PDE1C and obesity due to melanocortin 4 receptor deficiency: Eventually, we created a multivariable linear regression model, expressed by the combination of each variable and the corresponding coefficient, namely PDE1C = -0.004* p_Firmicutes + 3.059*DL-Glutamine − 571.6*Epiandrosterone + 206.5*3-Hydroxypicolinic-acid (Fig. 8E).This model suggested that the plasma metabolites Epiandrosterone, 3-Hydroxypicolinic_acid, Glutamine_D, and the gut microbiota p_Firmicutes may synergistically impact the expression levels of the PDE1C gene in the blood of obese children, promoting the onset and development of obesity and its associated complications.