rs9349379 — PHACTR1

Intronic regulatory variant in PHACTR1 that controls endothelin-1 and arterial compliance; the A allele is one of the strongest migraine GWAS hits (OR ~1.08, P=1×10⁻⁴⁷) while the G allele shows the opposite pattern — protective against migraine but a major coronary artery disease risk factor, demonstrating striking pleiotropy across five vascular diseases

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PHACTR1 rs9349379 — The Vascular Switcher: Migraine Risk Versus Heart-Attack Protection

A single nucleotide variant sitting in an intron of the PHACTR1 gene on chromosome 6 has one of the most remarkable genetic profiles in cardiovascular and neurological medicine: its two alleles pull risk in opposite directions across five vascular diseases. Carry the A allele and you are predisposed to migraine headaches, cervical artery dissection, and fibromuscular dysplasia. Carry the G allele and your migraine risk falls — but your risk of coronary artery disease and myocardial infarction rises. The same switch, flipped in opposite directions for two different arteries, illustrates why the PHACTR1 locus has attracted intense interest from both neurologists and cardiologists.

PHACTR111 PHACTR1
phosphatase and actin regulator 1 — a protein involved in cytoskeletal regulation, vascular compliance, and endothelial gene expression is expressed predominantly in endothelial and vascular smooth muscle cells. The rs9349379 variant lies in a large intron (between exons 5 and 6) but is not silent — it sits in a regulatory enhancer active in aortic tissue and alters the binding of myocyte enhancer factor-2 (MEF2) transcription factors to that enhancer.

The Mechanism

The molecular story has two layers. First, rs9349379 affects PHACTR1's own expression: the G allele disrupts MEF2 binding, reducing PHACTR1 transcription in human coronary arteries and aorta. Wang & Musunuru 201822 Wang & Musunuru 2018
Circulation Genomic Precision Med confirmed this using CRISPR-edited iPSC-derived endothelial cells with knock-in of each allele — GG homozygotes expressed less PHACTR1 than AA homozygotes.

Second, and more dramatically, rs9349379 acts as a distal enhancer for endothelin-1 (EDN1), located 600 kb upstream of PHACTR1. Gupta et al. 201733 Gupta et al. 2017
Cell used CRISPR deletion of the 88-bp regulatory element at rs9349379 in iPSC-derived endothelial cells and vascular smooth muscle cells; deletion increased EDN1 expression, and analysis of 99 healthy individuals confirmed that each G allele raises Big ET-1 plasma levels. Endothelin-1 is a potent vasoconstrictor that also promotes vascular smooth muscle proliferation, extracellular matrix deposition, and arterial fibrosis — effects consistent with coronary plaque vulnerability.

The opposing disease profiles arise because atherosclerotic coronary artery disease (plaque-dependent) and migraine with aura (vasospasm and cortical spreading depression) represent fundamentally different vascular failure modes. Higher ET-1 from the G allele promotes the chronic endothelial injury model of atherosclerosis while the A allele's arterial-wall compliance changes (fibromuscular dysplasia, CeAD) reflect a structural fragility model distinct from plaque. PHACTR1 itself, when reduced by the G allele, may also modulate endothelial inflammation via NF-κB-dependent ICAM-1/VCAM-1 expression.

The Evidence

Hautakangas et al. 202244 Hautakangas et al. 2022
Nature Genetics — the largest migraine GWAS to date (102,084 cases, 771,257 controls) — identified rs9349379 as the sole credible causal variant at the PHACTR1 locus with a posterior inclusion probability of 1.00. The association reached P ≈ 1×10⁻⁴⁷, placing it among the top migraine loci genome-wide. PHACTR1 was one of only two genes prioritized with strong evidence by both gene prioritization methods used in the study. The association held for migraine both with and without aura.

The pleiotropy was formally quantified by Winsvold et al. 201755 Winsvold et al. 2017
PLOS ONE using conjunctional FDR analysis across 23,285 migraine cases and multiple CAD cohorts: the A allele showed beta = +0.073 for migraine (P = 6.4×10⁻⁸) but beta = −0.159 for CAD (P = 6.5×10⁻²¹) — opposite signs, both highly significant.

For cervical artery dissection, Debette et al. 201566 Debette et al. 2015
Nature Genetics found the G allele protective (OR = 0.75, P = 4.5×10⁻¹⁰, 2,052 cases/17,064 controls). For fibromuscular dysplasia, Kiando et al. 201677 Kiando et al. 2016
PLoS Genetics found the A allele confers OR = 1.39 (P = 7.4×10⁻¹⁰, 1,154 FMD cases). The A allele is rare in Africans (~8%) but common in East Asians (~32% homozygous AA), producing dramatically different population-level vascular disease burdens.

