Genes for response to head injury?

A story in Monday's New York Times tells of the kinds of long-term trauma that can result from the head injuries football or hockey players so often sustain throughout their careers.  This is a report of the posthumous study of 85 brains, all males, most of whom had been athletes, and most of whom suffered from some form of brain disease.

Of the group of 85 people, 80 percent (68 men) — nearly all of whom played sports — showed evidence of chronic traumatic encephalopathy, or C.T.E., a degenerative and incurable disease whose symptoms can include memory loss, depression and dementia.

The age range of the study group stretched from 17 to 98, which, the study authors report, meant that they could follow the course of the disease as it developed.  Symptoms ranged from mild headache and difficulty concentrating to severe dementia, aggression and difficulty finding words.

While this is a serious topic, and this study a good early effort at determining the effects of head injury, it can't be concluded from this study alone that head injuries cause C.T.E., nor can it be estimated what fraction of athletes or others susceptible to head injury are likely to develop brain disease, because the samples were all from people who had some obvious form of brain disease.  Some people apparently do suffer head trauma with no ill effects.

A prospective study of healthy athletes would be required to estimate the former, and the study would have to include a random sample of individuals who had sustained head injuries regardless of the health of their brain, to get even a ballpark estimate of the latter. That said, this and other studies of the connection between brain trauma and disease do lead to concern about the effects of fairly routine trauma. 

Let's GWAS it!!
However, because response to head injury does seem to vary we can envision that some geneticist somewhere will decide there must be genes that protect against unwanted consequences. The idea, one might fancy seeing, would be to use 'personalized genomic medicine' to identify who should perhaps play patty-cake instead of football, because s/he is vulnerable to C.T.E.s.  Or, the mapping result will send hundreds of otherwise-idea-free human geneticists off to find what gene in the identified chromosome regions makes the brain vulnerable to being shaken around, and to make hundreds of poor transgenic mice with mutations engineered in each of the genes to study the neurobiology.

Gene ontology and other omics communities will seize these seizure results as well.  The identified genes will be added to the repertoire of neural system genes--and their now-assumed neural function will be forced into this category if need be.  They'll be added to what's taught to med students, studies of dissected brains will be done on those who have the culprit variants, etc.

Of course, could it just be that the genetic basis of head trauma isn't related to neural variation at all?  It could be related to muscle strength or firing rate, or to eye-hand coordination, or respiratory factors yielding greater endurance, and so on.  That is, the correlation may have nothing to do with causation, just that variants that get you into high levels of sports will also get you into high levels of having your bell rung.

Or perhaps it's the result of dysfunctional parents, or parents of particular ethnic groups who don't have access to wealth and privilege, and who encourage their kids into sports as a way out of poverty?  Fish around in that community hard enough and you're sure to find some genes.  Maybe even genes for skin color, since African Americans tend to live in more poverty than European Americans, and tend therefore to be more into football.

Then, of course, will be the other set of genes, associated with being white and middle class, and having a soccer mom.

You can see where the assumption of genetic determinism can take one.....