Intracranial Aneurysm Susceptibility Research Articles

Abstract 15566: Dissecting the Genetic Architecture of Intracranial Aneurysms

Introduction: The genetic risk of intracranial aneurysm (IA) development has been ascribed largely to smoking and hypertension. The contribution of IA risk loci to aberrant gene programs within cerebrovascular cell types remains unclear. Hypothesis: We hypothesized that candidate causal genes at IA susceptibility loci are enriched within extracellular matrix producing cell types. Methods: We identified participants enrolled in the Million Veterans Program (MVP) with and without IA. Thirty-two million genotyped and imputed variants were tested for association with IA using mixed effect regression modeling, controlling for age, sex, and population structure prior to external replication and meta-analysis. Candidate causal genes were prioritized through expression quantitative trait loci colocalization and transcriptome wide association studies. We constructed a cerebrovascular single nucleus RNA sequencing (snRNA-seq) dataset and integrated IA summary statistics to compute a ‘disease relevance score’ per nucleus using the scDRS pipeline. Cell type level analysis was used to assess association of cerebrovascular cell types with IA. Results: We identified 3165 participants (2280 European, 627 African, and 258 Hispanic ancestry) with and 592927 without IA in the MVP. After replication and meta-analysis with data from an additional 12273 cases and 591046 controls, we identified 22 loci (5 novel) associated with IA. We prioritized 16 candidate causal genes. Gene expression analysis of snRNA-seq genes revealed enrichment of several candidate genes, including EDNRA and PLCE1 within smooth muscle cells (SMCs) and pericytes. Integration of summary statistics and snRNA-seq data revealed significant association of matrix-producing pericytes and smooth muscle cell populations with IA. Conclusion: Here, we identify novel loci associated with IA and found enrichment of candidate causal genes in pericytes and SMCs. Integration of summary statistics with cerebrovascular snRNA-seq reveals association of cell-types involved in matrix production, suggesting an intrinsic deficit in matrix production and vascular integrity that may drive IA pathogenesis independent of systemic hypertension.

Genetic association between the lncRNA ANRIL rs10757272 polymorphism and intracranial aneurysm susceptibility in Asians.

Current epidemiological studies reporting the role of lncRNA ANRIL rs10757272 polymorphism and intracranial aneurysm risk remain controversial. In the present study, we conducted a meta-analysis to resolve this inconsistency. PubMed and EMBASE databases were retrieved to collect the publications evaluating the association with a time limit of August 20, 2021. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to estimate the strength of the association. Subgroup analysis, heterogeneity analyses, and publication bias were assessed in the meta-analysis. Finally, 2853 cases and 13,426 controls were enrolled in this meta-analysis based on inclusion criteria. The pooled results indicated that the rs10757272 polymorphism is significantly associated with the risk of intracranial aneurysms in all genetic models (homozygous model, odds ratio (OR) = 1.48, 95% confidence interval (CI) = 1.28-1.71, Pheterogeneity = 0.11, I2 = 50.9; heterozygous model, OR = 1.26, 95% CI = 1.09-1.46, Pheterogeneity = 0.15, I2 = 42.8; dominant model, OR = 1.37, 95% CI = 1.19-1.57, Pheterogeneity = 0.12, I2 = 48.1; and recessive model, OR = 1.23, 95% CI = 1.13-1.34, Pheterogeneity = 0.24, I2 = 28.8). Subgroup analyses showed consistent results. In conclusion, our findings provided evidence that the rs10757272 polymorphism is associated with susceptibility to intracranial aneurysms in Asians.

Whole-exome sequencing in a Japanese multiplex family identifies new susceptibility genes for intracranial aneurysms.

