What you carry at this position in your DNA and what research says about it.
Toxin Metabolism and Cancer: 6/10 evidence, 14 publications.
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Sample genotype (not yours): G/G
Typical Toxin Metabolism and Lower Cancer Risk
Carrying two copies of the common G allele is associated with typical CYP1A1 enzyme activity. This helps maintain a balanced detoxification process and is linked to a lower risk of toxin-induced cancers.
What this genotype means: Typical metabolic activation of environmental toxins; Lower risk of hepatocellular carcinoma; Optimal lung vital capacity.
Sample genotype (not yours): A/A
Increased Cancer Risk and Higher Toxin Sensitivity
Carrying two copies of the minor A allele is associated with significantly higher CYP1A1 expression. This accelerates the activation of environmental carcinogens, leading to an elevated risk of several cancers.
What this genotype means: Highly elevated activation of environmental carcinogens; Increased risk of liver, laryngeal, and bladder cancers; Lower lung vital capacity and higher sensitivity to smoke.
Sample genotype (not yours): G/A
Slightly Increased Cancer Risk from Toxins
Carrying one copy of the minor A allele is linked to slightly elevated CYP1A1 enzyme activity. This can increase the activation of environmental carcinogens, mildly raising the risk of certain cancers.
What this genotype means: Elevated activation of environmental carcinogens; Slightly increased risk of liver and laryngeal cancers; Increased sensitivity to tobacco smoke and air pollutants.
Gene function and biological role
Gene Function: The CYP1A1 gene encodes cytochrome P450 1A1, a critical phase I enzyme primarily responsible for metabolizing polycyclic aromatic hydrocarbons, steroid hormones, and various environmental toxins [1]. While this enzyme is essential for detoxifying many foreign compounds, its metabolic activity can also bioactivate certain procarcinogens into highly reactive, DNA-damaging intermediates [2]. It is highly expressed in extrahepatic tissues, particularly in the lungs, where it interacts directly with inhaled pollutants like tobacco smoke [3]. Genetic variations that alter the expression or activity of this enzyme can significantly shift the balance between toxin clearance and carcinogen activation [4].
Variant Impact: The rs4646421 variant is an intronic genetic change located within the CYP1A1 gene that influences gene expression levels and enzyme activity [1]. Carrying the minor A allele is associated with increased expression of the CYP1A1 enzyme, leading to accelerated processing of environmental toxins [2]. This elevated activity can increase the generation of reactive, DNA-damaging intermediates when individuals are exposed to pollutants like tobacco smoke or polycyclic aromatic hydrocarbons [4]. Consequently, this variant has been studied extensively for its role in modulating susceptibility to various cancers and respiratory conditions [3].
Key Insight: The CYP1A1 enzyme is highly active in the lungs rather than the liver, making its genetic variants particularly sensitive to inhaled pollutants like tobacco smoke. While faster metabolism is usually positive, for this gene, higher activity actually increases the production of dangerous, DNA-damaging cancer-causing agents.
Location: CYP1A1. Chromosome 15 · 15q24.1 · 74.7 Mb
Estimated prevalence by population
Global 63.2%; European 81.1%; African 41.7%; East Asian 34.8%; South Asian 48.3%; Americas 42.4%; Ashkenazi 76.6%; Finnish 77.1%; Middle Eastern 72.3%; Amish 77.7%.
Estimated GG genotype frequency.
Global 30.6%; European 17.9%; African 45.8%; East Asian 48.4%; South Asian 42.4%; Americas 45.4%; Ashkenazi 21.9%; Finnish 21.4%; Middle Eastern 25.5%; Amish 20.9%.
Estimated GA genotype frequency.
Global 6.2%; European 1.0%; African 12.6%; East Asian 16.8%; South Asian 9.3%; Americas 12.2%; Ashkenazi 1.6%; Finnish 1.5%; Middle Eastern 2.2%; Amish 1.4%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Cancer & Oncology
Gastrointestinal Cancers
Liver Cancer. Evidence: 3/10. Source: PMID 19110417. Typical Risk.
Head, Neck & Oral Cancers
Laryngeal Cancer. Evidence: 3/10. Source: PMID 29581776. Typical Risk.
Urologic Cancers
Bladder Cancer. Evidence: 3/10. Source: PMID 18798002. Typical Risk.
