rs3918226 — NOS3

The eNOS Promoter Switch — How rs3918226 Dials Down Nitric Oxide

Endothelial nitric oxide synthase (eNOS), encoded by NOS3, is the enzyme that keeps blood vessels relaxed and healthy. By producing nitric oxide (NO) in the inner lining of blood vessels, eNOS lowers blood pressure, prevents clot formation, and dampens inflammation. rs3918226 sits in the promoter region of NOS3 — the stretch of DNA that acts as a volume control for how much enzyme the cell makes.

The Mechanism

The rs3918226 T allele disrupts a binding site for ETS transcription factors¹¹ ETS transcription factors
E-twenty six (ETS) proteins are a family of transcription factors that activate gene expression by binding specific DNA sequences in promoters in the NOS3 promoter. When the T allele is present, ETS factors bind less effectively, and the cell transcribes less NOS3 mRNA. Cell experiments confirm that the T allele reduces eNOS promoter activity by 20–40% compared to the reference C allele. Less eNOS means less nitric oxide, which means blood vessels are less able to relax on demand — a direct path to higher blood pressure and endothelial dysfunction.

This variant is distinct from two other well-studied NOS3 polymorphisms: rs2070744 (T-786C, a second promoter variant) and rs1799983 (Glu298Asp, a missense variant affecting enzyme stability). All three reduce NO bioavailability through different mechanisms and can interact when present together.

The Evidence

A genome-wide association study²² genome-wide association study
Salvi E et al. Genomewide association study identifies novel essential hypertension susceptibility locus. Hypertension, 2012 combining 21,714 subjects found rs3918226 to be among the strongest genetic predictors of essential hypertension identified to date: OR 1.34 (95% CI 1.25–1.44; P = 1.032 × 10⁻¹⁴), with each T allele adding approximately 1.9 mmHg systolic and 1.4 mmHg diastolic blood pressure on average.

A follow-up prospective study³³ prospective study
Salvi E et al. Target sequencing, cell experiments, and a population study establish eNOS gene as hypertension susceptibility gene. Hypertension, 2013 in 2,722 European adults followed for 7.6 years showed that TT homozygotes experienced a blood pressure rise of 9.7/6.8 mmHg (systolic/diastolic) compared to 3.8/1.9 mmHg in C-allele carriers. Among the 2,013 who were normotensive at baseline, TT homozygosity conferred a hazard ratio of 2.04 (95% CI 1.24–3.37; P = 0.005) for developing hypertension — a doubling of risk. The T allele is rare globally (5–8% frequency) but enriched in European populations (~8%), where the hypertension burden is also high.

Practical Actions

Because this variant reduces eNOS transcription rather than enzyme function, approaches that supply nitric oxide through alternative pathways are particularly relevant. Dietary nitrates from beetroot, spinach, arugula, and celery are converted by oral bacteria to nitrite, and then to NO in the acidic environment of the stomach and blood — entirely bypassing eNOS. This pathway has been shown to lower blood pressure by 4–10 mmHg in clinical trials of high-nitrate diets.

Antioxidant support matters because reduced eNOS activity can shift the enzyme toward producing superoxide (oxidative stress) rather than NO — a state called eNOS uncoupling. Vitamin C helps recycle the eNOS cofactor BH4, keeping what enzyme is present in its NO-producing mode.

Blood pressure monitoring is actionable: a sustained reading above 130/80 mmHg warrants discussion with a clinician about pharmacological support. CT/TT carriers on antihypertensive medications may respond differently to drug classes that modulate NO signaling, as shown by pharmacogenomic studies of this locus.

Interactions

rs3918226 can interact with the nearby NOS3 promoter variant rs2070744 (T-786C) and the coding variant rs1799983 (Glu298Asp) to produce compounded reductions in NO bioavailability. Carriers of the T allele at rs3918226 who also carry the C allele at rs2070744 and/or the T allele at rs1799983 face additive risk from multiple independent impairments to eNOS expression and enzyme stability. These interactions are described in the Salvi 2013 study and in haplotype analyses of NOS3 variants in migraine and cardiovascular disease cohorts.