(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.
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.