Prader–Willi Syndrome (PWS) a is genetic disorder caused by a loss of function of specific genes on chromosome 15. At birth, individuals will have muscle weakness, failure to feed, and slowed development. Characteristic hyperphagia begins in childhood, and children become at high risk for obesity and type 2 diabetes. Individuals have marked mild to moderate intellectual impairment and behavioural difficulties throughout the lifespan.
No risk factors are known for the disorder. Parents of children with PWS have a less than a 1% chance of another child with PWS.