This study will investigate the potential for FK506 binding protein 5 (FKBP5) (and other gene expression markers, for example pentraxin 3 [PTX-3], serum/glucocorticoid regulated kinase 1 [SGK1], and glycogen synthase kinase 3 beta [GSK3b]) to be developed as a biomarker for use in diagnosis of Cushing's syndrome, assessment of effectiveness of medical or surgical treatment, and detection of relapse of endogenous Cushing's syndrome after surgery.