WAS and Wiskott-Aldrich syndrome: Reduced or absent WASp expression may result in the primary immunodeficiency disorder Wiskott–Aldrich Syndrome (WAS), which is characterized by a classical triad of microthrombocytopenia, eczema and immune deficiency, affecting 1–10 in 1 000 000 live births (Ochs and Thrasher 2006).