Factor V Leiden Mutation and Associated Thrombotic Risks

Molecular Mechanism and Epidemiology

• Factor V Leiden is a single point mutation that results in substitution of glutamine for arginine at position 506, making factor Va resistant to inactivation by activated protein C (APC) and creating a hypercoagulable state, according to the American College of Medical Genetics 1
• The mutation prevents normal APC cleavage at the R506 position, which is required for optimal exposure and subsequent rapid inactivation of factor V at positions R306 and R679, as reported by the American College of Medical Genetics 2
• This resistance to APC degradation allows factor Va to remain active longer, perpetuating thrombin generation and increasing thrombotic risk, as stated by the American College of Medical Genetics 3
• Factor V Leiden accounts for 85-95% of patients with APC resistance, depending on the functional assay used, according to the American College of Medical Genetics 4
• Approximately 5% of Caucasians carry the heterozygous mutation, with lower prevalence in Hispanic-Americans and African-Americans, and virtual absence in Africans and Asians, as reported by the American College of Medical Genetics 5
• It is the most common hereditary thrombophilia, found in 11-20% of individuals presenting with their first episode of venous thrombosis, according to the American College of Medical Genetics 6
• In selected populations (age <50 years and/or recurrent thrombosis), up to 40% carry the Factor V Leiden genotype, as stated by the American College of Medical Genetics 7

Thrombotic Risk and Other Blood Clotting Factor Abnormalities

• Homozygotes have an 80-fold increased risk for venous thromboembolism (VTE), as reported by the American College of Medical Genetics 8
• The recognized coagulation abnormalities that can coexist with Factor V Leiden include deficiencies in antithrombin III, protein C, and protein S, which collectively account for 5-20% of venous thromboembolism patients, according to the American College of Medical Genetics 2
• Antithrombin III deficiency is a serine protease inhibitor that irreversibly inhibits thrombin by covalently binding its active site, and familial reductions in antithrombin III activity are strongly associated with deep vein thrombosis and pulmonary embolism, as stated by the American College of Medical Genetics 6
• Protein C is a vitamin K-dependent zymogen activated to APC by the thrombin-thrombomodulin complex, and APC functions as a natural anticoagulant by inactivating procoagulant factors Va and VIIIa in the presence of protein S, according to the American College of Medical Genetics 8
• Protein S serves as a cofactor for APC in the inactivation of factors Va and VIIIa, and familial reductions in protein S activity are strongly associated with venous thromboembolism, as reported by the American College of Medical Genetics 7
• The prevalence of these previously recognized familial thrombophilias (antithrombin III, protein C, protein S deficiencies) among venous thromboembolism patients ranges from 5-20%, depending on cohort selection, according to the American College of Medical Genetics 5

Factor V Leiden and Deep Vein Thrombosis

Prevalence and Risk

• Factor V Leiden is present in approximately 15-20% of patients with an initial episode of deep vein thrombosis, making it the most common known heritable thrombophilic risk factor 9
• The American College of Medical Genetics recommends awareness that Factor V Leiden is found in roughly 11-20% of individuals presenting with their first episode of venous thrombosis 10
• In selected populations, such as those under 50 years old and/or with recurrent thrombosis, up to 40% carry the Factor V Leiden genotype 10
• Approximately 5% of the Caucasian population carries Factor V Leiden in heterozygous form, with lower rates in Hispanic-Americans and African-Americans, and virtual absence in Africans and Asians 10

Clinical Context and Risk Magnitude

• Heterozygotes have a 4- to 7-fold increased risk for initial VTE episode, with a lifetime risk of approximately 10% 9, 11
• Homozygotes have a 9- to 80-fold increased risk, with lifetime risk exceeding 80% 9, 11

Factor V Leiden: Prevalence and Guideline Recognition as the Leading Inherited Thrombophilia

Epidemiology

• Approximately 5 % of Caucasian individuals in the United States carry the Factor V Leiden mutation in the general population. 12
• The mutation is identified in about 20 % of patients who experience an idiopathic first venous thromboembolism. 13
• Among pregnant individuals who develop venous thrombosis, roughly 60 % are found to have the Factor V Leiden mutation. 12

Comparative Prevalence of Other Inherited Thrombophilias

• The prothrombin G20210A mutation is the second‑most common inherited risk factor for venous thrombosis, but its prevalence is substantially lower than that of Factor V Leiden. 14

Historical Context

• The Factor V Leiden mutation was discovered in 1994 and was immediately recognized as the most common genetic risk factor for venous thrombosis. 13

Guideline Consensus

• The American College of Medical Genetics states that Factor V Leiden is “the most common genetic risk factor for venous thrombosis.” 12
• The EGAPP Working Group identifies Factor V Leiden as “the most common known inherited risk factor for thrombosis.” 14
• Because of its high frequency in the population, Factor V Leiden is considered the most common inherited cause of thrombosis, outweighing less prevalent but potentially higher‑risk disorders such as antithrombin III deficiency. 13