An investigation into genetic polymorphisms and abdominal aortic aneurysms

Introduction: A wide variety of genetic polymorphisms have demonstrated a significant association to the disease abdominal aortic aneurysm (AAA). Polymorphisms in rs217120 (Cathepsin C gene CTSC) and rs1466535 (low density lipoprotein receptor related protein 1 gene, LRP1) have both been associated with AAA, rs1466535 from a genome wide association study (GWAS). Materials & Methods: Associations were first confirmed then exons in close proximity to the polymorphisms were re-sequenced in order to detect new mutations. Protein levels were assayed and tissue was stained in order to determine the arterial layer that the LRP1 protein resides within. TaqMan genotyping was undertaken in order to determine allele frequency of the SNPs of interest in cohorts from Belfast (211 AAA, 262 controls), Viborg (473 AAA, 195 controls), Leeds (214 AAA and 249 controls) and Leicester (266 AAA, 143 controls). Subsequently a list of linked SNPs was generated and the same samples were analysed in order to fine map the gene(s) of interest. Samples from Leicester (96 AAA, 96 controls) were sequenced. Serum protein concentrations were measured with an ELISA (43 AAA, 26 controls). Immunohistochemical analysis of aortic biopsies (n = 6) was also performed. Results: rs217120 failed to associate with AAA in 3 of 4 the replication cohorts and meta-analysis of all data was also not significant, odds ratio 1.17 (95% Confidence Interval 0.98-1.39), P value = 0.08. rs1466535 did not significantly associate with AAA in the replication cohorts however when the data was meta-analysed with the discovery phase of the GWAS (1866 AAA, 5435 controls) the association was significant, odds ratio 1.23 (95% Confidence Interval 1.14-1.33), P value 1.25x¹⁰⁻⁷. A second SNP within LRP1, rs11172114, was found to have a more significant association, odds ratio 1.23 (95% Confidence Interval 1.14 to 1.31), P value 3.87x¹⁰⁻⁸. Re-sequencing of the 3 LRP1 exons did not detect any novel mutations. Serum LRP1 levels between cases and controls were not different (mean concentration 583.4 v 631.3ng/ml, P value = 0.69). There was also no significant difference when samples were analysed by SNP genotype, rs1466535 P value = 0.07. Analysis of aortic tissue biopsies did not determine an association between LRP1 genotype and cellular location. Conclusion: SNPs within LRP1 associate with AAA, with rs11172114 being most significant. However the polymorphism is not associated with protein levels in serum and is not clearly localizing to any given layer of the arterial wall. More investigation is required to determine how LRP1 affects aneurysm development and growth.