rs1693482 — ADH1C Arg272Gln (ADH1C*1/*2)

The Other Alcohol Metabolism Gene — Why ADH1C Genotype Determines Cancer Risk and Heart Protection in Drinkers

Most people who've heard of alcohol genetics know about ADH1B — the gene behind the "Asian flush." But there's a second, equally important alcohol dehydrogenase variant that operates in the same enzyme family and influences who gets hurt by alcohol and who gets heart-protective benefits. ADH1C encodes the gamma subunit of [alcohol dehydrogenase | The enzyme that catalyzes the first step of alcohol metabolism, converting ethanol to acetaldehyde in the liver] and exists in two functionally distinct forms.

The rs1693482 variant (chromosome 4, position 99342808 on GRCh38) defines the ADH1C*1 (Arg272) and ADH1C*2 (Gln272) alleles. ADH1C*1 encodes a faster enzyme with approximately 2.5-fold higher activity for ethanol oxidation compared to ADH1C*2. This enzymatic speed difference has measurable consequences for alcohol-related cancer risk and for the cardiovascular benefit that some drinkers obtain from moderate alcohol consumption.

The C allele on the genomic plus strand corresponds to ADH1C*1 (Arg272, fast); the T allele corresponds to ADH1C*2 (Gln272, slow). In the older literature, these are called gamma1 (fast) and gamma2 (slow) isoforms. ADH1C*1 predominates in Europeans (~58% C allele frequency) but is highly prevalent in East Asians (~93%) and moderately common in South Asians (~68%) and Latinos (~68%).

The Mechanism

ADH1C is one of three class I alcohol dehydrogenase enzymes (along with ADH1A and ADH1B) that catalyze the [NAD⁺-dependent | Nicotinamide adenine dinucleotide acts as the electron acceptor, being reduced to NADH during ethanol oxidation] oxidation of ethanol to acetaldehyde. The Arg272Gln substitution falls within the catalytic domain and alters the enzyme's kinetic parameters: the ADH1C*1 (gamma1) isoform has a higher Vmax for ethanol oxidation, meaning it generates acetaldehyde faster.

The consequences of this enzymatic speed difference flow in two directions. First, faster acetaldehyde production in heavy drinkers translates to greater cumulative acetaldehyde exposure in tissues like the esophagus, liver, and upper aerodigestive tract — acetaldehyde is a Group 1 human carcinogen and directly damages DNA. Second, in moderate drinkers, the rate of ethanol oxidation influences how long ethanol remains in the bloodstream; slower ADH1C*2 activity may prolong ethanol's presence and enhance its effects on HDL cholesterol and other cardiovascular mediators.

The Evidence

Cancer Risk in Heavy Drinkers:

A study of 818 heavy drinkers¹¹ A study of 818 heavy drinkers
Homann N et al. ADH1C*1 allele is a genetic marker for alcohol-associated cancer in heavy drinkers. International Journal of Cancer, 2006 found that the ADH1C*1/*1 (CC) genotype was significantly overrepresented among heavy drinkers who developed malignant tumors compared to those with non-cancerous alcohol-related organ damage. Compared to *1/*1 homozygotes, cancer risks were substantially lower for those with ADH1C*2 alleles, producing the following risk estimates for CC homozygotes: esophageal cancer OR=2.93, hepatocellular cancer OR=3.56, and head and neck cancer OR=2.20.

The mechanism is consistent with the enzyme kinetics: faster acetaldehyde production in ADH1C*1/*1 carriers means more carcinogenic acetaldehyde exposure per unit of alcohol consumed. This effect operates in addition to — and in synergy with — ALDH2 rs671 status, which controls the clearance rate of acetaldehyde.

Alcoholic Liver Disease:

A meta-analysis of 16 case-control studies (1,375 cases, 1,802 controls)²² A meta-analysis of 16 case-control studies (1,375 cases, 1,802 controls)
He L et al. Association between ADH1C gene polymorphism and alcoholic liver cirrhosis risk. PLOS ONE, 2015 found ethnicity-dependent effects: in Asian populations, the *1/*2 genotype increased alcoholic liver cirrhosis risk vs *1/*1 (OR=1.63, 95% CI 1.07–2.49), while in Caucasians the *1/*2 genotype was modestly protective vs *1/*1 (OR=0.76, 95% CI 0.61–0.95). No significant overall association emerged across all ethnicities, underscoring the importance of population context in interpreting this variant.

An earlier meta-analysis of 50 studies³³ meta-analysis of 50 studies
Zintzaras E et al. Alcohol-metabolizing enzyme gene polymorphisms, alcoholism, and pancreatitis. Pancreas, 2006 showed the ADH1C*2 allele associated with increased alcoholism risk overall (OR=1.32, 95% CI 1.12–1.57), with a much stronger effect in East Asians (OR=1.91, 95% CI 1.45–2.53), where ADH1C*1 is nearly universal and ADH1C*2 is the minority allele.

Alcohol Use Disorder:

A Turkish case-control study of 90 alcohol-dependent patients and 100 controls⁴⁴ Turkish case-control study of 90 alcohol-dependent patients and 100 controls
Kortunay S et al. ADH1C polymorphism and alcohol dependence risk in Turkish patients. Alcohol, 2012 found the ADH1C*2 allele frequency was nearly 3-fold higher in alcohol-dependent individuals (0.32 vs 0.11, p<0.0001), with the heterozygous *1/*2 genotype significantly overrepresented among dependent patients (42% vs 23%, p<0.0001). The *1/*1 CC genotype was more common among controls (77% vs 51%), suggesting the fast-metabolizing ADH1C*1 genotype may be somewhat protective against AUD in European-ancestry populations — possibly because faster ethanol clearance reduces alcohol's rewarding duration.

