Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Prader-Willi Syndrome ?
    ### Response:
    Prader-Willi Syndrome (PWS) is a rare genetic disorder. It causes poor muscle tone, low levels of sex hormones and a constant feeling of hunger. The part of the brain that controls feelings of fullness or hunger does not work properly in people with PWS. They overeat, leading to obesity.
    