With different degrees of involvement, FKBP51 has been previously associated with substance abuse [166,167], autism [168], bipolar disorder [169,170], depression [12,116], schizophrenia [171], post-traumatic stress disorder (PTSD) [172,173], suicide [174], attention-deficit/hyperactivity disorder [175], anxiety [176], and the effects of early trauma and stress in general [177,178,179]. Here, FKBP4 is linked to major depressive disorder.