Blood expression levels of genes targeted by the stress hormones called glucocorticoids could be a physical measure, or biomarker, of risk for developing Post-Traumatic Stress Disorder (PTSD), researchers report. PTSD is triggered by a terrifying event, either witnessed or experienced. Symptoms may include flashbacks, nightmares and severe anxiety, as well as uncontrollable thoughts about the event. Not everyone who experiences trauma develops PTSD, which is why the study aimed to identify biomarkers that could better measure each person's vulnerability to the disorder.