WAS and Wiskott-Aldrich syndrome: Wiskott-Aldrich syndrome (WAS; OMIM 301000) is a complex and severe X-linked primary immunodeficiency characterized by both cellular and humoral immunodeficiency, microthrombocytopenia, eczema, and increased risk of autoimmunity and lymphomas.1,2 The gene responsible for WAS encodes a 502-amino-acid protein (Wiskott-Aldrich syndrome protein [WASp]) that is a key regulator of actin polymerization.3