What you carry at this position in your DNA and what research says about it.
COPD and Cancer Risk: 7/10 evidence, 18 publications.
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Sample genotype (not yours): A/A
Higher Risk of COPD and Tobacco-Related Cancers
Two copies of the reference A allele result in lower microsomal epoxide hydrolase activity. Slower detoxification of environmental toxins is linked to an increased susceptibility to lung injury and certain cancers.
What this genotype means: Slower clearance of environmental toxins; Increased susceptibility to smoking-related lung damage; Higher risk of tobacco-related cancers.
Sample genotype (not yours): A/G
Typical to Lower Risk of COPD and Cancers
One copy of the G variant allele provides intermediate to fast enzyme activity. Enhanced clearance of environmental toxins offers some protection against lung disease and tobacco-related cancers.
What this genotype means: More efficient clearance of inhaled toxins; Reduced risk of chronic lung disease; Altered metabolism of certain anti-seizure medications.
Sample genotype (not yours): G/G
Lower Risk of COPD and Tobacco-Related Cancers
Two copies of the G variant allele result in high microsomal epoxide hydrolase activity. Fast detoxification of inhaled pollutants helps protect the lungs and reduces the risk of tobacco-related cancers.
What this genotype means: Highly efficient detoxification of environmental pollutants; Significantly lower risk of smoking-related lung injury; Altered response to specific medications.
Gene function and biological role
Gene Function: The EPHX1 gene encodes microsomal epoxide hydrolase, a critical biotransformation enzyme highly active in the liver and lungs [1]. This enzyme plays a vital role in the detoxification of highly reactive epoxide intermediates, which are produced during the metabolism of environmental toxins, cigarette smoke, and certain medications [1]. By converting these unstable epoxides into more water-soluble and less toxic compounds, EPHX1 helps protect cellular structures from oxidative damage and chemical carcinogenesis [1]. Variations in this gene can significantly alter its catalytic efficiency, making individuals more or less susceptible to toxic exposures and chronic lung conditions [2].
Variant Impact: Located in exon 4 of the EPHX1 gene, rs2234922 is a missense mutation resulting in a histidine-to-arginine substitution at position 139 (p.His139Arg) [1]. This specific amino acid change alters the catalytic efficiency of the microsomal epoxide hydrolase enzyme [2]. The variant G allele (encoding arginine) increases enzyme activity by approximately 25% compared to the reference A allele (encoding histidine) [1]. Because it accelerates the breakdown of reactive epoxides, this fast variant allele is generally associated with enhanced detoxification of certain environmental carcinogens and tobacco smoke toxins [1]. Consequently, this variant has been widely studied for its protective effects against chronic obstructive pulmonary disease (COPD) and various cancers [2].
Key Insight: The fast variant of this gene actually increases enzyme activity, helping the body clear certain environmental toxins and cigarette smoke byproducts more rapidly.
Location: EPHX1. Chromosome 1 · 1q42.12 · 225.8 Mb
Estimated prevalence by population
Global 60.3%; European 64.3%; African 43.8%; East Asian 74.8%; South Asian 58.7%; Americas 70.8%; Ashkenazi 74.0%; Finnish 71.4%; Middle Eastern 65.9%; Amish 81.6%.
Estimated AA genotype frequency.
Global 34.0%; European 31.8%; African 44.8%; East Asian 23.4%; South Asian 35.8%; Americas 26.7%; Ashkenazi 24.1%; Finnish 26.2%; Middle Eastern 30.6%; Amish 17.4%.
Estimated AG genotype frequency.
Global 5.7%; European 3.9%; African 11.4%; East Asian 1.8%; South Asian 5.5%; Americas 2.5%; Ashkenazi 2.0%; Finnish 2.4%; Middle Eastern 3.5%; Amish 0.9%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Organ Systems
Respiratory Health
COPD. Evidence: 3/10. Source: PMID 20932192. Increased Risk.
Cancer & Oncology
General Cancer Risk
Tobacco-Related Cancer. Evidence: 3/10. Source: PMID 21653646. Increased Risk.
Pharmacogenomics
Antiepileptic & Mood-Stabilizer Response
Carbamazepine Response. Evidence: 5/10. Source: PMID 19620853. Typical Metabolism.
