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ImportanceRepetitive head impact (RHI) exposure is the chief risk factor for chronic traumatic encephalopathy (CTE). However, the occurrence and severity of CTE varies widely among those with similar RHI exposure. Limited evidence suggests that the APOEε4 allele may confer risk for CTE, but previous studies were small with limited scope.ObjectiveTo test the association between APOE genotype and CTE neuropathology and related endophenotypes.Design, Setting, and ParticipantsThis cross-sectional genetic association study analyzed brain donors from February 2008 to August 2019 from the Veterans Affairs–Boston University–Concussion Legacy Foundation Brain Bank. All donors had exposure to RHI from contact sports or military service. All eligible donors were included. Analysis took place between June 2020 and April 2022.ExposuresOne or more APOEε4 or APOEε2 alleles.Main Outcomes and MeasuresCTE neuropathological status, CTE stage (0-IV), semiquantitative phosphorylated tau (p-tau) burden in 11 brain regions (0-3), quantitative p-tau burden in the dorsolateral frontal lobe (log-transformed AT8+ pixel count per mm2), and dementia.ResultsOf 364 consecutive brain donors (100% male; 53 [14.6%] self-identified as Black and 311 [85.4%] as White; median [IQR] age, 65 [47-77] years) 20 years or older, there were 294 individuals with CTE and 70 controls. Among donors older than 65 years, APOEε4 status was significantly associated with CTE stage (odds ratio [OR], 2.34 [95% CI, 1.30-4.20]; false discovery rate [FDR]–corrected P = .01) and quantitative p-tau burden in the dorsolateral frontal lobe (β, 1.39 [95% CI, 0.83-1.94]; FDR-corrected P = 2.37 × 10−5). There was a nonsignificant association between APOEε4 status and dementia (OR, 2.64 [95% CI, 1.06-6.61]; FDR-corrected P = .08). Across 11 brain regions, significant associations were observed for semiquantitative p-tau burden in the frontal and parietal cortices, amygdala, and entorhinal cortex (OR range, 2.45-3.26). Among football players, the APOEε4 association size for CTE stage was similar to playing more than 7 years of football. Associations were significantly larger in the older half of the sample. There was no significant association for CTE status. Association sizes were similar when donors with an Alzheimer disease neuropathological diagnosis were excluded and were reduced but remained significant after adjusting for neuritic and diffuse amyloid plaques. No associations were observed for APOEε2 status. Models were adjusted for age at death and race.Conclusions and RelevanceAPOEε4 may confer increased risk for CTE-related neuropathological and clinical outcomes among older individuals with RHI exposure. Further work is required to validate these findings in an independent sample.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy associated with repetitive head impacts (RHI), but the components of RHI exposure underlying this relationship are unclear. We create a position exposure matrix (PEM), composed of American football helmet sensor data, summarized from literature review by player position and level of play. Using this PEM, we estimate measures of lifetime RHI exposure for a separate cohort of 631 football playing brain donors. Separate models examine the relationship between CTE pathology and players’ concussion count, athletic positions, years of football, and PEM-derived measures, including estimated cumulative head impacts, linear accelerations, and rotational accelerations. Only duration of play and PEM-derived measures are significantly associated with CTE pathology. Models incorporating cumulative linear or rotational acceleration have better model fit and are better predictors of CTE pathology than duration of play or cumulative head impacts alone. These findings implicate cumulative head impact intensity in CTE pathogenesis.

BackgroundChronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy associated with repetitive head impact (RHI) exposure. We previously showed that duration of American football play is associated with risk and severity of CTE pathology. Helmet accelerometers have been used previously to examine frequency, linear acceleration, and rotational acceleration of hits sustained across youth, high school, and college football. Here we projected this data onto former American football playing brain donors to examine the relationship between cumulative frequency of hits, linear acceleration, and rotational acceleration during players’ athletic careers and CTE pathology.Method656 former American football playing brain donors from the Veterans Affairs‐Boston University‐Concussion Legacy Foundation Brain Bank were examined for CTE pathology and severity. Years and position of play at each level (youth, high school, college, professional) were acquired through retrospective clinical interviews with brain donors next‐of‐kin. From a literature search of studies using helmet accelerometers, we calculated the mean frequency of hits, linear acceleration (g‐force), and rotational acceleration (rad/sec2) for one year of play at each level‐position combination. These values were projected onto brain donors’ career exposure to derive cumulative frequency of head impacts (CHII), cumulative linear acceleration (CHII‐G), and cumulative rotational acceleration (CHII‐R). Separate logistic regression models examined the relationship of years of play, CHII, CHII‐G, and CHII‐R on CTE status and severity (low vs. high), adjusting for age at death.ResultThe mean (SD) age at death was 59.7 (20.1) and 451 (68.8%) had CTE pathology. Each cumulative measure was significantly associated with presence of CTE (p’s<.001) and severity of CTE (p’s<.001). Based on ROC analyses, CHII‐R (AUC=0.765, p<.001) and CHII‐G (AUC= 0.758, p<.001) performed significantly better than years of play (AUC=0.716) in classifying CTE pathology, and there was no difference between years of play and CHII (AUC=0.698, p=0.25). Similar relationships were observed for CTE severity. Model fit and cross‐validation statistics were also consistent (Table 2).ConclusionAmong former American football playing brain donors, cumulative linear and rotational acceleration were better predictors of CTE pathology than duration of play or cumulative hits. The findings suggest head impact intensity is an important factor in developing CTE pathology.

BackgroundRepetitive head impacts (RHI) from American football and other sources are associated with the neurodegenerative tauopathy chronic traumatic encephalopathy (CTE). Moderate‐to‐severe traumatic brain injury (msTBI) has been suggested to be sufficient to precipitate CTE. Yet, this evidence is based on small case series of msTBI and the interplay between msTBI and RHI on CTE risk is unknown. We modeled the associations between msTBI history and years of American football play (proxy for RHI exposure duration) on CTE neuropathology among deceased American football players.MethodsThe sample included 471 deceased male football players from the UNITE brain bank, all 40+ years old. Informants of donors were administered the Ohio State University TBI Identification Method to assess TBI history. Loss of consciousness (LOC) for 30+ minutes defined msTBI. CTE was neuropathologically diagnosed and staged using published criteria. Outcomes included CTE status, CTE severity (low vs high), and cumulative p‐tau burden—summary of semi‐quantitative ratings of p‐tau severity across 11 brain regions (n = 402). Binary or linear regressions tested the association between msTBI and each outcome, controlling for age and years of football. A years of play x msTBI history interaction term was examined.ResultsTables 1‐2 shows sample characteristics (mean age = 67.89, SD = 12.70; 15.7% Black). Of the sample, 114 (24.2%) had a msTBI history. Years since last TBI with LOC was 37.16 (SD = 18.66) years. 344 (73.0%) had autopsy‐confirmed CTE. There was no association between msTBI and CTE status (OR = 1.38, 95% CI = 0.81,2.33, p = 0.24), CTE severity (OR = 0.77, CI = 0.41,1.44, p = 0.41), or cumulative p‐tau burden (beta = ‐1.03, 95% CI = ‐2.77,0.71, p = 0.25). In contrast, years of football play was associated with CTE status (OR = 1.15, 95% CI = 1.10,1.21, p<0.01), CTE severity (OR = 1.14, 95% CI = 1.08,1.21, p<0.01), and cumulative p‐tau burden (beta = 0.44, 95% CI = 0.32,0.56, p<0.01). There were no years of play x msTBI interaction effects (ps>0.05).ConclusionsmsTBI history was not associated with CTE neuropathology, nor did it modify the effect of years of football play on CTE status and severity. These findings argue against msTBI as a contributor to CTE in the setting of RHI. Examination of age at msTBI and msTBI frequency, as well as non‐CTE neuropathological correlates of msTBI are next steps.