rs12141494 — CHI3L1 CHI3L1 Intron 6 Variant

CHI3L1 Intron 6 Variant — The Independent Regulator of Airway YKL-40

CHI3L1 encodes YKL-40¹¹ CHI3L1 encodes YKL-40
YKL-40 is a chitinase-like protein secreted by macrophages, neutrophils, bronchial epithelial cells, and smooth muscle cells; it drives airway inflammation, bronchial wall remodeling, and smooth muscle proliferation independent of classical eosinophilic Th2 pathways, making it one of the most clinically relevant biomarkers of non-T2, severe asthma. Most genetic studies of CHI3L1 have focused on the promoter variant rs4950928 (-131C>G), which modulates transcription start site activity and produces the largest common-variant effect on circulating YKL-40 levels. rs12141494 sits in intron 6 of CHI3L1 at chr1:203,182,297 (GRCh38), a region that modulates YKL-40 expression through a distinct mechanism — and crucially, does so independently of the promoter variant.

The Mechanism

Intronic variants can regulate gene expression through splicing enhancer/silencer sequences, effects on transcription elongation, or by altering the binding of regulatory RNA or chromatin-modifying complexes to the pre-mRNA. rs12141494 is a G>A transition on the plus strand; because CHI3L1 is encoded on the minus strand, this corresponds to a C>T change on the coding strand. In specific transcript isoforms (XP_047298829.1 and XP_047298835.1), this position falls at a coding boundary and produces a proline-to-serine missense change (Pro205Ser and Pro199Ser respectively), suggesting that the intron 6 position may have functional consequences beyond pure splicing regulation. However, in the canonical CHI3L1 transcript the variant is classified as an intron variant by dbSNP. Conditional analysis in the Gomez et al. 2015 study²² Conditional analysis in the Gomez et al. 2015 study
Jose L Gomez et al., Yale and SARP cohorts, n=1,178 asthmatic subjects of European ancestry; both cohorts analyzed independently and results intersected confirmed that rs12141494 influences YKL-40 levels and FEV1 independently of rs4950928, establishing it as a second, distinct CHI3L1 regulatory locus.

The Evidence

The primary evidence for rs12141494 comes from a two-cohort study of asthma severity and airway YKL-40 expression³³ two-cohort study of asthma severity and airway YKL-40 expression
Gomez et al. J Allergy Clin Immunol 2015; 259 Yale Center for Asthma and Airways Disease subjects and 919 SARP (Severe Asthma Research Program) subjects; all of European ancestry. Of 15 CHI3L1 SNPs associated with FEV1, serum YKL-40, or both, rs12141494 (intron 6) was the only SNP in European-ancestry subjects that was consistently associated in both cohorts with serum YKL-40 levels and post-bronchodilator FEV1. The A allele at rs12141494 was associated with higher airway YKL-40 expression and worse asthma severity (P≤0.05). The G allele was associated with lower YKL-40 expression and higher FEV1 percent predicted, i.e. better preserved lung function.

The clinical importance of YKL-40 as a severity biomarker is well-established. A meta-analysis of 17 studies covering 5,696 subjects⁴⁴ meta-analysis of 17 studies covering 5,696 subjects
Jin et al. Sleep Breath 2022 confirmed that serum YKL-40 is significantly elevated in asthma versus controls, rising further with severity and acute exacerbations. YKL-40 correlates specifically with bronchial wall thickening (r=0.45), blood neutrophils (r=0.63), and exhaled nitric oxide (r=0.48) in therapy-resistant pediatric asthma⁵⁵ bronchial wall thickening (r=0.45), blood neutrophils (r=0.63), and exhaled nitric oxide (r=0.48) in therapy-resistant pediatric asthma
Konradsen et al. J Allergy Clin Immunol 2013; therapy-resistant vs controlled asthma; serum YKL-40 19.2 vs 13.8 ng/mL, P=0.03 — all markers of active airway remodeling rather than simple allergen sensitization. In a 2023 phenotype review⁶⁶ 2023 phenotype review
Specjalski et al. Front Med 2023, YKL-40 was highest in severe neutrophilic and obesity-associated asthma, correlating with therapy resistance, exacerbation frequency, and FEV1 decline.

Practical Actions

Carriers of the A allele at rs12141494 have a genetically elevated YKL-40 set-point that drives airway remodeling independently of promoter-driven YKL-40 regulation. For asthmatic A-allele carriers, serum YKL-40 measurement provides direct insight into the biological activity of this genetic predisposition. Because YKL-40 elevation is relatively steroid-insensitive (it marks non-T2 remodeling rather than eosinophilic inflammation), standard inhaled corticosteroid escalation may undertreat the remodeling process it drives. Exposure to occupational dust, mold, and biomass smoke are the principal environmental triggers documented to amplify YKL-40-driven airway remodeling, and are specifically relevant for A-allele carriers with occupational asthma or indoor air quality concerns.

Interactions

rs12141494 operates independently of the CHI3L1 promoter variant rs4950928, which is already in the GeneOps database. Carriers of the A allele at rs12141494 who also carry the C allele at rs4950928 are doubly predisposed to elevated YKL-40 through two mechanistically distinct routes: reduced transcriptional suppression (rs4950928) and altered intron 6 splicing or transcript regulation (rs12141494). The SARP/Yale study specifically confirmed the independence of these effects through conditional analysis; having risk alleles at both loci would be expected to produce the highest YKL-40 burden of any CHI3L1 genotype combination.