Deep learning reveals disease-specific signatures of white matter pathology in tauopathies.

Although pathology of tauopathies is characterized by abnormal tau protein aggregation in both gray and white matter regions of the brain, neuropathological investigations have generally focused on abnormalities in the cerebral cortex because the canonical aggregates that form the diagnostic criteria for these disorders predominate there. This corticocentric focus tends to deemphasize the relevance of the more complex white matter pathologies, which remain less well characterized and understood. We took a data-driven machine-learning approach to identify novel disease-specific morphologic signatures of white matter aggregates in three tauopathies: Alzheimer disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). We developed automated approaches using whole slide images of tau immunostained sections from 49 human autopsy brains (16 AD,13 CBD, 20 PSP) to identify cortex/white matter regions and individual tau aggregates, and compared tau-aggregate morphology across these diseases. Tau burden in the gray and white matter for individual subjects strongly correlated in a highly disease-specific fashion. We discovered previously unrecognized tau morphologies for AD, CBD and PSP that may be of importance in disease classification. Intriguingly, our models classified diseases equally well based on either white or gray matter tau staining. Our results suggest that tau pathology in white matter is informative, disease-specific, and linked to gray matter pathology. Machine learning has the potential to reveal latent information in histologic images that may represent previously unrecognized patterns of neuropathology, and additional studies of tau pathology in white matter could improve diagnostic accuracy.

Structure-based classification of tauopathies.

The ordered assembly of tau protein into filaments characterizes several neurodegenerative diseases, which are called tauopathies. It was previously reported that, by cryo-electron microscopy, the structures of tau filaments from Alzheimer's disease1,2, Pick's disease3, chronic traumatic encephalopathy4 and corticobasal degeneration5 are distinct. Here we show that the structures of tau filaments from progressive supranuclear palsy (PSP) define a new three-layered fold. Moreover, the structures of tau filaments from globular glial tauopathy are similar to those from PSP. The tau filament fold of argyrophilic grain disease (AGD) differs, instead resembling the four-layered fold of corticobasal degeneration. The AGD fold is also observed in ageing-related tau astrogliopathy. Tau protofilament structures from inherited cases of mutations at positions +3 or +16 in intron 10 of MAPT (the microtubule-associated protein tau gene) are also identical to those from AGD, suggesting that relative overproduction of four-repeat tau can give rise to the AGD fold. Finally, the structures of tau filaments from cases of familial British dementia and familial Danish dementia are the same as those from cases of Alzheimer's disease and primary age-related tauopathy. These findings suggest a hierarchical classification of tauopathies on the basis of their filament folds, which complements clinical diagnosis and neuropathology and also allows the identification of new entities-as we show for a case diagnosed as PSP, but with filament structures that are intermediate between those of globular glial tauopathy and PSP.

Cellular and pathological heterogeneity of primary tauopathies.

Microtubule-associated protein tau is abnormally aggregated in neuronal and glial cells in a range of neurodegenerative diseases that are collectively referred to as tauopathies. Multiple studies have suggested that pathological tau species may act as a seed that promotes aggregation of endogenous tau in naïve cells and contributes to propagation of tau pathology. While they share pathological tau aggregation as a common feature, tauopathies are distinct from one another with respect to predominant tau isoforms that accumulate and the selective vulnerability of brain regions and cell types that have tau inclusions. For instance, primary tauopathies present with glial tau pathology, while it is mostly neuronal in Alzheimer's disease (AD). Also, morphologies of tau inclusions can greatly vary even within the same cell type, suggesting distinct mechanisms or distinct tau conformers in each tauopathy. Neuropathological heterogeneity across tauopathies challenges our understanding of pathophysiology behind tau seeding and aggregation, as well as our efforts to develop effective therapeutic strategies for AD and other tauopathies. In this review, we describe diverse neuropathological features of tau inclusions in neurodegenerative tauopathies and discuss what has been learned from experimental studies with mouse models, advanced transcriptomics, and cryo-electron microscopy (cryo-EM) on the biology underlying cell type-specific tau pathology.

