Prader-Willi Syndrome has a birth incidence rate of about 1:25,000. The syndrome results from the loss of expression of paternally expressed genes from the q11-13 region of the paternally inherited chromosome 15 (the Prader-Willi Syndrome critical region). There is an initial extreme hypotonia and failure to thrive, followed in early childhood by a marked preoccupation with food, developmental and cognitive delay, and evidence of relative deficiencies in the growth and sex hormones. These multigenic defects eventually lead to the hallmark symptom of hyperphagia (a life-threatening compulsive eating behavior) and disabling neuropsychiatric behaviors and disorders including temper outbursts, repetitive and ritualistic behaviors, rigid thinking, skin picking, depression, and psychosis in some cases. There is no approved pharmaceutical intervention for hyperphagia in PWS.
Video credit Foundation for Prader-Willi Research, (https://youtu.be/1FRSSQco_pk)