FKBP4 was found to be associated with major depressive disorder (Binder et al., 2004; Tatro et al., 2009a, b) and might be critical to early steps in neuronal differentiation (Quintá and Galigniana, 2012), chemotropic guidance of neuronal growth cones (Shim et al., 2009), and regulating neuroprotective activities with calcium channels (Ruan et al., 2008). This evidence concerns the gene FKBP4 and major depressive disorder.