Prader-Willi syndrome is a genetic disorder affecting approximately 1 in 10-15,000 births. Individuals with Prader-Willi syndrome have characteristic facial features including almond shaped eyes, elongated face and a prominent nose. Organ systems can also be affected. Individuals with Prader-Willi syndrome often display an obsession with food (hyperphagia) as children, which can lead to obesity in later life. Adults are typically very short in stature due to a lack of growth hormone. PWS is a spectrum disorder and so affects individuals to varying degrees. Most people with Prader-Willi syndrome will have borderline or moderate learning disabilities. Additionally, emotional and social skills are often under-developed. Prader-Willi syndrome is caused by an abnormality on chromosome 15 which occurs at the time of conception.