Genome scan for familial abdominal aortic aneurysm using sex and family history as covariates suggests genetic heterogeneity and identifies linkage to chromosome 19q13

Extravascular administration of IGF1R antagonists protects against aortic aneurysm in rodent and porcine models

An abdominal aortic aneurysm (AAA) is a life-threatening cardiovascular disease. We identified plasma insulin-like growth factor 1 (IGF1) as an independent risk factor in patients with AAA by correlating plasma IGF1 with risk. Smooth muscle cell- or fibroblast-specific knockout of Igf1r, the gene encoding the IGF1 receptor (IGF1R), attenuated AAA formation in two mouse models of AAA induced by angiotensin II infusion or CaCl2 treatment. IGF1R was activated in aortic aneurysm samples from human patients and mice with AAA. Systemic administration of IGF1C, a peptide fragment of IGF1, 2 weeks after disease development inhibited AAA progression in mice. Decreased AAA formation was linked to competitive inhibition of IGF1 binding to its receptor by IGF1C and modulation of downstream alpha serine/threonine protein kinase (AKT)/mammalian target of rapamycin signaling. Localized application of an IGF1C-loaded hydrogel was developed to reduce the side effects observed after systemic administration of IGF1C or IGF1R antagonists in the CaCl2-induced AAA mouse model. The inhibitory effect of the IGF1C-loaded hydrogel administered at disease onset on AAA formation was further evaluated in a guinea pig-to-rat xenograft model and in a sheep-to-minipig xenograft model of AAA formation. The therapeutic efficacy of IGF1C for treating AAA was tested through extravascular delivery in the sheep-to-minipig model with AAA established for 2 weeks. Percutaneous injection of the IGF1C-loaded hydrogel around the AAA resulted in improved vessel flow dynamics in the minipig aorta. These findings suggest that extravascular administration of IGF1R antagonists may have translational potential for treating AAA.

Proteomics Analysis of Genetic Liability of Abdominal Aortic Aneurysm Identifies Plasma Neogenin and Kit Ligand: The ARIC Study

BACKGROUND

Genome-wide association studies have reported 23 gene loci related to abdominal aortic aneurysm (AAA)-a potentially lethal condition characterized by a weakened dilated vessel wall. This study aimed to identify proteomic signatures and pathways related to these risk loci to better characterize AAA genetic susceptibility.

METHODS

Plasma concentrations of 4870 proteins were determined using a DNA aptamer-based array. Linear regression analysis estimated the associations between the 23 risk alleles and plasma protein levels with adjustments for potential confounders in a race-stratified analysis of 1671 Black and 7241 White participants. Significant proteins were then evaluated for their prediction of clinical AAA (454 AAA events in 11 064 individuals), and those significantly associated with AAA were further interrogated using Mendelian randomization analysis.

RESULTS

Risk variants proximal to PSRC1-CELSR2-SORT1, PCIF1-ZNF335-MMP9, RP11-136O12.2/TRIB1, ZNF259/APOA5, IL6R, PCSK9, LPA, and APOE were associated with 118 plasma proteins in Whites and 59 were replicated in Black participants. Novel associations with clinical AAA incidence were observed for kit ligand (HR, 0.59 [95% CI, 0.42-0.82] for top versus first quintiles) and neogenin (HR, 0.64 [95% CI, 0.46-0.88]) over a median 21.2-year follow-up; neogenin was also associated with ultrasound-detected asymptomatic AAA (N=4295; 57 asymptomatic AAA cases). Mendelian randomization inverse variance weighted estimates suggested that AAA risk is promoted by lower levels of kit ligand (OR per SD=0.67; P=1.4×10-5) and neogenin (OR per SD=0.50; P=0.03).

CONCLUSIONS

Low levels of neogenin and kit ligand may be novel risk factors for AAA development in potentially causal pathways. These findings provide insights and potential targets to reduce AAA susceptibility.

Cromolyn prevents cerebral vasospasm and dementia by targeting WDR43

Background

Cerebral vasospasm (CV) can cause inflammation and damage to neuronal cells in the elderly, leading to dementia.

Purpose

This study aimed to investigate the genetic mechanisms underlying dementia caused by CV in the elderly, identify preventive and therapeutic drugs, and evaluate their efficacy in treating neurodegenerative diseases.

Methods

Genes associated with subarachnoid hemorrhage and CV were acquired and screened for differentially expressed miRNAs (DEmiRNAs) associated with aneurysm rupture. A regulatory network of DEmiRNAs and mRNAs was constructed, and virtual screening was performed to evaluate possible binding patterns between Food and Drug Administration (FDA)-approved drugs and core proteins. Molecular dynamics simulations were performed on the optimal docked complexes. Optimally docked drugs were evaluated for efficacy in the treatment of neurodegenerative diseases through cellular experiments.

Results

The study found upregulated genes (including WDR43 and THBS1) and one downregulated gene associated with aneurysm rupture. Differences in the expression of these genes indicate greater disease risk. DEmiRNAs associated with ruptured aortic aneurysm were identified, of which two could bind to THBS1 and WDR43. Cromolyn and lanoxin formed the best docking complexes with WDR43 and THBS1, respectively. Cellular experiments showed that cromolyn improved BV2 cell viability and enhanced Aβ42 uptake, suggesting its potential as a therapeutic agent for inflammation-related disorders.

Conclusion

The findings suggest that WDR43 and THBS1 are potential targets for preventing and treating CV-induced dementia in the elderly. Cromolyn may have therapeutic value in the treatment of Alzheimer's disease and dementia.

Abdominal Aortic Aneurysm Formation with a Focus on Vascular Smooth Muscle Cells

Abdominal aortic aneurysm (AAA) is a lethal degenerative vascular disease that affects, mostly, the elder population, with a high mortality rate (>80%) upon rupture. It features a dilation of the aortic diameter to larger than 30 mm or more than 50%. Diverse pathological processes are involved in the development of AAA, including aortic wall inflammation, elastin breakdown, oxidative stress, smooth muscle cell (SMC) phenotypic switching and dysfunction, and extracellular matrix degradation. With open surgery being the only therapeutic option up to date, the lack of pharmaceutical treatment approach calls for identifying novel and effective targets and further understanding the pathological process of AAA. Both lifestyle and genetic predisposition have an important role in increasing the risk of AAA. Several cell types are closely related to the pathogenesis of AAA. Among them, vascular SMCs (VSMCs) are gaining much attention as a critical contributor for AAA initiation and/or progression. In this review, we summarize what is known about AAA, including the risk factors, the pathophysiology, and the established animal models of AAA. In particular, we focus on the VSMC phenotypic switching and dysfunction in AAA formation. Further understanding the regulation of VSMC phenotypic changes may provide novel therapeutic targets for the treatment or prevention of AAA.

