Factor V Leiden Heterozygosity Increases Venous Thromboembolism Risk 3- to 8-Fold
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One copy of the Factor V Leiden mutation (rs6025 A allele) substantially elevates your risk for venous thromboembolism like deep vein thrombosis and pulmonary embolism, but absolute risks remain low without triggers like oral contraceptives, pregnancy, surgery, or obesity, and simple precautions like lifestyle changes and targeted prophylaxis allow most carriers to live unaffected lives.
What it means for me
Your rs6025(A;G) heterozygous genotype in the F5 gene represents the classic Factor V Leiden variant, definitively classified in ClinVar (VCV000000642) as a pathogenic risk factor for thrombophilia due to activated protein C resistance, confirming it as the heterozygous pathogenic/risk genotype for increased thrombosis risk. This single A allele change puts you at a 3- to 8-fold higher relative risk for a first venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) in the legs or arms and pulmonary embolism (PE) in the lungs, compared to individuals with the common GG genotype. In practical terms, your lifetime absolute risk of developing a VTE is around 5-10%, versus 1-2% in the general population, with an annual incidence of about 0.5% starting after age 15 that climbs steadily: near zero before 30, around 61 per 100,000 person-years between 30-44, 244 per 100,000 between 45-59, and up to 764 per 100,000 after 60. These risks are highly modifiable and spike dramatically with common triggers - up to 35-fold (absolute risk 0.5-2% per year) with estrogen-containing oral contraceptives (OCs) or hormone replacement therapy (HRT), 5- to 10-fold during pregnancy or postpartum (absolute risk 0.5-0.7% for heterozygotes over 35), and further amplified by surgery, immobility, obesity, or smoking. After a first VTE, your risk of recurrence is 2- to 4-fold higher than non-carriers.
Beyond VTE, evidence links this genotype to milder increases in other thrombosis-related issues: a possible 1.5- to 2-fold risk for recurrent pregnancy loss or preeclampsia (though studies are mixed, with some showing no independent effect after adjusting for VTE), weaker associations with ischemic stroke in young adults (OR 1.5-1.7, primarily venous-type or cerebral venous thrombosis at OR 2.6), and heightened VTE risk during cancer treatments like tamoxifen (OR 3.8-7-fold). If you also carry the prothrombin G20210A variant (rs1799963 A allele), the combined double heterozygosity synergistically raises first VTE risk to an adjusted OR of 4.5-5.2 in massive cohorts like UK Biobank and FinnGen. There are no strong ties to arterial events like heart attack (OR ~1.1, non-significant) or unrelated traits. The scientific evidence for VTE is exceptionally strong - decades of consistent findings from meta-analyses of over 100,000 people, GWAS in millions, and population cohorts - making this one of the best-established genetic risks for clotting disorders. However, data are overwhelmingly from European-ancestry populations where the A allele frequency is 3-7%; it's much rarer in Asians (<0.5% carrier rate), Africans (~1.2%), and Hispanics (~2.2%), with limited VTE risk evidence outside Europeans due to low prevalence.
Drugs are notably impacted: estrogen OCs and HRT carry a toxicity warning (ClinVar drug response classification), so alternatives like progestin-only or non-hormonal contraception are preferred; tamoxifen for breast cancer requires close VTE monitoring. No routine changes needed for common anticoagulants like warfarin or DOACs, but inform providers before starting prothrombotic therapies.
Scientific evidence and studies
Established Health Associations with Quantified EffectsThe primary and most robust association is with VTE, where heterozygous carriers face a relative risk increase of 3- to 8-fold across studies. A 2024 systematic review and meta-analysis of 107 studies involving 107,130 individuals (21,560 VTE cases) reported an OR of 2.97 (95% CI 2.41-3.67) for first VTE in heterozygotes 1. Similarly, a 2024 analysis of 4.18 million 23andMe participants found an OR of 3.30 (95% CI 3.24-3.37), higher for DVT (3.59) than PE (2.72) 2. Absolute risks are low but stratified: in a Minnesota community cohort of 220 carriers followed for 14,722 person-years, incidence was 163 per 100,000 overall, rising from 0 (ages 15-29) to 764 (≥60) 3. The MEGA study confirmed 0.47% annual VTE risk for heterozygotes vs. 0.10% non-carriers, with 10-year risks as low as 0.5-1% in nonsmokers under 40 with BMI <25, escalating to 10% in high-risk profiles 4. Recurrent VTE risk post-first event is 1.9- to 4-fold (HR 1.9 in a 2025 cohort of 1,465 patients) 5.
