What you carry at this position in your DNA and what research says about it.
Blood Clotting and Heart Health: 8/10 evidence, 34 publications.
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Sample genotype (not yours): G/G
Typical Clotting and Lower Heart Risk
This genotype is associated with normal levels of coagulation factor XII and standard blood clotting times. It avoids the elevated cardiovascular risk linked to the minor variant.
What this genotype means: Normal factor XII levels; Standard blood clotting times; Baseline cardiovascular risk.
Sample genotype (not yours): A/A
Slower Clotting and Higher Heart Risk
Carrying two copies of the A allele significantly reduces factor XII levels, resulting in slower blood clotting. Some clinical studies associate this genotype with a modest increase in overall heart disease risk, though findings remain mixed.
What this genotype means: Significantly reduced factor XII levels; Longer blood clotting times; Modestly increased cardiovascular risk.
Sample genotype (not yours): A/G
Slightly Slower Clotting and Higher Heart Risk
Carrying one copy of the A allele slightly reduces factor XII levels, leading to marginally slower blood clotting. Despite slower clotting, some population studies link this genotype to a slightly elevated risk of heart disease.
What this genotype means: Slightly reduced factor XII levels; Marginally longer blood clotting times; Slightly increased cardiovascular risk.
Gene function and biological role
Gene Function: The F12 gene encodes coagulation factor XII, a critical protein in the blood coagulation cascade that initiates clotting and inflammatory pathways [1]. Factor XII circulates as an inactive zymogen until it is activated by contact with negatively charged surfaces [1]. Once active, it cleaves factor XI to continue the intrinsic pathway of clot formation [2]. It also plays a key role in the kallikrein-kinin system, which helps regulate blood pressure and inflammation [2]. Variations in this gene can significantly alter plasma factor XII levels, influencing clotting efficiency and cardiovascular risk [1] [2].
Variant Impact: The rs1801020 variant, also known as 46C to T, is located in the 5 prime untranslated region of the F12 gene and directly alters translation efficiency [3]. The minor A allele reduces the efficiency of protein translation, leading to significantly lower levels of circulating factor XII [3]. Conversely, the major G allele maintains normal, higher translation levels of the clotting factor [3]. This single nucleotide change is one of the most well-studied genetic determinants of activated partial thromboplastin time, a key measure of blood clotting speed [1].
Key Insight: A single letter change in the non-coding region of this gene acts like a dimmer switch, significantly lowering the production of a key clotting protein.
Location: F12. Chromosome 5 · 5q35.3 · 177.4 Mb
Estimated prevalence by population
Global 12.7%; European 6.2%; African 20.1%; East Asian 55.7%; South Asian 23.1%; Americas 11.3%; Ashkenazi 3.4%; Finnish 6.7%; Middle Eastern 5.2%; Amish 1.6%.
Estimated AA genotype frequency.
Global 41.7%; European 37.4%; African 49.5%; East Asian 37.9%; South Asian 49.9%; Americas 44.6%; Ashkenazi 30.1%; Finnish 38.4%; Middle Eastern 35.2%; Amish 22.0%.
Estimated AG genotype frequency.
Global 45.6%; European 56.4%; African 30.4%; East Asian 6.4%; South Asian 27.0%; Americas 44.1%; Ashkenazi 66.6%; Finnish 54.8%; Middle Eastern 59.6%; Amish 76.4%.
Estimated GG genotype frequency.
Showing effects for G/G genotype
Cardiovascular & Metabolic
Heart Disease
Heart Disease. Evidence: 4/10. Source: PMID 18974842. Normal risk.
Coagulation & Clotting
Blood Clotting Speed. Evidence: 8/10. Source: PMID 20303064. Typical speed.
Thrombin Levels. Evidence: 8/10. Source: PMID 34814699. Higher levels.
Organ Systems
Digestive & Gut Disorders
Peptic Ulcer. Evidence: 6/10. Source: PMID 38036781. Typical risk.
Showing effects for A/A genotype
Heart Disease. Evidence: 4/10. Source: PMID 18974842. 1.31x increased risk.
Blood Clotting Speed. Evidence: 8/10. Source: PMID 20303064. Slower clotting.
Thrombin Levels. Evidence: 8/10. Source: PMID 34814699. Lower levels.
Peptic Ulcer. Evidence: 6/10. Source: PMID 38036781. Higher risk.
Showing effects for A/G genotype
Blood Clotting Speed. Evidence: 8/10. Source: PMID 20303064. Slightly slower.
Thrombin Levels. Evidence: 8/10. Source: PMID 34814699. Intermediate levels.
Peptic Ulcer. Evidence: 6/10. Source: PMID 38036781. Slightly higher risk.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Having two copies of the G allele results in normal translation efficiency of the F12 gene, maintaining typical levels of circulating factor XII in the bloodstream [1]. This translates to standard blood coagulation times and a baseline risk profile for cardiovascular diseases [2]. While some studies suggest that higher factor XII levels can theoretically promote clot formation, this genotype is generally associated with a normal, baseline risk of heart disease compared to carriers of the A allele [2]. However, in specific clinical scenarios such as stroke treatment, individuals with this genotype may have a slightly different response to clot-dissolving therapies [3].
Normal factor XII levels; Standard blood clotting times; Baseline cardiovascular risk.
Sample genotype: AA (Homozygous)
Having two copies of the A allele significantly decreases the translation efficiency of the F12 gene, leading to the lowest levels of circulating factor XII [1]. This reduction markedly prolongs blood coagulation times, meaning the blood takes longer to form clots [2]. While slower clotting can be protective against certain types of thrombosis, large-scale genetic analyses have linked this genotype to a 1.31-fold increased risk of coronary heart disease in certain populations [3]. However, other clinical trials suggest a protective effect against acute coronary syndromes, highlighting the dual and highly debated role of factor XII in cardiovascular health [4].
Significantly reduced factor XII levels; Longer blood clotting times; Modestly increased cardiovascular risk.
Sample genotype: AG (Heterozygous)
This heterozygous genotype results in a moderate reduction in F12 translation efficiency, leading to intermediate levels of circulating factor XII [1]. Consequently, blood coagulation times are slightly prolonged compared to the G/G baseline [2]. Interestingly, epidemiological data presents a complex picture: while lower clotting factor levels might be expected to protect against clots, some cohort studies have observed a modest 1.31-fold increase in cardiovascular risk for carriers of this allele [3]. This apparent paradox may stem from the complex role of factor XII in both clotting and inflammatory pathways, or from population-specific genetic backgrounds [3].
Slightly reduced factor XII levels; Marginally longer blood clotting times; Slightly increased cardiovascular risk.
Variants with shared genetic architecture
rs2731672 · F12 Gene · Chr 5 · Blood Clotting Speed
rs4981022 · NT5DC3 Gene · Chr 12 · Blood Clotting Levels
rs2066865 · FGG Gene · Chr 4 · Blood Clot Risk
Gender differences in genetic risk profiles for cardiovascular disease.
Content updated August 2026.
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