Participation in the METRE-PL study may last for at least 17 months. In this study, you (or your child) will receive either metreleptin or a placebo, as an injection under your skin. A placebo injection looks like the metreleptin injection but does not contain any active medication. Both metreleptin and placebo will be referred to as the “study medication.” Neither you nor the study physician will know if metreleptin or a placebo is given. As part of your (or your child’s) participation, you (or your child) will receive a daily dose of the study medication for 12 months. The first study medication dose will be administered to you (or your child) at your study location, and you are responsible for administering all subsequent doses for the remainder of the study. The daily dose requires an injection of the study medication under your (or your child’s) skin. After completing the 12-month study, you will be offered to enroll in an expanded access program (EAP) where you will receive metreleptin as per your country specific rules. During the study, you (or your child) will be required to: Take the study medication daily Go to the study location for study visits Follow a specific diet Continue taking your (or your child’s) regular medications while receiving the study medication, if applicable In addition, there will be several laboratory assessments designed to monitor your (or your child’s) health and condition throughout the study’s duration. These assessments include, but are not limited to, blood tests, urine tests, fasting, and optional genetic testing to confirm diagnosis of FPLD. To provide comprehensive support for enrolled study participants and their caregivers, all expenses related to travel, accommodation, and study assessments will be covered.