Objectives: To confirm and define the genetic association of STAT4 and systemic lupus erythematosus (SLE), investigate the possibility of correlations with differential splicing and/or expression levels, and genetic interaction with IRF5.
Methods: 30 tag SNPs were genotyped in an independent set of Spanish cases and controls. SNPs surviving correction for multiple tests were genotyped in five new sets of cases and controls for replication. STAT4 cDNA was analysed by 5′-RACE PCR and sequencing. Expression levels were measured by quantitative PCR.
Results: In the fine mapping, four SNPs were significant after correction for multiple testing, with rs3821236 and rs3024866 as the strongest signals, followed by the previously associated rs7574865, and by rs1467199. Association was replicated in all cohorts. After conditional regression analyses, two major independent signals, represented by SNPs rs3821236 and rs7574865, remained significant across the sets. These SNPs belong to separate haplotype blocks. High levels of STAT4 expression correlated with SNPs rs3821236, rs3024866 (both in the same haplotype block) and rs7574865 but not with other SNPs. Transcription of alternative tissue-specific exons 1, indicating the presence of tissue-specific promoters of potential importance in the expression of STAT4, was also detected. No interaction with associated SNPs of IRF5 was observed using regression analysis.
Conclusions: These data confirm STAT4 as a susceptibility gene for SLE and suggest the presence of at least two functional variants affecting levels of STAT4. The results also indicate that the genes STAT4 and IRF5 act additively to increase the risk for SLE.
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Additional figures and tables are published online only at http://ard.bmj.com/content/vol68/issue11
A-KA, AMD-V, SVK, ES, JM and MEA-R, at their respective positions, contributed equally to this work
Funding This work has been supported in part by grants from the European CVDIMMUNE project from the European Commission LSHM-CT-2006-037227, the Swedish Research Council (12673), the Torsten and Ragnar Söderbersstiftelse, the Swedish Association Against Rheumatism, the King Gustaf the Vth 80th-Jubilee Foundation and the Knut and Alice Wallenberg Foundation for supporting MEAR through the Royal Swedish Academy of Sciences. This study was also supported by grant SAF2006-00398 from the Spanish Ministerio de Educacion y Ciencia, grant PI052409 from the Fondo de Investigación Sanitaria (Spain), C2.12 from BMBF Kompetenznetz Rheuma in Germany and FISM, Regione Piemonte (CIPE) and the Consejo Nacional de Ciencia y Tecnología (CONACYT: SALUD-2004-01-153). MEAR is a Greenberg Scholar at the OMRF.
Competing interests JW and HA are employees of Merck Serono Inc and produced the Argentine 100k data on which our investigation and search for STAT4 variants was first based.
Ethics approval Ethics committee approval from each of the participating institutions.