WASP Levels in Platelets and Lymphocytes of Wiskott-Aldrich Syndrome Patients Correlate with Cell Dysfunction

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Abstract
Wiskott-Aldrich syndrome, an inherited blood cell disorder due to mutations of the X-chromosome gene WASP (Wiskott-Aldrich syndrome protein), was characterized originally by thrombocytopenia, immunodeficiency, and eczema. Whereas platelet dysfunction is severe and consistent, immune defects are clinically variable, ranging from negligible to life threatening. To understand this heterogeneity, we quantified WASP in PBMC and platelets, and also in neutrophils, of patients with diverse mutations. A surprisingly complex pattern of WASP expression found for lymphoid cells formed the basis for dividing the patient mutations into four groups. Group A have low WASP levels in PBMC and higher levels in EBV cell lines, as well as near normal WASP RNA levels (7 patients, most with mild disease), suggesting that group A WASP molecules are hypersusceptible to proteolysis. Group B have low WASP levels in PBMC and EBV cells and similar low RNA levels (2 patients, moderate disease). Group C have discordant expression: WASP-positive peripheral T cells and WASP-negative peripheral B cells and EBV cell lines (9 patients, variable disease severity). Noteworthy among group C kindred are several instances of B cell lymphomas. In group D, PBMC and EBV cell lines are WASP negative (7 patients, severe disease). In contrast to the complex lymphoid cell expression patterns, all patient platelets examined were WASP negative (18 diverse patients). WASP absence in platelets provides an apparent molecular explanation for the universally severe platelet dysfunction in this disease, and the cumulative lymphoid cell findings suggest that WASP levels play a substantial role in determining immune outcome.