Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Gamma heavy chain disease ?
    ### Response:
    Gamma heavy chain disease is characterized by the abnormal production of antibodies. Antibodies are made up of light chains and heavy chains. In this disorder, the heavy chain of the gamma antibody (IgG) is overproduced by the body.  Gamma heavy chain disease mainly affects older adults and is similar to aggressive malignant (cancerous) lymphoma.
    