FKBP5 and major depressive disorder: For instance, polymorphisms in corticotrophin releasing hormone receptor 1 and 2 (CRHR1 and CRHR2), glucocorticoid receptor (GR), FK506-binding protein 5 (FKBP5), and arginine vasopressin (AVP) have been previously associated with HPA (dys) regulation, MDD and/or antidepressant response [15-19].