Familial abdominal aortic aneurysms

A prospective longitudinal study of risk factors for abdominal aortic aneurysm

The aim of this study was to identify risk factors for abdominal aortic aneurysm (AAA) from the largest Welsh screening cohort to date. Patients were recruited from 1993 (to 2015) as part of the South East Wales AAA screening programme through general practitioners. Demographic data and risk factors were collected by means of a self-report questionnaire. Statistical tests were performed to determine whether associations could be observed between AAA and potential risk factors. Odds ratios (OR) were also calculated for each of the risk factors identified. A total of 6879 patients were included in the study. Two hundred and seventy-five patients (4.0%) presented with AAA, of which 16% were female and 84% were male. Patients with AAA were older than the (no AAA) control group (p < 0.0001). The following risk factors were identified for AAA: family history of AAA (p < 0.0001); history of vascular surgery (p < 0.0001), cerebrovascular accident (p < 0.0001), coronary heart disease (p < 0.0001), diabetes (p < 0.0001), medication (p = 0.0018), claudication (p < 0.0001), smoking history (p = 0.0001) and chronic obstructive pulmonary disorder (p = 0.0007). AAA is associated with classical vascular risk factors, in addition to other less-well-documented risk factors including previous vascular surgery. These findings have practical implications with the potential to improve future clinical screening of patients in order to reduce AAA mortality.

Air pollutants, genetic susceptibility, and abdominal aortic aneurysm risk: a prospective study

BACKGROUND AND AIMS

Air pollutants are important contributors to cardiovascular diseases, but associations between long-term exposure to air pollutants and the risk of abdominal aortic aneurysm (AAA) are still unknown.

METHODS

This study was conducted using a sample of 449 463 participants from the UK Biobank. Hazard ratios and 95% confidence intervals for the risk of AAA incidence associated with long-term exposure to air pollutants were estimated using the Cox proportional hazards model with time-varying exposure measurements. Additionally, the cumulative incidence of AAA was calculated by using the Fine and Grey sub-distribution hazards regression model. Furthermore, this study investigated the combined effects and interactions between air pollutants exposure and genetic predisposition in relation to the risk of AAA onset.

RESULTS

Long-term exposure to particulate matter with an aerodynamic diameter <2.5 µm [PM2.5, 1.21 (1.16, 1.27)], particulate matter with an aerodynamic diameter <10 µm [PM10, 1.21 (1.16, 1.27)], nitrogen dioxide [NO2, 1.16 (1.11, 1.22)], and nitrogen oxides [NOx, 1.10 (1.05, 1.15)] was found to be associated with an elevated risk of AAA onset. The detrimental effects of air pollutants persisted even in participants with low-level exposure. For the joint associations, participants with both high levels of air pollutants exposure and high genetic risk had a higher risk of developing AAA compared with those with low concentrations of pollutants exposure and low genetic risk. The respective risk estimates for AAA incidence were 3.18 (2.46, 4.12) for PM2.5, 3.09 (2.39, 4.00) for PM10, 2.41 (1.86, 3.13) for NO2, and 2.01 (1.55, 2.61) for NOx.

CONCLUSIONS

In this study, long-term air pollutants exposure was associated with an increased risk of AAA incidence.

Comprehensive bioinformatics analysis revealed potential key genes and pathways underlying abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a permanent, asymptomatic segmental dilatation of the abdominal aorta, with a high mortality risk upon rupture. Identification of potential key genes and pathways may help to develop curative drugs for AAA. We conducted RNA-seq on abdominal aortic tissues from both AAA patients and normal individuals as a control group. Integrated bioinformatic analysis was subsequently performed to comprehensively reveal potential key genes and pathways. A total of 1148 differential expressed genes (DEGs) (631 up-regulated and 517 down-regulated) were identified in our study. Gene Ontology (GO) analysis revealed enrichment in terms related to extracellular matrix organization, while KEGG analysis indicated enrichment in hematopoietic cell lineage and ECM-receptor interaction. Protein-protein interaction (PPI) network analysis revealed several candidate key genes, and differential expression of 6 key genes (CXCL8, CCL2, PTGS2, SELL, CCR7, and CXCL1) was validated by Gene Expression Omnibus (GEO) datasets. Receiver operating characteristic curve (ROC) analysis demonstrated these genes' high discriminatory ability between AAA and normal tissues. Immunohistochemistry indicated that several key genes were highly expressed in AAA tissues. Single-cell RNA sequencing revealed differential distribution patterns of these identified key genes among various cell types. 26 potential drugs linked to our key genes were found through DGIdb. Overall, our study provides a comprehensive evaluation of potential key genes and pathways in AAA, which could pave the way for the development of curative pharmacological therapies.

