Akar, NejatErik, Zafer2022-04-272022-04-272009http://hdl.handle.net/20.500.12575/79547latelets are small, disk-shaped cells with an average diameter of 2 to 3µm. They are derived from cytoplasmic fragmentation of megakaryocytes. Their mean life-span is 7?10 days. Lots of cytokines (thrombopoietin and others) are responsible for megakaryocyte development and platelet formation. Platelets have two forms; one is resting platelet which is circulating during normal circulation and the other is active platelet. When the vascular injury occurs, platelets are rapidly activated and aggregate with each other to form a plug on the vessel wall that prevents vascular leakage.An abnormality or disease of the platelets is called a thrombocytopathy which could be either a decrease (thrombocytopenia) or an increase in the number of (thrombocytosis). In this study patients with giant platelet syndrome which is usually accompanied by thrombocytopenia were analyzed. Hence, it is also called macrotrombocytopenia. Macrotrombocytopenia is characterized by the presence of abnormally large platelets this dissertation is focused on the analysis of Myosin Heavy Chain 9, Nonmuscle (MYH9)-related mactrombositopenia. MYH9 gene, located on chromosome 22q12?13, encodes for a non muscle myosin heavy chain type II-A (NMMHC II-A). Mutations in this gene are responsible for May-Hegglin anomaly, Sebastian, Fechtner and Epstein syndromes. These four diseases are autosomal dominant macrotrombocytopenias distinguished by different combinations of clinical and laboratory signs (such as sensorineural hearing loss, cataract, nephritis, and Döhle-like bodies).Consequently, we aimed to investigate the relationship between a possible mutation in MYH9 gene and the diseases via mutation scanning of patients with macrotrombositopenia. 122 patients with macrotrombositopenia were examined by SSCP and DNA sequencing of the MYH9 gene. After mutation scanning of all patients, a single base alteration (c.366C>T, p.45Ser>Ser) which causing a silent mutation in exon 1 in an affected individualtrMakrotrombositopeniMutasyonTrombositmasterThesis