Association of Kallikrein Gene Polymorphisms With Intracranial Aneurysms

Genetic basis of intracranial aneurysm formation and rupture: clinical implications in the postgenomic era

OBJECTIVE

Despite the prevalence and impact of intracranial aneurysms (IAs), the molecular basis of their pathogenesis remains largely unknown. Moreover, there is a dearth of clinically validated biomarkers to efficiently screen patients with IAs and prognosticate risk for rupture. The aim of this study was to survey the literature to systematically identify the spectrum of genetic aberrations that have been identified in IA formation and risk of rupture.

METHODS

A literature search was performed using the Medical Subject Headings (MeSH) system of databases including PubMed, EMBASE, and Google Scholar. Relevant studies that reported on genetic analyses of IAs, rupture risk, and long-term outcomes were included in the qualitative analysis.

RESULTS

A total of 114 studies were reviewed and 65 were included in the qualitative synthesis. There are several well-established mendelian syndromes that confer risk to IAs, with variable frequency. Linkage analyses, genome-wide association studies, candidate gene studies, and exome sequencing identify several recurrent polymorphic variants at candidate loci, and genes associated with the risk of aneurysm formation and rupture, including ANRIL (CDKN2B-AS1, 9p21), ARGHEF17 (11q13), ELN (7q11), SERPINA3 (14q32), and SOX17 (8q11). In addition, polymorphisms in eNOS/NOS3 (7q36) may serve as predictive markers for outcomes following intracranial aneurysm rupture. Genetic aberrations identified to date converge on posited molecular mechanisms involved in vascular remodeling, with strong implications for an associated immune-mediated inflammatory response.

CONCLUSIONS

Comprehensive studies of IA formation and rupture have identified candidate risk variants and loci; however, further genome-wide analyses are needed to identify high-confidence genetic aberrations. The literature supports a role for several risk loci in aneurysm formation and rupture with putative candidate genes. A thorough understanding of the genetic basis governing risk of IA development and the resultant aneurysmal subarachnoid hemorrhage may aid in screening, clinical management, and risk stratification of these patients, and it may also enable identification of putative mechanisms for future drug development.

Intracranial Aneurysms: Pathology, Genetics, and Molecular Mechanisms

Intracranial aneurysms (IA) are local dilatations in cerebral arteries that predominantly affect the circle of Willis. Occurring in approximately 2-5% of adults, these weakened areas are susceptible to rupture, leading to subarachnoid hemorrhage (SAH), a type of hemorrhagic stroke. Due to its early age of onset and poor prognosis, SAH accounts for > 25% of years lost for all stroke victims under the age of 65. In this review, we describe the cerebrovascular pathology associated with intracranial aneurysms. To understand IA genetics, we summarize syndromes with elevated incidence, genome-wide association studies (GWAS), whole exome studies on IA-affected families, and recent research that established definitive roles for Thsd1 (Thrombospondin Type 1 Domain Containing Protein 1) and Sox17 (SRY-box 17) in IA using genetically engineered mouse models. Lastly, we discuss the underlying molecular mechanisms of IA, including defects in vascular endothelial and smooth muscle cells caused by dysfunction in mechanotransduction, Thsd1/FAK (Focal Adhesion Kinase) signaling, and the Transforming Growth Factor β (TGF-β) pathway. As illustrated by THSD1 research, cell adhesion may play a significant role in IA.

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.

Identification of the soluble form of tyrosine kinase receptor Axl as a potential biomarker for intracranial aneurysm rupture

Background

Subarachnoid hemorrhage caused by a ruptured intracranial aneurysm (RIA) is a devastating condition with significant morbidity and mortality. Despite the fact that RIAs can be prevented by microsurgical clipping or endovascular coiling, there are no reliable means of effectively predicting IA patients at risk for rupture. The purpose of our study was to discover differentially-expressed glycoproteins in IAs with or without rupture as potential biomarkers to predict rupture.

Methods

Forty age/gender-matched patients with RIA, unruptured IA (UIA), healthy controls (HCs) and disease controls (DCs) (discovery cohort, n = 10 per group) were recruited and a multiplex quantitative proteomic method, iTRAQ (isobaric Tagging for Relative and Absolute protein Quantification), was used to quantify relative changes in the lectin-purified glycoproteins in CSF from RIAs and UIAs compared to HCs and DCs. Then we verified the proteomic results in an independent set of samples (validation cohort, n = 20 per group) by enzyme-linked immunosorbent assay. Finally, we evaluated the specificity and sensitivity of the candidate marker with receiver operating characteristic (ROC) curve methods.

