Cognitive trajectory in mild cognitive impairment due to primary age-related tauopathy

Temporo-frontoparietal hypoconnectivity as a biomarker for isolated language impairment in mild cognitive impairment: A cross-cohort comparison

INTRODUCTION

Whether brain functional connectivity (FC) is consistently disrupted in individuals with mild cognitive impairment (MCI) with isolated language impairment (ilMCI), and its potential to differentiate between MCI subtypes remains uncertain.

METHODS

Cross-sectional data from 404 participants in two cohorts (the Chinese Preclinical Alzheimer's Disease Study and the Alzheimer's Disease Neuroimaging Initiative) were analyzed, including neuropsychological tests, resting-state functional magnetic resonance imaging (fMRI), cerebral amyloid positivity, and apolipoprotein E (APOE) status.

RESULTS

Temporo-frontoparietal FC, particularly between the bilateral superior temporal pole and the left inferior frontal/supramarginal gyri, was consistently decreased in ilMCI compared to amnestic MCI (aMCI) and normal controls, which was correlated with semantic impairment. Using mean temporo-frontoparietal FC as a classifier could improve accuracy in identifying ilMCI subgroups with positive cerebral amyloid deposition and APOE risk alleles.

DISCUSSION

Temporal-frontoparietal hypoconnectivity was observed in individuals with ilMCI, which may reflect semantic impairment and serve as a valuable biomarker to indicate potential mechanisms of underlying neuropathology.

HIGHLIGHTS

Temporo-frontoparietal hypoconnectivity was observed in impaired language mild cognitive impairment (ilMCI). Temporo-frontoparietal hypoconnectivity may reflect semantic impairment. Temporo-frontoparietal functional connectivity can classify ilMCI subtypes.

Prevalence and clinicopathological features of primary age-related tauopathy (PART): A large forensic autopsy study

INTRODUCTION

Primary age-related tauopathy (PART), often regarded as a minimally symptomatic pathology of old age, lacks comprehensive cohorts across various age groups.

METHODS

We examined PART prevalence and clinicopathologic features in 1589 forensic autopsy cases (≥40 years old, mean age ± SD 70.2 ± 14.2 years).

RESULTS

PART cases meeting criteria for argyrophilic grain diseases (AGD) were AGD+PART (n = 181). The remaining PART cases (n = 719, 45.2%) were classified as comorbid conditions (PART-C, n = 90) or no comorbid conditions (pure PART, n = 629). Compared to controls (n = 208), Alzheimer's disease (n = 133), and AGD+PART, PART prevalence peaked in the individuals in their 60s (65.5%) and declined in the 80s (21.5%). No significant clinical background differences were found (excluding controls). However, PART-C in patients inclusive of age 80 had a higher suicide rate than pure PART (p < 0.05), and AGD+PART showed more dementia (p < 0.01) and suicide (p < 0.05) than pure PART.

DISCUSSION

Our results advocate a reevaluation of the PART concept and its diagnostic criteria.

HIGHLIGHTS

We investigated 1589 forensic autopsy cases to investigate the features of primary age-related tauopathy (PART). PART peaked in people in their 60s in our study. Many PART cases over 80s had comorbid pathologies in addition to neurofibrillary tangles pathology. Argyrophilic grain disease and Lewy pathology significantly affected dementia and suicide rates in PART. Our results suggest that the diagnostic criteria of PART need to be reconsidered.

Distinct biological property of tau in tau-first cognitive proteinopathy: Evidence by longitudinal clinical neuroimaging profiles and compared with late-onset Alzheimer disease

BACKGROUND

Tau-first cognitive proteinopathy (TCP) denotes a clinical phenotype of Alzheimer disease (AD) showing Florzolotau(18F) positron emission tomography (PET) positivity but a negative amyloid status.

AIM

We explored the biological property of tau using longitudinal cognitive and neuroimaging data in TCP and compared with late-onset AD (LOAD).

METHOD

We enrolled 56 patients with LOAD, 34 patients with TCP, and 26 cognitive unimpaired controls. All of the participants had historical data of 2 to 4 three-dimensional T1 images and 2 to 6 annual cognitive evaluations over a follow-up period of 7 years. Tau topography was measured using Florzolotau(18F) PET. In the LOAD and TCP groups, we constructed tau or gray matter clusters covarying with the cognitive measurements. We used mediator analysis to explore the regional tau load as predictor, gray matter partitions as mediators, and significant cognitive test scores as outcomes. Longitudinal cognitive decline and cortical thickness degeneration pattern were analyzed using a linear mixed-effects model.

RESULTS

The TCP group had longitudinal declines in nonexecutive domains. The deterministic factor predicting the short-term memory score in TCP was the hippocampal volume and not directly via the medial and lateral temporal tau load. These features formed the conceptual differences with LOAD.

DISCUSSION

The biological properties of tau and the longitudinal cognitive-imaging trajectory support the conceptual distinction between TCP and LOAD. TCP represents one specific entity featuring salient short-term memory impairment, declines in nonexecutive domains, a slower gray matter degenerative pattern, and a restricted impact of tau.

Clinical Significance of the Plasma Biomarker Panels in Amyloid-Negative and Tau PET-Positive Amnestic Patients: Comparisons with Alzheimer's Disease and Unimpaired Cognitive Controls

The purpose of this study was to investigate whether plasma biomarkers can help to diagnose, differentiate from Alzheimer disease (AD), and stage cognitive performance in patients with positron emission tomography (PET)-confirmed primary age-related tauopathy, termed tau-first cognitive proteinopathy (TCP) in this study. In this multi-center study, we enrolled 285 subjects with young-onset AD (YOAD; n = 55), late-onset AD (LOAD; n = 96), TCP (n = 44), and cognitively unimpaired controls (CTL; n = 90) and analyzed plasma Aβ42/Aβ40, pTau181, neurofilament light (NFL), and total-tau using single-molecule assays. Amyloid and tau centiloids reflected pathological burden, and hippocampal volume reflected structural integrity. Receiver operating characteristic curves and areas under the curves (AUCs) were used to determine the diagnostic accuracy of plasma biomarkers compared to hippocampal volume and amyloid and tau centiloids. The Mini-Mental State Examination score (MMSE) served as the major cognitive outcome. Logistic stepwise regression was used to assess the overall diagnostic accuracy, combining fluid and structural biomarkers and a stepwise linear regression model for the significant variables for MMSE. For TCP, tau centiloid reached the highest AUC for diagnosis (0.79), while pTau181 could differentiate TCP from YOAD (accuracy 0.775) and LOAD (accuracy 0.806). NFL reflected the clinical dementia rating in TCP, while pTau181 (rho = 0.3487, p = 0.03) and Aβ42/Aβ40 (rho = -0.36, p = 0.02) were significantly correlated with tau centiloid. Hippocampal volume (unstandardized β = 4.99, p = 0.01) outperformed all of the fluid biomarkers in predicting MMSE scores in the TCP group. Our results support the superiority of tau PET to diagnose TCP, pTau181 to differentiate TCP from YOAD or LOAD, and NFL for functional staging.

The diagnostic and prognostic value of tau-PET in amnestic MCI with different FDG-PET subtypes

OBJECTIVES

Mild cognitive impairment presenting with an amnestic syndrome (aMCI) and amyloid positivity is considered due to AD. Many subjects, however, can show an overall very slow progression relevant for differential diagnosis, prognosis, and treatment. This study assessed PET biomarkers, including brain glucose metabolism, tau, and amyloid load, in a series of comparable aMCI at baseline, clinically evaluated at follow-up.

METHODS

We included 72 aMCI subjects from Geneva Memory Center (N = 31) and ADNI cohorts (N = 41), selected based on available FDG-PET, tau-PET, amyloid-PET, and clinical follow-up (2.3 years ± 1.2). A data-driven algorithm classified brain metabolic patterns into subtypes that were then compared for clinical and PET biomarker measures and cognitive decline. Voxel-wise comparisons were performed both with FDG-PET and tau-PET data.

