Citations

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

Abstract Importance Decline in olfactory function may be used as a predictor of cognitive decline, to enhance early detection models, improve risk stratification, and enable early intervention. Objective To assess the longitudinal association between olfactory decline, cognitive decline, and postmortem neuropathology. Design, setting and participants Retrospective longitudinal analysis with clinicopathological correlations of a prospective population-based cohort study using data from the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND) and its Brain and Body Donation Program. Participants included cognitively unimpaired individuals without parkinsonism that converted to mild cognitive impairment (MCI) and/or dementia or remained cognitively stable. Main Outcomes and Measures longitudinal change in olfaction, neuropsychiatric symptoms, motor function and memory, conversion to MCI/dementia, postmortem neuropathology Results Over a mean follow-up period of 7.7 ± 5.4 years, out of 922 participants who were cognitively unimpaired at the first cognitive conference, 643 remained cognitively unimpaired, 279 converted to MCI, and 82 developed dementia. Of these, 633 individuals had at least 2 olfactory tests. Converters showed reduced olfactory function (t=-12.6, p <0.0001), faster progression in neuropsychiatric symptom burden (t=3.42, p < 0.001), and faster decline in memory (t= -7.33, p <0.0001) prior to conversion while no significant differences were observed in motor scores between converters and non-converters. Using ROC analysis, olfactory decline, increased neuropsychiatric symptom burden, as well as motor and memory decline predicted conversion to MCI with a consistent accuracy of ∼ 70% up to 5 years before conversion, while UPSIT alone had an accuracy of ∼ 60%. Longitudinal decline in olfaction was associated with a higher burden of a-synuclein (t= -8.21, p <0.0005), tau tangle (t= -2.66, p < 0.01) and amyloid plaque burden (t= -2.85, p < 0.005) and a faster decline over time was associated with a higher burden of tau (t=5.66, p<0.0001). Conclusions and Relevance A reduction in olfactory identification ability is observed up to a decade prior to conversion to MCI and is associated with underlying burden of neuropathology markers, underscoring the value of incorporating olfactory testing in cognitively unimpaired individuals to identify those at-risk of future cognitive decline.

Abstract Background : Traumatic encephalopathy syndrome (TES) is a clinical research construct used to identify individuals at risk for chronic traumatic encephalopathy (CTE) following exposure to repetitive head impacts (RHI). Adjudication of TES relies on clinical features such as progressive cognitive impairment and neurobehavioral dysregulation. Blood-based biomarkers and structural neuroimaging abnormalities have been associated with TES but are not part of the criteria. This study evaluated whether TES identification was associated with the combined contribution of cognitive performance, blood biomarkers, and structural neuroimaging measures across two well-characterized cohorts. Methods : Participants included 158 professional fighters from the Professional Athletes Brain Health Study and 149 former American football players from The DIAGNOSE CTE Research Project. Three indices were constructed representing complementary domains: a cognitive index reflecting cohort-specific cognitive features, a blood biomarker index including plasma neurofilament light chain, glial fibrillary acidic protein, total tau, tau phosphorylated at amino acid 231, and APOE -ε4 carrier status, and an imaging index comprising volumetric MRI measures of subcortical structures, ventricles, and corpus callosum subregions. Grouped weighted quantile sum regression models were estimated within each cohort to evaluate associations between these indices and TES while adjusting for age, race, competition status, and RHI exposure. Results : Multidomain models demonstrated improved model performance compared with single-domain models in both cohorts (PABHS: AUC=0.91, PPV=0.80; DIAGNOSE CTE: AUC=0.84, PPV=0.85). Biomarker and imaging indices contributed additional information across cohorts, although imaging contributions were more prominent in fighters whereas blood biomarker associations were stronger in football players. Conclusion : TES in RHI-exposed athletes was associated with a convergent clinicobiological profile observed across two independent cohorts with distinct exposure patterns. These findings support multidomain analytic frameworks for evaluating correlated biological signals in RHI-exposed populations and may inform future studies of TES and CTE.

Abstract Skin biopsies analyzed with α-synuclein seed amplification assays (SAAs) are a simple way to clinically interrogate the presence of α-synuclein aggregates. We determined the accuracy of skin biopsy SAA in predicting the clinical diagnoses of Parkinson disease (PD), PD with dementia (PDD) and dementia with Lewy bodies (DLB). Blinded SAAs were performed in 3 independent laboratories. Subjects diagnosed with PD, PDD and DLB were analyzed together as group 1, clinically unaffected subjects as group 2 and those with risk factors for LBD as group 3. Punch biopsies were taken from the posterior neck and analyzed by the 3 labs in 6 separate SAAs. Pairwise agreement between labs and assays ranged from excellent (kappa 0.82) to moderate (kappa 0.40-0.68). Sensitivity across assays ranged between 50.0% and 61.3%; specificity ranged between 68.6% and 100%. Comparisons of group 1 vs group 2 produced the greatest specificities, between 77.3% and 100%. In 17 cases that subsequently came to autopsy, 93% of SAAs were positive in those at the neocortical LBD stage but in only &lt;10% of those at lower stages. Skin biopsy α-synuclein SAA may be useful as a diagnostic and progression biomarker in Lewy body dementia clinical trials.

