1\. Diagnosis of congenital or acquired GLD as defined by Multi-Society Practice Guidelines
For Part A only:
1. Participants ≥2 years of age at screening
2. At least one of the below criteria are fulfilled during screening (measurements can be repeated once during screening period)
* HbA1c ≥7%
* Fasting TG ≥500 mg/dL
* Fasting TG value of ≥300 mg/dL and the presence of another complication of GLD consistent with leptin deficiency (history of diabetes mellitus, hyperphagia, Metabolic Associated Fatty Liver Disease (MAFLD), polycystic ovary syndrome, etc)
3. Weight ≥15 kg at screening
4. Willing and able to provide, or have the treating physician provide, values of HbA1c and fasting TG from at least 6 months prior to screening, as described in the protocol
For Part B only:
1. Participants \<12 years of age at screening
2. Weighing ≥7 kg at screening
3. No metabolic criteria for study entry is required, as described in the protocol
You may not be if
1. Has a current diagnosis of familial or acquired partial lipodystrophy or autoimmune (Type 1) diabetes mellitus
2. Any malignancy, eg, lymphoma, within the past 1 year, prior to screening visit, as described in the protocol
3. eGFR of \<30 mL/min/1.73 m2 based on Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine or Schwartz equation, as applicable, at screening. Assessment can be repeated once
4. History of heart failure hospitalization, diagnosis of a myocardial infarction, stroke, clinically significant arrhythmia, as described in the protocol
5. Treatment with over-the-counter or prescription medications with the intention of weight loss within 3 months prior to the screening visit
For Part A only:
1. Treatment with metreleptin within 3 months of the screening visit
2. Addition or discontinuation of prescription medications or over-the-counter supplements for diabetes and/or dyslipidemia within 3 months prior to the start of the screening period, or changes in the use of these medications, as described in the protocol
3. Significant changes to lifestyle and diet, as described in the protocol
4. Current chronic treatment with high-dose corticosteroids, defined as use of higher than physiologic doses, as described in the protocol
