Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pelizaeus-Merzbacher disease ?
    ### Response:
    Pelizaeus-Merzbacher disease is a disorder that affects the brain and spinal cord. It is a type of leukodystrophy and is characterized by problems with coordination, motor skills, and learning. The age of onset and the severity of the symptoms varies greatly depending on the type of disease.
    