Vascular Smooth Muscle Cells in Aortic Aneurysm: From Genetics to Mechanisms

Aortic aneurysm, including thoracic aortic aneurysm and abdominal aortic aneurysm, is the second most prevalent aortic disease following atherosclerosis, representing the ninth-leading cause of death globally. Open surgery and endovascular procedures are the major treatments for aortic aneurysm. Typically, thoracic aortic aneurysm has a more robust genetic background than abdominal aortic aneurysm. Abdominal aortic aneurysm shares many features with thoracic aortic aneurysm, including loss of vascular smooth muscle cells (VSMCs), extracellular matrix degradation and inflammation. Although there are limitations to perfectly recapitulating all features of human aortic aneurysm, experimental models provide valuable tools to understand the molecular mechanisms and test novel therapies before human clinical trials. Among the cell types involved in aortic aneurysm development, VSMC dysfunction correlates with loss of aortic wall structural integrity. Here, we discuss the role of VSMCs in aortic aneurysm development. The loss of VSMCs, VSMC phenotypic switching, secretion of inflammatory cytokines, increased matrix metalloproteinase activity, elevated reactive oxygen species, defective autophagy, and increased senescence contribute to aortic aneurysm development. Further studies on aortic aneurysm pathogenesis and elucidation of the underlying signaling pathways are necessary to identify more novel targets for treating this prevalent and clinical impactful disease.

Identification of novel genetic susceptibility loci for thoracic and abdominal aortic aneurysms via genome-wide association study using the UK Biobank Cohort

BACKGROUND

Thoracic aortic aneurysm (TAA) and abdominal aortic aneurysm (AAA) are known to have a strong genetic component.

METHODS AND RESULTS

In a genome-wide association study (GWAS) using the UK Biobank, we analyzed the genomes of 1,363 individuals with AAA compared to 27,260 age, ancestry, and sex-matched controls (1:20 case:control study design). A similar analysis was repeated for 435 individuals with TAA compared to 8,700 controls. Polymorphism with minor allele frequency (MAF) >0.5% were evaluated. We identified novel loci near LINC01021, ATOH8 and JAK2 genes that achieved genome-wide significance for AAA (p-value <5x10-8), in addition to three known loci. For TAA, three novel loci in CTNNA3, FRMD6 and MBP achieved genome-wide significance. There was no overlap in the genes associated with AAAs and TAAs. Additionally, we identified a linkage group of high-frequency variants (MAFs ~10%) encompassing FBN1, the causal gene for Marfan syndrome, which was associated with TAA. In FinnGen PheWeb, this FBN1 haplotype was associated with aortic dissection. Finally, we found that baseline bradycardia was associated with TAA, but not AAA.

CONCLUSIONS

Our GWAS found that AAA and TAA were associated with distinct sets of genes, suggesting distinct underlying genetic architecture. We also found association between baseline bradycardia and TAA. These findings, including JAK2 association, offer plausible mechanistic and therapeutic insights. We also found a common FBN1 linkage group that is associated with TAA and aortic dissection in patients who do not have Marfan syndrome. These FBN1 variants suggest shared pathophysiology between Marfan disease and sporadic TAA.

Pathophysiological Aspects of the Development of Abdominal Aortic Aneurysm with a Special Focus on Mitochondrial Dysfunction and Genetic Associations

Abdominal aortic aneurysm (AAA) is a complex degenerative vascular disease, with considerable morbidity and mortality rates among the elderly population. The mortality of AAA is related to aneurysm expansion (the enlargement of the aortic diameter up to 30 mm and above) and the subsequent rupture. The pathogenesis of AAA involves several biological processes, including aortic mural inflammation, oxidative stress, vascular smooth muscle cell apoptosis, elastin depletion, and degradation of the extracellular matrix. Mitochondrial dysfunction was also found to be associated with AAA formation. The evidence accumulated to date supports a close relationship between environmental and genetic factors in AAA initiation and progression. However, a comprehensive pathophysiological understanding of AAA formation remains incomplete. The open surgical repair of AAA is the only therapeutic option currently available, while a specific pharmacotherapy is still awaited. Therefore, there is a great need to clarify pathophysiological cellular and molecular mechanisms underlying AAA formation that would help to develop effective pharmacological therapies. In this review, pathophysiological aspects of AAA development with a special focus on mitochondrial dysfunction and genetic associations were discussed.

Kallikrein-1 Blockade Inhibits Aortic Expansion in a Mouse Model and Reduces Prostaglandin E2 Secretion From Human Aortic Aneurysm Explants

Background Abdominal aortic aneurysm (AAA) is an important cause of mortality in older adults. The kinin B2 receptor agonist, bradykinin, has been implicated in AAA pathogenesis through promoting inflammation. Bradykinin is generated from high- and low-molecular-weight kininogen by the serine protease kallikrein-1. The aims of this study were first to examine the effect of neutralizing kallikrein-1 on AAA development in a mouse model and second to test how blocking kallikrein-1 affected cyclooxygenase-2 and prostaglandin E₂ in human AAA explants. Methods and Results Neutralization of kallikrein-1 in apolipoprotein E-deficient (ApoE^-/-) mice via administration of a blocking antibody inhibited suprarenal aorta expansion in response to angiotensin (Ang) II infusion. Kallikrein-1 neutralization decreased suprarenal aorta concentrations of bradykinin and prostaglandin E₂ and reduced cyclooxygenase-2 activity. Kallikrein-1 neutralization also decreased protein kinase B and extracellular signal-regulated kinase 1/2 phosphorylation and reduced levels of active matrix metalloproteinase 2 and matrix metalloproteinase 9. Kallikrein-1 blocking antibody reduced levels of cyclooxygenase-2 and secretion of prostaglandin E₂ and active matrix metalloproteinase 2 and matrix metalloproteinase 9 from human AAA explants and vascular smooth muscle cells exposed to activated neutrophils. Conclusions These findings suggest that kallikrein-1 neutralization could be a treatment target for AAA.

Dilatation of Aortic Neck and Common Iliac Arteries after Open Repair of Abdominal Aortic Aneurysms: Long-Term Follow-Up According to Aortic Reconstruction Configuration

BACKGROUND

Several studies in the literature report continued proximal aorta and distal iliac artery dilatation after surgical correction of an abdominal aortic aneurysm (AAA). The purpose of this study is to evaluate these findings, in a South American population, and relate them to the type of configuration of the open procedure aortic reconstruction.

