rs2070676 — CYP2E1

Intronic CYP2E1 variant tagging the *1B haplotype; C allele marks reduced CYP2E1 expression and is associated with adverse drug reactions during tuberculosis treatment

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CYP2E1*1B — Population-Specific Variation in a Key Metabolic Enzyme

CYP2E1 is the liver enzyme at the centre of two important clinical scenarios: it converts a fraction of every acetaminophen dose into NAPQI11 NAPQI
N-acetyl-p-benzoquinone imine — the reactive metabolite responsible for centrilobular liver necrosis in overdose, and it generates reactive intermediates from isoniazid, the backbone of tuberculosis treatment. rs2070676 is an intronic variant in CYP2E1 that serves as a tag SNP for the [CYP2E1*1B haplotype | A haplotype is a group of variants that are inherited together; *1B marks a region of CYP2E1 associated with lower enzyme expression compared to the reference *1A haplotype] — a set of co-inherited variants including the synonymous exon-8 change rs2515641. Together, these variants define a lower-expression CYP2E1 background found at widely varying frequencies across global populations.

The Mechanism

Unlike functional missense or promoter variants, rs2070676 itself lies in intron 7 (c.1156-118G>C) and does not directly alter the CYP2E1 protein or its promoter. Its clinical relevance derives from [linkage disequilibrium | LD: the tendency for nearby variants to be inherited together because they are rarely separated by recombination] with rs2515641, a synonymous coding variant (c.1263C>T) that demonstrably reduces CYP2E1 mRNA and protein levels22 demonstrably reduces CYP2E1 mRNA and protein levels
Chen et al. 2020 showed significantly lower CYP2E1 transcript and protein in HepG2 cells expressing the T allele at rs2515641. Carrying the C allele at rs2070676 tags the same low-expression haplotype as the T allele at rs2515641. The result is approximately 20–30% lower CYP2E1 protein for the drugs and substrates the enzyme handles — acetaminophen, isoniazid, ethanol at high concentrations, halothane, and industrial solvents including benzene and trichloroethylene.

The Evidence

Tuberculosis adverse drug reactions: The most directly actionable finding comes from Yu et al. (2019)33 Yu et al. (2019)
Yu YY et al. Association of Drug Metabolic Enzyme Genetic Polymorphisms and Adverse Drug Reactions in Patients Receiving Rifapentine and Isoniazid Therapy for Latent Tuberculosis. Int J Environ Res Public Health, 2019, who enrolled 377 patients receiving weekly rifapentine plus isoniazid (the 3HP regimen) for latent tuberculosis. Nearly half the cohort (48.4%) developed adverse drug reactions. Among those with the CC genotype at rs2070676, the odds of experiencing an ADR were 1.56-fold higher compared to CG+GG carriers (OR 1.563, 95% CI 1.022–2.389). The mechanism is counterintuitive: isoniazid itself requires CYP2E1-mediated activation into reactive intermediates for its antibacterial effect — when enzyme activity is lower, these intermediates accumulate differently and may overwhelm detoxification pathways at therapeutic doses.

Kawasaki disease and coronary risk: A study by Chang et al. (2017)44 Chang et al. (2017)
Chang LS et al. CYP2E1 Gene Polymorphisms Related to the Formation of Coronary Artery Lesions in Kawasaki Disease. Pediatr Infect Dis J, 2017 found that the GG genotype at rs2070676 was associated with significantly greater risk of coronary artery lesion (CAL) formation in children with Kawasaki disease (P=0.007). This is the opposite direction from the TB finding, reflecting how the two alleles have distinct effects in inflammatory versus drug-metabolism contexts.

Parkinson's disease: A case-control study from Shen et al. (2022)55 Shen et al. (2022)
Shen C et al. Polymorphisms of Cytochromes P450 and Glutathione S-Transferases Synergistically Modulate Risk for Parkinson's Disease. Front Aging Neurosci, 2022 (1,026 participants) found that neither allele at rs2070676 independently altered PD risk, but in combination with specific CYP1A1 variants, the GG+GC genotypes conferred a protective effect (OR 0.393, 95% CI 0.216–0.715, P=0.002). This illustrates how CYP enzyme polymorphisms interact synergistically — a pattern that no single-SNP analysis captures.

Alcohol response: Webb et al. (2011)66 Webb et al. (2011)
Webb A et al. The investigation into CYP2E1 in relation to the level of response to alcohol through a combination of linkage and association analysis. Alcohol Clin Exp Res, 2011 identified significant associations between rs2070676 genotype and subjective alcohol response (SHAS score) in a family-based alcohol challenge study, consistent with the *1B haplotype's influence on CYP2E1-mediated ethanol oxidation and reactive oxygen species production.