Abstract INTRODUCTION Repetitive head impacts (RHI) from contact sports may cause a unique pattern of white matter hyperintensities (WMH) on T2‐weighted fluid‐attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI), termed RHI‐associated WMH (RHI‐WMH). These lesions are punctate, circular, and located at the gray–white matter boundary, an area vulnerable to trauma‐related damage. METHODS We investigated the association of RHI with these lesions in two aging cohorts: (1) former American football players versus asymptomatic unexposed men and (2) individuals with RHI from various contact sports versus non‐RHI participants. RHI‐WMH were assessed using visual ratings and a novel automated quantification pipeline. RESULTS Individuals with RHI had greater RHI‐WMH by both detection methods in both cohorts. RHI‐WMH were associated with plasma neurofilament light and p‐tau231, and flortaucipir positron emission tomography (PET) uptake. DISCUSSION RHI‐WMH may represent a new supportive biomarker for the detection of RHI‐related neuropathologies later in life.

ABSTRACT Braak and others have proposed that Lewy body pathology (LBP) in Parkinson’s disease (PD) may arise not only in the brain but alternatively from an initial site in the gastrointestinal (GI) tract with subsequent passage to the central nervous system CNS through the vagus nerve or other routes. We tested this hypothesis by using both immunohistochemistry (IHC) and RT QuIC a form of alpha synuclein seed amplification assay (SAA) to detect alpha synuclein LBP in samples from selected brain regions and 10 GI tract sites taken from autopsies of 50 PD subjects and 128 elderly subjects without parkinsonism or dementia including 34 with IHC identified CNS incidental Lewy body disease (ILBD) and 94 with no Lewy body IHC pathology detected (NLB). A positive SAA or IHC result was restricted to the GI tract in only 2 subjects while LBP by either SAA or IHC was restricted to the brain in 11 subjects. To fairly compare GI-only with brain-only synucleinopathy, however, we would have to do SAA on brain samples from all ILBD and NLB cases in at least 4 critical brain regions: olfactory bulb, medulla, pons, and amygdala. Further SAA of brain regions is estimated, based on the proportional results to date, to potentially identify 21 additional brain-only LBP subjects, for a total of 32, if it were done on all of the NLB subjects. From this brain-only LBP is estimated to be 16 times more common than GI-only LBP. To assess the clinical impact of SAA-positive GI sites we found that the number of positive sites per subject is significantly correlated with UPDRS motor score and SCOPA-AUT GI related scores including those for salivation, straining, constipation, and bowel movement.

Abstract Genome-wide association studies (GWAS) have linked more than a hundred non-coding genomic loci to Parkinson’s disease (PD) risk. Deciphering their functional impact on gene regulation requires cell type-aware modeling approaches to assess the effects of sequence variation on enhancer function and target gene expression. To address this challenge, we generated a comprehensive matched dataset from 190 human donors (115 controls and 75 PD), comprising long-read whole-genome sequencing alongside single nucleus multiome atlases (snATAC-seq and snRNA-seq for 3.1 and 1.1 million nuclei respectively) of the anterior cingulate cortex and substantia nigra. By integrating chromatin accessibility quantitative trait loci (caQTL), DNA methylation QTL (meQTL), and allele-specific chromatin accessibility (ASCA), we identified 53,841 high-confidence cis -acting genetic variants that modulate cell type-specific enhancer accessibility in one or both brain regions. We further demonstrate that sequence-to-function models can accurately predict the impact of these variants directly from the genomic sequence. Novel explainability approaches allowed stratifying these variants according to their regulatory function, with the majority disrupting specific transcription factor binding sites in a cell type specific manner. Integrating these “enhancer variants” (EV) with eQTL mapping and gene locus modeling linked a subset of EVs to their target genes. Finally, we applied these models to prioritize regulatory variants at known PD GWAS loci, bypassing statistical limitations in rare disease-relevant populations like dopaminergic neurons. All together, we establish a unique resource and new sequence modeling strategies to interpret functional non-coding variation in the human brain.

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.