FKBP5 and psychiatric disorder: Variants of the FK506-binding protein 5 (FKBP5) gene that can potentially increase the levels of the FKBP51 protein have been implicated in numerous psychiatric disorders, including PTSD.13, 14 FKBP51, in part, is involved in regulating glucocorticoid receptor (GR)-mediated stress response via its interaction with heat shock protein 90 (Hsp90).15