Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pelizaeus-Merzbacher disease ?
    ### Response:
    Pelizaeus-Merzbacher disease is an inherited condition involving the brain and spinal cord (central nervous system). This disease is one of a group of genetic disorders called leukodystrophies. Leukodystrophies are characterized by degeneration of myelin, which is the covering that protects nerves and promotes the efficient transmission of nerve impulses.
    