Intracranial aneurysms (IAs) cause subarachnoid hemorrhage, which has high rates of mortality and morbidity when ruptured. Recently, the role of rare variants in the genetic background of complex diseases has been increasingly recognized. The aim of this study was to identify rare variants for susceptibility to IA. Whole-exome sequencing was performed on seven members of a Japanese pedigree with highly aggregated IA. Candidate genes harboring co-segregating rare variants with IA were re-sequenced and tested for association with IA using additional 500 probands and 323 non-IA controls. Functional analysis of rare variants detected in the pedigree was also conducted. We identified two gene variants shared among all four affected participants in the pedigree. One was the splicing donor c.1515+1G>A variant in NPNT (Nephronectin), which was confirmed to cause aberrant splicing by a minigene assay. The other was the missense p.P83T variant in CBY2 (Chibby family member 2). Overexpression of p.P83T CBY2 fused with red fluorescent protein tended to aggregate in the cytoplasm. Although Nephronectin has been previously reported to be involved in endothelial angiogenic functions, CBY2 is a novel molecule in terms of vascular pathophysiology. We confirmed that CBY2 was expressed in cerebrovascular smooth muscle cells in an isoform2-specific manner. Targeted CBY2 re-sequencing in additional case-control samples identified three deleterious rare variants (p.R46H, p.P83T, and p.L183R) in seven probands, showing a significant enrichment in the overall probands (8/501) compared to the controls (0/323) (p = 0.026, Fisher's extract test). NPNT and CBY2 were identified as novel susceptibility genes for IA. The highly heterogeneous and polygenic architecture of IA susceptibility can be uncovered by accumulating extensive analyses that focus on each pedigree with a high incidence of IA.

Fine-mapping of intracranial aneurysm susceptibility based on a genome-wide association study

In addition to conventional genome-wide association studies (GWAS), a fine-mapping analysis is increasingly used to identify the genetic function of variants associated with disease susceptibilities. Here, we used a fine-mapping approach to evaluate candidate variants based on a previous GWAS involving patients with intracranial aneurysm (IA). A fine-mapping analysis was conducted based on the chromosomal data provided by a GWAS of 250 patients diagnosed with IA and 296 controls using posterior inclusion probability (PIP) and log10 transformed Bayes factor (log10BF). The narrow sense of heritability (h2) explained by each candidate variant was estimated. Subsequent gene expression and functional network analyses of candidate genes were used to calculate transcripts per million (TPM) values. Twenty single-nucleotide polymorphisms (SNPs) surpassed a genome-wide significance threshold for creditable evidence (log10BF > 6.1). Among them, four SNPs, rs75822236 (GBA; log10BF = 15.06), rs112859779 (TCF24; log10BF = 12.12), rs79134766 (OLFML2A; log10BF = 14.92), and rs371331393 (ARHGAP32; log10BF = 20.88) showed a completed PIP value in each chromosomal region, suggesting a higher probability of functional candidate variants associated with IA. On the contrary, these associations were not shown clearly under different replication sets. Our fine-mapping analysis suggested that four functional candidate variants of GBA, TCF24, OLFML2A, and ARHGAP32 were linked to IA susceptibility and pathogenesis. However, this approach could not completely replace replication sets based on large-scale data. Thus, caution is required when interpreting results of fine-mapping analysis.

Antisense Non-Coding Ribonucleic Acid in the INK4 Locus Long Noncoding Ribonucleic Acid Rs1333040 Polymorphism and Susceptibility to the Intracranial Aneurysm in Asian Population

Several researchers have suggested that the antisense non-coding ribonucleic acid in the INK4 locus long non-coding ribonucleic acid (cyclin-dependent kinase inhibitor 2B antisense ribonucleic acid 1) plays a key role in the pathogenesis of the intracranial aneurysm. However, because single studies are often underpowered due to inadequate sample sizes, the role of the antisense non-coding ribonucleic acid in the INK4 locus rs1333040 polymorphism in intracranial aneurysms has been inconclusive among Asian population. To obtain a comprehensive conclusion, we conducted a meta-analysis with 4260 cases and 14 536 controls to estimate the association between the rs1333040 polymorphism and intracranial aneurysms susceptibility. The electronic databases of PubMed and Embase were searched before May 2022, to identify the relevant literature. Cochran’s Q statistics and the I2 test were applied to assess heterogeneity among the included investigations. The summary pooled odds ratios and 95 % confidence intervals were evaluated for the strength of association using the random or fixed-effects model. A total of 6 eligible studies were enrolled in this meta-analysis, involving 4260 cases and 14 536 controls. The pooled results indicated a significant association between the rs1333040 polymorphism and the intracranial aneurysm in Asians under 3 genetic models (TT vs. CC: Odds ratio=1.48, 95 % confidence interval=1.30-1.70; TC vs. CC: Odds ratio=1.20, 95 % confidence interval=1.05-1.38; dominant model-TT+TC vs. CC: Odds ratio=1.34, 95 % confidence interval=1.18-1.53). The findings of this meta-analysis emphasize the rs1333040 polymorphism as a common risk factor for intracranial aneurysms in Asian people.

