Elastin polymorphism haplotype and intracranial aneurysms are not associated in Central Europe

Understanding the genetics of intracranial aneurysms: A primer

The genetics of intracranial aneurysms is complex. Much work has been done looking at the extracellular matrix surrounding cerebral vasculature as well as the role of matrix metalloproteinases. This comprehensive review summarizes what is known to date about the important genetic components that predispose to aneurysm formation and critically discusses the published findings. We discuss promising pre-clinical models of aneurysm formation and subarachnoid hemorrhage, and highlight avenues for future discovery, while considering limitations in the research to date. This review will further serve as a comprehensive reference guide to understand the genetic underpinnings for aneurysm pathophysiology and act as a primer for further investigation.

Factor XIII polymorphism and risk of aneurysmal subarachnoid haemorrhage in a south Indian population

BACKGROUND

The rupture of a brain aneurysm causes bleeding in the subarachnoid space and is known as aneurysmal subarachnoid haemorrhage (aSAH). In our study, we evaluated the association of factor XIII polymorphism and the risk of Aneurysmal subarachnoid haemorrhage (aSAH) in South Indian population.

METHODS

The study was performed in 200 subjects with aSAH and 205 healthy control subjects. Genotyping of rs5985(c.103G > T (p.Val35Leu)) and rs5982(c.1694C > T (p.Pro564Leu)) polymorphism was performed by Taqman® allelic discrimination assay.

RESULTS

In our study, Val/Leu genotype frequency was higher in control subjects (18%) compared to aSAH patients (9%).The Val/Leu genotype was associated with lower risk of aSAH (OR = 0.48, 95%CI = 0.26-0.88, p = 0.02). When compared with Val allele, Leu allele was significantly associated with lower risk of aSAH (OR = 0.55, 95%CI = 0.32-0.95, p = 0.03). In subtyping, we found a significant association of Leu/Leu genotype with the Basilar top aneurysm (OR = 3.59, 95%CI = 1.11-11.64, p = 0.03). In c.1694C > T (p.Pro565Leu) variant, Pro/Pro Vs Pro/Leu genotype (OR = 2.06, 95%CI = 1.10-3.85, p = 0.02) was significantly associated with higher risk of aSAH. The 564Leu allelic frequency in aSAH patients (36%) was higher when compared with that in healthy controls (30%) in our study. When allele frequency (Pro Vs Leu) was compared, 564Leu allele was found to be significantly associated with higher aSAH risk (OR = 1.36, 95%CI = 1.01-1.83, p = 0.04). (OR = 1.36, 95%CI = 1.01-1.83, p = 0.04). Regarding rs5985 and rs5982, significant association was found in the log-additive model (OR = 0.57, 95%CI = 0.33-0.97, p = 0.034; OR = 1.32, 95%CI = 1.00-1.72, p = 0.043).

CONCLUSION

These results suggest that 34Leu allele was a protective factor for lower risk of aSAH whereas 564Leu allele was associated with higher risk of aSAH in South Indian population.

Plasma Soluble Human Elastin Fragments as an Intra-Aneurysmal Localized Biomarker for Ruptured Intracranial Aneurysm

Background Fragmentation of the tunica media is a hallmark of intracranial aneurysm formation, often leading to aneurysmal progression and subsequent rupture. The objective of this study is to determine the plasma level of elastin fragments in the lumen of ruptured versus unruptured human intracranial aneurysms. Methods and Results One hundred consecutive patients with/without ruptured saccular intracranial aneurysms undergoing endovascular coiling or stent-assisted coiling were recruited. Blood samples were collected from the lumen of intracranial aneurysm using a microcatheter. The tip of the microcatheter was placed inside the aneurysm's sac in close proximity to the inner wall of the dome. Plasma levels of elastin fragments were measured using an ELISA -based method. Mean plasma level of soluble human elastin fragments was significantly greater in ruptured aneurysms when compared with nonruptured aneurysms (102.0±15.5 versus 39.3±9.6 ng/mL; P<0.001). Mean plasma level of soluble human elastin fragments did not have significant correlation with age, sex, size, or aneurysm location. Conclusions The present study revealed that a significantly higher concentration of soluble human elastin fragments in the lumen of ruptured intracranial aneurysms when compared with nonruptured ones.

