Genetic Variants and Persistent Impairment Following Mild Traumatic Brain Injury: A Systematic Review.

The search was limited to papers published in English. Quality varied widely and, on the authors' own scoring, many included studies were small and drawn from narrow groups such as military veterans or collegiate athletes, which limits how far the results apply to other patients. Studies scoring below 5 out of 9 were treated as high risk of bias, and the authors name small sample size, narrow populations, and recall bias from self-report questionnaires among the problems across the set. Follow-up ranged from 10 days to 6 years and the studies differed in design and in which outcomes they measured, so the results do not add up to a single estimate; no meta-analysis was done. Most studies had no information on how people were doing before their injury, so it is hard to tell whether a gene variant caused a difference or the difference was already there. A subset of studies did test people before and after injury, which is the better design. Only 12 of the 46 studies reported that the allele frequencies in their sample matched what would be expected by chance, and the rest did not report this at all.

The paper's only funding and conflict statement says the remaining authors have no conflicts of interest or funding to declare, and no funder is named anywhere in the text. The word 'remaining' implies at least one author had something declared elsewhere, but the supplied text does not say what. The publication record lists NIH extramural research support, which sits oddly with a statement of no funding.

Do not use this paper to predict how one patient will recover, and do not take it as a reason to ask about or order genetic testing. Carrying APOE ε4 was linked to worse outcomes in most studies but not in all: two studies found better outcomes and five found no difference, and the authors say controlled prospective studies are still needed before genetic information could be used to screen or counsel anyone.