Association of Versican Gene Polymorphisms with Intracranial Aneurysm Susceptibility in the Eastern Chinese Population

ObjectiveThe proteoglycan versican (VCAN) plays an important role in extracellular matrix (ECM) assembly, and diminished maintenance of the ECM has been increasingly regarded as an important factor in the development of intracranial aneurysms (IAs). Previous studies have revealed that single-nucleotide polymorphisms (SNPs) of the VCAN gene are associated with susceptibility to IAs in European or Japanese populations. However, the association between IA susceptibility and VCAN SNPs in the Eastern Chinese population remains unclear. This study aimed to investigate the associations of the SNPs rs251124, rs2287926, and rs173686 with IA susceptibility in the Eastern Chinese population.MethodsA total of 162 patients with IA and 182 controls were enrolled in this study. The study was conducted between January 2017 and December 2020. SNP genotyping for rs251124, rs2287926, and rs173686 was performed using Kompetitive Allele Specific PCR (KASP) after DNA extraction. The SNP data were analysed with CFX Manager Software version 3.1 (Bio-Rad).Resultsrs251124 and rs173686 were significantly associated with susceptibility to IA. The frequency of rs251124-TT in IA was higher than in controls (OR =1.26, 95% CI: 1.07–1.49; P<0.01), and its risk mainly came from the T allele. Furthermore, logistic regression analysis showed that the T/T genotype and T allele of rs251124 were independent risk factors for IA (OR=1.726, 95% CI: 1.136–2.263; P=0.011). Moreover, the G/G genotype and G allele of rs173686 were associated with increased IA susceptibility (OR=2.52, 95% CI: 1.261–5.037; P=0.009).ConclusionThe SNPs rs251124 and rs173686 were strongly associated with genetic susceptibility to IA in the Eastern Chinese population; however, no such association was found in the SNP rs2287926 of VCAN. Our findings suggest that the VCAN gene is an IA susceptible gene that should be further studied as a screening marker for IAs.

Polymorphisms in Lysyl Oxidase Family Genes Are Associated With Intracranial Aneurysm Susceptibility in a Chinese Population.

PurposeIntracranial aneurysms (IA) comprise a multifactorial disease with unclear physiological mechanisms. The lysyl oxidase (LOX) family genes (LOX, LOX–like 1–4) plays important roles in extracellular matrix (ECM) reconstruction and has been investigated in terms of susceptibility to IA in a few populations. We aimed to determine whether polymorphisms in LOX family genes are associated with susceptibility to IA in a Chinese population.MethodsThis case-control study included 384 patients with IA and 384 healthy individuals without IA (controls). We genotyped 27 single nucleotide polymorphisms (SNPs) of LOX family genes using the Sequenom MassARRAY® platform. These SNPs were adjusted for known risk factors and then, odds ratios (OR) and 95% confidence intervals (CI) were evaluated using binary logistic regression analysis.ResultsThe result showed that LOX rs10519694 was associated with the risk of IA in recessive (OR, 3.88; 95% CI, 1.12–13.47) and additive (OR, 1.56; 95%CI, 1.05–2.34) models. Stratified analyses illustrated that LOX rs10519694 was associated with the risk of single IA in the recessive (OR, 3.95; 95%CI, 1.04–15.11) and additive (OR, 1.64; 95%CI, 1.04–2.56) models. The LOXL2 rs1010156 polymorphism was associated with multiple IA in the dominant model (OR, 1.92; 95%CI, 1.02–3.62). No associations were observed between SNPs of LOXL1, LOXL3, and LOXL4 and risk of IA.ConclusionLOX and LOXL2 polymorphisms were associated with risk of single IA and multiple IA in a Chinese population, suggesting potential roles of these genes in IA. The effects of these genes on IA require further investigation.