RESULTS

The algorithm classified three metabolic subtypes, namely "Hippocampal-sparing with cortical hypometabolism" (Type1; N = 27), "Hippocampal and cortical hypometabolism" (Type 2; N = 23), and "Medial temporal hypometabolism" (Type 3; N = 22). Amyloid positivity and tau accumulation in the medial temporal and neocortical regions characterized Type 1 and Type 2, whereas Type 3 showed no significant tau pathology, variable amyloid positivity, and stability at follow-up. All tau-positive patients, independently of the FDG-based subtype, showed faster cognitive decline.

INTERPRETATION

aMCI subjects can differ in metabolic patterns, tau and amyloid pathology, and clinical progression. Here, we complemented with PET tau biomarker the specific brain hypometabolic patterns at the individual level in the prodromal phase, contributing to the patient's classification. Tau PET is the most accurate biomarker in supporting or excluding the AD diagnosis in aMCI across metabolic subtypes and also predicting the risk of decline.

Disentangling and quantifying the relative cognitive impact of concurrent mixed neurodegenerative pathologies

Neurodegenerative pathologies such as Alzheimer disease neuropathologic change (ADNC), Lewy body disease (LBD), limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC), and cerebrovascular disease (CVD) frequently coexist, but little is known about the exact contribution of each pathology to cognitive decline and dementia in subjects with mixed pathologies. We explored the relative cognitive impact of concurrent common and rare neurodegenerative pathologies employing multivariate logistic regression analysis adjusted for age, gender, and level of education. We analyzed a cohort of 6,262 subjects from the National Alzheimer's Coordinating Center database, ranging from 0 to 6 comorbid neuropathologic findings per individual, where 95.7% of individuals had at least 1 neurodegenerative finding at autopsy and 75.5% had at least 2 neurodegenerative findings. We identified which neuropathologic entities correlate most frequently with one another and demonstrated that the total number of pathologies per individual was directly correlated with cognitive performance as assessed by Clinical Dementia Rating (CDR®) and Mini-Mental State Examination (MMSE). We show that ADNC, LBD, LATE-NC, CVD, hippocampal sclerosis, Pick disease, and FTLD-TDP significantly impact overall cognition as independent variables. More specifically, ADNC significantly affected all assessed cognitive domains, LBD affected attention, processing speed, and language, LATE-NC primarily affected tests related to logical memory and language, while CVD and other less common pathologies (including Pick disease, progressive supranuclear palsy, and corticobasal degeneration) had more variable neurocognitive effects. Additionally, ADNC, LBD, and higher numbers of comorbid neuropathologies were associated with the presence of at least one APOE ε4 allele, and ADNC and higher numbers of neuropathologies were inversely correlated with APOE ε2 alleles. Understanding the mechanisms by which individual and concomitant neuropathologies affect cognition and the degree to which each contributes is an imperative step in the development of biomarkers and disease-modifying therapeutics, particularly as these medical interventions become more targeted and personalized.

The Relationship between p-tau217, p-tau231, and p-tau205 in the Human Brain Is Affected by the Cellular Environment and Alzheimer's Disease Pathology

The levels of p-tau217 and p-tau231 in cerebrospinal fluid (CSF) are associated with early amyloid beta (Aß) changes in the brain, while the CSF levels of p-tau205 are foremost related to tau pathology in the later stages of the disease. To investigate if the three p-tau variants are found to the same degree in different tau structures and if their co-localization is affected by the diagnosis and presence of Aß plaques, we immunostained sections of the entorhinal cortex (EC) and inferior temporal gyrus (ITG) from non-demented controls (NC), patients with Alzheimer's disease (AD), and primary age-related tauopathy (PART) against p-tau217, p-tau231, and p-tau205 together with Methoxi-X04. An analysis using confocal microscopy showed that the co-localization variable, the Pearson correlation coefficient (PCC), was significantly higher between p-tau231 and p-tau205 in neurofibrillary tangles compared to neuropil threads and dystrophic neurites in plaques. The PCC value between all three p-tau variants in the neuropil threads was significantly lower in the ECs of patients with AD compared to the NC and in the ITGs of patients with AD, with a high Aß load compared to PART. The lowered value was associated with proportionally higher amounts of non-colocalized p-tau231 and p-tau217 compared to p-tau205, and the PCC values were negatively correlated with Aß and the tangle loads in patients with AD, but positively correlated with tangles in PART. These results suggest that the proportion of and co-localization between p-tau217, p-tau231, and p-tau205 are dependent on cellular localization and are altered in response to AD pathology in a spatial-temporal manner.

Explaining variability in early stages of [18F]-flortaucipir tau-PET binding: Focus on sex differences

INTRODUCTION

Female sex is associated with increased [18F]-flortaucipir signal, which may be affected by amyloid pathology, age, and off-target binding in skull and meninges.

METHODS

In this cross-sectional study comprising 52 females and 52 matched males, we examined sex-related differences in regional tau-positron emission tomography (PET) with and without considering off-target binding. We assessed the respective contributions of sex, age, amyloid-PET burden, and off-target binding to tau-PET signal. We explored associations between age at menopause and hormone replacement therapy (HRT) use with regional tau-PET signals.

RESULTS

Female sex was associated with increased regional tau both independently and interactively with amyloid, but amyloid-independent associations were largely reduced when controlling for off-target binding. Age but not age*sex interactions explained a small but significant amount of tau-PET signal in temporoparietal regions. Considering the sample size and limited range of amyloid-PET burden, no clear associations between regional tau-PET signals and age at menopause or HRT use could be found.

DISCUSSION

Female sex is associated with increased [18F]-flortaucipir signal mainly through its interaction with amyloid.

Amyloid-Negative, Neurodegeneration-Negative Amnestic Mild Cognitive Impairment

Background

The concept of amnestic mild cognitive impairment (aMCI) was developed to identify patients at an initial stage of Alzheimer's disease (AD). However, some patients with aMCI do not present biomarkers of amyloid pathology or neuronal injury.

Objective

To know the natural history of amyloid-negative and neurodegeneration-negative patients with aMCI, namely to ascertain: 1) whether these patients remain cognitively stable or they present a slow decline in neuropsychological tests; 2) whether the memory complaints subside with the apparently benign clinical course of the disorder or if they persist along the time.

Methods

Patients who fulfilled criteria for aMCI with no biomarkers of amyloid pathology or neuronal injury were selected from a large cohort of non-demented patients with cognitive complaints, and were followed with clinical and neuropsychological assessments.

Results

Twenty-one amyloid-negative and neurodegeneration-negative aMCI patients were followed for 7.1±3.7 years. At the baseline they had more pronounced deficits in verbal learning (California Verbal Learning Test) and were also impaired in Word Recall and Logical Memory. However, they did not decline in any cognitive test during follow-up. The patients maintained a high level of subjective memory complaints from baseline (9.7±4.1) to the follow-up visit (9.2±4.1, a non-significant difference), in spite of a statistically significant decrease in the depressive symptoms, with Geriatric Depression Scale (15 items) score 4.9±2.8 at baseline and 3.2±1.8 at the follow-up visit.

Conclusions

Amyloid-negative, neurodegeneration-negative aMCI is a chronic clinical condition characterized by the long-term persistence of cognitive deficits and distressing memory complaints. Adequate strategies to treat this condition are needed.

FDG-PET markers of heterogeneity and different risk of progression in amnestic MCI

INTRODUCTION

Amnestic mild cognitive impairment (aMCI) is emerging as a heterogeneous condition.

METHODS

We looked at a cohort of N = 207 aMCI subjects, with baseline fluorodeoxyglucose positron emission tomography (FDG-PET), T1 magnetic resonance imaging, cerebrospinal fluid (CSF), apolipoprotein E (APOE), and neuropsychological assessment. An algorithm based on FDG-PET hypometabolism classified each subject into subtypes, then compared biomarker measures and clinical progression.

RESULTS

Three subtypes emerged: hippocampal sparing-cortical hypometabolism, associated with younger age and the highest level of Alzheimer's disease (AD)-CSF pathology; hippocampal/cortical hypometabolism, associated with a high percentage of APOE ε3/ε4 or ε4/ε4 carriers; medial-temporal hypometabolism, characterized by older age, the lowest AD-CSF pathology, the most severe hippocampal atrophy, and a benign course. Within the whole cohort, the severity of temporo-parietal hypometabolism, correlated with AD-CSF pathology and marked the rate of progression of cognitive decline.

