Adler, Charles H.

Objective To investigate sex differences in Alzheimer's disease (AD) related pathology among autopsy-confirmed Parkinson's disease (PD) cases. Background AD and PD frequently co-occur in older adults, yet the influence of sex on AD pathology in the context of PD remains unexplored. Methods All subjects were enrolled in the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND) and Brain and Body Donation Program (BBDP) and had annual standardized research clinical assessments by neuropsychologists, subspecialty behavioral and movement disorders neurologists, as well as comprehensive neuropathological examinations after death. Results Among 230 autopsy-confirmed PD cases, females exhibited greater amyloid plaque pathology burden than males, regardless of a co-occurring AD diagnosis. Specifically, females with PD had significantly higher mean cortical total plaque scores (mean 6.5/15 vs. 4.9/15, p = 0.045) and greater CERAD neuritic plaque density (mean 1.7/3 vs. 1.3/3, p = 0.035). Females were also more likely to have a higher cortical plaque burden (plaque total ≥ 5: 56.8% vs. 39.7%, p = 0.015). In multivariable logistic regression models, female subjects showed greater than twice the odds of having an amyloid plaque burden ≥5 compared to males (OR = 2.18; 95% CI = 1.17–4.06; p = 0.014), when controlling for ApoE ε4 status, Lewy body density score, and age at death. Conclusions Female sex is associated with increased amyloid plaque pathology in PD, independent of ApoE ε4 status. These findings highlight a sex-specific vulnerability to AD pathology in PD patients and support the need for sex-informed approaches to reseach in mixed neurodegenerative disease.

Importance In vivo biomarkers for detecting neuropathologies from repetitive head impacts (RHI), including chronic traumatic encephalopathy (CTE), are needed. Objective To evaluate the utility of plasma phosphorylated tau 217 (p-tau217), assess its performance as a beta-amyloid (Aβ) biomarker in participants with RHI exposure at risk for CTE, and explore concordance with CTE neuropathology in a postmortem subsample. Design, Setting, and Participants This longitudinal, multicenter, case-control study used data from the Diagnostics, Imaging, and Genetics Network for the Objective Study and Evaluation of CTE (DIAGNOSE CTE) Research Project, collected from September 2016 to October 2023. Participants were former American football players (case participants) and asymptomatic men unexposed to RHI (control participants). A subsample had available neuropathologic data. Exposures RHI, traumatic encephalopathy syndrome (TES) diagnoses, and levels of CTE certainty. Main Outcomes and Measures Plasma p-tau217 (classified as positive [≥0.63 pg/mL], intermediate [0.40-0.62 pg/mL], and negative [<0.40 pg/mL]), Aβ–positron emission tomography (PET; 18 F-florbetapir; with Aβ-positive defined as a standardized uptake value ratio [SUVR] ≥1.10), and tau-PET ( 18 F-flortaucipir). TES diagnoses were assigned by multidisciplinary consensus conference. Analyses of postmortem brains controlled for age, race, and APOE ε4 status. Results Among 231 participants (mean [SD] age, 57.75 [8.25] years), 177 were former football players (117 professional and 60 college) and 54 were unexposed participants. Former football players had higher baseline mean (SD) p-tau217 concentrations than unexposed participants (0.35 [0.26] pg/mL vs 0.27 [0.14] pg/mL; P = .008), although this was driven by a higher proportion of Aβ-PET–positive participants among former players. Plasma p-tau217 increased over time across the sample (B = 0.207 [95% CI, 0.117-0.298]; P < .001), with no significant time × exposure group interactions. Among football players, p-tau217 showed no time × group interactions with TES diagnosis, TES-CTE certainty, or RHI metrics. Higher p-tau217 concentration correlated with higher global Aβ-PET SUVR (B = 0.058 [95% CI, 0.053-3.501; P = .01), with a few discordant cases (5 participants were p-tau217–negative and Aβ-PET–positive; 7 participants were p-tau217–positive and Aβ-PET–negative). P-tau217 had similar areas under the curve for projecting Aβ-PET positivity as cerebrospinal fluid (CSF) p-tau181/Aβ42 and CSF Aβ40/42 measures (p-tau217: AUC, 0.88 [95% CI, 0.80-0.96]; CSF p-tau181/Aβ42: AUC, 0.89 [95% CI, 0.79-1.00]; CSF Aβ40/42: AUC, 0.85 [95% CI, 0.72-0.98]). Among 9 brain donors, 6 had CTE (stages II-IV; none with Alzheimer disease). Seven had negative or intermediate p-tau217, concordant with Aβ-PET. Two p-tau217 outliers with stage III CTE had normal concentrations upon additional testing. Conclusions and Relevance The findings of this study suggest that plasma p-tau217 concentration is unlikely to be useful for the detection of CTE, but it does show utility for ruling out Aβ pathology in participants at risk for CTE.

Abstract INTRODUCTION Chronic traumatic encephalopathy (CTE) is a tauopathy linked to repetitive head impacts. Factors influencing brain regional susceptibility to tau deposition and spreading remain unclear. METHODS We used three datasets: [18F]flortaucipir positron emission tomography (PET) in 157 former professional American football players and 53 controls (DIAGNOSE CTE); cortical myelin water fractions (MWF) in 50 healthy individuals (Myelin Water Atlas); and white matter (WM) tract MWF and functional connectivity (FC) in 100 healthy individuals (Human Connectome Project). We tested associations between tau‐PET uptake and covariance in football players and typical cortical gray matter (GM) MWF, WM tract MWF, and FC. RESULTS Cortical regions with lower typical GM MWF showed higher tau‐PET uptake ( β = −0.399, p = 0.001). WM tracts with lower typical MWF were associated with higher tau‐PET covariance ( β = −0.238, p < 0.001). Higher typical FC was associated with higher tau‐PET covariance ( β = 0.447, p < 0.001). DISCUSSION In former football players at risk for CTE, regional susceptibility to tau deposition may be driven by low myelin and high FC.