Results

The proteomic findings identified 294 proteins, 40 of which displayed quantitative changes unique to RIA, 13 to UIA, and 20 to IA. One of these proteins, receptor tyrosine kinase Axl, was significantly increased in RIA, as confirmed in CSF from the discovery cohort as well as in CSF and plasma from the validation cohort (p <0.05). Spearman’s correlation analysis revealed that the CSF and plasma Axl levels were strongly correlated (r = 0.93, p <0.0001). The ROC curve indicated an optimal CSF Axl threshold of 0.12 nM for discriminating RIA from UIA with corresponding sensitivity/specificity of 73.33%/90% and an area under the curve (AUC) of 0.89 (95% CI: 0.80-0.97, p < 0.0001). The optimal threshold for plasma Axl was 1.7 nM with corresponding sensitivity/specificity of 50%/80% and an AUC of 0.71 (95% CI: 0.54-0.87, p = 0.027).

Conclusions

Both CSF and plasma Axl levels are significantly elevated in RIA patients. Axl might serve as a promising biomarker to predict the rupture of IA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-015-0282-8) contains supplementary material, which is available to authorized users.

Molecular basis and genetic predisposition to intracranial aneurysm

Intracranial aneurysms, also called cerebral aneurysms, are dilatations in the arteries that supply blood to the brain. Rupture of an intracranial aneurysm leads to a subarachnoid hemorrhage, which is fatal in about 50% of the cases. Intracranial aneurysms can be repaired surgically or endovascularly, or by combining these two treatment modalities. They are relatively common with an estimated prevalence of unruptured aneurysms of 2%-6% in the adult population, and are considered a complex disease with both genetic and environmental risk factors. Known risk factors include smoking, hypertension, increasing age, and positive family history for intracranial aneurysms. Identifying the molecular mechanisms underlying the pathogenesis of intracranial aneurysms is complex. Genome-wide approaches such as DNA linkage and genetic association studies, as well as microarray-based mRNA expression studies, provide unbiased approaches to identify genetic risk factors and dissecting the molecular pathobiology of intracranial aneurysms. The ultimate goal of these studies is to use the information in clinical practice to predict an individual's risk for developing an aneurysm or monitor its growth or rupture risk. Another important goal is to design new therapies based on the information on mechanisms of disease processes to prevent the development or halt the progression of intracranial aneurysms.

Circulating microRNAs serve as novel biological markers for intracranial aneurysms

Background

Biological markers that can be used to predict the risk of intracranial aneurysms (IAs) are not available.

Methods and Results

To clarify whether circulating microRNAs could be used as biomarkers for IA, we carried out microarray assays in a screening cohort of 40 IA patients (20 unruptured and 20 ruptured) and 20 healthy volunteers. We identified 20 microRNAs that were unanimously changed in both ruptured and unruptured patients. We confirmed 60% of these changed microRNAs by a separate microarray test with an independent validation cohort (n=143 including 93 IA patients). To identify potential biomarkers, we combined the 2 cohorts and performed quantitative real‐time polymerase chain reactions for selected target microRNAs. Logistic regression analysis demonstrated that miR‐16 and miR‐25 were independent factors for IA occurrence (P<0.001). After controlling for age, sex, smoking, and history of hypertension, the contributions of miR‐16 and miR‐25 were still highly significant (P<0.001). The adjusted odds ratio values for miR‐16 and miR‐25 were 1.52 (95% CI 1.31 to 1.77) and 1.53 (1.30 to 1.79). Combining both miR‐16 and miR‐25 in a single model did not improve the performance of risk association.

Conclusions

Our data suggest that circulating miRNAs may be novel biological markers that are useful in assessing the likelihood of IA occurrence.

Association of Kallikrein gene polymorphisms with sporadic intracranial aneurysms in the Chinese population

OBJECT

Variants of Kallikreins have been shown to be risk factors for intracranial aneurysm (IA) in a Finnish population. In the present study, the authors investigated the correlation between polymorphisms in the Kallikrein gene cluster and IAs in the Chinese population.

METHODS

The association of Kallikrein variants (rs1722561 and rs1701946) with sporadic IAs was tested in 308 cases and 443 controls. The differences in allelic frequencies between patients and the control group were evaluated with the chi-square test.

RESULTS

The C allele of rs1722561 showed a significant reduction in the risk of sporadic IA (OR 0.71, 95% CI 0.53-0.95; p = 0.023). However, no association of the variant rs1701946 with sporadic IA was found (OR 0.78, 95% CI 0.57-1.06; p = 0.115).

CONCLUSIONS

The variant rs1722561 of Kallikreins might reduce the risk of sporadic IAs among individuals of Chinese Han ethnicity. This study confirms the association between Kallikreins and IAs.