Human abdominal aortic aneurysm (AAA): Evidence for an autoimmune antigen-driven disease

Abdominal aortic aneurism (AAA) is a complex immunological disease with a strong genetic component, and one of the ten leading causes of death of individuals 55-74 years old worldwide. Strong evidence has been accumulated suggesting that AAA is an autoimmune specific antigen-driven disease. Mononuclear cells infiltrating AAA lesions comprised of T and B lymphocytes and other cells expressing early-, intermediate- and late-activation antigens, and the presence of antigen-presenting cells have been documented, demonstrating an ongoing immune response. The three components of the trimolecular complex, T-cell receptor (TCR)/peptide (antigen)/HLA have been identified in AAA, and specifically: (i) clonal expansions of T-cell clones in AAA lesions; (ii) the association of AAA with particular HLA Class I and Class II; and (iii) self or nonself putative AAA-associated antigens. IgG autoantibodies recognizing proteins present in normal aortic tissue have been reported in patients with AAA. Molecular mimicry, defined as the sharing of antigenic epitopes between microorganisms (bacteria, viruses) and self antigens, maybe is responsible for T-cell responses and antibody production in AAA. Also, the frequency and the suppressor activity of CD4 + CD25 + FOXP3+ Tregs and the expression of FOXP3 transcripts and protein have been reported to be significantly impaired in AAA patients vs normal donors.

The TAGA Study: A Study of Factors Determining Aortic Diameter in Families at High Risk of Abdominal Aortic Aneurysm Reveal Two New Candidate Genes

A variety of disorders are known to be related with aortic geometry, among them abdominal aortic aneurysm (AAA). This work aims to present the main determinants of abdominal aortic diameter in a new cohort of families at high risk of AAA. The Triple-A Genomic Analysis (TAGA) study comprises 407 individuals related in 12 families. Each family was collected through a proband with AAA. We calculated heritability and genetic correlations between abdominal aortic diameter and clinical parameters. A genome-wide linkage scan was performed based on 4.6 million variants. A predictive model was calculated with conditional forest. Heritability of the abdominal aortic diameter was 34%. Old age, male sex, higher height, weight, creatinine levels in serum, and better lung capacity were the best predictors of aortic diameter. Linkage analyses suggested the implication of Epidermal Growth Factor Receptor (EGFR) and Betacellulin (BTC) genes with aortic diameter. This is the first study to evaluate genetic components of variation of the aortic diameter in a population of AAA high-risk individuals. These results reveal EGFR, a gene that had been previously implicated in AAA, as a determinant of aortic diameter variation in healthy genetically enriched individuals, and might indicate that a common genetic background could determine the diameter of the aorta and future risk of AAA.

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.

Abdominal Aortic Aneurysm: Evolving Controversies and Uncertainties

Abdominal aortic aneurysm (AAA) is defined as a permanent dilatation of the abdominal aorta that exceeds 3 cm. Most AAAs arise in the portion of abdominal aorta distal to the renal arteries and are defined as infrarenal. Most AAAs are totally asymptomatic until catastrophic rupture. The strongest predictor of AAA rupture is the diameter. Surgery is indicated to prevent rupture when the risk of rupture exceeds the risk of surgery. In this review, we aim to analyze this disease comprehensively, starting from an epidemiological perspective, exploring etiology and pathophysiology, and concluding with surgical controversies. We will pursue these goals by addressing eight specific questions regarding AAA: (1) Is the incidence of AAA increasing? (2) Are ultrasound screening programs for AAA effective? (3) What causes AAA: Genes versus environment? (4) Animal models: Are they really relevant? (5) What pathophysiology leads to AAA? (6) Indications for AAA surgery: Are surgeons over-eager to operate? (7) Elective AAA repair: Open or endovascular? (8) Emergency AAA repair: Open or endovascular?

