Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Myasthenia Gravis ?
    ### Response:
    Myasthenia gravis is disease that causes weakness in the muscles under your control. It happens because of a problem in communication between your nerves and muscles. Myasthenia gravis is an autoimmune disease. Your body's own immune system makes antibodies that block or change some of the nerve signals to your muscles.
    