Prader–Willi syndrome is also frequently associated with an extreme and insatiable appetite, often resulting in morbid obesity. There is currently no consensus as to the cause for this particular symptom, although genetic abnormalities in chromosome 15 disrupt the normal functioning of the hypothalamus. Given that the hypothalamus regulates many basic processes, including appetite, there may well be a link. However, no organic defect of the hypothalamus has been discovered on post mortem investigation.
Prader–Willi syndrome patients have high ghrelin levels, which are thought to directly contribute to the increased appetite, hyperphagia, and obesity seen in this syndrome. Cassidy states the need for a clear delineation of behavioural expectations, the reinforcement of behavioural limits and the establishment of regular routines.
The main mental health difficulties experienced by people with PWS include compulsive behaviour (usually manifested in skin-picking) and anxiety. Psychiatric symptoms, for example, hallucinations, paranoia and depression have been described in some cases and affect approximately 5–10% of young adults.Psychiatric and behavioural problems are the most common cause of hospitalization.