DISCUSSION

FDG-PET can distinguish clinically comparable aMCI at single-subject level with different risk of progression to AD dementia or stability. The obtained results can be useful for the optimization of pharmacological trials and automated-classification models.

HIGHLIGHTS

Algorithm based on FDG-PET hypometabolism demonstrates distinct subtypes across aMCI; Three different subtypes show heterogeneous biological profiles and risk of progression; The cortical hypometabolism is associated with AD pathology and cognitive decline; MTL hypometabolism is associated with the lowest conversion rate and CSF-AD pathology.

Cognitive symptoms progress with limbic-predominant age-related TDP-43 encephalopathy stage and co-occurrence with Alzheimer disease

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is a neuropathologic entity characterized by transactive response DNA-binding protein of 43-kDa (TDP-43)-immunoreactive inclusions that originate in the amygdala and then progress to the hippocampi and middle frontal gyrus. LATE-NC may mimic Alzheimer disease clinically and often co-occurs with Alzheimer disease neuropathologic change (ADNC). This report focuses on the cognitive effects of isolated and concomitant LATE-NC and ADNC. Cognitive/neuropsychological, neuropathologic, genetic, and demographic variables were analyzed in 28 control, 31 isolated LATE-NC, 244 isolated ADNC, and 172 concurrent LATE-NC/ADNC subjects from the National Alzheimer's Coordinating Center. Cases with LATE-NC and ADNC were significantly older than controls; cases with ADNC had a significantly higher proportion of cases with at least one APOE ε4 allele. Both LATE-NC and ADNC exhibited deleterious effects on overall cognition proportional to their neuropathological stages; concurrent LATE-NC/ADNC exhibited the worst overall cognitive effect. Multivariate logistic regression analysis determined an independent risk of cognitive impairment for progressive LATE-NC stages (OR 1.66; p = 0.0256) and ADNC levels (OR 3.41; p < 0.0001). These data add to the existing knowledge on the clinical consequences of LATE-NC pathology and the growing literature on the effects of multiple concurrent neurodegenerative pathologies.

Age-, sex-, and pathology-related variability in brain structure and cognition

This work aimed to investigate potential pathways linking age and imaging measures to early age- and pathology-related changes in cognition. We used [18F]-Flutemetamol (amyloid) and [18F]-Flortaucipir (tau) positron emission tomography (PET), structural MRI, and neuropsychological assessment from 232 elderly individuals aged 50-89 years (46.1% women, 23% APOE-ε4 carrier, 23.3% MCI). Tau-PET was available for a subsample of 93 individuals. Structural equation models were used to evaluate cross-sectional pathways between age, amyloid and tau burden, grey matter thickness and volumes, white matter hyperintensity volume, lateral ventricle volume, and cognition. Our results show that age is associated with worse outcomes in most of the measures examined and had similar negative effects on episodic memory and executive functions. While increased lateral ventricle volume was consistently associated with executive function dysfunction, participants with mild cognitive impairment drove associations between structural measures and episodic memory. Both age and amyloid-PET could be associated with medial temporal lobe tau, depending on whether we used a continuous or a dichotomous amyloid variable. Tau burden in entorhinal cortex was related to worse episodic memory in individuals with increased amyloid burden (Centiloid >12) independently of medial temporal lobe atrophy. Testing models for sex differences revealed that amyloid burden was more strongly associated with regional atrophy in women compared with men. These associations were likely mediated by higher tau burden in women. These results indicate that influences of pathological pathways on cognition and sex-specific vulnerabilities are dissociable already in early stages of neuropathology and cognitive impairment.

The relationship between hippocampal amyloid beta burden and spatial distribution of neurofibrillary degeneration

INTRODUCTION

Neurofibrillary degeneration in Alzheimer's disease (AD) typically involves the entorhinal cortex and CA1 subregion of the hippocampus early in the disease process, whereas in primary age-related tauopathy (PART), there is an early selective vulnerability of the CA2 subregion.

METHODS

Image analysis-based quantitative pixel assessments were used to objectively evaluate amyloid beta (Aβ) burden in the medial temporal lobe in relation to the distribution of hyperphosphorylated-tau (p-tau) in 142 cases of PART and AD.

RESULTS

Entorhinal, CA1, CA3, and CA4 p-tau deposition levels are significantly correlated with Aβ burden, while CA2 p-tau is not. Furthermore, the CA2/CA1 p-tau ratio is inversely correlated with Aβ burden and distribution. In addition, cognitive impairment is correlated with overall p-tau burden.

DISCUSSION

These data indicate that the presence and extent of medial temporal lobe Aβ may determine the distribution and spread of neurofibrillary degeneration. The resulting p-tau distribution patterns may discriminate between PART and AD.

HIGHLIGHTS

Subregional hyperphosphorylated-tau (p-tau) distribution is influenced by hippocampal amyloid beta burden. Higher CA2/CA1 p-tau ratio is predictive of primary age-related tauopathy-like neuropathology. Cognitive function is correlated with the overall hippocampal p-tau burden.

Shared and unique effects of ApoEε4 and pathogenic gene mutation on cognition and imaging in preclinical familial Alzheimer's disease

BACKGROUND

Neuropsychology and imaging changes have been reported in the preclinical stage of familial Alzheimer's disease (FAD). This study investigated the effects of APOEε4 and known pathogenic gene mutation on different cognitive domains and circuit imaging markers in preclinical FAD.

METHODS

One hundred thirty-nine asymptomatic subjects in FAD families, including 26 APOEε4 carriers, 17 APP and 20 PS1 mutation carriers, and 76 control subjects, went through a series of neuropsychological tests and MRI scanning. Test scores and imaging measures including volumes, diffusion indices, and functional connectivity (FC) of frontostriatal and hippocampus to posterior cingulate cortex pathways were compared between groups and analyzed for correlation.

RESULTS

Compared with controls, the APOEε4 group showed increased hippocampal volume and decreased FC of fronto-caudate pathway. The APP group showed increased recall scores in auditory verbal learning test, decreased fiber number, and increased radial diffusivity and FC of frontostriatal pathway. All three genetic groups showed decreased fractional anisotropy of hippocampus to posterior cingulate cortex pathway. These neuropsychological and imaging measures were able to discriminate genetic groups from controls, with areas under the curve from 0.733 to 0.837. Circuit imaging measures are differentially associated with scores in various cognitive scales in control and genetic groups.

CONCLUSIONS

There are neuropsychological and imaging changes in the preclinical stage of FAD, some of which are shared by APOEε4 and known pathogenic gene mutation, while some are unique to different genetic groups. These findings are helpful for the early identification of Alzheimer's disease and for developing generalized and individualized prevention and intervention strategies.

Unlocking Modifiable Risk Factors for Alzheimer's Disease: Does the Oral Microbiome Hold Some of the Keys?

Advancing age is recognized as the primary risk factor for Alzheimer's disease (AD); however approximately one third of dementia cases are attributable to modifiable risk factors such as hypertension, diabetes, smoking, and obesity. Recent research also implicates oral health and the oral microbiome in AD risk and pathophysiology. The oral microbiome contributes to the cerebrovascular and neurodegenerative pathology of AD via the inflammatory, vascular, neurotoxic, and oxidative stress pathways of known modifiable risk factors. This review proposes a conceptual framework that integrates the emerging evidence regarding the oral microbiome with established modifiable risk factors. There are numerous mechanisms by which the oral microbiome may interact with AD pathophysiology. Microbiota have immunomodulatory functions, including the activation of systemic pro-inflammatory cytokines. This inflammation can affect the integrity of the blood-brain barrier, which in turn modulates translocation of bacteria and their metabolites to brain parenchyma. Amyloid-β is an antimicrobial peptide, a feature which may in part explain its accumulation. There are microbial interactions with cardiovascular health, glucose tolerance, physical activity, and sleep, suggesting that these modifiable lifestyle risk factors of dementia may have microbial contributors. There is mounting evidence to suggest the relevance of oral health practices and the microbiome to AD. The conceptual framework presented here additionally demonstrates the potential for the oral microbiome to comprise a mechanistic intermediary between some lifestyle risk factors and AD pathophysiology. Future clinical studies may identify specific oral microbial targets and the optimum oral health practices to reduce dementia risk.