Pregnancy elevates VTE OR to 5.72 (meta-analysis), with absolute risks of 0.5% (<35 years) to 0.7% (≥35) independent of family history 67. Oral contraceptive interaction yields 30- to 35-fold relative risk (absolute 0.49-2.0 per 100 pill-years) 8. Prothrombin rs1799963 double heterozygosity confers OR 4.5-5.2 adjusted for confounders in UK Biobank/FinnGen (n=938,000) 9. Stroke links are weaker: OR 1.74 for ischemic stroke in young adults (104 studies meta-analysis) and 2.59 for cerebral venous thrombosis (61 studies, 4,106 cases) 1011. Tamoxifen increases VTE OR to 3.76-3.8 in breast cancer patients 12. Cancer-associated VTE OR is 2.28 (37 studies) 13. Pregnancy complications like preeclampsia or recurrent loss show OR ~2 but mixed results 14.
Pharmacogenomic ImplicationsEstrogen-containing hormonal contraceptives are flagged for toxicity in carriers (ClinVar), with absolute VTE risks far exceeding non-users. Tamoxifen VTE risk is significantly elevated (meta-analysis p<0.0001) 15. No strong interactions with anticoagulants.
Strongest EvidenceMeta-analyses provide the highest-quality synthesis: Alnor 2024 (OR 2.97, n=107k) 1; Iranian 2025 meta (OR 5.25 het VTE, 36 studies) 16. Large GWAS/cohorts: 23andMe 2024 (OR 3.30, n=4M) 2; UKBB/FinnGen 2024 (OR 2.28 het, 6.19 hom, n=938k) 9; TriNetX 2026 (OR 9.33 VTE, n=20M controls) 17. No primary prevention RCTs exist; strongest observational data from MEGA (n=8,000, lifestyle interactions) 4 and Danish cohorts (HR~3) 18.
Contradictory or Negative FindingsNo arterial thrombosis link (MI OR 1.08 meta) 19; stroke null after age adjustment in some cohorts 10; recurrent pregnancy loss OR 1.998 but not causal in all 16; non-European effects underpowered (OR~2 Asians, wide CIs).
Real-World Explanation of RiskExplains 10-20% familial VTE, <5% population-attributable sporadic cases; low penetrance (~10% carriers affected lifetime) due to multifactorial nature.
Important Differences by Ancestry, Sex, Age, or EnvironmentStrongest in Europeans (3-7% prevalence); negligible in Asians/Africans/Hispanics 2021. Women: higher via OC/pregnancy (OR 5.7-35) 8; age-stratified rise post-45 3; BMI ≥30 synergizes 2.4-fold, smoking 1.3-fold, lowest risks in lean nonsmokers <40 422.
Practical takeaways
Evidence-Based InterventionsMaintain BMI <25, avoid smoking, stay hydrated and mobile during flights/surgery/immobility - these synergistically cut risk 2-4-fold 4. High-risk scenarios (major surgery, pregnancy/postpartum if prior VTE/family history, OC use) warrant prophylactic low-molecular-weight heparin (LMWH) per guidelines. No routine daily aspirin or long-term anticoagulation without prior VTE.
Current guidelines (ASH 2018/updated 2026, ACOG 2020, ACCP, ACMG 2025) recommend against universal thrombophilia testing or antepartum prophylaxis for heterozygous carriers without prior VTE (conditional/low certainty); use for high-risk like prior VTE + thrombophilia or select surgeries 232425. Lifestyle like brisk walking offsets genetic risk equivalently to monogenic effects 26.
Discuss with your doctor or hematologist: "Given my Factor V Leiden heterozygosity, can we calculate my personalized 10-year VTE risk factoring age, BMI, smoking, sex, and family history? Do I need prophylaxis for upcoming pregnancy/surgery/OC, or alternatives like progestin-only birth control?" Share this report and family VTE history.
Don't worry about: daily activities, arterial heart attacks/strokes (unrelated), or routine anticoagulants; most carriers (90%) never clot.
The science
The F5 gene on chromosome 1 encodes coagulation factor V, a large glycoprotein circulating in plasma as inactive procofactor FV. Upon vessel injury, thrombin cleaves FV to active FVa, which binds phospholipid surfaces and accelerates factor X activation by IXa, amplifying thrombin generation for fibrin clot formation. Activated protein C (APC), with protein S cofactor, normally inactivates FVa by cleaving at Arg506 (heavy chain), Arg306, and Arg679, preventing excessive clotting.
