Search

IntroductionAbnormal amyloid-beta (Aβ) and tau deposition define Alzheimer's Disease (AD), but non-elevated tau is relatively frequent in patients on the AD pathway.MethodsWe examined characteristics and regional patterns of 397 Aβ+ unimpaired and impaired individuals with low tau (A+T-) in relation to their higher tau counterparts (A+T+).ResultsSeventy-one percent of Aβ+ unimpaired and 42% of impaired Aβ+ individuals were categorized as A+T- based on global tau. In impaired individuals only, A+T- status was associated with older age, male sex, and greater cardiovascular risk. α-synuclein was linked to poorer cognition, particularly when tau was low. Tau burden was most frequently elevated in a common set of temporal regions regardless of T+/T- status.DiscussionLow tau is relatively common in patients on the AD pathway and is linked to comorbidities that contribute to impairment. These findings have implications for the selection of individuals for Aβ- and tau-modifying therapies.

Purpose of the report: Adults with Down Syndrome (DS) have a substantially increased risk for Alzheimer's disease (AD) due to the triplicated amyloid-precursor-protein gene on chromosome 21, resulting in amyloid and tau accumulation. However, tau PET assessments are not sufficiently implemented in DS-AD research or clinical work-up, and second-generation tau tracers such as [18F]PI-2620 have not been thoroughly characterized in adults with DS. We aim at illustrating feasibility and potential diagnostic value of tau PET imaging with [18F]PI-2620 for the diagnosis of DS-AD. Materials and methods: Five adults with DS (40% female, aged 43–62) and cognitive decline underwent clinical assessments, neuropsychological testing, lumbar puncture and multimodal neuroimaging. All underwent [18F]PI-2620 tau PET. Visual read of tau PET scans was performed by three blinded raters, assessing increased tracer uptake in brain areas corresponding to the six Braak stage regions and basal ganglia. Results: Visual read of tau burden revealed three tau-positive individuals which corresponded to their clinical decline while two cognitively stable individuals were rated as negative. Rating showed high inter-rater reliability for all Braak stages. Conclusion: Tau PET imaging is a feasible and important biomarker assessment in the differential diagnosis of cognitive decline in adults with DS at risk of developing AD. [ABSTRACT FROM AUTHOR]

INTRODUCTION: The A/T/N (amyloid/tau/neurodegeneration) framework provides a biological basis for Alzheimers disease (AD) diagnosis and can encompass additional changes such as inflammation (I). A spectrum of T/N/I imaging and plasma biomarkers was acquired in a phase 2 clinical trial of rasagiline in mild to moderate AD patients. We evaluated these to understand biomarker distributions and relationships within this population. METHODS: Plasma biomarkers of pTau-181, neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), other inflammation-related proteins, imaging measures including fluorodeoxyglucose (FDG) positron emission tomography (PET), flortaucipir PET, and volumetric magnetic resonance imaging (MRI), and cognitive endpoints were analyzed to assess characteristics and relationships for the overall population (N = 47 at baseline and N = 21 for longitudinal cognitive comparisons) and within age-decade subgroups (57-69, 70-79, 80-90 years). RESULTS: Data demonstrate wide clinical and biomarker heterogeneity in this population influenced by age and sex. Plasma pTau-181 and GFAP correlate with tau PET, most strongly in left inferior temporal cortex (p = 0.0002, p = 0.0006, respectively). In regions beyond temporal cortex, tau PET uptake decreased with age for the same pTau-181 or GFAP concentrations. FDG PET and brain volumes correlate with tau PET in numerous regions (such as inferior temporal: p = 0.0007, p = 0.00001, respectively). NfL, GFAP, and all imaging modalities correlate with baseline MMSE; subsequent MMSE decline is predicted by baseline parahippocampal and lateral temporal tau PET (p = 0.0007) and volume (p = 0.0006). Lateral temporal FDG PET (p = 0.006) and volume (p = 0.0001) are most strongly associated with subsequent ADAS-cog decline. NfL correlates with FDG PET and baseline MMSE but not tau PET. Inflammation biomarkers are intercorrelated but correlated with other biomarkers in only the youngest group. DISCUSSION: Associations between plasma biomarkers, imaging biomarkers, and cognitive status observed in this study provide insight into relationships among biological processes in mild to moderate AD. Findings show the potential to characterize AD patients regarding likely tau pathology, neurodegeneration, prospective clinical decline, and the importance of covariates such as age. HIGHLIGHTS: Plasma pTau-181 and GFAP correlated with regional and global tau PET in mild to moderate AD.NfL correlated with FDG PET and cognitive endpoints but not plasma pTau-181 or tau PET.Volume and FDG PET showed strong relationships to tau PET, one another, and cognitive status.Temporal volumes most strongly predicted decline in both MMSE and ADAS-cog.Volume and plasma biomarkers can enrich for elevated tau PET with age a significant covariate.

PurposeWe evaluated the impact of partial volume correction (PVC) methods on the quantification of longitudinal [18F]GTP1 tau positron-emission tomography (PET) in Alzheimer's disease and the suitability of describing the tau pathology burden temporal trajectories using linear mixed-effects models (LMEM).MethodsWe applied van Cittert iterative deconvolution (VC), 2-compartment, and 3-compartment, and the geometric transfer matrix plus region-based voxelwise methods to data acquired in an Alzheimer's disease natural history study over 18 months at a single imaging site. We determined the optimal PVC method by comparing the standardized uptake value ratio change (%ΔSUVR) between diagnostic and tau burden-level groups and the longitudinal repeatability derived from the LMEM. The performance of LMEM analysis for calculating %ΔSUVR was evaluated in a natural history study and in a multisite clinical trial of semorinemab in prodromal to mild Alzheimer's disease by comparing results to traditional per-visit estimates.ResultsThe VC, 2-compartment, and 3-compartment PVC methods had similar performance, whereas region-based voxelwise overcorrected regions with a higher tau burden. The lowest within-subject variability and acceptable group separation scores were observed without PVC. The LMEM-derived %ΔSUVR values were similar to the per-visit estimates with lower variability.ConclusionThe results indicate that the tested PVC methods do not offer a clear advantage or improvement over non-PVC images for the quantification of longitudinal [18F]GTP1 PET data. LMEM offers a robust framework for the longitudinal tau PET quantification with low longitudinal test-retest variability.Clinical trial registrationNCT02640092 and NCT03289143.

Tau PET has enabled the visualization of paired helical filaments of 3 or 4 C-terminal repeat tau in Alzheimer disease (AD), but its ability to detect aggregated tau in frontotemporal lobar degeneration (FTLD) spectrum disorders is uncertain. We investigated 2-(2-([18F]fluoro)pyridin-4-yl)-9H-pyrrolo[2,3-b:4,5c']dipyridine ([18F]PI-2620), a newer tracer with ex vivo evidence for binding to FTLD tau, in a convenience sample of patients with suspected FTLD and AD using a static acquisition protocol and parametric SUV ratio (SUVr) images. Methods: We analyzed [18F]PI-2620 PET data from 65 patients with clinical diagnoses associated with AD or FTLD neuropathology; most (60/65) also had amyloid-β (Aβ) PET. Scans were acquired 30-60 min after injection; SUVr maps (reference, inferior cerebellar cortex) were created for the full acquisition and for 10-min truncated sliding windows (30-40, 35-45,…50-60 min). Age- and sex-adjusted z score maps were computed for each patient, relative to 23 Aβ-negative cognitively healthy controls (HC). Mean SUVr in the globus pallidus, substantia nigra, subthalamic nuclei, dentate nuclei, white matter, and temporal gray matter was extracted for the full and truncated windows. Results: Patients with suspected AD neuropathology (Aβ-positive patients with mild cognitive impairment or AD dementia) showed high-intensity temporoparietal cortex-predominant [18F]PI-2620 binding. At the group level, patients with clinical diagnoses associated with FTLD (progressive supranuclear palsy with Richardson syndrome [PSP Richardson syndrome], corticobasal syndrome, and nonfluent-variant primary progressive aphasia) exhibited higher globus pallidus SUVr than did HCs; pallidal retention was highest in the PSP Richardson syndrome group, in whom SUVr was correlated with symptom severity (ρ = 0.53, P = 0.05). At the individual level, only half of PSP Richardson syndrome, corticobasal syndrome, and nonfluent-variant primary progressive aphasia patients had a pallidal SUVr above that of HCs. Temporal SUVr discriminated AD patients from HCs with high accuracy (area under the receiver operating characteristic curve, 0.94 [95% CI, 0.83-1.00]) for all time windows, whereas discrimination between patients with PSP Richardson syndrome and HCs using pallidal SUVr was fair regardless of time window (area under the receiver operating characteristic curve, 0.77 [95% CI, 0.61-0.92] at 30-40 min vs. 0.81 [95% CI, 0.66-0.96] at 50-60 min; P = 0.67). Conclusion: [18F]PI-2620 SUVr shows an intense and consistent signal in AD but lower-intensity, heterogeneous, and rapidly decreasing binding in patients with suspected FTLD. Further work is needed to delineate the substrate of [18F]PI-2620 binding and the usefulness of [18F]PI2620 SUVr quantification outside the AD continuum.