Abstract Background Cumulative head trauma, encompassing repetitive head impacts (RHI) and traumatic brain injury (TBI), has been associated with later‐life neurodegenerative disease. Studies on parkinsonism/Parkinson's disease (PD) have evaluated RHI and TBI in isolation, yielding mixed results. Cumulative head trauma may better predict PD risk. Objective To examine independent and cumulative effects of RHI through soccer participation and TBI history on PD diagnosis and age at diagnosis. Methods We used a cross‐sectional cohort design with data from the Fox Insight study. Participants completed self‐report questionnaires on PD diagnosis, TBI (no TBI, TBI with loss of consciousness [LOC], TBI without LOC), and sport participation. Multivariable logistic regressions examined the effects of soccer, TBI group, and their interaction on PD diagnosis. Cox proportional hazards examined associations with time to PD diagnosis. Covariates included age, sex, race, education, income, body mass index, heart disease/diabetes, and family PD history. Results Among 1231 participants (mean[SD] age = 66.12[10.60]), 278 played soccer (953 non–contact and collision sport [CCS] athletes). Participants reported no TBI (390[33%]), TBI without LOC (495[43%]), or TBI with LOC (258[23%]). Overall, 768(62%) reported a PD diagnosis (mean[SD] age at diagnosis = 59.02[9.86]). A significant soccer × TBI interaction indicated that soccer players with TBI with LOC had 2.6× higher odds of PD compared to non‐CCS athletes without TBI (OR [95% CI] = 2.600[1.085–6.305], P = 0.033). Former soccer players with TBI with LOC had a 15.6% higher hazard of early PD diagnosis (HR = 1.469, P = 0.027) compared to non‐CCS athletes with no TBI. Conclusion Cumulative head trauma (RHI + TBI) increased PD risk and lowered age at onset. © 2026 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Abstract Repetitive head impacts sustained during American football have been associated with neuropathological changes such as white matter shear injuries. However, the impact of specific factors, such as age of first exposure and cumulative head impact burden, on white matter integrity remains unclear. This study investigated in vivo white matter microstructural changes using diffusion tensor imaging and tract-based spatial statistics in 165 male former American football players (mean age 57.3 years, range 45–74) and 52 unexposed asymptomatic male controls (mean age 59.4 years, range 45–74) in the DIAGNOSE CTE Research Project. Compared to controls, former football players exhibited significantly higher fractional anisotropy (FA) in 1.97% of the white matter skeleton (1552 voxels; Cohen’s d = 0.587) and higher tissue-corrected FA (FAt) in 1.48% of the white matter skeleton (1004 voxels; Cohen’s d = 0.616). No significant differences were observed for mean diffusivity, axial diffusivity, radial diffusivity, or free water between football players and controls. Among football players, there were no significant differences in the white matter microstructure between players diagnosed with traumatic encephalopathy syndrome and those without the diagnosis. Lower FA was significantly associated with older age (P &lt; 0.00001) and an earlier age of first exposure to tackle football (P &lt; 0.01), while lower FAt was associated with greater cumulative head impact burden, specifically higher linear acceleration (P &lt; 0.04) and rotational force (P &lt; 0.02). This study highlights the influential role of exposure factors on white matter microstructure in former American football players, as well as the utility of diffusion tensor imaging to aid in characterizing the long-term effects of repetitive head impacts in contact sport athletes.

Objective Positive α‐synuclein seed amplification assay (SAA) is a biomarker found in most people with Parkinson's disease (PD). We explored if free‐water (FW) imaging detects microstructural differences in the brains of patients with early PD with SAA+ or SAA– status. Methods We studied patients with PD with baseline diffusion imaging and α‐synuclein SAA data from the Parkinson's Progression Markers Initiative (PPMI). We compared FW, FW corrected fractional anisotropy (FA T ), and clinical characteristics between SAA+ and SAA– groups. We also applied the Automated Imaging Differentiation for Parkinsonism (AIDP) at baseline to classify PD versus atypical parkinsonism, stratified by SAA status. Results Among 462 participants (41 SAA– and 421 SAA+), individuals with SAA+ had hyposmia and shorter motor symptom duration before baseline magnetic resonance imaging (MRI). AIDP identified PD in 92.4% (n = 427, 91.6% had SAA+) and classified 7.6% as atypical parkinsonism (n = 35, 85.7% had SAA+). At baseline, SAA+ individuals had lower FW in the superior cerebellar peduncle, compared to SAA– (pFDR < 0.05). No significant differences in FA T were found between groups. Interpretation Positive α‐synuclein SAA was associated with focal microstructural differences but did not distinguish broader diffusion MRI (dMRI) changes across FW and FA T metrics. These findings indicate that molecular confirmation of synuclein aggregation (via SAA) provides limited stratification of neurodegeneration detected by FW imaging in early PD. ANN NEUROL 2026;100:295–304