Genetic Risk Assessment of Elastin Gene Polymorphisms with Intracranial Aneurysm in Koreans

Elastin encoded by elastin gene (ELN) is a crucial extracellular matrix protein responsible for arterial resilience. The objective of this study was to identify single nucleotide polymorphisms (SNPs) of ELN gene susceptible to intracranial aneurysm (IA) in Korean population. Two SNPs of ELN gene, rs2071307 (Gly422Ser) and rs2856728 (intron), were genotyped in 90 patients with IA and 90 age and frequency matched controls. Fisher’s exact test was conducted to evaluate allelic association with IA. Of the two SNPs in ELN gene, T allele of rs2856728 (intron) showed statistically significant association with increased development of IA (odds ratio [OR]: 2.34, 95% confidence interval [CI]: 1.44–3.81, P = 7.6 × 10⁻⁴). However, G allele of rs2071307 (Gly422Ser) had no significant association with the development of IA (OR: 1.27, 95% CI: 1.44–3.81, P = 0.607). Interestingly, the odds of having rs2856728 variant was approximately 2-fold higher in males than that in females (OR: 3.46 vs. 1.88, P < 0.05). However, none of SNPs showed difference between single and multiple IA in this study. This preliminary study implies that the rs2856728 variant in ELN gene polymorphisms might play crucial roles in the development and pathogenesis of IA in Korean population.

Molecular mechanisms of the formation and progression of intracranial aneurysms

Until recently, only a little was understood about molecular mechanisms of the development of an intracranial aneurysm (IA). Recent advancements over the last decade in the field of genetics and molecular biology have provided us a wide variety of evidences supporting the notion that chronic inflammation is closely associated with the pathogenesis of IA development. In the field of genetics, large-scale Genome-wide association studies (GWAS) has identified some IA susceptible loci and genes related to cell cycle and endothelial function. Researches in molecular biology using human samples and animal models have revealed the common pathway of the initiation, progression, and rupture of IAs. IA formation begins with endothelial dysfunction followed by pathological remodeling with degenerative changes of vascular walls. Medical treatments inhibiting inflammatory cascades in IA development are likely to prevent IA progression and rupture. Statins and aspirin are expected to suppress IA progression by their anti-inflammatory effects. Decoy oligodeoxynucleotides (ODNs) inhibiting inflammatory transcription factors such as nuclear factor kappa-B (NF-κB) and Ets-1 are the other promising choice of the prevention of IA development. Further clarification of molecular mechanisms of the formation and progression of IAs will shed light to the pathogenesis of IA development and provide insight into novel diagnostic and therapeutic strategies for IAs.

The genetics of sporadic ruptured and unruptured intracranial aneurysms: a genetic meta-analysis of 8 genes and 13 polymorphisms in approximately 20,000 individuals

Object

Intracranial aneurysms (IAs) are thought to have a multifactorial origin. The authors undertook a comprehensive meta-analysis on all genes investigated using a case-control model in ruptured (subarachnoid hemorrhage) and unruptured aneurysms.

Methods

Electronic databases were searched until and including July 2008 for any candidate gene studied in IA or subarachnoid hemorrhage using a case-control model. The ORs and 95% CIs were determined for each gene-disease association using fixed and random effect models.

Results

Thirty studies of 8 genes and 13 polymorphisms were analyzed among 19,961 individuals (6622 cases and 13,339 controls). Two genes and 3 polymorphisms were associated with IA. The eNOS gene T786C polymorphism (OR 1.24, 95% CI 1.0–1.54; p = 0.05) and IL-6 gene G572C polymorphism (OR 7.08, 95% CI 2.85–17.57; p < 0.0001) both showed a significant association with ruptured/unruptured IA. The IL-6/G174C polymorphism exerted a significant protective effect against IA (OR 0.49, 95% CI 0.25–0.95; p = 0.04). The other candidate genes investigated (ACE, endoglin, APOE, elastin, MMP-3, and SERPINA3) showed no significant associations.

Conclusions

There is a likely genetic basis to sporadic IAs. However, the evidence base is small when compared against other complex disorders.

Polymorphism rs42524 of COL1A2 and sporadic intracranial aneurysms in the Chinese population

Object

The COL1A2 gene at 7q22.1 has been shown to be associated with familial intracranial aneurysms (IAs) in the Japanese population. In the present study, the authors investigated the correlation between the presence of the rs42524 polymorphism in COL1A2 and the occurrence of sporadic IAs in Chinese patients.

Methods

The polymorphism rs42524 of the COL1A2 gene was identified by polymerase chain reaction–based restriction analysis in genomic DNA from 226 patients with sporadic IAs (mean age 51.49 ± 11.47 years) and 326 control participants (mean age 52.33 ± 10.50 years). Neurological assessments were performed using the Hunt and Hess grading system, and differences in allelic and genotypic frequencies between the patient and control groups were evaluated with the chi-square test.

Results

There was a significant difference in either the genotype distribution (χ2 = 11.99, p = 0.002) or allelic frequencies (χ2 = 11.96, p = 0.001, odds ratio 2.579, 95% confidence interval 1.486–4.476) between patients with IAs and patients in the control group.