Combined ADH1B + ADH1C Effects:

An Israeli household study⁵⁵ An Israeli household study
Meyers JL et al. Alcohol-metabolizing genes and alcohol phenotypes in an Israeli household sample. Alcoholism, 2013 found that ADH1B and ADH1C jointly influence AUD risk in ways that neither gene captures alone. The absence of protective alleles for both genes was associated with OR=3.16 for AUD, compared to those possessing protective alleles for both, demonstrating that combined genotyping provides substantially better risk stratification than either gene in isolation.

Cardiovascular Benefits of Moderate Alcohol:

The gamma2 isoform confers a striking amplification of the cardiovascular benefits associated with moderate alcohol consumption.

In the Physicians' Health Study⁶⁶ In the Physicians' Health Study
Hines LM et al. Genetic variation in alcohol dehydrogenase and the beneficial effect of moderate alcohol consumption on myocardial infarction. NEJM, 2001, men who consumed at least one drink per day and were homozygous for gamma2 (TT) had relative risk of myocardial infarction of 0.14 (95% CI 0.04–0.45) compared to gamma1 homozygotes who drank the same amount — an 86% reduction. Gamma1/gamma1 moderate drinkers had RR=0.62, a much more modest 38% reduction. The gamma2 advantage was attributed to prolonged ethanol exposure and higher HDL elevation per drink.

A subsequent multi-cohort study⁷⁷ A subsequent multi-cohort study
Hines LM et al. ADH1C genotype, alcohol consumption, and plasma levels of HDL cholesterol and apolipoprotein AI. Circulation, 2005 confirmed that gamma2/gamma2 moderate drinkers had 5.3 mg/dL higher HDL than gamma1/gamma1 moderate drinkers (P=0.02), providing a plausible mechanism: slower ethanol oxidation prolongs alcohol's HDL-raising effect. This interaction was absent in premenopausal women and postmenopausal women using hormones, suggesting that endogenous estrogen already maximizes the HDL signal.

The Second Northwick Park Heart Study (n=2,773 men, 220 CHD events)⁸⁸ The Second Northwick Park Heart Study (n=2,773 men, 220 CHD events)
Younis J et al. ADH1C genotype, alcohol consumption, and risk of coronary heart disease. Atherosclerosis, 2005 found that gamma2/gamma2 men who drank just 1–3 units/week achieved HR=0.22 (95% CI 0.05–0.94) for CHD — a 78% reduction — compared to gamma1/gamma1 drinkers at the same modest intake. Crucially, the protective effect appeared at lower consumption levels than previously reported.

Practical Actions

For CC (ADH1C*1/*1) genotype: You carry the fast-metabolizing form of ADH1C on both chromosomes. In the context of heavy or regular alcohol consumption, this generates more acetaldehyde per drink compared to carriers of ADH1C*2. The practical implication is that your esophageal, hepatic, and upper aerodigestive tissues are exposed to more carcinogenic acetaldehyde per drink than in ADH1C*2 carriers. If you drink regularly, periodic upper endoscopy and liver function monitoring are clinically relevant. The cardiovascular benefit from moderate alcohol is real but smaller in your genotype than in ADH1C*2 carriers.

For CT (ADH1C*1/*2) genotype: You have one fast and one slow allele; your enzyme activity and acetaldehyde exposure are intermediate. Your cancer risk from drinking is lower than CC homozygotes, and your cardiovascular response to moderate alcohol is somewhat enhanced compared to CC carriers, though not as pronounced as TT individuals.

For TT (ADH1C*2/*2) genotype: You carry the slow-metabolizing form on both chromosomes. Ethanol is oxidized to acetaldehyde more slowly, producing less acute acetaldehyde per drink. This appears to lower your AUD risk in non-Asian populations (where this genotype is less common) and substantially amplifies the cardiovascular benefit of light-to-moderate drinking — the Physicians' Health Study found an 86% reduction in heart attack risk in TT moderate drinkers. However, in the context of alcohol misuse, ADH1C*2 is associated with higher AUD rates in some populations, possibly because slower metabolism allows ethanol to remain in the bloodstream longer, sustaining its reinforcing effects.

Interactions

The most important interaction is with ADH1B rs1229984 (His48Arg). ADH1B controls the overall speed of ethanol-to-acetaldehyde conversion at the beta subunit level, while ADH1C modulates it at the gamma subunit level. Combined ADH1B + ADH1C diplotype analysis consistently shows better AUD risk prediction than either gene alone. Carriers of protective alleles in both genes show OR=3+ lower AUD risk compared to those lacking both protective alleles.

The second key interaction is with ALDH2 rs671 (Lys487Glu). ALDH2 clears acetaldehyde after it's produced. ADH1C*1 fast production combined with ALDH2 deficiency creates the same acetaldehyde accumulation dynamic as seen with ADH1B His48 + ALDH2 deficiency — faster production and impaired clearance. This combination is relevant particularly in East Asian populations where ALDH2 deficiency is common.

The rs698 (Ile350Val) variant in ADH1C is in near-complete [linkage disequilibrium | When two alleles are inherited together more often than expected by chance, making them nearly interchangeable as genetic markers] with rs1693482, meaning the ADH1C*1 haplotype typically carries both the Arg272 and Ile350 alleles, and the ADH1C*2 haplotype carries Gln272 and Val350.