Prader-Willi syndrome causes physical, mental and behavioral problems, and people who have the condition most commonly suffer from constant hunger, or hyperphagia, notes Mayo Clinic. Prader-Willi is a rare disorder that is present at birth, and people usually begin experiencing hyperphagia at about 2 years old.
Prader-Willi syndrome is a genetic disorder, and while doctors have been unable to identify the exact gene that leads to the condition, they have narrowed it down to a particular section of chromosome 15, states Mayo Clinic. People with Prader-Willi are missing or have a defect in the paternal gene on chromosome 15, or they have two copies of chromosome 15 contributed by their mothers and none from their fathers. This interferes with the functions of the hypothalamus, the portion of the brain that controls hunger and releases substances that regulate growth and sexual development.
Poor muscle tone; distinct facial features, such as almond-shaped eyes; a failure to gain weight properly due to poor sucking reflexes; lack of eye coordination; and general unresponsive are symptoms of Prader-Willi syndrome in infants, according to Mayo Clinic. In addition to their inability to feel full, older children and adults with the syndrome experience complications such as underdeveloped sex organs, poor physical development with high body fat and low muscle mass, intellectual disabilities and sleep disorders.