Prader-Willi syndrome and hyperphagia: a challenge to investigate.

Prader-Willi syndrome (PWS) is a genetic disease caused by the loss of expression of genes of paternal origin in the region 15q11--q13 of chromosome 15. The main characteristics of the syndrome include neonatal hypotonia, feeding problems in infancy, characteristic facies, intellectual disability, behavioral changes, GH deficiency, hypogonadism, and hyperphagia. Hyperphagia leads to the development of obesity at an early age, which, together with its complications, is the main cause of morbidity and mortality in PWS. PWS is the leading genetic cause of obesity. Despite this, it is a rare disease, with an incidence of approximately 1:10,000--1:30,000 of the population. It could therefore be relegated to the group of rare diseases, trying to awake the interest of a few people. This is however a model of extreme obesity whose main feature is hyperphagia, and is therefore an excellent model to investigate the complex mechanisms regulating appetite. Two different nutritional stages have traditionally been reported in children with PWS: a first stage during infancy marked by feeding and growth difficulties, and a second stage where hyperphagia starts and leads to development of obesity. The process is however more complex than it