What you carry at this position in your DNA and what research says about it.
Lung Health and Smoking Risk: 9/10 evidence, 23 publications.
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Sample genotype (not yours): T/T
Typical Lung Disease and Smoking Risk
Two copies of the T allele are associated with a typical risk profile for chronic lung diseases and lower nicotine dependence. This genotype is the most common globally and represents the baseline genetic risk for respiratory health.
What this genotype means: Typical risk for chronic obstructive pulmonary disease; Lower genetic predisposition to heavy smoking; Typical baseline risk for lung cancer.
Sample genotype (not yours): C/C
Higher Lung Disease and Smoking Risk
Two copies of the C allele are associated with a significantly higher risk of chronic obstructive pulmonary disease and lung cancer. This genotype is also linked to a stronger genetic drive for heavy smoking.
What this genotype means: Increased risk of chronic obstructive pulmonary disease; Higher genetic predisposition to heavy nicotine use; Elevated risk of lung cancer and atherosclerosis.
Sample genotype (not yours): T/C
Slightly Higher Lung Disease and Smoking Risk
Carrying one copy of the C allele is linked to a slightly elevated risk of chronic lung conditions and a higher tendency for nicotine dependence. This genetic profile suggests a mild increase in vulnerability to tobacco-related health issues.
What this genotype means: Slightly elevated risk of chronic obstructive pulmonary disease; Slightly higher genetic drive to smoke more cigarettes; Slightly increased susceptibility to lung cancer.
Gene function and biological role
Gene Function: The CHRNA3 gene encodes the alpha-3 subunit of the nicotinic acetylcholine receptor, which is highly expressed in both the central nervous system and lung tissue. These receptors act as binding sites for nicotine and play a crucial role in mediating the rewarding effects of tobacco use. Genetic variations within this gene cluster are heavily linked to nicotine dependence, smoking behaviors, and susceptibility to chronic respiratory diseases. Additionally, altered receptor activity can influence cellular pathways involved in inflammation and cell proliferation in the lungs.
Variant Impact: The rs8040868 variant is a synonymous change located in exon 3 of the CHRNA3 gene, meaning it does not alter the encoded amino acid sequence of the receptor. However, this genetic change is associated with altered expression levels of the nicotinic receptor gene cluster in lung tissue. This alteration in expression is believed to influence both the physical response to inhaled nicotine and the baseline vulnerability of lung tissue to chronic inflammation. Consequently, this variant serves as a significant genetic marker for respiratory health and tobacco-related risks.
Key Insight: This variant is synonymous and does not alter the protein structure, yet it significantly impacts lung disease risk by modifying gene expression levels. The same genetic pathway that influences how heavily a person smokes also independently affects their baseline risk for lung cancer.
Location: CHRNA3. Chromosome 15 · 15q25.1 · 78.6 Mb
Estimated prevalence by population
Global 39.8%; European 35.4%; African 43.6%; East Asian 42.6%; South Asian 54.6%; Americas 46.1%; Ashkenazi 33.2%; Finnish 39.2%; Middle Eastern 30.7%; Amish 31.2%.
Estimated TT genotype frequency.
Global 46.3%; European 48.2%; African 44.9%; East Asian 45.3%; South Asian 38.6%; Americas 43.6%; Ashkenazi 48.9%; Finnish 46.8%; Middle Eastern 49.4%; Amish 49.3%.
Estimated TC genotype frequency.
Global 13.9%; European 16.4%; African 11.5%; East Asian 12.1%; South Asian 6.8%; Americas 10.3%; Ashkenazi 18.0%; Finnish 14.0%; Middle Eastern 19.9%; Amish 19.5%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Organ Systems
Respiratory Health
COPD. Evidence: 9/10. Source: PMID 33106845. Typical Risk.
Cancer & Oncology
Lung Cancer
Lung Cancer. Evidence: 9/10. Source: PMID 29924316. Typical Risk.