Autoimmunity in the Abdominal Aortic Aneurysm and its Association with Smoking

Smoking increases the risk of abdominal aortic aneurysm (AAA) in both humans and mice, although the underlying mechanisms are not completely understood. An adventitial aortic antigen, AAAP-40, has been partially sequenced. It has motifs with similarities to all three fibrinogen chains and appears to be connected in evolution to a large family of proteins called fibrinogen-related proteins. Fibrinogen may undergo non-enzymatic nitration, which may result from exposure to nitric oxide in cigarette smoke. Nitration of proteins renders them more immunogenic. It has recently been reported that anti-fibrinogen antibody promotes AAA development in mice. Also, anti-fibrinogen antibodies are present in patients with AAA. These matters are reviewed in the overall context of autoimmunity in AAA. The evidence suggests that smoking amplifies an auto-immune reaction that is critical to the pathogenesis of AAA.

Female Mice With an XY Sex Chromosome Complement Develop Severe Angiotensin II-Induced Abdominal Aortic Aneurysms

BACKGROUND

Abdominal aortic aneurysms (AAAs) are a deadly pathology with strong sexual dimorphism. Similar to humans, female mice exhibit far lower incidences of angiotensin II-induced AAAs than males. In addition to sex hormones, the X and Y sex chromosomes, and their unique complements of genes, may contribute to sexually dimorphic AAA pathology. Here, we defined the effect of female (XX) versus male (XY) sex chromosome complement on angiotensin II-induced AAA formation and rupture in phenotypically female mice.

METHODS

Female low-density lipoprotein receptor (Ldlr) deficient mice with an XX or XY sex chromosome complement were infused with angiotensin II for 28 days to induce AAAs. Abdominal aortic lumen diameters were quantified by ultrasound, whereas AAA diameters were quantified at study end point. DNA microarrays were performed on abdominal aortas. To mimic males, female mice were administered a single dose of testosterone as neonates or as adults before angiotensin II infusions.

RESULTS

Female Ldlr^-/- deficient mice with an XX and XY sex chromosome complement had similar sex organ weights and low serum testosterone concentrations. Abdominal aortas from female XY mice selectively expressed Y chromosome genes, whereas genes known to escape X inactivation were higher in XX females. The majority of aortic gene differences in XY versus XX females fell within inflammatory pathways. AAA incidences doubled and aneurysms ruptured in XY females. AAAs from XY females exhibited inflammation, and plasma interleukin-1β concentrations were increased in XY females. Moreover, aortas from XY females had augmented matrix metalloproteinase activity and increased oxidative stress. Last, testosterone exposure applied chronically, or as a single bolus at postnatal day 1, markedly worsened AAA outcomes in XY in comparison with XX adult females.

CONCLUSIONS

An XY sex chromosome complement in phenotypic females profoundly influenced aortic gene expression profiles and promoted AAA severity. When XY females were exposed to testosterone, aneurysm rupture rates were striking. Mechanisms for augmented AAA severity in XY females include increased inflammation, augmented matrix metalloproteineases, and oxidative stress. Our results demonstrate that genes on the sex chromosomes regulate aortic vascular biology and contribute to sexual dimorphism of AAAs. Sex chromosome genes may serve as novel targets for sex-specific AAA therapeutics.

Abdominal Aortic Aneurysms and Risk Factors for Adverse Events

An abdominal aortic aneurysm (AAA) is a focal full thickness dilatation of the abdominal aorta, greater than 1.5 times its normal diameter. Although some patients with AAA experience back or abdominal pain, most remain asymptomatic until rupture. The prognosis after AAA rupture is poor. Management strategies for patients with asymptomatic AAAs include risk factor reduction, such as smoking cessation, optimizing antihypertensive treatment, and treating dyslipidemia, as well as surveillance by ultrasound. Currently, aneurysm diameter alone is often used to assess risk of rupture. Once the aneurysm diameter reaches 5.5 cm, the risk of rupture is considered greater than the risk of intervention and elective aneurysm repair is undertaken. There is increasing interest in detecting AAAs early, and national screening programs are now in place. Furthermore, there is increasing research interest in biomarkers, genetics, and functional imaging to improve detection of AAAs at risk of progression and rupture. In this review, we discuss risk factors for AAA rupture, which should be considered during the management process, to advance current deficiencies in management pathways.

Familial Incidence of Abdominal Aortic Aneurysms

The rupture of an abdominal aortic aneurysms (AAAs) is associated with a mortality rate exceeding 50%. To reduce this figure it is necessary to increase the frequency of early diagnosis and elective surgery. Screening the general population for occult AAAs has proven cost ineffective. Only by identifying high-risk subgroups will screening programs be improved. The aim of this report was to investigate by ultrasonography the prevalence of previously unknown aortic dilatations among first-degree relatives (parents, siblings, and children) of patients operated on for AAAs.

