Genetics Of Intracranial Aneurysms

Intracranial Aneurysms and Genetics: An Extensive Overview of Genomic Variations, Underlying Molecular Dynamics, Inflammatory Indicators, and Forward-Looking Insights

This review initiates by outlining the clinical relevance of IA, underlining the pressing need to comprehend its foundational elements. We delve into the assorted risk factors tied to IA, spotlighting both environmental and genetic influences. Additionally, we illuminate distinct genetic syndromes linked to a pronounced prevalence of intracranial aneurysms, underscoring the pivotal nature of genetics in this ailment's susceptibility. A detailed scrutiny of genome-wide association studies allows us to identify key genomic changes and locations associated with IA risk. We further detail the molecular and physiopathological dynamics instrumental in IA's evolution and escalation, with a focus on inflammation's role in affecting the vascular landscape. Wrapping up, we offer a glimpse into upcoming research directions and the promising horizons of personalized therapeutic strategies in IA intervention, emphasizing the central role of genetic insights. This thorough review solidifies genetics' cardinal role in IA, positioning it as a cornerstone resource for professionals in the realms of neurology and genomics.

Endothelial nitric oxide synthase rs1799983 gene polymorphism is associated with the risk of developing intracranial aneurysm

PURPOSE

The intracranial aneurysm (IA) rupture is associated with a subarachnoid hemorrhage. One third of patients die, and one third remain depend for daily activities. Genetic factors are crucial in the formation and clinical evolution of IAs. Multiple loci have been associated with AIs, much of them implicating multiple pathways related to vascular endothelial maintenance and extracellular matrix integrity. Thus, the aim of our study was to characterize whether polymorphisms in genes implicated in the vascular endothelial maintenance could modify the risk of developing IAs.

SUBJECTS AND METHODS

We have studied 176 patients with IA recruited in the Service of Neurosurgery at the University Hospital of Valladolid (Spain) and a control group if 150 sex-matched healthy subjects. Clinical variables were collected from each patient. We have analyzed VEGFA rs833061, VEGFR2 rs2071559, endothelin rs5370, endoglin rs3739817, and eNOS rs1799983 polymorphisms.

RESULTS

Our results showed that allele T of the eNOS rs1799983 polymorphism is correlated with decreased risk of developing the disease; thus, allele G of the eNOS rs1799983 polymorphism increased the risk of developing IA.

CONCLUSION

The association of eNOS rs1799983 polymorphism with the risk to suffer IA reinforces the hypothesis that genetic variants in eNOS gene could be crucial in the pathogenesis of IA.

Bilateral aneurysms, one of which is embedded in a meningioma: a rare case report and literature review

BACKGROUND

Although the coexistence of primary brain neoplasms with intracranial aneurysms is rare, this phenomenon has become more recognized. Meningioma is the most frequently occurring type of tumor associated with an aneurysm. However, meningiomas encasing aneurysms are extremely rare, posing a diagnostic and therapeutic challenge to healthcare providers.

CASE DESCRIPTION

We report a case of a 46-year-old female patient admitted to our hospital with headache and dizziness for ten years. Enhanced magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) indicated a mass in the right sphenoid ridge, surrounding a posterior communicating artery aneurysm of the right internal carotid artery. Digital subtraction angiography (DSA) revealed left ophthalmic segment aneurysm and right posterior communicating artery aneurysm. We first clipped the aneurysm and then removed intracranial tumor during the same operation. The postoperative pathological diagnosis of tumor was meningioma (World Health Organization grade I). The patient's postoperative course was uneventful, with only a mild reduction in lateral vision of both eyes.

CONCLUSIONS

We reported a rare case in which an intracranial aneurysm was encased in a meningioma and could be safely treated during the same operation. Notably, embolizing or clipping aneurysm first and then removing intracranial tumor appears to enhance the safety of patients. This is the best treatment option if the aneurysm and meningioma can be treated concurrently in the hybrid operating room. Additionally, it may be necessary to carefully evaluate preoperative MRA or computed tomography angiography (CTA), and it is critical to confirm the existence of any vascular lesions in patients with brain tumors using MRA or CTA.

Effects of Low and High Aneurysmal Wall Shear Stress on Endothelial Cell Behavior: Differences and Similarities

Background: Intracranial aneurysms (IAs) result from abnormal enlargement of the arterial lumen. IAs are mostly quiescent and asymptomatic, but their rupture leads to severe brain damage or death. As the evolution of IAs is hard to predict and intricates medical decision, it is essential to improve our understanding of their pathophysiology. Wall shear stress (WSS) is proposed to influence IA growth and rupture. In this study, we investigated the effects of low and supra-high aneurysmal WSS on endothelial cells (ECs).

Methods: Porcine arterial ECs were exposed for 48 h to defined levels of shear stress (2, 30, or 80 dyne/cm²) using an Ibidi flow apparatus. Immunostaining for CD31 or γ-cytoplasmic actin was performed to outline cell borders or to determine cell architecture. Geometry measurements (cell orientation, area, circularity and aspect ratio) were performed on confocal microscopy images. mRNA was extracted for RNAseq analysis.

Results: ECs exposed to low or supra-high aneurysmal WSS were more circular and had a lower aspect ratio than cells exposed to physiological flow. Furthermore, they lost the alignment in the direction of flow observed under physiological conditions. The effects of low WSS on differential gene expression were stronger than those of supra-high WSS. Gene set enrichment analysis highlighted that extracellular matrix proteins, cytoskeletal proteins and more particularly the actin protein family were among the protein classes the most affected by shear stress. Interestingly, most genes showed an opposite regulation under both types of aneurysmal WSS. Immunostainings for γ-cytoplasmic actin suggested a different organization of this cytoskeletal protein between ECs exposed to physiological and both types of aneurysmal WSS.

Conclusion: Under both aneurysmal low and supra-high WSS the typical arterial EC morphology molds to a more spherical shape. Whereas low WSS down-regulates the expression of cytoskeletal-related proteins and up-regulates extracellular matrix proteins, supra-high WSS induces opposite changes in gene expression of these protein classes. The differential regulation in EC gene expression observed under various WSS translate into a different organization of the ECs’ architecture. This adaptation of ECs to different aneurysmal WSS conditions may affect vascular remodeling in IAs.

A Preliminary Study of the Association between SOX17 Gene Variants and Intracranial Aneurysms Using Exome Sequencing

OBJECTIVE

Conflicting results regarding SOX17 genes and the risk of intracranial aneurysms (IA) exist in the Korean population, although significant positive correlations were noted in genome-wide association studies in European and Japanese populations. Therefore, we aimed to investigate an association between SOX17 gene variants and IA using exome sequencing data.