Neurology & Mental Health
Addiction & Reward
Cigarettes Per Day. Evidence: 8/10. Source: PMID 30643251. Typical Consumption.
Cardiovascular & Metabolic
Vascular Health & Aneurysm
Atherosclerosis. Evidence: 8/10. Source: PMID 39024449. Typical Risk.
Showing effects for C/C genotype
COPD. Evidence: 9/10. Source: PMID 33106845. ~1.3x Increased Risk.
Lung Cancer. Evidence: 9/10. Source: PMID 29924316. ~1.3x Increased Risk.
Cigarettes Per Day. Evidence: 8/10. Source: PMID 30643251. Higher Consumption.
Atherosclerosis. Evidence: 8/10. Source: PMID 39024449. Increased Risk.
Showing effects for T/C genotype
COPD. Evidence: 9/10. Source: PMID 33106845. Slightly Increased.
Lung Cancer. Evidence: 9/10. Source: PMID 29924316. Slightly Increased.
Cigarettes Per Day. Evidence: 8/10. Source: PMID 30643251. Slightly Higher.
Atherosclerosis. Evidence: 8/10. Source: PMID 39024449. Slightly Increased.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Carrying the T/T genotype is associated with a lower risk of developing chronic obstructive pulmonary disease compared to carrying the C allele. Research indicates that individuals with this genetic profile tend to smoke fewer cigarettes per day if they do smoke, suggesting a lower genetic predisposition to heavy nicotine dependence. This genotype is also linked to better overall lung function measurements, such as a higher FEV1/FVC ratio, which reflects healthier airflow. Furthermore, the T/T genotype is associated with a typical baseline risk for lung cancer, avoiding the elevated risk seen in carriers of the C allele. Maintaining a smoke-free lifestyle remains the most effective way to protect respiratory health regardless of this genetic advantage.
Typical risk for chronic obstructive pulmonary disease; Lower genetic predisposition to heavy smoking; Typical baseline risk for lung cancer.
Sample genotype: CC (Homozygous)
Carrying the C/C genotype is associated with an elevated risk of developing chronic obstructive pulmonary disease, with studies showing a notable increase in susceptibility. This genetic profile is strongly linked to higher nicotine dependence, often manifesting as smoking a greater number of cigarettes per day. Individuals with this genotype also tend to have lower lung function, as indicated by reduced FEV1/FVC ratios and forced expiratory volumes. Furthermore, the C/C genotype is associated with a higher risk of lung cancer, including squamous cell lung cancer. There is also an associated increase in the risk of developing atherosclerosis, highlighting a broader impact on cardiovascular health. Given these combined risks, avoiding tobacco exposure and monitoring respiratory health are highly recommended strategies.
Increased risk of chronic obstructive pulmonary disease; Higher genetic predisposition to heavy nicotine use; Elevated risk of lung cancer and atherosclerosis.
Sample genotype: TC (Heterozygous)
Having the T/C genotype is associated with a moderately increased risk of developing chronic obstructive pulmonary disease. Individuals with this genetic profile may experience a stronger urge to smoke more cigarettes per day due to altered nicotinic receptor sensitivity in the brain. This genotype is also linked to slightly lower lung function measurements, such as a reduced FEV1/FVC ratio, which can impact overall respiratory capacity. Additionally, carriers of the C allele have a slightly higher susceptibility to lung cancer, particularly when exposed to tobacco smoke. Because this genetic risk is highly interactive with environmental factors, avoiding smoking and secondhand smoke is particularly beneficial for individuals with this genotype.
Slightly elevated risk of chronic obstructive pulmonary disease; Slightly higher genetic drive to smoke more cigarettes; Slightly increased susceptibility to lung cancer.
Variants with shared genetic architecture
rs1051730 · CHRNA3 Gene · Chr 15 · Nicotine and Lung Risk
rs12914385 · CHRNA3 Gene · Chr 15 · Lung and Respiratory Health
rs8042374 · CHRNA3 Gene · Chr 15 · Lung Cancer Risk
Content updated August 2026.
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