Ninety-one (52.6%) of the 173 living first degree-relatives of 51 patients who underwent AAA resection were submitted to an aortoiliac ultrasonographic examina tion to establish aortic diameter and morphology. There was at least 1 first-degree relative with an AAA (multiplex family) in 10 families (19.6%) before ultrasound screening. With ultrasound a previously unknown infrarenal aortic dilatation was detected in 14 subjects (9 men/5 women; 10 siblings and 4 children) of 12 different families. Specifically, these aortic dilatations consisted of 10 AAAs (diameters ranged from 2.6 to 4.3 cm) and 4 aortic blebs. These occult aortic dilatations were located in 50% of cases in the lower third of the infrarenal abdominal aorta. The cumulative incidence of multiplex families was 35.3%. This study suggests a familial tendency to have an important etiologic role in the formation of AAAs. Family screening of, above all, male siblings older than forty-five years will help identify occult AAAs and reduce the mortality rates associated with their rupture.

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.

Patients with familial abdominal aortic aneurysms are at increased risk for endoleak and secondary intervention following elective endovascular aneurysm repair

OBJECTIVE

A recent investigation has documented an increased risk of aneurysm-related complications after endovascular aneurysm repair (EVAR) of familial abdominal aortic aneurysms (fAAAs). We hypothesized that fAAA patients are not at increased risk for complications following open AAA repair or EVAR when compared with sporadic abdominal aortic aneurysm (spAAA) patients. To this end, we performed a single institution retrospective review.

METHODS

Epidemiologic data were collected through the electronic medical record. Family history data were obtained from a questionnaire administered at the initial vascular surgery consultation. Major adverse events were defined as myocardial infarction, respiratory failure, renal failure, bowel ischemia, limb ischemia, multisystem organ failure, intracranial hemorrhage, paraplegia, hemorrhage, or death. Endoleaks were classified in accordance with the standardized reporting practices of the Society for Vascular Surgery. AAA-related complications were defined as the need for a secondary intervention due to endoleak, limb ischemia, or postimplantation rupture.

RESULTS

A total of 392 patients with complete clinical data underwent elective AAA repair from 2004 to 2014. Of these 392 patients, 89 (23%) were classified as fAAA patients and 303 (77%) were classified as spAAA patients. With the exception of increased rates of chronic obstructive pulmonary disease (P = .0009) and pack-years smoked (P = .03) in spAAA patients, demographics did not differ. Sixty-two percent (n = 55) of fAAA patients and 68% (n = 205) of spAAA patients underwent EVAR (P = .30). fAAA patients did not incur any significant difference in major adverse events following open AAA repair (fAAA, 9% vs spAAA, 11%; P = .75). Additionally, fAAA patients did not incur any significant difference in major adverse events following EVAR (fAAA, 4% vs spAAA, 5%; P = .70). Patients with fAAA did have a significantly increased rate of endoleak (fAAA, 24% vs spAAA, 12%; P = .03) and secondary intervention following EVAR (fAAA, 21% vs spAAA, 12%; P = .04).

CONCLUSIONS

The current study shows that patients with fAAA do not have increased perioperative morbidity following open or endovascular AAA repair. However, patients with fAAA do have an increased risk of endoleak and secondary intervention following EVAR. These findings suggest that EVAR and open AAA repair are both safe and effective for fAAA patients. The increased rate of endoleak and secondary intervention in patients with fAAA suggests that this subpopulation may benefit from closer post-EVAR surveillance or open surgical repair in good risk patients.

Expanding Horizons for Abdominal Aortic Aneurysms

Recent technological advances have allowed researchers to interrogate the genetic basis of abdominal aortic aneurysms in great detail. The results from these studies are expected to transform our understanding of this complex disease with both multiple genetic and environmental risk factors. Clinicians need to keep abreast of these genetic findings and understand the implications for their practice. Patients will become increasingly informed on genetic risk, and a new era of individualized risk assessment for AAA is just beginning. This brief update aims to provide the clinician with a succinct précis of the recent progress in this area.

Genomic insights into abdominal aortic aneurysms

INTRODUCTION

An individual's genetic background plays a significant role in his or her chances of developing an abdominal aortic aneurysm (AAA). This risk is likely to be due to a combination of multiple small effect genetic factors acting together, resulting in considerable difficulty in the identification of these factors.