METHODS

This study included 26 age-gender matched IA patients and 26 control subjects. The SOX17 gene variants identified from whole-exome sequencing data were examined. Genetic associations to estimate odds ratio (OR) and 95% confidence interval (CI) were performed using the software EPACTS.

RESULTS

The mean age of the IA and control groups were 51.0±9.3 years and 49.4±14.3 years, respectively (p=0.623). Seven variants of SOX17, including six single nucleotide polymorphisms and one insertion and deletion, were observed. Among these variants, rs12544958 (A>G) showed the most association with IA, but the association was not statistically significant (OR, 1.97; 95% CI, 0.81-4.74; p=0.125). Minor allele frequencies of the IA patients and controls were 0.788 and 0.653, respectively. None of the remaining variants were significantly associated with IA formation.

CONCLUSION

No significant association between SOX17 gene variants and IA were noted in the Korean population. A large-scale exome sequencing study is necessary to investigate any Korean-specific genetic susceptibility to IA.

Genome-wide blood DNA methylation analysis in patients with delayed cerebral ischemia after subarachnoid hemorrhage

Little is known about the epigenetic changes associated with delayed cerebral ischemia (DCI) pathogenesis after subarachnoid hemorrhage (SAH). Here, we investigated genome-wide DNA methylation profiles specifically associated with DCI, which is a major contributor to poor clinical outcomes. An epigenome-wide association study (EWAS) and quantitative real-time PCR (qRT-PCR) were conducted in 40 SAH patients (DCI, n = 13; non-DCI, n = 27). A replication study using bisulfite modification and methylation-specific PCR was further performed in 36 patients (DCI, n = 12; non-DCI, n = 24). The relative degree of methylation was described as the median and 25th–75th percentile. No significant differences in clinical characteristics between DCI and non-DCI groups were observed. Among the top 10 differentially methylated genes analyzed via EWAS, two aberrantly methylated CpG sites of cg00441765 (INSR gene) and cg11464053 (CDHR5 gene) were associated with decreased mRNA expression (2^−ΔCt). They include INSR [0.00020 (0.00012–0.00030) in DCI vs. 0.00050 (0.00030–0.00068) in non-DCI] and CDHR5 [0.114 (0.053–0.143) in DCI vs. 0.170 (0.110–0.212) in non-DCI]. Compared with non-DCI cases, patients with DCI exhibited an increased degree of methylation in the replication study: INSR, 0.855 (0.779–0.913) in DCI vs. 0.582 (0.565–0.689) in non-DCI; CDHR5, 0.786 (0.708–0.904) in DCI vs. 0.632 (0.610–0.679) in non-DCI. Hypermethylation of two novel genes, INSR and CDHR5 may serve as a biomarker for early detection of DCI following SAH.

Feeding artery aneurysms associated with large meningiomas: case report and review of the literature

Though brain tumors and intracranial aneurysms co-exist, the occurrence of feeding artery aneurysms with meningiomas are unusual. We describe here a large falcine meningioma that was associated with three feeding artery aneurysms of the anterior circulation. These aneurysms can be treated either by pre-operative endovascular therapy or during the meningioma surgery. The management strategy for these patients will depend on the clinical presentation, morphology and localization of these aneurysms with respect to the tumor.

Volume variation may be a relevant metric in the study of aneurysm pulsatility: a study using ECG-gated 4D-CTA (PULSAN)

​Background and purpose

Intracranial aneurysms are a frequently occurring disease, with an estimated prevalence of 2–5% in the general population. They usually remain silent until rupture occurs, with a mortality rate of 35–50% and a high rate of morbidity, including long-term disability. However, preventative treatments have their own risk of complications and morbi-mortality rates, including stroke and hemorrhage. ECG-gated four-dimensional CT angiography (4D-CTA) allows the acquisition of time-resolved three-dimensional reconstructions. The aim of our study was to evaluate different intracranial aneurysm metrics over the cardiac cycle using ECG-gated 4D-CTA.

​Materials and methods

ECG-gated 4D-CTA datasets were acquired in patients presenting with intracranial aneurysms. Seven aneurysm metrics, including aneurysm height, aneurysm length, ostium width, aspect ratio, ostium area, volume, and volume-to-ostium ratio, were analysed over different cardiac phases. Intra-reader agreement, inter-reader agreement, and inter-cycle agreement were calculated through the intraclass correlation coefficient.

​Results

Twenty-one aneurysms from 11 patients were considered for inclusion. Post-processing failed for three aneurysms, and 18 aneurysms were finally analysed. There was good intra-reader agreement for each metric (ICC >0.9). Agreements among three consecutive cardiac cycles were calculated for six aneurysms and were especially good for the volume metric (ICC >0.9). Volume variation appears to be the most relevant metric and seems especially perceptible for aneurysms larger than 5 mm.

​Conclusions

Quantification of aneurysm volume changes during the cardiac cycle seems quantitatively possible and reproducible, especially for aneurysms larger than 5 mm. Further studies need to be conducted to validate this parameter for intracranial aneurysm assessment.

Impact of perioperative aneurysm rebleeding after subarachnoid hemorrhage

OBJECTIVE

Aneurysm rebleeding is a major cause of death and morbidity in patients with aneurysmal subarachnoid hemorrhage (SAH). Recognizing the predictors of rebleeding might help to identify patients who will benefit from acute management. This study was performed to investigate the predictors of aneurysm rebleeding and their impact on clinical outcomes in the preoperative, intraoperative, and postoperative periods.

METHODS

The incidence of rebleeding, demographic data, and clinical data from 4933 patients with aneurysmal SAH beginning in the year 2000 were retrospectively analyzed in the Nagasaki SAH Registry Study. The authors performed multiple logistic regression analyses to identify the risk factors contributing to rebleeding and outcome after SAH.

RESULTS

Preoperative rebleeding occurred in 7.2% of patients. Patient age (p = 0.01), multiple aneurysms (p < 0.01), aneurysm size (p < 0.0001), and heart disease (p = 0.03) were significantly associated with preoperative rebleeding. Conversely, intraoperative rebleeding occurred in 11.2% of patients. Aneurysm location (anterior communicating artery [ACoA]), family history (p = 0.02), preoperative rebleeding (p < 0.01), and clipping/coiling (p < 0.0001) were significantly associated with intraoperative rebleeding. Interaction analysis showed that clipping significantly affected intraoperative rebleeding at the ACoA (OR 4.00; 95% CI 1.82-8.80; p < 0.001). Postoperative rebleeding occurred in 2.4% of patients. Coiling/clipping (p < 0.0001) and intraoperative rebleeding (p < 0.01) were significantly associated with postoperative rebleeding. Rebleeding in all time periods examined significantly contributed to the clinical outcome after SAH.