Globular glial tauopathy, a newly recognized white matter tauopathy, with depression/anxiety disorder: report and review of classification.

Several studies have recently described 4-repeat tauopathies that are characterized by the presence of globular glial inclusions. These inclusions are astrocytic or oligodendroglial, show extensive white matter involvement, and have a wide range of neuropathological and clinical presentations. Globular glial tauopathy (GGT) is classified into three subtypes according to clinical manifestations. Type I is characterized by frontotemporal lobar degeneration and represents a group of diseases with diverse clinical and histopathological features. Some of these disorders are associated with abnormal microtubule-associated protein tau gene. Type II presents as motor impairment due to pyramidal involvement, whereas type III is a combination of the features of types I and II. This report describes a rare case of GGT that manifested as depression and anxiety and demonstrates its neuropathological features. We have also compared the features of this case with those of previously reported cases and have revisited the classification.

A Practical Approach to Differentiate the Frontotemporal Tauopathy Subtypes.

This study proposes a practical approach, using the minimum number of brain regions and stains, to consolidate previously published neuropathological criteria into one operationalized schema to differentiate subtypes of frontotemporal lobar degeneration with tau-immunopositive inclusions (FTLD-tau). This approach uses the superior frontal and precentral cortices and hippocampus stained for phosphorylated-tau, p62 and modified Bielschowsky silver, and the midbrain stained only for modified Bielschowsky silver. Accuracy of interrater reliability was determined by 10 raters in 24 FTLD-tau cases (Pick disease = 4, corticobasal degeneration = 9, progressive supranuclear palsy = 5, globular glial tauopathy = 6) including 4 with a mutation in MAPT collected with consent by Sydney Brain Bank. All brain regions and stains assessed proved informative for accurate pathological subtyping, and many neuropathological features were identified as common across the FTLD-tau subtypes. By identifying subtype-specific neuropathological features in the sections selected, 10 independent observers assigned the cases to a FTLD-tau subtype with almost perfect agreement between raters, emphasizing the requirement for the assessment of subtype-specific features for the accurate subtyping of FTLD-tau. This study consolidates current consensus diagnostic criteria for classifying FTLD-tau subtypes with an efficient, simple and accurate approach that can be implemented in future clinicopathological studies.

Immune profiling of plasma-derived extracellular vesicles identifies Parkinson disease.

OBJECTIVE: To develop a diagnostic model based on plasma-derived extracellular vesicle (EV) subpopulations in Parkinson disease (PD) and atypical parkinsonism (AP), we applied an innovative flow cytometric multiplex bead-based platform. METHODS: Plasma-derived EVs were isolated from PD, matched healthy controls, multiple system atrophy (MSA), and AP with tauopathies (AP-Tau). The expression levels of 37 EV surface markers were measured by flow cytometry and correlated with clinical scales. A diagnostic model based on EV surface markers expression was built via supervised machine learning algorithms and validated in an external cohort. RESULTS: Distinctive pools of EV surface markers related to inflammatory and immune cells stratified patients according to the clinical diagnosis. PD and MSA displayed a greater pool of overexpressed immune markers, suggesting a different immune dysregulation in PD and MSA vs AP-Tau. The receiver operating characteristic curve analysis of a compound EV marker showed optimal diagnostic performance for PD (area under the curve [AUC] 0.908; sensitivity 96.3%, specificity 78.9%) and MSA (AUC 0.974; sensitivity 100%, specificity 94.7%) and good accuracy for AP-Tau (AUC 0.718; sensitivity 77.8%, specificity 89.5%). A diagnostic model based on EV marker expression correctly classified 88.9% of patients with reliable diagnostic performance after internal and external validations. CONCLUSIONS: Immune profiling of plasmatic EVs represents a crucial step toward the identification of biomarkers of disease for PD and AP.