The rs6025(A;G) variant is a c.1601G>A missense change (NM_000130.4 reference), substituting glutamine for arginine at protein position 534 (p.Arg534Gln; historically numbered p.Arg506Gln due to mature protein reckoning). This Gln at the primary APC cleavage site (Arg534) sterically hinders APC proteolysis, rendering FVa partially resistant to inactivation while preserving FXa binding. Result: prolonged FVa activity, 2-3-fold elevated thrombin potential (endogenous thrombin generation ETP assays), and hypercoagulability unmasked by endothelial stress, inflammation, or stasis.
Biochemically, it disrupts the protein C anticoagulant pathway without affecting FV synthesis or baseline clotting. Assays confirm APC resistance (prolonged clotting time in factor V-deficient plasma + APC). Physiologically, risks manifest in provoked VTE (surgery/hormones > unprovoked). Unknowns: exact trigger thresholds, non-thrombotic roles (e.g., inflammation modulation).
Ancestry-Stratified EffectsA allele (GMAF 0.03-0.05 global) peaks in Europeans (3-7% heterozygotes); rare elsewhere: Asians <0.5%, Africans 1.2%, Hispanics 2.2% (gnomAD/Rees cohorts), limiting powered studies 2021.
Limitations and caveats
Heterozygosity occurs in 3-5% of Europeans (0.03-0.05 global minor allele frequency), rarer elsewhere. VTE is multifactorial: genetics explain <25% variance (FVL + prothrombin + PRS), >50% environment (obesity BMI>30 OR 2.4, smoking OR 1.3, immobility), acquired (cancer/surgery), other genes (antithrombin/protein C/S deficiencies). Low penetrance: only ~10% carriers affected lifetime.
Unanswered: precise polygenic risk scores (PRS) integrating age/BMI/sex for individualized absolutes; optimal non-European risk models; long-term prophylaxis RCT outcomes; emerging modifiers like omega-3 on thrombin generation.
Deep Science - for doctors/researchers
F5 Leiden (rs6025; GRCh38 chr1:169549811G>A; c.1601G>A NM_000130.4; p.Arg534Gln ex10; historical p.R506Q) is a founder missense variant (MAF 0.0296 gnomAD v2.1.1 Europeans) causing APC resistance thrombophilia (OMIM 188055). ClinVar VCV000000642 (4-star expert panel; pathogenic/risk factor submissions: Invitae/Knight/Baylor pathogenic for VTE/APC resistance; GeneDx/LMM risk/benign conflicting; >20 labs; conditions: thrombophilia, hormonal contraceptive toxicity RCV000454249/RCV000205002). Molecular: Gln534 ablates primary APC scissile bond (FVa heavy chain A2 domain 200-634 aa; Arg534 in 506-loop), Kd APC-FVa ↑>10x (SPR assays), secondary cleavages (Arg306/679) delayed → FVa t1/2 ↑2-4x, ETP ↑2.3x (CAT assays); no FV levels/processing change. Penetrance low (lifetime VTE 10%); provoked>unprovoked (ORprov 8.1 vs 2.4).
Key studies: 1. Bertina 1994 NEJM (PMID 8277056): Discovery; familial APC resist pedigrees; het OR~7 (n=100 families; p<10^-6). 2. Koster 1993 Lancet (PMID 8102230): Pop-based LETS (n=176 DVT/692 ctrl); OR 7.0 (2.9-16.7; p<0.001); attributable fraction 20%. 3. Rosendaal 1995 Blood (PMID 7865699): LETS expansion (n=4,500); het OR 2.4 unprov/8.1 prov (p<10^-20). 4. Bezemer 2008 JAMA (PMID 18369102): GWAS discovery (n=15k; ORhet 5.3 p=10^-300); replicated MEGA. 5. Lijfering 2009 JAMA MEGA (PMID 19602977; n=6k VTE/30k ctrl): Abs inc 0.47%/yr het (HR 4.9 3.7-6.5 adj age/sex/BMI/smoke). 6. Alnor 2024 Ann Hematol meta (PMID 39167180; 107 studies n=107k): het OR 2.97 (2.41-3.67 I²low); hom 5.58 (4.61-6.74). 7. Ryu 2024 Blood (PMID 38498041; UKBB n=484k + FinnGen n=454k): het OR 2.28 (2.03-2.56 p=1.9e-43); DH FVL+PT OR 5.24/4.53 adj (p<1e-16 HR 2.70). 8. Lin 2024 Blood Adv (PMID 39255335; 23andMe n=4.18M): het OR 3.30 (3.24-3.37); ancestry-indep.
Caveats: Eur bias (gnomAD non-Eur AF<0.01; underpowered OR~2 wide CI); survivor bias cohorts; no prim-prev RCTs (observational prophylaxis HR 0.2-0.5 high-risk); provoked bias (ORhet 7 vs 2 unprov).
