This study is testing a new medicine called iptacopan for people with a kidney problem known as C3 glomerulopathy (C3G). C3G is a disease that affects the kidney's ability to filter waste from the blood. The study will compare iptacopan to a placebo (a fake treatment) and standard care to see if it helps improve kidney function.

**Key Points:**

• The study involves multiple centers and requires regular check-ups.
• Participants must be aged 12-60, and certain vaccinations are needed before starting.
• Participants should not have had any recent organ transplants or severe kidney damage.

The study is controlled and double-blind, meaning neither the doctors nor the patients know who is receiving the actual medicine versus the placebo. To join, participants need a confirmed diagnosis of C3G and must have been on certain medications for at least 90 days. The study will measure things like protein levels in urine (UPCR) and kidney function (eGFR) to see if iptacopan helps. It also checks for safety and side effects. Kidney biopsies, a procedure to take a small piece of kidney tissue for testing, will be done for adults to see if there are improvements. Participants with certain infections or other conditions may not join.