METHODS

This is a retrospective review of ultrasonographic follow-up of patients submitted to open repair of AAA from 1989 to 2013, reporting proximal aorta dilatation (≥3 cm) and distal iliac artery dilatation (≥1.5 cm).

RESULTS

A total of 155 patients were included. Life-table freedom at the intervals 11 < 15 years and ≥15 years were 47% and 23% for proximal dilatation and 63% and 38% for distal iliac arteries dilatation, respectively. There were more proximal and distal dilatations in patients submitted to more extensive aortic reconstructions (aorto-aortic 13% and 22% vs aorto-bilateral common iliacs 27% and 8% vs aorto-unilateral or bilateral external iliacs 27% and 32% and aorto-femoral 67% and 0%) P < 0.0001. Juxtarenal anastomosis was also correlated with more proximal dilatations (42% vs 21%, P = 0,046). There were two proximal and three distal anastomosis pseudoaneurysms.

CONCLUSIONS

The presence of more extensive degenerative disease at the time of operation, requiring juxtarenal or more distal iliac reconstructions, may pose an increased risk of proximal aorta and iliac artery dilatation during follow-up. This study corroborates that significant changes are found after 7 to 10 years of the operation, reinforcing the need for long-term monitoring.

Genetics of Thoracic and Abdominal Aortic Diseases

Dissections or ruptures of aortic aneurysms remain a leading cause of death in the developed world, with the majority of deaths being preventable if individuals at risk are identified and properly managed. Genetic variants predispose individuals to these aortic diseases. In the case of thoracic aortic aneurysm and dissections (thoracic aortic disease), genetic data can be used to identify some at-risk individuals and dictate management of the associated vascular disease. For abdominal aortic aneurysms, genetic associations have been identified, which provide insight on the molecular pathogenesis but cannot be used clinically yet to identify individuals at risk for abdominal aortic aneurysms. This compendium will discuss our current understanding of the genetic basis of thoracic aortic disease and abdominal aortic aneurysm disease. Although both diseases share several pathogenic similarities, including proteolytic elastic tissue degeneration and smooth muscle dysfunction, they also have several distinct differences, including population prevalence and modes of inheritance.

Type III collagen (COL3A1): Gene and protein structure, tissue distribution, and associated diseases

Collagen alpha-1(III) chain, also known as the alpha 1 chain of type III collagen, is a protein that in humans is encoded by the COL3A1 gene. Three alpha 1 chains are required to form the type III collagen molecule which has a long triple-helical domain. Type III collagen, an extracellular matrix protein, is synthesized by cells as a pre-procollagen. It is found as a major structural component in hollow organs such as large blood vessels, uterus and bowel. Other functions of type III collagen include interaction with platelets in the blood clotting cascade and it is also an important signaling molecule in wound healing. Mutations in the COL3A1 gene cause the vascular type of Ehlers-Danlos syndrome (vEDS; OMIM 130050). It is the most serious form of EDS, since patients often die suddenly due to a rupture of large arteries. Inactivation of the murine Col3a1 gene leads to a shorter life span in homozygous mutant mice. The mice die prematurely from a rupture of major arteries mimicking the human vEDS phenotype. The biochemical and cellular effects of COL3A1 mutations have been studied extensively. Most of the glycine mutations lead to the synthesis of type III collagen with reduced thermal stability, which is more susceptible for proteinases. Intracellular accumulation of this normally secreted protein is also found. Ultrastructural analyses have demonstrated dilated rough endoplasmic reticulum and changes in the diameter of collagen fibers. Other clinical conditions associated with type III collagen are several types of fibroses in which increased amounts of type III collagen accumulate in the target organs.

Abdominal aortic aneurysms

An abdominal aortic aneurysm (AAA) is a localized dilatation of the infrarenal aorta. AAA is a multifactorial disease, and genetic and environmental factors play a part; smoking, male sex and a positive family history are the most important risk factors, and AAA is most common in men >65 years of age. AAA results from changes in the aortic wall structure, including thinning of the media and adventitia due to the loss of vascular smooth muscle cells and degradation of the extracellular matrix. If the mechanical stress of the blood pressure acting on the wall exceeds the wall strength, the AAA ruptures, causing life-threatening intra-abdominal haemorrhage - the mortality for patients with ruptured AAA is 65-85%. Although AAAs of any size can rupture, the risk of rupture increases with diameter. Intact AAAs are typically asymptomatic, and in settings where screening programmes with ultrasonography are not implemented, most cases are diagnosed incidentally. Modern functional imaging techniques (PET, CT and MRI) may help to assess rupture risk. Elective repair of AAA with open surgery or endovascular aortic repair (EVAR) should be considered to prevent AAA rupture, although the morbidity and mortality associated with both techniques remain non-negligible.

Risk Factor Assessment in a Greek Cohort of Patients With Large Abdominal Aortic Aneurysms

Environmental and genetic risk factors contribute to the etiology of abdominal aortic aneurysms (AAAs). Matrix metalloproteinases (MMPs) have been associated with the pathophysiology of AAAs. A prospective, nonrandomized case-control study was undertaken to investigate the risk factors for large AAAs (≥5.5 cm) among 175 male Greek AAA patients and to compare the results with a cohort of 166 male controls free from any aortic dilatation, as confirmed by ultrasonography from an existing AAA screening program in the same region. We also assessed the potential association between 2 functional single nucleotide polymorphisms in the genes MMP9 (-1561C/T; rs3918242) and MMP13 (-77A/G; rs2252070), and the presence of large AAAs. Multiple logistic regression analysis revealed AAA family history ( P = .028), hypercholesterolemia ( P < .001), and current smoking ( P < .001) as AAA risk factors. Statistical difference was reached in genotype ( P = .047) and allele ( P = .037) frequencies for rs2252070, but the results did not remain significant after correction for multiple testing. No significant differences in genotype or allele frequencies for rs3918242 were detected. In summary, AAA family history, hypercholesterolemia, and current smoking were found to be risk factors for large AAAs.

