Open-label Extension Study to Evaluate Metreleptin in Patients With Partial Lipodystrophy

Inclusion Criteria: 1. Age ≥13 years of age, inclusive, at the time of signing the informed consent form (ICF). 2. Subjects must have completed the Parent study APG-20 and, in the opinion of the Investigator and Sponsor, have been compliant with study procedures through Parent study Month 12 visit. 3. Negative pregnancy test (urine or serum) for female subjects of childbearing potential 4. Female subjects must be postmenopausal (defined as cessation of menses for at least 1 year), surgically sterile (hysterectomy, bilateral oophorectomy, or tubal ligation), or willing to use a highly effective method of contraception (such methods include combined \[estrogen and progestogen containing\] hormonal contraception associated with inhibition of ovulation: oral/intravaginal; transdermal/progestogen-only hormonal contraception associated with inhibition of ovulation: oral/injectable; implantable/intrauterine device \[IUD\]/intrauterine hormone-releasing system \[IUS\]/bilateral tubal occlusion/vasectomized partner/sexual abstinence) for the duration of the study (from the time they sign an ICF, until 4 weeks after the last dose of study treatment). Hormonal contraception alone (including oral, injectable, transdermal, and implantable) is not acceptable; an additional barrier method must be used. Intravaginal hormonal contraception or IUS alone are allowed per Investigator's discretion. Subjects on oral contraceptives will not be required to discontinue medication. Subjects will not be permitted to commence oral contraceptives while taking study treatment during the study. 5. Male subjects must be surgically sterile or willing to use an acceptable method of contraception for the duration of the study (from the time they sign an ICF), until 4 weeks after the last dose of study treatment. An acceptable method of contraception would be a barrier method, such as condoms, restraining from having sex, or a partner using the approved methods of contraception for female subjects as per Inclusion Criteria #4. 6. Subjects who are blood/egg/sperm donors should be willing to halt donations during the study and for 4 weeks following their last dose of study treatment. 7. Subjects who are willing to provide informed consent/assent prior to any study-specific procedures. If a minor, the subject has a parent or legal guardian able to read, understand, and sign the ICF and/or a Child Assent Form (if applicable), communicate with the Investigator, and understand and comply with the protocol requirements. Adolescent subjects must also read and understand the Child Assent Form. 8. Subjects who are willing to follow the dietary restrictions recommended by the Investigator. Exclusion Criteria: 1. Severe hypersensitivity reactions to the study treatment of the Parent study APG-20. 2. Known to have tested positive for human immunodeficiency virus (HIV) or known to be diagnosed with HIV-related LD. Positive HIV test in countries requiring HIV testing. 3. Are immunocompromised or receiving immunomodulatory drugs. 4. Estimated glomerular filtration rate (eGFR) \<30 mL/min/1.73m2 calculated by Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) for subjects ≥18 years of age and by Bedside Schwartz for subjects \<18 years of age. 5. Diagnosis of clinically significant hematological abnormalities (including but not limited to clinically significant leukopenia, neutropenia, bone marrow abnormalities, leukemia or lymphoma, or clinically significant pathological lymphadenopathy). 6. Malignancy that is ongoing/not in remission or that currently requires or has required active treatment within the past year (with the exception of basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or carcinoma in situ \[e.g., breast carcinoma, cervical cancer in situ\] that have undergone potentially curative therapy). 7. For females only: currently pregnant (confirmed with a positive pregnancy test) or breastfeeding. 8. Any condition where, in the opinion of the Investigator, participation in this study may pose a significant risk to the subject.