Citations

Abstract Objective: Subjective cognitive complaints (SCC) can precede cognitive decline and are associated with demographic, exposure, lifestyle, and psychological factors. Prevalences of SCC and their correlates in individuals with repetitive head impacts (RHI) are poorly understood. This study characterized SCC in former elite American football players by frequency, mood and behavioral correlates, concordance with informant reports, and associations with neuropsychological test performance, cerebrospinal fluid (CSF), and magnetic resonance imaging (MRI) markers of neurodegeneration. Method: Former American football players ( n = 180) completed measures of global and domain-specific SCC, neuropsychiatric symptom questionnaires, neuropsychological testing, lumbar puncture, and MRI. Elastic net regression evaluated the relative importance of potential SCC correlates. Intraclass correlation coefficients measured concordance between self and informant reports. Multiple linear regressions tested associations between SCC and verbal memory and executive functioning scores. CSF Aβ 1-42 , p-tau 181 , t-tau, neurofilament light (NfL), hippocampal volume, and regional cortical thickness were examined for their potential associations with SCC. Results: Rates of SCC ranged from 43 to 77% depending on the domain. Symptoms of depression, impulsivity, and anxiety were strongly associated with SCC. Self- and informant-reported SCC showed moderate inter-rater agreement. Adjusting for age, race, education, APOE ϵ4 carrier status, and depressive symptoms, SCC were associated with lower objective verbal memory and executive functioning performance. SCC were associated with lower parahippocampal cortical thickness but not with hippocampal volume or any of the measured CSF tests. Conclusions: SCC are strongly associated with neuropsychiatric factors in former American football players. SCC may also be a marker of cognitive decline and neurodegeneration.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to repetitive head impacts (RHIs), characterized by tau tangles around small blood vessels at the depths of the sulci. Currently, CTE can be diagnosed only postmortem , but can present with an array of cognitive, behavioral, mood, and motor symptoms. However, traumatic brain injury is also associated with increased risk of Alzheimer’s disease (AD) and may lead to comorbid neuropathology. Characterization of the in vivo biomarkers of CTE is a necessary next step to facilitate accurate diagnoses. We examined the profile of cerebrospinal fluid (CSF) biomarkers of amyloid-β, total tau (tTau), and phospho-tau (pTau) in a cohort of former professional (PRO, n = 100) and college (COL, n = 40) football players at high risk of CTE compared to asymptomatic unexposed controls (UE, n = 43). CSF was collected under controlled conditions using collection, processing, and cryostorage kits provided by the DIAGNOSE CTE Research Project Biomarker Core, and concentrations of Aβ 40 , Aβ 42 , tTau, and pTau (pTau 181 , pTau 217 , pTau 231 ) were measured at the University of Gothenburg, Sweden, using immunoassays. Associations between CSF biomarker levels with football history, and diagnosis of traumatic encephalopathy syndrome (TES) were examined using linear regression, and corrected for age, education, APOE -ε4 allele status, race, and body mass index. Our analysis revealed that football exposure affected both CSF Aβ 40 ( p = 0.039) and Aβ 42 ( p = 0.038), particularly among those under 60 years of age in the PRO compared to the UE exposure group. Among former football players, estimates of RHI exposure were not generally associated with CSF Aβ, tTau, and pTau biomarker levels. CSF Aβ 40 ( p = 0.0041) and Aβ 42 ( p = 0.011) were lower in former football players with TES diagnosis compared to unexposed participants, although CSF Aβ, tTau, and pTau biomarker levels did not differ between former players with and without a TES diagnosis. Among former football players, reduced CSF Aβ 40 ( p = 0.011) and Aβ 42 (p = 6e-04) were observed in those with cognitive impairment compared to those with neurobehavioral dysregulation. The findings of significant associations of reduced CSF Aβ levels with RHI in elite football players are in line with recent postmortem studies; however, the lack of relationship with CSF tTau and pTau species observed to be altered in the setting of AD suggests that the pathological features of CTE reflected in fluid biomarkers are complex and require further study. The overlapping comorbid age-dependent features of neurodegeneration that occur in those at risk for CTE suggest that tau pathology in CTE is not reliably reflected by currently available fluid biomarkers and that the use of multiple biomarkers related to the compound characteristics of CTE may be required for early detection.

