rs2036527 — CHRNA5/CHRNA3

The Regulatory Driver: How an Enhancer Variant Shapes Nicotine Addiction Risk

Most genetic research on nicotine dependence has focused on a single amino acid change in the CHRNA5 gene (rs16969968, D398N), but the 15q25.1 locus harbors a second distinct mechanism: a cis-regulatory variant that controls how much CHRNA3 and CHRNA5 are made in the first place. rs2036527 sits approximately 511 base pairs upstream of CHRNA5¹¹ rs2036527 sits approximately 511 base pairs upstream of CHRNA5
Located in an intergenic enhancer between PSMA4 and CHRNA5, this variant was long assumed to be a proxy for rs16969968 but recent functional work shows it acts independently in a regulatory element that loops to the CHRNA3 promoter and simultaneously influences CHRNA5 expression. The A allele is the risk form — it reduces enhancer activity and perturbs the output of both nicotinic receptor genes in concert.

rs2036527 is especially important for people of African ancestry. In Europeans the closely related coding variant rs16969968 is common (~35% minor allele frequency) and dominates association signals; in African Americans rs16969968 is nearly absent, yet 15q25.1 still strongly predicts smoking behavior. The African ancestry GWAS meta-analysis spanning 32,389 individuals²² The African ancestry GWAS meta-analysis spanning 32,389 individuals
Study of Tobacco in Minority Populations Genetics Consortium across 13 cohorts found rs2036527 to be the top genome-wide significant hit for cigarettes per day in this population (P=1.84×10⁻⁸), meaning it captures an independent regulatory signal that the rs16969968-centred haplotype misses entirely in non-European cohorts.

The Mechanism

The CHRNA5 gene and the adjacent CHRNA3 gene encode the α5 and α3 subunits of the nicotinic acetylcholine receptor (nAChR), the brain's principal sensor for nicotine. rs2036527 lies within a chromatin domain that physically loops to contact the CHRNA3 promoter — a long-range regulatory interaction confirmed by 3C (chromosome conformation capture) assay³³ 3C (chromosome conformation capture) assay
3C quantifies how often two genomic segments touch, which indicates functional regulatory contact. The risk-A allele alters the binding site for the transcription factor FOXA2 (forkhead box A2)⁴⁴ FOXA2 (forkhead box A2)
FOXA2 is a pioneer transcription factor that opens chromatin and recruits other activators, reducing enhancer activity as demonstrated by luciferase reporter assay. Because the same enhancer loops to both CHRNA3 and CHRNA5, impaired FOXA2 binding suppresses expression of both receptor subunits simultaneously.

This regulatory mechanism is distinct from, and partially independent of, the D398N amino acid variant in rs16969968. In Europeans the two signals are in high LD (r²≈0.93), making it difficult to separate their contributions. In African Americans, where rs16969968 is nearly monomorphic (minor allele frequency ~2%), rs2036527 acts as the sole carrier of genetic risk at this locus — demonstrating its independent causal role.

The Evidence

The regulatory function of rs2036527 was established by Peng et al. 2025⁵⁵ Peng et al. 2025
Peng et al. Identification of rs2036527 as a cis-regulatory variant for CHRNA3 and CHRNA5. Am J Addictions, 2025, who combined allele-specific expression analysis, chromatin conformation capture, luciferase assay, and expression quantitative trait locus (eQTL) validation to pin the mechanistic responsibility on rs2036527 rather than on surrounding proxy variants.

For smoking behavior, the STOMP Genetics Consortium meta-analysis⁶⁶ STOMP Genetics Consortium meta-analysis
Study of Tobacco in Minority Populations Genetics Consortium, pooling data from 13 studies found that each copy of the A allele increases cigarettes smoked per day by approximately one cigarette (β=0.040 in log-CPD units). Mean daily consumption by genotype was 14.6 cigarettes for AA, 13.5 for AG, and 12.8 for GG, demonstrating a clean additive gradient.

For lung cancer, a GWAS in 4,702 African American cases and controls⁷⁷ GWAS in 4,702 African American cases and controls
Confirmed 15q25.1 as a lung cancer locus in this population found rs2036527 associated with risk (OR=1.32, 95% CI 1.20–1.44, P=1.3×10⁻⁹). An earlier case-control study reported OR=1.67 (95% CI 1.26–2.21) in African Americans, and even among never-smokers rs2036527 remained associated with lung cancer risk (OR=1.58, 95% CI 1.12–2.26, P=9.9×10⁻³), suggesting both behavioral and potentially direct tissue effects.

Cessation pharmacotherapy outcomes also vary by genotype. A pharmacogenomics study in 1,295 African-American smokers randomized to nicotine gum or bupropion⁸⁸ 1,295 African-American smokers randomized to nicotine gum or bupropion
Randomized clinical trial design; one of the few cessation pharmacogenomics studies in an African American population found that A allele carriers had substantially lower abstinence rates with active pharmacotherapy during treatment (OR=0.42, P<0.001) and at end of treatment (OR=0.55, P=0.004). The effect was most pronounced for nicotine gum (OR=0.31, P<0.001 during treatment). Interestingly, a complementary study found that in women, the GA and AA genotypes were associated with higher cessation success rates⁹⁹ higher cessation success rates
41.5% and 56.5% for GA and AA vs 34.8% for GG in women, suggesting sex and treatment context modulate the genotype effect.

Practical Actions

The A allele weakens expression of nicotinic receptor subunits, blunting the normal aversive response to high nicotine doses that acts as a brake on heavy smoking. The consequence is the same as for rs16969968 carriers — easier escalation to heavy smoking, harder cessation — but the molecular route is different (gene expression rather than receptor function). In non-European populations where rs16969968 is rare, rs2036527 provides the actionable genetic signal.

Awareness of the genotype is most useful for (a) pre-smoking risk counseling, (b) selecting cessation pharmacotherapy, and (c) lung cancer surveillance planning. Nicotine replacement monotherapy appears less effective for A allele carriers; agents acting on nAChRs by a different route — specifically varenicline — are preferable. Lung cancer screening discussions should incorporate this variant, especially in individuals with any smoking history.

Interactions

In European populations, rs2036527 is in substantial LD (r²≈0.93) with the nonsynonymous CHRNA5 variant rs16969968 and near-complete LD with the CHRNA3 synonymous variant rs1051730, meaning all three variants are usually inherited together. A person whose genome includes both rs16969968(A) and rs2036527(A) carries a compounded mechanism: impaired receptor function (D398N structural change) plus reduced receptor gene expression (enhancer disruption). In African and other non-European populations, the LD breaks down (r²=0.44–0.50 with rs1051730 in African ancestry; rs16969968 nearly absent), making rs2036527 the primary causal variant — and the only variant providing meaningful genetic risk information at this locus for most people outside European ancestry.

The 15q25.1 locus has also been associated with risk for schizophrenia and bipolar disorder through variants in strong LD with rs1051730, suggesting that nicotinic receptor expression regulated by this enhancer cluster may influence broader neuropsychiatric vulnerability beyond tobacco dependence.