A Neocentric Isochromosome Yp Present as Additional Small Supernumerary Marker Chromosome – Evidence against U-Type Exchange Mechanism?

Abstract

Here we report the first case of an inverted duplicated neocentric small supernumerary marker chromosome present in a karyotype 47,XX,+mar(Y). As expected a partial disomy of Ypter to Yp11.2 did not lead to any major malformations. However, the formation of an inverted duplicated chromosome from a Y chromosome is not possible by a U-type exchange, as has been suggested for such kind of neocentric marker chromosomes. Thus, some evidence is here provided that this concept might not always be true.