CONCLUSIONS

Aneurysm rebleeding after SAH has specific characteristics in the preoperative, intraoperative, and postoperative periods, and all of these characteristics contribute to the clinical outcome. The ACoA has a higher risk of intraoperative rebleeding, and endovascular coiling could be a good candidate in terms of techniques for preventing intraoperative rebleeding, although complete aneurysm obliteration should be accomplished.

Correlation Between Altered DNA Methylation of Intergenic Regions of ITPR3 and Development of Delayed Cerebral Ischemia in Patients with Subarachnoid Hemorrhage

BACKGROUND

Delayed cerebral ischemia (DCI) is related to the major causes of morbidity and mortality in patients following subarachnoid hemorrhage (SAH); however, little is known about the role of epigenetics in the pathogenesis of DCI. We investigated the specific DNA methylation profile that may affect the expression of inositol 1-,4-,5-trisphosphate receptor (ITPR3) responsible for cerebral vasospasm following SAH.

METHODS

We prospectively studied patients with SAH between March 2015 and October 2018. The degree of methylation in the distal intergenic region (IGR) located on ITPR3 and gene expression were measured using methylation-specific polymerase chain reaction (MSP) and quantitative real-time polymerase chain reaction (qPCR). To investigate the regulatory mechanims of DNA hypermethylation, we further analyzed the mRNA expression of DNA methyltransferase (DNMT1) and ten-eleven translocation enzymes (TET1, TET2, and TET3).

RESULTS

A total of 42 patients were included in our analysis. Patients with SAH and DCI had significantly higher levels of methylation intensity of distal IGR upstream of ITPR3 than those without DCI (median, 0.941 [interquartile range (IQR), 0.857-0.984] versus (0.670 [IQR, 0.543-0.761]; P < 0.001). In addition, patients with DCI showed decreased mRNA expression of ITPR3 compared with patients without DCI (median, 0.039 [IQR, 0.030-0.045] vs. 0.047 [IQR, 0.038-0.064]; P = 0.0328). Patients with DCI had higher DNMT1 expression (P < 0.001) and lower TET1 expression (P = 0.040) than those without DCI; however, differences in TET2 and TET3 levels between the 2 groups were not statistically significant.

CONCLUSIONS

Hypermethylation of the distal IGR located upstream of ITPR3 is related to greater DCI development in patients with SAH. Further studies of the precise mechanisms of methylation degree and DCI development using in vitro and in vivo models are needed.

Genomic Variations in Susceptibility to Intracranial Aneurysm in the Korean Population

Genome-wide association studies found genetic variations with modulatory effects for intracranial aneurysm (IA) formations in European and Japanese populations. We aimed to identify the susceptibility of single nucleotide polymorphisms (SNPs) to IA in a Korean population consisting of 250 patients, and 294 controls using the Asian-specific Axiom Precision Medicine Research Array. Twenty-nine SNPs reached a genome-wide significance threshold (5 × 10⁻⁸). The rs371331393 SNP, with a stop-gain function of ARHGAP32 (11q24.3), showed the most significant association with the risk of IA (OR = 43.57, 95% CI: 21.84–86.95; p = 9.3 × 10⁻²⁷). Eight out of 29 SNPs—GBA (rs75822236), TCF24 (rs112859779), OLFML2A (rs79134766), ARHGAP32 (rs371331393), CD163L1 (rs138525217), CUL4A (rs74115822), LOC102724084 (rs75861150), and LRRC3 (rs116969723)—demonstrated sufficient statistical power greater than or equal to 0.8. Two previously reported SNPs, rs700651 (BOLL, 2q33.1) and rs6841581 (EDNRA, 4q31.22), were validated in our GWAS (Genome-wide association study). In a subsequent analysis, three SNPs showed a significant difference in expressions: the rs6741819 (RNF144A, 2p25.1) was down-regulated in the adrenal gland tissue (p = 1.5 × 10⁻⁶), the rs1052270 (TMOD1. 9q22.33) was up-regulated in the testis tissue (p = 8.6 × 10⁻¹⁰), and rs6841581 (EDNRA, 4q31.22) was up-regulated in both the esophagus (p = 5.2 × 10⁻¹²) and skin tissues (1.2 × 10⁻⁶). Our GWAS showed novel candidate genes with Korean-specific variations in IA formations. Large population based studies are thus warranted.

Demographic and clinical predictors of multiple intracranial aneurysms in patients with subarachnoid hemorrhage

OBJECTIVE

Pathophysiological differences that underlie the development and subsequent growth of multiple aneurysms may exist. In this study, the authors assessed the factors associated with the occurrence of multiple aneurysms in patients presenting with aneurysmal subarachnoid hemorrhage (SAH).

METHODS

Consecutive patients presenting with aneurysmal SAH between 1996 and 2012 were prospectively enrolled in the Subarachnoid Hemorrhage Outcome Project. Patients harboring 1, 2, or 3 or more aneurysms were stratified into groups, and the clinical and radiological characteristics of each group were compared using multivariate logistic regression.

RESULTS

Of 1277 patients with ruptured intracranial aneurysms, 890 had 1 aneurysm, 267 had 2 aneurysms, and 120 had 3 or more aneurysms. On multinomial regression using the single-aneurysm cohort as base case, risk factors for patients presenting with 2 aneurysms were female sex (relative risk ratio [RRR] 1.80, p < 0.001), higher body mass index (BMI) (RRR 1.02, p = 0.003), more years of smoking (RRR = 1.01, p = 0.004), and black race (RRR 1.83, p = 0.001). The risk factors for patients presenting with 3 or more aneurysms were female sex (RRR 3.10, p < 0.001), higher BMI (RRR 1.03, p < 0.001), aneurysm in the posterior circulation (RRR 2.59, p < 0.001), and black race (RRR 2.15, p = 0.001). Female sex, longer smoking history, aneurysms in the posterior circulation, BMI, and black race were independently associated with the development of multiple aneurysms in our adjusted multivariate multinomial model.

CONCLUSIONS

Significant demographic and clinical differences are found between patients presenting with single and multiple aneurysms in the setting of aneurysmal SAH. These predictors of multiple aneurysms likely reflect a predisposition toward inflammation and endothelial injury.

Cigarette Smoke Initiates Oxidative Stress-Induced Cellular Phenotypic Modulation Leading to Cerebral Aneurysm Pathogenesis

OBJECTIVE

Cigarette smoke exposure (CSE) is a risk factor for cerebral aneurysm (CA) formation, but the molecular mechanisms are unclear. Although CSE is known to contribute to excess reactive oxygen species generation, the role of oxidative stress on vascular smooth muscle cell (VSMC) phenotypic modulation and pathogenesis of CAs is unknown. The goal of this study was to investigate whether CSE activates a NOX (NADPH oxidase)-dependent pathway leading to VSMC phenotypic modulation and CA formation and rupture.

