Single nucleotide polymorphisms in the human interleukin-1B gene affect transcription according to haplotype context.

We questioned the significance of haplotype structure in gene regulation by testing whether individual single nucleotide polymorphisms (SNPs) within a gene promoter region [interleukin-1-beta (IL1B)] might affect promoter function and, if so, whether function was dependent on haplotype context. We sequenced genomic DNA from 25 individuals of diverse ethnicity, focusing on exons and upstream flanking regions of genes of the cluster. We identified four IL1B promoter region SNPs that were active in transient transfection reporter gene assays. To substantiate allelic differences found in reporter gene assays, we also examined nuclear protein binding to promoter sequence oligonucleotides containing different alleles of the SNPs. The effect of individual SNPs on reporter gene transcription varied according to which alleles of the three other SNPs were present in the promoter construct. The SNP patterns that influenced function reflected common haplotypes that occur in the population, suggesting functionally significant interactions between SNPs according to haplotype context. Of the haplotypes that include the four functional IL1B promoter SNPs (-3737, -1464, -511, -31), the four haplotypes that showed different contextual effects on SNP function accounted for >98% of the estimated haplotypes in Caucasian and African-American populations. This finding underlines the importance of understanding the haplotype structure of populations used for genetic studies and may be especially important in the functional analysis of genetic variation across gene regulatory regions.

Clearance of hepatitis C virus is not associated with single nucleotide polymorphisms in the IL-1, -6, or -10 genes.

Hepatitis C virus (HCV) commonly causes a chronic infection, but a minority of patients are able to clear the virus and do not run the risk of developing HCV-induced organ damage. Genetic associations between immunoregulatory cytokines interleukin (IL)-1, -6, and -10 with clinical features of HCV, including virus clearance, have been inconsistent. We determined cytokine genotypes in 606 patients who had serologic evidence of HCV exposure, 190 (18%) of whom were consistently negative for HCV RNA, indicating successful virus clearance. There was no significant difference in genotype frequencies between HCV clearance and nonclearance groups for IL-1B (-511 and +3954), IL-1A (+4845), IL-1RN (+2018), IL-6 (-174), or IL-10 (-1082). We conclude that these single nucleotide polymorphisms are unlikely to play an important, if any, role in determining the likelihood of clearing HCV infection.