Is there an association between angiotensin converting enzyme (ACE) genotypes and abdominal aortic aneurysm?

Abdominal Aortic Aneurysm Genetic Associations: Mostly False? A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND

Many associations between abdominal aortic aneurysm (AAA) and genetic polymorphisms have been reported. It is unclear which are genuine and which may be caused by type 1 errors, biases, and flexible study design. The objectives of the study were to identify associations supported by current evidence and to investigate the effect of study design on reporting associations.

METHODS

Data sources were MEDLINE, Embase, and Web of Science. Reports were dual-reviewed for relevance and inclusion against predefined criteria (studies of genetic polymorphisms and AAA risk). Study characteristics and data were extracted using an agreed tool and reports assessed for quality. Heterogeneity was assessed using I(2) and fixed- and random-effects meta-analyses were conducted for variants that were reported at least twice, if any had reported an association. Strength of evidence was assessed using a standard guideline.

RESULTS

Searches identified 467 unique articles, of which 97 were included. Of 97 studies, 63 reported at least one association. Of 92 studies that conducted multiple tests, only 27% corrected their analyses. In total, 263 genes were investigated, and associations were reported in polymorphisms in 87 genes. Associations in CDKN2BAS, SORT1, LRP1, IL6R, MMP3, AGTR1, ACE, and APOA1 were supported by meta-analyses.

CONCLUSION

Uncorrected multiple testing and flexible study design (particularly testing many inheritance models and subgroups, and failure to check for Hardy-Weinberg equilibrium) contributed to apparently false associations being reported. Heterogeneity, possibly due to the case mix, geographical, temporal, and environmental variation between different studies, was evident. Polymorphisms in nine genes had strong or moderate support on the basis of the literature at this time. Suggestions are made for improving AAA genetics study design and conduct.

Associations between the insertion/deletion polymorphism of the angiotensin-converting enzyme and susceptibility to aortic aneurysms: A meta-analysis

INTRODUCTION

The purpose of this study is to examine whether the insertion (I) and deletion (D) polymorphism of the angiotensin-converting enzyme (ACE) confers susceptibility to aortic aneurysms (AAs).

MATERIALS AND METHODS

A meta-analysis was conducted on the associations between the ACE I/D polymorphism and all AAs and abdominal aortic aneurysms (AAAs).

RESULTS

Ten studies consisting of 2784 cases and 2682 controls were available for the meta-analysis. Meta-analysis showed a significant association between the D allele and all types of AA (OR 1.378, 95% CI 1.103-1.723, p = 0.005) and AAA (OR 1.274, 95% CI 1.004-1.617, p = 0.046). Meta-analysis of both the DD genotype and the DD vs. II genotype showed an association with AAAs. Stratification by ethnicity indicated an association between the D allele of the ACE I/D polymorphism and AAAs in Europeans (OR = 1.338, 95% CI = 1.026-1.745, p = 0.031), but not in Asians (OR = 0.927, 95% CI = 0.660-1.303, p = 0.663). Furthermore, analysis using the recessive model, dominant model, and homozygote contrast all showed the same pattern for the D allele.

CONCLUSIONS

Our meta-analysis demonstrates that the ACE I/D polymorphism is associated with susceptibility to AAAs in European populations.

Impaired abdominal aortic wall integrity in elderly men carrying the angiotensin-converting enzyme D allele

OBJECTIVE

A polymorphism in the angiotensin-converting-enzyme gene (ACE I/D) has been associated with abdominal aortic aneurysm and a link between aortic aneurysm and aortic stiffness has been suggested. This study aimed to explore the links between ACE I/D polymorphism, circulating ACE and abdominal aortic wall integrity as reflected by abdominal aortic wall stiffness.

MATERIAL

A total of 212 men and 194 women, aged 70-88 years, were studied.

METHODS

Mechanical properties of the abdominal aorta were determined using the Wall Track System, ACE genotype using the polymerase chain reaction (PCR) and circulating ACE level by enzyme-linked immunosorbent assay (ELISA).

RESULTS

In men, pulsatile diameter change differed between genotypes (II 0.70, ID 0.55 and DD 0.60 mm, P = 0.048), whereas a tendency was seen for distensibility coefficient (DC) (II 10.38, ID 7.68 and ID 8.79, P = 0.058). Using a dominant model (II vs. ID/DD), men carrying the ACE D allele had lower pulsatile diameter change (P = 0.014) and DC (P = 0.017) than II carriers. Multiple regression analyses showed additional associations between the D allele and increased stiffness β, and reduced compliance coefficient.

CONCLUSION

Men carrying the ACE D allele have stiffer abdominal aortas compared with II carriers. Deranged abdominal aortic stiffness indicates impaired vessel wall integrity, which, along with other local predisposing factors, may be important in aneurysmal disease.

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.