Abstract Background In vivo biomarkers that can detect long‐term neuropathologies from repetitive head impact (RHI) exposure are needed, especially for the neurodegenerative tauopathy chronic traumatic encephalopathy (CTE). Here, we evaluated plasma p ‐tau217 as a potential biomarker for CTE p ‐tau pathology, and examined the concordance between plasma p ‐tau217 and Aβ pathology in an at‐risk for CTE sample. Method The sample included 180 male former football players (120 professional, 60 college), and 56 asymptomatic men without RHI (i.e., controls). Participants completed blood draws, 18F‐florbetapir (Aβ+=SUVR≥1.10), and 18F‐flortaucipir PET. Traumatic encephalopathy syndrome (TES) diagnoses were made. Single molecule array for plasma p ‐tau217 (ALZpath) was performed (≥0.6 cutoff used to maximize sensitivity). Nine participants had post‐mortem tissue. ANCOVA examined group differences in p ‐tau217 (football vs controls; TES‐CTE no, TES‐CTE suggestive, TES‐CTE possible/probable). Multivariable regression models tested associations between p ‐tau217 and florbetapir/flortaucipir PET. Covariates included age, race and APOE e4 . Result Sample characteristics are in Table 1. p ‐tau217 concentrations were higher in former football players compared to controls (est. marginal mean difference=‐0.217, p = 0.005). There were no group differences in Aβ‐PET SUVR. No differences were found across TES‐CTE certainty levels. In football players, higher p ‐tau217 was associated with higher Aβ‐PET SUVR (B=1.380, 95%CI[0.597‐2.155], p = 0.001) but not when Aβ+ ( n = 17) participants and those with kidney/liver disease ( n = 5) were excluded. Aβ+ participants had the highest p ‐tau217 (Figure 1). When compared against Aβ‐PET, several false Aβ‐positives (high p ‐tau217, Aβ‐) were identified, including one extreme outlier (assay related) and a cluster of Aβ‐ participants with p ‐tau217 between 0.60–1.0. There were no associations with flortaucipir SUVR (frontal, mesial temporal, left parietal). Two extreme p ‐tau217 outliers had autopsy‐confirmed CTE stage III (AD‐, Table 2). Of the remaining donors, all were AD‐ and four had CTE (stages II‐IV) with ptau217 between 0.125‐0.449. Conclusion Plasma p ‐tau217 has usefulness in quantifying Aβ pathology but restricted utility for detection of CTE. In this at‐risk for CTE sample, p ‐tau217 and Aβ‐PET were associated at the group level. At the individual level, false Aβ‐positives (and negatives) existed, including Aβ‐ participants with high p ‐tau217. We will explore whether this discrepancy is due to disease or peripheral interference with the N‐terminal binding in p ‐tau assays.

