Direct duplication 12p11.21-p13.31 mediated by segmental duplications: a new recurrent rearrangement?

We describe the characterization of an interstitial duplication of 12p, dup(12)(p11.21p13.31), by array-CGH and FISH in a patient with mental retardation and dysmorphic features. The sequence analysis of the breakpoints revealed the presence of homologous low copy repeats (LCRs) flanking the duplication region, thus suggesting that they have mediated the rearrangement. Pip-maker analysis showed that a third cluster of homologous LCRs lie distally to the two mediating the 12p duplication. We hypothesize that this duplication might be a new recurrent rearrangement and that, thanks to the different orientations of the homologous regions lying within each cluster, the three clusters are responsible for at least some of the several 12p aneuploidies reported in the literature such as direct and inverted duplications, deletions and supernumerary analphoid chromosomes. Moreover, we excluded that polymorphic inversions between these three clusters are present in the normal population.