Characterization of Genetic Risk Factors in Sjögrens Syndrome

Our genes define us. They determine the colour of your eyes, the length of your fingers, and the shape of your ears. They may also protect you from certain types of cancer, or put you at risk for various diseases. Several gene variants have already been identified as risk factors for autoimmune disease, and in a large international cohort of Sjögren's syndrome (SS) patients, we will identify and characterize disease specific genes that may unravel the pathology behind SS. Using a technique known as genome wide association studies, in which common genetic variants in individuals is examined to see whether they are associated with a specific feature, we aim to identify genes of interest. We have recently identified a couple of regions that do not map directly to any known genes, and we are utilising a new technique, HiChIP, to decide whether chromatin conformation and modifications are what causes biological effects.

Collective evidence establishes a complex genetic architecture for SS. Loci involved in both innate and adaptive immune responses are implicated and emphasize the importance of Type I and Type II interferon responses, IL12/STAT4 signaling, T and B cell involvement, and antigen presentation. Additional gene identification and characterization is imperative if we are to understand the role of genetics in SS. We plan to expand our successful Phase I GWAS, and expect that over the course of this project, additional genetic associations with SS will be identified (Aim 1). AIM 1: We will perform an expanded Phase II GWAS in additional cases and controls to increase our statistical power to detect associations as defined by genome-wide thresholds. We will use several analytical techniques and approaches that will allow us to characterize the novel candidates, including logistic regression, haplotype analyses, imputation, fine mapping genotyping, DNA sequencing, bioinformatics and functional genomic databases. AIM 2: Laboratory-based experiments will be conducted to test the most likely candidate variants for biological effects. We will compare subjects that are homozygous risk, heterozygous, and homozygous non-risk in a variety of experiments, testing for alterations in function based on genotype using approaches that address transcriptional effects, translational effects, and protein function. The specific experiments will be tailored to address the hypotheses developed as a result of completing Aim 1. We will begin by testing and confirming the hypothesis that expression traits are affected by risk alleles in the IL12A locus, characterizing IL12A mRNA transcript levels in relevant cell subsets, assess association and determine if functional consequences are specific to a particular cell type, characterize IL12A protein levels in serum, assess IL12A expression in salivary glands, evaluate downstream effects of IL12A, and compare genotype specific groups.