What you carry at this position in your DNA and what research says about it.
Toxin Metabolism and Cancer: 4/10 evidence, 40 publications.
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Sample genotype (not yours): A/A
Typical Risk of Toxin-Related Conditions
Possessing two copies of the common A allele is associated with typical baseline risk for lung cancer, heart disease, and hormone-related conditions. The body processes environmental toxins and estrogens at a standard, balanced rate.
What this genotype means: Typical baseline risk of lung and cervical cancers; Standard rate of environmental toxin metabolism; Typical baseline risk of coronary artery disease.
Sample genotype (not yours): A/G
Slightly Elevated Risk of Toxin-Related Conditions
Inheriting one copy of the G variant is linked to a slightly higher risk of certain cancers and heart disease, particularly when exposed to tobacco smoke. This genetic change slightly increases the rate at which some chemicals are activated into harmful compounds.
What this genotype means: Slightly increased risk of lung and cervical cancers; Slightly elevated risk of coronary artery disease, especially with smoking; Slightly higher susceptibility to polycystic ovary syndrome.
Sample genotype (not yours): G/G
Elevated Risk of Toxin-Related Conditions
Possessing two copies of the G variant is associated with a higher risk of certain cancers and coronary artery disease, with the impact being strongly amplified by tobacco smoke and environmental pollutants. This genotype leads to higher enzyme activity, which can more rapidly convert toxins into DNA-damaging agents.
What this genotype means: Elevated risk of lung and laryngeal cancers, especially in smokers; Increased susceptibility to coronary artery disease; Higher risk of polycystic ovary syndrome and cervical cancer.
Gene function and biological role
Gene Function: The CYP1A1 gene encodes cytochrome P450 1A1, a critical phase I enzyme responsible for metabolizing environmental toxins, polycyclic aromatic hydrocarbons, and estrogens. This enzyme is primarily active in extrahepatic tissues like the lungs, where it processes inhaled carcinogens from tobacco smoke. While its primary role is detoxification, the metabolic process can sometimes convert benign compounds into highly reactive, DNA-damaging intermediates. Variations in this gene can alter enzyme activity and expression, directly affecting how efficiently the body processes these foreign chemicals. Consequently, CYP1A1 is heavily studied for its role in modulating susceptibility to various cancers and cardiovascular conditions.
Variant Impact: The rs4646903 variant, also known as the CYP1A1*2A or MspI polymorphism, is a single nucleotide change located in the downstream 3-flanking region of the CYP1A1 gene. This specific genetic change involves a thymine-to-cytosine substitution, represented as A to G on the positive strand. Although it is located in a non-coding region, this variation is associated with increased enzyme activity and higher inducibility of the cytochrome P450 1A1 enzyme. This heightened activity can lead to a more rapid activation of environmental pro-carcinogens into active DNA-damaging agents. As a result, this variant is widely investigated as a genetic modifier of risk for lung, cervical, and laryngeal cancers, particularly when combined with environmental exposures like smoking.
Key Insight: This variant does not directly cause disease but acts as a genetic modifier, meaning its health impact is heavily influenced by lifestyle factors like smoking and exposure to environmental pollutants.
Location: CYP1A1. Chromosome 15 · 15q24.1 · 74.7 Mb
Estimated prevalence by population
Global 67.4%; European 80.7%; African 58.0%; East Asian 34.2%; South Asian 45.3%; Americas 43.3%; Ashkenazi 76.9%; Finnish 76.0%; Middle Eastern 70.0%; Amish 77.5%.
Estimated AA genotype frequency.
Global 28.3%; European 18.2%; African 36.3%; East Asian 48.6%; South Asian 44.0%; Americas 45.0%; Ashkenazi 21.6%; Finnish 22.4%; Middle Eastern 27.3%; Amish 21.1%.
Estimated AG genotype frequency.
Global 4.3%; European 1.0%; African 5.7%; East Asian 17.2%; South Asian 10.7%; Americas 11.7%; Ashkenazi 1.5%; Finnish 1.6%; Middle Eastern 2.7%; Amish 1.4%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Cancer & Oncology
Lung Cancer
Lung Cancer. Evidence: 4/10. Source: PMID 19608585. Typical Risk.
Gynecological Cancers
Cervical Cancer. Evidence: 4/10. Source: PMID 32871478. Typical Risk.
Cardiovascular & Metabolic
Heart Disease
Coronary Artery Disease. Evidence: 4/10. Source: PMID 28513235. Typical Risk.
