Autoimmune diseases — connecting risk alleles with molecular traits of the immune system

Genome-wide approaches have advanced the study into mechanisms triggering autoimmunity. This Review illustrates how this has been achieved for twelve common autoimmune diseases, and discusses recent functional genomics approaches that have the potential to help define key immune molecular traits, cell types and cell states. Genome-wide strategies have driven the discovery of more than 300 susceptibility loci for autoimmune diseases. However, for almost all loci, understanding of the mechanisms leading to autoimmunity remains limited, and most variants that are likely to be causal are in non-coding regions of the genome. A critical next step will be to identify the in vivo and ex vivo immunophenotypes that are affected by risk variants. To do this, key cell types and cell states that are implicated in autoimmune diseases will need to be defined. Functional genomic annotations from these cell types and states can then be used to resolve candidate genes and causal variants. Together with longitudinal studies, this approach may yield pivotal insights into how autoimmunity is triggered.