tailieunhanh - Desk Reference for hematology - part 10

Loại 2N VWD là do một khiếm khuyết / đột biến trong trang yếu tố ràng buộc VIII của VWF. Khác với giảm đáng kể ràng buộc của yếu tố VIII, loại protein 2N VWF là bình thường trong tất cả các chức năng khác và số lượng. Loại 2N là kiểu hình tương tự để nhẹ hemophilia A và cần được loại trừ | VON WILLEBRAND DISEASE 897 TABLE 156 Classification of Von Willebrand Disease Type 2 Subtype High-Molecular-Weight Multimers Ristocetin-Induced Platelet Aggregation Factor VIII Binding Capacity 2A Absent Decreased Normal 2B Reduced absent Increased Normal 2M Normal Decreased Normal 2N Normal Normal Markedly reduced for type 2B VWD is often associated with a mild consumptive thrombocytopenia. Type 2B VWD is phenotypically similar to pseudo-Von Willebrand Disease. Type 2N VWD is due to a defect mutation in the factor VIII binding site of VWF. Other than markedly reduced binding of factor VIII type 2N VWF protein is normal in all other functions and quantity. Type 2N is phenotypically similar to mild hemophilia A and should be excluded in all cases of mild hemophilia A and in women who appear to be hemophilia A carriers but with no previous family history. It requires diagnosis by use of a specific factor VIII VWF binding assay. Type 2M VWD is defined as a qualitative variant of VWF with decreased platelet-dependent function that is not caused by the absence of HMW multimers. In essence it is similar to type 2A but multimer analysis is normal. Candidate mutations have been identified around the specific GpIb binding site that mediates the platelet-dependent function of VWF. Type 2M is becoming increasingly recognized and a number of type 1 cases may often be reclassified as type 2M upon closer examination. Treatment This is dependent upon the severity of VWD and bleeding problem. DDAVP will raise levels of WF and factor VIII by two- to fourfold and is the mainstay of treatment for mild VWD. Responses to DDAVP are tachyphylactic a factor that must be considered for prolonged courses of treatment. Tranexamic acid used in conjunction with DDAVP or alone is a useful adjunctive therapy. Use of DDAVP is controversial in type 2B VWD where it could release further abnormal VWF which aggravates the preexisting thrombocytopenia and in vivo platelet aggregation potentially .