Associations between Inflammatory Cytokine Gene Polymorphisms and Susceptibilities to Intracranial Aneurysm in Chinese Population

Intracranial aneurysm (IA) is a complex disease caused by genetic and environmental factors. Evidence indicates that inflammation plays an important role in IA occurrence. We aimed to explore the associations between inflammatory cytokine gene polymorphisms and IA in a Chinese population. This study enrolled 768 participants of Han ethnicity, including 384 patients with IA and 384 healthy individuals. Sixteen single nucleotide polymorphisms (SNPs) of IL1, IL6, IL12, and TNF-α genes were genotyped using the Sequenom MassARRAY platform. Univariate and multivariate logistic regression analyses were used to analyze the associations. We found IL12B rs3181216 was significantly associated with IA in the recessive and additive models (OR = 0.46, 95% CI = 0.23–0.89, P = 0.022; OR = 0.74, 95% CI = 0.56–0.98, P = 0.034, respectively). TNF-α rs1799964 was associated with IA in dominant and additive models (OR = 0.67, 95% CI = 0.46–0.98, P = 0.041; OR = 0.71, 95% CI = 0.51–0.98, P = 0.034, respectively). IL1A rs17561 was associated with single IA susceptibility (dominant model: OR = 0.52, 95% CI = 0.31–0.85, P = 0.040). The IL12B rs3181216 polymorphism was associated with single IA susceptibility in the recessive model (OR = 0.41, 95% CI = 0.18–0.93, P = 0.033). The IL12B rs2195940 polymorphism was associated with multiple IAs susceptibility (dominant model: OR = 0.28, 95% CI = 0.09–0.89, P = 0.031; additive model: OR = 0.28, 95% CI = 0.09–0.90, P = 0.032). TNF-α rs1799964 was associated with multiple IAs susceptibility in the dominant model (OR = 0.54, 95% CI = 0.30–0.97, P = 0.040). No associations were found between other polymorphisms and IA susceptibility. Therefore, IL1A, IL12B, and TNF-α gene polymorphisms are associated with IA susceptibility in a Chinese population.

Gene Polymorphisms Increasing the Risk of Intracranial Aneurysms: Interleukin-6 -174G>C and -572G>C (Part II).

Introduction:The interleukin-6 (IL-6), a proinflammatory cytokine, supports the adaptive immune response and regulates inflammatory processes. The -174 G>C and -572 G>C promoter polymorphisms of the IL-6 gene take part in the pathogenesis of intracranial aneurysms (IAs) and influence the clinical presentation of subarachnoid hemorrhage. This meta-analysis purposes to evaluate whether and which IL-6 allelic variations are related to a risk of IAs formation.Methods:A PRISMA-based literature search was performed on the PubMed/Medline and Web of Science databases. The keywords used were “interleukin-6,” “IL-6,” “polymorphism,” “interleukin-6 genotype,” combined with “intracranial aneurysms” and “subarachnoid hemorrhage.” Only human case-control studies, with a study (IAs) and a control group, written in English, and published in the last 15 years were selected. A meta-analysis was performed, estimating odds ratios and 95% confidence intervals in fixed-or random-effects models, as applicable. Statistical analysis was conducted with RevMan 5.0 software.Results:9 studies were eligible. No associations were found between -174 G>C polymorphisms and IAs susceptibility. Notable results were reported by the analysis of -572G>C polymorphisms. -572GG/GC/CC genotypes were strongly related to IAs occurrence with a statistical significance of p=0.03, p=0.0009, and p=0.00001, respectively.Conclusion:A higher incidence of -572G>C promoter polymorphisms were demonstrated in the IAs group, highlighting the pivotal role of inflammatory genes in the natural history of brain aneurysms. Additional studies are required considering the racial heterogenicity and the need to widen the population sample. (www.actabiomedica.it)

The Association between Genes Polymorphisms of Heparan Sulfate Proteoglycan 2 (HSPG2) and Chondroitin Sulfate Proteoglycan 2 (CSPG2) and Intracranial Aneurysm Susceptibility: A Meta-Analysis

