This study focuses on polyarticular-course juvenile idiopathic arthritis, a type of chronic joint inflammation that affects multiple joints in children and adolescents. The research aims to evaluate the safety and effectiveness of the drug filgotinib, which is also referred to by the code name GLPG0634. This medication is administered as an oral use treatment in the form of film-coated tablets.

The study will monitor how the body processes the medication, a process known as pharmacokinetics. It will also look at how well the drug works to reduce symptoms and whether it causes any side effects. During the course of the study, participants will be observed over several weeks to track changes in their condition and any potential reactions to the treatment.