Deep vein thrombosis has a substantial hereditary component. Studies estimate that genetic factors account for roughly 40 to 60 percent of the variation in who develops blood clots in the veins, with the remainder driven by environmental and lifestyle triggers. But “hereditary” does not mean a single gene passes DVT from parent to child like eye color. The genetics behind venous clotting involve a handful of well-known mutations, a much larger pool of common gene variants with small individual effects, and the way all of them interact with things like hormones, immobility, and surgery.
How Much of DVT Risk Is Genetic
Two landmark studies help frame the answer. The GAIT study, which examined extended families in Spain, attributed more than 60 percent of the variation in thrombosis susceptibility to genetic factors.1PubMed Central. Genetic susceptibility to thrombosis and its relationship to physiological risk factors: the GAIT study. Genetic Analysis of Idiopathic Thrombophilia. A later Swedish study using sibling data came in somewhat lower, estimating heritability at about 47 percent for men and 40 percent for women.2PubMed. A sibling based design to quantify genetic and shared environmental effects of venous thromboembolism in Sweden The Swedish study also found that the shared environment between siblings, things like growing up in the same household, contributed essentially zero percent to risk. That is a striking finding: it means the familial clustering people observe in DVT is overwhelmingly genetic rather than the result of shared habits or living conditions.
Separately from heritability estimates, family-based studies show that having a sibling who experienced a venous clot roughly doubles your own risk compared to the general population.3PubMed Central. Environmental and genetic risk factors associated with venous thromboembolism Family history of clotting remains a strong risk factor for DVT even when researchers account for all known susceptibility genes, which suggests that plenty of genetic contributors have yet to be identified.4Nature Reviews Cardiology. Inherited risk factors for venous thromboembolism
Factor V Leiden and the Prothrombin Mutation
If you have heard of any “clotting gene,” it is probably Factor V Leiden (often abbreviated FVL). This single-letter change in the gene for coagulation factor V is the most common inherited cause of thrombophilia. Having one copy of the mutation raises the risk of a first venous clot about sevenfold; having two copies pushes that to roughly 80-fold.5JAMA Internal Medicine. The Risk of Recurrent Venous Thromboembolism in Heterozygous Carriers of Factor V Leiden and a First Spontaneous Venous Thromboembolism Those numbers sound alarming, but context matters. The absolute risk of DVT in young, healthy adults is very low to begin with, so multiplying a small number by seven still yields a relatively small number for most carriers in any given year.
The prothrombin G20210A mutation is the second most studied inherited risk factor. Carriers produce higher levels of the clotting protein prothrombin, which nudges the blood toward a more clot-prone state.6PubMed Central. Epidemiology of Prothrombin G20210A Mutation in the Mediterranean Region One Italian study found an 8.7-fold increase in DVT risk among carriers, with about two-thirds of them having prothrombin levels in the highest quarter of the normal range.7PubMed. The G20210A mutation of the prothrombin gene in patients with previous first episodes of deep-vein thrombosis
What makes these two mutations especially interesting is how they behave together. Carrying Factor V Leiden alone does not appear to raise the risk of a second clot after a first event. But people who are heterozygous for both Factor V Leiden and the prothrombin mutation face about 2.6 times the recurrence risk compared to people with Factor V Leiden alone.8PubMed. The risk of recurrent deep venous thrombosis among heterozygous carriers of both factor V Leiden and the G20210A prothrombin mutation The combination of inherited defects, rather than any single one, is often what tips a person from “theoretical risk” into “clinical clot.”
Deficiencies in Natural Anticoagulant Proteins
Your body has its own braking system for clotting: proteins called antithrombin, protein C, and protein S. Inherited deficiencies in any of these are rarer than Factor V Leiden but tend to be more potent risk factors. People who lack adequate amounts of these natural anticoagulants are prone to clots at younger ages, often before 40 or 45, and without the typical triggers like surgery or long immobilization.9PubMed Central. Deficiencies of proteins C, S and antithrombin and activated protein C resistance–their involvement in the occurrence of Arterial thromboses
These deficiencies are relatively uncommon in the general population. In one study of outpatients with DVT, about 8 percent had a deficiency in one of these proteins, compared with roughly 2 percent of controls.10PubMed. Deficiencies of coagulation-inhibiting and fibrinolytic proteins in outpatients with deep-vein thrombosis Frequencies vary by population, though. A study of Japanese DVT patients found mutations in the genes for protein S, protein C, or antithrombin in about 32 percent of cases, suggesting that in populations where Factor V Leiden is virtually absent, these anticoagulant deficiencies fill a larger share of the hereditary risk.11PubMed. Prevalence of genetic mutations in protein S, protein C and antithrombin genes in Japanese patients with deep vein thrombosis
High Factor VIII and Blood Type
Beyond the “classic” thrombophilia mutations, elevated levels of coagulation factor VIII are an underappreciated and very common risk factor for DVT. Levels above 150 percent of normal are linked to a five- to sixfold increase in clotting risk, and about a quarter of people presenting with a first DVT have factor VIII levels in that range.12PubMed. Heritability of elevated factor VIII antigen levels in factor V Leiden families with thrombophilia Researchers studying large families with thrombophilia found strong familial clustering of high factor VIII levels that persisted even after accounting for blood group, confirming that the trait is genetically driven by factors beyond blood type alone.
