A new study found that people who'd suffered concussions had less gray matter in areas of the brain related to dementia—but only if they also carried high-risk genes for Alzheimer's disease.

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For people who carry genes linked to Alzheimer's, blows to the head may entail an added risk. New research suggests that people who have had a concussion can experience more memory problems and atrophy in areas of the brain that are typically damaged by the disease if they have those high-risk genes.

It’s known that moderate to severe traumatic brain injury is a strong risk factor for developing neurodegenerative diseases, including Alzheimer’s. But it’s still unclear whether less serious head trauma, including concussions, also raise a person’s risk.

To investigate, researchers performed magnetic resonance imaging (MRI) brain scans on 160 Iraq and Afghanistan war veterans, some who were diagnosed with mild traumatic brain injury and some who were not. Most of the soldiers lost consciousness and had memory issues after their concussions, and many also had post-traumatic stress disorder. The researchers measured the thickness of gray matter in several brain regions—including some regions that are the first to show atrophy in cases of Alzheimer’s disease.

The researchers also gave the participants a simple memory test, and analyzed their genetic material to determine who carried genes that predisposed them to an increased risk of Alzheimer’s.

The results, published in the journal Brain, showed that veterans with both a history of concussion and a genetic risk for Alzheimer’s disease had reduced gray matter in those regions associated with Alzheimer’s, compared to the rest of their peers. This group also performed worse when asked to recall a list of words they’d learned 20 minutes previously.

The findings only show a correlation between concussions, thinner gray matter, and impaired short-term memory in young adults, almost all of whom were men; the study authors can’t say for sure what this will mean as they get older. But their research with the veterans is ongoing, and they will continue to study them to see who does and does not develop dementia in the future.

“Right now we’re seeing the start of a pattern that looks like Alzheimer’s disease, both in terms of reduction in cortical thickness as well as delayed recall,” says corresponding author Jasmeet Hayes, PhD, assistant professor of psychiatry at Boston University and research psychologist at the National Center for PTSD at the VA Boston Healthcare System.

Because these abnormalities were detected in relatively young adults—the study participants were aged 19 to 58 and had an average age of 32—Hayes hopes this research may pave the way for earlier detection of brain atrophy related to Alzheimer’s disease and other neurodegenerative diseases, such as Parkinson’s disease and chronic traumatic encephalopathy (a condition that can occur in athletes who play contact sports).

“If we can identify those people early in their lives, maybe in their 30s or 40s, maybe we can delay the process," Hayes says.

No treatments have yet been shown to do just that, she adds, but this research serves as an important step in that direction. Plus, if people know they have an increased likelihood for developing Alzheimer’s, she adds—because of a family history combined with a concussion, for example—they can make healthy lifestyle choices to hopefully counteract some of that risk.

The research also shows why it’s so important for doctors and patients to document when concussions occur and keep track of any subsequent symptoms, says Hayes, even if the injury seems mild.

But while a potential link between mild concussion and Alzheimer’s disease is troubling, Hayes stresses that the association was not seen in all of the veterans. “This is good news for all those out there who have suffered from concussion,” she says. “You have to have a concussion and genetic risk.”