Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Juvenile-onset dystonia ?
    ### Response:
    Juvenile-onset dystonia is a form of dystonia, which is a movement disorder characterized by involuntary muscle contractions that cause repetitive movements and/or abnormal postures. The severity and frequency of the movements vary significantly; in some affected people, they may be barely noticeable while in others, the movements are severely disabling and painful.
    