Prader-Willi Syndrome Prader-Willi Syndrome is a serious genetic disorder that begins at birth with no known cure ; causing mental retardation,short stature,low muscle tone,incomplete sexual development,and its main charecteristic,the desire to eat everything and anything in sight. Prader-Willi syndrome was first known as Prader-Labhart-Willi Syndrome after three Swiss doctors who first described the disorder in 1956. The doctors described a small group of kids with obesity, short stature and mental deficiency , neonatal hypotonia (floppiness) and a desire to constantly eat because they are always hungry.