METHODS

Methods for the identification of genetic factors associated with disease are usually based on the analysis of genetic variants in case-control studies. Over the last decade, owing to advances in bioinformatics and laboratory technology, these studies have progressed from focusing on the examination of a single genetic variant in each study to the examination of many millions of variants in a single experiment. We have conducted a series of such experiments using these methods.

RESULTS

Our original methods using candidate gene approaches led to the initial identification of a genetic variant in the interleukin-10 gene associated with AAA. However, further studies failed to confirm this association and highlighted the necessity for adequately powered studies to be conducted, as well as the need for confirmatory studies to be performed, prior to the acceptance of a variant as a risk for disease. The subsequent application of genomic techniques to our sample set, in a global collaboration, has led to the identification of three robustly verified risk loci for AAA in the LRP1, LDLR and SORT1 genes.

CONCLUSIONS

Genomic studies of AAA have led to the identification of new pathways involved in the pathogenesis of AAA. The exploration of these pathways has the potential to unlock new avenues for therapeutic intervention to prevent the development and progression of AAA.

Family history of aortic aneurysm is an independent risk factor for more rapid growth of small abdominal aortic aneurysms in Japan

OBJECTIVE

We aimed to investigate risk factors associated with more rapid growth of abdominal aortic aneurysms (AAA) <50 mm (small AAAs) in Japan.

METHODS

We retrospectively investigated the clinical data of 374 patients with small AAAs (maximum diameter, ≤50 mm) who were referred to The University of Tokyo Hospital, Tokyo Medical University Hospital, or Saitama Medical Center, between 1995 and 2008.

RESULTS

A total of 374 patients (321 men and 53 women) were followed up for a median of 66 months. The median diameter on initial examination was 40 mm, and the median growth rate of the AAAs was 2.1 mm/y. The growth rate of AAAs with an initial diameter ≥45 mm was significantly greater than those with an initial diameter <45 mm (3.3 mm/y vs 2.0 mm/y, respectively; P = .007). The growth rate of AAAs was significantly greater in patients with hypertension than in those without (2.3 mm/y vs 1.7 mm/y, respectively; P = .006) and in patients with a family history of aortic aneurysm than in those without (4.2 mm/y vs 2.0 mm/y, respectively; P = .009). Logistic regression analysis revealed that a large initial diameter and family history of aortic aneurysm were independent predictors of accelerated growth rate of small AAAs in Japan.

CONCLUSIONS

In the present study, a large initial diameter and family history of aortic aneurysm were independent risk factors for more rapid growth of small AAAs. Although few studies have reported similar findings thus far, family history of aortic aneurysm should be carefully considered during follow-up of patients with small AAAs.

Family members of patients with abdominal aortic aneurysms are at increased risk for aneurysms: analysis of 618 probands and their families from the Liège AAA Family Study

BACKGROUND

The objectives were to answer the following questions with the help of a well-characterized population in Liège, Belgium: 1) what percentage of patients with abdominal aortic aneurysm (AAA) have a positive family history for AAA? 2) what is the prevalence of AAAs among relatives of patients with AAA? and 3) do familial and sporadic AAA cases differ in clinical characteristics?

METHODS

Patients with unrelated AAA diagnosed at the Cardiovascular Surgery Department, University Hospital of Liège, Belgium, between 1999 and 2012 were invited to the study. A detailed family history was obtained in interviews and recorded using Progeny software. We divided the 618 patients into 2 study groups: group I, 296 patients with AAA (268; 91% men) were followed up with computerized tomography combined with positron emission tomography; and group II, 322 patients with AAA (295; 92% men) whose families were invited to ultrasonographic screening.

RESULTS

In the initial interview, 62 (10%) of the 618 patients with AAA reported a positive family history for AAA. Ultrasonographic screening identified 24 new AAAs among 186 relatives (≥50 years) of 144 families yielding a prevalence of 13%. The highest prevalence (25%) was found among brothers. By combining the number of AAAs found by ultrasonographic screening with those diagnosed previously the observed lifetime prevalence of AAA was estimated to be 32% in brothers. The familial AAA cases were more likely to have a ruptured AAA than the sporadic cases (8% vs. 2.4%; P < 0.0001).

CONCLUSIONS

The findings confirm previously found high prevalence of AAA among brothers, support genetic contribution to AAA pathogenesis, and provide rationale for targeted screening of relatives of patients with AAA.

