Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to familial hemophagocytic lymphohistiocytosis ?
    ### Response:
    Familial hemophagocytic lymphohistiocytosis may be caused by mutations in any of several genes. These genes provide instructions for making proteins that help destroy or deactivate lymphocytes that are no longer needed. By controlling the number of activated lymphocytes, these genes help regulate immune system function.
    