Aetiology and management of hereditary aortopathy

Aortic aneurysms are a major health problem because they account for 1-2% of all deaths in the Western population. Although abdominal aortic aneurysms (AAAs) are more prevalent than thoracic aortic aneurysms (TAAs), TAAs have been more exhaustively studied over the past 2 decades because they have a higher heritability and affect younger individuals. Gene identification in both syndromic and nonsyndromic TAA is proceeding at a rapid pace and has already pinpointed >20 genes associated with familial TAA risk. Whereas these genes explain <30% of all cases of familial TAA, their functional characterization has substantially improved our knowledge of the underlying pathological mechanisms. As such, perturbed extracellular matrix homeostasis, transforming growth factor-β signalling, and vascular smooth muscle cell contractility have been proposed as important processes in TAA pathogenesis. These new insights enable novel treatment options that are currently being investigated in large clinical trials. Moreover, together with the advent of next-generation sequencing approaches, these genetic findings are promoting a shift in the management of patients with TAA by enabling gene-tailored interventions. In this Review, we comprehensively describe the molecular landscape of familial TAA, and we discuss whether familial TAA, from a biological point of view, can serve as a paradigm for the genetically more complex forms of the condition, such as sporadic TAA or AAA.

Risk factors associated with increased prevalence of abdominal aortic aneurysm in women

Background

Four randomized trials of men aged 65–80 years showed that aneurysm-related mortality was reduced by 40 per cent by ultrasound screening. Screening is considered economically viable when the prevalence of abdominal aortic aneurysm (AAA) is 1·0 per cent or higher. This is not the case for women, in whom the prevalence of AAA is less than 1 per cent. The aim of the present investigation was to determine the prevalence of AAA 3·0 cm or larger in women screened with ultrasound imaging, the risk factors associated with AAA in this population, and whether high-risk groups can be identified with an AAA prevalence of 1 per cent or greater.

Methods

Demographic data and risk factors were collected from the first 50 000 women who attended for private cardiovascular screening in the UK. Tests included ultrasound screening for AAA, ankle : brachial pressure index (ABPI), carotid duplex imaging for carotid atherosclerosis, and electrocardiography for atrial fibrillation.

Results

AAA was detected in 82 of 50 000 women screened; these aneurysms were rare below the age of 66 years (7 of 24 499). In the 66–85-years age group there were 72 AAAs in 25 170 women (0·29 per cent). Univariable analysis demonstrated that a history of stroke/transient ischaemic attack (TIA), hypertension, smoking, atrial fibrillation, ABPI of less than 0·9 and internal carotid artery stenosis of at least 50 per cent were associated with an increased prevalence of AAA (P &lt; 0·001). In multivariable linear logistic regression of risk factors, age 76 years or more, history of stroke/TIA, hypertension and smoking were independent predictors of AAA. This model had an area under the receiver operating characteristic (ROC) curve (AUC) of 0·711 (95 per cent c.i. 0·649 to 0·772) and could identify 2235 women who had 22 AAAs (prevalence 0·98 per cent). By adding ABPI, atrial fibrillation and carotid stenosis, the prediction improved to an AUC of 0·775 (0·724 to 0·826). This model could identify 3701 women who had 58 AAAs (prevalence 1·57 per cent).

Conclusion

This report should stimulate consideration of a targeted AAA screening programme for women aged over 65 years.

Understanding the pathogenesis of abdominal aortic aneurysms

An aortic aneurysm is a dilatation in which the aortic diameter is ≥3.0 cm. If left untreated, the aortic wall continues to weaken and becomes unable to withstand the forces of the luminal blood pressure resulting in progressive dilatation and rupture, a catastrophic event associated with a mortality of 50-80%. Smoking and positive family history are important risk factors for the development of abdominal aortic aneurysms (AAA). Several genetic risk factors have also been identified. On the histological level, visible hallmarks of AAA pathogenesis include inflammation, smooth muscle cell apoptosis, extracellular matrix degradation and oxidative stress. We expect that large genetic, genomic, epigenetic, proteomic and metabolomic studies will be undertaken by international consortia to identify additional risk factors and biomarkers, and to enhance our understanding of the pathobiology of AAA. Collaboration between different research groups will be important in overcoming the challenges to develop pharmacological treatments for AAA.

An update on the etiology of abdominal aortic aneurysms: implications for future diagnostic testing

Abdominal aortic aneurysm (AAA) disease is multifactorial with both environmental and genetic risk factors. The current research in AAA revolves around genetic profiles and expression studies in both human and animal models. Variants in genes involved in extracellular matrix degradation, inflammation, the renin-angiotensin system, cell growth and proliferation and lipid metabolism have been associated with AAA using a variety of study designs. However, the results have been inconsistent and without a standard animal model for validation. Thus, despite the growing body of knowledge, the specific variants responsible for AAA development, progression and rupture have yet to be determined. This review explores some of the more significant genetic studies to provide an overview of past studies that have influenced the current understanding of AAA etiology. Expanding our understanding of disease pathogenesis will inform research into novel diagnostics and therapeutics and ultimately to improve outcomes for patients with AAA.

Increased cardiovascular risk without generalized arterial dilating diathesis in persons who do not have abdominal aortic aneurysm but who are first-degree relatives of abdominal aortic aneurysm patients

There is a strong genetic predisposition towards abdominal aortic aneurysm (AAA), but it is unknown whether persons without AAA but with first-degree relatives who are AAA patients have a generalized dilating diathesis, defect arterial wall mechanics, or increased cardiovascular risk. The aim of the study was to investigate arterial diameters and wall mechanics at multiple arterial sites in these subjects and compare them with controls without a family history of AAA. This study included 118 first-degree relatives of patients with AAA and 66 controls (age: 40-80 years). The abdominal aorta, common carotid artery, common femoral artery, and popliteal artery were investigated by echo-tracking ultrasound. The relatives had no arterial dilatation, but they did tend to have smaller diameters than controls. Relatives had a higher heart rate, diastolic blood pressure, and mean arterial pressure than controls. The distensibility coefficient and the compliance coefficient were decreased in all arteries in male relatives, adjusted for age and smoking; these coefficients were normalized after adjustment for mean arterial pressure and heart rate. Female relatives had a lower compliance coefficient in the abdominal aorta, adjusted for age and smoking. After adjustment for mean arterial pressure and heart rate, the difference disappeared. No general arterial dilatation in relatives without AAA was found, supporting the hypothesis that the dilating diathesis is linked to the aneurysmal manifestation in the abdominal aorta. Although the threat of aneurysmal dilatation and rupture seems to be lacking in these subjects, heart rate, blood pressure, and arterial wall stiffness were all increased, which may indicate a higher risk of developing cardiovascular morbidity and mortality.

Cardiometabolic effects of genetic upregulation of the interleukin 1 receptor antagonist: a Mendelian randomisation analysis

BACKGROUND

To investigate potential cardiovascular and other effects of long-term pharmacological interleukin 1 (IL-1) inhibition, we studied genetic variants that produce inhibition of IL-1, a master regulator of inflammation.

