rs9818870 — MRAS

MRAS rs9818870 — A Vascular Signaling Risk Variant at 3q22.3

The MRAS gene (Muscle RAS Oncogene Homolog) on chromosome 3q22.3 encodes a small GTPase¹¹ GTPase
a molecular switch protein that cycles between active (GTP-bound) and inactive (GDP-bound) states to relay signals inside cells belonging to the Ras superfamily. MRAS is highly expressed in cardiovascular tissue — particularly the heart and aorta — where it participates in MAPK/ERK and PI3K/AKT signaling²² MAPK/ERK and PI3K/AKT signaling
pathways that control cell growth, proliferation, migration, and survival in vascular smooth muscle cells. The rs9818870 variant, located in the 3' untranslated region of MRAS, was identified in 2009 as one of the earliest GWAS-confirmed susceptibility loci for coronary artery disease beyond the landmark 9p21 locus.

The Mechanism

rs9818870 sits in the 3' UTR of MRAS, in close proximity to a cluster of microRNA binding sites³³ microRNA binding sites
short sequences that let regulatory microRNA molecules bind to the mRNA and control how much protein is made. The T allele alters the local mRNA secondary structure at this region, disrupting miRNA binding and resulting in higher MRAS transcript levels in arterial and cardiac tissue. This eQTL effect — the T allele raising MRAS mRNA levels specifically in the aorta and heart — is the proposed causal mechanism by which the variant increases atherosclerosis susceptibility.

Elevated MRAS activity in vascular smooth muscle cells (VSMCs) promotes cell proliferation, migration, and phenotypic switching through MAPK/ERK signaling. These processes are central to atherosclerotic plaque formation: VSMCs that migrate into the intimal layer, proliferate, and change phenotype from contractile to synthetic contribute to plaque growth and destabilization. Additionally, single-cell coronary artery epigenomic studies identified that an intronic CAD susceptibility variant in high LD with rs9818870 (rs13324341) disrupts a MEF2-binding site⁴⁴ MEF2-binding site
myocyte enhancer factor 2, a transcription factor that regulates genes controlling VSMC response to atherosclerotic stimuli specifically in smooth muscle cells, providing further mechanistic support.

The Evidence

Erdmann et al. 2009⁵⁵ Erdmann et al. 2009
Three-stage GWAS in 19,407 cases and 21,366 controls of European ancestry identified rs9818870 on chromosome 3q22.3 as a robust CAD susceptibility locus with an odds ratio of 1.15 (95% CI: 1.11–1.19) and genome-wide significant p-value of 7.44 × 10⁻¹³ — a highly consistent signal replicated across four independent datasets. The T allele frequency was higher in cases (19.5%) than controls (15.0%) in the discovery cohort.

Subsequent studies confirmed the variant as a predictor of cardiovascular events in healthy individuals⁶⁶ predictor of cardiovascular events in healthy individuals
Genomic risk variants at 1p13.3, 1q41, and 3q22.3 associated with cardiovascular outcomes in CAD-free subjects, PMID 21984477 free of established coronary disease (p=0.045 in the healthy volunteer cohort). A Chinese study also found the TT homozygous genotype associated with significantly elevated atherosclerosis risk (p=0.041).

However, replication has been inconsistent across all populations. The Czech population study⁷⁷ The Czech population study
2,452 ACS patients (1,779 male, 673 female) and controls did not confirm the association with acute coronary syndrome (OR 1.05, 95% CI 0.89–1.24), and Pakistani cohorts similarly found no significant association. The T allele frequency is notably lower in East Asian (~3.5%) and African (~7%) populations compared to Europeans (~15%), limiting the power of non-European replication studies. The variant's effect appears strongest and most consistently demonstrated in populations of European ancestry.

The 2024 MRAS review confirms that CAD risk variants in this gene, including rs9818870, increase MRAS expression primarily in arterial and aortic tissue through eQTL effects, with the mechanism operating specifically through smooth muscle cell biology rather than lipid metabolism — making this risk pathway mechanistically distinct from traditional lipid-based cardiovascular risk.

Practical Actions

Because the rs9818870 mechanism operates through vascular smooth muscle cell biology and inflammatory signaling rather than lipid metabolism, the most relevant interventions target arterial health and cardiovascular risk factor management. For T allele carriers — particularly CT and TT — closer attention to cardiovascular biomarker monitoring is warranted, as the genetic risk operates independently of standard lipid levels.

Statin therapy remains the most evidence-based pharmacological intervention for modifiable cardiovascular risk reduction, and the pleiotropic (lipid-independent) effects of statins on vascular inflammation and smooth muscle cell function may be particularly relevant to the MRAS pathway. Monitoring high-sensitivity CRP alongside traditional lipid panels provides a fuller picture of vascular inflammatory risk.

Interactions

rs9818870 was identified in the same GWAS framework as rs1333049⁸⁸ rs1333049
9p21 locus, the strongest known CAD genetic risk factor, in CDKN2B-AS1. Both variants act through non-lipid mechanisms affecting vascular smooth muscle cell biology, and their effects on CAD risk are additive and independent of each other and of traditional risk factors. Carriers of risk alleles at multiple CAD loci (including 9p21 and 3q22.3) accumulate risk in a log-additive fashion; users with elevated risk at both loci should treat cardiovascular prevention as a high priority.