Classical Prader-Willi syndrome with trisomy 15(pter----q12) plus de novo variant 15p11.

We describe a boy with the classical Prader Willi syndrome (PWS), clinically, who had a chromosome abnormality not previously described in PWS. The karyotype was 47,XY,+mar, var(15)(p11). The marker was a fragment of 15 from 15pter----q12 and the variant 15p11 was de novo in origin. Overall, this karyotype contains increased 15 heterochromatin and we discuss alteration in the amount of 15 heterochromatin in PWS.