What you carry at this position in your DNA and what research says about it.
Toxin Detoxification: 6/10 evidence, 49 publications.
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Sample genotype (not yours): T/T
Typical Detoxification and Normal Toxin Clearance
This genotype is associated with normal, fully active epoxide hydrolase enzyme function. It provides typical clearance of environmental toxins and standard processing of medications like carbamazepine.
What this genotype means: Normal epoxide hydrolase activity; Standard clearance of environmental toxins; Typical response to carbamazepine and phenprocoumon.
Sample genotype (not yours): C/C
Reduced Toxin Clearance and Altered Drug Sensitivity
Two copies of the variant allele reduce epoxide hydrolase activity by approximately 40%. This slow-metabolizer status increases susceptibility to environmental toxins and significantly alters how drugs are processed.
What this genotype means: Approximately 40% reduced epoxide hydrolase activity; Increased risk of tobacco-related cancers and emphysema; Altered sensitivity and dosing for carbamazepine and phenprocoumon.
Sample genotype (not yours): T/C
Slightly Reduced Toxin Clearance and Altered Drug Response
Carrying one copy of the variant allele results in moderately reduced epoxide hydrolase activity. This can slightly alter the clearance of environmental toxins and affect how the body processes certain medications.
What this genotype means: Moderately reduced epoxide hydrolase activity; Slightly increased risk of tobacco-related cancers in smokers; Altered response to carbamazepine.
Gene function and biological role
Gene Function: The EPHX1 gene encodes microsomal epoxide hydrolase, an essential enzyme found in the endoplasmic reticulum of many tissues, particularly the liver [1]. This enzyme plays a dual role in the body by detoxifying highly reactive epoxide intermediates into less toxic, water-soluble compounds that can be safely excreted [2]. However, for certain environmental chemicals, the enzyme can inadvertently activate pro-carcinogens into highly reactive, mutagenic forms [3]. It is heavily involved in the first-pass metabolism of various medications, including anticonvulsants and anticoagulants [4]. Variations in this gene can significantly alter the rate of toxin clearance and drug processing [5].
Variant Impact: The rs1051740 variant, also known as Tyr113His, is a missense mutation in exon 3 of the EPHX1 gene that replaces the amino acid tyrosine with histidine at position 113 [1]. This specific amino acid substitution alters the stability of the epoxide hydrolase protein, reducing its overall catalytic activity by approximately 40% [1]. Because of this functional reduction, individuals carrying the variant allele are often classified as having slow epoxide hydrolase activity [2]. This slow-metabolizer status can lead to the accumulation of reactive epoxide intermediates from tobacco smoke, air pollution, and dietary toxins [2]. Additionally, this variant significantly alters the pharmacokinetics of several therapeutic drugs that rely on epoxide hydrolase for clearance [5].
Key Insight: This variant reduces the enzyme's ability to clear environmental toxins but paradoxically speeds up the metabolism of the epilepsy drug carbamazepine, meaning carriers often show a reduced response.
Location: EPHX1. Chromosome 1 · 1q42.12 · 225.8 Mb
Estimated prevalence by population
Global 52.5%; European 48.9%; African 66.5%; East Asian 30.3%; South Asian 40.2%; Americas 45.1%; Ashkenazi 50.7%; Finnish 49.4%; Middle Eastern 56.5%; Amish 49.6%.
Estimated TT genotype frequency.
Global 39.3%; European 42.1%; African 30.1%; East Asian 49.5%; South Asian 46.4%; Americas 44.1%; Ashkenazi 41.0%; Finnish 41.7%; Middle Eastern 37.3%; Amish 41.6%.
Estimated TC genotype frequency.
Global 8.1%; European 9.0%; African 3.4%; East Asian 20.2%; South Asian 13.4%; Americas 10.8%; Ashkenazi 8.3%; Finnish 8.8%; Middle Eastern 6.2%; Amish 8.7%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Cancer & Oncology
General Cancer Risk
Tobacco-Related Cancer. Evidence: 3/10. Source: PMID 21653646. Typical Risk.
Pharmacogenomics
Antiepileptic & Mood-Stabilizer Response
Carbamazepine Response. Evidence: 6/10. Source: PMID 22188362. Slower Metabolism.
Anticoagulant & Blood Thinner Response
Phenprocoumon Response. Evidence: 5/10. Source: PMID 21057703. Typical Response.