APPROACH AND RESULTS

In cultured cerebral VSMCs, CSE increased expression of NOX1 and reactive oxygen species which preceded upregulation of proinflammatory/matrix remodeling genes (MCP-1, MMPs [matrix metalloproteinase], TNF-α, IL-1β, NF-κB, KLF4 [Kruppel-like factor 4]) and downregulation of contractile genes (SM-α-actin [smooth muscle α actin], SM-22α [smooth muscle 22α], SM-MHC [smooth muscle myosin heavy chain]) and myocardin. Inhibition of reactive oxygen species production and knockdown of NOX1 with siRNA or antisense decreased CSE-induced upregulation of NOX1 and inflammatory genes and downregulation of VSMC contractile genes and myocardin. p47phox^-/- NOX knockout mice, or pretreatment with the NOX inhibitor, apocynin, significantly decreased CA formation and rupture compared with controls. NOX1 protein and mRNA expression were similar in p47phox^-/- mice and those pretreated with apocynin but were elevated in unruptured and ruptured CAs. CSE increased CA formation and rupture, which was diminished with apocynin pretreatment. Similarly, NOX1 protein and mRNA and reactive oxygen species were elevated by CSE, and in unruptured and ruptured CAs.

CONCLUSIONS

CSE initiates oxidative stress-induced phenotypic modulation of VSMCs and CA formation and rupture. These molecular changes implicate oxidative stress in the pathogenesis of CAs and may provide a potential target for future therapeutic strategies.

Familial Intracranial Aneurysms in Saudi Arabia: What Do We Need To Do?

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating event with significant morbidity and mortality. The incidence of SAH might be influenced by environmental factors but genetic predisposition is evolving as an important effector in the risk of development of intracranial aneurysms and rupture of aneurysms. This requires strategies for effective screening of family members at risk of developing such a phenotype, in order to deliver preventive treatment to these target lesions. We discuss the potential for implementing these strategies in the Saudi Arabian health system and the future implications on our care for such a vulnerable group of subjects.

Biology of Saccular Cerebral Aneurysms: A Review of Current Understanding and Future Directions

Understanding the biology of intracranial aneurysms is a clinical quandary. How these aneurysms form, progress, and rupture is poorly understood. Evidence indicates that well-established risk factors play a critical role, along with immunologic factors, in their development and clinical outcomes. Much of the expanding knowledge of the inception, progression, and rupture of intracranial aneurysms implicates inflammation as a critical mediator of aneurysm pathogenesis. Thus, therapeutic targets exploiting this arm of aneurysm pathogenesis have been implemented, often with promising outcomes.

Apolipoprotein E polymorphism and the risk of intracranial aneurysms in a Chinese population

Background

The relationship between the apolipoprotein E (APOE) polymorphism and intracranial aneurysms has previously only been studied in Russia and Japan but not in Chinese populations. The purpose of this study was to investigate the association between APOE polymorphism and the risk of intracranial aneurysms in a Chinese population.

Methods

The study population consisted of 150 intracranial aneurysms patients and 150 matched control subjects. The APOE gene polymorphism was analyzed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

Results

Patients with intracranial aneurysms had a significantly higher frequency of APOE E2/E2 genotype [odds ratio (OR) =9.51, 95 % confidence interval (CI) = 1.19, 76.04; P = 0.03] and APOE E2/E3 genotype (OR = 1.87, 95 % CI = 1.03, 3.40; P = 0.04) than healthy controls. The APOE E4/E4 genotype frequencies (OR = 0.09, 95 % CI = 0.01, 0.74; P = 0.03) in the intracranial aneurysms group were significantly lower than those in the controls group. When stratified by the site, shape, size and the Fisher Grade of intracranial aneurysms, no statistically significant result was observed.

Conclusion

Our study suggested that APOE polymorphism might be associated with intracranial aneurysms in Chinese population. Additional studies are needed to confirm this finding.

ADAMTS genes and the risk of cerebral aneurysm

OBJECTIVE Cerebral aneurysms (CAs) affect 2%-5% of the population, and familial predisposition plays a significant role in CA pathogenesis. Several lines of evidence suggest that genetic variations in matrix metalloproteinase genes (MMP) are involved in the etiopathology of CAs. The authors performed a case-control study to investigate the effect of 4 MMP variants from the ADAMTS family on the pathogenesis of CAs. METHODS To identify susceptible genetic variants, the authors investigated 8 single nucleotide polymorphisms (SNPs) in 4 genes from the ADAMTS family (ADAMTS2, -7, -12, and -13) known to be associated with vascular diseases. The study included 353 patients with CAs and 1055 healthy adults. RESULTS The authors found significant associations between CA susceptibility and genetic variations in 3 members of the ADAMTS family. The largest risk for CA (OR 1.32, p = 0.006) was observed in carriers of the ADAMTS2 variant rs11750568, which has been previously associated with pediatric stroke. Three SNPs under investigation are associated with a protective effect in CA pathogenesis (ADAMTS12 variant rs1364044: OR 0.65, p = 0.0001; and ADAMTS13 variants rs739469 and rs4962153: OR 0.77 and 0.63, p = 0.02 and 0.0006, respectively), while 2 other ADAMTS13 variants may confer a significant risk (rs2301612: OR 1.26, p = 0.011; rs2285489: OR 1.24, p = 0.02). CONCLUSIONS These results suggest that reduced integrity of the endothelial wall, as conferred by ADAMTS variants, together with inflammatory processes and defective vascular remodeling plays an important role in CA pathogenesis, although the mechanism of action remains unknown. The authors' findings may lead to specific screening of at-risk populations in the future.

Guidelines for the Management of Patients With Unruptured Intracranial Aneurysms: A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association

PURPOSE

The aim of this updated statement is to provide comprehensive and evidence-based recommendations for management of patients with unruptured intracranial aneurysms.

METHODS

Writing group members used systematic literature reviews from January 1977 up to June 2014. They also reviewed contemporary published evidence-based guidelines, personal files, and published expert opinion to summarize existing evidence, indicate gaps in current knowledge, and when appropriate, formulated recommendations using standard American Heart Association criteria. The guideline underwent extensive peer review, including review by the Stroke Council Leadership and Stroke Scientific Statement Oversight Committees, before consideration and approval by the American Heart Association Science Advisory and Coordinating Committee.

