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

Normal Infrarenal Aortic Diameter in Men and Women in a Mediterranean Area

BACKGROUND

Infrarenal aortic diameter (AD) values currently considered normal are based on measurements from epidemiologic studies performed over 20 years ago. Knowledge of expected normal AD is important for understanding the relevance of abdominal aortic dilatation. The aim of this study was to define contemporary reference values for normal infrarenal AD and build a predictive model based on individual features.

METHODS

A cross-sectional study of participants in a population-based screening program for abdominal aortic aneurysm (AAA) was performed in a healthcare district with 400,000 inhabitants. Men and women aged 65 years were invited to participate. Cardiovascular (CV) risk factors, family history of AAA, personal history of other aneurysms, CV disease, and anthropometric parameters were evaluated. The largest anteroposterior inner-inner diameter of the infrarenal aorta was measured by ultrasound. Multiple linear regressions were used to determine independent predictors of AD. The best-fit model was obtained by randomly selecting 70% of the sample and validating the results in the remaining 30%.

RESULTS

A total of 4,730 people (2,089 men and 2,641 women) were invited. The participation rate was 50.4% for men and 44.0% for women. Mean AD (standard deviation, SD) was 16.51 (3.2) mm in the overall group, 17.91 (3.51) mm in men, and 15.25 (2.32) mm in women (P < 0.001). Male sex (P < 0.001), body surface area (P < 0.001), smoking habit (P = 0.012), and history of arterial aneurysms (P = 0.013) were independently associated with increased AD. Dyslipidemia was associated with decreased AD (P < 0.001). The findings were used to build a model for predicting AD based on individual characteristics.

CONCLUSIONS

ADs in our study population are smaller than those described in classic epidemiological studies. Men have a significantly larger diameter than women and the strongest predictor of increased AD is body surface area. A greater understanding of factors associated with AD will help predict expected sizes in individual members of the population.

Genetic and clinical determinants of abdominal aortic diameter: genome-wide association studies, exome array data and Mendelian randomization study

Progressive dilation of the infrarenal aortic diameter is a consequence of the ageing process and is considered the main determinant of abdominal aortic aneurysm (AAA). We aimed to investigate the genetic and clinical determinants of abdominal aortic diameter (AAD). We conducted a meta-analysis of genome-wide association studies in 10 cohorts (n = 13 542) imputed to the 1000 Genome Project reference panel including 12 815 subjects in the discovery phase and 727 subjects [Partners Biobank cohort 1 (PBIO)] as replication. Maximum anterior-posterior diameter of the infrarenal aorta was used as AAD. We also included exome array data (n = 14 480) from seven epidemiologic studies. Single-variant and gene-based associations were done using SeqMeta package. A Mendelian randomization analysis was applied to investigate the causal effect of a number of clinical risk factors on AAD. In genome-wide association study (GWAS) on AAD, rs74448815 in the intronic region of LDLRAD4 reached genome-wide significance (beta = -0.02, SE = 0.004, P-value = 2.10 × 10-8). The association replicated in the PBIO1 cohort (P-value = 8.19 × 10-4). In exome-array single-variant analysis (P-value threshold = 9 × 10-7), the lowest P-value was found for rs239259 located in SLC22A20 (beta = 0.007, P-value = 1.2 × 10-5). In the gene-based analysis (P-value threshold = 1.85 × 10-6), PCSK5 showed an association with AAD (P-value = 8.03 × 10-7). Furthermore, in Mendelian randomization analyses, we found evidence for genetic association of pulse pressure (beta = -0.003, P-value = 0.02), triglycerides (beta = -0.16, P-value = 0.008) and height (beta = 0.03, P-value < 0.0001), known risk factors for AAA, consistent with a causal association with AAD. Our findings point to new biology as well as highlighting gene regions in mechanisms that have previously been implicated in the genetics of other vascular diseases.