Cognitive Aging with Dementia, Mild Cognitive Impairment, or No Impairment: A Comparison of Same- and Mixed-Sex Couples

BACKGROUND

Lesbian and gay older adults have health disparities that are risk factors for Alzheimer's disease, yet little is known about the neurocognitive aging of sexual minority groups.

OBJECTIVE

To explore cross-sectional and longitudinal dementia outcomes for adults in same-sex relationships (SSR) and those in mixed-sex relationships (MSR).

METHODS

This prospective observational study utilized data from the National Alzheimer's Coordinating Center Uniform Data Set (NACC UDS) collected from contributing Alzheimer's Disease Research Centers. Participants were adults aged 55+ years at baseline with at least two visits in NACC UDS (from September 2005 to March 2021) who had a spouse, partner, or companion as a co-participant. Outcome measures included CDR® Dementia Staging Instrument, NACC UDS neuropsychological testing, and the Functional Activities Questionnaire. Multivariable linear mixed-effects models accounted for center clustering and repeated measures by individual.

RESULTS

Both MSR and SSR groups experienced cognitive decline regardless of baseline diagnosis. In general, MSR and SSR groups did not differ statistically on cross-sectional or longitudinal estimates of functioning, dementia severity, or neuropsychological testing, with two primary exceptions. People in SSR with mild cognitive impairment showed less functional impairment at baseline (FAQ M = 2.61, SD = 3.18 vs. M = 3.97, SD = 4.53, respectively; p < 0.01). The SSR group with dementia had less steep decline in attention/working memory (β estimates = -0.10 versus -0.18; p < 0.01).

CONCLUSION

Participants in SSR did not show cognitive health disparities consistent with a minority stress model. Additional research into protective factors is warranted.

Cognitive and Neuropsychological Profiles in Alzheimer's Disease and Primary Age-Related Tauopathy and the Influence of Comorbid Neuropathologies

BACKGROUND

Alzheimer's disease neuropathologic change (ADNC) is defined by the progression of both hyperphosphorylated-tau (p-tau) and amyloid-β (Aβ) and is the most common underlying cause of dementia worldwide. Primary age-related tauopathy (PART), an Aβ-negative tauopathy largely confined to the medial temporal lobe, is increasingly being recognized as an entity separate from ADNC with diverging clinical, genetic, neuroanatomic, and radiologic profiles.

OBJECTIVE

The specific clinical correlates of PART are largely unknown; we aimed to identify cognitive and neuropsychological differences between PART, ADNC, and subjects with no tauopathy (NT).

METHODS

We compared 2,884 subjects with autopsy-confirmed intermediate-high stage ADNC to 208 subjects with definite PART (Braak stage I-IV, Thal phase 0, CERAD NP score "absent") and 178 NT subjects from the National Alzheimer's Coordinating Center dataset.

RESULTS

PART subjects were older than either ADNC or NT patients. The ADNC cohort had more frequent neuropathological comorbidities as well as APOE ɛ4 alleles than the PART or NT cohort, and less frequent APOE ɛ2 alleles than either group. Clinically, ADNC patients performed significantly worse than NT or PART subjects across cognitive measures, but PART subjects had selective deficits in measures of processing speed, executive function, and visuospatial function, although additional cognitive measures were further impaired in the presence of neuropathologic comorbidities. In isolated cases of PART with Braak stage III-IV, there are additional deficits in measures of language.

CONCLUSION

Overall, these findings demonstrate underlying cognitive features specifically associated with PART, and reinforce the concept that PART is a distinct entity from ADNC.

Hypothesis review: Alzheimer's overture guidelines

National Institute on Aging-Alzheimer's Association definition and classification of sporadic Alzheimer's disease (sAD) is based on the assumption that β-amyloid drives the pathogenesis of sAD, and therefore, β-amyloid pathology is the sine-qua-non condition for the diagnosis of sAD. The neuropathological diagnosis is based on the concurrence of senile plaques (SPs) and neurofibrillary tangles (NFTs) designated as Alzheimer's disease neuropathological changes. However, NFTs develop in the brain decades before the appearance of SPs, and their distribution does not parallel the distribution of SPs. Moreover, NFTs are found in about 85% of individuals at age 65 and around 97% at age 80. SPs occur in 30% at age 65 and 50%-60% at age 80. More than 70 genetic risk factors have been identified in sAD; the encoded proteins modulate cell membranes, synapses, lipid metabolism, and neuroinflammation. Alzheimer's disease (AD) overture provides a new concept and definition of brain aging and sAD for further discussion. AD overture proposes that sAD is: (i) a multifactorial and progressive neurodegenerative biological process, (ii) characterized by the early appearance of 3R + 4Rtau NFTs, (iii) later deposition of β-amyloid and SPs, (iv) with particular non-overlapped regional distribution of NFTs and SPs, (v) preceded by or occurring in parallel with molecular changes affecting cell membranes, cytoskeleton, synapses, lipid and protein metabolism, energy metabolism, neuroinflammation, cell cycle, astrocytes, microglia, and blood vessels; (vi) accompanied by progressive neuron loss and brain atrophy, (vii) prevalent in human brain aging, and (viii) manifested as pre-clinical AD, and progressing not universally to mild cognitive impairment due to AD, and mild, moderate, and severe AD dementia.

Precuneus magnetic stimulation for Alzheimer's disease: a randomized, sham-controlled trial

Repetitive transcranial magnetic stimulation (rTMS) is emerging as a non-invasive therapeutic strategy in the battle against Alzheimer's disease. Alzheimer's disease patients primarily show alterations of the default mode network for which the precuneus is a key node. Here, we hypothesized that targeting the precuneus with TMS represents a promising strategy to slow down cognitive and functional decline in Alzheimer's disease patients. We performed a randomized, double-blind, sham-controlled, phase 2, 24-week trial to determine the safety and efficacy of precuneus stimulation in patients with mild-to-moderate Alzheimer's disease. Fifty Alzheimer's disease patients were randomly assigned in a 1:1 ratio to either receive precuneus or sham rTMS (mean age 73.7 years; 52% female). The trial included a 24-week treatment, with a 2-week intensive course in which rTMS (or sham) was applied daily five times per week, followed by a 22-week maintenance phase in which stimulation was applied once weekly. The Clinical Dementia Rating Scale-Sum of Boxes was selected as the primary outcome measure, in which post-treatment scores were compared to baseline. Secondary outcomes included score changes in the Alzheimer's Disease Assessment Scale-Cognitive Subscale, Mini-Mental State Examination and Alzheimer's Disease Cooperative Study-Activities of Daily Living scale. Moreover, single-pulse TMS in combination with EEG was used to assess neurophysiological changes in precuneus cortical excitability and oscillatory activity. Our findings show that patients that received precuneus repetitive magnetic stimulation presented a stable performance of the Clinical Dementia Rating Scale-Sum of Boxes score, whereas patients treated with sham showed a worsening of their score. Compared with the sham stimulation, patients in the precuneus stimulation group also showed also significantly better performances for the secondary outcome measures, including the Alzheimer's Disease Assessment Scale-Cognitive Subscale, Mini-Mental State Examination and Alzheimer's Disease Cooperative Study-Activities of Daily Living scale. Neurophysiological results showed that precuneus cortical excitability remained unchanged after 24 weeks in the precuneus stimulation group, whereas it was significantly reduced in the sham group. Finally, we found an enhancement of local gamma oscillations in the group treated with precuneus stimulation but not in patients treated with sham. We conclude that 24 weeks of precuneus rTMS may slow down cognitive and functional decline in Alzheimer's disease. Repetitive TMS targeting the default mode network could represent a novel therapeutic approach in Alzheimer's disease patients.