RESULTS

Evidence-based guidelines are presented for the care of patients presenting with unruptured intracranial aneurysms. The guidelines address presentation, natural history, epidemiology, risk factors, screening, diagnosis, imaging and outcomes from surgical and endovascular treatment.

Determining the critical size of intracranial aneurysm predisposing to subarachnoid hemorrhage in the Saudi population

Introduction:

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating event with a high rate of morbidity and mortality. With the improvement of diagnostic modalities and the adoption of different screening strategies, more aneurysms are being diagnosed prior to rupture. Based on large multi-center trials, size has become the most important determinant of treatment decisions. Unfortunately, these studies did not take into account the regional and racial variations, challenging the generalizability of their results.

Material and Methods:

We conducted a retrospective analysis on a series of 192 patients harboring 213 aneurysms.

Results:

The critical finding in our study is that the majority of patients presenting with SAH due to ruptured aneurysms are <10 mm in size.

Conclusion:

Decision to treatment of a given unruptured intracranial aneurysm should be individually assessed and not taken from general international literature as this may mistakenly apply factors from one population to another.

Genetic investigations on intracranial aneurysm: update and perspectives

Detection of an intracranial aneurysm (IA) is a common finding in MRI practice. Nowadays, the incidence of unruptured IA seems to be increasing with the continuous evolution of imaging techniques. Important modifiable risk factors for SAH are well defined, but familial history of IA is the best risk marker for the presence of IA. Numerous heritable conditions are associated with IA formation but these syndromes account for less than 1% of all IAs in the population. No diagnostic test based on genetic knowledge is currently available to identify theses mutations and patients who are at higher risk for developing IAs. In the longer term, a more comprehensive understanding of independent and interdependent molecular pathways germane to IA formation and rupture may guide the physician in developing targeted therapies and optimizing prognostic risk assessment.

Zebrafish models of cerebrovascular disease

Perturbations in cerebral blood flow and abnormalities in blood vessel structure are the hallmarks of cerebrovascular disease. While there are many genetic and environmental factors that affect these entities through a heterogeneous group of disease processes, the ultimate final pathologic insult in humans is defined as a stroke, or damage to brain parenchyma. In the case of ischemic stroke, blood fails to reach its target destination whereas in hemorrhagic stroke, extravasation of blood occurs outside of the blood vessel lumen, resulting in direct damage to brain parenchyma. As these acute events can be neurologically devastating, if not fatal, development of novel therapeutics are urgently needed. The zebrafish (Danio rerio) is an attractive model for the study of cerebrovascular disease because of its morphological and physiological similarity to human cerebral vasculature, its ability to be genetically manipulated, and its fecundity allowing for large-scale, phenotype-based screens.

Gene expression profiles in intracranial aneurysms

In this study, we extracted total RNA from 15 intracranial aneurysms and 17 superficial temporal artery samples, then performed genome-wide expression profiling using the Affymetrix U133 Plus 2.0 GeneChip. Genes that were differentially expressed between intracranial aneurysms and arterial samples were identified using significance analysis for microarrays, and the expression patterns of three randomly-selected genes were verified by real-time polymerase chain reaction analysis. We identified 3 736 differentially-expressed genes out of the 47,000 assayed transcripts. A total of 179 genes showed a >10-fold change in expression between the aneurysms and the arterial samples. Genes involved in the proliferation, migration, and apoptosis of vascular muscle cells, atherosclerosis, extracellular matrix disruption, and inflammatory reactions were associated with the formation of intracranial aneurysms. There were no significant differences in gene expression profile between unruptured and ruptured aneurysms.

Angiotensin-converting enzyme insertion/deletion gene polymorphism and risk of intracranial aneurysm in a Chinese population

Objective

The relationship between angiotensin-converting enzyme (ACE) insertion/deletion (I/D) gene polymorphisms and intracranial aneurysm (IA) has been studied in Caucasian and Japanese populations. The present study aimed to investigate this association in a Chinese population.

Methods

Patients with confirmed IA and age- and sex-matched control subjects without evidence of IA were enrolled. ACE I/D gene polymorphisms were analysed using polymerase chain reaction–restriction fragment length polymorphism.

Results

A total of 220 patients with IA and 220 matched controls were enrolled. In the IA group, 64, 106 and 50 patients were of the II, ID and DD genotypes, respectively, compared with 44, 99 and 77 subjects in the control group. The ACE DD genotype and D allele frequencies were significantly lower in the IA group compared with the control group. There were no statistically significant differences in the site, shape, size and Fisher Grade of aneurysms between genotypes in patients with IA.

Conclusion

The ACE DD genotype may be a protective factor for IA in a Chinese population.

Associations of collagen type I α2 polymorphisms with the presence of intracranial aneurysms in patients from Germany

OBJECTIVE

Subarachnoid hemorrhage from ruptured intracranial aneurysms is associated with a severe prognosis. Preventive treatment of unruptured intracranial aneurysms is possible and recommended. However, the identification of risk patients by genetic analyses is not possible because of lack of candidate genes. Collagen type I α2 (COL1A2) has been associated with the presence of aneurysms in patients from Japan, China, and Korea. In this study, we investigate whether COL1A2 is a possible aneurysm candidate gene in the German population.

METHODS

Patients admitted with intracranial aneurysms to our department and collaborating departments were enrolled. Three single-nucleotide polymorphisms (SNPs) of the COL1A2 gene, namely rs42524 in exon 28, rs1800238 in exon 32, and rs2621215 in intron 46 were investigated using restriction enzymes and sequencing. HapMap data were used for comparison of allelic frequencies with the normal population by χ2 test to identify significant associations between genotypes and the presence of aneurysms.

RESULTS

Two hundred sixty-nine patients were enrolled into the study. There was a significant correlation with the presence of aneurysms for the GC allele of the SNP rs42524 in exon 28 (P = .02). The other polymorphisms did not show significant correlations.

CONCLUSIONS

The COL1A2 gene is associated with intracranial aneurysms in a subset of the German population. However, it is not responsible for the majority of aneurysms, and further candidate genes need to be identified to develop sensitive genetic screening for patients at risk.

Physical factors effecting cerebral aneurysm pathophysiology

Many factors that are either blood-, wall-, or hemodynamics-borne have been associated with the initiation, growth, and rupture of intracranial aneurysms. The distribution of cerebral aneurysms around the bifurcations of the circle of Willis has provided the impetus for numerous studies trying to link hemodynamic factors (flow impingement, pressure, and/or wall shear stress) to aneurysm pathophysiology. The focus of this review is to provide a broad overview of such hemodynamic associations as well as the subsumed aspects of vascular anatomy and wall structure. Hemodynamic factors seem to be correlated to the distribution of aneurysms on the intracranial arterial tree and complex, slow flow patterns seem to be associated with aneurysm growth and rupture. However, both the prevalence of aneurysms in the general population and the incidence of ruptures in the aneurysm population are extremely low. This suggests that hemodynamic factors and purely mechanical explanations by themselves may serve as necessary, but never as necessary and sufficient conditions of this disease's causation. The ultimate cause is not yet known, but it is likely an additive or multiplicative effect of a handful of biochemical and biomechanical factors.

