Identification of additional risk loci for stroke and small vessel disease: a meta-analysis of genome-wide association studies

Abstract

Summary Background Genetic determinants of stroke, the leading neurological cause of death and disability, are poorly understood and have seldom been explored in the general population. Our aim was to identify additional loci for stroke by doing a meta-analysis of genome-wide association studies. Methods For the discovery sample, we did a genome-wide analysis of common genetic variants associated with incident stroke risk in 18 population-based cohorts comprising 84 961 participants, of whom 4348 had stroke. Stroke diagnosis was ascertained and validated by the study investigators. Mean age at stroke ranged from 45·8 years to 76·4 years, and data collection in the studies took place between 1948 and 2013. We did validation analyses for variants yielding a significant association (at p<5 × 10−6) with all-stroke, ischaemic stroke, cardioembolic ischaemic stroke, or non-cardioembolic ischaemic stroke in the largest available cross-sectional studies (70 804 participants, of whom 19 816 had stroke). Summary-level results of discovery and follow-up stages were combined using inverse-variance weighted fixed-effects meta-analysis, and in-silico lookups were done in stroke subtypes. For genome-wide significant findings (at p<5 × 10−8), we explored associations with additional cerebrovascular phenotypes and did functional experiments using conditional (inducible) deletion of the probable causal gene in mice. We also studied the expression of orthologs of this probable causal gene and its effects on cerebral vasculature in zebrafish mutants. Findings We replicated seven of eight known loci associated with risk for ischaemic stroke, and identified a novel locus at chromosome 6p25 (rs12204590, near FOXF2) associated with risk of all-stroke (odds ratio [OR] 1·08, 95% CI 1·05–1·12, p=1·48 × 10−8; minor allele frequency 21%). The rs12204590 stroke risk allele was also associated with increased MRI-defined burden of white matter hyperintensity—a marker of cerebral small vessel disease—in stroke-free adults (n=21 079; p=0·0025). Consistently, young patients (aged 2–32 years) with segmental deletions of FOXF2 showed an extensive burden of white matter hyperintensity. Deletion of Foxf2 in adult mice resulted in cerebral infarction, reactive gliosis, and microhaemorrhage. The orthologs of FOXF2 in zebrafish (foxf2b and foxf2a) are expressed in brain pericytes and mutant foxf2b−/− cerebral vessels show decreased smooth muscle cell and pericyte coverage. Interpretation We identified common variants near FOXF2 that are associated with increased stroke susceptibility. Epidemiological and experimental data suggest that FOXF2 mediates this association, potentially via differentiation defects of cerebral vascular mural cells. Further expression studies in appropriate human tissues, and further functional experiments with long follow-up periods are needed to fully understand the underlying mechanisms.

Multiancestry genome-wide association study of 520,000 subjects identifies 32 loci associated with stroke and stroke subtypes

“…For some loci, joint analysis of epigenetic regulatory effects and association statistics enabled prioritization of credible SNPs. When exploring the overall epigenetic patterns of identified stroke risk loci, we observed some enrichment in enhancer and promoter sites in developmental tissues, thus suggesting that some associations may be driven by developmental effects, as has recently been proposed for the FOXF2 locus 10 .…”

“…Previous genome-wide association studies (GWAS) in predominantly European-ancestry groups have identified ten loci robustly associated with stroke 3–12 . In most instances, the associations with stroke were attributed to individual subtypes of ischemic stroke, such as LAS 5,8,9 , CES 3,4 , and SVS 10,12 , or of ICH 6 , although some loci were associated with two or more stroke subtypes 7,9,11,13 or with any stroke 10 . We hypothesized that combining a substantially larger sample size with a transancestral analytic approach would identify additional risk loci and improve fine mapping of causal variants.…”

Deletion of 6p25.3 Is Associated with Cerebrovascular Dolichoectasia: Report of 2 Cases

“…Arterial ectasia can also lead to thinning of the vessel lining such that hemorrhage may occur, affecting the surrounding parenchyma. Chauhan et al [8] analyzed brain tissue from FOXF2 knockout mice and zebrafish and found similarly damaged smooth muscle cells in the developing cerebral vasculature, which resulted in areas of cerebral infarction and microhemorrhages in both species. This damage to the blood-brain barrier is likely attributed to the involvement of FOXF2 and FOXC1 in the development of pericytes, which surround and support blood vessel walls [6, 8].…”

“…Chauhan et al [8] analyzed brain tissue from FOXF2 knockout mice and zebrafish and found similarly damaged smooth muscle cells in the developing cerebral vasculature, which resulted in areas of cerebral infarction and microhemorrhages in both species. This damage to the blood-brain barrier is likely attributed to the involvement of FOXF2 and FOXC1 in the development of pericytes, which surround and support blood vessel walls [6, 8]. FOXF2 forms a gene tandem triplet with FOXC1 and FOXQ1 at 6p25.3 and concurrent deletion of these genes results from 6p25.3 chromosomal deletions [4].…”

“…This gene is expressed in the brain, eye, heart, and kidney tissues in both embryos and adults, which explains the number of structures affected by its deletion [13]. Further, this gene is involved in pericyte development and defects in its function are associated with large, dysplastic vessels in animal models [6, 8]. Common features of 6p25 deletion syndrome include Axenfeld-Rieger syndrome (ARS), craniofacial dysmorphism, developmental delay, sensorineural hearing loss, brain malformations, and skeletal and cardiac abnormalities [13].…”