Artificial intelligence-derived neurofibrillary tangle burden is associated with antemortem cognitive impairment

Tauopathies are a category of neurodegenerative diseases characterized by the presence of abnormal tau protein-containing neurofibrillary tangles (NFTs). NFTs are universally observed in aging, occurring with or without the concomitant accumulation of amyloid-beta peptide (Aβ) in plaques that typifies Alzheimer disease (AD), the most common tauopathy. Primary age-related tauopathy (PART) is an Aβ-independent process that affects the medial temporal lobe in both cognitively normal and impaired subjects. Determinants of symptomology in subjects with PART are poorly understood and require clinicopathologic correlation; however, classical approaches to staging tau pathology have limited quantitative reproducibility. As such, there is a critical need for unbiased methods to quantitatively analyze tau pathology on the histological level. Artificial intelligence (AI)-based convolutional neural networks (CNNs) generate highly accurate and precise computer vision assessments of digitized pathology slides, yielding novel histology metrics at scale. Here, we performed a retrospective autopsy study of a large cohort (n = 706) of human post-mortem brain tissues from normal and cognitively impaired elderly individuals with mild or no Aβ plaques (average age of death of 83.1 yr, range 55-110). We utilized a CNN trained to segment NFTs on hippocampus sections immunohistochemically stained with antisera recognizing abnormal hyperphosphorylated tau (p-tau), which yielded metrics of regional NFT counts, NFT positive pixel density, as well as a novel graph-theory based metric measuring the spatial distribution of NFTs. We found that several AI-derived NFT metrics significantly predicted the presence of cognitive impairment in both the hippocampus proper and entorhinal cortex (p < 0.0001). When controlling for age, AI-derived NFT counts still significantly predicted the presence of cognitive impairment (p = 0.04 in the entorhinal cortex; p = 0.04 overall). In contrast, Braak stage did not predict cognitive impairment in either age-adjusted or unadjusted models. These findings support the hypothesis that NFT burden correlates with cognitive impairment in PART. Furthermore, our analysis strongly suggests that AI-derived metrics of tau pathology provide a powerful tool that can deepen our understanding of the role of neurofibrillary degeneration in cognitive impairment.

Amyloid-Tau-Neurodegeneration Profiles and Longitudinal Cognition in Sporadic Young-Onset Dementia

We examined amyloid-tau-neurodegeneration biomarker effects on cognition in a Southeast-Asian cohort of 84 sporadic young-onset dementia (YOD; age-at-onset <65 years) patients. They were stratified into A+N+, A– N+, and A– N– profiles via cerebrospinal fluid amyloid-β1–42 (A), phosphorylated-tau (T), MRI medial temporal atrophy (neurodegeneration– N), and confluent white matter hyperintensities cerebrovascular disease (CVD). A, T, and CVD effects on longitudinal Mini-Mental State Examination (MMSE) were evaluated. A+N+ patients demonstrated steeper MMSE decline than A– N+ (β = 1.53; p = 0.036; CI 0.15:2.92) and A– N– (β = 4.68; p = 0.001; CI 1.98:7.38) over a mean follow-up of 1.24 years. Within A– N+, T– CVD+ patients showed greater MMSE decline compared to T+CVD– patients (β = – 2.37; p = 0.030; CI – 4.41:– 0.39). A+ results in significant cognitive decline, while CVD influences longitudinal cognition in the A– sub-group.

Divergent magnetic resonance imaging atrophy patterns in Alzheimer's disease and primary age-related tauopathy

Our study compared brain MRI with neuropathological findings in patients with primary age-related tauopathy (PART) and Alzheimer's disease (AD), while assessing the relationship between brain atrophy and clinical impairment. We analyzed 233 participants: 32 with no plaques ("definite" PART-BRAAK stage higher than 0 and CERAD 0), and 201 cases within the AD spectrum, with 25 with sparse (CERAD 1), 76 with moderate (CERAD 2), and 100 with severe (CERAD 3) degrees of neuritic plaques. Upon correcting for age, sex, and age difference at MRI and death, there were significantly higher levels of atrophy in CERAD 3 compared to CERAD 1-2 and a trend compared to PART (p = 0.06). In the anterior temporal region, there was a trend for higher levels of atrophy in PART compared to Alzheimer's disease spectrum cases with CERAD 1 (p = 0.08). We then assessed the correlation between regional brain atrophy and CDR sum of boxes score for PART and AD, and found that overall cognition deficits are directly correlated with regional atrophy in the AD continuum, but not in definite PART. We further observed correlations between regional brain atrophy with multiple neuropsychological metrics in AD, with PART showing specific correlations between language deficits and anterior temporal atrophy. Overall, these findings support PART as an independent pathologic process from AD.

Intraneuronal sortilin aggregation relative to granulovacuolar degeneration, tau pathogenesis and sorfra plaque formation in human hippocampal formation

Extracellular β-amyloid (Aβ) deposition and intraneuronal phosphorylated-tau (pTau) accumulation are the hallmark lesions of Alzheimer’s disease (AD). Recently, “sorfra” plaques, named for the extracellular deposition of sortilin c-terminal fragments, are reported as a new AD-related proteopathy, which develop in the human cerebrum resembling the spatiotemporal trajectory of tauopathy. Here, we identified intraneuronal sortilin aggregation as a change related to the development of granulovacuolar degeneration (GVD), tauopathy, and sorfra plaques in the human hippocampal formation. Intraneuronal sortilin aggregation occurred as cytoplasmic inclusions among the pyramidal neurons, co-labeled by antibodies to the extracellular domain and intracellular C-terminal of sortilin. They existed infrequently in the brains of adults, while their density as quantified in the subiculum/CA1 areas increased in the brains from elderly lacking Aβ/pTau, with pTau (i.e., primary age-related tauopathy, PART cases), and with Aβ/pTau (probably/definitive AD, pAD/AD cases) pathologies. In PART and pAD/AD cases, the intraneuronal sortilin aggregates colocalized partially with various GVD markers including casein kinase 1 delta (Ck1δ) and charged multivesicular body protein 2B (CHMP2B). Single-cell densitometry established an inverse correlation between sortilin immunoreactivity and that of Ck1δ, CHMP2B, p62, and pTau among pyramidal neurons. In pAD/AD cases, the sortilin aggregates were reduced in density as moving from the subiculum to CA subregions, wherein sorfra plaques became fewer and absent. Taken together, we consider intraneuronal sortilin aggregation an aging/stress-related change implicating protein sorting deficit, which can activate protein clearance responses including via enhanced phosphorylation and hydrolysis, thereby promoting GVD, sorfra, and Tau pathogenesis, and ultimately, neuronal destruction and death.

Clinical Spectrum of Tauopathies

Tauopathies are both clinical and pathological heterogeneous disorders characterized by neuronal and/or glial accumulation of misfolded tau protein. It is now well understood that every pathologic tauopathy may present with various clinical phenotypes based on the primary site of involvement and the spread and distribution of the pathology in the nervous system making clinicopathological correlation more and more challenging. The clinical spectrum of tauopathies includes syndromes with a strong association with an underlying primary tauopathy, including Richardson syndrome (RS), corticobasal syndrome (CBS), non-fluent agrammatic primary progressive aphasia (nfaPPA)/apraxia of speech, pure akinesia with gait freezing (PAGF), and behavioral variant frontotemporal dementia (bvFTD), or weak association with an underlying primary tauopathy, including Parkinsonian syndrome, late-onset cerebellar ataxia, primary lateral sclerosis, semantic variant PPA (svPPA), and amnestic syndrome. Here, we discuss clinical syndromes associated with various primary tauopathies and their distinguishing clinical features and new biomarkers becoming available to improve in vivo diagnosis. Although the typical phenotypic clinical presentations lead us to suspect specific underlying pathologies, it is still challenging to differentiate pathology accurately based on clinical findings due to large phenotypic overlaps. Larger pathology-confirmed studies to validate the use of different biomarkers and prospective longitudinal cohorts evaluating detailed clinical, biofluid, and imaging protocols in subjects presenting with heterogenous phenotypes reflecting a variety of suspected underlying pathologies are fundamental for a better understanding of the clinicopathological correlations.

