Whole Exome Sequencing of an X-linked Thrombocytopenia Patient with Normal Sized Platelets

Wiskott-Aldrich Syndrome (WAS) is a rare X-linked recessive Primary Immunodeficiency (PID) caused by mutations in WAS gene which encodes a protein known as WASp. WASp plays important roles in cytoskeletal functions that compromise multiple aspects of normal cellular activity including proliferation, phagocytosis, immune synapse formation, adhesion and directed migration. WASp defect particularly causes platelets abnormality which is presented in forms of decrease of Mean Platelet Volume (MPV) and thrombocytopenia in most WAS conditions; nevertheless, some studies reported WAS patients with a normal or large size of platelets in recent years. This phenomenon is unique and the exact mechanism of thrombocytopenia with a normal or large size of platelets is still unknown. In this study, Next Generation Sequencing (NGS) was utilized to discover the causing mutation in WAS gene; furthermore, an attempt was made to evaluate the possibility of other mutations or genes especially WASp interacting proteins and inherited platelet disorder genes in patient clinical symptoms for the purpose of understanding the origin of such unique symptom and to perform further analysis if it is required. Therefore, clinical manifestations and immunologic functions of the patient were checked and Whole Exome Sequencing (WES) was performed to analyze all exonic variations which can be associated with patient phenotypes. Finally, a novel de novo mutation in WAS gene which truncates WASp to half of its normal size was determined as the only cause of clinical manifestation.