This study is researching a new drug called mibavademab (called "study drug"). The study involves participants with a condition called Generalized Lipodystrophy (GLD). The aim of the study is to see how well mibavademab works and what side effects it has. Researchers will also look at how much mibavademab is in the body at different times.

This is a 2-part study: Part A is an efficacy study in pediatric and adult participants, Part B is a safety and pharmacokinetic study in pediatric participants.

The study is researching several other questions, including:

• How mibavademab affects the amount of sugar in the blood
• How mibavademab affects the amount of fat (triglycerides) in the blood
• How mibavademab affects the amount of fat that has built up in the liver
• Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects)

Key Inclusion Criteria:

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

Key Exclusion Criteria:

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

NOTE: Other protocol defined inclusion/exclusion criteria apply.

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf