Distinct involvement of the cranial and spinal nerves in progressive supranuclear palsy

The most frequent neurodegenerative proteinopathies include diseases with deposition of misfolded tau or α-synuclein in the brain. Pathological protein aggregates in the PNS are well-recognized in α-synucleinopathies and have recently attracted attention as a diagnostic biomarker. However, there is a paucity of observations in tauopathies. To characterize the involvement of the PNS in tauopathies, we investigated tau pathology in cranial and spinal nerves (PNS-tau) in 54 tauopathy cases [progressive supranuclear palsy (PSP), n = 15; Alzheimer's disease (AD), n = 18; chronic traumatic encephalopathy (CTE), n = 5; and corticobasal degeneration (CBD), n = 6; Pick's disease, n = 9; limbic-predominant neuronal inclusion body 4-repeat tauopathy (LNT), n = 1] using immunohistochemistry, Gallyas silver staining, biochemistry, and seeding assays. Most PSP cases revealed phosphorylated and 4-repeat tau immunoreactive tau deposits in the PNS as follows: (number of tau-positive cases/available cases) cranial nerves III: 7/8 (88%); IX/X: 10/11 (91%); and XII: 6/6 (100%); anterior spinal roots: 10/10 (100%). The tau-positive inclusions in PSP often showed structures with fibrillary (neurofibrillary tangle-like) morphology in the axon that were also recognized with Gallyas silver staining. CBD cases rarely showed fine granular non-argyrophilic tau deposits. In contrast, tau pathology in the PNS was not evident in AD, CTE and Pick's disease cases. The single LNT case also showed tau pathology in the PNS. In PSP, the severity of PNS-tau involvement correlated with that of the corresponding nuclei, although, occasionally, p-tau deposits were present in the cranial nerves but not in the related brainstem nuclei. Not surprisingly, most of the PSP cases presented with eye movement disorder and bulbar symptoms, and some cases also showed lower-motor neuron signs. Using tau biosensor cells, for the first time we demonstrated seeding capacity of tau in the PNS. In conclusion, prominent PNS-tau distinguishes PSP from other tauopathies. The morphological differences of PNS-tau between PSP and CBD suggest that the tau pathology in PNS could reflect that in the central nervous system. The high frequency and early presence of tau lesions in PSP suggest that PNS-tau may have clinical and biomarker relevance.

[Neuropathology of the Neurodegenerative Diseases]

A definite diagnosis of neurodegenerative diseases is required for neuropathological examination during an autopsy. Each neurodegenerative disease has specific vulnerable regions and affected systems (system degeneration), and is typified by an accumulation of abnormal protein with the formation of characteristic morphological aggregates in the nerve and glial cells, called proteinopathy. The most common neurodegenerative diseases are tauopathy, such as progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick's disease (PiD); α-synucleinopathy, including multiple system atrophy (MSA); and TAR DNA-binding protein of 43 kDa (TDP-43) proteinopathy, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). PSP and CBD show characteristic tau-positive astrocytic inclusions known as tufted astrocytes and astrocytic plaques, respectively. PiD shows tau-positive neuronal inclusions termed Pick bodies. MSA is characterized by α-synuclein-positive oligodendroglial inclusions, called glial cytoplasmic inclusions. ALS- and FTLD-TDP show TDP-43-positive neuronal inclusions, such as skein-like and round inclusions. Huntington's disease shows polyglutamine-positive neuronal inclusions, and Creutzfeldt-Jakob disease shows diffuse deposition of granular prions in the neuropil. The atypical proteins in these diseases have abnormal conformational properties. A comprehensive comparison of the clinical findings and neuropathological observations, including neuroanatomy and images acquired during life, is important to improve the sensitivity of clinical diagnosis.

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.

Lateral geniculate body is spared of tau pathology in Pick disease

The pathobiology of tau is of great importance for understanding the mechanisms of neurodegeneration in aging and age-associated disorders such as Alzheimer disease (AD) and frontotemporal dementias. It is critical to identify neuronal populations and brain regions that are vulnerable or resistant to tau pathological changes. Pick disease (PiD) is a three-repeat (3R) tauopathy that belongs to the group of frontotemporal lobar degenerations. The neuropathologic changes of PiD are characterized by globular tau-positive neuronal intracytoplasmic inclusions, called Pick bodies, in the granule cells of the dentate gyrus and frontal and temporal neocortices, and ballooned neurons, named Pick neurons, in the neocortex. In the present study, we examined 13 autopsy-confirmed cases of PiD. Using immunohistochemistry for phospho-tau (AT8) and 3R tau isoform, all PiD cases demonstrated extensive lesions involving the hippocampus and neocortex. However, the lateral geniculate body (LGB) is spared of significant tau lesions in contrast to the neighboring hippocampus and other thalamic nuclei. Only 1 PiD case (7.7%) had tau-positive neurons, and 4 cases had tau-positive neurites (31%) in the LGB. By contrast, the LGB does consistently harbor tau lesions in other tauopathies including progressive supranuclear palsy, corticobasal degeneration, and AD.

