Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Juvenile Huntington disease ?
    ### Response:
    What causes Juvenile Huntington disease (HD)? Mutations in the HTT gene cause Huntington disease. The HTT gene provides instructions for making a protein called huntingtin. Although the function of this protein is unknown, it appears to play an important role in nerve cells (neurons) in the brain.
    