Sequence variations in the von Hippel-Lindau tumor suppressor gene in patients with intracranial aneurysms

BACKGROUND

The rupture of intracranial aneurysms leads to subarachnoid hemorrhage, which is often associated with poor outcome. Preventive treatment of unruptured intracranial aneurysms is possible and recommended. However, the lack of candidate genes precludes identifying patients at risk by genetic analyses. We observed intracranial aneurysms in 2 patients with von Hippel-Lindau (VHL) disease and the known disease-causing mutation c.292T > C (p.Tyr98His) in the VHL tumor suppressor gene. This study investigates whether the VHL gene is a possible candidate gene for aneurysm formation.

METHODS

Patients with intracranial aneurysms admitted to our department between 2006 and 2009 were enrolled. The peripheral leukocyte DNA of 200 patients was investigated for sequence variations in the VHL gene using denaturing high performance liquid chromatography. Peripheral leukocyte DNA of 100 randomly sampled probands was investigated as a control group. The allelic frequencies of sequence variations between both groups were compared using the Fisher exact test.

RESULTS

Fourteen of 200 patients with intracranial aneurysms had sequence variations at 6 different loci in the VHL gene. In contrast, no sequence variations were identified in 100 probands in the control group (P = 0.0062). However, none of the single-sequence variations had a statistically significant difference in the allelic frequencies compared to the control group.

CONCLUSIONS

There is accumulating evidence for a genetic basis of aneurysm development. Our investigations lead to the conclusion that the VHL gene is potentially involved in the formation of intracranial aneurysms in a subset of patients. Additional candidate genes need to be identified in order to develop sensitive genetic screening for at-risk patients.

Is type I alpha 2 collagen gene responsible for intracranial aneurysm in Northeast China?

In this study, we investigated whether a single nucleotide polymorphism (rs42524 G > C) in the type I alpha 2 collagen gene was associated with sporadic ruptured intracranial aneurysm or its clinical characteristics in patients from Northeast China. Genotyping of the rs42524 G > C polymorphism was carried out using a polymerase chain reaction-restriction fragment length polymorphism assay. The data showed that the frequency of the rs42524 GC + CC genotype was significantly higher than the GG genotype among intracranial aneurysm patients whose Hunt and Hess grading scale was > 3. In addition, the rs42524 G > C genotype was found to have a statistically significant association with intracranial aneurysm risk. These findings indicate that the type I alpha 2 collagen gene gene may be involved in a predisposition to intracranial aneurysm in the Northeast Chinese population. Crucially, the rs42524 C allele may be an important risk factor for increased severity of the condition in patients with ruptured intracranial aneurysms.

Epidemiology and genetics of intracranial aneurysms

Intracranial aneurysms are acquired lesions (5-10% of the population), a fraction of which rupture leading to subarachnoid hemorrhage with devastating consequences. Until now, the exact etiology of intracranial aneurysms formation remains unclear. The low incidence of subarachnoid hemorrhage in comparison with the prevalence of unruptured IAs suggests that the vast majority of intracranial aneurysms do not rupture and that identifying those at highest risk is important in defining the optimal management. The most important factors predicting rupture are aneurysm size and site. In addition to ambiental factors (smoking, excessive alcohol consumption and hypertension), epidemiological studies have demonstrated a familiar influence contributing to the pathogenesis of intracranial aneurysms, with increased frequency in first- and second-degree relatives of people with subarachnoid hemorrhage. In comparison to sporadic aneurysms, familial aneurysms tend to be larger, more often located at the middle cerebral artery, and more likely to be multiple. Other than familiar occurrence, there are several heritable conditions associated with intracranial aneurysm formation, including autosomal dominant polycystic kidney disease, neurofibromatosis type I, Marfan syndrome, multiple endocrine neoplasia type I, pseudoxanthoma elasticum, hereditary hemorrhagic telangiectasia, and Ehlers-Danlos syndrome type II and IV. The familial occurrence and the association with heritable conditions indicate that genetic factors may play a role in the development of intracranial aneurysms. Genome-wide linkage studies in families and sib pairs with intracranial aneurysms have identified several loci on chromosomes showing suggestive evidence of linkage, particularly on chromosomes 1p34.3-p36.13, 7q11, 19q13.3, and Xp22. For the loci on 1p34.3-p36.13 and 7q11, a moderate positive association with positional candidate genes has been demonstrated (perlecan gene, elastin gene, collagen type 1 A2 gene). Moreover, 3 of the polymorphisms analyzed in 2 genes (endothelial nitric oxide synthase T786C, interleukin-6 G572C, and interleukin-6 G174C) were found to be significantly associated with ruptured/unruptured aneurysms: the endothelial nitric oxide synthase gene single-nucleotide polymorphisms increased the risk, while IL-6 G174C seemed protective. More recently, two genomic loci (endothelin receptor A and cyclin-dependent kinase inhibitor 2BAS) have been found to be significantly associated with intracranial aneurysms in the Japanese population; endothelin-1 is a potent vasoconstrictor produced by the endothelial cells. Until now, there are no diagnostic tests for specific genetic risk factors to identify patients who are at a high risk of developing intracranial aneurysms. Knowledge of the genetic determinants may be useful in order to allow clues on stopping aneurysm formation and obtain diagnostic tools for identifying individuals at increased risk. Further multicenter studies have to be carried out.

Cigarette smoke and inflammation: role in cerebral aneurysm formation and rupture

Smoking is an established risk factor for subarachnoid hemorrhage yet the underlying mechanisms are largely unknown. Recent data has implicated a role of inflammation in the development of cerebral aneurysms. Inflammation accompanying cigarette smoke exposure may thus be a critical pathway underlying the development, progression, and rupture of cerebral aneurysms. Various constituents of the inflammatory response appear to be involved including adhesion molecules, cytokines, reactive oxygen species, leukocytes, matrix metalloproteinases, and vascular smooth muscle cells. Characterization of the molecular basis of the inflammatory response accompanying cigarette smoke exposure will provide a rational approach for future targeted therapy. In this paper, we review the current body of knowledge implicating cigarette smoke-induced inflammation in cerebral aneurysm formation/rupture and attempt to highlight important avenues for future investigation.