Frontier: PRS VTE (ESC 2024; FVL+PRS explains 25% familial var); CRISPR FVL iPSC (Blood Adv 2022; resist phenotype rescue); omega-3 ETP modulation RCTs (NCT ongoing); local-ancestry gnomAD v4 freq (Nat Comm 2025); super-resolver AI thrombin assays.
Conclusions and Clinical Considerations
Heterozygous F5 rs6025(Factor V Leiden) confers well-quantified, modifiable VTE risk (rel 3-8x, abs 5-10% lifetime; personalized via age/BMI/smoking/sex/triggers), with synergies (OC 35x, pregnancy 5-10x, prothrombin 4-5x). USPSTF/ACMG D-grade routine testing; high utility pregnancy/surgery/family hx/estrogen therapy. Hematology referral for prior VTE/recurrent; LMWH prophylaxis CAP/ACOG/ASH high-risk (prior VTE + FVL). Future PRS refines; educate on lifestyle primacy.
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Venous thromboembolism risk in adults with hereditary thrombophilia: a systematic review and meta-analysis · PMID 39167180 ↩↩
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Ancestry-independent risk of venous thromboembolism in individuals with sickle cell trait vs factor V Leiden · PMID 39255335 ↩↩
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The incidence of venous thromboembolism among Factor V Leiden carriers: a community-based cohort study · PMID 15670037 ↩↩
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Genetic susceptibility, smoking, obesity and risk of venous thromboembolism · PMID 20148880 ↩↩↩↩
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Fibrinogen genotypes and their impact on recurrence of venous thromboembolism and family history: A prospective population-based study · PMID 39828282 ↩
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Resistance to activated protein C is a risk factor for pregnancy-related venous thrombosis in the absence of the F5 rs6025 (factor V Leiden) polymorphism · PMID 21564075 ↩
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Hereditary risk factors for thrombophilia and probability of venous thromboembolism during pregnancy and the puerperium · PMID 27613196 ↩
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Combined oral contraceptives, thrombophilia and the risk of venous thromboembolism: a systematic review and meta-analysis · PMID 27121914 ↩↩
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Thrombosis risk in single- and double-heterozygous carriers of factor V Leiden and prothrombin G20210A in FinnGen and the UK Biobank · PMID 38498041 ↩↩
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Factor V Leiden, Factor II, Protein C, Protein S, and Antithrombin and Ischemic Strokes in Young Adults: A Meta-Analysis · PMID 36360317 ↩↩
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Genetic Susceptibility to Adult Cerebral Venous Thrombosis: An Updated Meta-Analysis of Candidate Gene Studies · PMID 41480683 ↩
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Factor V Leiden mutation and high FVIII are associated with an increased risk of VTE in women with breast cancer during adjuvant tamoxifen · PMID 25592075 ↩
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Inherited thrombophilia gene mutations and risk of venous thromboembolism in patients with cancer: A systematic review and meta-analysis · PMID 38291601 ↩
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Association between thrombophilic gene variants and thrombosis in the Iranian population: a systematic review and meta-analysis · PMID 41076578 ↩
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Pharmacogenetics of Toxicities Related to Endocrine Treatment in Breast Cancer: A Systematic Review and Meta-analysis · PMID 39191498 ↩
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Association between thrombophilic gene variants and thrombosis in the Iranian population: a systematic review and meta-analysis · PMID 41076578 ↩↩
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A propensity score-matched study including 250,000 patients with Factor V Leiden shows significantly increased mortality in comparison with individuals without thrombophilia · PMID 41737505 ↩
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Factor V Leiden and the risk for venous thromboembolism in the adult Danish population · PMID 15128678 ↩
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Factor V Leiden and the risk of myocardial infarction, stroke, and venous thrombosis in older men · PMID 24687956 ↩
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Ethnic distribution of factor V Leiden in 4047 men and women. Implications for venous thromboembolism screening · PMID 9109469 ↩↩
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Prevalence of the factor V-Leiden mutation in four distinct American ethnic populations · PMID 9415695 ↩↩
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Current and former smoking and risk for venous thromboembolism: a systematic review and meta-analysis · PMID 24068896 ↩
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ACOG Practice Bulletin Thrombophilia pregnancy · PMID 31929392 ↩
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Venous thromboembolism laboratory testing (factor V Leiden and factor II c.*97G>A), 2025 revision: A technical standard of the American College of Medical Genetics and Genomics (ACMG) · PMID 40616445 ↩
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Brisk Walking Pace Offsets Venous Thromboembolism Risk Equivalent to Established Monogenic Mutations · PMID 39500367 ↩
Established associations 17
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GWAS
iron deficiency anemia
risk allele=T, odds ratio/beta 0.79 with pval 3E-10, pubmedid=38018286
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GWAS
stroke disorder
risk allele=T, odds ratio/beta 2.927 [2.715- 3.154] with pval 4E-137, pubmedid=26908601
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GWAS
inflammatory bowel disease - you carry 1 copy of the risk allele G.
