Since GR is a crucial part of the stress hormone axis, also known as HPA (hypothalamus–pituitary–adrenals) axis, and since increasing evidence became available for dysregulated GR in stress-related diseases, such as depression [11], the finding of FKBP51 as an inhibitor of GR inspired a genotype association study on depression [12]. Here, FKBP4 is linked to major depressive disorder.