Duplication of proximal 15q as a cause of Prader-Willi syndrome.

We describe an apparent duplication of proximal 15q, i.e., 15q11q12 or 15q12q13 in two patients. Prometaphase chromosome analysis, C-banding and distamycin A/DAPI staining were used to exclude a translocation between the abnormal 15 homolog and another chromosome. The 2 patients have many manifestations of the Prader-Willi syndrome (PWS) including at least 5 of the following: obesity, compulsive eating, mental retardation, short stature, central hypotonia, hypogonadism, small hands and feet, hypopigmentation, and feeding problems in infancy. Results of high resolution chromosome analysis of the parents of both patients were normal. A comparison between these patients and 2 subjects from previous reports demonstrates phenotypic heterogeneity among the duplication 15q PWS patients. Two patients have the hypopigmentation seen in chromosomally normal and deletion PWS patients. These cases add to the variety of chromosome 15 aberrations which are associated with PWS.