rs13324341 — MRAS

MRAS — A Molecular Switch That Steers Your Artery Walls

Deep inside the walls of your coronary arteries, smooth muscle cells (SMCs) exist in two fundamentally different states. In their quiet, contractile phenotype¹¹ contractile phenotype
Maintains vessel tone and wall integrity; expresses SMC marker genes such as ACTA2 and MYH11, they hold the arterial wall together. Under stress — lipid exposure, inflammation, mechanical injury — they can flip into a synthetic phenotype²² synthetic phenotype
Migratory, proliferative, secretes matrix proteins; contributes to fibrous cap and neointima, becoming pro-atherogenic builders of plaque. MRAS (Muscle RAS Oncogene Homolog) is a small GTPase³³ small GTPase
A molecular switch cycling between GDP-bound inactive and GTP-bound active states that sits at the heart of the signaling network governing this switch.

The Mechanism

The rs13324341 variant lies in intron 1 of MRAS on chromosome 3q22.3. A 2022 single-nucleus chromatin accessibility study⁴⁴ 2022 single-nucleus chromatin accessibility study
Applied snATAC-seq to 28,316 nuclei from coronary artery segments of 41 CAD patients; identified 14 distinct cell-type clusters published in Nature Genetics identified rs13324341 as a functional regulatory variant: the minor T allele creates a MEF2 transcription factor binding site that is absent on the common C allele background. The result is increased chromatin accessibility specifically in smooth muscle cells, functioning simultaneously as a chromatin accessibility QTL (caQTL) and a strong expression QTL⁵⁵ chromatin accessibility QTL (caQTL) and a strong expression QTL
GTEx arterial tissue eQTL; strongest effect in the aorta in GTEx arterial tissues. T allele carriers produce more MRAS mRNA, particularly in aortic and arterial tissue.

Elevated MRAS protein amplifies the SHOC2–MRAS–PP1C holophosphatase complex⁶⁶ SHOC2–MRAS–PP1C holophosphatase complex
A GTP-bound MRAS recruits SHOC2 and PP1C phosphatase; together they dephosphorylate RAF at Ser259, releasing an inhibitory 14-3-3 interaction and potentiating MAPK cascade activation, which dephosphorylates RAF and potentiates MAPK/ERK signaling. In smooth muscle cells, excess MAPK/ERK activity promotes proliferation, migration, and phenotypic switching toward the synthetic state — exactly the cellular behaviors that build and destabilize atherosclerotic plaques.

The Evidence

The MRAS 3q22.3 locus was originally discovered in a three-stage GWAS⁷⁷ three-stage GWAS
German MI cases (n=1,222), in-silico replication in three GWAS datasets, validation in ~25,000 subjects by Erdmann et al. (Nature Genetics, 2009), with the index variant rs9818870 reaching P=7.44×10⁻¹³ and OR=1.15 (95% CI 1.11–1.19) across 19,407 cases and 21,366 controls. A subsequent large meta-analysis⁸⁸ large meta-analysis
Encompassing 22,233 cases and 64,762 controls, all of European ancestry, followed by 60,738 additional individuals confirmed the locus as one of 13 genome-wide significant CAD risk loci.

rs13324341 is in very high LD with rs9818870 (r²>0.9), meaning they almost always appear on the same haplotype. The T allele at rs13324341 is rare in East Asian populations (MAF <1%), which is consistent with the finding that MRAS genetic risk for CAD shows attenuated effects in Han Chinese cohorts compared to European populations.

A 2024 comprehensive mechanistic review⁹⁹ 2024 comprehensive mechanistic review
Shah et al. IUBMB Life, summarizing MRAS biology from GWAS discovery through structural analyses of the SHOC2 complex confirmed that MRAS risk variants increase arterial expression and are associated with cytokine imbalance — specifically elevated TNF-to-IL10 ratios — in carriers, linking the variant to both structural remodeling and vascular inflammation.

Practical Actions

rs13324341 T carriers have modest but independently validated elevated risk (OR ~1.15 per allele). The variant's mechanism — excess MAPK/ERK-driven SMC proliferation and phenotypic switching — means the actionable window is plaque initiation and early progression rather than acute events. For T carriers, the most meaningful interventions target smooth muscle cell quiescence and vascular inflammation:

High-dose EPA¹⁰¹⁰ EPA
Eicosapentaenoic acid — the omega-3 that most directly reduces PDGF-driven SMC proliferation suppresses PDGF-BB-mediated SMC growth and migration, the same proliferative axis amplified by MRAS overexpression. Monitoring arterial wall health — through coronary artery calcium scoring in the mid-40s if other risk factors are present — provides an evidence-based early window to detect subclinical disease before symptoms emerge.

Interactions

rs13324341 is in high LD with rs9818870 (r²>0.9); for practical purposes they tag the same biological signal. The broader 3q22.3 haplotype also includes rs185244, rs13059110, and rs11713141, which together define the full MRAS CAD risk haplotype. Within the MAPK pathway, MRAS works downstream of receptor tyrosine kinases and upstream of RAF–MEK–ERK; variants in pathway partners such as SHOC2 or BRAF could compound the effect of elevated MRAS on smooth muscle cell signaling, though these specific compound effects have not been formally studied in population cohorts.