We aimed to investigate whether the polymorphisms of gene heparan sulfate proteoglycan 2 (HSPG2) and chondroitin sulfate proteoglycan 2 (CSPG2) are associated with increased risk of intracranial aneurysms (IAs) susceptibility. The Cochrane Library, Medline, PubMed, and Embase databases were carefully searched for potential researches before Mar 30, 2018. The title, abstract, and full text were assessed to determine whether the paper was suitable for inclusion. The pooled odds ratios (ORs) with 95% confidence intervals (CIs) were presented to assess the associations between CSPG2 and HSPG2 polymorphisms and IAs susceptibility. We enrolled 7 papers, 4 matched single nucleotide polymorphisms (SNPs) of CSPG2 (rs173686, rs251124) or HSPG2 (rs173686, rs251124), and a total of 8651 participations (3674 with IAs and 4977 for control). For the rs251124 polymorphism of CSPG2, the quantitative synthesis from 5 studies showed significant difference in the gene allele comparison of T vs. C (OR, 1.129; 95% CI, 1.029, 1.238; P=0.01). Similar results were found for rs3767137 of HSPG2 (A vs. G, OR, 0.842, 95% CI=0.759-0.935, P=0.001). However, for the rs173686 polymorphism of CSPG2 and rs7556412 polymorphism of HSPG2, no significant difference was found (P=0.259 and P=0.474, respectively). The SNPs rs251124 of CSPG2 and rs3767137 of HSPG2 had statistically significant associations with IAs susceptibility. The minor allele T of rs251124 demonstrated a harmful effect but the minor allele A of rs3767137 demonstrated a protective role with regard to the risk of IAs. However, no such associations were found in the SNPs rs173686 of CSPG2 and rs7556412 of HSPG2.

Association of Endothelin Receptor Type A with Intracranial Aneurysm in 20,609 East Asians: An Updated Meta-Analysis

Genome-wide association studies have reported an association between the EDNRA gene and intracranial aneurysm (IA) in European and Japanese populations; however, there is no study on this polymorphism in other Asian populations. Therefore, we performed an extensive large-scale meta-analysis for association of the rs6841581 variant of EDNRA with IA susceptibility in East Asian population. We conducted a systemic review via electronic search for papers published between January 2002 and February 2019. We used fixed and random effect models and applied the inverse variance method. The statistical power of the result was estimated in the genome-wide significant threshold under an additive inheritance model. Our meta-analysis included 5873 patients with IA and 14,736 non-IA controls from 6 independent populations: 4 Japanese, 1 Chinese, and 1 Korean. The risk (major) G allele of rs6841581 showed the highest significant association with the increased risk of IA under the fixed effect model in the East-Asian population (odds ratio= 1.244, 95% confidence interval: 1.174-1.318, P= 1.36E-13). The rs6841581 variant showed sufficient statistical power (80.3%) in this meta-analysis under the additive model. In subsequent analysis, the frequencies of the risk G allele showed similar pattern in all of the Japanese, Chinese, and Korean populations (69%, 80%, and 78%, respectively). In the in silico functional analysis, none of the functional variants was correlated with rs6841581. The genetic variant of EDNRA, rs6841581, was significantly associated with increased risk of IA. Our findings indicate that it could be used as an IA-predicting variant in East Asian populations.

Replication of GWAS Loci Revealed an Increased Risk of BET1L and H19 Polymorphisms with Intracranial Aneurysm.

A genome-wide association study (GWAS) identified that BET1L rs2280543 at chromosome 11p15.5 was a susceptibility loci of intracranial aneurysm (IA). Long noncoding RNA H19, located in this region, was reported to play a crucial role in the formation of IA. In this study, we aimed to examine whether BET1L rs2280543 and potentially functional polymorphisms in H19 influence the risk of IA. A hospital-based case-control study was performed involving 542 IA patients and 588 age- and gender-matched controls. The BET1L rs2280543 and H19 polymorphisms were genotyped using the TaqMan assay. The BET1L rs2280543 CT, CT/TT genotypes, and T allele were associated with an increased risk of IA (CT vs. CC, adjusted OR = 1.43, 95% CI: 1.08-1.90, P = 0.01; CT/TT vs. CC, adjusted OR = 1.48, 95% CI: 1.12-1.94, P = 0.005; and T vs. C, adjusted OR = 1.44, 95% CI: 1.13-1.83, P = 0.003). Similarly, the H19 rs217727 TT genotype and T allele were associated with an increased risk of IA (TT vs. CC, adjusted OR = 1.90, 95% CI: 1.35-2.67, P < 0.001; T vs. C, adjusted OR = 1.38, 95% CI: 1.16-1.64, P < 0.001). Combined analyses revealed that the rs2280543 CC-rs217727 CT/TT, rs2280543 CT/TT-rs2735971 GG, and rs217727 CT/TT-rs2735971 GG genotypes were related to the risk of IA. Interaction analysis showed that the 3-loci model of rs2280543-rs217727-rs2839698 contributed to an increased risk of IA. These findings suggest that the GWAS-discovered risk loci BET1L rs2280543 may increase IA susceptibility by interacting with lncRNA H19.