Conclusions

The rs42524 polymorphism of COL1A2 could be a genetic risk factor for sporadic IAs among individuals of Chinese Han ethnicity. This study is the first to confirm the association between COL1A2 and IAs.

Molecular Genetics of Human Intracranial Aneurysms

Intracranial aneurysms (IAs) are the dilatations of blood vessels in the brain and pose potential risk of rupture leading to subarachnoid hemorrhage. Although the genetic basis of IAs is poorly understood, it is well-known that genetic factors play an important part in the pathogenesis of IAs. Therefore, the identifying susceptible genetic variants might lead to the understanding of the mechanism of formation and rupture of IAs and might also lead to the development of a pharmacological therapy. To elucidate the molecular pathogenesis of diseases has become a crucial step in the development of new treatment strategies. Although extensive genetic research and its potential implications for future prevention of this often fatal condition are urgently needed, efforts to elucidate the susceptibility loci of IAs are hindered by the issues bewildering the most common and complex genetic disorders, such as low penetrance, late onset, and uncertain modes of inheritance. These efforts are further complicated by the fact that many IA lesions remain asymptomatic or go undiagnosed. In this review, we present and discuss the current status of genetic studies of IAs and we recommend comprehensive genome-wide association studies to identify genetic loci that underlie this complex disease.

Genome screen to detect linkage to intracranial aneurysm susceptibility genes: the Familial Intracranial Aneurysm (FIA) study

BACKGROUND AND PURPOSE

Evidence supports a substantial genetic contribution to the risk of intracranial aneurysm (IA). The purpose of this study was to identify chromosomal regions likely to harbor genes that contribute to the risk of IA.

METHODS

Multiplex families having at least 2 individuals with "definite" or "probable" IA were ascertained through an international consortium. First-degree relatives of individuals with IA who were at increased risk of an IA because of a history of hypertension or present smoking were offered cerebral magnetic resonance angiography. A genome screen was completed using the Illumina 6K SNP system, and the resulting data from 192 families, containing 1155 genotyped individuals, were analyzed. Narrow and broad disease definitions were used when testing for linkage using multipoint model-independent methods. Ordered subset analysis was performed to test for a gene x smoking (pack-years) interaction.

RESULTS

The greatest evidence of linkage was found on chromosomes 4 (LOD=2.5; 156 cM), 7 (LOD=1.7; 183 cM), 8 (LOD=1.9; 70 cM), and 12 (LOD=1.6; 102 cM) using the broad disease definition. Using the average pack-years for the affected individuals in each family, the genes on chromosomes 4 (LOD=3.5; P=0.03), 7 (LOD=4.1; P=0.01) and 12 (LOD=3.6; P=0.02) all appear to be modulated by the degree of smoking in the affected members of the family. On chromosome 8, inclusion of smoking as a covariate did not significantly strengthen the linkage evidence, suggesting no interaction between the loci in this region and smoking.

CONCLUSIONS

We have detected possible evidence of linkage to 4 chromosomal regions. There is potential evidence for a gene x smoking interaction with 3 of the loci.

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.

Subarachnoid hemorrhage: tests of association with apolipoprotein E and elastin genes

Background

Apolipoprotein E (APOE) and elastin (ELN) are plausible candidate genes involved in the pathogenesis of stroke. We tested for association of variants in APOE and ELN with subarachnoid hemorrhage (SAH) in a population-based study. We genotyped 12 single nucleotide polymorphisms (SNPs) on APOE and 10 SNPs on ELN in a sample of 309 Caucasian individuals, of whom 107 are SAH cases and 202 are age-, race-, and gender-matched controls from the Greater Cincinnati/Northern Kentucky region. Associations were tested at genotype, allele, and haplotype levels. A genomic control analysis was performed to check for spurious associations resulting from population substructure.

Results

At the APOE locus, no individual SNP was associated with SAH after correction for multiple comparisons. Haplotype analysis revealed significant association of the major haplotype (Hap1) in APOE with SAH (p = 0.001). The association stemmed from both the 5' promoter and the 3' region of the APOE gene. APOE ε2 and ε 4 were not significantly associated with SAH. No association was observed for ELN at genotype, allele, or haplotype level and our study failed to confirm previous reports of ELN association with aneurysmal SAH.

Conclusion

This study suggests a role of the APOE gene in the etiology of aneurysmal SAH.