Abstract Background Plasma phosphorylated‐tau217 (pTau217) is a blood‐based biomarker of Alzheimer's Disease (AD) pathology. Cognitive resilience describes the presence of neurodegenerative pathology and preserved cognition. Cognitive resistance describes avoidance of neurodegeneration. This post hoc analysis of the Post‐Operative Delirium Belfast (PODB) cohort aimed to define cognitive resilience using plasma pTau217 and Mini Mental State Examination (MMSE) measures. Methods PODB was an observational cohort study, investigating people aged 65 and over, without a diagnosis of dementia, undergoing elective hip and knee replacement between 2012‐2014 with subsequent long‐term follow‐up. In this analysis, pre‐operative plasma pTau217 was used as a marker of neuropathology. A cutoff of 0.42 pg/mL was used (Ashton NJ et al. 2024). Pre‐operative and 8‐year follow‐up MMSE scores were used as a marker of cognition. A score of ≥24 was considered preserved. Definitions used were: Cognitive resilience = pTau217 ≥0.42 pg/mL plus MMSE ≥24. Cognitive resistance = pTau217 <0.42pg/mL plus MMSE ≥24. Affected = pTau217 ≥0.42 pg/mL plus MMSE <24. Those with normal markers plus poor cognition were defined as pTau217 <0.42pg/mL plus MMSE <24. These four groups were identified at baseline and follow‐up, respectively. In this analysis, 231 participants were included at baseline, 104 at follow‐up. Results Of the n = 231 participants included at baseline, n = 147/231 (64%) were cognitively resilient, n = 65/231 (28%) resistant, n = 17/231 (7%) affected, and n = 2/231 (<1%) had normal markers and MMSE <24. Of the n = 104 participants with follow‐up information included in this analysis, n = 61/104 (59%) were cognitively resilient, n = 33/104 (32%) were resistant, n = 8/104 (8%) affected, and n = 2/104 (<1%) had normal markers and MMSE <24. Cognitively resilient participants at baseline were younger ( p = 0.011) and tended to be female ( p = 0.977) compared to affected participants. At follow‐up, those who were cognitively resilient tended to be younger ( p = 0.196) and female ( p = 0.212) compared to affected participants (Table 1). Of those cognitively resilient at follow up, n = 59/61 (97%) of these participants were also cognitively resilient at baseline. Conclusions Using pTAu217, at the cut‐off quoted, we found a high incidence of cognitive resilience in an older elective surgical cohort.

Abstract Background The quantification of Neurofilament Light chain (NfL) in blood and cerebrospinal fluid (CSF) has proven valuable for diagnosing and prognosing various neurological disorders, including Alzheimer's disease, frontotemporal dementia, amyotrophic lateral sclerosis, parkinsonism, multiple sclerosis, and ischemic damage. However, there is considerable variability in clinical and laboratory practices between centers, primarily due to different contexts of use (COU), analytical methods, and the application of cutoffs or scales. Additionally, for the same biochemical profile, the interpretation and reporting of results may vary from one center to another, raising concerns about the commutability of the tests. To date, no consensus has been reached among laboratories to define the most appropriate use of cutoffs or conclusions/comments based on NfL profiles. Method This international project involves 38 laboratories across 18 countries, all specialized in the biochemical diagnosis of neurological disorders. Using a questionnaire, we obtained descriptions from each center regarding their COU, pre‐analytical and analytical protocols (including the biological fluid and methods used to quantify NfL). Through a consensus approach, we developed a harmonized strategy for the use and reporting of NfL results across different centres according to their respective COU. Results Among the centers, 63% quantified NfL in the CSF, 87% in blood and 53% in both fluids. COU were as follow: frontotemporal dementia (71%), Alzheimer disease (71%), multiple sclerosis (61%), amyotrophic lateral sclerosis (61%), psychiatric syndrome (45%), Creutzfeldt‐Jakob disease (32%), Parkinson disease (39%), peripheral neuropathy (29%), traumatic brain injury (21%), Huntington's disease (13%), amyloid transthyretin related (11%) and cardiac arrest (8%). Most of the centers define pathological cutoffs based on publications (50%) and take age into account for this purpose (42%). Reporting is mostly transmitted through numeric results (95%). Conclusion Harmonizing cutoffs, reporting, and interpretation across various clinical contexts will facilitate the incorporation of this biomarker into routine clinical practice.