Classification of atypical parkinsonism per pathology versus phenotype.

The umbrella term "atypical parkinsonism" refers to a clinical presentation with various causes, emphasizing the clinical commonality of diseases in which atypical parkinsonism can present. This term is useful for describing the phenomenology of a movement disorder and to classify patients according to their clinical presentation. In contrast to this classification per phenotype, a classification per pathology is needed when it comes to understanding the pathogenesis and designing and delivering disease-modifying therapeutic interventions. Clinico-pathological correlation studies have revealed enormous clinical heterogeneity and vast clinical overlap in pathologically defined diseases related to atypical parkinsonism. Thus, the classification of patients with atypical parkinsonism per phenotype has limited validity for predicting the underlying pathology. This chapter will contrast the phenotype-driven classification and the pathology-driven classification of neurodegenerative diseases related to atypical parkinsonism and discuss future directions to improve pathology-specific diagnosis.

Tau Subtypes of Alzheimer's Disease Determined in vivo Using Flortaucipir PET Imaging.

At autopsy, individuals with Alzheimer's disease (AD) exhibit heterogeneity in the distribution of neurofibrillary tangles in neocortical and hippocampal regions. Subtypes of AD, defined using an algorithm based on the relative number of tangle counts in these regions, have been proposed-hippocampal sparing (relative sparing of the hippocampus but high cortical load), limbic predominant (high hippocampal load but lower load in association cortices), and typical (balanced neurofibrillary tangles counts in the hippocampus and association cortices) AD-and shown to be associated with distinct antemortem clinical phenotypes. The ability to distinguish these AD subtypes from the more typical tau signature in vivo could have important implications for clinical research. Flortaucipir positron emission tomography (PET) images acquired from 45 amyloid-positive participants, defined clinically as mild cognitive impairment or AD, aged 50-92 years, 56% female, and estimated to be Braak V-VI based on their PET pattern of tau pathology, were studied. By translating the neuropathologic algorithm to flortaucipir PET scans, patterns of tau pathology consistent with autopsy findings, and with a similar prevalence, were identified in vivo. 6/45 (13%) participants were identified as hippocampal sparing and 6/45 (13%) as limbic predominant AD subtypes. Hippocampal sparing participants were significantly younger than those assigned to the other two subtypes. Worse performance on delayed recall was associated with increased hippocampal tau signal, and worse performance on the trail making test B-A was associated with lower values of the hippocampus to cortex ratio. Prospective studies can further validate the flortaucipir SUVR cut-points and the phenotype of the corresponding AD subtypes.

Tau monomer encodes strains.

Tauopathies have diverse presentation, progression, and neuropathology. They are linked to tau prion strains, self-replicating assemblies of unique quaternary conformation, whose origin is unknown. Strains can be propagated indefinitely in cultured cells, and induce unique patterns of transmissible neuropathology upon inoculation into mice. DS9 and DS10 cell lines propagate different synthetic strains that derive from recombinant tau. We previously observed that tau monomer adopts two conformational states: one that is inert (Mi) and one that is seed-competent (Ms) (Mirbaha et al., 2018). We have now found that Ms itself is comprised of multiple stable ensembles that encode unique strains. DS9 monomer inoculated into naive cells encoded only DS9, whereas DS10 monomer encoded multiple sub-strains. Sub-strains each induced distinct pathology upon inoculation into a tauopathy mouse model (PS19). Ms purified from an Alzeimer's disease brain encoded a single strain. Conversely, Ms from a corticobasal degeneration brain encoded three sub-strains, in which monomer from any one re-established all three upon inoculation into cells. Seed competent tau monomer thus adopts multiple, stable seed-competent conformations, each of which encodes a limited number of strains. This provides insight into the emergence of distinct tauopathies, and may improve diagnosis and therapy.

New classification of tauopathies.

