Neocentric small supernumerary marker chromosomes (sSMC)--three more cases and review of the literature.

Here we report on three new patients with neocentric small supernumerary marker chromosomes (sSMC) derived from chromosome 2, 13 and 15, respectively. The sSMC(13) and sSMC(15) had inverted duplicated shapes and the sSMC(2) a ring chromosome shape. All three cases were clinically severely abnormal. A review of the available sSMC literature revealed that up to the present 73 neocentric sSMC cases including these three new cases have been reported. Seven of these cases were not characterized morphologically; in the remainder, 80% had an inverted duplication, 17% a ring and 3% a minute shape. 81% of the reported neocentric sSMC carriers showed severe, 12% moderate and 8% no clinical abnormalities. In summary, we report three more neocentric sSMC cases, provide a review on all up to now published cases, highlight their special characteristics and compare them to centric sSMC.