Genetic and morphologic determinants of pneumothorax in lymphangioleiomyomatosis

Lymphangioleiomyomatosis, a multisystem disease affecting women, is characterized by proliferation of abnormal smooth muscle-like cells in the lungs, leading to cystic destruction of the parenchyma and recurrent pneumothoraces. Clinical characteristics of lymphangioleiomyomatosis patients were analyzed to determine the relationship of pneumothoraces to disease progression. Patients were genotyped for polymorphisms in genes of extracellular matrix proteins collagen, elastin, and matrix metalloproteinase-1 to assess their association with pneumothoraces. Clinical data and polymorphisms in the genes for types I and III collagen, elastin, and matrix metalloproteinase-1 were compared with the prevalence of pneumothorax. Of 227 patients, 57% reported having had at least one pneumothorax. Cyst size on high-resolution computed tomography scans was associated with pneumothorax; patients with a history of pneumothorax were more likely to have larger cysts than patients who had no pneumothoraces. In patients with mild disease, those with a history of pneumothorax had a faster rate of decline in forced expiratory volume in 1 s (FEV(1); P = 0.001, adjusted for age) than those without. Genotype frequencies differed between patients with and without pneumothorax for polymorphisms in the types I and III collagen and matrix metalloproteinase-1 genes. Larger cysts may predispose lymphangioleiomyomatosis patients to pneumothorax, which, in early stages of disease, correlates with a more rapid rate of decline in FEV(1). Polymorphisms in types I and III collagen and matrix metalloproteinase-1 genes may cause differences in lung extracellular matrix that result in greater susceptibility to pneumothorax.

Model-based linkage analyses confirm chromosome 19q13.3 as a susceptibility locus for intracranial aneurysm

BACKGROUND AND PURPOSE

In previous studies of familial intracranial aneurysm (IA), parametric linkage analyses have been undertaken for five unrelated families, four providing maximum logarithm of odds (LOD) scores with dominant models and one with a recessive model. Each family was linked to a distinct locus, indicating locus heterogeneity. This study aimed to examine whether Japanese IA families consistent with autosomal-dominant mode of inheritance support linkage to these loci.

METHODS

We performed genomewide linkage analysis using the GENEHUNTER program. Affected-only parametric linkage analysis was used for 41 affected members in nine unrelated IA families with dominant models, which were selected from 29 families used for a nonparametric (model-free) linkage analysis in our previous study.

RESULTS

We failed to support the linkage to previously reported autosomal-dominant loci. Instead, we found linkage to chromosome 19q13.3 with a maximum multipoint LOD score of 4.10. The LOD-1 interval (regions with LOD scores of >1) was 8.0 cM between D19S198 and D19S902.

CONCLUSIONS

A genomewide scan for IA families with dominant models in Japan confirmed the locus at chromosome 19q13.3, which has also been reported as a candidate locus in a Finnish population.

Chondroitin sulfate proteoglycan 2 (CSPG2) gene polymorphisms rs173686 and rs251124 are not associated with intracranial aneurysms in Chinese Han nationality

BACKGROUND

There is evidence suggesting that genetic variants in the chondroitin sulfate proteoglycan2 (CSPG2, also known as versican) gene are involved in the pathogenesis of intracranial aneurysms (IAs). Some authors have demonstrated that single nucleotide polymorphisms (SNPs) rs173686 and rs251124 in the promoter region of the CSPG2 gene are associated with IAs. We performed a case-control study to investigate whether these SNPs might affect the development of IAs in Chinese Han nationality.

METHODS

The study group comprised 240 Chinese Han nationality patients with at least one intracranial aneurysm and 240 healthy Han nationality controls. Genomic DNA was isolated from blood leukocytes. The SNPs rs173686 and rs251124 were genotyped by PCR amplification and DNA sequencing. Differences in genotype and allele frequencies between patients and controls were tested by the chi-square method.

RESULTS

Genotype and allele frequencies of the SNPs rs173686 and rs251124 were both demonstrated to be in Hardy-Weinberg equilibrium. No significant difference in genotype or allele frequencies between case and control groups was detected at either of the two SNPs.

CONCLUSIONS

The data do not support the hypothesis that the two SNPs (rs173686 and rs251124) in the promoter region of the CSPG2 gene influence the development of intracranial aneurysms in Chinese Han nationality.