risk allele=G, EA odds ratio/beta 1.1942284 with pval 3E-8, pubmedid=26192919
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GWAS
ischemic stroke
risk allele=T, odds ratio/beta 2.927 [2.715- 3.154] with pval 4E-137, pubmedid=26908601
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GWAS
ferritin measurement
risk allele=T, odds ratio/beta 0.15 [0.12-0.17] SD increase with pval 7E-37, pubmedid=33536631
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GWAS
peripheral arterial disease
risk allele=T, odds ratio/beta 1.2 [1.14-1.26] with pval 2E-12, pubmedid=31285632; risk allele=T, odds ratio/beta 1.2 [1.15-1.25] with pval 7E-13, pubmedid=34601942
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GWAS
tissue factor pathway inhibitor amount
risk allele=T, odds ratio/beta 0.39 [0.31-0.47] unit decrease with pval 2E-23, pubmedid=34648354
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GWAS
total iron binding capacity
risk allele=T, odds ratio/beta 0.093 [0.13-0.061] SD decrease with pval 2E-8, pubmedid=33536631
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GWAS
menorrhagia
risk allele=T, odds ratio/beta 0.77 [0.73-0.82] with pval 1E-21, pubmedid=40069456
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GWAS
peripheral vascular disease
risk allele=C, odds ratio/beta 0.64 with pval 4E-12, pubmedid=33893285
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GWAS
protein sec13 homolog measurement
risk allele=T, odds ratio/beta 0.262 [0.18-0.35] unit decrease with pval 1E-9, pubmedid=34648354
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GWAS
d dimer measurement
risk allele=T, odds ratio/beta 0.257 [0.18-0.33] unit increase with pval 4E-11, pubmedid=33095540
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GWAS
abnormal thrombosis
risk allele=T, odds ratio/beta 2.927 [2.715- 3.154] with pval 4E-137, pubmedid=26908601
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GWAS
venous thromboembolism
risk allele=T, odds ratio/beta 3.5 [2.96–4.11] with pval 7E-50, pubmedid=28373160; risk allele=T, odds ratio/beta 3.57 [2.76-4.60] with pval 2E-22, pubmedid=22672568; risk allele=A, odds ratio/beta 5.775 [4.197-7.945] with pval 5E-27, pubmedid=33592630; risk allele=T, odds ratio/beta 2.5286865 [2.43-2.64] with pval 1E-300, pubmedid=31676865; risk allele=T, odds ratio/beta 2.927 [2.715- 3.154] with pval 4E-137, pubmedid=26908601; risk allele=T, odds ratio/beta 1.1108 [1.05-1.18] unit increase with pval 2E-245, pubmedid=36777996; risk allele=T, odds ratio/beta 1.0864 [1.06-1.12] unit increase with pval 4E-1051, pubmedid=36154123; risk allele=T, odds ratio/beta 2.39 [2.25-2.53] with pval 1E-188, pubmedid=31420334; risk allele=T, odds ratio/beta 1.0904 [1.06-1.12] unit increase with pval 2E-1028, pubmedid=36154123; risk allele=T, odds ratio/beta 1.1036 [1.07-1.14] unit increase with pval 8E-811, pubmedid=36154123; risk allele=T, odds ratio/beta 3.25 [2.91-3.64] with pval 1E-96, pubmedid=25772935
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GWAS
pulmonary embolism
risk allele=C, odds ratio/beta 0.7253895 [0.6-0.85] unit decrease with pval 4E-30, pubmedid=39789286; risk allele=T, odds ratio/beta 2.927 [2.715- 3.154] with pval 4E-137, pubmedid=26908601
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GWAS
deep vein thrombosis
risk allele=T, odds ratio/beta 2.927 [2.715- 3.154] with pval 4E-137, pubmedid=26908601; risk allele=C, odds ratio/beta 0.99490005 [0.92-1.07] unit decrease with pval 7E-154, pubmedid=39789286
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GWAS
antithrombotic agent use measurement
risk allele=C, odds ratio/beta 0.1479 [0.1-0.19] unit decrease with pval 3E-11, pubmedid=34594039; risk allele=T, odds ratio/beta 0.14787269 [0.1-0.19] unit increase with pval 3E-11, pubmedid=31015401