Brain Injury, Mental Decline, and the APOE Gene

Editor’s note: Pending an FDA decision, 23andMe no longer offers new customers access to health reports referred to in this post. Customers who purchased prior to November 22, 2013 will still be able to see their health reports, but those who purchased after that time will not. Those customers will have access to ancestry information as well as access to their uninterpreted raw data.

Mounting evidence points to brain trauma as a risk factor for mental decline. Football players who’ve had multiple concussions perform worse on tests of brain function and are more likely to have memory problems later on. Repeated blows to the head can also cause certain types of dementia — medically referred to as “chronic traumatic encephalopathy” and historically called “punch-drunk syndrome” in boxers. These athletes usually suffer repeated onslaughts, but research suggests that even an isolated severe brain injury might be enough to increase risk for conditions like Alzheimer’s disease.

(A severe traumatic brain injury is one that leads to a concussion and unconsciousness for 30 minutes or more.)

Research also suggests that DNA may play a role in how susceptible we are to mental decline after head trauma. Numerous genes have been implicated but the most plausible connection is with a gene named APOE. A version of this gene called e4 is firmly linked to higher risk for Alzheimer’s and researchers are studying people with the e4 variant to see if they are more likely to show signs of mental decline after brain injury compared to people without this genetic variant.

But how might the APOE e4 variant affect our ability to recover from a traumatic brain injury? Research on Alzheimer’s offers some clues.

Sizing up head trauma
More than 10 million people around the world suffer a traumatic brain injury every year and a staggering 1.7 million of these injuries occur in the USA. This makes traumatic brain injury the leading cause of death and disability in Americans under the age of 35. Most cases of brain injury result from falls and car accidents, but contact sports and modern warfare are also contributors.

It’s not clear exactly why people with the e4 variant are more likely to develop Alzheimer’s, but it is known that the brains of people with this variant have more protein clumps, called amyloid plaques, than the brains of people without the variant. It’s possible that these plaques cause neurons in the brain to die.

Up to 30% of people who suffer a severe traumatic brain injury also have plaques. These plaques seem to develop very quickly — sometimes within two hours — after injury. It’s possible that people with the e4 variant are simply more likely to develop plaques in their brains — perhaps even more so with trauma — and this predisposes them for developing cognitive problems.

Scientists have long thought that our genes interact with our environment to impact our health. In the case of mental decline and dementia, preliminary research suggests a connection between the APOE e4 variant and severe brain injury, but findings are inconsistent and more research is needed to know for sure.

Not everyone who suffers a brain injury or has the e4 variant will develop dementia or other cognitive problems. But being aware of the risk can help you be proactive in avoiding head injuries in the first place. You can keep your brain active, through social engage­ment or “brain games” like Sudoku, in order to lower your risk of mental decline.

Recommended reading:
What types of brain injury carry a risk for mental decline?
Traumatic brain injury and Alzheimer’s disease
Prevention strategies for Alzheimer’s disease