Phenotypically concordant distribution of pick bodies in aphasic versus behavioral dementias

Pick's disease (PiD) is a subtype of the tauopathy form of frontotemporal lobar degeneration (FTLD-tau) characterized by intraneuronal 3R-tau inclusions. PiD can underly various dementia syndromes, including primary progressive aphasia (PPA), characterized by an isolated and progressive impairment of language and left-predominant atrophy, and behavioral variant frontotemporal dementia (bvFTD), characterized by progressive dysfunction in personality and bilateral frontotemporal atrophy. In this study, we investigated the neocortical and hippocampal distributions of Pick bodies in bvFTD and PPA to establish clinicopathologic concordance between PiD and the salience of the aphasic versus behavioral phenotype. Eighteen right-handed cases with PiD as the primary pathologic diagnosis were identified from the Northwestern University Alzheimer's Disease Research Center brain bank (bvFTD, N = 9; PPA, N = 9). Paraffin-embedded sections were stained immunohistochemically with AT8 to visualize Pick bodies, and unbiased stereological analysis was performed in up to six regions bilaterally [middle frontal gyrus (MFG), superior temporal gyrus (STG), inferior parietal lobule (IPL), anterior temporal lobe (ATL), dentate gyrus (DG) and CA1 of the hippocampus], and unilateral occipital cortex (OCC). In bvFTD, peak neocortical densities of Pick bodies were in the MFG, while the ATL was the most affected in PPA. Both the IPL and STG had greater leftward pathology in PPA, with the latter reaching significance (p < 0.01). In bvFTD, Pick body densities were significantly right-asymmetric in the STG (p < 0.05). Hippocampal burden was not clinicopathologically concordant, as both bvFTD and PPA cases demonstrated significant hippocampal pathology compared to neocortical densities (p < 0.0001). Inclusion-to-neuron analyses in a subset of PPA cases confirmed that neurons in the DG are disproportionately burdened with inclusions compared to neocortical areas. Overall, stereological quantitation suggests that the distribution of neocortical Pick body pathology is concordant with salient clinical features unique to PPA vs. bvFTD while raising intriguing questions about the selective vulnerability of the hippocampus to 3R-tauopathies.

Glial reactivity and T cell infiltration in frontotemporal lobar degeneration with tau pathology

Frontotemporal lobar degeneration with tau (FTLD-tau) is a group of tauopathies that underlie ∼50% of FTLD cases. Identification of genetic risk variants related to innate/adaptive immunity have highlighted a role for neuroinflammation and neuroimmune interactions in FTLD. Studies have shown microglial and astrocyte activation together with T cell infiltration in the brain of THY-Tau22 tauopathy mice. However, this remains to be confirmed in FTLD-tau patients. We conducted a detailed post-mortem study of FTLD-tau cases including 45 progressive supranuclear palsy with clinical frontotemporal dementia, 33 Pick's disease, 12 FTLD-MAPT and 52 control brains to characterize the link between phosphorylated tau (pTau) epitopes and the innate and adaptive immunity. Tau pathology was assessed in the cerebral cortex using antibodies directed against: Tau-2 (phosphorylated and unphosphorylated tau), AT8 (pSer202/pThr205), AT100 (pThr212/pSer214), CP13 (pSer202), PHF1 (pSer396/pSer404), pThr181 and pSer356. The immunophenotypes of microglia and astrocytes were assessed with phenotypic markers (Iba1, CD68, HLA-DR, CD64, CD32a, CD16 for microglia and GFAP, EAAT2, glutamine synthetase and ALDH1L1 for astrocytes). The adaptive immune response was explored via CD4+ and CD8+ T cell quantification and the neuroinflammatory environment was investigated via the expression of 30 inflammatory-related proteins using V-Plex Meso Scale Discovery. As expected, all pTau markers were increased in FTLD-tau cases compared to controls. pSer356 expression was greatest in FTLD-MAPT cases versus controls (P < 0.0001), whereas the expression of other markers was highest in Pick's disease. Progressive supranuclear palsy with frontotemporal dementia consistently had a lower pTau protein load compared to Pick's disease across tau epitopes. The only microglial marker increased in FTLD-tau was CD16 (P = 0.0292) and specifically in FTLD-MAPT cases (P = 0.0150). However, several associations were detected between pTau epitopes and microglia, supporting an interplay between them. GFAP expression was increased in FTLD-tau (P = 0.0345) with the highest expression in Pick's disease (P = 0.0019), while ALDH1L1 was unchanged. Markers of astrocyte glutamate cycling function were reduced in FTLD-tau (P = 0.0075; Pick's disease: P < 0.0400) implying astrocyte reactivity associated with a decreased glutamate cycling activity, which was further associated with pTau expression. Of the inflammatory proteins assessed in the brain, five chemokines were upregulated in Pick's disease cases (P < 0.0400), consistent with the recruitment of CD4+ (P = 0.0109) and CD8+ (P = 0.0014) T cells. Of note, the CD8+ T cell infiltration was associated with pTau epitopes and microglial and astrocytic markers. Our results highlight that FTLD-tau is associated with astrocyte reactivity, remarkably little activation of microglia, but involvement of adaptive immunity in the form of chemokine-driven recruitment of T lymphocytes.