Preventive neurosurgery: population-wide check-up examinations and correction of asymptomatic pathologies of the nervous system

BACKGROUND

Prevention in healthcare is attracting more and more attention. Early identification and correction of anomalies harbouring the risk of a catastrophic event such as aneurysms is the principal rationale for brain check-up programmes. The other aim of preventive screening is to identify progressive lesions with little reversibility such as gliomas. The purpose of the current analysis is to review the frequency of the various incidental findings, the inherent risk and the therapeutic options. RATIONALE FOR CHECK-UP IMAGING AND PREVENTIVE TREATMENT: The average prevalence of asymptomatic intracranial benign tumours, aneurysms and carotid stenoses must be estimated as approximately 1% each. Meningiomas, aneurysms and carotid stenosis become more frequent with increasing age. Mainly vascular anomalies harbour a risk of a catastrophic event, i.e. carotid stenosis and intracranial aneurysms. Only gliomas potentially lose reversibility with time passing. The case of glioma appears to be lost since asymptomatic gliomas are extremely rarely identified on screening examinations, and on the other hand current treatment series do not support that infiltrating gliomas can be cured if only treated early enough. Treatment of the benign tumours, hydrocephalus and arachnoid cysts in the asymptomatic stage does not appear to provide any benefit. RATIONALE FOR GENETIC SCREENING: A number of intracranial tumours, vascular anomalies and degenerative changes are genetically determined. Examples are neurofibromatosis, tuberous sclerosis, von Hippel-Lindau disease and Rendu-Osler's disease. Although familial clustering of aneurysms is well known, the exact genetic anomaly is unknown and probably several genes play a role. Because of the variable penetrance of the inherited disorders with known genetic alterations, screening of affected families is recommended. The conditions are too rare to justify screening of the entire population. Apolipoprotein E genotype is the only accepted predictor of dementia. Routine screening APOE may be considered today, but is highly problematic due to the lack of clear consequences and the potentially negative psychological impact.

COSTS

Implementation of population-wide screening programmes and preventive measures would lead to a substantial additional financial burden. Brain-check-up programmes cannot be considered in isolation. Cardiovascular and oncological programmes would also have to be included from that point of view.

CONCLUSIONS

Population-wide screening with regard to intracranial aneurysms or carotid stenosis with non-invasive imaging techniques and preventive surgery/endovascular therapy can be justified, provided that treatment-associated morbidity is very low. There is no evidence for the rationale of screening for asymptomatic intracranial tumours, cysts or hydrocephalus. Genetic screening cannot be generally recommended, except among families affected by inherited conditions.

Association of a polymorphism of the ACVRL1 gene with sporadic arteriovenous malformations of the central nervous system

OBJECT

Important central nervous system (CNS) manifestations in patients with hereditary hemorrhagic telangiectasia (HHT) include arteriovenous malformations (AVMs) and dural arteriovenous fistulas (DAVFs). Hereditary hemorrhagic telangiectasia is caused by germline mutations of two genes: ENG (HHT Type 1) and ACVRL1 (HHT Type 2). The ENG gene variations have been associated with the formation of intracranial aneurysms. The authors studied whether sequence variations in ACVRL1 or ENG are associated with the development of clinically sporadic arteriovenous dysplasias and aneurysms of the CNS.

METHODS

The coding sequence (in 44 patients with AVMs and 27 with aneurysms) and the 5' end and the polyA site (in 53 patients with AVMs) of the ACVRL1 gene were analyzed for sequence variations using direct sequencing and single-strand conformational polymorphism analysis. One ENG and three ACVRL1 gene polymorphisms were genotyped using restriction enzyme-based analysis in 101 patients with sporadic AVMs and DAVFs of the CNS, 79 patients treated for intracranial aneurysms, and 202 control volunteers. The authors identified a statistically significant association between the IVS3 -35A/T polymorphism in intron 3 of the ACVRL1 gene and the development of AVMs and DAVFs (p = 0.004; odds ratio [OR] 1.73; 95% confidence interval [CI] 1.19-2.51; after adjustments for age and sex), but not aneurysms (crude OR 0.82; 95% CI 0.55-1.18).

CONCLUSIONS

The results of this study link ACVRL1 (HHT Type 2 gene) to the formation of the clinically sporadic variants of vascular malformations of the CNS most commonly seen in patients with HHT, that is, AVMs and DAVFs.

The genetics of intracranial aneurysms

The rupture of an intracranial aneurysm (IA) leads to a subarachnoid hemorrhage, a sudden onset disease that can lead to severe disability and death. Several risk factors such as smoking, hypertension and excessive alcohol intake are associated with subarachnoid hemorrhage. IAs, ruptured or unruptured, can be treated either surgically via a craniotomy (through an opening in the skull) or endovascularly by placing coils through a catheter in the femoral artery. Even though the etiology of IA formation is mostly unknown, several studies support a certain role of genetic factors. In reports so far, genome-wide linkage studies suggest several susceptibility loci that may contain one or more predisposing genes. Studies of several candidate genes report association with IAs. To date, no single gene has been identified as responsible for IA formation or rupture. The identification of susceptible genes may lead to the understanding of the mechanism of formation and rupture and possibly lead to the development of a pharmacological therapy.

