Post-traumatic stress disorder risk may be partly genetic

A new study has demonstrated that levels of a hormone involved in the response to stress could explain why some people develop post-traumatic stress disorder (PTSD).

The research, conducted by scientists at Emory University and the University of Vermont in the US, studied a group of patients considered at high-risk of developing PTSD, based on their exposure to traumatic events such as domestic abuse. They found that blood samples taken from these individuals differed in their levels of a hormone called PACAP (pituitary adenylate cyclase-activating polypeptide), with higher levels associated with more severe PTSD symptoms, particularly in women.

The researchers also discovered that variation in another gene, this time linked to the hormone's receptor, was additionally associated with both the risk and severity of PTSD, as well as problems telling the difference between fear and safety signals. The finding was confirmed in a second group of patients exposed to trauma, and was again limited to women. This variation was in the same region of the gene as an oestrogen response element - a sequence of DNA that binds to complexes of oestrogen and its receptor - providing a possible explanation for its exclusivity in females and the increased risk of PTSD in women compared to men.

Lead author Dr Kerry Ressler said, 'What this says is that men and women who have been traumatized may arrive at PTSD by different biological pathways. In this case, we have a clue how that works, in that the genetic data point to changes in the ability to respond to oestrogen'.

The team also found that methylation (chemical alteration of DNA that can prevent the expression of certain genes) of the PACAP receptor gene was possible, and that levels of methylation were again associated with risk of PTSD, but this time in men and women. Methylation can be altered by environmental factors, suggesting that repeated instances of trauma could alter an individual's response to further stress. The researchers also showed that mice and rats have the PACAP receptor gene and that this could be activated by both fear and oestrogen in these animals respectively.

Another senior member of the research team, Professor Victor May said, 'These studies may offer opportunities to distinguish people with PTSD and related anxiety disorders from other behavioural disorders, and identify people in high stress occupations or environments who may be prone to PTSD'.

PTSD is a condition where individuals who have experienced a traumatic event may then experience flashbacks or nightmares following the incident, as well as other symptoms including anxiety and depression. In recent years the disorder has been strongly linked to soldiers returning from the conflicts in Iraq and Afghanistan, but can occur in anyone experiencing a trauma in their life.

The study was published in Nature.