By Kyle Garratt
Researchers from the University of Toronto recently looked at whether certain people might be genetically predisposed to sustaining a concussion. Though the findings were inconclusive, scientists believe more such studies are on the way.
While some research suggest females and athletes who participate in certain contact sports may be more susceptible to concussions, few studies have considered whether people can be genetically predisposed to suffering concussions, until recently. Researchers at the University of Toronto tested the hypothesis that carriers of the apolipoprotein E epsilon4 allele (one form of a particular gene) are more likely to sustain a concussion than those who don't carry it.
"There was a lot of literature suggesting that this allele was associated with delayed recovery after a concussion," says Vicki Kristman, PhD, co-author of the study and post-doctoral fellow at Toronto Western Hospital. "It is also a risk factor for Alzheimer's disease, and some of the top medical literature has shown that a severely concussed or injured brain is very similar pathologically to an Alzheimer's brain. Nobody had really looked at susceptibility, so that's what we wanted to do."
The researchers took blood samples from Toronto varsity athletes in football, field hockey, men's and women's basketball, ice hockey, lacrosse, rugby, soccer, and volleyball. The study followed them from September 2002 through April 2006 until they suffered a concussion or ended their collegiate career. The authors found no significant association between carrying the allele and an individual's susceptibility to concussion, but Kristman believes there will be more research on genetic predisposition.
"I think it's just starting," she says. "The study I conducted was very preliminary, because nobody has looked at this question before. We don't see many of these studies because they require a large sample size, but I think we'll see more as people become concerned that genetics may lead to increased risk of concussions or other outcomes."
Previous studies explored the relationship between the allele and concussion recovery, with somewhat conflicting results. "For the first few years people were studying this allele as it relates to recovery after a concussion, they found that those who carried the APOE allele were more likely to recover slowly than those who didn't have it," says Kristman. "But then a larger study found that if there is any association, it is quite weak, and it's probably only in younger individuals."
Kristman says her study is not conclusive, because only 28 of the athletes involved sustained concussions, but a sample size of roughly double that could provide a concrete conclusion. "The study was designed very well. We had on-site athletic trainers so the athletes were monitored the entire time they were training, but it's almost impossible to completely eliminate under-reporting, because if an athlete doesn't want you to know they are concussed, you can't really prevent that."
Kristman's study found that those who carry the allele had a relative risk of 1.2, meaning they are only slightly more likely to sustain a concussion than those who don't carry the allele. But if a large enough study found athletes with a certain genetic trait held a relative risk closer to 2.0, meaning they are twice as likely to suffer a concussion, the information would be very useful to athletic trainers and athletes.
"The information could be used for prognosis," explains Kristman. "When an athletic trainer sees an athlete with a concussion, and they know that person carries a particular allele, that may help them determine when the athlete can return to play. They might better understand how long recovery will take. The big benefit is providing athletes with information to make decisions about what's best for them."
An abstract of the Toronto study can be found here.
For information about recent concussion studies, check out The Invisible Injury, our cover story in the May/June 2009 issue of T&C.
Kyle Garratt is an Assistant Editor at Training & Conditioning.