X-linked lymphoproliferative disease due to SAP deficiency

Definition

A rare, genetic, primary immunodeficiency disorder characterized by an abnormal immune response to Epstein-Barr virus (EBV) infection, caused by hemizygous mutations in the X-linked SH2D1A gene, resulting in B cell lymphoproliferation and manifesting with various phenotypes which include EBV-driven severe or fulminant mononucleosis, hemophagocytic lymphohistiocytosis (presenting with fulminant hepatitis, hepatic necrosis, bone marrow hypoplasia, and neurological involvement), hypogammaglobulinemia, and B-cell lymphoma. Additional variable manifestations include vasculitis, lymphomatoid granulomatosis, aplastic anemia, and chronic gastritis. Occasionally, T-cell lymphoma may be observed. Laboratory findings include normal or increased activated T cells and reduced memory B cells.