Phenytoin Sensitivity. Evidence: 5/10. Source: PMID 19952982. Typical Risk.
Endocrine & Reproductive
Hormone Levels & Endocrine Regulation
SHBG Levels. Evidence: 7/10. Source: PMID 32042192. Higher Levels.
Showing effects for A/G genotype
COPD. Evidence: 3/10. Source: PMID 20932192. Slightly Lower Risk.
Tobacco-Related Cancer. Evidence: 3/10. Source: PMID 21653646. Typical Risk.
Carbamazepine Response. Evidence: 5/10. Source: PMID 19620853. Slower Metabolism.
Phenytoin Sensitivity. Evidence: 5/10. Source: PMID 19952982. Increased Risk.
SHBG Levels. Evidence: 7/10. Source: PMID 32042192. Typical Levels.
Showing effects for G/G genotype
COPD. Evidence: 3/10. Source: PMID 20932192. Lower Risk.
Tobacco-Related Cancer. Evidence: 3/10. Source: PMID 21653646. Lower Risk.
Carbamazepine Response. Evidence: 5/10. Source: PMID 19620853. Altered Metabolism.
SHBG Levels. Evidence: 7/10. Source: PMID 32042192. Lower Levels.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
A pair of reference A alleles encodes the slow form of the microsomal epoxide hydrolase enzyme [1]. With lower enzymatic activity, the body clears reactive epoxide intermediates from environmental pollutants and cigarette smoke more slowly [1]. This delay allows toxic compounds to persist longer in tissues, increasing the risk of oxidative damage and cellular mutation [1]. Large-scale studies have shown that individuals with this slower detoxification profile have a significantly higher risk of developing chronic obstructive pulmonary disease (COPD) [2]. Furthermore, this genotype is associated with an elevated risk of tobacco-related cancers among smokers [1]. On the other hand, individuals with this genotype typically exhibit standard metabolism of medications like carbamazepine and phenytoin [3].
Slower clearance of environmental toxins; Increased susceptibility to smoking-related lung damage; Higher risk of tobacco-related cancers.
Sample genotype: AG (Heterozygous)
A single copy of the G variant allele encodes the fast version of the microsomal epoxide hydrolase enzyme [1]. Increased enzyme activity allows for more rapid breakdown of reactive epoxides from cigarette smoke and air pollution [1]. This efficient clearance helps protect lung tissues from oxidative stress and reduces the likelihood of chronic airway inflammation [2]. Consequently, individuals with this genotype have a lower risk of developing chronic obstructive pulmonary disease (COPD) compared to those with the slow-acting AA genotype [2]. They also exhibit a reduced susceptibility to tobacco-related cancers [1]. However, this genotype may alter the metabolism of certain medications, such as carbamazepine, and is associated with a higher risk of specific side effects if taking phenytoin.
More efficient clearance of inhaled toxins; Reduced risk of chronic lung disease; Altered metabolism of certain anti-seizure medications.
Sample genotype: GG (Homozygous)
Two copies of the G variant allele encode the highly active fast form of the microsomal epoxide hydrolase enzyme [1]. With approximately 25% higher enzyme activity, the body is able to rapidly neutralize reactive epoxide intermediates generated from environmental toxins and tobacco smoke [1]. This rapid detoxification minimizes the accumulation of harmful compounds, protecting cellular DNA and lung tissues from oxidative damage [1]. Research indicates that this fast-clearing genotype is associated with a significantly lower risk of developing chronic obstructive pulmonary disease (COPD) [2]. It also provides a protective effect against tobacco-related cancers in individuals exposed to smoke [1]. However, this high-activity genotype can influence how the body processes certain drugs, potentially leading to slower carbamazepine metabolism or an increased risk of side effects from phenytoin.
Highly efficient detoxification of environmental pollutants; Significantly lower risk of smoking-related lung injury; Altered response to specific medications.
Variants with shared genetic architecture
rs1051740 · EPHX1 Gene · Chr 1 · Toxin Detoxification
rs17486278 · CHRNA5 Gene · Chr 15 · Lung Disease Risk
rs28929474 · SERPINA1 Gene · Chr 14 · Alpha-1 Antitrypsin Deficiency
Genetic variants in microsomal epoxide hydrolase influence carbamazepine dosing.
Content updated August 2026.
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