NTN1 and obesity due to melanocortin 4 receptor deficiency: Several studies report higher serum netrin-1 in individuals with obesity, prediabetes, or newly diagnosed type 2 diabetes, with positive correlations to insulin-resistance indices (e.g., HOMA-IR) and glycemic markers (Shalaby et al., 2021; Yim et al., 2018; Akbaba E. et al., 2021).