Association Analysis of Common Variants of ELN, NOS2A, APOE and ACE2 to Intracranial Aneurysm

Background and Purpose— Previous studies have shown positive evidence of linkage of the intracranial aneurysm (IA) at chromosome 7q11, 17cen, 19q13, and Xp22. These regions contain elastin ( ELN ), nitric oxide synthetase 2A ( NOS2A ), apolipoprotein E ( APOE ), and angiotensin-I converting enzyme 2 ( ACE2 ), which are considered to be promising candidate genes for IA. We aimed to examine the association of single-nucleotide polymorphisms (SNPs) with IA in these candidate genes.

Methods— To identify polymorphisms in NOS2A and ACE2 , all exons and exon-intron boundaries were screened by direct sequencing in 30 randomly selected controls. The program tagSNPs was used to select an optimal set of haplotype-tagging SNPs. For ELN and APOE , SNPs were selected from previous reports. These selected SNPs were then genotyped in 362 cases with IA and 332 residential area matched controls. THESIAS software was used to investigate the association of alleles and haplotypes with IA by adjusting with covariates.

Results— We genotyped 8 SNPs in ELN , 8 SNPs in NOS2A , 3 ε alleles in APOE and 1 SNP in ACE2 . No alleles or haplotypes of 4 candidate genes revealed any significant association with IA.

Conclusions— Investigated polymorphisms in this study were not associated with IA.

A haplotype spanning two genes, ELN and LIMK1, decreases their transcripts and confers susceptibility to intracranial aneurysms

The rupture of an intracranial aneurysm (IA) results in subarachnoid hemorrhage, a catastrophic neurological condition with high morbidity and mortality. Following-up on our previous genome-wide linkage study in Japanese population, we extensively analyzed a 4.6 Mb linkage region around D7S2472 on 7q11 by genotyping 168 single nucleotide polymorphisms (SNPs). SNP association and window scan haplotype-based association studies revealed a susceptibility locus for IA on a single LD block covering the 3'-untranslated region (3'-UTR) of ELN and the entire region of LIMK1. An association study with 404 IA patients and 458 non-IA controls revealed that the ELN 3'-UTR G(+659)C SNP has the strongest association to IA (P=0.000002) and constitutes a tag-SNP for an at-risk haplotype, which contains two functional SNPs, the ELN 3'-UTR (+502) A insertion and the LIMK1 promoter C(-187)T SNP. These allelic and haplotype-based associations were confirmed in a Korean population. Ex vivo and in vitro analyses demonstrate that the functional impact of both SNPs is the decrease of transcript levels, either through accelerated ELN mRNA degradation or through decreased LIMK1 promoter activity. Elastin and LIMK1 protein are involved in the same actin depolymerization signaling pathway; therefore, these lines of evidence suggest a combined effect of the SNPs in the at-risk haplotype possibly by weakening the vascular wall and promoting the development of IA.

Size and location of ruptured and unruptured intracranial aneurysms measured by 3-dimensional rotational angiography

OBJECTIVE

The aim of the study was to report about accurate size and location of a consecutive series of ruptured and unruptured aneurysms taking the complex 3-dimensional (3D) anatomy and parent vessel morphology into consideration by using the newly developed 3D rotational angiography (3D-RA).

METHODS

One hundred eighteen consecutive patients with 155 saccular intracranial aneurysms were included in the study and received 3D-RA reconstructions for measurement of maximal height and width of the aneurysmal sac. Statistical evaluation compared values for ruptured (n = 83) and unruptured (n = 72) aneurysms.

RESULTS

Mean height and width of unruptured aneurysms were 5.7 and 5.7 mm; of ruptured aneurysms, 6.7 and 6.1 mm (not significant, P = .7 for height and P = .9 for width). The majority of ruptured aneurysms, 81.9% and 59%, were smaller than 10 and 7 mm; likewise, 81.9% and 68.1% of unruptured aneurysms were smaller than 10 and 7 mm. The difference in frequency of small (<10/<7 mm) aneurysms between unruptured and ruptured aneurysms was not significant (P = 1.0 and .32, respectively). The majority (69.4%) of small ruptured aneurysms (<7 mm) were located in the anterior circulation. Most ruptured aneurysms were in the size group 4 to 6 mm in height and 2 to 4 mm in width, and a critical threshold size for aneurysm rupture could not be identified.

CONCLUSIONS

An automated calibration procedure applied to all images and excellent visualization of aneurysm and parent vessel morphology using 3D-RA allow accurate size measurement of intracranial aneurysms which may be smaller than previously thought. Small aneurysm (<7 mm), also in the anterior circulation, should be carefully evaluated for treatment.