Background: To establish simple screening tests to suspect Alzheimer's disease (AD) pathology, the clinical sign "head-turning sign" (HTS), which is a patient's behavior of turning their head towards their partner to seek assistance with questions posed by the examiner during the interview, and the simple screening questionnaire for dementia named "Neucop-Q" were validated in participants diagnosed with amyloid and tau positron emission tomography (PET). Methods: We enrolled 155 patients: 47 cognitive normal, 36 with mild cognitive impairment, 64 with dementia, and 8 with psychiatric disorders. All participants underwent Neucop-Q [three questions: Consciousness/self-awareness of cognitive disabilities (C) normal/impaired (nor/imp), Pleasure/pastime (P) nor/imp, and News/knowledge on current topics (N) nor/imp] and amyloid/tau PET. Additionally, we measured plasma amyloid β (Aβ) 42/40 ratio, phosphorylated tau 181 (pTau181), glial fibrillary acidic protein (GFAP), and neurofilament light (NFL) levels and compared with HTS and Neucop-Q results. Results: The specificity and positive predictive value (PPV) of HTS positivity (HTSpos) were the highest (amyloid PET: 0.930 and 0.870, tau PET: 0.944 and 0.957, respectively), while Cimp and Nimp had a high negative predictive value (NPV) for amyloid PET (negativity) (0.750 and 0.725). Pimp showed high specificity for predicting non-AD tau positivity among non-AD participants without amyloid PET positivity (0.854). To validate these findings with PET results, we examined the correlation between well-established AD blood biomarkers and results obtained from these screening tests. HTSpos, Cimp, and Nimp were strongly associated with Aβ42/40 ratio (P < 0.0001, P = 0.0022, and P = 0.001), pTau181 (P < 0.0001, P = 0.0095, and P = 0.001), GFAP (P = 0.0372, P = 0.0088, and P = 0.0002), and amyloid PET Centiloid (P < 0.0001, P = 0.0210, and P = 0.0006), whereas Pimp increased neuroinflammation (GFAP; P = 0.0061) and was associated with non-AD tauopathy. The combination of Neucop-Q questions showed that Cimp/Pnor/Nimp subjects have the highest specificity and PPV (0.972 and 0.833) and were strongly associated with Aβ42/40 ratio (P = 0.0006), pTau181 (P = 0.0006), and amyloid PET Centiloid (P < 0.0001). Conclusion: HTSpos, Cimp, and Nimp have diagnostic utility in suspecting MCI due to AD and AD, and Pimp has diagnostic value in non-AD tauopathy. HTSpos, Cimp, and Nimp were associated with biomarkers of Aβ pathology. HTS and Neucop-Q may serve as powerful first-line screening in memory clinics. Trial registration: UMIN Clinical Trials Registry (UMIN-CTR) under registration numbers 000032027 (Registration date: 2018/03/31) and 000030248 (Registration date: 2018/01/01). [ABSTRACT FROM AUTHOR]

Purpose: [18F]-D3FSP is a new β-amyloid (Aβ) PET imaging tracer designed to decrease nonspecific signals in the brain by reducing the formation of the N-demethylated product. However, its optimal reference region for calculating the standardized uptake value ratio (SUVR) and its relation to the well-established biomarkers of Alzheimer's disease (AD) are still unclear. Methods: We recruited 203 participants from the Greater Bay Area Healthy Aging Brain Study (GHABS) to undergo [18F]-D3FSP Aβ PET imaging. We analyzed plasma Aβ42/Aβ40, p-Tau181, glial fibrillary acidic protein (GFAP), and neurofilament light (NfL) using the Simoa platform. We compared the standardized uptake value (SUV) of five reference regions (cerebellum, cerebellum cortex, brainstem/PONs, white matter, composite of the four regions above) and AD typical cortical region (COMPOSITE) SUVR among different clinical groups. The association of D3FSP SUVR with plasma biomarkers, imaging biomarkers, and cognition was also investigated. Results: Brainstem/PONs SUV showed the lowest fluctuation across diagnostic groups, and COMPOSITE D3FSP SUVR had an enormous effect distinguishing cognitively impaired (CI) individuals from cognitively unimpaired (CU) individuals. COMPOSITE SUVR (Referred to brainstem/PONs) was positively correlated with p-Tau181 (p < 0.001), GFAP (p < 0.001), NfL (p = 0.014) in plasma and temporal-metaROI tau deposition (p < 0.001), and negatively related to plasma Aβ42/Aβ40 (p < 0.001), temporal-metaROI cortical thickness (p < 0.01), residual hippocampal volume (p < 0.001) and cognition (p < 0.001). The voxel-wise analysis replicated these findings. Conclusion: This study suggests brainstem/PONs as an optimal reference region for calculating D3FSP SUVR to quantify cortical Aβ plaques in the brain. [18F]-D3FSP could distinguish CI from CU and strongly correlates with well-established plasma biomarkers, tau PET, neurodegeneration, and cognitive decline. However, future head-to-head comparisons of [18F]-D3FSP PET images with other validated Aβ PET tracers or postmortem results are crucial. [ABSTRACT FROM AUTHOR]

IntroductionWe used sex and apolipoprotein E ε4 (APOE ε4) carrier status as predictors of pathologic burden in early-onset Alzheimer's disease (EOAD).MethodsWe included baseline data from 77 cognitively normal (CN), 230 EOAD, and 70 EO non-Alzheimer's disease (EOnonAD) participants from the Longitudinal Early-Onset Alzheimer's Disease Study (LEADS). We stratified each diagnostic group by males and females, then further subdivided each sex by APOE ε4 carrier status and compared imaging biomarkers in each stratification. Voxel-wise multiple linear regressions yielded statistical brain maps of gray matter density, amyloid, and tau PET burden.ResultsEOAD females had greater amyloid and tau PET burdens than males. EOAD female APOE ε4 non-carriers had greater amyloid PET burdens and greater gray matter atrophy than female ε4 carriers. EOnonAD female ε4 non-carriers also had greater gray matter atrophy than female ε4 carriers.DiscussionThe effects of sex and APOE ε4 must be considered when studying these populations.HighlightsNovel analysis examining the effects of biological sex and apolipoprotein E ε4 (APOE ε4) carrier status on neuroimaging biomarkers among early-onset Alzheimer's disease (EOAD), early-onset non-AD (EOnonAD), and cognitively normal (CN) participants. Female sex is associated with greater pathology burden in the EOAD cohort compared to male sex. The effect of APOE ε4 carrier status on pathology burden was the most impactful in females across all cohorts.

IntroductionWe compared white matter hyperintensities (WMHs) in early-onset Alzheimer's disease (EOAD) with cognitively normal (CN) and early-onset amyloid-negative cognitively impaired (EOnonAD) groups in the Longitudinal Early-Onset Alzheimer's Disease Study.MethodsWe investigated the role of increased WMH in cognition and amyloid and tau burden. We compared WMH burden of 205 EOAD, 68 EOnonAD, and 89 CN participants in lobar regions using t-tests and analyses of covariance. Linear regression analyses were used to investigate the association between WMH and cognitive impairment and that between amyloid and tau burden.ResultsEOAD showed greater WMHs compared with CN and EOnonAD participants across all regions with no significant differences between CN and EOnonAD groups. Greater WMHs were associated with worse cognition. Tau burden was positively associated with WMH burden in the EOAD group.DiscussionEOAD consistently showed higher WMH volumes. Overall, greater WMHs were associated with worse cognition and higher tau burden in EOAD.HighlightsThis study represents a comprehensive characterization of WMHs in sporadic EOAD. WMH volumes are associated with tau burden from positron emission tomography (PET) in EOAD, suggesting WMHs are correlated with increasing burden of AD. Greater WMH volumes are associated with worse performance on global cognitive tests. EOAD participants have higher WMH volumes compared with CN and early-onset amyloid-negative cognitively impaired (EOnonAD) groups across all brain regions.

Purpose of the reportAdults with Down Syndrome (DS) have a substantially increased risk for Alzheimer’s disease (AD) due to the triplicated amyloid-precursor-protein gene on chromosome 21, resulting in amyloid and tau accumulation. However, tau PET assessments are not sufficiently implemented in DS-AD research or clinical work-up, and second-generation tau tracers such as [18F]PI-2620 have not been thoroughly characterized in adults with DS. We aim at illustrating feasibility and potential diagnostic value of tau PET imaging with [18F]PI-2620 for the diagnosis of DS-AD.Materials and methodsFive adults with DS (40% female, aged 43–62) and cognitive decline underwent clinical assessments, neuropsychological testing, lumbar puncture and multimodal neuroimaging. All underwent [18F]PI-2620 tau PET. Visual read of tau PET scans was performed by three blinded raters, assessing increased tracer uptake in brain areas corresponding to the six Braak stage regions and basal ganglia.ResultsVisual read of tau burden revealed three tau-positive individuals which corresponded to their clinical decline while two cognitively stable individuals were rated as negative. Rating showed high inter-rater reliability for all Braak stages.ConclusionTau PET imaging is a feasible and important biomarker assessment in the differential diagnosis of cognitive decline in adults with DS at risk of developing AD.

Quantitative susceptibility mapping (QSM) has been used to study susceptibility changes that may occur based on tissue composition and mineral deposition. Iron is a primary contributor to changes in magnetic susceptibility and of particular interest in applications of QSM to neurodegeneration and aging. Iron can contribute to neurodegeneration through inflammatory processes and via interaction with aggregation of disease-related proteins. To better understand the local susceptibility changes observed on QSM, its signal has been studied in association with other imaging metrics such as positron emission tomography (PET). The associations of QSM and PET may provide insight into the pathophysiology of disease processes, such as the role of iron in aging and neurodegeneration, and help to determine the diagnostic utility of QSM as an indirect indicator of disease processes typically evaluated with PET. In this review we discuss the proposed mechanisms and summarize prior studies of the associations of QSM and amyloid PET, tau PET, TSPO PET, FDG-PET, 15O-PET, and F-DOPA PET in evaluation of neurologic diseases with a focus on aging and neurodegeneration.

