Open Access Research article

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

John H Lillvis1, Yoshiki Kyo19, Gerard Tromp2, Guy M Lenk110, Ming Li3, Qing Lu34, Robert P Igo4, Natzi Sakalihasan5, Robert E Ferrell6, Charles M Schworer2, Zoran Gatalica7, Susan Land18 and Helena Kuivaniemi2*

Author Affiliations

1 Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan, USA

2 Sigfried and Janet Weis Center for Research, Geisinger Clinic, Danville, 100 North Academy Avenue, Pennsylvania 17822-2610, USA

3 Department of Epidemiology, Michigan State University, East Lansing, Michigan, USA

4 Department of Epidemiology and Biostatistics, Case Western Reserve University, Cleveland, Ohio, USA

5 Department of Cardiovascular Surgery, University Hospital of Liège, Liège, Belgium

6 Department of Human Genetics, University of Pittsburgh, School of Public Health, Pittsburgh, Pennsylvania, USA

7 Department of Pathology, Creighton University School of Medicine, Omaha, Nebraska, USA

8 Applied Genomics Technology Center, Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, Michigan, USA

9 Department of Cardiovascular Surgery, Higashihiroshima Medical Center, Hiroshima, Japan

10 Department of Human Genetics, University of Michigan, Ann Arbor, MI, USA

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BMC Medical Genetics 2011, 12:14  doi:10.1186/1471-2350-12-14

Published: 19 January 2011

Abstract

Background

Abdominal 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.

Methods

Nine 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.

Results

Several 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.

Conclusions

Association 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.