XIAP deficiency syndrome in humans

The X-linked inhibitor of apoptosis (XIAP) deficiency, also known as the X-linked lymphoproliferative syndrome type 2 (XLP-2), is a rare primary immunodeficiency. XIAP deficiency is characterized by a key triad of clinical manisfestations, which consist of a high susceptibility to develop hemophagocytic lymphohistiocytosis (HLH) frequently triggered by Epstein–Barr virus (EBV) infection, recurrent splenomegaly and inflammatory bowel disease (IBD) with the features of a Crohn's disease. XIAP deficiency can be considered as one of the genetic causes for inherited IBD. XIAP is an anti-apoptotic molecule, but it is also involved in many other pathways. Recent findings demonstrate the role of XIAP in innate immunity and in the negative regulation of inflammation. In this review, we focus on the clinical aspects, the molecular etiology and the immunopathogenesis of XIAP deficiency. We also discuss recent progress in the understanding of XIAP function in relation to the pathophysiology of XLP-2.