A Variant in LDLR Is Associated With Abdominal Aortic Aneurysm

Background—

Abdominal aortic aneurysm (AAA) is a common cardiovascular disease among older people and demonstrates significant heritability. In contrast to similar complex diseases, relatively few genetic associations with AAA have been confirmed. We reanalyzed our genome-wide study and carried through to replication suggestive discovery associations at a lower level of significance.

Methods and Results—

A genome-wide association study was conducted using 1830 cases from the United Kingdom, New Zealand, and Australia with infrarenal aorta diameter ≥30 mm or ruptured AAA and 5435 unscreened controls from the 1958 Birth Cohort and National Blood Service cohort from the Wellcome Trust Case Control Consortium. Eight suggestive associations with P <1×10 −4 were carried through to in silico replication in 1292 AAA cases and 30 503 controls. One single-nucleotide polymorphism associated with P <0.05 after Bonferroni correction in the in silico study underwent further replication (706 AAA cases and 1063 controls from the United Kingdom, 507 AAA cases and 199 controls from Denmark, and 885 AAA cases and 1000 controls from New Zealand). Low-density lipoprotein receptor ( LDLR ) rs6511720 A was significantly associated overall and in 3 of 5 individual replication studies. The full study showed an association that reached genome-wide significance (odds ratio, 0.76; 95% confidence interval, 0.70–0.83; P =2.08×10 −10 ).

Conclusions—

LDLR rs6511720 is associated with AAA. This finding is consistent with established effects of this variant on coronary artery disease. Shared causal pathways with other cardiovascular diseases may present novel opportunities for preventative and therapeutic strategies for AAA.

A pilot study on low-density lipoprotein receptor-related protein-1 in Chinese patients with abdominal aortic aneurysm

OBJECTIVE

There are no published data on the expression of low-density lipoprotein receptor-related protein 1 (LRP1) in human aortic tissues with abdominal aortic aneurysm (AAA), although some researchers have suggested that LRP1 may be a crucial regulator in the pathogenesis of AAA. The aim of this pilot study is to investigate LRP1 expression in aortic tissues from Chinese patients with AAA compared with normal control tissues.

MATERIALS AND METHODS

This study used human abdominal aortic tissues with or without AAA as a research model. Aneurysmal abdominal aortas were collected from Chinese patients with AAA (n = 12) during open surgical aneurysmal repair at our institution, and normal control non-aneurysmal abdominal aortas were collected from Chinese healthy organ donors (n = 12) during organ transplantation. Protein expression of LRP1 was analyzed by western blotting and immunohistochemistry.

RESULTS

LRP1 protein expression was significantly lower in AAA (mean LRP1AAA/LRP1(Normal Control) = 0.51 ± 0.28) than in normal control aortic tissues (mean LRP1(Normal Control)/LRP1(Normal Control) = 1 ± 0.18) in our small sample cohort (p < .001). No significant correlation was shown between LRP1 protein expression and the size of AAA (p > .05).

CONCLUSIONS

Our pilot result suggests that a reduction in LRP1 protein expression may be associated with aneurysm progression.

Genomic research to identify novel pathways in the development of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease with a large heritable component. There is a need to improve our understanding of AAA pathogenesis in order to develop novel treatment paradigms. Genomewide association studies have revolutionized research into the genetic variants that underpin the development of many complex diseases including AAA. This article reviews the progress that has been made to date in this regard, including mechanisms by which loci identified by GWAS may contribute to the development of AAA. It also highlights potential post-GWAS analytical strategies to improve our understanding of the disease further.

Coding polymorphisms in the genes of the alternative complement pathway and abdominal aortic aneurysm

Variants in the genes of the alternative complement pathway are associated with risk of numerous inflammatory diseases. Abdominal aortic aneurysm is associated with inflammation and is a common cause of illness and death among European populations. This study tested 49 single nucleotide polymorphisms, including common putatively functional polymorphisms, in the genes of the alternative complement cascade (CFH, CFB, CFD, CFI, properdin, CR1, CR1L, CR2, CD46, vitronectin, C3, C5, C6, C7, C8A, C8B, C8G and C9). The study group were 434 cases with infra-renal aortic diameter ≥30 mm and 378 disease-free controls from two UK centres, all with self-reported European ancestry. There was no evidence for significant association with presence or size of aneurysm following correction for multiple testing. This study suggests that variation in the genes of the alternative pathway is not an important cause of abdominal aortic aneurysm development.

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.

