Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency disease characterized by microthrombocytopenia, eczema, immunodeficiency, and susceptibility to lymphoid malignancy. Loss-of-function mutations in the WAS gene have been identified to cause disorders with platelet defects including WAS and X-linked thrombocytopenia. The WAS disease is caused by alterations in the WAS protein (WASP), and 80% of the missense mutations are located in the WH1 domain, the region essential for interaction with the WASP-interacting protein (WIP). It has been suggested that loss of WASP-WIP interaction is causal to the disease. Several studies show that WAS protein (WASp) plays a key role in the function of certain lymphocyte subsets. T-cell dysfunction is thought to be central to the immunodeficiency state seen in patients with the Wiskott-Aldrich syndrome.