SEVERE COMBINED IMMUNODEFICIENCY CAUSED BY DEFECTS IN COMMON CYTOKINE RECEPTOR γ c SIGNALING PATHWAYS

Severe combined immunodeficiency (SCID) syndromes are a group of congenital disorders characterized by severe impairment of cellular and humoral immunity, leading to death at an early age. Human SCID comprises genotypically and phenotypically heterogeneous conditions of which the genetic basis for many of the underlying immunologic defects have been recently elucidated. All SCID phenotypes are defined by the absence of mature T cells. Other characteristics, including the presence or absence of B cells and natural killer (NK) cells and the particular genes involved, help to distinguish the various subtypes of these disorders (Fig. 1).