Practical Actions

For carriers of the AA genotype (two A alleles): migraine susceptibility is elevated, and while the vascular mechanism is distinct from classical atherosclerosis, the endothelial and arterial-wall changes associated with the A allele also raise risk of cervical artery dissection and fibromuscular dysplasia. Vasoconstrictive migraine treatments (ergotamine, dihydroergotamine) carry theoretical concern in individuals already predisposed to arterial wall pathology, and triptans — which carry black-box warnings for coronary vasospasm — are worth discussing with a neurologist who knows this genotype.

For GG carriers: migraine risk is low, but the G allele's higher ET-1 production and reduced PHACTR1 expression increase coronary artery disease risk independently of traditional risk factors. Standard cardiovascular risk management is therefore especially important.

Interactions

The PHACTR1 locus interacts at the pathway level with other vascular endothelial variants. The EDN1 pathway is shared with rs5370 (EDN1 Lys198Asn), which directly alters the endothelin-1 peptide sequence and affects vasoconstrictor tone. Variants in EDNRA and EDNRB (endothelin receptor genes) could compound the rs9349379 regulatory effect on ET-1 signalling. NOS3 variants (e.g., rs1799983 ENOS Glu298Asp) affecting nitric oxide production operate antagonistically to endothelin-1 in vascular tone regulation; a combined PHACTR1-AA / NOS3-risk genotype may produce additive vascular wall dysfunction. These pathway interactions are candidates for compound actions but require published evidence of combined effects before they can be formally modelled.

Genotype Interpretations

What each possible genotype means for this variant.

GG Migraine-Protective Variant Normal

No migraine-risk A alleles — lowest migraine susceptibility at this locus, but elevated coronary artery disease risk via G allele

You carry two G alleles at rs9349379 in PHACTR1. For migraine, this is the protective genotype — about 15% of people globally carry GG, and this genotype is associated with the lowest migraine risk at this locus in the largest migraine GWAS ever conducted (102,084 cases). However, the G allele is also the coronary artery disease risk allele: GG individuals have higher endothelin-1 production and reduced PHACTR1 expression in arterial tissue, which is independently associated with myocardial infarction risk (OR ~1.37 per G allele in some cohorts). The G allele is also associated with lower risk of cervical artery dissection and fibromuscular dysplasia. Your PHACTR1 genotype presents a split vascular profile: favourable for brain vessels, less favourable for coronary arteries.

AG Heterozygous Carrier Intermediate

One migraine-risk A allele — intermediate migraine susceptibility with mixed vascular risk profile

The PHACTR1 locus operates through two mechanisms: regulation of PHACTR1's own expression (the A allele supports higher PHACTR1 expression via MEF2 binding) and distal regulation of endothelin-1. The G allele disrupts the MEF2 binding site and increases ET-1, which promotes coronary plaque vulnerability. The A allele keeps ET-1 lower but alters arterial-wall structural properties in a way that predisposes to non-atherosclerotic arterial pathology — cervical dissection and fibromuscular dysplasia — and to migraine, likely via cortical spreading depression susceptibility.

As a heterozygote, your PHACTR1 expression and ET-1 levels will be intermediate between the two homozygous states. In European populations, around 48% of people carry the AG genotype; in East Asian populations, where the A allele is more common, AG frequency is lower as AA is more prevalent.

AA High-Risk Variant High Risk

Two migraine-risk A alleles — highest migraine susceptibility at this locus, with increased risk of cervical artery dissection and fibromuscular dysplasia

The PHACTR1 rs9349379 locus sits at the intersection of two different vascular pathologies. The A allele maintains higher PHACTR1 expression (via intact MEF2 binding) and lower endothelin-1 levels than the G allele — which sounds protective, but in the context of arterial-wall structural biology, this translates to higher risk of arterial wall fragility conditions rather than plaque-based disease. Fibromuscular dysplasia (OR = 1.39 per A allele, Kiando 2016) involves abnormal smooth muscle and fibrous tissue proliferation in medium-sized arteries — particularly renal and carotid arteries — leading to aneurysm, stenosis, and dissection risk. Cervical artery dissection (OR = 0.75 for G allele = protective; therefore A allele increases risk, Debette 2015) is spontaneous tearing of the carotid or vertebral artery wall, a major cause of stroke in young adults.

The migraine risk is likely mediated through altered cortical spreading depression susceptibility and vascular reactivity in cerebral vessels. At this genotype, vascular-mechanism migraines (those triggered by vasoactive stimuli such as hormonal fluctuations, altitude, barometric pressure, vasodilators, alcohol) may be especially prominent. Triptans and CGRP-pathway medications are the evidence-based treatment choices; vasoconstrictive ergotamine-class drugs are particularly inappropriate given the structural arterial phenotype.