Prader-Willi Syndrome (PWS)  is a genetic disorder genetically caused by errors or deletions of genes related to chromosomes 15.

Research indicates that this happens for one of three reasons:

• Paternal genes on chromosome 15 are missing
• Errors or defects in paternal genes on Chromosome 15
• Two copies of chromosome 15 from the mother are inherited by the child and no chromosome 15 from the father.

The hypothalamus (part of the brain which controls hunger and thirst and hormones related to growth and sexual development)  does not function properly in people with PWS. This disruption in functioning of  the hypothalamus due to chromosome 15 defects results in the breaking down of functions and causes uncontrollable hunger, lack of satiety,  stunted growth, under developed sex hormones, affected emotional expression and sleep cycles and many more body functions.