Department of Rheumatology and 1 Section of Molecular Epidemiology, Department of Medical Statistics and Bioinformatics, Leiden University Medical Center, Leiden, The Netherlands
Correspondence to: J. Wesoly, Department of Rheumatology, Leiden University Medical Center, Postbus 9600, 2300 RC Leiden, The Netherlands. E-mail: j.z.wesoly{at}lumc.nl
SIR, Among a number of genes, RUNX1, a haematopoietic transcription activator and repressor, has been recently identified as a rheumatoid arthritis (RA) susceptibility gene [1]. In order to replicate and confirm this finding, we set out to determine the genotype and allele frequencies of RUNX1 intronic gene variant (rs2268277) in a Caucasian population of RA patients.
Six hundred and sixty-five RA patients and 632 ethnically matched controls were included in the analysis. All RA patients fulfilled criteria of the American College of Rheumatology. Our institutional review board (Commissie Medische Ethiek) approved all protocols and subjects were enrolled with informed consent. Three hundred and ninety of the patients were participants in the population-based arthritis inception cohort [2]; shared epitope (SE) genotyping (n = 313) and serological [rheumatoid factor (RF), n = 254; antibodies to cyclic citrullinated peptide (anti-CCP), n = 341] data were available for the patients. The other 275 patients were consecutive patients from an out-patient clinic and have been described by Brinkman et al. [3].
Patients and controls were genotyped for the RUNX1 SNP using time-of-flight mass spectrometry based Sequenom Mass Array Platform (Sequenom, San Diego, CA, USA). In both groups genotypes were in HardyWeinberg equilibrium. The 2 test was used for association analysis.
Interestingly, in contrast with a previous report [1], we did not observe a significant difference in genotype frequencies between patients and controls, as shown in Table 1. Similarly, the minor allele frequencies did not vary between the two groups (0.36 vs 0.35, P = 0.46).
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It is unlikely that this intronic SNP or another RUNX1 polymorphism in linkage disequilibrium (LD) with the SNP analysed here is a functional variant in our population. The inconsistencies could be explained by a possible difference in LD between the Japanese and European populations; if this were the case, the intronic RUNX1 SNP might not be a good marker to use to explain previously observed effects [1].
Association of the polymorphism in intron 6 of RUNX1 has also been investigated in the Newfoundland cohort of patients with psoriatic arthritis (PsA), which was defined as an autoimmune disease combining features of RA, psoriasis and inflammatory bowel disease [4]. Similarly to our findings, no association of RUNX1 SNP with PsA was observed in this analysis. The current data suggest that RUNX1 is not an RA susceptibility gene for the Western European population but may still be of relevance in Asian populations.
This study was supported by the Center for Medical Systems Biology (CMSB), a center of excellence approved by the Netherlands Genomic Initiative/Netherlands Organization for Scientific Research (NWO).
The authors have declared no conflicts of interest.
References
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