Pathogenesis and diagnosis of X-linked lymphoproliferative disease.

X-linked lymphoproliferative syndrome (XLP) is a rare, often fatal, primary immunodeficiency that has profound and damaging effects on the immune system of affected individuals. It is characterized by a dysregulated immune response, most commonly to Epstein-Barr viral infection. The defective gene in this syndrome has been identified as SAP-SLAM (signaling lymphocyte activation molecule)-associated protein. It is an adapter molecule that is required for appropriate function of the SLAM-related receptors. There is now a greater understanding of the molecular associations and cellular pathogenesis of SAP and this review will summarize the most recent findings. Clinically, XLP may be difficult to diagnose as a result of its varied clinical phenotype, and protein and genetic assays are currently used to make a definitive diagnosis. With the advances in gene analysis and genomics technology, it is likely that better and more rapid diagnostic techniques will become available.