Tauopathies are a group of neurodegenerative diseases characterized by pathological intracellular deposits of the protein tau. Isoform composition, morphology and anatomical distribution of cellular tau-immunoreactivities are defining distinct tauopathies as molecular pathological disease entities. The clinical spectrum of tauopathies includes syndromes with primary motor symptoms and with primary cognitive dysfunction. The traditional syndrome-based classification is currently being complemented by a molecular-pathological classification. While the syndrome-based classification is helpful to select symptomatic therapies, and to generate clinical working hypotheses about underlying etiologies, the molecular-pathological classification is most important for the development and application of molecularly tailored disease-modifying therapies.

Sequential stages and distribution patterns of aging-related tau astrogliopathy (ARTAG) in the human brain.

Aging-related tau astrogliopathy (ARTAG) describes tau pathology in astrocytes in different locations and anatomical regions. In the present study we addressed the question of whether sequential distribution patterns can be recognized for ARTAG or astroglial tau pathologies in both primary FTLD-tauopathies and non-FTLD-tauopathy cases. By evaluating 687 postmortem brains with diverse disorders we identified ARTAG in 455. We evaluated frequencies and hierarchical clustering of anatomical involvement and used conditional probability and logistic regression to model the sequential distribution of ARTAG and astroglial tau pathologies across different brain regions. For subpial and white matter ARTAG we recognize three and two patterns, respectively, each with three stages initiated or ending in the amygdala. Subependymal ARTAG does not show a clear sequential pattern. For grey matter (GM) ARTAG we recognize four stages including a striatal pathway of spreading towards the cortex and/or amygdala, and the brainstem, and an amygdala pathway, which precedes the involvement of the striatum and/or cortex and proceeds towards the brainstem. GM ARTAG and astrocytic plaque pathology in corticobasal degeneration follows a predominantly frontal-parietal cortical to temporal-occipital cortical, to subcortical, to brainstem pathway (four stages). GM ARTAG and tufted astrocyte pathology in progressive supranuclear palsy shows a striatum to frontal-parietal cortical to temporal to occipital, to amygdala, and to brainstem sequence (four stages). In Pick's disease cases with astroglial tau pathology an overlapping pattern with PSP can be appreciated. We conclude that tau-astrogliopathy type-specific sequential patterns cannot be simplified as neuron-based staging systems. The proposed cytopathological and hierarchical stages provide a conceptual approach to identify the initial steps of the pathogenesis of tau pathologies in ARTAG and primary FTLD-tauopathies.

Astrocytic Tau Pathologies in Argyrophilic Grain Disease and Related Four-repeat Tauopathies.

Neurodegenerative diseases in which tau accumulation plays a cardinal role in the pathogenic process are called tauopathies, and when tau isoforms having four repeats of the microtubule binding sites, four-repeat tau, are selectively accumulated as pathological hallmarks, the term four-repeat tauopathy is used. The major four-repeat tauopathies are progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and argyrophilic grain disease (AGD). Historically, neuronal cytopathologies, e.g., neurofibrillary tangles and ballooned neurons, were emphasized as characteristic lesions in PSP and CBD. Now, however, astrocytic tau pathologies, i.e., tufted astrocytes (TAs) and astrocytic plaques (APs), are considered to be highly disease-specific lesions. Although granular/fuzzy astrocytes (GFAs) frequently develop in the limbic system in AGD cases, the specificity is not conclusive yet. Some AGD cases have a few TAs, and to a lesser frequency, a few APs in the frontal cortex and subcortical nuclei. The number of astrocytic tau pathologies including TAs and GFAs increases with the progression of AGD. In this paper, histopathological features of astrocytic tau pathologies in PSP, CBD, and AGD are first reviewed. Then, recent findings regarding the coexistence of these tauopathies are summarized from a viewpoint of astrocytic tau pathologies. Further biochemical and pathological studies focusing tau-positive astrocytic lesions may be useful to increase understanding of the pathological process in four-repeat tauopathies and to develop novel therapeutic strategies for patients with these diseases.

