| Background Vitiligo is a genetically complex skin disorder that afflicts 0.1%-2% of the population throughout the world. Although the etiology of vitiligo remains obscure, the inherited nature and its frequent association with autoimmune disease indicate that genetic and immunological components play a role in the pathogenesis of the disease. Up to date, linkage analysis has identified six significant susceptible loci harboring the genetic risk factors of vitiligo and many candidate genes have been proposed. Our previous genome wide linkage scan of 143 Chinese families identified a significant genetic susceptibility locus for generalized vitiligo on chromosome 22q12. X-box binding protein 1(XBP1) gene is within this locus. With a view to the autoimmunity feature of vitiligo supported by the significant linkage to the MHC region on 6p21-p22 and evidences for the association of HLA-DR with vitiligo, XBP1 is a strong biological candidate gene for vitiligo due to its plausible role in the development of the disease through its interaction with HLA-DR.Objective To systematic investigate the association between the XBP1 gene common variation and susceptibility to vitiligo in Chinese Population.Method We performed a series of genetic association and functional analyses. Firstly, we sequenced all the exons, exon-intron boundaries as well as some 5'and 3'flanking sequences of XBP1 in 319 cases and 294 controls of Chinese Hans. We then performed an association analysis by genotyping a putative regulatory polymorphism within the promoter region of XBP1 in other two independent samples involving 365 cases vs 404 controls and 1402 cases vs1288 controls, including 94 trios. We also genotyped HLA-DRB4*01,DRB1*04,DRB1*07,DRB1*12 alleles using PCR-SSP and tested the epistatic interaction between this variation and HLA-DR alleles using logistical regression analysis. Subsequently, we performed an in-vitro reporter assay analysis to evaluate whether the promoter sequences carrying different SNP alleles have differential promoter activity. Then we analyzed the expression of XBP1 mRNA and protein level in the paired lesional and non-lesional skins using quantitative real-time PCR and immunohistochemistry analysis, respectively.Result We sequenced all the exons, exon-intron boundaries as well as some 5'and 3'flanking sequences of XBP1 in 319 cases and 294 controls of Chinese Hans. Of the 8 common variants identified, the significant association was observed at rs2269577 (p_trend=0.007, OR=1.36, 95%CI=1.09–1.71), a putative regulatory polymorphism within the promoter region of XBP1. We then sequenced the variant in additional 365 cases and 404 controls and found the supporting evidence for the association (p_trend =0.008, OR=1.31, 95%CI=1.07–1.59). To further validate the association, we genotyped the variant in another independent sample of 1402 cases and 1288 controls, including 94 parent-child trios, and confirmed the association by both case-control analysis (p=0.003, OR=1.18, 95%CI=1.06–1.32) and the family-based TDT test (p= 0.005, OR=1.93, 95%CI=1.21–3.07). The analysis of the combined 2086 cases and 1986 controls provided highly significant evidence for the association (p_trend= 2.94×10-6, OR=1.23, 95%CI=1.13–1.35). We also found the HLA-DRB1*07 allele to be significantly associated with vitiligo (p= 4.53×10-21, OR=1.98, 95%CI= 1.72-2.29) and observed a significant interaction between rs2269577 and HLA-DRB1*07 (p=0.033). Our subsequent functional study showed that the risk-associated C allele of rs2269577 had a stronger promoter activity than the non-risk G allele (P<0.05), and there was an elevated expression of XBP1 in the lesional skins of patients carrying the risk-associated C allele.Conclusion Our study has found a common regulatory variant, rs2269577, in the promoter region of XBP1 that is associated with increased risk for vitiligo and this association is probably due to the transcriptional modulation of XBP1 expression which was shown to be important for the development of vitiligo lesion. |
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