INTRODUCTION: Spatial extent‐based measures of how far amyloid beta (Aβ) has spread throughout the neocortex may be more sensitive than traditional Aβ‐positron emission tomography (PET) measures of Aβ level for detecting early Aβ deposits in preclinical Alzheimer's disease (AD) and improve understanding of Aβ's association with tau proliferation and cognitive decline. METHODS: Pittsburgh Compound‐B (PIB)‐PET scans from 261 cognitively unimpaired older adults from the Harvard Aging Brain Study were used to measure Aβ level (LVL; neocortical PIB DVR) and spatial extent (EXT), calculated as the proportion of the neocortex that is PIB+. RESULTS: EXT enabled earlier detection of Aβ deposits longitudinally confirmed to reach a traditional LVL‐based threshold for Aβ+ within 5 years. EXT improved prediction of cognitive decline (Preclinical Alzheimer Cognitive Composite) and tau proliferation (flortaucipir‐PET) over LVL. DISCUSSION: These findings indicate EXT may be more sensitive to Aβ's role in preclinical AD than level and improve targeting of individuals for AD prevention trials. Highlights: Aβ spatial extent (EXT) was measured as the percentage of the neocortex with elevated Pittsburgh Compound‐B.Aβ EXT improved detection of Aβ below traditional PET thresholds.Early regional Aβ deposits were spatially heterogeneous.Cognition and tau were more closely tied to Aβ EXT than Aβ level.Neocortical tau onset aligned with reaching widespread neocortical Aβ. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Sleep is crucial for memory consolidation and the clearance of toxic proteins associated with Alzheimer's disease (AD). We examined the association between sleep characteristics and imaging biomarkers of early amyloid beta (Aβ) and tau pathology as well as neurodegeneration in brain regions known to be affected in the incipient stages of AD. METHODS: Thirty‐nine cognitively unimpaired (CU) participants of the Harvard Aging Brain Study underwent at‐home polysomnography as well as tau positron emission tomography (flortaucipir‐PET), amyloid PET (Pittsburgh compound B [PiB]‐PET), and magnetic resonance imaging–derived assessment of cortical thickness (CT). RESULTS: Increased N1 sleep was associated with a higher tau PET signal (β = 0.009, p = 0.001) and lower CT in the temporal composite region of interest (β = –0.017, p = 0.007). Decreased slow‐wave sleep (SWS) was associated with higher tau burden in the temporal composite (β = –0.008, p = 0.005) and lower CT (β = 0.008, p = 0.002), even after controlling for global PiB‐PET. DISCUSSION: In CU older adults, lower SWS and higher N1 sleep were associated with higher tau burden and lower CT in brain regions associated with early tau deposition and vulnerable to AD‐related neurodegeneration through mechanisms dissociable from amyloid deposition. Highlights: We report the results of an observational study, which leveraged ‐a well‐characterized cohort of healthy aging (Harvard Aging Brain Study) by adding in‐home full polysomnograms.By adding at‐home polysomnograms to this unique and deeply phenotyped cohort, we examined variations in sleep architecture that are associated with Alzheimer's disease (AD) pathologic changes.Our results confirmed the association of sleep changes with early tau and cortical neurodegenerative changes that were independent of amyloid.The results will be of importance in monitoring sleep‐related variations in relation to the natural history of AD pathology and in designing sleep‐focused clinical trials. [ABSTRACT FROM AUTHOR]

Overlap between language and visual variants of atypical Alzheimer's disease (AD) has been reported. However, the extent, frequency of overlap, and its neuroanatomical underpinnings remain unclear. Eighty-two biomarker-confirmed AD patients who presented with either predominant language (n = 34) or visuospatial/perceptual (n = 48) deficits underwent detailed clinical examinations, MRI, and [18F]flortaucipir-PET. Subgroups were defined based on language/visual testing and patterns of volume loss and tau uptake were assessed. 28% of the language group had visual dysfunction (marked in 8%), and 47% of the visual group had language impairment (marked in 26%). Progressive involvement of the parieto-occipital and frontal lobes was noted with greater visual impairment in the language group, and greater left parieto-temporal and frontal involvement with worsening language impairment in the visual group. Only 25% of our cohort showed a pure language or visual presentation, highlighting the high frequency of syndromic overlap in atypical AD and the diagnostic challenge of categorical phenotyping. [ABSTRACT FROM AUTHOR]

Abstract Background Tau pathology plays a crucial role in neurodegeneration diseases including Alzheimer’s disease (AD) and non-AD diseases such as progressive supranuclear palsy. Tau positron emission tomography (PET) is an in-vivo and non-invasive medical imaging technique for detecting and visualizing tau deposition within a human brain. In this work, we aim to investigate the biodistribution of the dosimetry in the whole body and various organs for the [18F]Florzolotau tau-PET tracer. A total of 12 healthy controls (HCs) were enrolled at Chang Gung Memorial Hospital. All subjects were injected with approximately 379.03 ± 7.03 MBq of [18F]Florzolotau intravenously, and a whole-body PET/CT scan was performed for each subject. For image processing, the VOI for each organ was delineated manually by using the PMOD 3.7 software. Then, the time-activity curve of each organ was acquired by optimally fitting an exponential uptake and clearance model using the least squares method implemented in OLINDA/EXM 2.1 software. The absorbed dose for each target organ and the effective dose were finally calculated. Results From the biodistribution results, the elimination of [18F]Florzolotau is observed mainly from the liver to the intestine and partially through the kidneys. The highest organ-absorbed dose occurred in the right colon wall (255.83 μSv/MBq), and then in the small intestine (218.67 μSv/MBq), gallbladder wall (151.42 μSv/MBq), left colon wall (93.31 μSv/MBq), and liver (84.15 μSv/MBq). Based on the ICRP103, the final computed effective dose was 34.9 μSv/MBq with CV of 10.07%. Conclusions The biodistribution study of [18F]Florzolotau demonstrated that the excretion of [18F]Florzolotau are mainly through the hepatobiliary and gastrointestinal pathways. Therefore, a routine injection of 370 MBq or 185 MBq of [18F]Florzolotau leads to an estimated effective dose of 12.92 or 6.46 mSv, and as a result, the radiation exposure to the whole-body and each organ remains within acceptable limits and adheres to established constraints. Trial registration Retrospectively Registered at Clinicaltrials.gov (NCT03625128) on 12 July, 2018, https://clinicaltrials.gov/study/NCT03625128 .

Purpose: [18F]MK-6240, a second-generation tau PET tracer, is increasingly used for the detection and the quantification of in vivo cerebral tauopathy in Alzheimer's disease (AD). Given that neurological symptoms are better explained by the topography rather than by the nature of brain lesions, our study aimed to evaluate whether cognitive impairment would be more closely associated with the spatial extent than with the intensity of tau-PET signal, as measured by the standard uptake value ratio (SUVr). Methods: [18F]MK6240 tau-PET data from 82 participants in the AD spectrum were quantified in three different brain regions (Braak ≤ 2, Braak ≤ 4, and Braak ≤ 6) using SUVr and the extent of tauopathy (EOT, percentage of voxels with SUVr ≥ 1.3). PET data were first compared between diagnostic categories, and ROC curves were computed to evaluate sensitivity and specificity. PET data were then correlated to cognitive performances and cerebrospinal fluid (CSF) tau values. Results: The EOT in the Braak ≤ 2 region provided the highest diagnostic accuracies, distinguishing between amyloid-negative and positive clinically unimpaired individuals (threshold = 9%, sensitivity = 79%, specificity = 82%) as well as between prodromal AD and preclinical AD (threshold = 38%, sensitivity = 81%, specificity = 93%). The EOT better correlated with cognition than SUVr (∆R2 + 0.08–0.09) with the best correlation observed for EOT in the Braak ≤ 4 region (R2 = 0.64). Cognitive performances were more closely associated with PET metrics than with CSF values. Conclusions: Quantifying [18F]MK-6240 tau PET in terms of EOT rather than SUVr significantly increases the correlation with cognitive performances. Quantification in the mesiotemporal lobe is the most useful to diagnose preclinical AD or prodromal AD. [ABSTRACT FROM AUTHOR]

