IFNG and obesity due to melanocortin 4 receptor deficiency: Severity of obesity resulted to be associated with lower plasma levels of oxytocin (p = 0.053), vitamin D deficiency (p = 0.006) and higher plasma levels of IFN-γ (p = 0.004), IL-6 (p = 0.013), IL-7 (p = 0.013), TNF-alpha (p = 0.036) and chemokine ligand 3 (CCL3) (p = 0.013, R2 = 0.03).