Original articleA genetic association study of the CLEC12A gene in rheumatoid arthritis
Introduction
Rheumatoid arthritis (RA) is a disabling autoimmune disorder that affects peripheral joints leading to cartilage destruction and bone erosions [1]. Complex interactions between environmental factors (e.g. smoking) and several genetic determinants lead to the development of RA [2]. The key genetic factor that predisposes to RA, the HLA locus, represents about 30% of the genetic component of this disorder. In search of the remaining genetic determinants of RA, over 30 additional genetic loci have been identified by genome-wide linkage or association studies during the past 7 years [3], [4], [5].
Several lines of evidence indicate that genes within the natural killer gene complex (NKC) are linked to autoimmune disorders including RA [6], [7]. The NKC maps to chromosome 12p13.1 in humans and the syntenic region on chromosome 6 in mice [8]. It encompasses several multi-gene families that encode for C-type lectin receptors expressed either by NK or myeloid cells [9]. The C-type lectin receptors expressed by myeloid cells are distributed in two clusters, namely, the dectin-1 family and the dendritic cell immunoreceptor (DCIR) family that is located centromeric to the NKC. The CLEC4A gene in the DCIR cluster was recently reported to be associated with susceptibility to anti-cyclic citrullinated peptide (CCP) negative RA [10]. The CLEC4A gene encodes for DCIR, an inhibitory receptor with an immunoreceptor tyrosine inhibitory motif in its cytoplasmic domain [9]. Corroborating the genetic association between CLEC4A and RA, CLEC4A knock-out mice are more susceptible to collagen-induced arthritis than their wild-type litter mates [11]. DCIR is expressed by monocytes, macrophages, neutrophils, dendritic cells and B lymphocytes and is involved in multiple processes, from the inhibition of IFN-α production in plasmacytoid dendritic cells and of Ca2+ mobilization in B cells to antigen presentation [12].
Similar to CLEC4A, the CLEC12A gene also maps to the NKC and codes for a C-type lectin with an immunoreceptor tyrosine-based inhibitory motif in its cytoplasmic domain known as the myeloid inhibitory C-type lectin-like receptor (MICL) [13], [14], [15]. MICL is also expressed by cells of the myeloid lineage such as macrophages and dendritic cells and modulates cytokine synthesis [16], [17]. The cross-linking of MICL during the stimulation of monocyte-derived dendritic cells with LPS, for instance, suppresses LPS-induced TNF-α, IL-12p40 and IL-12p70 production. Since (i) MICL shares structural and functional characteristics with DCIR and (ii) an increased gene expression of CLEC12A in rheumatoid fibroblast-like synovial cells was previously reported to correlate with elevated rheumatoid factor (RF) values [18], we sought to determine whether a genetic association exists between the CLEC12A gene and RA by combining a candidate gene study and phenotype-based approach.
Section snippets
Methods
The present study was approved by the Ethics Committee of Hôpital Kremlin-Bicêtre (Paris, France) and all individuals provided an informed consent before participating in the study.
Verification of Hardy-Weinberg equilibrium for each TagSNP
Genotyping of the discovery cohort of trio families revealed that the eight TagSNPs chosen for this study were in Hardy-Weinberg equilibrium in the control group (data not shown).
Association analysis between individual TagSNPs and RA in the discovery cohort
Analysis of the genotyping data by TDT identified an overtransmission of the C allele of the rs1323461 SNP located in the fifth intron of CLEC12A gene according to Genehunter (56.6% of allele C transmission, uncorrected P = 0.046), as well as to the family-based test (P = 0.046) (Table 1). The C allele frequency was higher
Discussion
The present study aimed at searching for a genetic association between the CLEC12A candidate gene and RA in a discovery cohort consisting of 384 trio families and in a second case-only sample of 747 unrelated RA patients, all of Western European ethnicity. An overtransmission of the C allele of the TagSNP located in the fifth intron of CLEC12A was identified in the discovery cohort, and the global distribution of genotypes for this TagSNP was significantly different between patients and
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.
Acknowledgments
L.M. is supported by a career award from the Fonds de la Recherche en Santé du Québec (FRSQ). J.-M.L. is a recipient of a Canadian Arthritis Society (CAN) and a Fonds de recherche sur l’arthrite et les maladies rhumatismales (FRAM-Université Laval) scholarship. This research was funded by operating funds awarded to M.J.G.F. by the Canadian Arthritis Network (CAN) and the Natural Sciences and Engineering Research Council of Canada (NSERC). The authors are grateful to the RA patients, their
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Cited by (0)
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The European Consortium on Rheumatoid Arthritis Families (ECRAF): F. Cornélis (coordinator), T. Bardin (France), P. Migliorini, S. Bombardieri (Italy), R. Westhovens, J. Dequeker (Belgium), A. Balsa, D. Pascuale-Salcedo (Spain), P. Barrera, L. Van de Putte, P. Van Riel, T.R. Radstake (The Netherlands), and H. Alves, A. Lopes-Vaz, M. Fernandes, C. Vaz (Portugal).