Prader-Willi syndrome (PWS) is a non-inherited genetic condition that happens as the result of a spontaneous mutation at the time of conception. There is nothing parents do that causes it and no practical way to prevent it.
Symptoms occur across a spectrum, with some individuals being more affected than others. Primary symptoms include an overwhelming desire to over-eat and a substantial risk for the development of obesity that starts in childhood. People with PWS often have cognitive, motor and language delays. There are distinct behaviors commonly associated with PWS. They can include temper tantrums, stubbornness, manipulation, and obsessive compulsive behaviors. People with PWS vary greatly in medical complexity, intelligence, and behaviors.
Although the cause is complex, PWS results from an abnormality on the 15th chromosome. It occurs in males and females equally and in all races. Prevalence estimates have ranged from 1:8,000 to 1:25,000 with the most likely figure being 1:15,000.