β-Amyloid in blood neuronal-derived extracellular vesicles is elevated in cognitively normal adults at risk of Alzheimer's disease and predicts cerebral amyloidosis

Background

Blood biomarkers that can be used for preclinical Alzheimer’s disease (AD) diagnosis would enable trial enrollment at a time when the disease is potentially reversible. Here, we investigated plasma neuronal-derived extracellular vesicle (nEV) cargo in patients along the Alzheimer’s continuum, focusing on cognitively normal controls (NCs) with high brain β-amyloid (Aβ) loads (Aβ+).

Methods

The study was based on the Sino Longitudinal Study on Cognitive Decline project. We enrolled 246 participants, including 156 NCs, 45 amnestic mild cognitive impairment (aMCI) patients, and 45 AD dementia (ADD) patients. Brain Aβ loads were determined using positron emission tomography. NCs were classified into 84 Aβ− NCs and 72 Aβ+ NCs. Baseline plasma nEVs were isolated by immunoprecipitation with an anti-CD171 antibody. After verification, their cargos, including Aβ, tau phosphorylated at threonine 181, and neurofilament light, were quantified using a single-molecule array. Concentrations of these cargos were compared among the groups, and their receiver operating characteristic (ROC) curves were constructed. A subset of participants underwent follow-up cognitive assessment and magnetic resonance imaging. The relationships of nEV cargo levels with amyloid deposition, longitudinal changes in cognition, and brain regional volume were explored using correlation analysis. Additionally, 458 subjects in the project had previously undergone plasma Aβ quantification.

Results

Only nEV Aβ was included in the subsequent analysis. We focused on Aβ₄₂ in the current study. After normalization of nEVs, the levels of Aβ₄₂ were found to increase gradually across the cognitive continuum, with the lowest in the Aβ− NC group, an increase in the Aβ+ NC group, a further increase in the aMCI group, and the highest in the ADD group, contributing to their diagnoses (Aβ− NCs vs. Aβ+ NCs, area under the ROC curve values of 0.663; vs. aMCI, 0.857; vs. ADD, 0.957). Furthermore, nEV Aβ₄₂ was significantly correlated with amyloid deposition, as well as longitudinal changes in cognition and entorhinal volume. There were no differences in plasma Aβ levels among NCs, aMCI, and ADD individuals.

Conclusions

Our findings suggest the potential use of plasma nEV Aβ₄₂ levels in diagnosing AD-induced cognitive impairment and Aβ+ NCs. This biomarker reflects cortical amyloid deposition and predicts cognitive decline and entorhinal atrophy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01010-x.

Biomarkers and Tools for Predicting Alzheimer's Disease in the Preclinical Stage

Alzheimer's disease (AD) is the only leading cause of death for which no disease-modifying therapy is currently available. Over the past decade, a string of disappointing clinical trial results has forced us to shift our focus to the preclinical stage of AD, which represents the most promising therapeutic window. However, the accurate diagnosis of preclinical AD requires the presence of brain β- amyloid deposition determined by cerebrospinal fluid or amyloid-positron emission tomography, significantly limiting routine screening and diagnosis in non-tertiary hospital settings. Thus, an easily accessible marker or tool with high sensitivity and specificity is highly needed. Recently, it has been discovered that individuals in the late stage of preclinical AD may not be truly "asymptomatic" in that they may have already developed subtle or subjective cognitive decline. In addition, advances in bloodderived biomarker studies have also allowed the detection of pathologic changes in preclinical AD. Exosomes, as cell-to-cell communication messengers, can reflect the functional changes of their source cell. Methodological advances have made it possible to extract brain-derived exosomes from peripheral blood, making exosomes an emerging biomarker carrier and liquid biopsy tool for preclinical AD. The eye and its associated structures have rich sensory-motor innervation. In this regard, studies have indicated that they may also provide reliable markers. Here, our report covers the current state of knowledge of neuropsychological and eye tests as screening tools for preclinical AD and assesses the value of blood and brain-derived exosomes as carriers of biomarkers in conjunction with the current diagnostic paradigm.

The Outcome of Patients with Amyloid-Negative Amnestic Mild Cognitive Impairment

Background: Patients with amnestic mild cognitive impairment (aMCI) are usually at an initial stage of Alzheimer’s disease (AD). However, some patients with aMCI do not present biomarkers of amyloid pathology characteristic of AD. The significance of amyloid-negative aMCI is not presently clear. Objective: To know the etiology and prognosis of amyloid-negative aMCI. Methods: Patients who fulfilled criteria for aMCI and were amyloid negative were selected from a large cohort of non-demented patients with cognitive complaints and were followed with clinical and neuropsychological assessments. Results: Few amyloid-negative aMCI had evidence of neurodegeneration at the baseline, as reflected in cerebrospinal fluid elevated tau protein levels. About half of the patients remained essentially stable for long periods of time. Others manifested a psychiatric disorder that was not apparent at baseline, namely major depression or bipolar disorder. Remarkably, about a quarter of patients developed neurodegenerative disorders other than AD, mostly frontotemporal dementia or Lewy body disease. Conclusion: Amyloid-negative aMCI is a heterogeneous condition. Many patients remain clinically stable, but others may later manifest psychiatric conditions or evolve to neurodegenerative disorders. Prudence is needed when communicating to the patient and family the results of biomarkers, and clinical follow-up should be advised.

Primary Age‐Related Tauopathy (PART) in a Finnish Population‐Based Study of the Oldest Old (Vantaa 85+)

Aims

Few studies have investigated primary age‐related tauopathy (PART) in a population‐based setting. Here, we assessed its prevalence, genetic background, comorbidities and features of cognitive decline in an unselected elderly population.

Methods

The population‐based Vantaa 85+ study includes all 601 inhabitants of Vantaa aged ≥ 85 years in 1991. Neuropathological assessment was possible in 301. Dementia (DSM IIIR criteria) and Mini‐Mental State Examination (MMSE) scores were assessed at the baseline of the study and follow‐ups. PART subjects were identified according to the criteria by Crary et al and were compared with subjects with mild and severe Alzheimer's disease (AD) neuropathological changes. The effects of other neuropathologies were taken into account using multivariate and sensitivity assays. Genetic analyses included APOE genotypes and 29 polymorphisms of the MAPT 3′ untranslated region (3′UTR region).

Results

The frequency of PART was 20% (n = 61/301, definite PART 5%). When PART subjects were compared with those with severe AD pathology, dementia was less common, its age at onset was higher and duration shorter. No such differences were seen when compared with those with milder AD pathology. However, both AD groups showed a steeper decline in MMSE scores in follow‐ups compared with PART. APOE ε4 frequency was lower, and APOE ε2 frequency higher in the PART group compared with each AD group. The detected nominally significant associations between PART and two MAPT 3′UTR polymorphisms and haplotypes did not survive Bonferroni correction.

Conclusions

PART is common among very elderly. PART subjects differ from individuals with AD‐type changes in the pattern of cognitive decline, associated genetic and neuropathological features.

The correlation of blood pressure variability and cognitive function in hypertension patients: A meta-analysis

BACKGROUND

Cognitive impairment (CI) is very common in patients with hypertension. It is necessary to conduct a meta-analysis to evaluate the association between cognitive function and blood pressure variability in patients with hypertension, to provide insights into the clinical management of hypertension and cognitive impairment.

METHODS

We searched PubMed and other databases for case-control studies on the association between blood pressure variability and cognitive function up to 15 July 2021. Two researchers independently screened the literature and retrieved the data. RevMan 5.3 was used for meta-analysis.

RESULTS

A total of 13 studies involving 2754 patients were included. Meta-analysis indicated that 24-hours systolic (MD = 3.54, 95% CI [2.48, 4.60]) and diastolic (MD = 2.43, 95% CI [1.55, 3.31]) blood pressure variation coefficients in the CI group were significantly higher than that of non-CI group (all P < .05). Standard deviations of systolic (MD = 2.20, 95% CI [0.27, 4.13]) and diastolic (MD = 1.79, 95% CI [0.80, 2.79]) blood pressure variation in the CI group were significantly higher than that of the non-CI group (all P < .05). Mean systolic (MD = 3.73, 95% CI [0.92, 6.53]) and diastolic (MD = 5.41, 95% CI [0.42, 10.40]) blood pressure variation in the CI group were significantly higher than that of non-CI group (all P < .05). There were no statistically significant differences in the morning peak systolic (MD = 7.85, 95% CI [-1.30, 17.01]) and diastolic (MD = 4.44, 95% CI [-6.00, 14.89]) blood pressure drop between the CI group and non-CI group (all P > .05).

