Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Leukodystrophy ?
    ### Response:
    Leukodystrophy refers to progressive degeneration of the white matter of the brain due to imperfect growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fiber. Myelin, which lends its color to the white matter of the brain, is a complex substance made up of at least ten different chemicals.
    