severe combined immunodeficiency X-linked
severe combined immunodeficiency X-linkedA form (OMIM:300400) of severe combined immunodeficiency (SCID), a genetically and clinically heterogeneous group of rare congenital disorders characterised by impairment of both humoral and cell-mediated immunity, leukopaenia, and low or absent antibody levels. The common characteristic of all types of SCID is absence of T-cell-mediated cellular immunity due to a defect in T-cell development. Patients with SCIDX1 have an early onset of infections, often before 3 months of age, followed by lymphopenia, persistent pneumonitis, moniliasis, frequent rashes and death in infancy, despite treatment with gammaglobulin.
Defects in IL2RG, which encodes the gamma chain, an important signalling component of many IL receptors (e.g., IL-2, IL-4, IL-7 and IL-21), cause X-linked severe combined immunodeficiency (XSCID/SCIDX1).