Pathological Tau Strains from Human Brains Recapitulate the Diversity of Tauopathies in Nontransgenic Mouse Brain.

Pathological tau aggregates occur in Alzheimer's disease (AD) and other neurodegenerative tauopathies. It is not clearly understood why tauopathies vary greatly in the neuroanatomical and histopathological patterns of tau aggregation, which contribute to clinical heterogeneity in these disorders. Recent studies have shown that tau aggregates may form distinct structural conformations, known as tau strains. Here, we developed a novel model to test the hypothesis that cell-to-cell transmission of different tau strains occurs in nontransgenic (non-Tg) mice, and to investigate whether there are strain-specific differences in the pattern of tau transmission. By injecting pathological tau extracted from postmortem brains of AD (AD-tau), progressive supranuclear palsy (PSP-tau), and corticobasal degeneration (CBD-tau) patients into different brain regions of female non-Tg mice, we demonstrated the induction and propagation of endogenous mouse tau aggregates. Specifically, we identified differences in tau strain potency between AD-tau, CBD-tau, and PSP-tau in non-Tg mice. Moreover, differences in cell-type specificity of tau aggregate transmission were observed between tau strains such that only PSP-tau and CBD-tau strains induce astroglial and oligodendroglial tau inclusions, recapitulating the diversity of neuropathology in human tauopathies. Furthermore, we demonstrated that the neuronal connectome, but not the tau strain, determines which brain regions develop tau pathology. Finally, CBD-tau- and PSP-tau-injected mice showed spatiotemporal transmission of glial tau pathology, suggesting glial tau transmission contributes to the progression of tauopathies. Together, our data suggest that different tau strains determine seeding potency and cell-type specificity of tau aggregation that underlie the diversity of human tauopathies.SIGNIFICANCE STATEMENT Tauopathies show great clinical and neuropathological heterogeneity, despite the fact that tau aggregates in each disease. This heterogeneity could be due to tau aggregates forming distinct structural conformations, or strains. We now report the development of a sporadic tauopathy model to study human tau strains by intracerebrally injecting nontransgenic mice with pathological tau enriched from human tauopathy brains. We show human tau strains seed different types and cellular distributions of tau neuropathology in our model that recapitulate the heterogeneity seen in these human diseases.

Age-specific and sex-specific prevalence of cerebral ß-amyloidosis, tauopathy, and neurodegeneration in cognitively unimpaired individuals aged 50-95 years: a cross-sectional study.