In rare cases, the genetic basis is dramatic. Researchers identified an Italian family in which a partial duplication of the gene that makes factor VIII caused persistently extreme levels, above 400 percent, and recurrent clots before age 50.13PubMed. Partial F8 gene duplication (factor VIII Padua) associated with high factor VIII levels and familial thrombophilia
Blood type itself plays a role, too. People with non-O blood types (A, B, or AB) carry higher levels of von Willebrand factor, a protein that stabilizes factor VIII in the bloodstream. A study of DVT patients found that those with non-O blood had substantially higher von Willebrand factor levels than those with type O blood.14PubMed. Application of VWF Antigen and Activity Testing Based on ABO Blood Group in Risk Assessment of Deep Vein Thrombosis Because your ABO blood type is inherited, this is another avenue by which your DNA influences clotting risk without involving any of the well-known thrombophilia mutations.
Polygenic Risk and the Bigger Genetic Picture
Focusing only on single high-impact mutations misses the way most genetic risk actually works. For most people, susceptibility to DVT is shaped by dozens or hundreds of common gene variants, each contributing a small nudge. Researchers have begun bundling these into polygenic risk scores. In one model, people in the top 10 percent of polygenic risk had a 3.4-fold increased risk of DVT. Even after excluding Factor V Leiden carriers, those in the top decile still faced 2.3 times the average risk.15PubMed. Polygenic risk scores and risk stratification in deep vein thrombosis The estimated cumulative risk of DVT by age 80 was about 10 percent for Factor V Leiden carriers in that top genetic decile and about 5 percent for non-carriers.
A large UK Biobank study found even stronger effects when genetic and clinical risk scores were combined. People at high genetic risk had about triple the clot rate of those at low genetic risk. But people who scored high on both the genetic and clinical scales (accounting for factors like age, BMI, smoking, cancer history, and recent fracture) had nearly an eightfold increase.16Scientific Reports. Prediction of primary venous thromboembolism based on clinical and genetic factors within the U.K. Biobank The combined model significantly outperformed either score on its own, which reinforces the point that genes and environment work together.
When Genes and Environment Collide
Some of the most dramatic risk amplification happens when inherited susceptibility meets a strong environmental trigger. Oral contraceptives are the best-studied example. A meta-analysis of 14 studies found that combined oral contraceptive users who carried a mild thrombophilia (such as a single copy of Factor V Leiden or the prothrombin mutation) faced about a sixfold increase in clot risk. For those with severe thrombophilia, the increase was more than sevenfold.17Journal of Thrombosis and Haemostasis. Venous thromboembolism risk in users of oral contraceptives containing factor V Leiden or prothrombin mutation: a systematic review and meta-analysis
A Danish registry study drilled deeper into timing. Women in the top decile of polygenic risk who also carried Factor V Leiden faced roughly a ninefold increase in clot risk during the first two years of oral contraceptive use. Those carrying the prothrombin mutation in that same high-risk genetic decile had more than a tenfold increase. And for the unlucky women carrying both mutations plus a high polygenic score, the hazard ratio during those first two years reached nearly 15 compared to low-risk women not on the pill.18American Journal of Obstetrics and Gynecology. Genetic factors and risk of venous thromboembolism in women using oral contraceptives After the first two years the risk dropped but remained elevated. This gene-hormone interaction explains why some clinicians argue for genetic screening before prescribing hormonal contraceptives, though as we will see, guidelines remain cautious about routine testing.
Population Differences in Genetic Risk
The prevalence of Factor V Leiden varies enormously by ancestry. In a study of more than 4,000 Americans, the carrier frequency was about 5.3 percent among white Americans, 2.2 percent among Hispanic Americans, 1.2 percent among Black Americans, and under 0.5 percent among Asian Americans.19PubMed. Ethnic distribution of factor V Leiden in 4047 men and women. Implications for venous thromboembolism screening. Globally, FVL ranges from near zero in East Asian and sub-Saharan African populations up to 13 to 15 percent in some Mediterranean and Middle Eastern countries.20PubMed Central. Frequency of Factor V Leiden in Deep Vein Thrombosis
Among patients on chronic anticoagulation, the pattern holds: one study found Factor V Leiden in about 8.6 percent of European American patients but only 1.4 percent of African American patients.21PubMed Central. Racial differences in the prevalence of Factor V Leiden mutation among patients on chronic warfarin therapy These disparities do not mean that DVT is less hereditary in populations where FVL is rare. They mean the specific mutations involved differ. In East Asian populations, for instance, protein S and protein C deficiencies carry more of the inherited risk, as the Japanese data mentioned earlier show.
