<P> Von Willebrand factor is mainly active in conditions of high blood flow and shear stress . Deficiency of vWF, therefore, shows primarily in organs with extensive small vessels, such as skin, gastrointestinal tract, and uterus . In angiodysplasia, a form of telangiectasia of the colon, shear stress is much higher than in average capillaries, and the risk of bleeding is increased concomitantly . </P> <P> vWF carries Factor VIII </P> <P> In more severe cases of type 1 vWD, genetic changes are common within the vWF gene and are highly penetrant . In milder cases of type 1 vWD, a complex spectrum of molecular pathology may exist in addition to polymorphisms of the vWF gene alone . The individual's ABO blood group can influence presentation and pathology of vWD . Those individuals with blood group O have a lower mean level than individuals with other blood groups . Unless ABO group--specific vWF: antigen reference ranges are used, normal group O individuals can be diagnosed as type I vWD, and some individuals of blood group AB with a genetic defect of vWF may have the diagnosis overlooked because vWF levels are elevated due to blood group . </P> <Table> <Tr> <Td> </Td> <Td> This section needs more medical references for verification or relies too heavily on primary sources . Please review the contents of the section and add the appropriate references if you can . Unsourced or poorly sourced material may be challenged and removed . (June 2016) </Td> <Td> </Td> </Tr> </Table>

Von willebrand disease - wikipedia the free encyclopedia