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

John H Lillvis,Ming Li,Natzi Sakalihasan,Susan Land,Zoran Gatalica,Robert E Ferrell,Helena Kuivaniemi,Gerard Tromp,Robert P Igo,Charles M Schworer,Yoshiki Kyo,Qing Lu,Guy M Lenk

doi:10.1186/1471-2350-12-14

Abstract

BackgroundAbdominal 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.MethodsNine 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.ResultsSeveral 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.ConclusionsAssociation 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.

Highlights

Abdominal aortic aneurysm (AAA) is a complex disorder with multiple genetic risk factors
In order to identify a smaller set of strong candidate genes for further study, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional annotations were used to identify nine genes with functions relevant to AAA pathogenesis (Table 1)
Since genes not expressed in aortic tissue, either diseased or non-diseased, would be less likely to contribute to aneurysm formation, mRNA expression of each candidate gene was assessed using microarray expression profiles of AAA and control aortic tissue

Summary

Introduction

Abdominal aortic aneurysm (AAA) is a complex disorder with multiple genetic risk factors. 15% of AAA patients have a positive family history [10] and genetic association studies have identified risk alleles in cardiovascular risk genes such as DAB2IP [11], CDKN2BAS [12], AGTR1 [13,14], ACE [13,14], and MTHFR [14]. These polymorphisms, explain only a small fraction of an individual’s genetic risk for AAA. Chromosome 19q13 may harbour risk alleles for several aneurysm phenotypes, as linkage to this region has been reported for intracranial aneurysms [17,18,19] and the Kawasaki disease [20]

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Results

Discussion

Conclusion