Examination of ELN as a Candidate Gene in the Utah Intracranial Aneurysm Pedigrees

Background and Purpose— A study of intracranial aneurysm (IA) sibpairs suggested association of an ELN haplotype with IA risk. Subsequent linkage analysis of the ELN region on chromosome 7q11 in high-risk Utah IA pedigrees significantly confirmed linkage between IA and the ELN region.

Methods— We have investigated the ELN gene as a potential candidate gene for IA in Utah pedigrees. One IA case from each pedigree, who shared an ELN region haplotype segregating in the pedigree, was screened for mutation. The promoter region, 34 exons, and the 3′UTR (UnTranslated Region) of the ELN gene were screened for variants using DHPLC.

Results— Variants were observed in the promoter region, exons 4 and 6, and the 3′UTR. Variants in exon 6 and in one 3′UTR position were unique to Utah. The remaining variants were absent in the controls. There was no evidence for segregation of the ELN variants found in IA cases with the hypothesized chromosome 7 haplotypes segregating in pedigrees.

Conclusion— Our analysis does not support ELN as the gene responsible for familial IA in the linked Utah IA pedigrees.

The Familial Intracranial Aneurysm (FIA) study protocol

Background

Subarachnoid hemorrhage (SAH) due to ruptured intracranial aneurysms (IAs) occurs in about 20,000 people per year in the U.S. annually and nearly half of the affected persons are dead within the first 30 days. Survivors of ruptured IAs are often left with substantial disability. Thus, primary prevention of aneurysm formation and rupture is of paramount importance. Prior studies indicate that genetic factors are important in the formation and rupture of IAs. The long-term goal of the Familial Intracranial Aneurysm (FIA) Study is to identify genes that underlie the development and rupture of intracranial aneurysms (IA).

Methods/Design

The FIA Study includes 26 clinical centers which have extensive experience in the clinical management and imaging of intracerebral aneurysms. 475 families with affected sib pairs or with multiple affected relatives will be enrolled through retrospective and prospective screening of potential subjects with an IA. After giving informed consent, the proband or their spokesperson invites other family members to participate. Each participant is interviewed using a standardized questionnaire which covers medical history, social history and demographic information. In addition blood is drawn from each participant for DNA isolation and immortalization of lymphocytes. High- risk family members without a previously diagnosed IA undergo magnetic resonance angiography (MRA) to identify asymptomatic unruptured aneurysms. A 10 cM genome screen will be performed to identify FIA susceptibility loci. Due to the significant mortality of affected individuals, novel approaches are employed to reconstruct the genotype of critical deceased individuals. These include the intensive recruitment of the spouse and children of deceased, affected individuals.

Discussion

A successful, adequately-powered genetic linkage study of IA is challenging given the very high, early mortality of ruptured IA. Design features in the FIA Study that address this challenge include recruitment at a large number of highly active clinical centers, comprehensive screening and recruitment techniques, non-invasive vascular imaging of high-risk subjects, genome reconstruction of dead affected individuals using marker data from closely related family members, and inclusion of environmental covariates in the statistical analysis.

Mapping a Mendelian form of intracranial aneurysm to 1p34.3-p36.13

The identification of pathways that underlie common disease has been greatly impacted by the study of rare families that segregate single genes with large effect. Intracranial aneurysm is a common neurological problem; the rupture of these aneurysms constitutes a frequently catastrophic neurologic event. The pathogenesis of these aneurysms is largely unknown, although genetic and environmental factors are believed to play a role. Previous genomewide studies in affected relative pairs have suggested linkage to several loci, but underlying genes have not been identified. We have identified a large kindred that segregates nonsyndromic intracranial aneurysm as a dominant trait with high penetrance. Genomewide analysis of linkage was performed using a two-stage approach: an analysis of ~10,000 single-nucleotide polymorphisms in the 6 living affected subjects, followed by the genotyping of simple tandem repeats across resulting candidate intervals in all 23 kindred members. Analysis revealed significant linkage to a single locus, with a LOD score of 4.2 at 1p34.3-p36.13 under a dominant model with high penetrance. These findings identify a Mendelian form of intracranial aneurysm and map the location of the underlying disease locus.

Mutations in the Lysyl Oxidase Gene Not Associated with Intracranial Aneurysm in Central European Families

BACKGROUND

Lysyl oxidase is a promising candidate gene for a mutation search in intracranial aneurysm families because (a) it controls the processing, cross-linking and maturation of collagen and elastin fibers in the blood vessel wall, (b) its expression levels and activity are altered in different animal models of aneurysm pathogenesis, and (c) it is encoded within the chromosome 5q22-31 region of suggestive linkage to intracranial aneurysms.

