APA Dictionary of Psychology

a congenital spectrum disorder marked by short stature, hypotonia (flaccid muscles), hypogonadism (underdeveloped sex organs), obesity, insensitivity to pain, short hands and feet, mild to moderate intellectual impairment, and learning disabilities. Most cases (about 70%) occur when a segment of the paternal chromosome 15 is deleted in each cell. Another 25% of cases have two copies of the maternal chromosome 15 instead of one copy from each parent. Affected individuals have an excessive appetite and are constantly eating. When diabetes mellitus is associated with the condition, it is called Royer’s syndrome. Also called Prader–Labhart–Willi syndrome; Prader–Labhart–Willi–Fanconi syndrome. [reported in 1956 by Andrea Prader (1919–2001) and Heinrich Willi (1900–1971), with Alexis Labhart (1916–1994), Swiss pediatricians]