Treatment of ruptured saccular aneurysms of the fenestrated vertebrobasilar junction with balloon remodeling technique. A short case series and review of the literature

Fenestration of the intracranial arteries is a relatively common occurrence. This anatomic variation may predispose to aneurysm formation at certain sites. Treatment of such aneurysms is difficult as it may occlude one of the limbs of fenestration with resultant deficit. Thus, preservation of both the limbs with adequate exclusion of the aneurysm from the circulation should be the aim of any treatment. We describe a series of four cases of ruptured aneurysms arising from a fenestrated vertebrobasilar junction treated with endovascular balloon remodeling technique.

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.

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.

The physiology and pathobiology of human kallikrein-related peptidase 6 (KLK6)

The human kallikrein-related peptidase 6 (KLK6) gene belongs to the 15-member kallikrein (KLK) gene family mapping to chromosome 19q13.3-13.4. Encoding for an enzyme with trypsin-like properties, KLK6 can degrade components of the extracellular matrix. The successful utilisation of another KLK member (KLK3/PSA) for prostate cancer diagnosis has led many to evaluate KLK6 as a potential biomarker for other cancer and diseased states. The observed dysregulated expression in cancers, neurodegenerative diseases and skin conditions has led to the discovery that KLK6 participates in other cellular pathways including inflammation, receptor activation and regulation of apoptosis. Moreover, the improvements in high-throughput genomics have not only enabled the identification of sequence polymorphisms, but of transcript variants, whose functional significances have yet to be realised. This comprehensive review will summarise the current findings of KLK6 pathophysiology and discuss its potential as a viable biomarker.

A single nucleotide polymorphism in exon 3 of the kallikrein 1 gene is associated with large but not small abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a late onset degenerative condition with an inherited component thought to be due to multiple risk alleles. A locus on chromosomes 19q13 has been previously associated with AAA. The gene encoding kallikrein 1 (KLK1) is located on chromosome 19q13 and the single nucleotide polymorphism (SNP) rs5516 has been previously shown to lead to structural changes in the KLK1 transcription regulatory region. The aim of this study was to investigate whether rs5516 was associated with AAA and aortic diameter.

METHODS

We performed a case-control study on two independent subject groups from Western Australia (n=1304) and Queensland (n=325) of which 609 and 225 had an AAA, respectively. In addition, we analysed RNA extracted from abdominal aortic biopsies from 12 patients undergoing AAA surgery and 6 organ donors.

RESULTS

After adjusting for other risk factors the G allele of the rs5516 polymorphism was associated with large but not small AAA using a dominant model in the Western Australian men and a recessive model in Queensland subjects. In subjects with large AAA the G allele was associated with aortic diameter. The short splice variant of KLK1 was upregulated within AAA compared to control biopsies.

CONCLUSION

This study suggests that a genetic polymorphism in KLK1 may contribute to the risk of developing later stage AAA.

Saccular Intracranial Aneurysm Disease

OBJECTIVE

Finnish saccular intracranial aneurysm (sIA) disease associates to 2q33, 8q11, and 9p21 loci and links to 19q13, Xp22, and kallikrein cluster in sIA families. Detailed phenotyping of familial and sporadic sIA disease is required for fine mapping of the Finnish sIA disease.

METHODS

Eastern Finland, which is particularly isolated genetically, is served by Kuopio University Hospital's Department of Neurosurgery. We studied the site and size distribution of unruptured and ruptured sIAs in correlation to age and sex in 316 familial and 1454 sporadic sIA patients on first admission from 1993 to 2007.

RESULTS

The familial and sporadic aneurysmic subarachnoid hemorrhage patients had slightly different median ages (46 vs 51 years in men; 50 vs 57 years in women), different proportion of males (50% vs 42%), equal median diameter of ruptured sIAs (7 mm vs 7 mm) with no correlation to age, and equally unruptured sIAs (30% vs 28%). The unruptured sIAs were most frequent at the middle cerebral artery (MCA) bifurcation (44% vs 39%) and the anterior communicating artery (12% vs 13%), in contrast to the ruptured sIAs at the anterior communicating artery (37% vs 29%) and MCA bifurcation (29% vs 29%). The size of unruptured sIAs increased by age in the sporadic group.

CONCLUSION

The MCA bifurcation was most prone to develop unruptured sIAs, suggesting that MCA branching during the embryonic period might be involved. The different site distribution of ruptured and unruptured sIAs suggests different etiologies for sIA formation and rupture. The lack of correlation of size and age at rupture (exposure to risk factors) suggests that the size at rupture is more dependent on hemodynamic stress.

