rs8192780 — CYP2E1

Downstream regulatory variant near CYP2E1 associated with nasopharyngeal carcinoma risk in smokers through altered carcinogen metabolism

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CYP2E1 rs8192780 — A Regulatory Tag Variant and Smoking Interaction

CYP2E1 is the liver and lung enzyme that metabolizes ethanol, acetaminophen, and a wide spectrum of environmental carcinogens including tobacco-specific nitrosamines (NNK), polycyclic aromatic hydrocarbons, benzene, and chlorinated solvents. rs8192780 sits approximately 1.5 kilobases downstream of the CYP2E1 gene in a 3' flanking regulatory region. Unlike the well-studied upstream *5B variant (rs2031920), this SNP has limited direct functional characterization, but one moderately-sized genetic association study links it to nasopharyngeal carcinoma (NPC) risk — particularly among young smokers of Cantonese ancestry.

The Mechanism

The variant is located in the 3' flanking region of CYP2E1 11 The 3' flanking region contains regulatory elements including polyadenylation signals and enhancers that can influence mRNA stability and transcription termination. It falls within the CYP2E1 RefSeqGene locus (NG_008383.1) and is located on the plus strand. No protein-coding change is produced. The mechanistic hypothesis is that the T allele alters a cis-regulatory element22 cis-regulatory element
DNA sequences near a gene that control its expression in the same cell affecting CYP2E1 mRNA stability or transcriptional read-through, potentially modulating basal enzyme expression in tissues relevant to NPC — particularly the nasopharyngeal epithelium and liver. However, no in vitro or luciferase reporter studies have directly confirmed altered transcriptional activity for this specific SNP. Its significance may also arise in part because it tags a broader CYP2E1 haplotype block shared with functionally characterized upstream variants.

The Evidence

The primary evidence comes from a case-control and family-based study in Cantonese individuals33 case-control and family-based study in Cantonese individuals
Jia WH et al. A case-control and family-based association study revealing an association between CYP2E1 polymorphisms and nasopharyngeal carcinoma risk in Cantonese. Carcinogenesis, 2009. The study examined 546 nuclear families (2,499 individuals) and 755 cases with 755 controls. Among the eight CYP2E1 SNPs genotyped, rs8192780 emerged as significantly associated with NPC in the family-based analysis. In a case-control analysis restricted to smokers under age 46, odds ratios for rs8192780 ranged from 1.88 to 2.99. Haplotype analysis identified two high-risk haplotypes (h2: OR=1.65, P=0.026; h5: OR=2.58, P=0.007), with false-positive report probabilities below 0.015, supporting the robustness of the findings. NPC is highly prevalent in Cantonese and other Southern Chinese populations, where Epstein-Barr virus (EBV) infection interacts with tobacco carcinogens and genetic susceptibility. CYP2E1 activates the tobacco-derived nitrosamine NNK44 nitrosamine NNK
4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, the major lung carcinogen in tobacco to DNA-reactive species.

For the canonical upstream CYP2E1 c2 haplotype (most commonly defined by rs2031920), large meta-analyses present a complex picture. The c2 allele appears protective against hepatocellular carcinoma in East Asians (OR 0.75, 95% CI 0.59–0.95 in a 12-study meta-analysis of 1,552 HCC cases55 (OR 0.75, 95% CI 0.59–0.95 in a 12-study meta-analysis of 1,552 HCC cases
Tian Z et al. CYP2E1 RsaI/PstI polymorphism and liver cancer risk among east Asians. Asian Pac J Cancer Prev, 2012) and also protective against lung cancer in Asians (OR 0.734 in homozygotes across 21 studies66 (OR 0.734 in homozygotes across 21 studies
Zhan P et al. CYP2E1 Rsa I/Pst I polymorphism is associated with lung cancer risk among Asians. Lung Cancer, 2010), yet associated with increased oral cancer risk in Asians (c1/c2 OR 1.30, 95% CI 1.04–1.62 in 12 studies77 (c1/c2 OR 1.30, 95% CI 1.04–1.62 in 12 studies
Niu Y et al. CYP2E1 Rsa I/Pst I polymorphism contributes to oral cancer susceptibility. Mol Biol Rep, 2012). These discordant findings across cancer types illustrate that CYP2E1 variant effects are tissue-specific and exposure-dependent, making extrapolation from the canonical variants to rs8192780 uncertain.

Practical Actions

The most direct implication of rs8192780 is for smokers, particularly those of East Asian or African ancestry where the T allele is substantially more common. The combination of CYP2E1 variant status and tobacco smoke exposure is the documented risk context. Reducing or eliminating tobacco exposure directly attacks the CYP2E1-mediated carcinogen activation pathway. No specific drug dosing guidance exists for this variant given the absence of clinical guidelines.

Interactions

rs8192780 lies within the CYP2E1 gene region and likely captures some of the same haplotype signal as the upstream *5B variant (rs2031920) and other CYP2E1 regulatory polymorphisms. The Jia et al. study analyzed rs8192780 alongside rs9418990, rs915908, rs3813865, rs915906, and rs2249695, finding that the rs8192780 signal was among the strongest. No direct studies assess interaction between rs8192780 and other pharmacogenomic loci such as NQO1 rs1800566 or GSTP1 rs1695, though pathway logic suggests these detoxification variants would modulate downstream consequences of CYP2E1 carcinogen activation.

Drug Interactions

tobacco carcinogens (NNK, PAHs) increased_toxicity literature

Genotype Interpretations

What each possible genotype means for this variant.

GG Common Genotype Normal

Common CYP2E1 downstream genotype

You carry two copies of the common G allele at this CYP2E1 downstream regulatory position. About 55% of people globally share this genotype, rising to approximately 64% in Europeans. The T allele associated with elevated nasopharyngeal carcinoma risk in one Cantonese study is absent from your results. This does not eliminate all CYP2E1-related risk, as other CYP2E1 variants and exposures (alcohol, acetaminophen, occupational chemicals) remain relevant to enzyme activity.

GT Heterozygous T Carrier Intermediate

One copy of the NPC-associated T allele

The T allele at rs8192780 sits in the 3' flanking region of CYP2E1, approximately 1.5 kb downstream of the gene's coding sequence. Its mechanism of action — if it has a direct one rather than acting as a haplotype tag — is not established by in vitro studies. The Jia et al. 2009 family-based study found significant NPC associations with a false-positive report probability below 0.015, suggesting the finding is unlikely to be a false positive, but single-study evidence in a specific population limits generalizability. The T allele is notably more prevalent in populations where NPC is common (East and Southeast Asians, ~42%; Africans, ~64%) than in Europeans (~20%), consistent with a potential contribution to population-level NPC incidence differences, though EBV exposure is the dominant risk factor.

TT Homozygous T Carrier High Risk

Two copies of the NPC-associated T allele

Homozygous TT individuals carry maximal T-allele exposure at this downstream CYP2E1 position. The original NPC association was reported with codominant or recessive models; TT individuals represent the highest genotype-risk group in the association study. Beyond the NPC data, other CYP2E1 haplotype studies find that the c2 haplotype (to which rs8192780 may contribute as a tag SNP) has tissue-specific and exposure-dependent effects on cancer risk — modestly protective for HCC and lung cancer in Asians, but associated with elevated oral cancer and NPC risk. The key modifiable interaction is with tobacco smoke: eliminating tobacco exposure removes the principal substrate that CYP2E1 activates into NPC-relevant genotoxins.