Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Russell-Silver syndrome ?
    ### Response:
    Russell-Silver syndrome is a growth disorder characterized by slow growth before and after birth. Babies with this condition have a low birth weight and often fail to grow and gain weight at the expected rate (failure to thrive). Head growth is normal, however, so the head may appear unusually large compared to the rest of the body.
    