This study focuses on young people aged 12 to 17 who have Chronic Immune Thrombocytopenia (ITP), a rare blood disorder where the body’s immune system mistakenly attacks and destroys blood platelets, leading to easy bruising and bleeding. The study will test a medication called efgartigimod, given through intravenous infusion, compared to placebo to find the right dose for young patients with this condition.

The study consists of two parts. In the first part, participants will be randomly assigned to receive either efgartigimod or placebo through regular infusions. Neither the participants nor their doctors will know which treatment they are receiving during this phase. In the second part, all participants will receive the actual medication efgartigimod.

Throughout the study, researchers will monitor how the medication moves through the body, its effects on blood components, particularly platelets and antibodies, and its overall safety. They will also track any bleeding episodes and assess how the treatment impacts the participants’ quality of life. The study will evaluate if efgartigimod can help maintain adequate platelet counts in young patients with chronic ITP.