Microsurgical principles for anterior circulation aneurysms

Microneurosurgical techniques introduced by Prof. Yaşargil have been modified by the senior author (JH) when treating more than 4,000 patients with aneurysms at two of the Departments of Neurosurgery in Finland, Kuopio and Helsinki, with a total catchment area of close to three million people. This experience is reviewed, and the treatment of anterior circulation aneurysms by simple, fast, normal anatomy preserving strategy is presented.Most of the aneurysms of the anterior circulation are treated by using the lateral supraorbital approach, a less invasive, more frontally located modification of the pterional approach. To avoid extensive skull base surgery, a slack brain is needed and achieved by experienced neuroanesthesia and by surgical tricks for removal of CSF.Diagnosis of cerebral aneurysm before rupture improves treatment results more than any technical advances. Until this is realized, we continue to treat cerebral aneurysms by simple, fast, preserving normal anatomy-strategy, which has served our patients well.Patients with cerebral aneurysms should be treated at specialized neurovascular centers.

Fenestrated anterior cerebral artery with associated arterial anomalies. Case reports and literature review

SUMMARY

Fenestration of the A2 segment is extremely rare. Cerebrovascular fenestration may be associated with an increased incidence of cerebral aneurysm and other vascular anomalies. Two case reports are presented which identify a fenestration of the A2 segment and other normal variations of the intra-cerebral circulation. A review of the literature has been undertaken to determine the prevalence and embryology of anterior cerebral artery fenestrations, their clinical significance and the association with aneurysm formation and other intracranial vascular anomalies.

Association analyses confirming a susceptibility locus for intracranial aneurysm at chromosome 14q23

Previous linkage analyses of intracranial aneurysm (IA) have proposed several genetic susceptibility loci; however, some loci remain contradictory. The objective of this study was to confirm these loci in a Japanese population using allelic and haplotype association analyses. We set high-density single nucleotide polymorphism markers in previously suggested IA loci and conducted an association analysis in 29 cases and 35 controls from a small community in Akita, Japan. Genotyping was carried out using the GeneChip 10 K mapping array, and the association analysis was performed using GeneSpring GT2 software. The result was confirmed in a replication cohort consisting of 237 cases and 253 controls from all over Japan. Only one variant, rs767603, at chromosome 14q23, was significantly associated with IA, both in allelic analysis (p=0.00017, Bonferroni-corrected p=0.021) and haplotype analysis (p=0.00178, Bonferroni-corrected p=0.048). This association was confirmed in the replication cohort (p=0.0046 for allelic association, p=0.0060 for haplotype association). Our findings confirm 14q23 to be a susceptibility locus for intracranial aneurysm.

The same sequence variant on 9p21 associates with myocardial infarction, abdominal aortic aneurysm and intracranial aneurysm

Recently, two common sequence variants on 9p21, tagged by rs10757278-G and rs10811661-T, were reported to be associated with coronary artery disease (CAD) and type 2 diabetes (T2D), respectively. We proceeded to further investigate the contributions of these variants to arterial diseases and T2D. Here we report that rs10757278-G is associated with, in addition to CAD, abdominal aortic aneurysm (AAA; odds ratio (OR) = 1.31, P = 1.2 x 10(-12)) and intracranial aneurysm (OR = 1.29, P = 2.5 x 10(-6)), but not with T2D. This variant is the first to be described that affects the risk of AAA and intracranial aneurysm in many populations. The association of rs10811661-T to T2D replicates in our samples, but the variant does not associate with any of the five arterial diseases examined. These findings extend our insight into the role of the sequence variant tagged by rs10757278-G and show that it is not confined to atherosclerotic diseases.

A consolidated catalogue and graphical annotation of dbSNP polymorphisms in the human tissue kallikrein (KLK) locus

The human tissue kallikreins, 15 secreted serine proteases, may play diverse roles in pathophysiology. The National Center for Biotechnology Information's dbSNP was mined for polymorphisms located within the kallikrein (KLK) locus using custom-designed "ParSNPs" and "LocusAnnotator" software tools. Using "ParSNPs", a filterable catalogue of 1856 KLK polymorphisms (1023 validated) was generated. "LocusAnnotator" was used to annotate the KLK locus sequence with gene and polymorphism features. A second locus was examined to validate the use of both programs on a non-kallikrein locus. This report may assist in the informed selection of KLK polymorphisms for future association and biochemical studies in relation to disease. Furthermore, "ParSNPs" and "LocusAnnotator" are available at no cost from our website (www.acdcLab.org/annotations) to examine other loci.