Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) prion disease ?
    ### Response:
    Prion disease represents a group of conditions that affect the nervous system in humans and animals. In people, these conditions impair brain function, causing changes in memory, personality, and behavior; a decline in intellectual function (dementia); and abnormal movements, particularly difficulty with coordinating movements (ataxia).
    