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As has been widely reported, the internet has the potential to bring us closer to the cutting edge of sports medicine. This week in the journal Annals of Neurology a group of researchers from Leiden in the Netherlands published a fascinating study that has significant implications for the study of sport related brain injury, and in particular, the so called second impact syndrome (SIS).1
The paper is only available in an online format at present, but in due course the print version will arrive after the usual delays with postage and shipping. We find the same thing with our online full text journal. A forthcoming issue can be posted on the web site ahead of print publication. Rapid response correspondence to articles can already be underway even before the print version arrives. It is conceivable that this editorial will be online at the British Journal of Sports Medicine web site before I receive a print copy of the other journal! Welcome to the future of publishing.
The Dutch paper reports the association between delayed cerebral oedema after minor head trauma and an abnormality with the CACNA1A calcium channel subunit gene. It is known that in people predisposed to familial hemiplegic migraine, attacks of migraine may be triggered by trivial head trauma and such attacks may be accompanied by coma caused by cerebral oedema. Calcium channel subunit mutations of the CACNA1A gene on chromosome 19 were associated with this phenomenon. A single amino acid substitution at codon 218 (S218L) resulted in this mutation.
This finding may have a number of important implications for sports medicine. First, the spectre of SIS has always plagued the concussion literature. If proved, the Dutch study suggests that there may be a small group of patients with a specific genetic abnormality that may put them at risk of this vanishingly rare phenomenon. Proponents of SIS have argued that recurrent concussion is the main risk factor, but detailed analysis of published cases has failed to find a compelling argument for this position.2 It has been known for decades that even a single episode of brain injury can provoke lethal cerebral swelling, a phenomenon more common in children than adults. The Dutch paper may provide the missing link to explain why we do not see more of SIS given the high incidence of concussive injury.
Secondly, the role of molecular biology in teasing out some of the difficult problems in sports medicine is starting to be felt. In other branches of medicine, new genes and genetic haplotypes are associated with ever increasing numbers of diseases. In the field of sporting head injury, Barry Jordan, a sports neurologist from New York, has shown that the Apolipoprotein E4 (ApoE4) allele is a risk factor for chronic traumatic encephalopathy in boxers.3, 4 Other groups have shown that ApoE4 is also associated with poorer outcome from head injury.5
This leads to a tangled web of ethical issues for sports physicians. Do we now screen our athletes for these known genetic markers of adverse (and usually lethal) outcomes from brain injury? As well as the risk to the athlete, there may also be important management information for the clinician. For example, if an athlete who is ApoE4 positive suffers a concussion, should we be more conservative in his or her return to play protocol? Should such an athlete be more vigorously monitored over their career from the standpoint of neuropsychological testing? With the findings from the Dutch study, should an athlete with an S218L calcium subunit abnormality play contact sport at any age?
Will informed consent to participate in sport be contingent on such abnormalities being tested for? I wonder how the lawyers will deal with this new information. I suspect professional boxing may well be the testing ground for some of these medicolegal issues. The risk in boxing is clear and the ApoE4 data are robust enough to make it a valid concern at the present time.
These matters may well be the ethical dilemmas that cutting edge technology delivers us at the moment; however, the future is closer than we realise. Although sports medicine is often seen as a “Cinderella” specialty within medicine, the application of the blow torch of science should make mainstream medicine realise that the advances made in research laboratories apply equally well to athletes.