Understanding the genetic contribution to rheumatoid arthritis

The identification of the genetic variants that mediate the risk for susceptibility and severity of rheumatoid arthritis will allow the development of new drug targets and also increase the ability to predict disease course. Technical and methodologic progress has fueled the advances in this field.

The second risk factor for rheumatoid arthritis, the PTPN22 polymorphism, has been identified. This genetic variant regulates the threshold of T cell activation. Intriguingly, this variant is a risk factor for diabetes as well. Moreover, it has been shown that multiple genetic variants in one pathway (both in a transcription factor, RUNX-1, as in the transcription factor binding site of RUNX1 in the SLC22A4 gene) can each confer very small risks but by gene-gene interactions can confer a ninefold risk for rheumatoid arthritis. These genetic risk factors have been found to confer risk for multiple autoimmune diseases. Phenotype-genotype interactions were described by the enhanced prevalence of a rheumatoid arthritis-specific autoantibody (anti-cyclic citrullinated peptide antibodies) in rheumatoid arthritis patients that harbor the rheumatoid arthritis-associated human leukocyte antigen class II genes, the shared epitope alleles. An environmental factor, smoking was demonstrated to confer risk for rheumatoid arthritis, especially in patients positive for both shared epitope and rheumatoid arthritis-specific anti-cyclic citrullinated peptide antibodies.

Two new pathways, T cell receptor signaling and a hematopoietic-specific signal transduction pathway, have been discovered that allow future pharmacologic interventions. The description of the new genetic risk factors and the interaction with environmental triggers as well as phenotypic features are gradually expanding the ability to predict disease susceptibility and course.