An Observational,Prospective Natural History Study of Early-Onset Extreme Obesity Due to Bi-Allelic Loss-of-Function Mutations in the POMC, PCSK1 or LEPR Genes

Inclusion Criteria: 1. Age 2 years or older 2. Study participant and/or parent or guardian is able to communicate well with the investigator, to understand and comply with the requirements of the study, and be able to understand and sign the written informed consent/assent. 3. Have documented results of DNA sequencing for the three genes of interest: POMC, PCSK1 and LEPR. 4. Bi-allelic, homozygous or compound heterozygous (a different gene mutation on each allele) genetic status for either the POMC or PCSK1 genes, resulting in a severe POMC deficiency obesity clinical phenotype, or a similar bi-allelic gene status for the LEPR gene leading to identified LEPR deficiency obesity. 5. Patients who are willing to come in for routine office visits approximately every 6 months. Exclusion Criteria: 1. Participation within the past 3 months in a clinical trial of any investigational medicine for obesity. 2. Confirmed diagnosis of Prader-Willi syndrome, Bardet-Biedl syndrome, Alström syndrome, or other syndromic form of genetic obesity.