Practical Actions

The primary practical implication is for tuberculosis treatment: CC carriers have meaningfully higher ADR risk on isoniazid-rifapentine regimens. This warrants proactive liver enzyme monitoring before and during therapy. The *1B haplotype also tags reduced acetaminophen-metabolizing capacity; while standard doses remain appropriate, high-dose or chronic acetaminophen use in CC carriers carries a theoretically altered NAPQI generation profile compared to GG carriers.

Population context matters here. The C allele is the population-major allele in Europeans (~88%) and East Asians (~80%), but less dominant in African-ancestry populations (~31%). A clinician interpreting this variant in an African-ancestry patient is working with a different prior probability distribution than in a European-ancestry patient.

Interactions

rs2070676 is in complete linkage disequilibrium with rs2515641 (CYP2E1 exon-8, c.1263C>T) — these two variants almost always co-occur on the same chromosome. The compound effect of both sites is captured by the *1B haplotype designation. Additionally, this locus interacts with CYP1A1 variants in Parkinson's disease risk, and the broader CYP2E1 haplotype block also includes the 5' promoter variants rs2070672 and rs2031920 (*5B), which act in the opposite direction (increasing CYP2E1 expression). The *1B reduced-expression haplotype carrying rs2070676 C allele is effectively antagonistic to the *5B high-expression haplotype; a person can carry different alleles at both loci.

Drug Interactions

isoniazid increased_toxicity literature
rifapentine increased_toxicity literature
acetaminophen increased_toxicity literature
ethanol altered_metabolism literature

Genotype Interpretations

What each possible genotype means for this variant.

GG CYP2E1 Reference Normal

Reference allele homozygote — standard CYP2E1 haplotype background

You carry two copies of the G (reference) allele at rs2070676. This genotype is found in approximately 10% of people globally, but varies substantially by ancestry — more common in African-ancestry populations (~47%) and less common in Europeans (~1–2%). The G allele tags the *1A reference background rather than the lower-expression *1B haplotype.

Standard CYP2E1 enzyme levels mean you process acetaminophen, isoniazid, and ethanol at expected rates. In Kawasaki disease, the GG genotype has been linked to higher coronary artery lesion risk — but this association is specific to that inflammatory context and does not affect routine drug metabolism interpretation.

CC CYP2E1 *1B/*1B Reduced

Homozygous *1B — reduced CYP2E1 expression, elevated tuberculosis drug ADR risk

The CC genotype at rs2070676 defines the homozygous CYP2E1*1B/*1B state. The *1B designation historically referred to a region of lower CYP2E1 expression; the mechanism was clarified when Chen et al. (2020) demonstrated that rs2515641 (in complete LD with rs2070676) reduces CYP2E1 mRNA stability and protein translation through codon-usage-driven effects on elongation and transcript stability.

The TB finding from Yu et al. (2019) is the most actionable: of 377 latent TB patients on the 3HP regimen, nearly half experienced adverse drug reactions, and CC genotype at rs2070676 was independently associated with 56% higher ADR odds (OR 1.563, 95% CI 1.022–2.389). Isoniazid ADRs include peripheral neuropathy, hepatitis, and systemic hypersensitivity reactions.

For acetaminophen, the in vitro evidence from Chen et al. suggests CC carriers produce less NAPQI per dose than GG carriers, potentially offering a marginal protection at standard doses — but this does not mean acetaminophen is safe at high doses or in combination with alcohol. CYP3A4 and CYP1A2 compensate at high doses regardless of CYP2E1 genotype.

Population context: the CC genotype is the norm in European and East Asian populations, meaning clinical studies in these cohorts will have predominantly CC carriers; findings reported for the "wild-type" in European-cohort studies typically represent the *1B/*1B state.

CG CYP2E1 *1B Carrier Carrier

One *1B haplotype copy — partially reduced CYP2E1 expression

The *1B haplotype that this C allele tags is defined by co-inheritance with rs2515641 (c.1263C>T), a synonymous coding variant that reduces CYP2E1 mRNA stability and protein output. As a CG heterozygote, one copy of your CYP2E1 is expressed at near-normal levels (from the G-allele chromosome) while the other copies less enzyme (from the C-allele chromosome).

Population data show the C allele at rs2070676 is common across most global populations (~88% in Europeans, ~80% in East Asians, ~31% in Africans) — meaning most people of non-African ancestry carry at least one copy, making this genotype the statistical norm in those populations.