Common genetic variants of the IFN-γ and IFNGR1 regions : disease associations and functional properties
There is growing evidence that susceptibility to many inflammatory and infectious diseases may be influenced by our genetic make up. Genetic variants in important immune genes may partially explain variation in susceptibility to common diseases. Interferon-γ (IFNγ) is one of the central mediators of the innate and adaptive immunity and has been implicated in a wide range of infectious and inflammatory disease processes. Severe disruptive mutations in coding regions of the IFN-γ receptor 1 gene (IFNGR1) have been found to be associated with fatal but very rare mycobacterial infections. This study looked at common polymorphisms in potentially regulatory non-coding regions of the IFNγ gene and the IFNGR1 gene and investigated their association with susceptibility to severe malaria, a disease for which there have been indications of a genetic component to susceptibility. Malaria is one of the major causes of childhood deaths in Africa. IFNγ and its receptor have been shown to be critically involved in the host response to the malaria parasites. The promoter regions of IFNGR1 and its neighbouring genes, located on chromosome 6q23, and IFNγ and its neighbours, on chromosome 12ql4, were screened for polymorphisms. Haplotypes and linkage disequilibrium maps were constructed, signatures of natural selection were investigated, haplotype tagging SNPs were dentified, and association with disease was analysed. One of these preliminary results was a putative association between the IFNGRl-470ddel allele and susceptibility to severe malaria in the Mandinka ethnic group. This allele was in strong linkage disequilibrium (LD) with markers which are a considerable distance away which might represent a signature of natural selection. To assess the potential functional significance of the IFNGR1-47Q polymorphism, its effects on DNA-protein interactions and gene expression was investigated further in various cell lines. Evidence of tissue-specific nuclear protein binding to this site which seems to be involved in transcriptional regulation was observed.