A certain genetic signature gives some people the ability to form stronger memories. But that edge also has a dark side: increased risk of post-traumatic stress disorder.
Although the genetic effect is small, the results help scientists better understand the link between especially powerful memories and sensitivity to past trauma.
Scientists led by neuroscientist Dominique de Quervain of the University of Basel in Switzerland looked at how genetic differences related to a memory task. A population of 723 healthy young Swiss adults viewed 72 photographs. After a 10-minute wait, the volunteers were asked to remember as many images as possible.
Volunteers who could remember more pictures carried a particular DNA signature in at least one copy of a gene that encodes protein kinase C alpha. In animal studies, this protein has been shown to play a role in the formation of emotional memories. The volunteers’ heightened recall was true for disturbing, pleasant and neutral pictures.
Further evidence came from brain scans performed in a different group of Swiss people. While viewing the pictures, people with the genetic signature had stronger brain activation in parts of the prefrontal cortex compared with those who lacked the genetic feature, the researchers report online the week of May 14 in the Proceedings of the National Academy of Sciences.
Because memory is known to be an important part of PTSD, de Quervain and his team wanted to see if their results might have importance beyond the laboratory. The researchers looked at the genes of 347 people who had survived the brutal 1994 Rwandan genocide and now live in a refugee camp in Uganda. The genocide was marked by extreme violence and war rape. About a third of those studied met the clinical criteria for PTSD.
Among the Rwandan refugees, having the strong-memory signature was linked to a doubled risk of PTSD compared with the rate among those without the genetic signature. The signature was relatively rare in the Rwandan population, even though it was almost universal among the Swiss.
“I think this work is of great theoretical interest,” says PTSD researcher Roger Pitman of Massachusetts General Hospital and Harvard Medical School. The study supports the idea that stronger memories are linked to a heightened risk of PTSD, a theory that’s been discussed but hasn’t had much evidence, he says. “This is another piece of the puzzle.”
The results explain only a small sliver of memory formation and PTSD. “But that doesn’t mean this gene isn’t important,” de Quervain says. The results give a deeper understanding of the link between strong memories and diseases such as PTSD, he says. Studying the role of protein kinase C alpha may reveal more about how memories form and perhaps even why some prove so troubling.