Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) X-linked severe combined immunodeficiency ?
    ### Response:
    X-linked severe combined immunodeficiency (SCID) is an inherited disorder of the immune system that occurs almost exclusively in males. Boys with X-linked SCID are prone to recurrent and persistent infections because they lack the necessary immune cells to fight off certain bacteria, viruses, and fungi.
    