Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) myoclonus-dystonia ?
    ### Response:
    Myoclonus-dystonia is a movement disorder that typically affects the upper half of the body. Individuals with this condition experience quick, involuntary muscle jerking or twitching (myoclonus) that usually affects their arms, neck, and trunk. Less frequently, the legs are involved as well.
    