Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Prader-Willi syndrome ?
    ### Response:
    Prader-Willi syndrome is a complex genetic condition that affects many parts of the body. In infancy, this condition is characterized by weak muscle tone (hypotonia), feeding difficulties, poor growth, and delayed development. Beginning in childhood, affected individuals develop an insatiable appetite, which leads to chronic overeating (hyperphagia) and obesity.
    