Association of the AIRE gene with susceptibility to rheumatoid arthritis in a European population: a case control study

García-Lozano et al. Arthritis Research & Therapy 2013, 15:R11 http://arthritis-research.com/content/15/1/R11 RESEARCH ARTICLE Open Access Association of the AIRE gene with susceptibility to rheumatoid arthritis in a European population: a case control study José-Raúl García-Lozano1, Belén Torres-Agrela1, Marco-Antonio Montes-Cano1, Lourdes Ortiz-Fernández1, Marta Conde-Jaldón1, María Teruel2, Alicia García3, Antonio Núñez-Roldán1, Javier Martín2 and María-Francisca González-Escribano1* Abstract Introduction: AIRE is a transcriptional regulator playing a functional role in thymocyte education and negative selection by controlling the expression of peripheral antigens in the thymus. Recently, the AIRE gene was identified as a genetic risk factor for rheumatoid arthritis (RA) in genome wide association (GWA) studies performed in the Japanese population. According to the available data this association is restricted to the Asian population. However, different facts could influence the lack of association in Caucasian populations. The aim of this study was to further investigate the possible role of the AIRE gene in susceptibility to RA in a Caucasian population. Methods: A total of 472 Spanish Caucasian RA patients and 475 ethnically matched controls were included in the study. Three single-nucleotide polymorphisms (SNPs) (rs2776377, rs878081 and rs1055311) with a minor allele frequency >0.05 in the Caucasian population which were not included in the high-throughput platforms used in the GWA studies performed in susceptibility to RA, and two SNPs (rs2075876 and rs1800520) associated with RA in the Japanese population, were selected and genotyped using TaqMan assays. Results: No significant differences in the distribution of the alleles of rs2776377, rs2075876, rs1055311 and rs1800520 SNPs between RA patients and controls were observed. Nevertheless, the frequency of the C allele of rs878081 was significantly higher among RA patients (80.5% vs. 74.6% in the control group, pc = 0.012, OR = 1.41, 95%CI 1.13-1.75). Regarding the distribution of the rs878081 genotypes, a higher frequency of CC homozygous individuals was found in the RA patient group (65.56% vs. 56.47% in the control group, pc = 0.013, OR = 1.47, 95% CI 1.12-1.93). The in silico analysis predicted lower affinity to the binding-site of a motif of the transcription NF-B family and lower transcription levels of AIRE gene for the rs878081C risk variant Conclusions: Our findings suggest that the AIRE gene is associated with susceptibility to RA in the Spanish population. Probably, this association has not been detected in the European population in the GWA studies because the earliest high-throughput platforms did not include SNP suitable markers (e.g. rs878081). Introduction Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease that often leads to disability from joint damage and inflammation. Although RA is an uncommon disease with a worldwide prevalence of approximately 1%, this pathology has a large economic and societal cost in * Correspondence: 1 Servicio de Inmunología, Hospital Universitario Virgen del Rocío (IBiS, CSIC, US), Avenida Manuel Siurot s/n, 41013-Sevilla, Spain Full list of author information is available at the end of the article terms of work-related disability [1]. Both environmental and genetic factors are considered to be associated with the onset and progression of this disease. Genome-wide associations (GWA) studies have identified common genetic variations associated with numerous complex diseases [2]. Contrary to the candidate gene approach, in which a limited number of genes chosen on the basis of known or suspected biological considerations are tested, the aim of GWA studies is to check association in the whole genome without a priori hypotheses. Many gene © 2013 García-Lozano et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. García-Lozano et al. Arthritis Research & Therapy 2013, 15:R11 http://arthritis-research.com/content/15/1/R11 loci have been identified as risk factors for RA in different GWA studies in European and East Asian populations. Some of these loci have been found to be restricted to a particular ethnic group but others, such as, CCR6, STAT4 and TNFAIP3, have been described as associated with RA in different populations [3]. Recently, the AIRE gene was identified as a genetic risk factor for RA in a GWA study performed in a Japanese population [4]. AIRE is a transcriptional regulator primarily expressed in medullary thymic epithelial cells, playing a functional role in thymocyte education and negative selection by controlling the expression of peripheral antigens in the thymus [5]. Therefore, AIRE is a good functional candidate in autoimmune diseases regardless of the population. In fact, mutations in this gene cause autoimmune polyendocrinopathy syndrome (APS1), which is one of the few known monogenic autoimmune diseases. Nevertheless, AIRE has not been identified as associated to RA in the European population, either in a large-scale GWA study or in a meta-analysis of GWA studies [6-10]. However, both of these studies had strong detection power, and therefore, the association of AIRE with RA, like that of PAD14, could be specific to some populations, such as in the Japanese study [4]. However, this gene has different linkage disequilibrium (LD) blocks in European and Asian populations (Figure 1), and the earliest GWA high-throughput platforms do not include any adequate tag single-nucleotide polymorphisms (SNPs) for the European population. This fact could influence the lack of association in Caucasian populations, therefore, we decided to further investigate the possible role of the AIRE gene in susceptibility to RA in a Spanish population. Materials and methods Study subjects A total of 472 RA patients (351 women and 121 men) who were unrelated were included in the study. All patients meet the American College of Rheumatology (ACR) revised RA criteria [11]. The mean (SD) age of onset was 49.23 (14.8) years. Information on rheumatoid factor, anti-cyclic citrullinated peptide antibodies and Disease Activity Score in 28 joints (DAS28) for RA activity was obtained. Patients were rheumatoid factor-positive in 85.2% of the cases and anti-cyclic citrullinated peptide antibodies were present in 82.2% of them. The control population consisted of 475 ethnically matched healthy bone marrow donors who were unrelated. All the subjects were Spanish Caucasian, and they were recruited from two Southern Spanish hospitals: Hospital Universitario Virgen del Rocío (Sevilla) and Hospital Universitario Virgen de las Nieves (Granada). No significant differences in clinical features, ratio of rheumatoid f (...truncated)