METHODS

We created a genetic score combining the effects of alleles of two common variants (rs6743376 and rs1542176) that are located upstream of IL1RN, the gene encoding the IL-1 receptor antagonist (IL-1Ra; an endogenous inhibitor of both IL-1α and IL-1β); both alleles increase soluble IL-1Ra protein concentration. We compared effects on inflammation biomarkers of this genetic score with those of anakinra, the recombinant form of IL-1Ra, which has previously been studied in randomised trials of rheumatoid arthritis and other inflammatory disorders. In primary analyses, we investigated the score in relation to rheumatoid arthritis and four cardiometabolic diseases (type 2 diabetes, coronary heart disease, ischaemic stroke, and abdominal aortic aneurysm; 453,411 total participants). In exploratory analyses, we studied the relation of the score to many disease traits and to 24 other disorders of proposed relevance to IL-1 signalling (746,171 total participants).

FINDINGS

For each IL1RN minor allele inherited, serum concentrations of IL-1Ra increased by 0.22 SD (95% CI 0.18-0.25; 12.5%; p = 9.3 × 10(-33)), concentrations of interleukin 6 decreased by 0.02 SD (-0.04 to -0.01; -1.7%; p = 3.5 × 10(-3)), and concentrations of C-reactive protein decreased by 0.03 SD (-0.04 to -0.02; -3.4%; p = 7.7 × 10(-14)). We noted the effects of the genetic score on these inflammation biomarkers to be directionally concordant with those of anakinra. The allele count of the genetic score had roughly log-linear, dose-dependent associations with both IL-1Ra concentration and risk of coronary heart disease. For people who carried four IL-1Ra-raising alleles, the odds ratio for coronary heart disease was 1.15 (1.08-1.22; p = 1.8 × 10(-6)) compared with people who carried no IL-1Ra-raising alleles; the per-allele odds ratio for coronary heart disease was 1.03 (1.02-1.04; p = 3.9 × 10(-10)). Per-allele odds ratios were 0.97 (0.95-0.99; p = 9.9 × 10(-4)) for rheumatoid arthritis, 0.99 (0.97-1.01; p = 0.47) for type 2 diabetes, 1.00 (0.98-1.02; p = 0.92) for ischaemic stroke, and 1.08 (1.04-1.12; p = 1.8 × 10(-5)) for abdominal aortic aneurysm. In exploratory analyses, we observed per-allele increases in concentrations of proatherogenic lipids, including LDL-cholesterol, but no clear evidence of association for blood pressure, glycaemic traits, or any of the 24 other disorders studied. Modelling suggested that the observed increase in LDL-cholesterol could account for about a third of the association observed between the genetic score and increased coronary risk.

INTERPRETATION

Human genetic data suggest that long-term dual IL-1α/β inhibition could increase cardiovascular risk and, conversely, reduce the risk of development of rheumatoid arthritis. The cardiovascular risk might, in part, be mediated through an increase in proatherogenic lipid concentrations.

Update on abdominal aortic aneurysm research: from clinical to genetic studies

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta with a diameter of at least 3.0 cm. AAAs are often asymptomatic and are discovered as incidental findings in imaging studies or when the AAA ruptures leading to a medical emergency. AAAs are more common in males than females, in individuals of European ancestry, and in those over 65 years of age. Smoking is the most important environmental risk factor. In addition, a positive family history of AAA increases the person's risk for AAA. Interestingly, diabetes has been shown to be a protective factor for AAA in many large studies. Hallmarks of AAA pathogenesis include inflammation, vascular smooth muscle cell apoptosis, extracellular matrix degradation, and oxidative stress. Autoimmunity may also play a role in AAA development and progression. In this Outlook paper, we summarize our recent studies on AAA including clinical studies related to surgical repair of AAA and genetic risk factor and large-scale gene expression studies. We conclude with a discussion on our research projects using large data sets available through electronic medical records and biobanks.

Genetics of abdominal aortic aneurysm

PURPOSE OF REVIEW

Family history is a risk factor for abdominal aortic aneurysm (AAA), suggesting that genetic factors play an important role in AAA development, growth and rupture. Identification of these factors could improve understanding of the AAA pathogenesis and be useful to identify at risk individuals.

RECENT FINDINGS

Many approaches are used to examine genetic determinants of AAA, including genome-wide association studies (GWAS) and DNA linkage studies. Two recent GWAS have identified genetic markers associated with an increased risk of AAA located within the genes for DAB2 interacting protein (DAB2IP) and low density lipoprotein receptor-related protein 1 (LRP1). In addition, a marker on 9p21 associated with other vascular diseases is also strongly associated with AAA. The exact means by which these genes currently control AAA risk is not clear; however, in support of these findings, mice with vascular smooth muscle cell deficiency of Lrp1 are prone to aneurysm development. Further current work is concentrated on other molecular mechanisms relevant in AAA pathogenesis, including noncoding RNAs such as microRNAs.

SUMMARY

Current studies assessing genetic mechanisms for AAA have significant potential to identify novel mechanisms involved in AAA pathogenesis of high relevance to better clinical management of the disease.

Family history of aortic disease predicts disease patterns and progression and is a significant influence on management strategies for patients and their relatives

BACKGROUND

While a positive family history (FH) is a known risk factor for developing an aneurysm, its association with the extent of disease has not been established. We evaluated the influence of a FH of aortic disease with respect to the pattern and distribution of aortic aneurysms in a given patient.

METHODS AND RESULTS

From November 1999 to November 2011, 1263 patients were enrolled in physician-sponsored endovascular device trials to treat aortic aneurysms. Of the 555 patients who were alive and returning for follow-up, we obtained 426 (77%) family histories. Three-dimensional imaging studies were used to identify the presence of aneurysms; 36% (155/426) of patients had a FH of aortic aneurysms and 5% (21/155) had isolated intracranial aneurysms. A logistic regression model was used to compare aortic morphology between patients with a positive or negative FH for aneurysms. Patients with a positive FH of aortic aneurysms were younger at their initial aneurysm (63 vs 70 years; P < .0001), more frequently had proximal aortic involvement (root: odds ratio [OR], 5.4; P < .0001; ascending: OR, 2.9; P < .001; thoracic: OR, 2.2; P = .01) with over 50% of FH patients ultimately developing suprarenal aortic involvement (P = .0001) and had a greater incidence of bilateral iliac artery aneurysm (OR, 1.8; P = .03).

