Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Prader-Willi syndrome ?
    ### Response:
    Prader-Willi syndrome (PWS) is a genetic condition that affects many parts of the body. Infants with PWS have severe hypotonia (low muscle tone), feeding difficulties, and slow growth. In later infancy or early childhood, affected children typically begin to eat excessively and become obese.
    