Pharmacogenetics: can genes determine treatment efficacy and safety in JIA?

Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic condition in childhood, with many children requiring immunomodulatory therapies for many years following diagnosis. A considerable proportion of children experience therapeutic inefficacy or substantial adverse effects, or both, but a lack of reliable clinical indicators and biomarkers to predict treatment response prevents optimization of existing therapies. The identification of valid candidate gene variants involved in the pathways of methotrexate and etanercept, the most commonly used medications in JIA, has seen little success to date. The limited success of these studies is possibly due to the presence of confounding variables in the study populations, the heterogeneity of outcome parameters used to determine treatment response and the small number of candidate gene variants analysed. The first genome-wide pharmacogenetic study in JIA has identified gene regions of particular biological interest, but these findings require validation. Moreover, epigenetic mechanisms as well as ontogeny processes might be additional factors influencing drug responses. Access to large, well-documented JIA cohorts and the rapid development of advanced genome analytics is ushering in a personalized approach to treatment. The discovery of new pharmacogenomic biomarkers and systems pathways can provide new drug targets and predictive tools for improved drug response and fewer adverse drug reactions in JIA.