Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Monomelic Amyotrophy ?
    ### Response:
    Monomelic amyotrophy (MMA) is characterized by progressive degeneration and loss of motor neurons, the nerve cells in the brain and spinal cord that are responsible for controlling voluntary muscles. It is characterized by weakness and wasting in a single limb, usually an arm and hand rather than a foot and leg.
    