In survivors of the World Trade Center attacks of 11 September 2001, reduced whole blood messenger RNA (mRNA) expression of FKBP5 has been shown to be associated with PTSD 87, a finding that might lead to enhanced GR responsiveness and explain the HPA axis dysregulation commonly associated with PTSD (i.e. lower basal cortisol levels as well as increased feedback sensitivity) 11, 12. This evidence concerns the gene FKBP5 and post-traumatic stress disorder.