TNF and major depressive disorder: The mechanisms underlying the observation that TNF-α and IL-6 were not elevated in our sample of patients with PWS in contrast to other studies on this population, as well as on patients with schizophrenia, bipolar mania or major depressive disorder (MDD), may be due to the fact that the vast majority of our patients were not overweight (only two patients with BMI over 90th percentile for sex and age).