rs10509679 — CYP2C9

CYP2C9 and Stroke Risk — When a Drug-Metabolism Gene Affects the Brain's Blood Supply

CYP2C9 is best known as the liver enzyme that metabolizes warfarin, ibuprofen, and dozens of other common medications. But CYP2C9 is also an epoxygenase — it converts arachidonic acid¹¹ arachidonic acid
A 20-carbon omega-6 fatty acid released from cell membranes during inflammation and stress; the precursor for a broad array of signaling lipids including prostaglandins, leukotrienes, and epoxyeicosatrienoic acids into epoxyeicosatrienoic acids (EETs), a family of lipid mediators that relax blood vessel walls, suppress inflammation, and actively protect brain tissue during ischemic episodes. rs10509679 is an intronic variant within CYP2C9 that tags a haplotype associated with increased susceptibility to ischemic stroke, most clearly documented in Chinese Han populations.

The Mechanism

EETs are produced in vascular endothelium and neurons by the epoxygenase branch of the arachidonic acid cascade — a pathway in which CYP2C8 and CYP2C9 are the dominant enzymes in human cerebral vessels. Once synthesized, EETs act as endothelium-derived hyperpolarizing factors: they open smooth muscle potassium channels, reduce intracellular calcium, and relax arterial tone. In the brain, EETs also suppress NF-κB-driven neuroinflammation and trigger preconditioning responses that limit infarct size during transient ischemia. The pathway's clinical relevance was established by Donnelly et al. 2015²² Donnelly et al. 2015
Donnelly MK et al. Genetic markers in the EET metabolic pathway are associated with outcomes in patients with aneurysmal subarachnoid hemorrhage. J Cereb Blood Flow Metab. 2015;35(2):267-76, who showed in 363 subarachnoid hemorrhage patients that genetic variants reducing EET biosynthesis worsened outcomes: CYP2C8*4 carriers showed 44% and 36% lower CSF EET levels and 2.2- to 2.5-fold higher rates of delayed cerebral ischemia and neurologic deterioration. Conversely, carrying a favorable CYP2C9 variant (g.816G) was associated with better long-term recovery. This was the first clinical demonstration that EET pathway genetics directly shapes cerebrovascular outcomes in humans.

rs10509679 sits 530 nucleotides into an intron of CYP2C9 (c.642+530, GRCh38 chr10:94,948,469). As an intronic variant, it does not change the CYP2C9 protein sequence directly. Its most likely mechanism is regulatory: intronic variants frequently influence mRNA splicing efficiency, pre-mRNA secondary structure, or binding affinity for intronic regulatory elements. In Asian populations — where the A allele frequency reaches 30% compared to 4% in African populations — this locus may tag a regional haplotype that modifies CYP2C9 expression in the brain vasculature, reducing EET output and thereby narrowing the window between normal cerebrovascular tone and ischemic injury.

The Evidence

The primary association evidence comes from Zhang et al. 2025³³ Zhang et al. 2025
Zhang J et al. CYP2C9 polymorphism is associated with susceptibility to ischemic stroke in a Chinese population. Ann Med. 2025;57(1):2506839, a matched case-control study of 643 ischemic stroke patients and 643 healthy controls from Inner Mongolia Medical University. Among four CYP2C9 intronic SNPs tested (rs10509679, rs1934967, rs1934968, rs9332220), only rs10509679 reached individual statistical significance: OR=1.48 (95% CI 1.05-2.09, p=0.024). A haplotype combining the risk alleles at all four loci — A(rs10509679)-C(rs1934967)-G(rs1934968)-G(rs9332220) — showed further elevated stroke risk, suggesting that the four intronic variants collectively tag a functional haplotype block. The study was limited to one ethnic group and a single centre, and the individual OR of 1.48 is modest; independent replication in larger, multi-ethnic cohorts is needed before this variant can be assigned a higher evidence grade.

The broader picture of CYP2C9 and stroke is reinforced by two large Taiwan Biobank analyses: Peng et al. 2021⁴⁴ Peng et al. 2021
Peng JW et al. Interactive association between CYP2C9 rs2860905 polymorphism and atrial fibrillation on ischemic stroke in Taiwan Biobank participants. Pharmacogenomics Pers Med. 2021;14:1199-1212 found that the CYP2C9 rs2860905 GG genotype enhanced stroke risk and interacted multiplicatively with atrial fibrillation (combined OR=4.68 vs 3.70 for AF alone, 17,726 participants). A companion study by Peng et al. 2022⁵⁵ Peng et al. 2022
Peng JW et al. Independent and interactive effects of sex and CYP2C9 variant rs4918758 on ischemic stroke risk. Int J Gen Med. 2022;15:3771-3780 demonstrated sex-stratified stroke risk for another CYP2C9 intronic variant, with significantly elevated risk in men (OR=1.32) but not women. Together, these studies establish a consistent, if still emerging, pattern linking CYP2C9 intronic variation to ischemic stroke susceptibility in East and South Asian populations, likely via EET pathway effects on cerebrovascular reactivity.

Practical Actions

For carriers of the A allele, the two most actionable levers are: (1) supporting EET production upstream by ensuring adequate omega-6 precursor handling via EPA/DHA competition — high omega-3 intake shifts arachidonic acid metabolism away from pro-inflammatory pathways and toward protective eicosanoids; and (2) monitoring for established stroke risk factors that compound the genetic vulnerability — particularly atrial fibrillation, which the Taiwan Biobank data suggest interacts with CYP2C9 variants to multiply stroke risk several-fold. Ibuprofen and other NSAIDs that compete for CYP2C9 enzyme activity may transiently reduce EET production; this is worth discussing with a prescriber for A/A homozygotes on regular NSAID regimens.

Interactions

rs10509679 resides in a four-SNP haplotype block with rs1934967, rs1934968, and rs9332220 within CYP2C9. The rs1934967 variant is independently catalogued in the pharmacogenomics section (also CYP2C9, chr10) and is associated with warfarin sensitivity and NSAID metabolism in Asian populations. Carrying risk alleles at both rs10509679 and rs1934967 places someone on the stroke-risk haplotype identified in the Zhang 2025 study. Both variants are informative for the same CYP2C9 functional domain and may compound.