Genome-Wide Association between the 2q33.1 Locus and Intracranial Aneurysm Susceptibility: An Updated Meta-Analysis Including 18,019 Individuals.

Previous genome-wide association studies did not show a consistent association between the BOLL gene (rs700651, 2q33.1) and intracranial aneurysm (IA) susceptibility. We aimed to perform an updated meta-analysis for the potential IA-susceptibility locus in large-scale multi-ethnic populations. We conducted a systematic review of studies identified by an electronic search from January 1990 to March 2019. The overall estimates of the “G” allele of rs700651, indicating IA susceptibility, were calculated under the fixed- and random-effect models using the inverse-variance method. Subsequent in silico function and cis-expression quantitative trait loci (cis-eQTL) analyses were performed to evaluate biological functions and genotype-specific expressions in human tissues. We included 4513 IA patients and 13,506 controls from five studies with seven independent populations: three European-ancestry, three Japanese, and one Korean population. The overall result showed a genome-wide significance threshold between rs700651 and IA susceptibility after controlling for study heterogeneity (OR = 1.213, 95% CI: 1.135–1.296). Subsequent cis-eQTL analysis showed significant genome-wide expressions in three human tissues, i.e., testis (p = 8.04 × 10−15 for ANKRD44), tibial nerves (p = 3.18 × 10−10 for SF3B1), and thyroid glands (p = 4.61 × 10−9 for SF3B1). The rs700651 common variant of the 2q33.1 region may be involved in genetic mechanisms that increase the risk of IA and may play crucial roles in regulatory functions.

TLR4 gene polymorphisms rs11536889 is associated with intracranial aneurysm susceptibility

Intracranial aneurysm (IA) is a common lesion which often present asymptomatic until the time of rupture and result in subarachnoid hemorrhage (SAH). The pathogenesis of IA formation is complex and is influenced by both genetic and environmental risk factors. For exploring the detailed molecular and cellular mechanisms involved in the pathogenesis of IA, recent studies indicated inflammatory pathways and their genetic variants may as potential biomarkers. In this study, functionally relevant polymorphisms in the toll-like receptor 4 (TLR4) were screened in 330 IA patients and 313 controls from a Han Chinese population. Eight single nucleotide gene polymorphisms (SNPs) genotyped by the Improved Multiple Ligase Detection Reaction (iMLDR) method. Our results indicated that the presence of the minor allele (C) of the TLR4 SNP rs11536889 was associated with a decreased risk of IA (C vs. G, OR = 0.731; 95% CI 0.567–0.943; P = 0.017). This association was also present at the genotype level in a codominant model (GC vs. GG, OR = 0.447; 95% CI 0.226–0.884; P = 0.020) and a recessive model (CC vs. GG + GC, OR = 0.489; 95% CI 0.250–0.955; P = 0.035). In summary, we firstly found that the TLR4 SNP rs11536889 was significantly associated with the susceptibility of IA. Our results indicated TLR4 SNP rs11536889 may be a marker for IA risk, though the exact functional roles of TLR4 SNP rs11536889 in IA formation are still not very clear.

Association between angiotensin-converting enzyme insertion/deletion polymorphisms and intracranial aneurysm susceptibility: A meta-analysis.

Various studies have evaluated the association between polymorphisms of angiotensin-converting enzyme (ACE) and intracranial aneurysm (IA) risk; however, the results remain inconsistent. The PubMed, Embase, and Wanfang Data databases were systematically searched until January 6th 2016. Case-control studies investigating the association between the ACE polymorphism and IA risk were included. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated with the fixed or random-effects model assuming allele, homozygote comparison of codominant, heterozygote comparison of codominant, dominant, and recessive models. Seven studies including 1,074 cases and 1,500 controls were included in the current meta-analysis. The results of the analysis indicated that the ACE polymorphism significantly increased IA risk in the allele, homozygote comparison of codominant and dominant models. According to the further stratified analysis by ethnicity, source of control and sample sizes, a significant association was identified between the ACE variant and IA risk in Asian individuals, hospital-based, or large (>300) subgroups in all of the genetic models, not including the recessive model. Furthermore, no significantly increased risk was indicated in Caucasian individuals, population-based, or small (<300) subgroups in the heterozygote comparison of codominant, dominant and recessive models. The available evidence indicates that the ACE polymorphism is associated with an increased risk of IA, particularly in Asian individuals. However, other factors may impact this association. Further large, well-designed multicenter studies are required to validate the findings from the present study.