BACKGROUND: A new classification for biomarkers in Alzheimer's disease and cognitive ageing research is based on grouping the markers into three categories: amyloid deposition (A), tauopathy (T), and neurodegeneration or neuronal injury (N). Dichotomising these biomarkers as normal or abnormal results in eight possible profiles. We determined the clinical characteristics and prevalence of each ATN profile in cognitively unimpaired individuals aged 50 years and older. METHODS: All participants were in the Mayo Clinic Study of Aging, a population-based study that uses a medical records linkage system to enumerate all individuals aged 50-89 years in Olmsted County, MN, USA. Potential participants are randomly selected, stratified by age and sex, and invited to participate in cognitive assessments; individuals without medical contraindications are invited to participate in brain imaging studies. Participants who were judged clinically as having no cognitive impairment and underwent multimodality imaging between Oct 11, 2006, and Oct 5, 2016, were included in the current study. Participants were classified as having normal (A-) or abnormal (A+) amyloid using amyloid PET, normal (T-) or abnormal (T+) tau using tau PET, and normal (N-) or abnormal (N+) neurodegeneration or neuronal injury using cortical thickness assessed by MRI. We used the cutoff points of standard uptake value ratio (SUVR) 1·42 (centiloid 19) for amyloid PET, 1·23 SUVR for tau PET, and 2·67 mm for MRI cortical thickness. Age-specific and sex-specific prevalences of the eight groups were determined using multinomial models combining data from 435 individuals with amyloid PET, tau PET, and MRI assessments, and 1113 individuals who underwent amyloid PET and MRI, but not tau PET imaging. FINDINGS: The numbers of participants in each profile group were 165 A-T-N-, 35 A-T+N-, 63 A-T-N+, 19 A-T+N+, 44 A+T-N-, 25 A+T+N-, 35 A+T-N+, and 49 A+T+N+. Age differed by ATN group (p<0·0001), ranging from a median 58 years (IQR 55-64) in A-T-N- and 57 years (54-64) in A-T+N- to a median 80 years (75-84) in A+T-N+ and 79 years (73-87) in A+T+N+. The number of APOE ε4 carriers differed by ATN group (p=0·04), with carriers roughly twice as frequent in each A+ group versus the corresponding A- group. White matter hyperintensity volume (p<0·0001) and cognitive performance (p<0·0001) also differed by ATN group. Tau PET and neurodegeneration biomarkers were discordant in most individuals who would be categorised as stage 2 or 3 preclinical Alzheimer's disease (A+T+N-, A+T-N+, and A+T+N+; 86% at age 65 years and 51% at age 80 years) or with suspected non-Alzheimer's pathophysiology (A-T+N-, A-T-N+, and A-T+N+; 92% at age 65 years and 78% at age 80 years). From age 50 years, A-T-N- prevalence declined and A+T+N+ and A-T+N+ prevalence increased. In both men and women, A-T-N- was the most prevalent until age late 70s. After about age 80 years, A+T+N+ was most prevalent. By age 85 years, more than 90% of men and women had one or more biomarker abnormalities. INTERPRETATION: Biomarkers of fibrillar tau deposition can be included with those of ß-amyloidosis and neurodegeneration or neuronal injury to more fully characterise the heterogeneous pathological profiles in the population. Both amyloid- dependent and amyloid-independent pathological profiles can be identified in the cognitively unimpaired population. The prevalence of each ATN group changed substantially with age, with progression towards more biomarker abnormalities among individuals who remained cognitively unimpaired. FUNDING: National Institute on Aging (part of the US National Institutes of Health), the Alexander Family Professorship of Alzheimer's Disease Research, the Mayo Clinic, and the GHR Foundation.

Outcomes after diagnosis of mild cognitive impairment in a large autopsy series.

OBJECTIVE: To determine clinical and neuropathological outcomes following a clinical diagnosis of mild cognitive impairment (MCI). METHODS: Data were drawn from a large autopsy series (N = 1,337) of individuals followed longitudinally from normal or MCI status to death, derived from 4 Alzheimer Disease (AD) Centers in the United States. RESULTS: Mean follow-up was 7.9 years. Of the 874 individuals ever diagnosed with MCI, final clinical diagnoses were varied: 39.2% died with an MCI diagnosis, 46.8% with a dementia diagnosis, and 13.9% with a diagnosis of intact cognition. The latter group had pathological features resembling those with a final clinical diagnosis of MCI. In terms of non-AD pathologies, both primary age-related tauopathy (p < 0.05) and brain arteriolosclerosis pathology (p < 0.001) were more severe in MCI than cognitively intact controls. Among the group that remained MCI until death, mixed AD neuropathologic changes (ADNC; ≥1 comorbid pathology) were more frequent than "pure" ADNC pathology (55% vs 22%); suspected non-Alzheimer pathology comprised the remaining 22% of cases. A majority (74%) of subjects who died with MCI were without "high"-level ADNC, Lewy body disease, or hippocampal sclerosis pathologies; this group was enriched in cerebrovascular pathologies. Subjects who died with dementia and were without severe neurodegenerative pathologies tended to have cerebrovascular pathology and carry the MCI diagnosis for a longer interval. INTERPRETATION: MCI diagnosis usually was associated with comorbid neuropathologies; less than one-quarter of MCI cases showed "pure" AD at autopsy. Ann Neurol 2017;81:549-559.