METHODS

We have performed genomic sequencing of all 7 exons including the intron-exon splice sites and of the putative promoter region for lysyl oxidase in 25 patients from intracranial aneurysm multiplex families resident in Central Europe.

RESULTS

We observed 4 genetic variants including 2 novel polymorphisms, 1 in the noncoding sequence of exon 7 and the other upstream from the lysyl oxidase promoter. None of these single nucleotide polymorphisms showed an allelic association or cosegregation with intracranial aneurysm in the families.

CONCLUSIONS

Genetic variants in the lysyl oxidase gene do not appear to be a major factor in the etiology of intracranial aneurysms in Central Europe.

Association of Polymorphisms and Haplotypes in the Elastin Gene in Dutch Patients With Sporadic Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

A locus containing the elastin gene has been linked to familial intracranial aneurysms in 2 distinct populations. We investigated the association of single-nucleotide polymorphisms (SNPs) and haplotypes of SNPs in the elastin gene with the occurrence of subarachnoid hemorrhage (SAH) from sporadic aneurysms in the Netherlands.

METHODS

We genotyped 167 SAH patients and 167 matching controls for 18 exonic and intronic SNPs in the elastin gene. A Bonferroni correction was applied for multiple comparisons with all novel associations, with a correction factor derived from the number of SNPs tested (P value after Bonferroni correction [P(corr)]).

RESULTS

SAH was statistically significant associated with an SNP in exon 22 of the elastin gene (minor allele frequency was 0.000 in patients and 0.028 in controls; odds ratio [OR], 0.0; 95% CI, 0.0 to 0.7; P=0.004; P(corr)=0.05) and possibly with an SNP in intron 5 (minor allele frequency was 0.062 in patients and 0.128 in controls; OR, 0.5; 95% CI, 0.2 to 0.8; P=0.007; P(corr)=0.08). Haplotypes of intron 5/exon 22 (P(corr)=0.002), intron 4/exon 22 (P(corr)=0.02), and intron 4/intron 5/exon 22 (P=9.0x10(-9)) were also associated with aneurysmal SAH.

CONCLUSIONS

Variants and haplotypes within the elastin gene are associated with the risk of sporadic SAH in Dutch patients. Gradual increase of statistical power with the inclusion of 2 or 3 SNPs in the studied haplotypes supports the validity of our conclusion that the elastin gene is a susceptibility locus for SAH.

Extended Single Nucleotide Polymorphism and Haplotype Analysis of the elastin Gene in Caucasians with Intracranial Aneurysms Provides Evidence for Racially/Ethnically Based Differences

BACKGROUND

There is growing evidence that genetic variants have an impact on the pathogenesis of intracranial aneurysm (IA). Recently, the genetic locus around the elastin gene (7q11) has been identified as linked to IA in a Japanese population. Our aim was to confirm these results in Caucasian populations.

METHODS

We conducted a case-control study in 120 Caucasian patients with IA and 172 controls to investigate 8 single nucleotide polymorphisms (SNPs) and various haplotypes within the elastin gene, which were frequently found and associated with the phenotype in the Japanese populations. Real-time PCR and melting curve analysis were used for the detection of genotypes.

RESULTS

Allele frequencies and genotypes were equally distributed between Caucasian cases and controls. We failed to identify haplotypes that are associated with the phenotype in our population, which is in contrast to the Japanese study. However, allele frequencies in control populations differ between Caucasians and Japanese.

CONCLUSIONS

We found no association between SNPs and haplotypes of the elastin gene and the occurrence of IA in our Caucasian populations. However, our data provide strong evidence for racial/ethnic differences in the association of SNP and specific haplotypes of the elastin gene with the phenotype. There might be other genetic variants of the elastin gene associated with IA in Caucasians.

Confirmation of chromosome 7q11 locus for predisposition to intracranial aneurysm

A significant linkage of intracranial aneurysm (IA) has recently been reported to chromosomal region 7q11 (MLS=3.22) in a genomic search of 85 Japanese nuclear families with at least two affected siblings (104 sib pairs). This region contains the elastin gene (ELN, OMIM 130160), which is a functional candidate gene for IA. We have replicated this finding through linkage analyses in 13 extended pedigrees from Utah, comprising 39 IA cases. We genotyped three markers flanking ELN and performed two-point and multipoint parametric analyses, employing simple dominant and recessive models. Analyses utilizing a recessive affecteds-only model yielded significant confirmation of linkage to the region (best evidence, multipoint TLOD=2.34, at D7S2421, corrected P=0.001). This study is the first to confirm the linkage of the 7q11 locus for IA.