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Factor V Leiden, MTHFR Thermolabile Variants, Prothrombin 20210G>A. The factor V Leiden mutation is the most common cause of activated protein C (APC) resistance, and most common genetic risk factor for thrombosis. Approximately 3-8% of the population is heterozygous, and have an estimated 5-10 fold increased risk of thrombosis. Homozygotes have a 50-100 fold increased risk.
The c.677C>T MTHFR polymorphism is present in the homozygous form in 5-15% of the general population. Individuals who are compound heterozygous or homozygous for the c.677C>T MTHFR variant may have mild elevations in blood homocysteine levels, especially in the setting of inadequate folate intake. Elevated homocysteine is an independent risk factor for venous thromboembolism. Approximately 20% of the population is compound heterozygous for both MTHFR variants. Less is known about the thrombotic risk associated with c.1298 A>C. The c.677C>T variant is also associated with methotrexate toxicity.
The common prothrombin c.20210G>A mutation is associated with elevated prothrombin levels, which promotes development of fibrin clots. 2-4 % of the population is heterozygous for PTV 20210. Heterozygotes have an estimated 3-11 fold increased risk of thrombosis.
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