Why Factor V Leiden Persists
If Factor V Leiden raises the risk of dangerous blood clots, you might expect natural selection to have weeded it out long ago. Instead, it is carried by up to 15 percent of Europeans. The likely explanation is that the mutation offered survival advantages that historically outweighed its costs. Women who carry FVL appear to have a lower risk of severe hemorrhage during childbirth and may maintain better iron stores thanks to reduced blood loss. There is also some evidence that FVL carriers fare slightly better during sepsis, because a blood system biased toward clotting can help wall off invading pathogens.22PubMed. Carriership of Factor V Leiden and evolutionary selection advantage In a historical world where maternal hemorrhage and infection were leading killers, these advantages may have been enough to maintain the mutation’s high frequency despite its modern-day thrombotic cost.23PubMed. On the evolutionary advantage of coagulation factor V Leiden (FVL)
Family History Often Outperforms Genetic Testing
You might assume that the best way to know your hereditary DVT risk is a thrombophilia panel. In practice, family history is surprisingly powerful and possibly more informative than the standard blood tests. A large case-control study found that family history and known genetic risk factors correlated poorly with each other: a person could test negative for every mutation on a standard panel and still have a strong family history that independently predicted clots. The positive predictive value of family history as a screening test for known genetic defects was low, suggesting that many of the hereditary factors driving familial clustering have not yet been identified in standard clinical tests.24JAMA Internal Medicine. The Value of Family History as a Risk Indicator for Venous Thrombosis
This is an underappreciated point. The genes we can currently test for explain only a fraction of the heritability. A clean thrombophilia panel does not mean you have no inherited risk, and a positive result for Factor V Leiden alone does not necessarily mean your clots will recur. Prospective data show that recurrence rates track most strongly with the combination of family history and thrombophilia status: patients with both a family history and a detectable thrombophilia had the highest recurrence rate, at about 7.7 events per 100 person-years, while those with neither had the lowest, at 2.6 per 100 person-years.25Journal of Thrombosis and Haemostasis. Role of family history of venous thromboembolism and thrombophilia as predictors of recurrence: a prospective follow‐up study
Should You Get Tested
Given all this, you might wonder whether everyone should be tested for thrombophilia genes. Most clinical guidelines say no. A review of recommendations from multiple scientific societies concluded that the absolute risk of DVT is low for most people, and blanket screening for inherited thrombophilia in patients or their unaffected relatives is not useful. Targeted testing, guided by a strong family history or an unexplained clot at a young age, is more likely to yield actionable results.26PubMed. Testing for inherited thrombophilia and consequences for antithrombotic prophylaxis in patients with venous thromboembolism and their relatives
Part of the concern is that a positive result on a direct-to-consumer or screening test can generate anxiety without meaningfully changing management. Most carriers of Factor V Leiden or the prothrombin mutation will never develop a clot. Knowing your status could lead to unnecessary long-term anticoagulation, which carries its own bleeding risks. That said, a survey of consumers who received direct-to-consumer results for these two mutations found that only about 36 percent of those testing positive reported increased worry afterward, while roughly 78 percent of positive individuals felt that knowing their risk was an advantage overall.27PubMed Central. Direct-to-consumer genetic testing for factor V Leiden and prothrombin 20210G>A: the consumer experience How people respond to this kind of information varies, and genetic counseling helps contextualize the numbers.
Inherited Thrombophilia in Children
DVT in children is uncommon, but when it happens, inherited thrombophilia plays a notable role. A systematic review and meta-analysis of pediatric studies found a statistically significant association between childhood clots and every inherited thrombophilia trait examined, even though more than 70 percent of affected children also had at least one clinical risk factor such as a central venous catheter or immobilization. The strongest genetic association was with antithrombin deficiency, which carried roughly a ninefold increased odds of clotting. Factor V Leiden and the prothrombin mutation were also significant for a first event, though Factor V Leiden did not predict recurrence in children any more than it does in adults.28PubMed. Impact of inherited thrombophilia on venous thromboembolism in children: a systematic review and meta-analysis of observational studies Pediatric DVT is almost always triggered by something clinical, but inherited susceptibility determines which children are most vulnerable to those triggers.
Epigenetics and Gene Editing on the Horizon
The genetics of DVT does not end at the DNA sequence you inherit. Emerging research points to epigenetic modifications, changes in how genes are expressed without altering the underlying code, as additional players. Certain small RNA molecules appear to be expressed at abnormal levels in people with active clotting, and one particular chemical modification of proteins called histone citrullination promotes the release of structures from white blood cells that accelerate clot formation.29Thrombosis Research. Genetics and epigenetics in venous thromboembolism: Clinical perspectives These findings are early-stage, but they hint at a layer of heritable clotting risk that conventional gene tests do not capture.
On the therapeutic side, researchers have demonstrated a proof-of-concept for using gene editing to treat inherited thrombophilia. In a 2022 study, scientists took blood cells from a patient with severe antithrombin deficiency, reprogrammed them into stem cells, and used CRISPR to correct the causative mutation. The edited cells were then coaxed into becoming liver-like cells and transplanted into mice that lacked antithrombin. The treated mice saw their antithrombin activity rise from about 47 percent to nearly 89 percent of normal, and their clot burden dropped significantly.30PubMed. Gene editing of human iPSCs rescues thrombophilia in hereditary antithrombin deficiency in mice This is a long way from a clinical therapy, but it represents the first demonstration that the specific genetic defects behind hereditary thrombophilia can, in principle, be corrected at their source.