FKBP5 and Adrenal insufficiency: Since promoter methylation usually negatively correlates with gene expression (11), we measured FKBP5 gene expression in a subset of 37 samples (14 overt Cushing’s syndrome, 10 mild Cushing’s syndrome, 7 eucortisolism, 6 adrenal insufficiency), for which whole blood RNA was available (Supplementary Methods).