Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Rheumatoid Arthritis ?
    ### Response:
    Rheumatoid arthritis (RA) is a form of arthritis that causes pain, swelling, stiffness and loss of function in your joints. It can affect any joint but is common in the wrist and fingers.    More women than men get rheumatoid arthritis. It often starts in middle age and is most common in older people.
    