Interactions of miR-34b/c and TP53 polymorphisms on the risk of intracranial aneurysm

Several lines of evidence indicate that inflammatory processes play a key role in the happening and development of intracranial aneurysm (IA). Recently, polymorphisms in the TP53 gene were shown to be associated with inflammation and inflammatory disease. The aim of this study was to investigate the interactions of miR-34b/c and TP53 Arg72-Pro polymorphisms on the risk of IA in a Chinese population. A total of 590 individuals (including 164 patients with IA and 426 controls) were involved in this study. The polymorphisms (i.e., miR-34b/c rs4938723 and TP53 Arg72-Pro) were genotyped by polymerase chain reaction-restriction fragment length polymorphism assay and DNA sequencing. We found that the CC genotype of miR-34b/c rs4938723 was significantly associated with a decreased risk of IA compared with the TT genotype. Moreover, a significant gene interaction of the carriers with the combined genotypes of miR-34b/c rs4938723CC and TP53 Arg72Pro CG/CC/GG had a decreased risk of IA, compared with those carrying miR-34b/c rs4938723CT/TT+TP53 Arg72Pro GG/CG/CC combined genotypes. These findings suggest that the miR-34b/c rs4938723CC and TP53 Arg72-Pro polymorphisms may be involved in the susceptibility to IA.

The interleukin-6-572G/C gene polymorphism and the risk of intracranial aneurysms in a Chinese population

Interleukin-6 (IL-6) is an important proinflammatory cytokine that plays an important role in the pathogenesis of intracranial aneurysms (IAs). The aim of this study was to investigate the association between the IL-6-572G/C polymorphism and the risk of IAs in a Chinese population. The IL-6-572G/C gene polymorphisms in 220 IA cases and 220 controls were analyzed using the polymerase chain reaction-restriction fragment length polymorphism method. The IL-6-572GG (odds ratio [OR]=3.35, 95% confidence intervals [CIs]=1.65, 6.82; p=0.001) and G allele frequencies (OR=1.48, 95% CIs=1.09, 2.00; p=0.01) in the IA group were higher than those in the control group. The C allele frequencies (OR=0.68, 95% CIs=0.50, 0.92; p=0.01) were significantly lower in patients than in controls. When stratified by the site, shape, size, and the Fisher Grade of IAs, no statistically significant result was observed. This study suggested that the IL-6-572GG genotype was associated with a higher risk of IA in a Chinese population.

Saccular intracranial aneurysm: pathology and mechanisms

Saccular intracranial aneurysms (sIA) are pouch-like pathological dilatations of intracranial arteries that develop when the cerebral artery wall becomes too weak to resist hemodynamic pressure and distends. Some sIAs remain stable over time, but in others mural cells die, the matrix degenerates, and eventually the wall ruptures, causing life-threatening hemorrhage. The wall of unruptured sIAs is characterized by myointimal hyperplasia and organizing thrombus, whereas that of ruptured sIAs is characterized by a decellularized, degenerated matrix and a poorly organized luminal thrombus. Cell-mediated and humoral inflammatory reaction is seen in both, but inflammation is clearly associated with degenerated and ruptured walls. Inflammation, however, seems to be a reaction to the ongoing degenerative processes, rather than the cause. Current data suggest that the loss of mural cells and wall degeneration are related to impaired endothelial function and high oxidative stress, caused in part by luminal thrombosis. The aberrant flow conditions caused by sIA geometry are the likely cause of the endothelial dysfunction, which results in accumulation of cytotoxic and pro-inflammatory substances into the sIA wall, as well as thrombus formation. This may start the processes that eventually can lead to the decellularized and degenerated sIA wall that is prone to rupture.

Do statins reduce the risk of aneurysm development: a case-control study

Object

Recent studies in rats have demonstrated that statins may have an inhibitory effect on intracranial aneurysm (IA) development. The purpose of this study was to assess whether long-term statin use is associated with a reduced risk of IA formation in humans.

Methods

This was a single-center case-control study that included consecutive patients admitted to the authors' institution between January 1, 2005, and December 31, 2008. A case was defined as a patient with a cerebral angiography–confirmed diagnosis of IA. Three controls were matched to each case based on age, sex, and index year of hospital admission. The primary exposure of interest was cumulative statin use. Conditional logistic regression was used to assess the relationship between statin intake and incidence of IA.

Results

In total, 1200 patients were included in the study. No overall association was found between statin use and incidence of IA formation (OR 1.08, 95% CI 0.69–1.69), nor when dichotomized into hydrophilic and lipophilic user, or between short (≤12-month) and long (≥36-month) duration of intake. Hypertension and smoking significantly increased the risk of IA development (OR 4.02, 95% CI 2.49–6.45, and OR 1.67, 95% CI 1.02–2.72, respectively).

Conclusions

In contrast to recent experimental reports of the association between statins and a reduction of IA formation, the authors' findings suggest that in humans statins may have no significant beneficial effect on IA suppression.

Concordant Symptomatic Intracranial Aneurysm in a Monozygotic Twin: A Case Report and Review of the Literature

The development of an intracranial aneurysm (IA) is a multifactorial process, involving genetic and environmental factors. The presence of IA or aneurysmal subarachnoid hemorrhage (aSAH) in twins is particularly interesting, since both genetic and environmental factors can be studied. It also raises the question of whether, when one twin is affected, the other asymptomatic twin should be examined for an IA. We report on a monozygotic (MZ) twin-pair with aSAH in both twins and we review all reported cases of IA in MZ twins. Including our case, we found only 14 MZ twin-pairs in which both twins harbored an IA, suggesting a heavy underreporting in the medical literature. In this small group, a high concordance was noted in the sites of IAs. In MZ twins, the preferred sites for IAs are the branching arteries, while aneurysms arising from fusion arteries are rare. These sites differ from the preferential sites seen in series of familial IAs and series of sporadic IAs. We therefore hypothesize that the twinning process might play a significant role in the development of IAs in MZ twins. To further explore and substantiate this, the large twin registries should be studied. Although IAs in MZ twins with a negative family history for IAs should not be regarded as familial IAs, screening of the asymptomatic twin should be seriously considered if one MZ twin presents with an aSAH or an IA, because of the high fatality rates reported in asymptomatic (and not screened) MZ twin-halves.

