Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Erdheim-Chester disease ?
    ### Response:
    Erdheim-Chester disease is a rare condition that can affect many different organs of the body. This condition, which usually affects adults, is characterized by excessive production and accumulation of histiocytes (specific cells that normally play a role in responding to infection and injury) within multiple tissues and organs.
    