Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Severe combined immunodeficiency ?
    ### Response:
    Severe combined immunodeficiencies (SCID) are inherited immune system disorders characterized by abnormalities with responses of both T cells and B cells (specific types of white blood cells needed for immune system function). Common signs and symptoms include an increased susceptibility to infections including ear infections; pneumonia or bronchitis; oral thrush; and diarrhea.
    