Due to the abovementioned dependencies, the aim of this research was to evaluate the dynamics of changes in the concentration of KS, HA and HAPLN1 as potential biomarkers of joint dysfunction, and the effectiveness of an anti-cytokine therapy in the blood of JIA patients both before, during and after the 24-month treatment with etanercept (ETA). The gene discussed is HAPLN1; the disease is juvenile idiopathic arthritis.