rs67338227 — FHL5

FHL5 rs67338227 — A Vascular Smooth Muscle Gene at the Heart of Migraine Risk

Migraine is not simply a brain pain disorder — it involves a coordinated failure in how blood vessels regulate their tone, particularly in the meninges and cranial arteries. FHL5 (four and a half LIM domains 5) encodes a transcriptional coactivator that regulates cAMP-responsive element modulator (CREM)¹¹ cAMP-responsive element modulator (CREM)
CREM is a transcription factor that controls gene expression programs downstream of cyclic AMP signaling; in vascular smooth muscle cells, CREM-dependent programs govern vessel tone and contractility. The FHL5 protein controls vascular disease-associated gene programs in smooth muscle cells, and common intronic variants in this gene — including rs67338227 — are among the most robust genetic determinants of migraine risk discovered in human genetics.

rs67338227 sits in an intron of FHL5 on chromosome 6q16. The T alternate allele is globally rare (approximately 0.3–1.5% depending on ancestry group) but its GWAS signal is exceptionally strong: the T allele carries an odds ratio of 1.09 per allele (95% CI 1.08–1.11) for migraine at p=2×10⁻²⁷, one of the most significant hits in the entire migraine genetics literature. The effect follows an additive model — each copy of T shifts risk upward — consistent with this variant tagging altered FHL5 expression levels in relevant tissues rather than a protein-disrupting change.

The Mechanism

FHL5 is a member of the LIM domain protein family, whose characteristic zinc-finger modules mediate protein-protein interactions in transcriptional complexes. FHL5 acts as a coactivator of CREM²² coactivator of CREM
CREM drives expression of genes involved in spermatid differentiation and has established roles in smooth muscle cell gene programs downstream of cAMP signaling. When cAMP levels rise in vascular smooth muscle — as occurs in response to vasoactive signals such as CGRP (calcitonin gene-related peptide, the primary trigger molecule in migraine attacks) — FHL5-CREM complexes regulate the transcriptional response that controls vessel relaxation and contractility.

An intronic variant such as rs67338227-T likely alters FHL5 expression levels or splicing in arterial smooth muscle cells. Supporting this, Jiang et al. 2021³³ Jiang et al. 2021
Common variants in KCNK5 and FHL5 genes contributed to the susceptibility of migraine without aura in Han Chinese population. Scientific Reports detected significant eQTL signals at the FHL5 locus in migraine patients, confirming that this genomic region influences FHL5 gene expression rather than protein structure. Altered FHL5 expression would dysregulate CREM-dependent gene programs in cranial smooth muscle cells, impairing the normal vasomotor response to migraine triggers.

The most direct functional evidence comes from Knol et al. 2020⁴⁴ Knol et al. 2020
Migraine Genetic Variants Influence Cerebral Blood Flow. Headache, which showed that the rs67338227 risk allele is associated with higher carotid flow velocity and smaller carotid cross-sectional area (p=3.7×10⁻⁸) in 4,665 participants. This is a direct measurement of altered vascular tone and structure in carriers — the biological intermediate between a gene expression change and the clinical migraine phenotype.

The Evidence

The FHL5 migraine locus has been independently replicated across four large genetic studies spanning over a decade:

Anttila et al. 2013⁵⁵ Anttila et al. 2013
Genome-wide meta-analysis identifies new susceptibility loci for migraine. Nature Genetics first identified rs67338227 at the FHL5 locus in a meta-analysis of 23,285 cases and 95,425 controls across 29 studies. The FHL5 region was one of five newly discovered migraine loci reaching genome-wide significance.

Gormley et al. 2016⁶⁶ Gormley et al. 2016
Meta-analysis of 375,000 individuals identifies 38 susceptibility loci for migraine. Nature Genetics substantially replicated and refined the FHL5 association using 59,674 migraine cases and 316,078 controls, pinpointing rs67338227-T at OR=1.09 (95% CI 1.08–1.11), p=2×10⁻²⁷. Notably, this study found that migraine loci as a group were enriched for expression in vascular and smooth muscle tissues — directly implicating FHL5's vascular role in the biology.

Hautakangas et al. 2022⁷⁷ Hautakangas et al. 2022
Genome-wide analysis of 102,084 migraine cases identifies 123 risk loci. Nature Genetics conducted the largest migraine GWAS to date and confirmed the FHL5 locus among 123 independent risk signals, with the FHL5 region meeting criteria as a high-confidence locus.

A 2025 multi-omics integration study (Wei et al. 2025, Journal of Headache Pain⁸⁸ Wei et al. 2025, Journal of Headache Pain) identified FHL5 as one of a small number of "high-confidence cross-subtype genes" supported by multiple analytical approaches, including colocalization with expression and chromatin data.

Practical Actions

Carrying the T allele at rs67338227 does not cause migraine — it increases susceptibility within a complex polygenic architecture. However, understanding the vascular mechanism points to specific, actionable strategies.

CGRP is the primary vasoactive peptide mediating migraine attacks, and FHL5 regulates smooth muscle cell responses to cAMP signaling downstream of CGRP receptors. This makes FHL5 T allele carriers especially relevant candidates for modern CGRP-targeting therapies: monoclonal antibodies targeting CGRP or its receptor (erenumab, fremanezumab, galcanezumab, eptinezumab) are now first-line preventive treatments for episodic and chronic migraine. The biological rationale for these drugs directly overlaps with the FHL5 pathway.

Additionally, the carotid hemodynamic changes documented in T allele carriers — higher flow velocity, smaller vessel diameter — suggest that cerebrovascular tone is measurably altered at baseline. Traditional migraine prophylactics that act on vascular smooth muscle tone (beta-blockers such as propranolol and metoprolol; calcium channel blockers such as flunarizine and verapamil) have established efficacy for migraine prevention and operate through overlapping pathways with FHL5's vascular smooth muscle regulatory function.

Interactions

The FHL5 locus has been studied in the context of migraine with and without aura. The Jiang 2021 study was specific to migraine without aura (MO) in a Han Chinese cohort and identified strong eQTL signals at the FHL5 region for this subtype. The broader European GWAS studies (Gormley 2016, Hautakangas 2022) analysed both migraine subtypes together.

rs11172113 (near TSPAN2) is another replicated migraine GWAS locus with evidence of vascular mechanism, and rs1835740 (near MTDH/SLC2A5) is an established migraine susceptibility variant that may compound the FHL5 vascular effect. The largest migraine polygenic risk scores incorporate both FHL5 and these pathway partners. Carriers of multiple migraine risk alleles at independent vascular loci may derive the greatest benefit from preventive therapy targeting the vascular component of migraine.