CONCLUSIONS

FH is an important tool that provides insight into the expected behavior of the untreated aorta and has significant implications for the development of treatment strategies. These findings should be used to guide patient's management with regard to treatment, follow-up paradigms, genetic testing, and screening of other family members.

A balanced translocation truncates Neurotrimin in a family with intracranial and thoracic aortic aneurysm

BACKGROUND

Balanced chromosomal rearrangements occasionally have strong phenotypic effects, which may be useful in understanding pathobiology. However, conventional strategies for characterising breakpoints are laborious and inaccurate. We present here a proband with a thoracic aortic aneurysm (TAA) and a balanced translocation t(10;11) (q23.2;q24.2). Our purpose was to sequence the chromosomal breaks in this family to reveal a novel candidate gene for aneurysm.

METHODS AND RESULTS

Intracranial aneurysm (IA) and TAAs appear to run in the family in an autosomal dominant manner: After exploring the family history, we observed that the proband's two siblings both died from cerebral haemorrhage, and the proband's parent and parent's sibling died from aortic rupture. After application of a genome-wide paired-end DNA sequencing method for breakpoint mapping, we demonstrate that this translocation breaks intron 1 of a splicing isoform of Neurotrimin at 11q25 in a previously implicated candidate region for IAs and AAs (OMIM 612161).

CONCLUSIONS

Our results demonstrate the feasibility of genome-wide paired-end sequencing for the characterisation of balanced rearrangements and identification of candidate genes in patients with potentially disease-associated chromosome rearrangements. The family samples were gathered as a part of our recently launched National Registry of Reciprocal Balanced Translocations and Inversions in Finland (n=2575), and we believe that such a registry will be a powerful resource for the localisation of chromosomal aberrations, which can bring insight into the aetiology of related phenotypes.

Reduced number and impaired function of circulating endothelial progenitor cells in patients with abdominal aortic aneurysm

AIM

Circulating endothelial progenitor cells (EPCs) are associated with coronary artery disease (CAD) and predict its outcome. Although the pathophysiology of abdominal aortic aneurysm (AAA) is different, it shares some risk factors with CAD. Therefore, the correlation between EPCs and AAA was investigated.

METHODS AND RESULTS

Seventy-eight subjects (age 77.2 ± 7.8 years) with suspected AAA were prospectively enrolled. Cut-off values (men, 3.5-5.5 cm; women, 3-5 cm) were used to define normal aorta, small AAA, and large AAA on thoraco-abdominal computer tomography. Endothelial function was measured by flow-mediated vasodilation (FMD). Flow cytometry and colony-forming units (CFUs) were used to evaluate circulating EPC numbers. Circulating EPCs were defined as mononuclear cells with low CD45 staining and double-positive staining for KDR, CD34, or CD133. Late out-growth EPCs were cultured from six patients with large AAAs and six age- and sex-matched controls to evaluate proliferation, adhesion, migration, tube formation, and senescence. FMD was significantly lower with large (5.26% ± 3.11%) and small AAAs (6.31% ± 3.66%) than in controls (8.88% ± 4.83%, P=0.008). Both CFUs (normal 38.39 ± 12.99, small AAA 21.22 ± 7.14, large AAA 6.98 ± 1.97; P=0.026) and circulating EPCs (CD34(+)/KDR(+) and CD133(+)/KDR(+)) were significantly fewer in AAA patients than in controls. On multivariate analysis, CFUs and circulating EPCs (CD34(+)/KDR(+)) were independently, inversely correlated to AAA diameter. Proliferation, adhesion, migration, tube formation, and senescence of late EPCs were significantly impaired in AAA patients.

CONCLUSION

The number and function of EPCs were impaired in AAA patients, suggesting their potential role in AAA.

Endothelial and smooth muscle cells from abdominal aortic aneurysm have increased oxidative stress and telomere attrition

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex multi-factorial disease with life-threatening complications. AAA is typically asymptomatic and its rupture is associated with high mortality rate. Both environmental and genetic risk factors are involved in AAA pathogenesis. Aim of this study was to investigate telomere length (TL) and oxidative DNA damage in paired blood lymphocytes, aortic endothelial cells (EC), vascular smooth muscle cells (VSMC), and epidermal cells from patients with AAA in comparison with matched controls.

METHODS

TL was assessed using a modification of quantitative (Q)-FISH in combination with immunofluorescence for CD31 or α-smooth muscle actin to detect EC and VSMC, respectively. Oxidative DNA damage was investigated by immunofluorescence staining for 7, 8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG).

RESULTS AND CONCLUSIONS

Telomeres were found to be significantly shortened in EC, VSMC, keratinocytes and blood lymphocytes from AAA patients compared to matched controls. 8-oxo-dG immunoreactivity, indicative of oxidative DNA damage, was detected at higher levels in all of the above cell types from AAA patients compared to matched controls. Increased DNA double strand breaks were detected in AAA patients vs controls by nuclear staining for γ-H2AX histone. There was statistically significant inverse correlation between TL and accumulation of oxidative DNA damage in blood lymphocytes from AAA patients. This study shows for the first time that EC and VSMC from AAA have shortened telomeres and oxidative DNA damage. Similar findings were obtained with circulating lymphocytes and keratinocytes, indicating the systemic nature of the disease. Potential translational implications of these findings are discussed.

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.

Diagnosis and monitoring of abdominal aortic aneurysm: current status and future prospects

Abdominal aortic aneurysm (AAA) remains an important cause of morbidity and mortality in elderly men, and prevalence is predicted to increase in parallel with a global aging population. AAA is commonly asymptomatic, and in the absence of routine screening, diagnosis is usually incidental when imaging to assess unrelated medical complaints. In the absence of approved diagnostic and prognostic markers, AAAs are monitored conservatively via medical imaging until aortic diameter approaches 50-55 mm and surgical repair is performed. There is currently significant interest in identifying molecular markers of diagnostic and prognostic value for AAA. Here we outline the current guidelines for AAA management and discuss modern scientific techniques currently employed to identify improved diagnostic and prognostic markers.

