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Blood is carried throughout the body within a network of blood vessels (arteries, veins, and capillaries). When our tissues are injured, the blood vessel is disrupted, and we bleed through the holes in the blood vessel wall. Normally, we stop bleeding through this process-the formation of the platelet plug and the formation of the blood clot. This is called "hemostasis." A protein in our blood, termed Von Willebrand factor (or vWf), causes the platelets to …

…they have severe Von Willebrand disease that is characterised by very low or undetectable levels of Von Willebrand factor with more severe bleeding symptoms. One reason for this discrepancy between recessive (asymptotic heterozygotes) and dominant (symptomatic heterozygotes) is that the level of Von Willebrand factor may be affected by other factors, such as blood type. This might result in carriers of the abnormal gene having higher levels of Von Willebrand factor and thus being asymptomatic.