This study is researching an experimental drug called mibavademab. The study is focused on participants with GLD who have been on metreleptin treatment for at least 6 months with no change in dose for the last 3 months. The aim of the study is to see how safe and tolerable mibavademab is when switching from treatment with metreleptin. The study is looking at several other research questions, including: * What side effects may happen from taking mibavademab * How much mibavademab is in the blood at different times * Whether the body makes antibodies against mibavademab (which could make mibavademab less effective or could lead to side effects)