Tau and tauopathies.

Most neurodegenerative diseases are characterized by intracellular aggregates of insoluble proteins. As for the majority of these disorders, aetiology and pathogenesis are only poorly understood; current nosological concepts are largely based on these molecular signatures of protein aggregates which also provide valuable tools for neuropathological differential diagnosis. The microtubule associated protein tau is one of these proteins that form intracellular fibrillary deposits in neurons and glial cells of a large variety of disorders today collectively referred to as tauopathies. While dysfunction of tau has unequivocally been shown to be able to cause neurodegeneration, the precise mechanisms of how tau is involved in neurodegenerative disorders is still poorly understood. After research has focused for several decades on the axonal function of tau and on the fibrillar tau aggregation, more recent cell biological studies have opened up new insights into the role of tau at the synapse and in the nucleus. According to currently emerging cell biological concepts, tau might play a role in the regulation of neuronal plasticity in a wide array of neuronal networks. In addition, it might be involved in regulating genome stability. The most intriguing question relevant both to physiological and pathophysiological function of tau is the biological meaning of the large heterogeneity of isoforms of tau which apparently is a rather promiscuous molecule. The present review is divided into two parts. First, we give an overview on the molecular biology and cell biology of tau and its physiological functions. The second part deals with the pathophysiology of tau and description of tauopathies which comprise more than 20 disorders including Alzheimer's disease, progressive supranuclear palsy, cortico basal degeneration, Pick's disease and others.

Biochemical classification of tauopathies by immunoblot, protein sequence and mass spectrometric analyses of sarkosyl-insoluble and trypsin-resistant tau.

Intracellular filamentous tau pathology is the defining feature of tauopathies, which form a subset of neurodegenerative diseases. We have analyzed pathological tau in Alzheimer's disease, and in frontotemporal lobar degeneration associated with tauopathy to include cases with Pick bodies, corticobasal degeneration, progressive supranuclear palsy, and ones due to intronic mutations in MAPT. We found that the C-terminal band pattern of the pathological tau species is distinct for each disease. Immunoblot analysis of trypsin-resistant tau indicated that the different band patterns of the 7-18 kDa fragments in these diseases likely reflect different conformations of tau molecular species. Protein sequence and mass spectrometric analyses revealed the carboxyl-terminal region (residues 243-406) of tau comprises the protease-resistant core units of the tau aggregates, and the sequence lengths and precise regions involved are different among the diseases. These unique assembled tau cores may be used to classify and diagnose disease strains. Based on these results, we propose a new clinicopathological classification of tauopathies based on the biochemical properties of tau.

Primary age-related tauopathy (PART): a common pathology associated with human aging.

We recommend a new term, "primary age-related tauopathy" (PART), to describe a pathology that is commonly observed in the brains of aged individuals. Many autopsy studies have reported brains with neurofibrillary tangles (NFTs) that are indistinguishable from those of Alzheimer's disease (AD), in the absence of amyloid (Aß) plaques. For these "NFT+/Aß-" brains, for which formal criteria for AD neuropathologic changes are not met, the NFTs are mostly restricted to structures in the medial temporal lobe, basal forebrain, brainstem, and olfactory areas (bulb and cortex). Symptoms in persons with PART usually range from normal to amnestic cognitive changes, with only a minority exhibiting profound impairment. Because cognitive impairment is often mild, existing clinicopathologic designations, such as "tangle-only dementia" and "tangle-predominant senile dementia", are imprecise and not appropriate for most subjects. PART is almost universally detectable at autopsy among elderly individuals, yet this pathological process cannot be specifically identified pre-mortem at the present time. Improved biomarkers and tau imaging may enable diagnosis of PART in clinical settings in the future. Indeed, recent studies have identified a common biomarker profile consisting of temporal lobe atrophy and tauopathy without evidence of Aß accumulation. For both researchers and clinicians, a revised nomenclature will raise awareness of this extremely common pathologic change while providing a conceptual foundation for future studies. Prior reports that have elucidated features of the pathologic entity we refer to as PART are discussed, and working neuropathological diagnostic criteria are proposed.

