severe combined immunodeficiency disorder
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severe combined immunodeficiency disorder (SCID) A congenital immunodeficiency of both T and B LYMPHOCYTES. The condition is due to a genetic defect that causes a lack of the intracellular enzyme adenosine deaminase. As a result neither of these classes of lymphocytes can become immunologically functional and the affected child is gravely susceptible to infections of all kinds. X-linked SCID (SCID-X1) has now been successfully treated by gene therapy.