FKBP5 and major depressive disorder: Finally, Cattaneo et al reported a 11% reduction in leukocyte FKBP51 RNA expression in MDD patients responding to 8-week antidepressant treatment (citalopram or nortriptyline), whereas no such change was found in nonresponders.[20] Because of its key role in glucocorticoid pathways, neurogenesis, and inflammation.