Newborn screening for SCID: three years of experience.

Over the past three years, newborn blood screening (NBS) for severe T cell lymphopenia/severe combined immunodeficiency (sTCL/SCID) using the T cell receptor excision circle (TREC) assay has revolutionized the early detection of infants with primary immunodeficiencies (PIDs) associated with T cell lymphopenia. Nonetheless, despite the comprehensive NBS protocols developed by each state, additional issues unique to screening for sTCL/SCID have surfaced, including variability in the performance of the TREC assay, diagnostic and treatment algorithms, definition of sTCL/SCID, and approach to the discovery of new genetic variants. Although NBS using the TREC assay has been highly successful, new and difficult challenges have emerged that need to be addressed to enhance our knowledge of the causes of sTCL/SCID and to optimize the detection and outcomes of affected infants.