Endocrine & Reproductive
Female Reproductive Health & Fertility
Polycystic Ovary Syndrome. Evidence: 3/10. Source: PMID 23852617. Typical Risk.
Showing effects for A/G genotype
Lung Cancer. Evidence: 4/10. Source: PMID 19608585. Slightly Increased.
Cervical Cancer. Evidence: 4/10. Source: PMID 32871478. Slightly Increased.
Coronary Artery Disease. Evidence: 4/10. Source: PMID 28513235. Slightly Increased.
Polycystic Ovary Syndrome. Evidence: 3/10. Source: PMID 23852617. Slightly Increased.
Showing effects for G/G genotype
Lung Cancer. Evidence: 4/10. Source: PMID 19608585. Increased Risk.
Cervical Cancer. Evidence: 4/10. Source: PMID 32871478. Increased Risk.
Coronary Artery Disease. Evidence: 4/10. Source: PMID 28513235. Increased Risk.
Polycystic Ovary Syndrome. Evidence: 3/10. Source: PMID 23852617. Increased Risk.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Possessing two copies of the standard A allele represents the typical genetic profile for the CYP1A1 gene. This genetic profile is associated with baseline, typical activity of the cytochrome P450 1A1 enzyme. Because the enzyme operates at a standard rate, there is no genetically driven acceleration in the conversion of environmental chemicals into reactive, DNA-damaging compounds. Consequently, individuals with this genotype do not have the elevated risk of lung cancer or laryngeal cancer seen in carriers of the variant allele. This typical baseline risk also extends to cardiovascular health, with studies showing standard susceptibility to coronary artery disease. Furthermore, hormone metabolism remains balanced, resulting in typical baseline risks for conditions like polycystic ovary syndrome. Maintaining a healthy lifestyle by avoiding tobacco smoke and minimizing exposure to environmental pollutants helps preserve this favorable baseline.
Typical baseline risk of lung and cervical cancers; Standard rate of environmental toxin metabolism; Typical baseline risk of coronary artery disease.
Sample genotype: AG (Heterozygous)
Inheriting a single copy of the G variant introduces a slight alteration in enzyme activity. This heterozygous profile is associated with slightly increased activity and inducibility of the CYP1A1 enzyme. The heightened enzyme activity can slightly accelerate the metabolic activation of inhaled or ingested toxins into reactive intermediates that can damage DNA. Research indicates that carriers of this variant have a slightly elevated susceptibility to non-small cell lung cancer, especially if they smoke. There is also a slight increase in the risk of developing coronary artery disease, with the risk being more pronounced in individuals exposed to cigarette smoke. Additionally, studies have noted a slight upward trend in susceptibility to cervical cancer and polycystic ovary syndrome. Minimizing exposure to tobacco smoke, air pollution, and charred meats is particularly beneficial for individuals with this genetic profile to reduce the activation of harmful compounds.
Slightly increased risk of lung and cervical cancers; Slightly elevated risk of coronary artery disease, especially with smoking; Slightly higher susceptibility to polycystic ovary syndrome.
Sample genotype: GG (Homozygous)
Possessing two copies of the G variant represents the homozygous state for this CYP1A1 polymorphism. This homozygous profile is associated with significantly higher activity and inducibility of the cytochrome P450 1A1 enzyme. This elevated activity can lead to a faster rate of converting environmental toxins, such as polycyclic aromatic hydrocarbons, into highly reactive compounds that can cause DNA damage. Consequently, individuals with this genotype have an increased susceptibility to lung and laryngeal cancers, particularly when exposed to tobacco smoke. There is also a notable increase in the risk of coronary artery disease, which is heavily modulated by smoking status. Furthermore, this genotype is linked to a higher risk of hormone-related conditions, including polycystic ovary syndrome and cervical cancer. Because the health risks associated with this genotype are highly dependent on environmental exposures, avoiding tobacco smoke and reducing exposure to pollutants are key strategies for managing risk.
Elevated risk of lung and laryngeal cancers, especially in smokers; Increased susceptibility to coronary artery disease; Higher risk of polycystic ovary syndrome and cervical cancer.
Variants with shared genetic architecture
rs2470893 · CYP1A1 Gene · Chr 15 · Caffeine and Kidney Health
rs2472297 · CYP1A1 Gene · Chr 15 · Caffeine and Kidney Health
rs4646421 · CYP1A1 Gene · Chr 15 · Toxin Metabolism and Cancer
Content updated August 2026.
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