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Factor II, Factor V, and Factor X Deficiencies
Introduction
Inherited deficiencies of factors II, V, and X (FII, FV, and FX) are rare (estimated frequencies are FII, 1 in 2,000,000; FV, 1 in 1,000,000; and FX, 1 in 1,000,000). Patients who are homozygous or compound heterozygous for defects in the F2, F5 , or F10 genes can have moderate to severe bleeding symptoms, with patients who have FX deficiency being more likely to manifest severe symptoms. The European Network of Rare Bleeding Disorders analyzed the correlation of factor activity and clinical bleeding in patients with rare bleeding disorders, observing a strong association for FX and combined FV and FVIII deficiencies and a weak association for FV and FII deficiencies. In general, however, the lower the factor levels, the more severe the bleeding. Overall, a spectrum of bleeding symptoms have been reported, including easy bruising, mucosal bleeding, menorrhagia, and surgical/trauma-induced bleeding, while hemarthroses and intracranial hemorrhage are less common. Heterozygotes are typically asymptomatic; however, easy bruising, mucosal bleeding, and bleeding with surgery/trauma have been reported.
Pathophysiology
FII (also known as prothrombin) is a vitamin K–dependent glycoprotein with a plasma concentration of approximately 100 μg/mL and a half-life of 3 days. It is synthesized in the liver and is the inactive zymogen of thrombin. FV is a nonenzymatic cofactor that is synthesized in both hepatocytes and megakaryocytes, with 80% being secreted and 20% being stored in platelet α-granules. The half-life of FV is 36 hours. FX is a vitamin K–dependent glycoprotein that is synthesized in the liver as an inactive zymogen and circulates at a concentration of 8–10 μg/mL. The half-life of FX is 40 hours.
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