A 1997 study determined that boxers with an ApoE4 copy scored worse on tests of brain impairment than boxers with similar length careers who did not have an ApoE4 copy. Three boxers in the study had severe brain function impairment, and all three had an ApoE4 gene variant. In 2000, a study of fifty-three active pro football players concluded that three factors caused certain players to score lower than their peers on tests of brain function: 1) age, 2) having been hit in the head often, and 3) having an ApoE4 variant.
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What went entirely unmentioned in media coverage, though, was that five of nine brain-damaged boxers and football players who had genetic data included in the report had an ApoE4 variant. That’s 56 percent, between double and triple the proportion in the general population.