Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Spinal Muscular Atrophy ?
    ### Response:
    Spinal Muscular Atrophy (SMA) Types I, II, and III belong to a group of hereditary diseases that cause weakness and wasting of the voluntary muscles in the arms and legs of infants and children. The disorders are caused by an abnormal or missing gene known as the survival motor neuron gene 1 (SMN1), which is responsible for the production of a protein essential to motor neurons.
    