What you carry at this position in your DNA and what research says about it.
Lung Disease Risk: 8/10 evidence, 47 publications.
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Sample genotype (not yours): T/T
Typical Lung Disease Risk
Carrying two copies of the common T allele is associated with typical risks for lung cancer and chronic obstructive pulmonary disease. This genotype is also linked to a lower likelihood of developing heavy nicotine dependence compared to carriers of the C variant.
What this genotype means: Typical risk of lung cancer; Lower risk of heavy nicotine dependence; Typical respiratory function.
Sample genotype (not yours): C/C
Significantly Elevated Lung Disease Risk
Carrying two copies of the C allele is associated with a significantly higher risk of lung cancer and chronic obstructive pulmonary disease. This genotype is also linked to stronger nicotine dependence and a reduced physical sensitivity to alcohol.
What this genotype means: Significantly elevated risk of lung cancer; Stronger nicotine dependence and higher smoking intensity; Decreased physical sensitivity to alcohol.
Sample genotype (not yours): T/C
Moderately Elevated Lung Disease Risk
Carrying one copy of the C allele is associated with a moderately increased risk of lung cancer and chronic obstructive pulmonary disease. It is also linked to a higher likelihood of nicotine dependence and smoking more cigarettes per day.
What this genotype means: Moderately elevated risk of lung cancer; Increased susceptibility to nicotine dependence; Slightly higher risk of COPD.
Gene function and biological role
Gene Function: The HYKK gene encodes hydroxylysine kinase, an enzyme involved in the metabolic breakdown of lysine, an essential amino acid 19064933. While its primary biochemical role is metabolic, the genomic region containing HYKK on chromosome 15q25 is highly active in the central nervous system and lung tissues 18385738. This region is physically adjacent to a cluster of nicotinic acetylcholine receptor genes, which regulate the brain response to nicotine 18957677. Because of this tight physical linkage, genetic variations in HYKK are strongly inherited alongside variations in these nicotinic receptors 19259974. Consequently, research frequently links this gene to smoking behaviors, nicotine addiction, and downstream respiratory diseases 19300482.
Variant Impact: The rs8034191 variant is an intronic change located within the HYKK gene on chromosome 15q25.1 18385676. Although it does not directly alter the amino acid sequence of the hydroxylysine kinase protein, it serves as a powerful genetic marker for a highly active genomic neighborhood 18780872. This variant is in strong linkage disequilibrium with functional changes in nearby nicotinic receptor genes, meaning they are almost always inherited together 19259974. The risk-associated C allele is consistently linked to increased expression or altered function of these receptors, which heightens the brain sensitivity to nicotine and increases addiction vulnerability 19706762. As a result, this single nucleotide change is one of the most heavily replicated genetic markers for respiratory disease and smoking-related behaviors 20548021.
Key Insight: This variant does not directly alter lung tissue but instead influences nicotinic receptors in the brain, which strongly shapes nicotine addiction and smoking intensity.
Location: HYKK. Chromosome 15 · 15q25.1 · 78.5 Mb
Estimated prevalence by population
Global 53.8%; European 42.1%; African 69.5%; East Asian 94.3%; South Asian 58.5%; Americas 58.9%; Ashkenazi 42.9%; Finnish 44.6%; Middle Eastern 34.2%; Amish 35.2%.
Estimated TT genotype frequency.
Global 37.9%; European 45.6%; African 27.7%; East Asian 5.6%; South Asian 36.0%; Americas 35.7%; Ashkenazi 45.2%; Finnish 44.4%; Middle Eastern 48.6%; Amish 48.3%.
Estimated TC genotype frequency.
Global 8.3%; European 12.3%; African 2.8%; East Asian 0.1%; South Asian 5.5%; Americas 5.4%; Ashkenazi 11.9%; Finnish 11.0%; Middle Eastern 17.2%; Amish 16.5%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Cancer & Oncology
Lung Cancer
Lung Cancer. Evidence: 8/10. Source: PMID 18385676. Typical Risk.
Neurology & Mental Health
Addiction & Reward
Nicotine Dependence. Evidence: 9/10. Source: PMID 33144568. Typical Risk.
Organ Systems
Respiratory Health
COPD. Evidence: 5/10. Source: PMID 19300482. Typical Risk.