Pick's disease presenting with corticobasal syndrome: A case report and clinicopathological review

Pick's disease (PiD) is a rare form of frontal temporal lobar degeneration. The pathognomonic feature is atrophy of the frontotemporal lobes and intraneuronal deposits of 3R-τ inclusions, the Pick body. Corticobasal syndrome (CBS) is an atypical parkinsonian syndrome with a heterogeneous spectrum of underlying pathologies. We report a case of clinically diagnosed CBS with a post-mortem diagnosis of PiD and conduct a clinicopathological review of the literature on this unusual presentation.

Frontotemporal dementia: Past, present, and future

INTRODUCTION

The history of frontotemporal dementia (FTD) is both old and new. This study explores its historical roots, dating back to the 19th century, while recognizes it as a distinct neurological entity only a few decades ago.

METHODS

This qualitative study and literature review provides an overview of FTD's historical background, birth, evolution, and future directions.

RESULTS

Recognition of FTD was hindered by rigid perceptions of dementia, the division between neurology and psychiatry, reliance on IQ-based assessment, limited neuroimaging capabilities, and lack of pathological proof. Overcoming these barriers involved revisiting early pioneers' approaches, focusing on focal impairment, establishing non-Alzheimer's disease cohorts, fostering collaboration, and developing diagnostic criteria. Current gaps include the need for biology-oriented psychiatry education, biological biomarkers, and culturally sensitive, objective clinical instruments predicting underlying pathology.

DISCUSSION

Independent multidisciplinary centers are essential. The future of FTD lies in disease-modifying therapies, presenting new opportunities for healthcare professionals and researchers.

Anti-tau antibodies targeting a conformation-dependent epitope selectively bind seeds

Neurodegenerative tauopathies are caused by the transition of tau protein from a monomer to a toxic aggregate. They include Alzheimer disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick disease (PiD). We have previously proposed that tau monomer exists in two conformational ensembles: an inert form (Mi), which does not self-assemble, and seed-competent form (Ms), which self-assembles and templates ordered assembly growth. We proposed that cis/trans isomerization of tau at P301, the site of dominant disease-associated S/L missense mutations, might underlie the transition of wild-type tau to a seed-competent state. Consequently, we created monoclonal antibodies using non-natural antigens consisting of fluorinated proline (P∗) at the analogous P270 in repeat 1 (R1), biased toward the trans-configuration at either the R1/R2 (TENLKHQP∗GGGKVQIINKK) or the R1/R3 (TENLKHQP∗GGGKVQIVYK) interfaces. Two antibodies, MD2.2 and MD3.1, efficiently immunoprecipitated soluble seeds from AD and PSP but not CBD or PiD brain samples. The antibodies efficiently stained brain samples of AD, PSP, and PiD, but not CBD. They did not immunoprecipitate or immunostain tau from the control brain. Creation of potent anti-seed antibodies based on the trans-proline epitope implicates local unfolding around P301 in pathogenesis. MD2.2 and MD3.1 may also be useful for therapy and diagnosis.

Modelling TDP-43 proteinopathy in Drosophila uncovers shared and neuron-specific targets across ALS and FTD relevant circuits

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) comprise a spectrum of neurodegenerative diseases linked to TDP-43 proteinopathy, which at the cellular level, is characterized by loss of nuclear TDP-43 and accumulation of cytoplasmic TDP-43 inclusions that ultimately cause RNA processing defects including dysregulation of splicing, mRNA transport and translation. Complementing our previous work in motor neurons, here we report a novel model of TDP-43 proteinopathy based on overexpression of TDP-43 in a subset of Drosophila Kenyon cells of the mushroom body (MB), a circuit with structural characteristics reminiscent of vertebrate cortical networks. This model recapitulates several aspects of dementia-relevant pathological features including age-dependent neuronal loss, nuclear depletion and cytoplasmic accumulation of TDP-43, and behavioral deficits in working memory and sleep that occur prior to axonal degeneration. RNA immunoprecipitations identify several candidate mRNA targets of TDP-43 in MBs, some of which are unique to the MB circuit and others that are shared with motor neurons. Among the latter is the glypican Dally-like-protein (Dlp), which exhibits significant TDP-43 associated reduction in expression during aging. Using genetic interactions we show that overexpression of Dlp in MBs mitigates TDP-43 dependent working memory deficits, conistent with Dlp acting as a mediator of TDP-43 toxicity. Substantiating our findings in the fly model, we find that the expression of GPC6 mRNA, a human ortholog of dlp, is specifically altered in neurons exhibiting the molecular signature of TDP-43 pathology in FTD patient brains. These findings suggest that circuit-specific Drosophila models provide a platform for uncovering shared or disease-specific molecular mechanisms and vulnerabilities across the spectrum of TDP-43 proteinopathies.