Background The association between lifestyle factors and Alzheimer's disease (AD) pathophysiology remains incompletely understood. Objective The aim of this study was to assess the association of alcohol consumption, smoking behavior, sleep quality and physical, cognitive, and social activity with cerebral amyloid pathology. Methods For this cross-sectional study, we selected participants from the Amyloid Biomarker Study data pooling initiative. We used generalized estimating equations to assess associations of dichotomized lifestyle measures with amyloid pathology. Results We included 9171 participants with normal cognition (NC) and 2555 participants with mild cognitive impairment (MCI) from the Amyloid Biomarker Study. Of participants with NC, 58% were women, 34% were APOE ε4 carrier, and 27% had amyloid pathology. Of participants with MCI, 48% were women, 47% were APOE ε4 carrier, and 57% had amyloid pathology. In NC, cognitively active participants were less likely to have amyloid pathology (OR = 0.77, 95%CI 0.66–0.89, p < 0.001). In MCI, participants who had ever smoked or had sleep problems were less likely to have amyloid pathology (OR = 0.85, 95%CI 0.73–0.99, p = 0.029; OR = 0.62, 95%CI 0.45–0.86, p = 0.004). Conclusions In NC, cognitive activity was associated with a lower frequency of amyloid pathology. In MCI, favorable lifestyle behaviors were not associated with a lower frequency of amyloid pathology. The results of the current study contribute to the broader evidence base on lifestyle and AD by further characterizing the role of lifestyle behaviors in AD pathology across different clinical stages.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to repetitive head impacts (RHI). In CTE, hyperphosphorylated tau (p-tau) aggregates are found in neurons at the depth of cortical sulci close to the gray matter/white matter (GM/WM) boundary. To date, CTE can only be diagnosed postmortem by neuropathological examination. Traumatic encephalopathy syndrome (TES) is the clinical syndrome purported to be associated with CTE pathology. The aim of this study is to investigate microstructural properties at the GM/WM boundary in individuals with a history of exposure to RHI and clinical features of CTE (i.e., TES). Diffusion magnetic resonance imaging (dMRI), TES diagnoses, and cerebrospinal fluid (CSF) biomarkers were acquired from 165 male former American football players (age: 57.29 ± 8.23 years) from the DIAGNOSE CTE Research Project, a multicenter, observational cohort study. Fractional anisotropy (FA) was measured at the GM/WM boundary of the whole brain. In addition, a widely used method (tract-based spatial statistics [TBSS]) was applied to measure FA of central WM. We used analyses of covariance to test associations between FA and TES. Furthermore, we used linear regressions to test associations between FA and nine CSF biomarkers (i.e., p-tau-181, -217, -231, total tau, amyloid β [Aβ] 1–40 , Aβ 1–42 , glial fibrillary acidic protein [GFAP], neurofilament light [NfL], and soluble triggering receptor expressed on myeloid cells-2 [sTREM2]). We report an association between higher FA at the GM/WM boundary and higher levels of certainty for CTE pathology ( F (1, 147) = 5.781, 95% confidence interval (CI) = 0.0003–0.003, p = 0.035) as well as neurobehavioral dysregulation ( F (1, 148) = 7.559, 95% CI = 0.001–0.009, p = 0.020), and functional dependence/dementia ( F (1, 148) = 5.046, 95% CI = 0.0004–0.006, p = 0.039). In addition, we report an association between higher FA at the GM/WM boundary and higher CSF p-tau-181 (β = 0.272, 95% CI = 0.078–0.466, p = 0.029) and p-tau-217 (β = 0.295, 95% CI = 0.102–0.488, p = 0.027). FA of the central WM was not associated with TES diagnoses. Taken together, these findings suggest that dMRI at the GM/WM boundary could be used to investigate microstructural alterations suggestive of tau pathology-associated neurodegeneration in individuals with TES, the clinical presentation of CTE. Future studies are needed to validate this approach and to identify clinically useful cutoff values for dMRI metrics.

