Susceptibility to post-traumatic stress disorder (PTSD) could be partially determined by gene variants, says a study.

A U.S. team looked at the DNA from 200 members of 12 families who survived the 1988 Armenian earthquake.

It found those who carried two gene variants which affect the production of serotonin - which affects mood and behavior - were more likely to display symptoms of PTSD.

PTSD can arise after any kind of experience that causes trauma, whether that be in war, after a natural disaster or because of child abuse or sexual assault. Symptoms can include flashbacks, feeling emotionally numb or hyper-alert to danger, and avoiding situations that act as reminders of the original trauma.

It is estimated that up to 3% of the general population is likely to be affected by PTSD at some point.

The earthquake hit the northern part of Armenia on December 7, 1988, killing at least 25,000 people.

All those who took part in the study had experienced the earthquake, 90% saw dead bodies and 92% saw people who had been seriously injured. They also undertook a recognized assessment to evaluate what, if any, PTSD symptoms they had experienced.

When the University of California, Los Angeles (UCLA) researchers analyzed the Armenian families' DNA, they saw that those who had experienced more PTSD symptoms were more likely to have two specific gene variants - TPH1 and TPH2.

Dr Armen Goenjian, a research professor of psychiatry who led the work, said: "We suspect that the gene variants produce less serotonin, predisposing these family members to PTSD after exposure to violence or disaster. Our next step will be to try and replicate the findings in a larger, more heterogeneous population."

But he said that, if larger studies did confirm the finding, they could eventually lead to new ways to screen people at risk of PTSD, and target specific medicines for preventing and treating the disorder, BBC News reported.