Mental retardation is common. It can be caused by a deletion of chromosome 15 inherited from the father; the same deletion inherited from the mother causes Angelman's syndrome which is an autosomal recessive syndrome characterized by jerky puppetlike movements, frequent laughter, mental and motor retardation; as well as, peculiar open-mouthed faces, and seizures.
Andrea Prader and Heinrich Willi were Swiss pediatricians. Prader was a professor of pediatrics in Zurich. His articles and chapters in textbooks dealt with such topics as genetics, growth, endocrinology, and metabolism in children and adolescents. Prader and Willi first described the Prader-Willi syndrome in 1956. Cases of the disorder were not diagnosed in the United States until the 1960s.