S100A9 and obesity due to melanocortin 4 receptor deficiency: Among these 46 immune system genes, 12 of them (or 26%) were previously associated with obesity-related traits and 10 of them had expression altered by antipsychotics only in the weight gain group (LTF, LCN2, MMP8, OLR1, MPO, LILRA3, AIM2, LILRA5, S100A9, and CHIT1).