Role of Endoglin Insertion and rs1800956 Polymorphisms in Intracranial Aneurysm Susceptibility: A Meta-Analysis.

Endoglin is an essential molecule during angiogenesis, vascular development, and integrity. Till now, many studies have investigated the association between endoglin polymorphisms and intracranial aneurysm (IA) risk, with the results remained inconclusive. Therefore, we performed a meta-analysis to summarize the possible association.We searched PubMed and Embase until June 2015 to identify studies addressing the association between endoglin polymorphisms and IA risk. The summary odds ratios (ORs) and their corresponding 95% confidence interval (CI) were calculated to assess the strength of the association.Eleven studies with a total of 1501 cases and 2012 controls were finally included in this meta-analysis, with 10 studies investigating endoglin 6-bp insertion (6bINS) polymorphism and 4 studies investigating 1800956 polymorphism. No significant association between endoglin 6bINS polymorphism and IA risk was detected in overall estimation (I/I vs wt/I + wt/wt: OR = 1.21, 95% CI = 0.87–1.69) or in the subgroup analysis by ethnicity, control source, or ruptured status. However, we observed an association with borderline significance of 6bINS with IA occurrence (I/I vs wt/I + wt/wt: OR = 1.49, 95% CI = 0.99–2.25, P = 0.058) in studies applying matched controls. Furthermore, we detected a significant association for 6bINS polymorphism of endoglin with increased risk of familial IA (I vs wt, OR = 1.64, 95% CI = 1.10–2.42) but not sporadic IA (I vs wt, OR = 1.09, 95% CI = 0.68–1.45). With regard to rs1800956, our pooled results indicated a significantly decreased IA risk in individuals carrying C allele (C/C vs G/C + G/G: OR = 0.65; 95% CI = 0.45–0.94).This meta-analysis provided no evidence for the association between 6bINS polymorphism with overall IA risk. However, we detected a significant association of 6bINS allele with increased risk of familial IA. Also, we found that rs1800956 was significantly related to IA occurrence. Further, well-designed studies with large sample size are warranted and updated meta-analysis is needed to verify our findings.

Genetic Variants Underlying Risk of Intracranial Aneurysms: Insights from a GWAS in Portugal.

Subarachnoid hemorrhage (SAH) is a life-threatening event that most frequently leads to severe disability and death. Its most frequent cause is the rupture of a saccular intracranial aneurysm (IA), which is a blood vessel dilation caused by disease or weakening of the vessel wall. Although the genetic contribution to IA is well established, to date no single gene has been unequivocally identified as responsible for IA formation or rupture. We aimed to identify IA susceptibility genes in the Portuguese population through a pool-based multistage genome-wide association study. Replicate pools were allelotyped in triplicate in a discovery dataset (100 IA cases and 92 gender-matched controls) using the Affymetrix Human SNP Array 6.0. Top SNPs (absolute value of the relative allele score difference between cases and controls |RASdiff|≥13.0%) were selected for technical validation by individual genotyping in the discovery dataset. From the 101 SNPs successfully genotyped, 99 SNPs were nominally associated with IA. Replication of technically validated SNPs was conducted in an independent replication dataset (100 Portuguese IA cases and 407 controls). rs4667622 (between UBR3 and MYO3B), rs6599001 (between SCN11A and WDR48), rs3932338 (214 kilobases downstream of PRDM9), and rs10943471 (96 kilobases upstream of HTR1B) were associated with IA (unadjusted allelic chi-square tests) in the datasets tested (discovery: 6.84E-04≤P≤1.92E-02, replication: 2.66E-04≤P≤2.28E-02, and combined datasets: 6.05E-05≤P≤5.50E-04). Additionally, we confirmed the known association with IA of rs1333040 at the 9p21.3 genomic region, thus validating our dataset. These novel findings in the Portuguese population warrant further replication in additional independent studies, and provide additional candidates to more comprehensively understand IA etiopathogenesis.

