Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Leukoencephalopathy with vanishing white matter ?
    ### Response:
    Leukoencephalopathy with vanishing white matter is a progressive disorder that mainly affects the central nervous system (CNS). This disorder causes deterioration of white matter, which consists of nerve fibers covered by myelin (the substance that protects the nerves).
    