Background: Tau pathology plays a crucial role in neurodegeneration diseases including Alzheimer's disease (AD) and non-AD diseases such as progressive supranuclear palsy. Tau positron emission tomography (PET) is an in-vivo and non-invasive medical imaging technique for detecting and visualizing tau deposition within a human brain. In this work, we aim to investigate the biodistribution of the dosimetry in the whole body and various organs for the [18F]Florzolotau tau-PET tracer. A total of 12 healthy controls (HCs) were enrolled at Chang Gung Memorial Hospital. All subjects were injected with approximately 379.03 ± 7.03 MBq of [18F]Florzolotau intravenously, and a whole-body PET/CT scan was performed for each subject. For image processing, the VOI for each organ was delineated manually by using the PMOD 3.7 software. Then, the time-activity curve of each organ was acquired by optimally fitting an exponential uptake and clearance model using the least squares method implemented in OLINDA/EXM 2.1 software. The absorbed dose for each target organ and the effective dose were finally calculated. Results: From the biodistribution results, the elimination of [18F]Florzolotau is observed mainly from the liver to the intestine and partially through the kidneys. The highest organ-absorbed dose occurred in the right colon wall (255.83 μSv/MBq), and then in the small intestine (218.67 μSv/MBq), gallbladder wall (151.42 μSv/MBq), left colon wall (93.31 μSv/MBq), and liver (84.15 μSv/MBq). Based on the ICRP103, the final computed effective dose was 34.9 μSv/MBq with CV of 10.07%. Conclusions: The biodistribution study of [18F]Florzolotau demonstrated that the excretion of [18F]Florzolotau are mainly through the hepatobiliary and gastrointestinal pathways. Therefore, a routine injection of 370 MBq or 185 MBq of [18F]Florzolotau leads to an estimated effective dose of 12.92 or 6.46 mSv, and as a result, the radiation exposure to the whole-body and each organ remains within acceptable limits and adheres to established constraints. Trial registration: Retrospectively Registered at Clinicaltrials.gov (NCT03625128) on 12 July, 2018, https://clinicaltrials.gov/study/NCT03625128. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a neuropathological disorder defined by the deposition of the proteins, tau and β-amyloid. Alzheimer's disease is commonly thought of as a disease of the elderly that is associated with episodic memory loss. However, the very first patient described with AD was in her 50's with impairments in multiple cognitive domains. It is now clear that AD can present with multiple different non-amnestic clinical variants which have been labeled as atypical variants of AD. Instead of these variants of AD being considered "atypical," I propose that they provide an excellent disease model of AD and reflect the true clinical heterogeneity of AD. The atypical variants of AD usually have a relatively young age at onset, and they show striking cortical tau deposition on molecular PET imaging which relates strongly with patterns of neurodegeneration and clinical outcomes. In contrast, elderly patients with AD show less tau deposition on PET, and neuroimaging and clinical outcomes are confounded by other age-related pathologies, including TDP-43 and vascular pathology. There is also considerable clinical and anatomical heterogeneity across atypical and young-onset amnestic variants of AD which reflects the fact that AD is a disease that causes impairments in multiple cognitive domains. Future studies should focus on careful characterization of cognitive impairment in AD and consider the full clinical spectrum of AD, including atypical AD, in the design of research studies investigating disease mechanisms in AD and clinical treatment trials, particularly with therapeutics targeting tau. [ABSTRACT FROM AUTHOR]

Given the prevalence of dementia and the development of pathology-specific disease-modifying therapies, high-value biomarker strategies to inform medical decision-making are critical. In vivo tau-PET is an ideal target as a biomarker for Alzheimer's disease diagnosis and treatment outcome measure. However, tau-PET is not currently widely accessible to patients compared to other neuroimaging methods. In this study, we present a convolutional neural network (CNN) model that imputes tau-PET images from more widely available cross-modality imaging inputs. Participants (n = 1192) with brain T1-weighted MRI (T1w), fluorodeoxyglucose (FDG)-PET, amyloid-PET and tau-PET were included. We found that a CNN model can impute tau-PET images with high accuracy, the highest being for the FDG-based model followed by amyloid-PET and T1w. In testing implications of artificial intelligence-imputed tau-PET, only the FDG-based model showed a significant improvement of performance in classifying tau positivity and diagnostic groups compared to the original input data, suggesting that application of the model could enhance the utility of the metabolic images. The interpretability experiment revealed that the FDG- and T1w-based models utilized the non-local input from physically remote regions of interest to estimate the tau-PET, but this was not the case for the Pittsburgh compound B-based model. This implies that the model can learn the distinct biological relationship between FDG-PET, T1w and tau-PET from the relationship between amyloid-PET and tau-PET. Our study suggests that extending neuroimaging's use with artificial intelligence to predict protein specific pathologies has great potential to inform emerging care models. [ABSTRACT FROM AUTHOR]

Abstract INTRODUCTION Sleep is crucial for memory consolidation and the clearance of toxic proteins associated with Alzheimer's disease (AD). We examined the association between sleep characteristics and imaging biomarkers of early amyloid beta (Aβ) and tau pathology as well as neurodegeneration in brain regions known to be affected in the incipient stages of AD. METHODS Thirty‐nine cognitively unimpaired (CU) participants of the Harvard Aging Brain Study underwent at‐home polysomnography as well as tau positron emission tomography (flortaucipir‐PET), amyloid PET (Pittsburgh compound B [PiB]‐PET), and magnetic resonance imaging–derived assessment of cortical thickness (CT). RESULTS Increased N1 sleep was associated with a higher tau PET signal (β = 0.009, p = 0.001) and lower CT in the temporal composite region of interest (β = –0.017, p = 0.007). Decreased slow‐wave sleep (SWS) was associated with higher tau burden in the temporal composite (β = –0.008, p = 0.005) and lower CT (β = 0.008, p = 0.002), even after controlling for global PiB‐PET. DISCUSSION In CU older adults, lower SWS and higher N1 sleep were associated with higher tau burden and lower CT in brain regions associated with early tau deposition and vulnerable to AD‐related neurodegeneration through mechanisms dissociable from amyloid deposition. Highlights We report the results of an observational study, which leveraged ‐a well‐characterized cohort of healthy aging (Harvard Aging Brain Study) by adding in‐home full polysomnograms. By adding at‐home polysomnograms to this unique and deeply phenotyped cohort, we examined variations in sleep architecture that are associated with Alzheimer's disease (AD) pathologic changes. Our results confirmed the association of sleep changes with early tau and cortical neurodegenerative changes that were independent of amyloid. The results will be of importance in monitoring sleep‐related variations in relation to the natural history of AD pathology and in designing sleep‐focused clinical trials.

Tauopathies, characterized by fibrillar tau accumulation in neurons and glial cells, constitute a major neuropathological category of neurodegenerative diseases. Neurofibrillary tau lesions are strongly associated with cognitive deficits in these diseases, but the causal mechanisms underlying tau‐induced neuronal dysfunction remain unresolved. Recent advances in cryo‐electron microscopy examination have revealed various core structures of tau filaments from different tauopathy patients, which can be used to classify tauopathies. In vivo visualization of tau pathology is now available using several tau positron emission tomography tracers. Among these radioprobes, PM‐PBB3 allows high‐contrast imaging of tau deposits in the brains of patients with diverse disorders and tauopathy mouse models. Selective degradation of pathological tau species by the ubiquitin‐proteasome system or autophagy machinery is a potential therapeutic strategy. Alternatively, the non‐cell‐autonomous clearance of pathological tau species through neuron–glia networks could be reinforced as a disease‐modifying treatment. In addition, the development of neuroinflammatory biomarkers is required for understanding the contribution of immunocompetent cells in the brain to preventing neurodegeneration. This review provides an overview of the current research and development of diagnostic and therapeutic agents targeting divergent tau pathologies.

The deposition of highly phosphorylated and aggregated tau is a characteristic of tauopathies, including Alzheimer's disease. It has long been known that different isoforms of tau are aggregated in different cell types and brain regions in each tauopathy. Recent advances in analytical techniques revealed the details of the biochemical and structural biological differences of tau specific to each tauopathy. In this review, we explain recent advances in the analysis of post‐translational modifications of tau, particularly phosphorylation, brought about by the development of mass‐spectrometry and Phos‐tag technology. We then discuss the structure of tau filaments in each tauopathy revealed by the advent of cryo‐EM. Finally, we describe the progress in biofluid and imaging biomarkers for tauopathy. This review summarizes current efforts to elucidate the characteristics of pathological tau and the landscape of the use of tau as a biomarker to diagnose and determine the pathological stage of tauopathy.

Abstract Background Corticobasal syndrome (CBS) is a neurodegenerative disease diagnosed based on clinical manifestations such as asymmetrical parkinsonism, limb apraxia, and speech and language impairment. The background pathology of CBS is commonly a variety of proteinopathies, but association with cerebrovascular disease has also been reported. Foix-Chavany-Marie syndrome (FCMS) is a rare neurological disorder characterized by facio-pharyngo-glossal diplegia with automatic-voluntary movement dissociation presenting with bilateral paresis of the facial, lingual, pharyngeal and masticatory muscles. FCMS is commonly attributable to stroke. Transactive response DNA binding protein of 43 kD (TDP-43) proteinopathy is also known as the pathological background of FCMS, while the pathological background of the majority of CBS cases consists of diverse tauopathies instead of TDP-43 proteinopathy. In this report, we describe a case mimicking FCMS that was finally diagnosed as CBS with suggested 4-repeat tauopathy. Case presentation A 68-year-old female started experiencing difficulty speaking followed by difficulty writing, and especially texting, several years before her visit. Her impairment had been gradually worsening, and she came to our hospital. On neurological examination, she demonstrated the facial apraxia, frontal lobe dysfunction, and upper motor neuron signs. She presented some characteristics suggestive of FCMS. Her symptoms exhibited rapid progression and myoclonus, parkinsonism, and left-side dominant cortical sensory deficit occurred, resulting in the fulfillment of diagnostic criteria for CBS after 9 months. Tau PET imaging displayed notable ligand uptake in the brainstem, subthalamic nuclei, basal ganglia, and bilateral subcortical frontal lobe, suggesting that her pathological background was 4-repeat tauopathy. As a result of her progressive dysphagia, she became unable to eat and passed away after 12 months. Conclusion We hereby present an atypical case of CBS showing clinical features mimicking FCMS at first presentation. TDP-43 proteinopathy was suspected based on the clinical symptoms in the early stages of the disease; however, the clinical course and imaging findings including tau PET suggested that her pathological background was 4-repeat tauopathy.

