Although greater cortisol and ACTH suppression after DST has been found in PTSD patients, this finding does not explain much about the contribution of higher brain areas to the activity of the HPA axis, because dexamethasone does not easily penetrate the blood-brain barrier; therefore, it does not bind to the mineralocorticoid receptor (MR) [38]. The gene discussed is POMC; the disease is post-traumatic stress disorder.