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Wiskott-Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency disorder (PID) characterized by microthrombocytopenia, bloody diarrhea, eczema, recurrent infections, and a high incidence of autoimmunity and malignancy. To investigate the mechanism of thrombocytopenia and infections in four boys of consanguineous parents from Lebanon. Patient gDNA was studied using Next Generation Sequencing and Sanger Sequencing. Protein expression was determined by immunoblotting, and mRNA expression by semi-quantitative RT-PCR. F-actin polymerization and cellular proliferation were assayed by flow cytometry. We identified a threonine to a methionine change at position 45 (T45M) of the WAS protein (WASp) that abolished protein expression and disturbed F-actin polymerization and T cell proliferation, but not B cell proliferation. In addition, the levels of the WAS-interacting protein (WIP) were significantly decreased in the patients. The mutation identified severely destabilizes WASp and affects the downstream signaling events important for T cell function, but not B cell function. It was previously known that the stability of WASp depends on WIP. In this manuscript, we report that the stability of WIP also depends on WASp. Finally, it is important to suspect X-linked PIDs even in consanguineous families. The patients are above the optimal age for transplant in WAS, and it is difficult to identify one or more donors for four patients, therefore, they represent ideal candidates for gene therapy or interleukin-2 therapy. • We revealed Wiskott-Aldrich Syndrome in four boys of consanguineous parents • The four patients had absent WASp and severely diminished WIP levels • F-actin polymerization and T cell proliferation were defective in the patients • X-linked diseases should not be ruled out in consanguineous families • The patients are ideal candidates for gene therapy or recombinant IL-2 therapy [ABSTRACT FROM AUTHOR]