Bardet-Biedl syndrome (BBS) and other rare disorders associated with impairment of the melanocortin-4 receptor (MC4R) pathway are characterized by severe early-onset obesity, hyperphagia, and substantial morbidity. Setmelanotide, an MC4R agonist, is approved in Europe for selected genetic obesity disorders and reimbursed in Germany for eligible patients. This study aims to evaluate the effectiveness, safety, treatment persistence, metabolic outcomes, and patient-reported outcomes of Setmelanotide under real-world conditions. The registry is designed to allow future inclusion of additional MC4R agonists as they become approved and clinically available. The study will primarily be conducted at University Hospital Essen and will collect longitudinal routine clinical data from pediatric and adult patients receiving MC4R agonist therapy according to approved indications.