The majority of traumatic encephalopathy syndrome (TES) cases have been reported in former contact sport athletes. This is the first case with TES in a 19-year-old male patient with progressive cognitive decline after daily domestic physical violence through repeated hits to the head for 15 years. The patient presented with a moderate depressive episode and progressive cognitive decline. Tau positron emission tomography (PET) with 220?MBq of [18F]PI-2620 revealed increased focal signal at the frontal and parietal white/gray matter border. Brain magnetic resonance imaging (MRI) showed a cavum septum pellucidum, reduced left-sided hippocampal volume, and a left midbrain lesion. Cerebrospinal fluid results showed elevated total and p-tau. Neurocognitive testing at admission showed memory deficits clearly below average, and hampered dysfunctions according to the slow processing speed with a low mistake rate, indicating the acquired, thus secondary, attentional deficits. We diagnosed the patient with a TES suggestive of chronic traumatic encephalopathy and classified him as having subtle/mild functional limitation with a most likely transition to mild dementia within the TES criteria. This report underlines child abuse as a relevant criterion in diagnosing TES in cases with repetitive hits to the head. In addition to clinical markers, we show the relevance of fluid tau biomarkers and tau-PET to support the diagnosis of TES according to the recently published diagnosis criteria for TES.

BackgroundThe 2018 NIA-AA Alzheimer's Disease (AD) Research Framework states that subtle cognitive decline in cognitively unimpaired individuals can be measured by subjective reports or evidence of objective decline on neuropsychological measures. Both subjective memory complaint (SMC) and objective subtle cognitive decline (Obj-SCD) have been shown to be associated with future cognitive decline and AD biomarkers. We examined whether there are differences in tau PET levels between (a) SMC- vs. SMC+ participants, (b) Obj-SCD- vs. Obj-SCD+ participants, and (c) participants with overlapping vs. discrepant SMC and Obj-SCD classifications.MethodsCognitively unimpaired participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 236) were classified at baseline as positive or negative for SMC (SMC- n = 77; SMC+ n = 159) based on the first 12 items of the Cognitive Change Index and/or classified as positive or negative for Obj-SCD (Obj-SCD- n = 173; Obj-SCD+ n = 63) based on previously defined neuropsychological criteria. Analyses of covariance, adjusting for age, sex, APOE ε4 carrier status, and pulse pressure, examined the group differences in tau PET (AV-1451) using a composite standardized uptake variable ratio (SUVR) for regions consistent with Braak stage III/IV. The chi-squared tests examined the tau positivity rates across the groups.ResultsObj-SCD+ participants had higher tau continuous SUVR levels (p = .035, ηp2 = .019) and higher rates of tau positivity (15.8% Obj-SCD- vs. 30.2% Obj-SCD+) than Obj-SCD- participants. Neither tau levels (p = .381, ηp2 = .003) nor rates of tau positivity (18.2% SMC- and 20.1% SMC+) differed between the SMC groups. There was very little agreement between SMC and Obj-SCD classifications (42%; κ = 0.008, p = .862). Participants who were Obj-SCD+ without SMC had the highest tau PET levels and differed from participants who were SMC+ without Obj-SCD (p = .022). Tau levels in participants with both SMC and Obj-SCD did not differ from those with only Obj-SCD (p = .216). Tau positivity rates across the SMC-/Obj-SCD-, SMC+/Obj-SCD-, SMC-/Obj-SCD+, and SMC+/Obj-SCD+ groups were 10.5%, 18.1%, 40.0%, and 25.6%, respectively.ConclusionParticipants with Obj-SCD had a greater tau PET burden than those without Obj-SCD, but SMC was not associated with higher tau levels. The combination of SMC and Obj-SCD did not have higher tau levels than Obj-SCD alone. Findings add to the evidence that the Obj-SCD classification is associated with AD biomarkers and faster cognitive decline in ADNI participants, but further work is needed to validate this approach in more representative/diverse cohorts.

BackgroundStudies have demonstrated that both tau and cardiovascular risk are associated with cognitive decline, but the possible synergistic effects of these pathologic markers remain unclear.ObjectiveTo explore the interaction of AD biomarkers with a specific vascular risk marker (pulse pressure) on longitudinal cognition.MethodsParticipants included 139 older adults from the Alzheimer's Disease Neuroimaging Initiative (ADNI). Biomarkers of tau, amyloid-β (Aβ), and vascular risk (pulse pressure) were assessed. Neuropsychological assessment provided memory, language, and executive function domain composite scores at baseline and 1-year follow-up. Multiple linear regression examined interactive effects of pulse pressure with tau PET independent of Aβ PET and Aβ PET independent of tau PET on baseline and 1-year cognitive outcomes.ResultsThe interaction between pulse pressure and tau PET significantly predicted 1-year memory performance such that the combined effect of high pulse pressure and high tau PET levels was associated with lower memory at follow-up but not at baseline. In contrast, Aβ PET did not significantly interact with pulse pressure to predict baseline or 1-year outcomes in any cognitive domain. Main effects revealed a significant effect of tau PET on memory, and no significant effects of Aβ PET or pulse pressure on any cognitive domain.ConclusionResults indicate that tau and an indirect marker of arterial stiffening (pulse pressure) may synergistically contribute to memory decline, whereas Aβ may have a lesser role in predicting cognitive progression. Tau and vascular pathology (particularly in combination) may represent valuable targets for interventions intended to slow cognitive decline.

Background: [18F]flortaucipir (FTP) tau PET quantification is known to be affected by non-specific binding in off-target regions. Although partial volume correction (PVC) techniques partially account for this effect, their inclusion may also introduce noise and variability into the quantification process. While the impact of these effects has been studied in cross-sectional designs, the benefits and drawbacks of PVC on longitudinal FTP studies is still under scrutiny. The aim of this work was to study the performance of the most common PVC techniques for longitudinal FTP imaging. Methods: A cohort of 247 individuals from the Alzheimer's Disease Neuroimaging Initiative with concurrent baseline FTP-PET, amyloid-beta (Aβ) PET and structural MRI, as well as with follow-up FTP-PET and MRI were included in the study. FTP-PET scans were corrected for partial volume effects using Meltzer's, a simple and popular analytical PVC, and both the region-based voxel-wise (RBV) and the iterative Yang (iY) corrections. FTP SUVR values and their longitudinal rates of change were calculated for regions of interest (ROI) corresponding to Braak Areas I-VI, for a temporal meta-ROI and for regions typically displaying off-target FTP binding (caudate, putamen, pallidum, thalamus, choroid plexus, hemispheric white matter, cerebellar white matter, and cerebrospinal fluid). The longitudinal correlation between binding in off-target and target ROIs was analysed for the different PVCs. Additionally, group differences in longitudinal FTP SUVR rates of change between Aβ-negative (A-) and Aβ-positive (A+), and between cognitively unimpaired (CU) and cognitively impaired (CI) individuals, were studied. Finally, we compared the ability of different partial-volume-corrected baseline FTP SUVRs to predict longitudinal brain atrophy and cognitive decline. Results: Among off-target ROIs, hemispheric white matter showed the highest correlation with longitudinal FTP SUVR rates from cortical target ROIs (R2=0.28–0.82), with CSF coming in second (R2=0.28–0.42). Application of voxel-wise PVC techniques minimized this correlation, with RBV performing best (R2=0.00–0.07 for hemispheric white matter). PVC also increased group differences between CU and CI individuals in FTP SUVR rates of change across all target regions, with RBV again performing best (No PVC: Cohen's d = 0.26–0.66; RBV: Cohen's d = 0.43–0.74). These improvements were not observed for differentiating A- from A+ groups. Additionally, voxel-wise PVC techniques strengthened the correlation between baseline FTP SUVR and longitudinal grey matter atrophy and cognitive decline. Conclusion: Quantification of longitudinal FTP SUVR rates of change is affected by signal from off-target regions, especially the hemispheric white matter and the CSF. Voxel-wise PVC techniques significantly reduce this effect. PVC provided a significant but modest benefit for tasks involving the measurement of group-level longitudinal differences. These findings are particularly relevant for the estimations of sample sizes and analysis methodologies of longitudinal group studies.

PurposeWe evaluated the impact of partial volume correction (PVC) methods on the quantification of longitudinal [18F]GTP1 tau positron-emission tomography (PET) in Alzheimer's disease and the suitability of describing the tau pathology burden temporal trajectories using linear mixed-effects models (LMEM).MethodsWe applied van Cittert iterative deconvolution (VC), 2-compartment, and 3-compartment, and the geometric transfer matrix plus region-based voxelwise methods to data acquired in an Alzheimer's disease natural history study over 18 months at a single imaging site. We determined the optimal PVC method by comparing the standardized uptake value ratio change (%ΔSUVR) between diagnostic and tau burden–level groups and the longitudinal repeatability derived from the LMEM. The performance of LMEM analysis for calculating %ΔSUVR was evaluated in a natural history study and in a multisite clinical trial of semorinemab in prodromal to mild Alzheimer's disease by comparing results to traditional per-visit estimates.ResultsThe VC, 2-compartment, and 3-compartment PVC methods had similar performance, whereas region-based voxelwise overcorrected regions with a higher tau burden. The lowest within-subject variability and acceptable group separation scores were observed without PVC. The LMEM-derived %ΔSUVR values were similar to the per-visit estimates with lower variability.ConclusionThe results indicate that the tested PVC methods do not offer a clear advantage or improvement over non-PVC images for the quantification of longitudinal [18F]GTP1 PET data. LMEM offers a robust framework for the longitudinal tau PET quantification with low longitudinal test–retest variability.Clinical trial registrationNCT02640092 and NCT03289143.