Genomic DNA pooling strategy for next-generation sequencing-based rare variant discovery in abdominal aortic aneurysm regions of interest-challenges and limitations

The costs and efforts for sample preparation of hundreds of individuals, their genomic enrichment for regions of interest, and sufficient deep sequencing bring a significant burden to next-generation sequencing-based experiments. We investigated whether pooling of samples at the level of genomic DNA would be a more versatile strategy for lowering the costs and efforts for common disease-associated rare variant detection in candidate genes or associated loci in a substantial patient cohort. We performed a pilot experiment using five pools of 20 abdominal aortic aneurysm (AAA) patients that were enriched on separate microarrays for the reported 9p21.3 associated locus and 42 additional AAA candidate genes, and sequenced on the SOLiD platform. Here, we discuss challenges and limitations connected to this approach and show that the high number of novel variants detected per pool and allele frequency deviations to the usually highly false positive cut-off region for variant detection in non-pooled samples can be limiting factors for successful variant prioritization and confirmation. We conclude that barcode indexing of individual samples before pooling followed by a multiplexed enrichment strategy should be preferred for detection of rare genetic variants in larger sample sets rather than a genomic DNA pooling strategy.

Analysis of positional candidate genes in the AAA1 susceptibility locus for abdominal aortic aneurysms on chromosome 19

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex disorder with multiple genetic risk factors. Using affected relative pair linkage analysis, we previously identified an AAA susceptibility locus on chromosome 19q13. This locus has been designated as the AAA1 susceptibility locus in the Online Mendelian Inheritance in Man (OMIM) database.

METHODS

Nine candidate genes were selected from the AAA1 locus based on their function, as well as mRNA expression levels in the aorta. A sample of 394 cases and 419 controls was genotyped for 41 SNPs located in or around the selected nine candidate genes using the Illumina GoldenGate platform. Single marker and haplotype analyses were performed. Three genes (CEBPG, PEPD and CD22) were selected for DNA sequencing based on the association study results, and exonic regions were analyzed. Immunohistochemical staining of aortic tissue sections from AAA and control individuals was carried out for the CD22 and PEPD proteins with specific antibodies.

RESULTS

Several SNPs were nominally associated with AAA (p < 0.05). The SNPs with most significant p-values were located near the CCAAT enhancer binding protein (CEBPG), peptidase D (PEPD), and CD22. Haplotype analysis found a nominally associated 5-SNP haplotype in the CEBPG/PEPD locus, as well as a nominally associated 2-SNP haplotype in the CD22 locus. DNA sequencing of the coding regions revealed no variation in CEBPG. Seven sequence variants were identified in PEPD, including three not present in the NCBI SNP (dbSNP) database. Sequencing of all 14 exons of CD22 identified 20 sequence variants, five of which were in the coding region and six were in the 3'-untranslated region. Five variants were not present in dbSNP. Immunohistochemical staining for CD22 revealed protein expression in lymphocytes present in the aneurysmal aortic wall only and no detectable expression in control aorta. PEPD protein was expressed in fibroblasts and myofibroblasts in the media-adventitia border in both aneurysmal and non-aneurysmal tissue samples.

CONCLUSIONS

Association testing of the functional positional candidate genes on the AAA1 locus on chromosome 19q13 demonstrated nominal association in three genes. PEPD and CD22 were considered the most promising candidate genes for altering AAA risk, based on gene function, association evidence, gene expression, and protein expression.

Genes and abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a multifactorial disease with a strong genetic component. Since the first candidate gene studies were published 20 years ago, approximately 100 genetic association studies using single nucleotide polymorphisms (SNPs) in biologically relevant genes have been reported on AAA. These studies investigated SNPs in genes of the extracellular matrix, the cardiovascular system, the immune system, and signaling pathways. Very few studies were large enough to draw firm conclusions and very few results could be replicated in another sample set. The more recent unbiased approaches are family-based DNA linkage studies and genome-wide genetic association studies, which have the potential of identifying the genetic basis for AAA, only when appropriately powered and well-characterized large AAA cohorts are used. SNPs associated with AAA have already been identified in these large multicenter studies. One significant association was of a variant in a gene called contactin-3, which is located on chromosome 3p12.3. However, two follow-up studies could not replicate this association. Two other SNPs, which are located on chromosome 9p21 and 9q33, were replicated in other samples. The two genes with the strongest supporting evidence of contribution to the genetic risk for AAA are the CDKN2BAS gene, also known as ANRIL, which encodes an antisense ribonucleic acid that regulates expression of the cyclin-dependent kinase inhibitors CDKN2A and CDKN2B, and DAB2IP, which encodes an inhibitor of cell growth and survival. Functional studies are now needed to establish the mechanisms by which these genes contribute toward AAA pathogenesis.

Novel genetic mechanisms for aortic aneurysms

Aortic aneurysms occur in the thoracic and abdominal sections of the aorta and are a deadly late-age-at-onset disease with complex pathobiology. Currently, the number of published genome-wide analyses including microarray-based expression profiling, DNA linkage studies, and genetic association studies is still limited and it is difficult to make generalizations about the disease pathogenesis or genetic risk factors contributing to aortic aneurysms, but it appears that thoracic aortic aneurysms differ in many ways from abdominal aortic aneurysms. Characterization of diseases at the molecular level is likely to lead to more accurate diagnoses and the use of "genomic nosology" of disease. The biggest future challenge will be to translate the genomic information to the clinic and improve our understanding of the disease processes, help us to develop better diagnostic tools, and lead to the design of new ways to manage aortic aneurysms in the era of personalized medicine.

Genome-wide association study identifies a sequence variant within the DAB2IP gene conferring susceptibility to abdominal aortic aneurysm

We performed a genome-wide association study on 1,292 individuals with abdominal aortic aneurysms (AAAs) and 30,503 controls from Iceland and The Netherlands, with a follow-up of top markers in up to 3,267 individuals with AAAs and 7,451 controls. The A allele of rs7025486 on 9q33 was found to associate with AAA, with an odds ratio (OR) of 1.21 and P = 4.6 x 10(-10). In tests for association with other vascular diseases, we found that rs7025486[A] is associated with early onset myocardial infarction (OR = 1.18, P = 3.1 x 10(-5)), peripheral arterial disease (OR = 1.14, P = 3.9 x 10(-5)) and pulmonary embolism (OR = 1.20, P = 0.00030), but not with intracranial aneurysm or ischemic stroke. No association was observed between rs7025486[A] and common risk factors for arterial and venous diseases-that is, smoking, lipid levels, obesity, type 2 diabetes and hypertension. Rs7025486 is located within DAB2IP, which encodes an inhibitor of cell growth and survival.

Abdominal aortic aneurysm: a review of the genetic basis

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex disease with a largely unknown pathophysiological background and a strong genetic component. Various studies have tried to link specific genetic variants with AAA.

METHODS

Systematic review of the literature (1947-2009).

RESULTS

A total of 249 studies were identified, 89 of which were eventually deemed relevant to this review. Genetic variants (polymorphisms) in a wide variety of genes, most of which encode proteolytic enzymes and inflammatory molecules, have been associated with AAA development and progression.

