What you carry at this position in your DNA and what research says about it.
Lung Health and Immunity: 8/10 evidence, 20 publications.
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Sample genotype (not yours): A/A
Optimal Lung Defense and Typical Respiratory Function
Two copies of the A allele encode the fully functional, highly multimerized form of surfactant protein D. This provides robust protection against chronic lung diseases and severe respiratory infections, though it is linked to a slightly higher metabolic risk.
What this genotype means: Highly stable surfactant protein D; Lower risk of COPD; Better lung function measurements.
Sample genotype (not yours): A/G
Balanced Lung Defense and Moderate Metabolic Profile
Carrying one A and one G allele results in a mix of both functional and less-active forms of surfactant protein D. This genotype generally maintains typical lung function and average susceptibility to respiratory conditions.
What this genotype means: Intermediate surfactant protein D levels; Typical risk of respiratory infections; Average metabolic baseline.
Sample genotype (not yours): G/G
Reduced Lung Surfactant Activity but Favorable Metabolic Profile
Two copies of the G allele lead to a less stable form of surfactant protein D, which lowers respiratory defense but offers significant protection against type 2 diabetes.
What this genotype means: Less stable surfactant protein D; Increased risk of COPD; Lower risk of type 2 diabetes.
Gene function and biological role
Gene Function: The SFTPD gene encodes surfactant protein D, a crucial component of the lung's innate immune system [1]. Produced primarily by alveolar cells in the airways, this protein acts as a frontline defender against inhaled pathogens, allergens, and environmental toxins [1]. It directly binds to bacteria, viruses, and fungi, promoting their clearance by immune cells and modulating inflammatory responses to prevent tissue damage [1]. Beyond the respiratory tract, surfactant protein D is also involved in maintaining lipid homeostasis and regulating systemic inflammatory pathways [2].
Variant Impact: The rs721917 variant is a missense mutation in the SFTPD gene that alters the 31st amino acid of the surfactant protein D from methionine to threonine [3]. This structural change significantly impacts how the protein assembles, reducing its ability to form large, highly active multimeric structures [3]. Consequently, the threonine-encoding G allele leads to lower circulating levels of functional surfactant protein D and weaker binding to inhaled pathogens [3]. This molecular alteration directly influences susceptibility to chronic lung conditions and respiratory infections [4].
Key Insight: The same genetic variant that increases the risk of lung diseases like COPD actually provides significant protection against type 2 diabetes.
Location: SFTPD. Chromosome 10 · 10q22.3 · 79.9 Mb
Estimated prevalence by population
Global 32.9%; European 33.0%; African 35.5%; East Asian 15.1%; South Asian 9.7%; Americas 34.3%; Ashkenazi 35.0%; Finnish 37.4%; Middle Eastern 33.8%; Amish 46.9%.
Estimated AA genotype frequency.
Global 48.3%; European 48.9%; African 48.2%; East Asian 47.5%; South Asian 42.9%; Americas 48.5%; Ashkenazi 48.3%; Finnish 47.5%; Middle Eastern 48.7%; Amish 43.2%.
Estimated AG genotype frequency.
Global 18.8%; European 18.1%; African 16.4%; East Asian 37.3%; South Asian 47.4%; Americas 17.1%; Ashkenazi 16.7%; Finnish 15.1%; Middle Eastern 17.5%; Amish 9.9%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Organ Systems
Respiratory Health
COPD. Evidence: 8/10. Source: PMID 28166215. Lower Risk.
Lung Function. Evidence: 8/10. Source: PMID 30804560. Better Function.
Immunity & Inflammation
Infection Susceptibility & Resistance
COVID-19 Severity. Evidence: 8/10. Source: PMID 35922517. Lower Risk.
Cardiovascular & Metabolic
Diabetes & Glycemic Traits
Type 2 Diabetes. Evidence: 3/10. Source: PMID 23577114. Increased Risk.
Showing effects for A/G genotype
COPD. Evidence: 8/10. Source: PMID 28166215. Typical Risk.
Lung Function. Evidence: 8/10. Source: PMID 30804560. Typical Function.
COVID-19 Severity. Evidence: 8/10. Source: PMID 35922517. Typical Risk.
Type 2 Diabetes. Evidence: 3/10. Source: PMID 23577114. Typical Risk.
Showing effects for G/G genotype
COPD. Evidence: 8/10. Source: PMID 28166215. 1.12x Higher Risk.
Lung Function. Evidence: 8/10. Source: PMID 30804560. Poorer Function.
COVID-19 Severity. Evidence: 8/10. Source: PMID 35922517. Increased Risk.
Type 2 Diabetes. Evidence: 3/10. Source: PMID 23577114. 33% Lower Risk.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Inheriting two copies of the A allele ensures the production of highly stable, multimerized surfactant protein D, which is essential for defending the airways against pathogens [1]. Research indicates this genotype is associated with a significantly lower risk of developing chronic obstructive pulmonary disease (COPD) and better overall lung function measurements [2]. During respiratory challenges, such as viral infections, these optimal protein levels help prevent severe inflammatory complications [3]. However, this efficient immune profile comes with a metabolic trade-off, as studies have linked the A/A genotype to higher fasting glucose levels and an increased susceptibility to type 2 diabetes [4]. Maintaining a healthy lifestyle can easily mitigate this modest metabolic risk while preserving excellent respiratory defense.
Highly stable surfactant protein D; Lower risk of COPD; Better lung function measurements.
Sample genotype: AG (Heterozygous)
Having one copy of each allele leads to the production of both the methionine and threonine variants of surfactant protein D, resulting in intermediate levels of the fully assembled protein [1]. This balanced state typically provides adequate protection against common respiratory pathogens and environmental irritants [2]. Population studies show that individuals with this genotype experience average risks for chronic obstructive pulmonary disease (COPD) and typical lung function parameters [3]. The metabolic profile is also intermediate, presenting a neutral baseline for fasting blood sugar and type 2 diabetes risk [4]. Because respiratory and metabolic markers remain near the population average, standard wellness practices are highly effective for maintaining long-term health.
Intermediate surfactant protein D levels; Typical risk of respiratory infections; Average metabolic baseline.
Sample genotype: GG (Homozygous)
Inheriting two copies of the G allele results in a structural change that impairs the multimerization of surfactant protein D, leading to lower active levels in the lungs [1]. This reduction in functional protein is linked to an increased susceptibility to chronic obstructive pulmonary disease (COPD) and a higher risk of severe respiratory infections [2]. Lung function measurements, such as the FEV1/FVC ratio, also tend to be slightly lower in this group [3]. On the positive side, this genotype is associated with a highly favorable metabolic profile, including lower fasting glucose, lower HbA1c, and a reduced risk of type 2 diabetes [4]. Supporting lung health through avoiding smoking and staying active is particularly beneficial for individuals with this genetic profile.
Less stable surfactant protein D; Increased risk of COPD; Lower risk of type 2 diabetes.
Variants with shared genetic architecture
rs2571445 · TNS1 Gene · Chr 2 · Lung Health and COPD Risk
rs34712979 · NPNT Gene · Chr 4 · Lung Health and COPD
rs1192415 · TGFBR3 Gene · Chr 1 · Glaucoma and Lung Risk
Common genetic variants of surfactant protein-D (SP-D) are associated with type 2 diabetes.
A systematic analysis of protein-altering exonic variants in chronic obstructive pulmonary disease.
GWAS and meta-analysis identifies 49 genetic variants underlying critical COVID-19.
Content updated August 2026.
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