Pathophysiology and epidemiology of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are found in up to 8% of men aged >65 years, yet usually remain asymptomatic until they rupture. Rupture of an AAA and its associated catastrophic physiological insult carries overall mortality in excess of 80%, and 2% of all deaths are AAA-related. Pathologically, AAAs are associated with inflammation, smooth muscle cell apoptosis, and matrix degradation. Once thought to be a consequence of advanced atherosclerosis, accruing evidence indicates that AAAs are a focal representation of a systemic disease of the vasculature. Risk factors for AAAs include increasing age, male sex, smoking, and low HDL-cholesterol levels. Familial associations exist and although susceptibility genes have been described on the basis of candidate-gene studies, robust genetic studies have failed to discover causative gene mutations. The surgical management of AAAs has been revolutionized by minimally invasive endovascular repair. Ongoing randomized trials will establish whether endovascular repair confers a survival advantage over open surgery for patients with a ruptured AAA. In many countries, centralization of vascular surgical services has largely been driven by the improved outcomes of elective aneurysm surgery in specialized centers, the widespread adoption of endovascular techniques, and the introduction of screening programs.

Abdominal aortic aneurysms in triplets

We report the case of 3 male triplets, 2 of whom, both lifelong smokers, presented with ruptured abdominal aortic aneurysm (AAA) within 24 hours of each other. One survived surgery but the other died from the rupture. The third brother, an ex-smoker, was found to have an ectatic aorta and was placed into a surveillance program. This case highlights and discusses the combination of genetic and environmental factors that underpin the etiology of aneurysms and demonstrates the importance of assessing first-degree relatives of patients presenting with 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.

Giant coronary aneurysm in a patient with familial aortic aneurysm/dissection: Medial degeneration extending to coronary artery

Familial thoracic aortic aneurysms and dissections occur as part of known syndromes such as Marfan syndrome, but can also be inherited in families in an autosomal dominant manner as an isolated condition. However, involvement of coronary artery aneurysm/dissections is rare in these patient subsets. A 37-year-old male, normal in skeletal appearance, with a distinct family history of aortic dissection, underwent four major cardiovascular surgeries since age 30 due to giant coronary aneurysm and coronary stenosis, abdominal aortic dissection, and Stanford type A aortic dissection. Pathological examinations demonstrated the left main coronary aneurysm was composed of degenerated, lacerated media, with findings of decreased elastic fibers, deposition of mucopolysaccharide, and cystic medial necrosis. These pathological features found in the coronary aneurysm were identical to those of the aortic wall and radial artery segments in this patient. This case suggests that initial coronary evaluation may be warranted in some families to optimize the clinical management of patients affected with this disease.

The role of the CCR5 Delta32 polymorphism in abdominal aortic aneurysms

BACKGROUND

C-C chemokine receptor 5 (CCR5) is involved in the regulation of the inflammatory response. Abdominal aortic aneurysms (AAA) may arise as the result of a chronic inflammatory process which is influenced by genetic predisposition. The CCR5 gene is associated with a 32 base pair deletion (the Delta32 polymorphism). The aim of this study was to investigate the role of the CCR5 Delta32 polymorphism in the development of AAA.

METHODS

A case-control study was conducted including 285 patients with AAA and 273 control subjects. A blood sample was taken from each individual and DNA was extracted. CCR5 genotype was determined using the polymerase chain reaction (PCR). Flow cytometry was used to investigate the biological activity of the Delta32 polymorphism.

RESULTS

There was no significant difference between the AAA and the control group in relation to the Delta32 allele frequency (AAA group 10%, control group = 12%, P = 0.82, chi-squared analysis). Genotype analysis revealed no significant difference between the groups (AAA vs. controls, wild-type homozygotes = 82% vs. 77%, heterozygotes = 16% vs. 21%, vs. Delta32 homozygotes = 2% and 2%, respectively, P = 0.33, chi-squared analysis). The polymorphism was shown to be biologically active with the number of Delta32 alleles correlating with cell expression of ccr5 as detected with flow cytometry (P < or = 0.05).

CONCLUSION

This study demonstrates that the ccr5 Delta32 is a biologically active genetic polymorphism; however, there is no association between this polymorphism and AAA.

The Low Prevalence of Abdominal Aortic Aneurysm in Relatives in Northern Ireland

INTRODUCTION

Mortality from ruptured abdominal aortic aneurysm (AAA) remains high and has given impetus to screening. Targeted screening towards high-risk groups would increase efficacy. Relatives of previous AAA patients have been suggested as one such group. The aim of this study was therefore to determine the prevalence of AAA in relatives of previous patients in Northern Ireland.

