CLDN5 and major depressive disorder: Given evidence for a role for CLDN5 in susceptibility to depression following stress (Menard et al., 2017), and phenotypic and genetic similarities between PTSD and depression (Dalvie et al., 2021; Ringwald et al., 2023), our aim was to examine, for the first time, the association between PTSD and CLDN5 epigenetics.