Epistatic interaction of ERAP1 and HLA-B in Behçet disease: a replication study in the Spanish population

Behçet's disease (BD) is a multifactorial disorder associated with the HLA region. Recently, the ERAP1 gene has been proposed as a susceptibility locus with a recessive model and with epistatic interaction with HLA-B51. ERAP1 trims peptides in the endoplasmic reticulum to optimize their length for MHC-I binding. Polymorphisms in this gene have been related with the susceptibility to other immune-mediated diseases associated to HLA class I. Our aim was, the replication in the Spanish population of the association described in the Turkish population between ERAP1 (rs17482078) and BD. Additionally, in order to improve the understanding of this association we analyzed four additional SNPs (rs27044, rs10050860, rs30187 and rs2287987) associated with other diseases related to HLA class I and the haplotype blocks in this gene region. According to our results, frequencies of the homozygous genotypes for the minor alleles of all the SNPs were increased among patients and the OR values were higher in the subgroup of patients with the HLA-B risk factors, although differences were not statistically significant. Moreover, the presence of the same mutation in both chromosomes increased the OR values from 4.51 to 10.72 in individuals carrying the HLA-B risk factors. Therefore, although they were not statistically significant, our data were consistent with an association between ERAP1 and BD as well as with an epistatic interaction between ERAP1 and HLA-B in the Spanish population

Genome-wide association study identifies variants in the MHC class I, IL10, and IL23R-IL12RB2 regions associated with Behcet's disease

Behcet's disease is a genetically complex disease of unknown etiology characterized by recurrent inflammatory attacks affecting the orogenital mucosa, eyes and skin. We performed a genome-wide association study with 311,459 SNPs in 1,215 individuals with Behcet's disease (cases) and 1,278 healthy controls from Turkey. We confirmed the known association of Behcet's disease with HLA-B*51 and identified a second, independent association within the MHC Class I region. We also identified an association at IL10 (rs1518111, P = 1.88 x 10(-8)). Using a meta-analysis with an additional five cohorts from Turkey, the Middle East, Europe and Asia, comprising a total of 2,430 cases and 2,660 controls, we identified associations at IL10 (rs1518111, P = 3.54 x 10(-18), odds ratio = 1.45, 95% CI 1.34-1.58) and the IL23R-IL12RB2 locus (rs924080, P = 6.69 x 10(-9), OR = 1.28, 95% CI 1.18-1.39). The disease-associated IL10 variant (the rs1518111 A allele) was associated with diminished mRNA expression and low protein production