TRISOMY-15 RESCUE WITH JUMPING TRANSLOCATION OF DISTAL 15Q IN PRADER-WILLI-SYNDROME

We report a patient with Prader-Willi syndrome (PWS) and mosaicism for a de novo jumping translocation of distal chromosome 15q, resulting i n partial trisomy for 15q24-qter. A maternal uniparental heterodisomy for chromosome 15 was present in all cells, defining the molecular bas is for the PWS in this patient. The translocated distal 15q fragment w as of paternal origin and was present as a jumping translocation, invo lving three different translocation partners, chromosomes 14q, 4q, and 16p. The recipient chromosomes appeared cytogenetically intact and in terstitial telomere DNA sequences were present at the breakpoint junct ions. This strongly suggests that the initial event leading to the tra nslocation of distal 15q was a non-reciprocal translocation, with fusi on between the 15q24 breakpoint and the telomeres of the recipient chr omosomes. These observations are best explained by a partial zygotic t risomy rescue and comprise a previously undescribed mechanism leading to partial trisomy.