Scientists in San Diego, Calif., think they have at least one of the answers to a question that has puzzled psychologists for years: why some soldiers are more resilient to combat stress than others.

They believe the answer is in their genes.

After studying the DNA of 13,000 American soldiers, researchers have found two genetic variants that they believe may explain why some combat vets are afflicted with PTSD, but others are not.

“The first, in samples from African-American soldiers with PTSD, was in a gene (ANKRD55) on chromosome 5,” said Dr. Murray Stein, Distinguished Professor of Psychiatry at the University of California-San Diego. “In prior research, this gene has been found to be associated with various autoimmune and inflammatory diseases, including multiple sclerosis, type II diabetes, celiac disease, and rheumatoid arthritis. The other variant was found on chromosome 19 in European-American samples.”

A team from the UC-San Diego School of Medicine, the VA San Diego Healthcare System, and the Uniformed Services University compared the genomes of 3,167 combat vets diagnosed with PTSD and another 4,607 combat vets who had not been diagnosed with PTSD.  A second study involved 947 diagnosed vets compared with 4,969 combat vets without PTSD.

“We compared the two groups in all markers for all genes and found differences that were distinctly different between the two groups,” Dr. Stein told me. “But it wasn’t a 100 percent difference. The group with the variant was about 60 percent more likely to develop PTSD.”                      Their hope is that one day in the future a DNA test during basic training will tell commanders which soldier will be more able to withstand combat stress and which might be better suited for an administrative role.

“In theory, that is how this could be used, but we’re nowhere near there yet,” Dr. Stein said. “We have a lot of work yet to do to be sure of these findings. But we may be able in the future to analyze this data and say someone would be very good at combat, while someone else might be better as a supply sergeant – or may need additional training to boost his resilience.”

In addition, further testing is needed to determine whether other racial groups – Asian Americans or American Indians, for example – express the same difference with different genes.