Globular glial tauopathies (GGT): consensus recommendations.

Recent studies have highlighted a group of 4-repeat (4R) tauopathies that are characterised neuropathologically by widespread, globular glial inclusions (GGIs). Tau immunohistochemistry reveals 4R immunoreactive globular oligodendroglial and astrocytic inclusions and the latter are predominantly negative for Gallyas silver staining. These cases are associated with a range of clinical presentations, which correlate with the severity and distribution of underlying tau pathology and neurodegeneration. Their heterogeneous clinicopathological features combined with their rarity and under-recognition have led to cases characterised by GGIs being described in the literature using various and redundant terminologies. In this report, a group of neuropathologists form a consensus on the terminology and classification of cases with GGIs. After studying microscopic images from previously reported cases with suspected GGIs (n = 22), this panel of neuropathologists with extensive experience in the diagnosis of neurodegenerative diseases and a documented record of previous experience with at least one case with GGIs, agreed that (1) GGIs were present in all the cases reviewed; (2) the morphology of globular astrocytic inclusions was different to tufted astrocytes and finally that (3) the cases represented a number of different neuropathological subtypes. They also agreed that the different morphological subtypes are likely to be part of a spectrum of a distinct disease entity, for which they recommend that the overarching term globular glial tauopathy (GGT) should be used. Type I cases typically present with frontotemporal dementia, which correlates with the fronto-temporal distribution of pathology. Type II cases are characterised by pyramidal features reflecting motor cortex involvement and corticospinal tract degeneration. Type III cases can present with a combination of frontotemporal dementia and motor neuron disease with fronto-temporal cortex, motor cortex and corticospinal tract being severely affected. Extrapyramidal features can be present in Type II and III cases and significant degeneration of the white matter is a feature of all GGT subtypes. Improved detection and classification will be necessary for the establishment of neuropathological and clinical diagnostic research criteria in the future.

Neuropathology of the hippocampus in FTLD-Tau with Pick bodies: a study of the BrainNet Europe Consortium.

AIMS: Frontotemporal lobar degeneration with Pick bodies (Pick's disease) is characterized by the presence of tau immunoreactive spherical structures in the cytoplasm of neurones. In view of confusion about the molecular pathology of Pick's disease, we aimed to evaluate the spectrum of tau pathology and concomitant neurodegeneration-associated protein depositions in the characteristically affected hippocampus. METHODS: We evaluated immunoreactivity (IR) for tau (AT8, 3R, 4R), α-synuclein, TDP43, p62, and ubiquitin in the hippocampus, entorhinal and temporal cortex in 66 archival cases diagnosed neuropathologically as Pick's disease. RESULTS: Mean age at death was 68.2 years (range 49-96). Fifty-two (79%) brains showed 3R immunoreactive spherical inclusions in the granule cells of the dentate gyrus. These typical cases presented mainly with the behavioural variant of frontotemporal dementia, followed by progressive aphasia, mixed syndromes or early memory disturbance. α-Synuclein IR was seen only in occasional spherical tau-positive inclusions, TDP-43 IR was absent, and 4R IR was present only as neurofibrillary tangles in pyramidal neurones. Aß IR was observed in 16 cases; however, the overall level of Alzheimer's disease-related alterations was mainly low or intermediate (n = 3). Furthermore, we identified six cases with unclassifiable tauopathy. CONCLUSIONS: (i) Pick's disease may occur also in elderly patients and is characterized by a relatively uniform pathology with 3R tau inclusions particularly in the granule cells of dentate gyrus; (ii) even minor deviation from these morphological criteria suggests a different disorder; and (iii) immunohistological revision of archival cases expands the spectrum of tauopathies that require further classification.