Lessons learned from whole exome sequencing in multiplex families affected by a complex genetic disorder, intracranial aneurysm.

Genetic risk factors for intracranial aneurysm (IA) are not yet fully understood. Genomewide association studies have been successful at identifying common variants; however, the role of rare variation in IA susceptibility has not been fully explored. In this study, we report the use of whole exome sequencing (WES) in seven densely-affected families (45 individuals) recruited as part of the Familial Intracranial Aneurysm study. WES variants were prioritized by functional prediction, frequency, predicted pathogenicity, and segregation within families. Using these criteria, 68 variants in 68 genes were prioritized across the seven families. Of the genes that were expressed in IA tissue, one gene (TMEM132B) was differentially expressed in aneurysmal samples (n=44) as compared to control samples (n=16) (false discovery rate adjusted p-value=0.023). We demonstrate that sequencing of densely affected families permits exploration of the role of rare variants in a relatively common disease such as IA, although there are important study design considerations for applying sequencing to complex disorders. In this study, we explore methods of WES variant prioritization, including the incorporation of unaffected individuals, multipoint linkage analysis, biological pathway information, and transcriptome profiling. Further studies are needed to validate and characterize the set of variants and genes identified in this study.

Genome-wide association study of intracranial aneurysm identifies a new association on chromosome 7.

Common variants have been identified using genome-wide association studies which contribute to intracranial aneurysms (IA) susceptibility. However, it is clear that the variants identified to date do not account for the estimated genetic contribution to disease risk. Initial analysis was performed in a discovery sample of 2617 IA cases and 2548 controls of white ancestry. Novel chromosomal regions meeting genome-wide significance were further tested for association in 2 independent replication samples: Dutch (717 cases; 3004 controls) and Finnish (799 cases; 2317 controls). A meta-analysis was performed to combine the results from the 3 studies for key chromosomal regions of interest. Genome-wide evidence of association was detected in the discovery sample on chromosome 9 (CDKN2BAS; rs10733376: P<1.0×10(-11)), in a gene previously associated with IA. A novel region on chromosome 7, near HDAC9, was associated with IA (rs10230207; P=4.14×10(-8)). This association replicated in the Dutch sample (P=0.01) but failed to show association in the Finnish sample (P=0.25). Meta-analysis results of the 3 cohorts reached statistical significant (P=9.91×10(-10)). We detected a novel region associated with IA susceptibility that was replicated in an independent Dutch sample. This region on chromosome 7 has been previously associated with ischemic stroke and the large vessel stroke occlusive subtype (including HDAC9), suggesting a possible genetic link between this stroke subtype and IA.

Intracranial Aneurysms Occur More Frequently at Bifurcation Sites That Typically Experience Higher Hemodynamic Stresses

Intracranial aneurysms (IAs) occur more frequently at certain bifurcations than at others. Hemodynamic stress, which promotes aneurysm formation in animal models, also differs among bifurcations, depending on flow and vessel geometry. To determine whether locations that are more likely to develop IAs experience different hemodynamic stresses that might contribute to higher IA susceptibility. We characterized the hemodynamic microenvironment at 10 sites in or around the circle of Willis where IAs commonly occur and examined statistical relationships between hemodynamic factors and the tendency for a site to form IAs. The tendency for each site to develop IAs was quantified on the basis of the site distribution from systematic literature analysis of 19 reports including 26418 aneurysms. Hemodynamic parameters for these sites were derived from image-based computational fluid dynamics of 114 cerebral bifurcations from 31 individuals. Wall shear stress and its spatial gradient were calculated in the impact zone surrounding the bifurcation apex. Linear and exponential regression analyses evaluated correlations between the tendency for IA formation and the typical hemodynamics of a site. IA susceptibility significantly correlated with the magnitudes of wall shear stress and positive wall shear stress gradient within the hemodynamic impact zone calculated for each site. IAs occur more frequently at cerebral bifurcations that typically experience higher hemodynamic shear stress and stronger flow acceleration, conditions previously shown to promote aneurysm initiation in animals.