Abstract Disclosure: M. Salama: None. F. Pinto e Vairo: None. D. Hassan: None. S. Pittock: None. A. Lteif: None. O. Olson: None. A. Al Nofal: None. K. Leopold: None. S. Kumar: None. Objective: This study aimed to evaluate the effects of semaglutide on body mass index (BMI) and cardiometabolic profiles in adolescents with genetic variants associated with a likely high risk of monogenic obesity. Methods: A retrospective chart review was conducted for adolescents with severe obesity who underwent multigene panel testing for monogenic obesity and were treated with semaglutide. Results: Data from 27 adolescents were analyzed. At baseline, the median BMI percent of the 95th percentile (IQR) was 148 (135-189), with a mean age (SD) of 15.5 years (1.93) at treatment initiation and a median (IQR) treatment duration of 8 months (6-12). The median semaglutide dose (IQR) was 1.7 mg weekly (1.0- 2.4). Seven participants comprised the ‘’likely monogenic risk’’ group, characterized by predicted deleterious variants in dominant genes and/or carrying known dominant risk alleles. Twenty patients formed the “indetermined/negative “group, defined as harboring single rare variants in recessive genes or negative panel testing. In the likely monogenic risk group, weight loss was 8.5% with a median decrease in BMI % of the 95th %ile of 17 (95% CI 1.5- 22, p = 0.02). In the indetermined/negative group, weight loss was 7.6% with a median decrease in BMI % of the 95th %ile of 14 (95% CI 11.5- 27.5, p = <0.001). There was no statistically significant difference in median BMI % of the 95th % ile reduction between the two groups (p = 0.8) or BMI percent change (p = 0.89). Cardiometabolic changes in the likely monogenic risk group included reductions in HbA1c by 0.3% (95% CI: 0.15- 0.4, p = 0.03), total cholesterol by 15 mg/dL (95% CI: 7- 48, p = 0.03), and non-HDL cholesterol by 16.5 mg/dL (95% CI: 12- 40, p = 0.03). No significant changes were observed in fasting blood glucose, triglycerides, LDL cholesterol, HDL cholesterol, or ALT levels. The indetermined/negative group exhibited a significant reduction in HbA1c by 0.25% (95% CI 0.1 - 0.7| p = 0.009). Conclusion: Semaglutide treatment was associated with significant reductions in BMI and improvements in several cardiometabolic parameters in adolescents with likely high-risk monogenic obesity variants. These findings suggest semaglutide as a potentially effective therapeutic option for managing severe obesity in this population. Larger prospective studies are warranted to confirm and further assess these outcomes. Presentation: Monday, July 14, 2025