It is poorly known how Aβ and tau accumulations associate at the spatiotemporal level in the in vivo human brain to impact cognitive changes in older adults prior to AD symptoms onset. In this study, we used a graph theory-based spatiotemporal analysis to characterize the cortical patterns of Aβ and tau deposits and their relationship with cognitive changes in the Harvard Aging Brain Study (HABS) cohort. We found that the temporal accumulations of interlinked Aβ and tau pathology display distinctive spatiotemporal correlations associated with early cognitive decline. Notably, we observed that baseline Aβ deposits—Thal amyloid phase II—related to future increase of tau deposits, Braak stages I–IV, both displaying linkage to the decline in multi-domain cognitive scores. We also found unimodal tau-to-tau and cognitive impairment associations in broad areas of Braak stages I–IV. The unimodal Aβ-to-Aβ progressions were not associated with cognitive changes. Our results revealed a multifaceted correlation of the spatiotemporal Aβ and tau associations with cognitive decline over time, in which tau-to-tau and tau–Aβ interactions, and not Aβ independently, might be critical contributors to clinical trajectories toward AD in older adults. [ABSTRACT FROM AUTHOR]

INTRODUCTION: The timing of plasma biomarker changes is not well understood. The goal of this study was to evaluate the temporal co‐evolution of plasma and positron emission tomography (PET) Alzheimer's disease (AD) biomarkers. METHODS: We included 1408 Mayo Clinic Study of Aging and Alzheimer's Disease Research Center participants. An accelerated failure time (AFT) model was fit with amyloid beta (Aβ) PET, tau PET, plasma p‐tau217, p‐tau181, and glial fibrillary acidic protein (GFAP) as endpoints. RESULTS: Individual timing of plasma p‐tau progression was strongly associated with Aβ PET and GFAP progression. In the population, GFAP became abnormal first, then Aβ PET, plasma p‐tau, and tau PET temporal meta‐regions of interest when applying cut points based on young, cognitively unimpaired participants. DISCUSSION: Plasma p‐tau is a stronger indicator of a temporally linked response to elevated brain Aβ than of tau pathology. While Aβ deposition and a rise in GFAP are upstream events associated with tau phosphorylation, the temporal link between p‐tau and Aβ PET was the strongest. Highlights: Plasma p‐tau progression was more strongly associated with Aβ than tau PET.Progression on plasma p‐tau was associated with Aβ PET and GFAP progression.P‐tau181 and p‐tau217 become abnormal after Aβ PET and before tau PET.GFAP became abnormal first, before plasma p‐tau and Aβ PET. [ABSTRACT FROM AUTHOR]

The deposition of highly phosphorylated and aggregated tau is a characteristic of tauopathies, including Alzheimer's disease. It has long been known that different isoforms of tau are aggregated in different cell types and brain regions in each tauopathy. Recent advances in analytical techniques revealed the details of the biochemical and structural biological differences of tau specific to each tauopathy. In this review, we explain recent advances in the analysis of post‐translational modifications of tau, particularly phosphorylation, brought about by the development of mass‐spectrometry and Phos‐tag technology. We then discuss the structure of tau filaments in each tauopathy revealed by the advent of cryo‐EM. Finally, we describe the progress in biofluid and imaging biomarkers for tauopathy. This review summarizes current efforts to elucidate the characteristics of pathological tau and the landscape of the use of tau as a biomarker to diagnose and determine the pathological stage of tauopathy. [ABSTRACT FROM AUTHOR]

Tauopathies, characterized by fibrillar tau accumulation in neurons and glial cells, constitute a major neuropathological category of neurodegenerative diseases. Neurofibrillary tau lesions are strongly associated with cognitive deficits in these diseases, but the causal mechanisms underlying tau‐induced neuronal dysfunction remain unresolved. Recent advances in cryo‐electron microscopy examination have revealed various core structures of tau filaments from different tauopathy patients, which can be used to classify tauopathies. In vivo visualization of tau pathology is now available using several tau positron emission tomography tracers. Among these radioprobes, PM‐PBB3 allows high‐contrast imaging of tau deposits in the brains of patients with diverse disorders and tauopathy mouse models. Selective degradation of pathological tau species by the ubiquitin‐proteasome system or autophagy machinery is a potential therapeutic strategy. Alternatively, the non‐cell‐autonomous clearance of pathological tau species through neuron–glia networks could be reinforced as a disease‐modifying treatment. In addition, the development of neuroinflammatory biomarkers is required for understanding the contribution of immunocompetent cells in the brain to preventing neurodegeneration. This review provides an overview of the current research and development of diagnostic and therapeutic agents targeting divergent tau pathologies. [ABSTRACT FROM AUTHOR]

Previous work has associated polymorphisms in the dopamine transporter gene (rs6347 in DAT1 / SLC6A3) and brain derived neurotrophic factor gene (Val66Met in BDNF) with atrophy and memory decline. However, it is unclear whether these polymorphisms relate to atrophy and cognition through associations with Alzheimer's disease pathology. We tested for effects of DAT1 and BDNF polymorphisms on cross-sectional and longitudinal β-amyloid (Aβ) and tau pathology (measured with positron emission tomography (PET)), hippocampal volume, and cognition. We analyzed a sample of cognitively normal older adults (cross-sectional n = 321) from the Alzheimer's Disease Neuroimaging Initiative (ADNI). DAT1 and BDNF interacted to predict Aβ-PET, tau-PET, and hippocampal atrophy. Carriers of both "non-boptimal" DAT1 C and BDNF Met alleles demonstrated greater pathology and atrophy. Our findings provide novel links between dopamine and neurotrophic factor genes and AD pathology, consistent with previous research implicating these variants in greater risk for developing AD. • DAT1 and BDNF polymorphisms relate to Aβ and tau pathology in healthy older adults. • Carriers of both DAT1 CC and BDNF Met exhibit higher Aβ and tau. • DAT1 CC and BDNF Met are also linked with greater hippocampal atrophy. [ABSTRACT FROM AUTHOR]

INTRODUCTION: We investigated how the associations between tau and cognitive measures differ by sex in the preclinical Alzheimer's disease (AD) stage. METHODS: A total of 343 cognitively unimpaired, amyloid‐positive individuals (205 women, 138 men) who self‐identified as non‐Hispanic White from the Anti‐Amyloid Treatment in Asymptomatic Alzheimer's (A4) Study were included. We assessed sex‐stratified associations between 18F‐flortaucipir positron emission tomography (PET) standardized uptake value ratio (SUVR) in the meta‐temporal region and Preclinical Alzheimer's Cognitive Composite (PACC) and Computerized Cognitive Composite (C3) components. RESULTS: We observed that higher tau level was significantly associated with worse cognitive performance only in women: PACC and its components except for Mini‐Mental State Examination (MMSE) and C3 components: First Letter Name Recall (FNLT) and One‐Card Learning Reaction Time (OCL RT). These associations except for FNLT were apolipoprotein E (APOE) ε4 independent. DISCUSSION: Women show stronger associations between tau PET and cognitive outcomes in preclinical AD. These findings have important implications for sex‐specific tau‐targeted preventive AD clinical trials. Highlights: The tau positron emission tomography (PET) signal in the meta‐temporal region was associated with poor cognitive performance in preclinical Alzheimer's disease (AD).After sex stratification, the associations between regional tau PET and cognitive outcomes were observed only in women.The associations between tau PET and some cognitive outcomes were independent of apolipoprotein E (APOE) ε4. [ABSTRACT FROM AUTHOR]

Carriers of mutations responsible for dominantly inherited Alzheimer disease provide a unique opportunity to study potential imaging biomarkers. Biomarkers based on routinely acquired clinical MR images, could supplement the extant invasive or logistically challenging) biomarker studies. We used 1104 longitudinal MR, 324 amyloid beta, and 87 tau positron emission tomography imaging sessions from 525 participants enrolled in the Dominantly Inherited Alzheimer Network Observational Study to extract novel imaging metrics representing the mean (μ) and standard deviation (σ) of standardized image intensities of T1‐weighted and Fluid attenuated inversion recovery (FLAIR) MR scans. There was an exponential decrease in FLAIR‐μ in mutation carriers and an increase in FLAIR and T1 signal heterogeneity (T1‐σ and FLAIR‐σ) as participants approached the symptom onset in both supramarginal, the right postcentral and right superior temporal gyri as well as both caudate nuclei, putamina, thalami, and amygdalae. After controlling for the effect of regional atrophy, FLAIR‐μ decreased and T1‐σ and FLAIR‐σ increased with increasing amyloid beta and tau deposition in numerous cortical regions. In symptomatic mutation carriers and independent of the effect of regional atrophy, tau pathology demonstrated a stronger relationship with image intensity metrics, compared with amyloid pathology. We propose novel MR imaging intensity‐based metrics using standard clinical T1 and FLAIR images which strongly associates with the progression of pathology in dominantly inherited Alzheimer disease. We suggest that tau pathology may be a key driver of the observed changes in this cohort of patients. [ABSTRACT FROM AUTHOR]

