Genetics a Likely Factor in Variability of Outcome Following Concussion
Most experts in traumatic brain injury (TBI) agree that there is a high degree of variability in outcomes after TBI, including concussions (usually characterized as “mild” TBIs – mTBI.) In other words, this injury is heterogenous; generalizations about recovery rates and outcomes are not particularly productive.
In prior posts we have discussed research finding physical differences between patients who recover quickly and patients with persistent symptoms (such as differences in DTI imaging and differences in the presence of certain proteins.) This research contradicts the position some clinicians previously held that persistent symptoms following mTBI were likely the result of a “somatoform” or mental health disorder. We have also discussed research identifying some of the individual factors that explain the variability of outcomes, such as prior TBIs and preexisting migraine. We have also discussed how the particular forces involved in a TBI may affect different structures of the brain producing different outcomes (such as changes in vision, changes in balance or changes in the function of the pituitary gland resulting in hormonal imbalances.)
It has always been suspected that one of the factors explaining such variability in outcome may be genetic differences. Researchers at Penn State recently found additional support for the conclusion that genetics does likely play a role. They identified one particular gene linked to outcome, the apolipoprotein E (APOE) gene. A central function of APOE is to maintain and restore neuronal membranes and tissue after they have been compromised. This gene has three primary “alleles” or alternative forms, e2, e3 and e4. The Penn State researchers studied 42 collegiate athletes who suffered concussions. The athletes reported on symptoms in four categories: physical symptoms, affective symptoms, cognitive symptoms and sleep symptoms. They found that the athletes with the e4 form of the APOE gene had significantly greater overall symptoms and significantly greater symptoms in the physical symptoms cluster and the cognitive symptoms cluster.
This study is not definitive, but it does clearly support further study of genetic factors. To the extent that genetics prove to be a significant factor in outcomes, a genetic screening tool may in the future play an important role in deciding whether to participate in activities with a high risk of brain injury.