Blood Cancers
Childhood Leukemia. Evidence: 3/10. Source: PMID 18691756. Typical Risk.
Organ Systems
Respiratory Health
Lung Function. Evidence: 6/10. Source: PMID 36914875. Higher Vital Capacity.
Cardiovascular & Metabolic
Hypertension
Blood Pressure. Evidence: 3/10. Source: PMID 19330903. Typical.
Showing effects for A/A genotype
Liver Cancer. Evidence: 3/10. Source: PMID 19110417. ~1.3x Increased Risk.
Laryngeal Cancer. Evidence: 3/10. Source: PMID 29581776. Increased Risk.
Bladder Cancer. Evidence: 3/10. Source: PMID 18798002. Increased Risk.
Childhood Leukemia. Evidence: 3/10. Source: PMID 18691756. Increased Risk.
Lung Function. Evidence: 6/10. Source: PMID 36914875. Lower Vital Capacity.
Blood Pressure. Evidence: 3/10. Source: PMID 19330903. Increased Risk.
Showing effects for G/A genotype
Lung Function. Evidence: 6/10. Source: PMID 36914875. Typical.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Having the G/G genotype means possessing two copies of the major, protective allele, which is associated with baseline CYP1A1 enzyme expression [1]. This typical level of activity reduces the rate at which environmental procarcinogens, such as those found in tobacco smoke, are converted into harmful DNA-damaging intermediates [2]. Consequently, individuals with this genotype exhibit a lower risk of developing hepatocellular carcinoma compared to carriers of the A allele [1]. This genotype is also associated with better lung function and higher vital capacity [3]. Furthermore, the risk of developing other toxin-related malignancies, such as laryngeal cancer, remains at the typical baseline level [4]. Maintaining a healthy lifestyle free from heavy smoke exposure further supports this natural protective advantage.
Typical metabolic activation of environmental toxins; Lower risk of hepatocellular carcinoma; Optimal lung vital capacity.
Sample genotype: AA (Homozygous)
Possessing two copies of the minor A allele significantly elevates the expression of the CYP1A1 enzyme, leading to rapid metabolism of inhaled and ingested toxins [1]. While rapid clearance sounds beneficial, in the case of CYP1A1, it results in a much higher rate of bioactivating procarcinogens into highly reactive, mutagenic compounds [2]. This metabolic imbalance is strongly linked to an increased risk of hepatocellular carcinoma, especially in certain populations [1]. It is also associated with lower lung function and reduced vital capacity, making the respiratory system more vulnerable to environmental insults [3]. Furthermore, the risk of developing laryngeal cancer and childhood leukemia is elevated, particularly when combined with parental or personal smoking. Adopting a proactive lifestyle that avoids tobacco smoke, heavy air pollution, and industrial chemicals is crucial to mitigate these genetic risks.
Highly elevated activation of environmental carcinogens; Increased risk of liver, laryngeal, and bladder cancers; Lower lung vital capacity and higher sensitivity to smoke.
Sample genotype: GA (Heterozygous)
Inheriting one copy of the minor A allele leads to a moderate increase in the expression and metabolic activity of the CYP1A1 enzyme [1]. When exposed to environmental pollutants like polycyclic aromatic hydrocarbons or cigarette smoke, this increased activity can accelerate the conversion of these compounds into reactive intermediates that damage DNA [2]. As a result, carriers of this genotype have a slightly elevated risk of developing hepatocellular carcinoma [1]. There is also a documented increase in susceptibility to laryngeal squamous cell carcinoma, particularly when combined with tobacco use [3]. Additionally, this genetic variation may interact with environmental exposures to affect overall lung function and respiratory health [4]. Minimizing exposure to secondhand smoke, air pollution, and charred foods is highly beneficial for individuals with this genotype.
Elevated activation of environmental carcinogens; Slightly increased risk of liver and laryngeal cancers; Increased sensitivity to tobacco smoke and air pollutants.
Variants with shared genetic architecture
rs2470893 · CYP1A1 Gene · Chr 15 · Caffeine and Kidney Health
rs2472297 · CYP1A1 Gene · Chr 15 · Caffeine and Kidney Health
rs1048943 · CYP1A1 Gene · Chr 15 · Environmental Cancer Risk
Content updated August 2026.
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