Newborn screening for primary immunodeficiencies: beyond SCID and XLA.

Primary immunodeficiencies (PID) encompass more than 250 disease entities, including phagocytic disorders, complement deficiencies, T cell defects, and antibody deficiencies. While differing in clinical severity, early diagnosis and treatment is of considerable importance for all forms of PID to prevent organ damage and life-threatening infections. During the past few years, neonatal screening assays have been developed to detect diseases hallmarked by the absence of T or B lymphocytes, classically seen in severe combined immunodeficiencies (SCID) and X-linked agammaglobulinemia (XLA). As described in this review, a reduction or lack of T and B cells in newborns is also frequently found in several other forms of PID, requiring supplemental investigation and involving the development of additional technical platforms in order to help classify abnormal screening results.