PATIENTS AND METHODS

All living AAA patients, who underwent surgery between August 2001 and December 2005 in our unit, or were attending for follow-up of small aneurysms were contacted and asked for details of siblings and their family history. Screening by ultrasound was offered to the siblings and children over 50 years, with a defining threshold diameter for an aneurysm of 3.0 cm. Overall prevalence of AAA in the relatives was calculated. Separate prevalence rates were calculated according to relationship and gender of the patient and relative.

RESULTS

513 previous patients were contacted. 132 gave details of living relatives, resulting in a total of 405 relatives suitable for screening. 105 declined a scan, leaving 300 in the study. Overall mean age of the group was 63.0+/-8.7 years and 68% were siblings of male patients. Overall ten AAAs were detected by screening, giving a prevalence of 3.3%. No aneurysms were found in the subgroup of children, while the highest prevalence (12.5%) was found in brothers of female patients. 20 additional AAAs were reported in these 132 families, resulting in 14 of the 132 families (10.6%) having two or more members with AAA.

CONCLUSION

The prevalence of screening detected AAA in this study is lower than anticipated. The reason is unclear, but demonstrates the multifactorial nature of the aetiology and genetic complexities yet to be unravelled by future research.

The Genetic Basis of Abdominal Aortic Aneurysms: A Review

INTRODUCTION

The pathogenesis of abdominal aortic aneurysm (AAA) remains poorly understood, however significant evidence has emerged in recent years to suggest a chronic inflammatory process. Observational studies have highlighted a familial trend towards AAA development among relatives of affected individuals and it is thought that inflammatory genes may influence an individual's susceptibility. Conflicting reports exist over single gene versus multiple gene inheritance patterns in addition to a collection of studies examining individual inflammatory genes. This paper reviews the evidence for a genetic predisposition to aneurysm formation including familial and segregation studies in addition to experimental evidence investigating specific candidate genes.

METHOD

Medline and Pubmed database searches were conducted using the search terms abdominal aortic aneurysm and gene. Papers were reviewed and references manually searched for further relevant publications which were added to the data. Papers were categorised under the headings familial, segregation and candidate gene studies.

RESULTS

A review of 58 papers is presented under sub-headings as above. In the case of the candidate gene section, a brief report of the functional relevance of each gene is included.

CONCLUSION

A summary of the evidence presented is given and the direction of future work in this field is briefly considered.

The role of human leukocyte antigen genes in the formation of abdominal aortic aneurysms

BACKGROUND

Increasing evidence suggests an autoimmune component to abdominal aortic aneurysm (AAA) formation. This study was conducted to determine if a difference exists in human leukocyte antigen (HLA) allele distribution between patients with AAA and population controls, and between patients with small and large AAA.

METHODS

Patients with known AAA attending the vascular unit were consented for recruitment. HLA-A, HLA-B and HLA-DR was determined by polymerase chain reaction and sequence-specific oligonucleotide probes. The distribution of these alleles in the Northern Ireland general population was obtained from the histocompatibility and immunogenetics database. The chi(2) test was used for statistical analysis with Bonferroni correction.

RESULTS

A total of 241 AAA patients were recruited, with a wide range of aneurysm size. In class I, the most frequent allele families were HLA-A*02 and *01 and HLA-B*07, *08, and *44. In class II, HLA-DRB1*03, *04, *07, and *15 were the most frequent. HLA-A*11 was lower in AAA cases (10.4% vs 15.0%; P = .08), whereas HLA-B*08 was lower in the controls (29.8% vs 36.5%; P = .05) and HLA-DRB1*11 was lower in cases (4.2% vs 8.1%; P = .05). After Bonferroni correction, however, the proportion of allele families was not significantly different in AAA patients compared with the proportion seen in controls. HLA-DRB1*11 and *14 had a lower prevalence in large AAAs (0.9% vs 6.7% [P = .05]; 0.0% vs 5.9% [P = .03]). HLA-A*68 was also lower in large AAA (1.9% vs 11.9%; P = .0075). After Bonferroni correction, however, no difference was demonstrated between small and large aneurysms.

CONCLUSION

This study provides more definitive results on this important subject and has failed to demonstrate the risk association between AAA and these alleles as reported by others. Therefore, the role of these particular genes and the autoimmune component in AAA etiology does not appear to be as crucial as previously proposed.