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 brain and spinal cord (central nervous system). This disorder causes deterioration of the central nervous system's white matter, which consists of nerve fibers covered by myelin.
    