CONCLUSION

The genetic basis of AAA remains unknown, and most results from ''candidate-gene'' association studies are contradictory. Further analyses in appropriately powered studies in large, phenotypically well-characterized populations, including genome-wide association studies, are necessary to elucidate the exact genetic contribution to the pathophysiology of AAA.

Atherosclerosis in abdominal aortic aneurysms: a causal event or a process running in parallel? The Tromsø study

OBJECTIVE

The pathogenesis of abdominal aortic aneurysm (AAA) formation is poorly understood. We investigated the relationship between carotid, femoral, and coronary atherosclerosis and abdominal aortic diameter, and whether atherosclerosis was a risk marker for AAA.

METHODS AND RESULTS

Ultrasound of the right carotid artery, the common femoral artery, and the abdominal aorta was performed in 6446 men and women from a general population. The burden of atherosclerosis was assessed as carotid total plaque area, common femoral lumen diameter, and self-reported coronary heart disease. An AAA was defined as maximal infrarenal aortic diameter > or =30 mm. No dose-response relationship was found between carotid atherosclerosis and abdominal aortic diameter <27 mm. However, significantly more atherosclerosis and coronary heart disease was found in aortic diameter > or =27 mm and in AAAs. The age- and sex-adjusted odds ratio (OR) (95% CI) for AAA in the top total plaque area quintile was 2.3 (1.5 to 3.4), as compared with subjects without plaques. The adjusted OR (95% CI) was 1.7 (1.1 to 2.6). No independent association was found between femoral lumen diameter and AAA.

CONCLUSIONS

The lack of a consistent dose-response relationship between atherosclerosis and abdominal aortic diameter suggests that atherosclerosis may not be a causal event in AAA but develops in parallel with or secondary to aneurismal dilatation.

Genetic and epigenetic mechanisms and their possible role in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease associated with significant cardiovascular morbidity and mortality. The pathogenesis of AAA is poorly defined, making targeting of new therapies problematic. Current evidence favours an interaction of multiple environmental and genetic factors in the initiation and progression of AAA. Epigenetics is the term used to define the properties of the genome that are not explained by the primary sequence, but are due to the modifications of DNA and/or associated proteins. Previous research indicates the association of gene specific promoter DNA hyper-methylation and global DNA hypo-methylation with atherosclerosis. Evidence also suggests an important role for epigenetic processes such as histone acetylation in cardiovascular diseases including atherosclerosis and restenosis. Altered DNA methylation or histone acetylation occur in inflammation, cellular proliferation and remodelling processes and therefore maybe relevant to the pathology of AAA. Important risk factors for AAA, including cigarette smoking, older age, male gender and hypertension, have been linked with epigenetic effects and thus could act in this way to promote AAA. In this review, we discuss the potential role of epigenetic mechanisms in AAA. Since epigenetic alterations are to some extent reversible, further study of this area may identify new treatment targets for AAA.

Association study of single nucleotide polymorphisms on chromosome 19q13 with abdominal aortic aneurysm

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex disorder in which environmental and genetic factors play a role in pathogenesis. Linkage to 2 adjacent loci on 19q13 in familiar AAA was previously demonstrated. We studied whether genetic variation within these regions predisposes to AAA.

METHODS

Common genetic variants in the described regions on 19q13 were analyzed using tag single nucleotide polymorphisms (SNPs) in a Dutch case-control population. Single nucleotide polymorphism genotyping was performed in a 2-stage approach.

RESULTS

In stage 1, 615 SNPs were genotyped in 376 AAA patients and 648 controls. In stage 2, 8 SNPs of stage 1 with a P value < .015 were genotyped in a second independent cohort of 360 cases and 376 controls. No differences in allele frequencies were observed.

CONCLUSION

Our findings suggest that there are no common AAA predisposing SNPs within the 19q13 loci. Hence, the genetic basis of familiar and sporadic AAA may differ.

The intracranial aneurysm susceptibility genes HSPG2 and CSPG2 are not associated with abdominal aortic aneurysm

BACKGROUND

A genetic variant on chromosome 9p21 associates with abdominal aortic aneurysm (AAA) and intracranial aneurysm (IA), indicating that despite the differences in pathology there are shared genetic risk factors. We investigated whether the IA susceptibility genes heparan sulfate proteoglycan 2 (HSPG2) and chondroitin sulfate proteoglycan 2 (CSPG2) associate with AAA as well.

METHODS

Using tag single nucleotide polymorphisms (SNPs), all common variants were analyzed in a Dutch AAA case-control population in a 2-stage genotyping approach. In stage 1, 12 tag SNPs in HSPG2 and 22 tag SNPs in CSPG2 were genotyped in 376 patients and 648 controls. Genotyping of significantly associated SNPs was replicated in a second independent cohort of 360 cases and 376 controls.

RESULTS

In stage 1, no HSPG2 SNPs and 1 CSPG2 SNP associated with AAA (rs2652106, P = .019). Association of this SNP was not replicated (P = .342).

CONCLUSIONS

Our findings demonstrate that, in contrast to IA, HSPG2 and CSPG2 do not associate with AAA.

Genome screen in familial intracranial aneurysm

Background

Individuals with 1st degree relatives harboring an intracranial aneurysm (IA) are at an increased risk of IA, suggesting genetic variation is an important risk factor.

Methods

Families with multiple members having ruptured or unruptured IA were recruited and all available medical records and imaging data were reviewed to classify possible IA subjects as definite, probable or possible IA or not a case. A 6 K SNP genome screen was performed in 333 families, representing the largest linkage study of IA reported to date. A 'narrow' (n = 705 definite IA cases) and 'broad' (n = 866 definite or probable IA) disease definition were used in multipoint model-free linkage analysis and parametric linkage analysis, maximizing disease parameters. Ordered subset analysis (OSA) was used to detect gene × smoking interaction.

Results

Model-free linkage analyses detected modest evidence of possible linkage (all LOD < 1.5). Parametric analyses yielded an unadjusted LOD score of 2.6 on chromosome 4q (162 cM) and 3.1 on chromosome 12p (50 cM). Significant evidence for a gene × smoking interaction was detected using both disease models on chromosome 7p (60 cM; p ≤ 0.01). Our study provides modest evidence of possible linkage to several chromosomes.

Conclusion

These data suggest it is unlikely that there is a single common variant with a strong effect in the majority of the IA families. Rather, it is likely that multiple genetic and environmental risk factors contribute to the susceptibility for intracranial aneurysms.