Background: Corticobasal syndrome (CBS) is a neurodegenerative disease diagnosed based on clinical manifestations such as asymmetrical parkinsonism, limb apraxia, and speech and language impairment. The background pathology of CBS is commonly a variety of proteinopathies, but association with cerebrovascular disease has also been reported. Foix-Chavany-Marie syndrome (FCMS) is a rare neurological disorder characterized by facio-pharyngo-glossal diplegia with automatic-voluntary movement dissociation presenting with bilateral paresis of the facial, lingual, pharyngeal and masticatory muscles. FCMS is commonly attributable to stroke. Transactive response DNA binding protein of 43 kD (TDP-43) proteinopathy is also known as the pathological background of FCMS, while the pathological background of the majority of CBS cases consists of diverse tauopathies instead of TDP-43 proteinopathy. In this report, we describe a case mimicking FCMS that was finally diagnosed as CBS with suggested 4-repeat tauopathy. Case presentation: A 68-year-old female started experiencing difficulty speaking followed by difficulty writing, and especially texting, several years before her visit. Her impairment had been gradually worsening, and she came to our hospital. On neurological examination, she demonstrated the facial apraxia, frontal lobe dysfunction, and upper motor neuron signs. She presented some characteristics suggestive of FCMS. Her symptoms exhibited rapid progression and myoclonus, parkinsonism, and left-side dominant cortical sensory deficit occurred, resulting in the fulfillment of diagnostic criteria for CBS after 9 months. Tau PET imaging displayed notable ligand uptake in the brainstem, subthalamic nuclei, basal ganglia, and bilateral subcortical frontal lobe, suggesting that her pathological background was 4-repeat tauopathy. As a result of her progressive dysphagia, she became unable to eat and passed away after 12 months. Conclusion: We hereby present an atypical case of CBS showing clinical features mimicking FCMS at first presentation. TDP-43 proteinopathy was suspected based on the clinical symptoms in the early stages of the disease; however, the clinical course and imaging findings including tau PET suggested that her pathological background was 4-repeat tauopathy. [ABSTRACT FROM AUTHOR]

Tau PET has allowed for critical insights into in vivo patterns of tau accumulation and change in individuals early in the Alzheimer's disease (AD) continuum. A key methodological step in tau PET analyses is the selection of a reference region, but there is not yet consensus on the optimal region especially for longitudinal tau PET analyses. This study examines how reference region selection influences results related to disease stage at baseline and over time. Longitudinal flortaucipir ([18F]-AV1451) PET scans were examined using several common reference regions (e.g., eroded subcortical white matter, inferior cerebellar gray matter) in 62 clinically unimpaired amyloid negative (CU A-) individuals, 73 CU amyloid positive (CU A+) individuals, and 64 amyloid positive individuals with mild cognitive impairment (MCI A+) from the Alzheimer's Disease Neuroimaging Initiative (ADNI). Cross-sectionally, both reference regions resulted in robust group differences between CU A-, CU A+, and MCI A+ groups, along with significant associations with CSF phosphorylated tau (pTau-181). However, these results were more focally specific and akin to Braak Staging when using eroded white matter, whereas effects with inferior cerebellum were globally distributed across most cortical regions. Longitudinally, utilization of eroded white matter revealed significant accumulation greater than zero across more regions whereas change over time was diminished using inferior cerebellum. Interestingly, the inferior temporal target region seemed most robust to reference region selection with expected cross-sectional and longitudinal signal across both reference regions. With few exceptions, baseline tau did not significantly predict longitudinal change in tau in the same region regardless of reference region. In summary, reference region selection deserves further evaluation as this methodological step may lead to disparate findings. Inferior cerebellar gray matter may be more sensitive to cross-sectional flortaucipir differences, whereas eroded subcortical white matter may be more sensitive for longitudinal analyses examining regional patterns of change.

PurposeIn vivo measurement of the spatial distribution of neurofibrillary tangle pathology is critical for early diagnosis and disease monitoring of Alzheimer's disease (AD).MethodsForty-nine participants were scanned with 18F-PI-2620 PET to examine the distribution of this novel PET ligand throughout the course of AD: 36 older healthy controls (HC) (age range 61 to 86), 11 beta-amyloid+ (Aβ+) participants with cognitive impairment (CI; clinical diagnosis of either mild cognitive impairment or AD dementia, age range 57 to 86), and 2 participants with semantic variant primary progressive aphasia (svPPA, age 66 and 78). Group differences in brain regions relevant in AD (medial temporal lobe, posterior cingulate cortex, and lateral parietal cortex) were examined using standardized uptake value ratios (SUVRs) normalized to the inferior gray matter of the cerebellum.ResultsSUVRs in target regions were relatively stable 60 to 90 min post-injection, with the exception of very high binders who continued to show increases over time. Robust elevations in 18F-PI-2620 were observed between HC and Aβ+ CI across all AD regions. Within the HC group, older age was associated with subtle elevations in target regions. Mildly elevated focal uptake was observed in the anterior temporal pole in one svPPA patient.ConclusionPreliminary results suggest strong differences in the medial temporal lobe and cortical regions known to be impacted in AD using 18F-PI-2620 in patients along the AD trajectory. This work confirms that 18F-PI-2620 holds promise as a tool to visualize tau aggregations in AD.

Abstract Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are distinct clinicopathological subtypes of frontotemporal lobar degeneration. They both have atypical parkinsonism, and they usually have distinct clinical features. The most common clinical presentation of PSP is Richardson syndrome, and the most common presentation of CBD is corticobasal syndrome. In this report, we describe a patient with a five-year history of Richardson syndrome and a family history of PSP in her mother and sister. A tau PET scan (18F-APN-1607) revealed low-to-moderate uptake in the substantia nigra, globus pallidus, thalamus and posterior cortical areas, including temporal, parietal and occipital cortices. Neuropathological evaluation revealed widespread neuronal and glial tau pathology in cortical and subcortical structures, including tufted astrocytes in the motor cortex, striatum and midbrain tegmentum. The subthalamic nucleus had mild-to-moderate neuronal loss with globose neurofibrillary tangles, consistent with PSP. On the other hand, there were also astrocytic plaques, a pathological hallmark of CBD, in the neocortex and striatum. To further characterize the mixed pathology, we applied two machine learning-based diagnostic pipelines. These models suggested diagnoses of PSP and CBD depending on the brain region – PSP in the motor cortex and superior frontal gyrus and CBD in caudate nucleus. Western blots of insoluble tau from motor cortex showed a banding pattern consistent with mixed features of PSP and CBD, whereas tau from the superior frontal gyrus showed a pattern consistent with CBD. Real-time quaking-induced conversion (RT-QuIC) using brain homogenates from the motor cortex and superior frontal gyrus showed ThT maxima consistent with PSP, while reaction kinetics were consistent with CBD. There were no pathogenic variants in MAPT with whole genome sequencing. We conclude that this patient had an unclassified tauopathy and features of both PSP and CBD. The different pathologies in specific brain regions suggests caution in diagnosis of tauopathies with limited sampling.

Purpose: The pattern of flortaucipir tau PET uptake is topographically similar to the pattern of magnetic susceptibility in progressive supranuclear palsy (PSP); both with increased signal in subcortical structures such as the basal ganglia and midbrain, suggesting that they may be closely related. However, their relationship remains unknown since no studies have directly compared these two modalities in the same PSP cohort. We hypothesized that some flortaucipir uptake in PSP is associated with magnetic susceptibility, and hence iron deposition. The aim of this study was to evaluate the regional relationship between flortaucipir uptake and magnetic susceptibility and to examine the effects of susceptibility on flortaucipir uptake in PSP. Methods: Fifty PSP patients and 67 cognitively normal controls were prospectively recruited and underwent three Tesla MRI and flortaucipir tau PET scans. Quantitative susceptibility maps were reconstructed from multi-echo gradient-echo MRI images. Region of interest (ROI) analysis was performed to obtain flortaucipir and susceptibility values in the subcortical regions. Relationships between flortaucipir and susceptibility signals were evaluated using partial correlation analysis in the subcortical ROIs and voxel-based analysis in the whole brain. The effects of susceptibility on flortaucipir uptake were examined by using the framework of mediation analysis. Results: Both flortaucipir and susceptibility were greater in PSP compared to controls in the putamen, pallidum, subthalamic nucleus, red nucleus, and cerebellar dentate (p

BackgroundA Phase II proof of concept (POC) randomized clinical trial was conducted to evaluate the effects of rasagiline, a monoamine oxidase B (MAO-B) inhibitor approved for Parkinson disease, in mild to moderate Alzheimer's disease (AD). The primary objective was to determine if 1 mg of rasagiline daily for 24 weeks is associated with improved regional brain metabolism (fluorodeoxyglucose-positron emission tomography [FDG-PET]) compared to placebo. Secondary objectives included measurement of effects on tau PET and evaluation of directional consistency of clinical end points.MethodsThis was a double-blind, parallel group, placebo-controlled, community-based, three-site trial of 50 participants randomized 1:1 to receive oral rasagiline or placebo (NCT02359552). FDG-PET was analyzed for the presence of an AD-like pattern as an inclusion criterion and as a longitudinal outcome using prespecified regions of interest and voxel-based analyses. Tau PET was evaluated at baseline and longitudinally. Clinical outcomes were analyzed using an intention-to-treat (ITT) model.ResultsFifty patients were randomized and 43 completed treatment. The study met its primary end point, demonstrating favorable change in FDG-PET differences in rasagiline versus placebo in middle frontal (P