Chemotherapy Response
Chemotherapy Kidney Damage. Evidence: 5/10. Source: PMID 24533712. Typical Risk.
Organ Systems
Respiratory Health
COPD. Evidence: 3/10. Source: PMID 9288046. Typical Risk.
Showing effects for C/C genotype
Tobacco-Related Cancer. Evidence: 3/10. Source: PMID 21653646. Increased Risk.
Carbamazepine Response. Evidence: 6/10. Source: PMID 22188362. Faster Metabolism.
Phenprocoumon Response. Evidence: 5/10. Source: PMID 21057703. Higher Bleeding Risk.
COPD. Evidence: 3/10. Source: PMID 9288046. Increased Risk.
Showing effects for T/C genotype
Chemotherapy Kidney Damage. Evidence: 5/10. Source: PMID 24533712. Increased Risk.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Individuals with this genotype carry two copies of the T allele, resulting in typical, fully functional microsomal epoxide hydrolase activity [1]. This normal enzyme activity helps efficiently neutralize reactive epoxides from environmental pollutants, charred foods, and tobacco smoke, maintaining a standard baseline risk for tobacco-related cancers [2]. In the context of respiratory health, this genotype is associated with typical lung function and does not elevate the risk of developing emphysema or chronic obstructive pulmonary disease [3]. When taking the anticonvulsant drug carbamazepine, individuals with this genotype exhibit standard drug metabolism and typically show a standard response [4]. However, some studies suggest a slightly slower metabolism of carbamazepine compared to variant carriers [4]. There is also a typical response to the anticoagulant phenprocoumon, with a standard risk of over-anticoagulation [5].
Normal epoxide hydrolase activity; Standard clearance of environmental toxins; Typical response to carbamazepine and phenprocoumon.
Sample genotype: CC (Homozygous)
Carrying two copies of the C allele results in a stable but slow-acting form of the epoxide hydrolase enzyme, reducing overall activity by about 40% [1]. This significantly limits the body's ability to detoxify reactive epoxides, which is linked to an increased risk of tobacco-related cancers in smokers [2]. It is also associated with a higher susceptibility to chronic obstructive pulmonary disease and emphysema, as the lungs are less protected against oxidative stress [3]. In pharmacogenomics, this slow-metabolizer status paradoxically leads to faster clearance of carbamazepine, so the drug reaches lower levels and has a correspondingly weaker effect in these patients [4]. However, for the anticoagulant phenprocoumon, this genotype is associated with greater sensitivity and a higher risk of over-anticoagulation and bleeding [5]. Additionally, when combined with specific immune risk factors, this genotype has been linked to severe drug hypersensitivity syndromes [6].
Approximately 40% reduced epoxide hydrolase activity; Increased risk of tobacco-related cancers and emphysema; Altered sensitivity and dosing for carbamazepine and phenprocoumon.
Sample genotype: TC (Heterozygous)
This genotype represents an intermediate state with one copy of the slow-acting histidine variant, leading to a moderate reduction in epoxide hydrolase activity [1]. In smokers, this reduced capacity to clear reactive epoxides is associated with a moderately increased risk of tobacco-related cancers [2]. The intermediate enzyme activity also influences how the body processes several clinical medications [3]. For instance, individuals with this genotype may metabolize the anticonvulsant carbamazepine more rapidly, so the drug reaches lower levels and has a correspondingly weaker effect [3]. Conversely, when undergoing chemotherapy with cisplatin or cyclophosphamide, this genotype has been linked to an increased risk of kidney damage [4]. It also represents a typical baseline for anticoagulant sensitivity, though overall toxin clearance is slightly less efficient than in non-carriers [5].
Moderately reduced epoxide hydrolase activity; Slightly increased risk of tobacco-related cancers in smokers; Altered response to carbamazepine.
Variants with shared genetic architecture
rs2234922 · EPHX1 Gene · Chr 1 · COPD and Cancer Risk
rs1800566 · NQO1 Gene · Chr 16 · Toxin Detoxification
rs4646421 · CYP1A1 Gene · Chr 15 · Toxin Metabolism and Cancer
Genetic variants in microsomal epoxide hydrolase influence carbamazepine dosing.
Pharmacogenomic assessment of cisplatin-based chemotherapy outcomes in ovarian cancer.
Content updated August 2026.
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