Common variant near the endothelin receptor type A (EDNRA) gene is associated with intracranial aneurysm risk

The pathogenesis of intracranial aneurysm (IA) formation and rupture is complex, with significant contribution from genetic factors. We previously reported genome-wide association studies based on European discovery and Japanese replication cohorts of 5,891 cases and 14,181 controls that identified five disease-related loci. These studies were based on testing replication of genomic regions that contained SNPs with posterior probability of association (PPA) greater than 0.5 in the discovery cohort. To identify additional IA risk loci, we pursued 14 loci with PPAs in the discovery cohort between 0.1 and 0.5. Twenty-five SNPs from these loci were genotyped using two independent Japanese cohorts, and the results from discovery and replication cohorts were combined by meta-analysis. The results demonstrated significant association of IA with rs6841581 on chromosome 4q31.23, immediately 5' of the endothelin receptor type A with P = 2.2 × 10(-8) [odds ratio (OR) = 1.22, PPA = 0.986]. We also observed substantially increased evidence of association for two other regions on chromosomes 12q22 (OR = 1.16, P = 1.1 × 10(-7), PPA = 0.934) and 20p12.1 (OR = 1.20, P = 6.9 × 10(-7), PPA = 0.728). Although endothelin signaling has been hypothesized to play a role in various cardiovascular disorders for over two decades, our results are unique in providing genetic evidence for a significant association with IA and suggest that manipulation of the endothelin pathway may have important implications for the prevention and treatment of IA.

Detection of Pulsation in Ruptured and Unruptured Cerebral Aneurysms by Electrocardiographically Gated 3-Dimensional Computed Tomographic Angiography With a 320-Row Area Detector Computed Tomography and Evaluation of Its Clinical Usefulness

BACKGROUND:

In ruptured cerebral aneurysms (RCAs), identification of the rupture point of a cerebral aneurysm is useful for treatment planning. In unruptured cerebral aneurysms (URCAs), detection of the risk of aneurysmal rupture is also useful for patient management.

OBJECTIVE:

Electrocardiographic (ECG)-gated 3D-CT angiography was performed for patients with RCAs and URCAs using 320-row area detector CT (ADCT) to detect pulsation of the cerebral aneurysms. The clinical usefulness of this method was then evaluated.

METHODS:

Twelve patients had 12 RCAs, and 39 patients had 53 URCAs. A 320-row ADCT system was used to scan. ECG-gated reconstruction was then performed with the R-R interval divided into 20 phases.

RESULTS:

Pulsation was observed in 10 of the 12 RCAs. The bleeding site was considered to correspond to the area of pulsation. Pulsation was observed in 14 of 53 URCAs. Thirteen patients with 18 URCAs were followed. Of the 11 URCAs in which pulsation was not observed, 1 showed a change in shape. Of the 7 URCAs in which pulsation was observed, 3 showed a change in shape. URCAs in which pulsation was observed were more likely to show a change in shape (P = .082).

CONCLUSION:

The area of pulsation was found to correspond to the bleeding site in many RCAs. This information would be extremely useful for treatment planning. The detection of pulsation in an URCA is therefore considered to provide useful information for patient management.

Sexual intercourse and cerebral aneurysmal rupture: potential mechanisms and precipitants

Aneurysmal subarachnoid hemorrhage (SAH) is a significant cause of death in young and middle-aged individuals and causes tremendous morbidity in affected patients. Despite the identification of various risk factors, the series of events leading to the formation, growth, and rupture of intracranial aneurysms is poorly understood. Cerebral aneurysm rupture has been associated with sexual intercourse and other forms of physical exercise. In fact, multiple case series reported that coitus was the immediate preceding activity in 3.8–14.5% of patients suffering from aneurysmal SAH. This may be related to the large elevations in mean arterial blood pressure that occur in both males and females during sexual intercourse (130–175 and 125–160 mm Hg, respectively). While coitus and physical exercise share important physiological similarities, each may differentially affect the probability that a preformed aneurysm will rupture. In this literature review and synthesis, the authors analyze the physiological human response to sexual intercourse in an effort to delineate those factors that may precipitate aneurysmal rupture. The authors' analysis is based on the original data collected by Masters and Johnson. To the authors' knowledge, this is the first review to address the link between sexual intercourse and intracranial aneurysmal rupture. While actual measurements of the physiological variables relevant to SAH were not performed in this article, the authors make reasonable assumptions based on the available data to help elucidate the mechanism of sexually induced aneurysmal rupture.

The role of the renin—angiotensin system in the pathogenesis of intracranial aneurysms

Introduction: Recent work has begun to elucidate the pathogenesis of intracranial aneurysms (IA) and has shown that many genes are involved in the risk for this condition. There has also been increasing research interest in the renin—angiotensin system (RAS) in the brain and its involvement in a range of cardiovascular and neurological disorders. The possibility that the RAS is implicated in the pathogenesis of IA merits further investigation. The aim of this article is to review the literature on the pathogenesis of IA and the pathophysiological significance of the brain RAS, and to identify directions for research into their association.

Methods and results : A survey of the literature in these fields shows that although factors contributing to systemic hypertension predispose to IA, a large number of genes involved in endothelial cell adhesion, smooth muscle activity, extracellular matrix dynamics and the inflammatory and immune responses are also implicated. The brain RAS has a significant role in regulating blood pressure and in maintaining cerebrovascular autoregulation, but angiotensin II receptors are also involved in the maintenance of endothelial cell and vascular smooth muscle function and in the inflammatory response in the brain.

Conclusions: There is strong, albeit largely circumstantial, evidence in the literature for a relationship between the brain RAS and the formation of IA. Research on the association between polymorphisms in RAS-related genes and the incidence of unruptured and ruptured IA is indicated.

Impact of LIMK1, MMP2 and TNF-α variations for intracranial aneurysm in Japanese population

Genetic factors are known to have an important role in intracranial aneurysm (IA) pathogenesis. The purpose of this study is to identify single-nucleotide polymorphisms (SNPs) that are associated with IA in Japanese population. A total of 2050 IA patients and 1835 controls recruited in Biobank Japan, The University of Tokyo were used in this study. In all, 45 SNPs in 24 genes encoding proteins, which have been considered to be possible risk factors to IA pathogenesis, were genotyped using multiplex PCR-invader assay. Association analysis was evaluated by logistic regression analysis before and after adjustment of age, smoking and hypertension status. This case-control association study revealed a SNP, rs6460071 located on LIMK1 gene (P = 0.00069) to be significantly associated with increased risk of IA. In addition, two SNPs, rs243847 (P = 0.00086) and rs243865 (P = 0.00090), on matrix metallopeptidase 2 (MMP2) gene and one SNP rs1799724 (P = 0.0026) on tumor necrosis factor-α (TNF-α) gene, are marginally associated with IA in male- and female-specific manner, respectively. In conclusion, a large-scale case-control association study was conducted to verify genetic variations associated with IA in Japanese population. This study gave insights on the importance of stratified analysis between genders, and suggested that the underlying mechanism of IA pathogenesis might differ between females and males.