ALB and major depressive disorder: Indeed, elevation of CSF‐to‐serum albumin ratio in a substantial subpopulation of MDD patients clearly supports BBB and/or blood–CSF barriers hyperpermeability (Bechter, Reiber, Herzog, Fuchs & Tumani, 2010; Gudmundsson, Skoog, Waern, Blennow & Palsson, 2007).