What you carry at this position in your DNA and what research says about it.
Asthma and Inflammation: 8/10 evidence, 29 publications.
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Sample genotype (not yours): G/G
Lower Asthma Risk and Lower Inflammation
Two copies of the protective G allele are associated with significantly lower levels of the inflammatory YKL-40 protein. This reduction in inflammation translates to a lower risk of developing asthma and better overall lung function.
What this genotype means: Significantly lower YKL-40 inflammatory protein levels; Reduced risk of asthma and respiratory hospitalizations; Better baseline lung function.
Sample genotype (not yours): C/C
Typical Asthma Risk and Baseline Inflammation
Two copies of the C allele represent the most common genetic baseline, associated with typical levels of the inflammatory YKL-40 protein. This profile carries a standard risk of asthma and average lung function.
What this genotype means: Typical baseline levels of YKL-40 inflammatory protein; Standard risk of developing asthma; Average baseline lung function.
Sample genotype (not yours): G/C
One copy of the protective G allele helps keep inflammatory YKL-40 protein levels low. This genetic profile is linked to a reduced risk of asthma and healthier lung function.
What this genotype means: Lower circulating YKL-40 inflammatory protein levels; Reduced risk of asthma and airway hyperresponsiveness; Fewer asthma-related hospital admissions.
Gene function and biological role
Gene Function: The CHI3L1 gene encodes chitinase 3-like 1, also known as YKL-40, a protein that plays a key role in inflammation and tissue remodeling [1]. YKL-40 is secreted by various cells, including immune cells and airway epithelial cells, in response to inflammatory signals [2]. Elevated levels of this protein are widely used as a biomarker for chronic inflammatory conditions, particularly asthma and joint diseases [1]. Research indicates that genetic variations in this gene directly influence how much YKL-40 is produced and released into the bloodstream [2].
Variant Impact: Located in the promoter region of the CHI3L1 gene, rs4950928 is a single-nucleotide change that directly affects transcription [1]. This specific change alters the binding efficiency of transcription factors, thereby regulating the baseline production of the YKL-40 protein [1]. The C allele is associated with significantly higher circulating levels of YKL-40, whereas the G allele leads to reduced expression [2]. Consequently, this variant is one of the most well-studied genetic determinants of systemic inflammation and respiratory health [1].
Key Insight: Carrying the G allele can cut the risk of developing asthma nearly in half by naturally keeping inflammatory protein levels low.
Location: CHI3L1. Chromosome 1 · 1q32.1 · 203.2 Mb
Estimated prevalence by population
Global 5.8%; European 4.4%; African 10.3%; East Asian 2.4%; South Asian 3.8%; Americas 2.7%; Ashkenazi 1.8%; Finnish 6.7%; Middle Eastern 1.8%; Amish 0.7%.
Estimated GG genotype frequency.
Global 35.1%; European 33.2%; African 43.6%; East Asian 26.1%; South Asian 31.4%; Americas 27.5%; Ashkenazi 23.2%; Finnish 38.4%; Middle Eastern 23.0%; Amish 14.9%.
Estimated GC genotype frequency.
Global 59.0%; European 62.4%; African 46.1%; East Asian 71.5%; South Asian 64.8%; Americas 69.7%; Ashkenazi 75.0%; Finnish 54.8%; Middle Eastern 75.2%; Amish 84.4%.
Estimated CC genotype frequency.
Showing effects for G/G genotype
Organ Systems
Respiratory Health
Asthma. Evidence: 6/10. Source: PMID 18403759. Lower Risk.
Lung Function. Evidence: 5/10. Source: PMID 18403759. Better Function.
Immunity & Inflammation
Inflammatory & Circulating Protein Markers
YKL-40 Protein Levels. Evidence: 8/10. Source: PMID 18403759. Lowest Levels.
Cardiovascular & Metabolic
Heart Rhythm & Conduction
Atrial Fibrillation. Evidence: 3/10. Source: PMID 23279705. Lower Risk.
Showing effects for C/C genotype
Asthma. Evidence: 6/10. Source: PMID 18403759. Typical Risk.
Lung Function. Evidence: 5/10. Source: PMID 18403759. Typical.
YKL-40 Protein Levels. Evidence: 8/10. Source: PMID 18403759. Typical Levels.
Atrial Fibrillation. Evidence: 3/10. Source: PMID 23279705. Typical Risk.
Showing effects for G/C genotype
YKL-40 Protein Levels. Evidence: 8/10. Source: PMID 18403759. Lower Levels.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Two copies of the G allele lead to the lowest baseline levels of circulating YKL-40 protein, an active driver of airway inflammation [1]. Because YKL-40 promotes tissue remodeling and swelling in the lungs, keeping its levels low helps maintain healthy airways [1]. Studies show that individuals with this genotype have a significantly reduced risk of developing asthma compared to those with the common CC genotype [1]. Additionally, this protective effect extends to a lower rate of asthma-related hospitalizations and better lung function measurements, such as FEV1 [2]. The lower inflammatory profile may also offer mild protection against other conditions linked to high YKL-40, such as atrial fibrillation [3].
Significantly lower YKL-40 inflammatory protein levels; Reduced risk of asthma and respiratory hospitalizations; Better baseline lung function.
Sample genotype: CC (Homozygous)
Double copies of the C allele represent the most common genetic profile globally, resulting in typical baseline levels of the inflammatory protein YKL-40 [1]. Because this genotype lacks the protective G allele, it does not benefit from the natural reduction in YKL-40 levels [1]. Consequently, individuals with this profile have a standard, typical risk of developing asthma and average lung function [1]. In those who do develop asthma, higher levels of YKL-40 can correlate with increased airway remodeling and severity [2]. This baseline level of inflammation is also associated with typical risks for other conditions influenced by YKL-40, such as atrial fibrillation and hypertension [3].
Typical baseline levels of YKL-40 inflammatory protein; Standard risk of developing asthma; Average baseline lung function.
Sample genotype: GC (Heterozygous)
A single copy of the protective G allele is associated with lower circulating levels of the inflammatory protein YKL-40 compared to the typical baseline [1]. This reduction in YKL-40 helps limit the inflammation and tissue remodeling that typically restrict airways in sensitive individuals [1]. Clinical research indicates that having even one G allele is sufficient to lower the risk of developing asthma [1]. Furthermore, young adults and children with this genotype experience fewer asthma-related hospital admissions and maintain better overall lung function [2]. This intermediate inflammatory profile is also associated with a lower risk of other cardiovascular and inflammatory complications driven by elevated YKL-40 [3].
Lower circulating YKL-40 inflammatory protein levels; Reduced risk of asthma and airway hyperresponsiveness; Fewer asthma-related hospital admissions.
Variants with shared genetic architecture
rs880633 · CHI3L1 Gene · Chr 1 · YKL-40 Protein Levels
rs37973 · GLCCI1-DT Gene · Chr 7 · Corticosteroid Response
rs17293632 · SMAD3 Gene · Chr 15 · Inflammatory Disease Risk
Effect of variation in CHI3L1 on serum YKL-40 level, risk of asthma, and lung function.
Content updated August 2026.
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