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What are congenital marcothrombocytes?

Q: Kindly give me detailed information about congenital marcothrombocytes.

A:Platelets (thrombocytes) are a type of blood cells, which are derived in the bone marrow from large cells called megakaryocytes. They are critical for the clotting of blood and have life-span of about 10 days. The ‘normal’ platelet is approximately 1.5-2.5 microns in size and is discoid in shape. Macrothrombocytes (or megathrombocytes or giant platelets) are large platelets which range in size from about 5-20 microns. Nearly 20 disorders (including variations of specific classifications of macrothrombocytopenia) have been reported in literature. These may be classified by using several laboratory techniques including flow cytometry and electron microscopy. Congenital giant platelet disorders comprise a heterogeneous group of rare autosomal dominant genetic disorders, characterized by giant platelets, thrombocytopenia and varying degrees of platelet dysfunction manifesting as bleeding tendency of variable severity. Some of the syndromes have, in addition, leukocyte inclusions, interstitial nephritis, sensorineural hearing loss and cataracts. Many of these disorders share common clinical and laboratory features, and patients are often misdiagnosed with and treated for idiopathic thrombocytopenic purpura (ITP). The classic giant platelet disorder is the Bernard-Soulier Syndrome which results from a deficiency of a specific platelet receptor. The four most common defects described are the May-Heggelin anomaly, the Fechtner syndrome, the Sebastian syndrome and Epstein syndrome. Recently they are all thought to be variants of a single disorder as they result from a common mutation of the non-muscle myosin heavy chain 9 gene (MYH9) although these syndromes had been clinically characterized as different disorders. In May-Heggelin anomaly (the most prevalent disorder) the platelets are large, almost the size of red cells and lymphocytes, and there are prominent leukocyte inclusions. Patients suffering from Fechtner syndrome have nephritis, hearing loss and cataracts and distinct spherical granules in their leukocytes. The platelets are enlarged but less so than in May-Heggelin patients. In Sebastian syndrome, the same leukocyte and platelet abnormalities as Fechtner patients are present but no organ defects. Epstein syndrome patients have nephritis and hearing loss along with defects in platelet adhesion and aggregation but no leukocyte inclusions. Patients with Eckstein syndrome have nephritis and deafness like Epstein patients but normal platelet function. Finally patients with the Enyeart syndrome have giant platelets and thrombocytopenia. In this case however, there are inclusions in the platelets but not in the leukocytes. Other disorders occur due to specific abnormalities affecting organelles such as the alpha granule in Medich giant platelet disorder and White platelet disorder. Another condition is Swiss Cheese Giant Platelet Syndrome in which a highly dilated open canalicular system and the absence of the circumferential band of microtubules render the platelets with a Swiss cheese appearance. Patients with the velocardiofacial syndrome have conotruncal cardiac defects and learning defects along with defective platelet GpIb as they have a deletion on 22q11.2. Mediterranean macrothrombocytopenia, seen in Greek and Italian populations, is characterized by varying degrees of thrombocytopenia and the presence of large to giant platelets.


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