As brothers, Eric and Brett Lindros realized the boyhood dream of almost every red-blooded Canadian male - playing professional hockey for a living in the National Hockey League.
But as they came to discover, their sibling bond extended beyond a shared affinity for big goals and even bigger bodychecks, the dream souring as multiple concussions deprived both of prolonged careers. Brett, the younger of the pair, was the first to go in 1996, forced to hang up his skates after just 51 NHL games having suffered three concussions in a little over a year. At that time Eric had yet to suffer his first, but once he did, in 1998, they came thick and fast, with seven more to follow over the next six seasons before he finally called it a day in 2007.
With last week's revelation that 14-year-old Taylor Crosby has followed in the footsteps of her older brother, NHL superstar Sidney, in the concussion stakes, it begs the question: is it just coincidence when siblings get concussions? Or do they have some sort of genetic predisposition to getting one?
In Montreal, Boston and Toronto, scientists are trying to understand the relationship between genes and concussions, but the work is still in its infancy.
"We just don't know about genetics," said Robert Stern, a research program director at the Center for the Study of Traumatic Encephalopathy at Boston University's School of Medicine. "Nothing is at all conclusive at this point."
He believes that the fact that two siblings, like the Lindroses or the Crosbys, have concussions may be more due to the fact that they're both athletic and active, than to any genetic predisposition.
"Concussions are really, really common," he said. "Like really common, much more so than anyone had ever been letting on."
There does seem to be a role played by a gene called the apolipoprotein epsilon4 allele in terms of long-term effects of brain injury, Mr. Stern said.
Louis de Beaumont, who has been studying the genetic connections to brain plasticity at the University of Montreal for the past six or seven months, says the presence of the gene indicates a poor prognosis for recovery from a concussion, rather than indicating a susceptibility to concussion.
It is a gene that has been linked to boxers with brain injuries. One of the most comprehensive studies assessed brain damage in 30 boxers with varying age and experience. All three boxers who exhibited evidence of severe brain damage or dysfunction had the APOE4 allele. Fifty per cent of them had the gene with moderate damage, and 25 per cent with mild damage.
Dr. Charles Tator, who is part of a Toronto group studying the role of genetics in concussion, says "there is a suspicion" that there is a genetic factor to concussions, especially after seeing siblings with concussions in his waiting room.
He was also involved in a study of University of Toronto varsity athletes a couple of years ago, conducted by Vicki Kristman, to determine the association between the APOE4 allele and concussion. The study did not find a connection in the varsity population. "It remains unproven," Dr. Tator said. "To my mind, there is something there and it requires more research."
Dr. Scott Delaney at McGill University says the boxing studies have created discussion that boxers should undergo blood testing to see if they should be allowed to step into the ring. "There is a lot of research going on looking at that type of thing in other sports, but we haven't been able to tease it out, yet, probably because the studies aren't large enough," he said.
Mr. De Beaumont is studying the role of other genes in his work, which hasn't been published yet.
The call for change has moved much faster than science could possibly move, Mr. Stern says. This kind of scientific investigation takes time and money, he said. One way his group is trying to understand chronic traumatic encephalopathy is by not only looking at brains of deceased people but studying large numbers of people throughout their lives before they donate their brains.
But one thing Mr. Stern's group does believe: a history of repetitive brain trauma is necessary to develop the disease, but it's not sufficient, meaning that not everyone with a history of repetitive brain trauma will develop the disease.
"We need to find out why one person will get it and another person won't," he said. "And that's again where genes come in. It's likely that it will be genetics that will help determine the susceptibility for the disease. But it will also involve other variables: the number of hits to the head, the severity of the hits, the frequency of the hits, the age at which someone is first exposed to repetitive brain trauma, and the overall duration of the exposure.
"All of those things, we just don't know yet."