Abstract BACKGROUND This systematic review and meta‐analysis aimed to assess the diagnostic test accuracy of blood‐based biomarkers (BBMs) for detecting Alzheimer's disease (AD) pathology in cognitively impaired individuals in specialized care settings. The overarching goal is to inform the development of a clinical practice guideline, led by the Alzheimer's Association, for use in clinical practice. METHODS A systematic search of MEDLINE, Embase, and Cochrane Library was conducted from January 2019 to November 2024. Studies evaluating the diagnostic test accuracy of plasma phosphorylated tau (p‐tau) and amyloid beta (Aβ) tests (p‐tau217, %p‐tau217, p‐tau181, p‐tau231, and Aβ42/Aβ40) compared to reference standard tests (cerebrospinal fluid [CSF] AD biomarkers, amyloid positron emission tomography [PET], or neuropathology) in individuals with cognitive impairment (mild cognitive impairment or dementia) in specialized care settings were included. Pooled diagnostic test accuracy measures were calculated, including sensitivity, specificity, and likelihood ratios. Across a range of pre‐test probabilities, we evaluated how much a positive or a negative test result would lead to a change in the probability of having amyloid positivity (post‐test probability). All analyses were conducted for each test within each biomarker. The Quality Assessment of Diagnostic Accuracy Studies 2 tool was used to evaluate the risk of bias, and the certainty of the evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation approach. RESULTS Across 49 observational studies meeting eligibility criteria, 31 different BBM tests were examined. When evaluated using a single cut‐point, the diagnostic test accuracy varied considerably across tests: the pooled sensitivity ranged from 49.3% (95% confidence interval [CI]: 41.2–57.4) to 91.4% (95% CI: 86.6–94.6), and the pooled specificity ranged from 61.5% (95% CI: 45.6–75.3) to 96.7% (95% CI: 87.8–99.2). Differences in post‐test probability based on a range of pre‐test probabilities varied greatly across tests. Furthermore, the certainty of evidence across tests ranged from moderate to very low. Most included studies were judged to be at high risk of bias, particularly in domains related to patient selection, index test conduct, and reference standard. CONCLUSION This systematic review provides a comprehensive synthesis of the current evidence on the diagnostic accuracy of BBMs for detecting AD pathology in cognitively impaired individuals in specialized care settings. The findings serve as a foundation for an accompanying clinical practice guideline that provides evidence‐based recommendations for BBM use in the clinical diagnostic pathway. Given continuous developments in this rapidly evolving field, ongoing evaluation will be critical to ensure the synthesized evidence and clinical guidelines remain up to date and maintain clinical relevance. Highlights This is the first comprehensive systematic review and meta‐analysis to evaluate the diagnostic accuracy of blood‐based biomarker (BBM) tests specifically in individuals with objective cognitive impairment seen in specialized care settings. Across 49 studies, BBM test performance varied widely. Pooled sensitivity ranged from 49.3% to 91.4% and specificity from 61.5% to 96.7%, depending on the analyte and assay platform. This review followed the Cochrane Handbook for Systematic Reviews of Diagnostic Test Accuracy, the Grading of Recommendations, Assessment, Development, and Evaluation approach to assess the certainty of evidence. This review served as the evidence base for the Alzheimer's Association's new clinical practice guidelines on BBMs, providing structured, evidence‐based guidance for implementing BBMs in the diagnostic workup of suspected Alzheimer's disease. The review underscores that BBM test performance is assay‐ and platform specific and advises clinicians and laboratory directors to interpret results in the context of the specific test used and integrate the results with a comprehensive clinical assessment.

Abstract Objectives Neurofilament light (NfL) is an established biofluid marker of neuroaxonal injury for neurological diseases. Several high-throughput and sensitive immunoassays have been developed to quantify NfL in blood and cerebrospinal fluid (CSF), facilitating the use of NfL as a biomarker in research and clinical practice. However, because of the lack of rigorous comparisons of assays, it has been difficult to determine whether data are comparable and whether assay performance differs. Here, we compared the performance of five NfL immunoassays. Methods To assess the five NfL immunoassays (Fujirebio, ProteinSimple, Quanterix, Roche and Siemens), we used pooled plasma or pooled CSF, as well as unique samples from 20 healthy controls and 20 individuals with El Escorial defined probable or definite amyotrophic lateral sclerosis (ALS), to evaluate precision, parallelism and/or bias. We also examined correlations between plasma and CSF NfL concentrations within and across assays and evaluated their ability to differentiate healthy controls from individuals with ALS. Results Four of the five assays demonstrated exemplary performance based on our analyses of precision and parallelism. Across the five assays, NfL concentrations were lower in plasma than in CSF, although they displayed a high degree of correlation. We noted bias across assays; plasma NfL concentrations were lowest for the Roche assay and highest for the ProteinSimple assay. In addition, all assays reliably distinguished healthy controls from individuals with ALS using plasma or CSF NfL. Conclusions Four NfL assays demonstrated similar analytic performance. Alongside performance, other factors such as costs, accessibility, usability, footprint, and intended use, should be considered.