This study focuses on Juvenile Idiopathic Arthritis, which is a type of chronic arthritis—a condition involving inflammation and swelling of the joints—that affects children and adolescents. The investigation aims to determine the long-term safety and how well the body handles the medication filgotinib, which is also known by the brand name Jyseleca. The treatment is administered as an oral medication, meaning it is taken by mouth in the form of film-coated tablets.

The study is an open-label extension, which means that all participants know which medication they are receiving during this phase. Participants will continue to take the medication over an extended period to monitor for any adverse events, which are unexpected or unpleasant side effects. The research also looks at the occurrence of uveitis, an inflammation that can happen inside the eye, to ensure the treatment is safe for long-term use in young people.