Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) adenosine deaminase deficiency ?
    ### Response:
    Adenosine deaminase (ADA) deficiency is an inherited disorder that damages the immune system and causes severe combined immunodeficiency (SCID). People with SCID lack virtually all immune protection from bacteria, viruses, and fungi. They are prone to repeated and persistent infections that can be very serious or life-threatening.
    