Most other studies of pesticide exposure have used a study design with nonexposed controls (e.g., Cataño et al. 2008; Ntow et al. 2009; Rendón von Osten et al. 2004) or a pre–post design (Gamlin et al. 2007; Thetkathuek et al. 2005) to identify cholinesterase depression. This evidence concerns the gene BCHE and major depressive disorder.