CONCLUSION

CI in hypertensive patients is closely associated with increased blood pressure variability. Clinical healthcare providers should pay attention to the management of blood pressure variability in hypertensive patients to reduce the occurrence of CI.

Amyloid-dependent and amyloid-independent effects of Tau in individuals without dementia

Objective

To investigate the relationship between the topography of amyloid‐β plaques, tau neurofibrillary tangles, and the overlap between the two, with cognitive dysfunction in individuals without dementia.

Methods

We evaluated 154 individuals who were assessed with amyloid‐β PET with [¹⁸F]AZD4694, tau‐PET with [¹⁸F]MK6240, structural MRI, and neuropsychological testing. We also evaluated an independent cohort of 240 individuals who were assessed with amyloid‐β PET with [¹⁸F]Florbetapir, tau‐PET with [¹⁸F]Flortaucipir, structural MRI, and neuropsychological testing. Using the VoxelStats toolbox, we conducted voxel‐wise linear regressions between amyloid‐PET, tau‐PET, and their interaction with cognitive function, correcting for age, sex, and years of education.

Results

In both cohorts, we observed that tau‐PET standardized uptake value ratio in medial temporal lobes was associated with clinical dementia rating Sum of Boxes (CDR‐SoB) scores independently of local amyloid‐PET uptake (FWE corrected at p < 0.001). We also observed in both cohorts that in regions of the neocortex, associations between neocortical tau‐PET and clinical function were dependent on local amyloid‐PET (FWE corrected at p < 0.001).

Interpretation

In medial temporal brain regions, characterized by the accumulation of tau pathology in the absence of amyloid‐β, tau had direct associations with cognitive dysfunction. In brain regions characterized by the accumulation of both amyloid‐β and tau pathologies such as the posterior cingulate and medial frontal cortices, tau’s relationship with cognitive dysfunction was dependent on local amyloid‐β concentrations. Our results provide evidence that amyloid‐β in Alzheimer’s disease influences cognition by potentiating the deleterious effects of tau pathology.

Abnormal tau in amyloid PET negative individuals

We examined the characteristics of individuals with biomarker evidence of tauopathy but without β-amyloid (Aβ) (A-T+) in relation to individuals with (A+T+) and without (A-T-) evidence of Alzheimer's disease (AD). We included 561 participants with Aβ and tau PET from the Alzheimer's Disease Neuroimaging Initiative (ADNI). We compared A-T- (n = 316), A-T+ (n = 63), and A+T+ (n = 182) individuals on demographics, amyloid, tau, hippocampal volumes, and cognition. A-T+ individuals were low on apolipoprotein E ɛ4 prevalence (17%) and had no evidence of subtly elevated brain Aβ within the negative range. The severity of tau deposition, hippocampal atrophy, and cognitive dysfunction in the A-T+ group was intermediate between A-T- and A+T+ (all p < 0.001). Tau uptake patterns in A-T+ individuals were heterogeneous, but approximately 29% showed tau deposition in the medial temporal lobe only, consistent with primary age-related tauopathy and an additional 32% showed a pattern consistent with AD. A-T+ individuals also share other features that are characteristic of AD such as cognitive impairment and neurodegeneration, but this group is heterogeneous and likely reflects more than one disorder.

Distinct amyloid and tau PET signatures are associated with diverging clinical and imaging trajectories in patients with amnestic syndrome of the hippocampal type

We aimed to investigate the amyloid and tau PET imaging signatures of patients with amnestic syndrome of the hippocampal type (ASHT) and study their clinical and imaging progression according to their initial PET imaging status. Thirty-six patients with a progressive ASHT and 30 controls underwent a complete neuropsychological assessment, 3 T brain MRI, [¹¹C]-PiB and [¹⁸F]-Flortaucipir PET imaging. Subjects were clinically followed-up annually over 2 years, with a second 3 T MRI (n = 27 ASHT patients, n = 28 controls) and tau-PET (n = 20 ASHT patients) at the last visit. At baseline, in accordance with the recent biological definition of Alzheimer's disease (AD), the AD PET signature was defined as the combination of (i) positive cortical amyloid load, and (ii) increased tau tracer binding in the entorhinal cortices and at least one of the following regions: amygdala, parahippocampal gyri, fusiform gyri. Patients who did not meet these criteria were considered to have a non-AD pathology (SNAP). Twenty-one patients were classified as AD and 15 as SNAP. We found a circumscribed tau tracer retention in the entorhinal cortices and/or amygdala in 5 amyloid-negative SNAP patients. At baseline, the SNAP patients were older and had lower ApoE ε4 allele frequency than the AD patients, but both groups did not differ regarding the neuropsychological testing and medial temporal lobe atrophy. During the 2-year follow-up, the episodic memory and language decline, as well as the temporo-parietal atrophy progression, were more pronounced in the AD sub-group, while the SNAP patients had a more pronounced progression of atrophy in the frontal lobes. Longitudinal tau tracer binding increased in AD patients but remained stable in SNAP patients. At baseline, distinct amyloid and tau PET signatures differentiated early AD and SNAP patients despite identical cognitive profiles characterized by an isolated ASHT and a similar degree of medial temporal atrophy. During the longitudinal follow-up, AD and SNAP patients diverged regarding clinical and imaging progression. Among SNAP patients, tau PET imaging could detect a tauopathy restricted to the medial temporal lobes, which was possibly explained by primary age-related tauopathy.

Tau and MAPT genetics in tauopathies and synucleinopathies

MAPT encodes the microtubule-associated protein tau, which is the main component of neurofibrillary tangles (NFTs) and found in other protein aggregates. These aggregates are among the pathological hallmarks of primary tauopathies such as frontotemporal dementia (FTD). Abnormal tau can also be observed in secondary tauopathies such as Alzheimer's disease (AD) and synucleinopathies such as Parkinson's disease (PD). On top of pathological findings, genetic data also links MAPT to these disorders. MAPT variations are a cause or risk factors for many tauopathies and synucleinopathies and are associated with certain clinical and pathological features in affected individuals. In addition to clinical, pathological, and genetic overlap, evidence also suggests that tau and alpha-synuclein may interact on the molecular level, and thus might collaborate in the neurodegenerative process. Understanding the role of MAPT variations in tauopathies and synucleinopathies is therefore essential to elucidate the role of tau in the pathogenesis and phenotype of those disorders, and ultimately to develop targeted therapies. In this review, we describe the role of MAPT genetic variations in tauopathies and synucleinopathies, several genotype-phenotype and pathological features, and discuss their implications for the classification and treatment of those disorders.

Predictors of cognitive impairment in primary age-related tauopathy: an autopsy study

Primary age-related tauopathy (PART) is a form of Alzheimer-type neurofibrillary degeneration occurring in the absence of amyloid-beta (Aβ) plaques. While PART shares some features with Alzheimer disease (AD), such as progressive accumulation of neurofibrillary tangle pathology in the medial temporal lobe and other brain regions, it does not progress extensively to neocortical regions. Given this restricted pathoanatomical pattern and variable symptomatology, there is a need to reexamine and improve upon how PART is neuropathologically assessed and staged. We performed a retrospective autopsy study in a collection (n = 174) of post-mortem PART brains and used logistic regression to determine the extent to which a set of clinical and neuropathological features predict cognitive impairment. We compared Braak staging, which focuses on hierarchical neuroanatomical progression of AD tau and Aβ pathology, with quantitative assessments of neurofibrillary burden using computer-derived positive pixel counts on digitized whole slide images of sections stained immunohistochemically with antibodies targeting abnormal hyperphosphorylated tau (p-tau) in the entorhinal region and hippocampus. We also assessed other factors affecting cognition, including aging-related tau astrogliopathy (ARTAG) and atrophy. We found no association between Braak stage and cognitive impairment when controlling for age (p = 0.76). In contrast, p-tau burden was significantly correlated with cognitive impairment even when adjusting for age (p = 0.03). The strongest correlate of cognitive impairment was cerebrovascular disease, a well-known risk factor (p < 0.0001), but other features including ARTAG (p = 0.03) and hippocampal atrophy (p = 0.04) were also associated. In contrast, sex, APOE, psychiatric illness, education, argyrophilic grains, and incidental Lewy bodies were not. These findings support the hypothesis that comorbid pathologies contribute to cognitive impairment in subjects with PART. Quantitative approaches beyond Braak staging are critical for advancing our understanding of the extent to which age-related tauopathy changes impact cognitive function.

