisomy 9q34.11qter in two sisters due to a maternal pericentric inversion

Pericentric inversions of chromosome 9 leading to unbalanced live-born offspring are relatively rare and so far only four cases have been reported. Here we present two sisters with an unbalanced recombinant chromosome 9 which resulted from a large maternal pericentric inversion inv(9)(p24.3q34.1). Further molecular characterisation of the aberrant chromosome 9 by 250k SNP array analysis showed a terminal 460kb loss of 9p24.3 and a terminal 8.9Mb gain of 9q34.11. We compared the clinical features of these two patients with the previous reported four cases as well as with patients with similar sized 9pter deletions or 9qter duplications. Based upon this study, we suggest that the recombinant chromosome 9 phenotype is mainly the result of duplication of a 3.4Mb region of chromosome 9q34.11q34.13. ► Pericentric inversion of chr 9 leading to unbalanced live-born offspring is rare. ► We molecularly characterised two new cases (sisters) with unbalanced rec chr 9. ► We compared our patients with previous patients with similar aberrations. ► We propose that the core phenotype is the result of duplication of a 3.4Mb region.