Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Alzheimer's Disease ?
    ### Response:
    Alzheimer's disease (AD) is the most common form of dementia among older people. Dementia is a brain disorder that seriously affects a person's ability to carry out daily activities.     AD begins slowly. It first involves the parts of the brain that control thought, memory and language.
    