The Necessity of POMC and MC3R Analysis in the First-Level Diagnosis of Monogenic Obesity: The Experience of Two Italian Centers

Background/Objectives: Obesity is a global health emergency with a complex etiology, in which monogenic forms, although rare, are significantly underdiagnosed. In our clinical setting, first-tier genetic screening panels targeting LEP, LEPR, BDNF, FTO, and MC4R often fail to identify a causative variant, leaving a significant diagnostic gap. This study aimed to assess the prevalence of variants in other critical genes of the melanocortin pathway to improve diagnostic yield. Methods: We analyzed 88 patients with non-syndromic obesity (Body Mass Index, BMI > 30 kg/m2), who were first screened for our standard obesity-related genes. In those testing negative, we expanded the analysis to include the MC3R and POMC genes. In silico bioinformatic tools were used to predict the functional consequences of identified variants on protein structure and splicing. Results: We found several variants in POMC, specifically within the regions coding for alpha-, beta-, and gamma-MSH peptides. A bioinformatic analysis suggests that these variants disrupt the melanocortin signaling pathway, likely contributing to an intermediate susceptibility phenotype in our adult cohort. Additionally, a clinical follow-up of a patient carrying the rare BDNF p.Thr2Ile variant revealed a suboptimal response to high-dose tirzepatide treatment (9% weight loss over 72 weeks), notably inferior to the average response observed in clinical trials. Conclusions: Our findings demonstrate that expanding first-level routine testing to include POMC and MC3R is essential to maximize diagnostic yield and improve clinical management.