ALDH1B1 and major depressive disorder: To further explore the key proteins related to NK1R which affected the development of diabetes and depression, we conducted PPI analysis and identified the five NK1R-related genes: aldehyde dehydrogenase 1B1 (ALDH1B1), forkhead box P2 (FOXP2), galanin (GAL), glutamate decarboxylase 1 (GAD1) and LIM homeobox 9 (LHX9).