A clinical diagnosis of Alzheimer's disease dementia (ADD) encompasses considerable pathological and clinical heterogeneity. While Alzheimer's disease patients typically show a characteristic temporo-parietal pattern of glucose hypometabolism on 18F-fluorodeoxyglucose (FDG)-PET imaging, previous studies have identified a subset of patients showing a distinct posterior-occipital hypometabolism pattern associated with Lewy body pathology. Here, we aimed to improve the understanding of the clinical relevance of these posterior-occipital FDG-PET patterns in patients with Alzheimer's disease-like amnestic presentations. Our study included 1214 patients with clinical diagnoses of ADD (n = 305) or amnestic mild cognitive impairment (aMCI, n = 909) from the Alzheimer's Disease Neuroimaging Initiative, who had FDG-PET scans available. Individual FDG-PET scans were classified as being suggestive of Alzheimer's (AD-like) or Lewy body (LB-like) pathology by using a logistic regression classifier trained on a separate set of patients with autopsy-confirmed Alzheimer's disease or Lewy body pathology. AD- and LB-like subgroups were compared on amyloid-β and tau-PET, domain-specific cognitive profiles (memory versus executive function performance), as well as the presence of hallucinations and their evolution over follow-up (≈6 years for aMCI, ≈3 years for ADD). Around 12% of the aMCI and ADD patients were classified as LB-like. For both aMCI and ADD patients, the LB-like group showed significantly lower regional tau-PET burden than the AD-like subgroup, but amyloid-β load was only significantly lower in the aMCI LB-like subgroup. LB- and AD-like subgroups did not significantly differ in global cognition (aMCI: d = 0.15, P = 0.16; ADD: d = 0.02, P = 0.90), but LB-like patients exhibited a more dysexecutive cognitive profile relative to the memory deficit (aMCI: d = 0.35, P = 0.01; ADD: d = 0.85 P < 0.001), and had a significantly higher risk of developing hallucinations over follow-up [aMCI: hazard ratio = 1.8, 95% confidence interval = (1.29, 3.04), P = 0.02; ADD: hazard ratio = 2.2, 95% confidence interval = (1.53, 4.06) P = 0.01]. In summary, a sizeable group of clinically diagnosed ADD and aMCI patients exhibit posterior-occipital FDG-PET patterns typically associated with Lewy body pathology, and these also show less abnormal Alzheimer's disease biomarkers as well as specific clinical features typically associated with dementia with Lewy bodies. [ABSTRACT FROM AUTHOR]

Identification of biomarkers for the early stages of Alzheimer's disease (AD) is an imperative step in developing effective treatments. Cerebral blood flow (CBF) is a potential early biomarker for AD; generally, older adults with AD have decreased CBF compared to normally aging peers. CBF deviates as the disease process and symptoms progress. However, further characterization of the relationships between CBF and AD risk factors and pathologies is still needed. We assessed the relationships between CBF quantified by arterial spin-labeled magnetic resonance imaging, hypertension, APOE ε 4, and tau and amyloid positron emission tomography in 77 older adults: cognitively normal, subjective cognitive decline, and mild cognitive impairment. Tau and amyloid aggregation were related to altered CBF, and some of these relationships were dependent on hypertension or APOE ε 4 status. Our findings suggest a complex relationship between risk factors, AD pathologies, and CBF that warrants future studies of CBF as a potential early biomarker for AD. [ABSTRACT FROM AUTHOR]

Purpose: Several [18F]Flortaucipir cutoffs have been proposed for tau PET positivity (T+) in Alzheimer's disease (AD), but none were data-driven. The aim of this study was to establish and validate unsupervised T+ cutoffs by applying Gaussian mixture models (GMM). Methods: Amyloid negative (A−) cognitively normal (CN) and amyloid positive (A+) AD-related dementia (ADRD) subjects from ADNI (n=269) were included. ADNI (n=475) and Geneva Memory Clinic (GMC) cohorts (n=98) were used for validation. GMM-based cutoffs were extracted for the temporal meta-ROI, and validated against previously published cutoffs and visual rating. Results: GMM-based cutoffs classified less subjects as T+, mainly in the A− CN (<3.4% vs >28.5%) and A+ CN (<14.5% vs >42.9%) groups and showed higher agreement with visual rating (ICC=0.91 vs ICC<0.62) than published cutoffs. Conclusion: We provided reliable data-driven [18F]Flortaucipir cutoffs for in vivo T+ detection in AD. These cutoffs might be useful to select participants in clinical and research studies. [ABSTRACT FROM AUTHOR]

Abstract Background Insulin resistance (IR) and type 2 diabetes have been found to increase the risk for Alzheimer’s clinical syndrome in epidemiologic studies but have not been associated with tau tangles in neuropathological research and have been inconsistently associated with cerebrospinal fluid P-tau181. IR and type 2 diabetes are well-recognized vascular risk factors. Some studies suggest that cardiovascular risk may act synergistically with cortical amyloid to increase tau measured using tau PET. Utilizing data from largely nondemented middle-aged and older adult cohorts enriched for AD risk, we investigated the association of IR and diabetes to tau PET and whether amyloid moderated those relationships. Methods Participants were enrolled in either the Wisconsin Registry for Alzheimer’s Prevention (WRAP) or Wisconsin Alzheimer’s Disease Research Center (WI-ADRC) Clinical Core. Two partially overlapping samples were studied: a sample characterized using HOMA-IR (n=280 WRAP participants) and a sample characterized on diabetic status (n=285 WRAP and n=109 WI-ADRC). IR was measured using the homeostasis model assessment of insulin resistance (HOMA-IR). Tau PET employing the radioligand 18F-MK-6240 was used to detect AD-specific aggregated tau. Linear regression tested the relationship of IR and diabetic status to tau PET standardized uptake value ratio (SUVR) within the entorhinal cortex and whether relationships were moderated by amyloid assessed by amyloid PET distribution volume ratio (DVR) and amyloid PET positivity status. Results Neither HOMA-IR nor diabetic status was significantly associated with tau PET SUVR. The relationship between IR and tau PET SUVR was not moderated by amyloid PET DVR or positivity status. The association between diabetic status and tau PET SUVR was not significantly moderated by amyloid PET DVR but was significantly moderated by amyloid PET positivity status. Among the amyloid PET-positive participants, the estimated marginal tau PET SUVR mean was higher in the diabetic (n=6) relative to the nondiabetic group (n=88). Conclusion Findings indicate that IR may not be related to tau in generally healthy middle-aged and older adults who are in the early stages of the AD clinicopathologic continuum but suggest the need for additional research to investigate whether a synergistic relationship between type 2 diabetes and amyloid is associated with increased tau levels.

Purpose: Tau pathology is associated with concurrent atrophy and decreased cerebral blood flow (CBF) in Alzheimer's disease (AD), but less is known about their temporal relationships. Our aim was therefore to investigate the association of concurrent and longitudinal tau PET with longitudinal changes in atrophy and relative CBF. Methods: We included 61 individuals from the Amsterdam Dementia Cohort (mean age 65.1 ± 7.5 years, 44% female, 57% amyloid-β positive [Aβ +], 26 cognitively impaired [CI]) who underwent dynamic [18F]flortaucipir PET and structural MRI at baseline and 25 ± 5 months follow-up. In addition, we included 86 individuals (68 CI) who only underwent baseline dynamic [18F]flortaucipir PET and MRI scans to increase power in our statistical models. We obtained [18F]flortaucipir PET binding potential (BPND) and R1 values reflecting tau load and relative CBF, respectively, and computed cortical thickness from the structural MRI scans using FreeSurfer. We assessed the regional associations between i) baseline and ii) annual change in tau PET BPND in Braak I, III/IV, and V/VI regions and cortical thickness or R1 in cortical gray matter regions (spanning the whole brain) over time using linear mixed models with random intercepts adjusted for age, sex, time between baseline and follow-up assessments, and baseline BPND in case of analyses with annual change as determinant. All analyses were performed in Aβ− cognitively normal (CN) individuals and Aβ+ (CN and CI) individuals separately. Results: In Aβ+ individuals, greater baseline Braak III/IV and V/VI tau PET binding was associated with faster cortical thinning in primarily frontotemporal regions. Annual changes in tau PET were not associated with cortical thinning over time in either Aβ+ or Aβ− individuals. Baseline tau PET was not associated with longitudinal changes in relative CBF, but increases in Braak III/IV tau PET over time were associated with increases in parietal relative CBF over time in Aβ + individuals. Conclusion: We showed that higher tau load was related to accelerated cortical thinning, but not to decreases in relative CBF. Moreover, tau PET load at baseline was a stronger predictor of cortical thinning than change of tau PET signal. [ABSTRACT FROM AUTHOR]

Quantitative susceptibility mapping (QSM) has been used to study susceptibility changes that may occur based on tissue composition and mineral deposition. Iron is a primary contributor to changes in magnetic susceptibility and of particular interest in applications of QSM to neurodegeneration and aging. Iron can contribute to neurodegeneration through inflammatory processes and via interaction with aggregation of disease-related proteins. To better understand the local susceptibility changes observed on QSM, its signal has been studied in association with other imaging metrics such as positron emission tomography (PET). The associations of QSM and PET may provide insight into the pathophysiology of disease processes, such as the role of iron in aging and neurodegeneration, and help to determine the diagnostic utility of QSM as an indirect indicator of disease processes typically evaluated with PET. In this review we discuss the proposed mechanisms and summarize prior studies of the associations of QSM and amyloid PET, tau PET, TSPO PET, FDG-PET, 15O-PET, and F-DOPA PET in evaluation of neurologic diseases with a focus on aging and neurodegeneration.