Early Selective Vulnerability of the CA2 Hippocampal Subfield in Primary Age-Related Tauopathy

Primary age-related tauopathy (PART) is a neurodegenerative entity defined as Alzheimer-type neurofibrillary degeneration primarily affecting the medial temporal lobe with minimal to absent amyloid-β (Aβ) plaque deposition. The extent to which PART can be differentiated pathoanatomically from Alzheimer disease (AD) is unclear. Here, we examined the regional distribution of tau pathology in a large cohort of postmortem brains (n = 914). We found an early vulnerability of the CA2 subregion of the hippocampus to neurofibrillary degeneration in PART, and semiquantitative assessment of neurofibrillary degeneration in CA2 was significantly greater than in CA1 in PART. In contrast, subjects harboring intermediate-to-high AD neuropathologic change (ADNC) displayed relative sparing of CA2 until later stages of their disease course. In addition, the CA2/CA1 ratio of neurofibrillary degeneration in PART was significantly higher than in subjects with intermediate-to-high ADNC burden. Furthermore, the distribution of tau pathology in PART diverges from the Braak NFT staging system and Braak stage does not correlate with cognitive function in PART as it does in individuals with intermediate-to-high ADNC. These findings highlight the need for a better understanding of the contribution of PART to cognitive impairment and how neurofibrillary degeneration interacts with Aβ pathology in AD and PART.

Early Dendritic Dystrophy in Human Brains With Primary Age-Related Tauopathy

Dystrophic neurites (DNs) are found in many neurological conditions such as traumatic brain injury and age-related neurodegenerative diseases. In Alzheimer's disease (AD) specifically, senile plaques containing silver-stained DNs were already described in the original literature defining this disease. These DNs could be both axonal and dendritic in origin, while axonal dystrophy relative to plaque formation has been more extensively studied. Here, we demonstrate an early occurrence of dendritic dystrophy in the hippocampal CA1 and subicular regions in human brains (n = 23) with primary age-related tauopathy (PART), with neurofibrillary tangle (NFT) burden ranging from Braak stages I to III in the absence of cerebral β-amyloid (Aβ) deposition. In Bielschowsky's silver stain, segmented fusiform swellings on the apical dendrites of hippocampal and subicular pyramidal neurons were observed in all the cases, primarily over the stratum radiatum (s.r.). The numbers of silver-stained neuronal somata and dendritic swellings counted over CA1 to subiculum were positively correlated among the cases. Swollen dendritic processes were also detected in sections immunolabeled for phosphorylated tau (pTau) and sortilin. In aged and AD brains with both Aβ and pTau pathologies, silver- and immunolabeled dystrophic-like dendritic profiles occurred around and within individual neuritic plaques. These findings implicate that dendritic dystrophy can occur among hippocampal pyramidal neurons in human brains with PART. Therefore, as with the case of axonal dystrophy reported in literature, dendritic dystrophy can develop prior to Alzheimer-type plaque and tangle formation in the human brain.

Regional Tau Effects on Prospective Cognitive Change in Cognitively Normal Older Adults

Studies suggest that tau deposition starts in the anterolateral entorhinal cortex (EC) with normal aging, and that the presence of β-amyloid (Aβ) facilitates its spread to neocortex, which may reflect the beginning of Alzheimer's disease (AD). Functional connectivity between the anterolateral EC and the anterior-temporal (AT) memory network appears to drive higher tau deposition in AT than in the posterior-medial (PM) memory network. Here, we investigated whether this differential vulnerability to tau deposition may predict different cognitive consequences of EC, AT, and PM tau. Using ¹⁸F-flortaucipir (FTP) and ¹¹C-Pittsburgh compound-B (PiB) positron emission tomography (PET) imaging, we measured tau and Aβ in 124 cognitively normal human older adults (74 females, 50 males) followed for an average of 2.8 years for prospective cognition. We found that higher FTP in all three regions was individually related to faster memory decline, and that the effects of AT and PM FTP, but not EC, were driven by Aβ+ individuals. Moreover, when we included all three FTP measures competitively in the same model, only AT FTP significantly predicted memory decline. Our data support a model whereby tau, facilitated by Aβ, transits from EC to cortical regions that are most closely associated with the anterolateral EC, which specifically affects memory in the initial stage of AD. Memory also appears to be affected by EC tau in the absence of Aβ, which may be less clinically consequential. These findings may provide clarification of differences between normal aging and AD, and elucidate the transition between the two stages.SIGNIFICANCE STATEMENT Tau and β-amyloid (Aβ) are hallmarks of Alzheimer's disease (AD) but are also found in cognitively normal people. It is unclear whether, and how, this early deposition of tau and Aβ may affect cognition in normal aging and the asymptomatic stage of AD. We show that tau deposition in the entorhinal cortex (EC), which is common in advanced age, predicts memory decline in older adults independent of Aβ, likely reflecting normal, age-related memory loss. In contrast, tau in anterior-temporal (AT) regions is most predictive of memory decline in Aβ+ individuals. These data support the idea that tau preferentially spreads to specific cortical regions, likely through functional connections, which plays a primary role in memory decline in the early stage of AD.

Mesial temporal tau is related to worse cognitive performance and greater neocortical tau load in amyloid-β-negative cognitively normal individuals

We examined whether mesial temporal (Me) tau relates to cognitive performance in 47 amyloid-β (Aβ)-negative, cognitively normal older adults (>60 years old). Me-tau was measured using [¹⁸F]flortaucipir-positron emission tomography standardized uptake value ratio. The effect of continuous and categorical (stratified at standardized uptake value ratio = 1.2 [21% Me-positive]) Me-tau on cognition (mini-mental state examination, pre-Alzheimer's cognitive composite, a memory composite, and a nonmemory composite score) was examined using general linear models, and associations between Me-tau and [¹⁸F]flortaucipir signal in the neocortex were assessed using voxelwise regressions (continuous) and voxelwise contrasts (categorical). In addition, we assessed the effect of age and Aβ burden on Me-tau. Both continuous and categorical Me-tau was associated with worse cognitive performance across all tests and with higher lateral temporal and parietal [¹⁸F]flortaucipir signal. Furthermore, we observed a marginal association between Me-tau and age, whereas there was no association with Aβ burden. Our findings indicate that Me-tau in Aβ-negative cognitively normal individuals, which is likely age-related (i.e., primary age-related tauopathy), might not be as benign as commonly thought.

Primary Age-Related Tauopathy (PART): Addressing the Spectrum of Neuronal Tauopathic Changes in the Aging Brain

PURPOSE OF REVIEW

Primary age-related tauopathy (PART) was recently proposed as a pathologic diagnosis for brains that harbor neurofibrillary tangles (Braak stage ≤ 4) with little, if any, amyloid burden. We sought to review the clinicopathologic findings related to PART.

RECENT FINDINGS

Most adult human brains show at least focal tauopathic changes, and the majority of individuals with PART do not progress to dementia. Older age and cognitive impairment correlate with increased Braak stage, and multivariate analyses suggest that the rate of cognitive decline is less than matched patients with Alzheimer disease (AD). It remains unclear whether PART is a distinct tauopathic entity separate from AD or rather represents an earlier histologic stage of AD. Cognitive decline in PART is usually milder than AD and correlates with tauopathic burden. Biomarker and ligand-based radiologic studies will be important to define PART antemortem and prospectively follow its natural history.