Familial adenomatous polyposis in a patient with unexplained mental retardation.

Background: A 22-year-old woman was referred to a genomic medicine clinic for evaluation of suspected Prader-Willi syndrome (PWS) after normal DNA methylation studies on chromosome 15 were obtained. Features suggestive of PWS included mental retardation, short stature, obesity, hypotonia, and small hands and feet. The patient, however, lacked many PWS-defining behavioral features, including hyperphagia, compulsive skin picking, and food-seeking behaviors.