Prader Willi ... It's the lack of cognitive control that causes them to eat more  No. Most mentally retarded people have ordinary body weights. People suffering from Prader-Willi syndrome have their hunger signals permanently turned up to 11. They respond to food the way an addict responds to cocaine: fanatical obsession. Their caretakers have to lock them up, and keep all food under lock and key. They break into neighbor's houses to eat. They eat out of dumpsters if left unsupervised. They climb into the roof and try to tunnel down into the pantry from above. They eat until their stomachs burst. They eat until they are too heavy to walk, and then start eating the walls and furniture within reach. This is not a lack of cognitive control. It takes a noticeable amount of smarts and planning to attack the pantry from the roof. Their defect is in the goal seeking drive. Angelman syndrome involves the opposite genetic defect to Prader-Willi. They also have a defect of goal seeking drive. Curiously they have normal body weights. Their obsession is listening to music. Many of them are enthralled by music.