Nutrition & Metabolism
Alcohol Metabolism
Alcohol Sensitivity. Evidence: 3/10. Source: PMID 19064933. Typical Response.
Showing effects for C/C genotype
Lung Cancer. Evidence: 8/10. Source: PMID 18385676. ~1.80x Risk.
Nicotine Dependence. Evidence: 9/10. Source: PMID 33144568. Higher Risk.
COPD. Evidence: 5/10. Source: PMID 19300482. ~1.4x Risk.
Alcohol Sensitivity. Evidence: 3/10. Source: PMID 19064933. Decreased Response.
Showing effects for T/C genotype
Lung Cancer. Evidence: 8/10. Source: PMID 18385676. ~1.27x Risk.
Nicotine Dependence. Evidence: 9/10. Source: PMID 33144568. Increased Risk.
COPD. Evidence: 5/10. Source: PMID 19300482. Increased Risk.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Inheriting two copies of the common T allele is associated with a baseline risk for lung cancer and chronic obstructive pulmonary disease 18385676. Research indicates that this genotype is linked to a lower likelihood of developing heavy nicotine dependence compared to those carrying the C variant 19259974. Because the T allele does not carry the risk-elevating properties of the 15q25.1 region, individuals with this genetic profile typically smoke fewer cigarettes per day if they do smoke 21810735. Furthermore, pulmonary function measurements, such as the FEV1/FVC ratio, tend to remain within normal ranges in the absence of heavy environmental exposures 26634245. While this genotype is protective against the elevated genetic risks of the C allele, avoiding tobacco smoke remains the most effective way to maintain optimal lung health 19300482. Studies also suggest a typical physical response to alcohol consumption, meaning there is no genetically lowered sensitivity to its effects 19064933.
Typical risk of lung cancer; Lower risk of heavy nicotine dependence; Typical respiratory function.
Sample genotype: CC (Homozygous)
Inheriting two copies of the C allele is associated with a significantly elevated risk of lung cancer, estimated at approximately 1.8 times the baseline risk 19654303. This genotype is also strongly linked to chronic obstructive pulmonary disease (COPD), with clinical databases classifying the C allele as a risk factor 19300482. The biological mechanism is tied to a heightened vulnerability to heavy nicotine dependence, making smoking cessation more difficult 19259974. Individuals with this profile tend to smoke more cigarettes per day and have higher overall tobacco smoke exposure 21810735. Furthermore, this genotype is associated with a decreased physical response to alcohol, which can lead to higher consumption to feel the same effects 19064933. Spirometric measures of lung function, such as forced expiratory volume, are often lower in individuals with this genetic profile 26634245. Because the risk is heavily mediated by smoking behavior, avoiding tobacco smoke is the most critical factor in mitigating these elevated risks 18385738.
Significantly elevated risk of lung cancer; Stronger nicotine dependence and higher smoking intensity; Decreased physical sensitivity to alcohol.
Sample genotype: TC (Heterozygous)
Carrying one copy of the C allele is associated with a moderately elevated risk of developing lung cancer, estimated at approximately 1.27 times the baseline risk 19654303. This genetic variation is also linked to an increased susceptibility to chronic obstructive pulmonary disease (COPD) 19300482. Individuals with this genotype are more likely to experience stronger nicotine dependence and may find it more challenging to quit smoking 19259974. Large-scale genetic studies show a direct correlation between this variant and smoking more cigarettes per day 21810735. The presence of the C allele is also associated with subtle reductions in lung function measurements, such as forced expiratory volume 26634245. While these genetic factors increase vulnerability, environmental exposure to tobacco smoke remains the primary driver of actual disease outcomes 18385738. Managing smoke exposure is particularly beneficial for individuals carrying this risk-conferring variant 22017462.
Moderately elevated risk of lung cancer; Increased susceptibility to nicotine dependence; Slightly higher risk of COPD.
Variants with shared genetic architecture
rs10519203 · HYKK Gene · Chr 15 · Smoking and Lung Risk
rs931794 · HYKK Gene · Chr 15 · Lung and Vascular Health
rs2036534 · HYKK Gene · Chr 15 · Lung Cancer and Nicotine Risk
Content updated August 2026.
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