The Spectrum of Cognitive Dysfunction in Amyotrophic Lateral Sclerosis: An Update

Cognitive dysfunction is an important non-motor symptom in amyotrophic lateral sclerosis (ALS) that has a negative impact on survival and caregiver burden. It shows a wide spectrum ranging from subjective cognitive decline to frontotemporal dementia (FTD) and covers various cognitive domains, mainly executive/attention, language and verbal memory deficits. The frequency of cognitive impairment across the different ALS phenotypes ranges from 30% to 75%, with up to 45% fulfilling the criteria of FTD. Significant genetic, clinical, and pathological heterogeneity reflects deficits in various cognitive domains. Modern neuroimaging studies revealed frontotemporal degeneration and widespread involvement of limbic and white matter systems, with hypometabolism of the relevant areas. Morphological substrates are frontotemporal and hippocampal atrophy with synaptic loss, associated with TDP-43 and other co-pathologies, including tau deposition. Widespread functional disruptions of motor and extramotor networks, as well as of frontoparietal, frontostriatal and other connectivities, are markers for cognitive deficits in ALS. Cognitive reserve may moderate the effect of brain damage but is not protective against cognitive decline. The natural history of cognitive dysfunction in ALS and its relationship to FTD are not fully understood, although there is an overlap between the ALS variants and ALS-related frontotemporal syndromes, suggesting a differential vulnerability of motor and non-motor networks. An assessment of risks or the early detection of brain connectivity signatures before structural changes may be helpful in investigating the pathophysiological mechanisms of cognitive impairment in ALS, which might even serve as novel targets for effective disease-modifying therapies.

A heterozygous splicing variant IVS9-7A > T in intron 9 of the MAPT gene in a patient with right-temporal variant frontotemporal dementia with atypical 4 repeat tauopathy

Right temporal variant frontotemporal dementia, also called right-predominant semantic dementia, often has an unclear position within the framework of the updated diagnostic criteria for behavioral variant frontotemporal dementia or primary progressive aphasia. Recent studies have suggested that this population may be clinically, neuropathologically, and genetically distinct from those with behavioral variant frontotemporal dementia or left-predominant typical semantic variant primary progressive aphasia. Here we describe a Japanese case of right temporal variant frontotemporal dementia with novel heterozygous MAPT mutation Adenine to Thymidine in intervening sequence (IVS) 9 at position -7 from 3' splicing site of intron 9/exon 10 boundary (MAPT IVS9-7A > T). Postmortem neuropathological analysis revealed a predominant accumulation of 4 repeat tau, especially in the temporal lobe, amygdala, and substantia nigra, but lacked astrocytic plaques or tufted astrocytes. Immunoelectron microscopy of the tau filaments extracted from the brain revealed a ribbon-like structure. Moreover, a cellular MAPT splicing assay confirmed that this novel variant promoted the inclusion of exon 10, resulting in the predominant production of 4 repeat tau. These data strongly suggest that the MAPT IVS9-7 A > T variant found in our case is a novel mutation that stimulates the inclusion of exon 10 through alternative splicing of MAPT transcript and causes predominant 4 repeat tauopathy which clinically presents as right temporal variant frontotemporal dementia.

Cerebral atrophy as a cause of aphasia: From Pick to the modern era

In his epoch-making monograph, Wernicke (1874) claimed that atrophy of the brain cannot cause aphasia. Refuting this claim, Pick (1892, 1898, 1901, 1904a) documented in increasing detail several cases of aphasia with circumscribed atrophy of the left temporal lobe, frontal lobe, or both, which persuaded Wernicke (1906). To explain why the atrophy is circumscribed and leads to focal symptoms, Pick (1908a) advanced a functional network account. Behavioral, neuroanatomical, and histopathological studies by Dejerine and Sérieux, Fischer, Alzheimer, Altman, Gans, Onari and Spatz, and Stertz further illuminated the clinical syndromes, the exact spatial distributions of the atrophy, the underlying disease, and its laminar specificity. Unaware of these seminal studies, research from the 1970s until now has independently rediscovered all key findings, and also supports Pick's forgotten functional account of the distribution of atrophy and the focal symptoms. His frontal and temporal forms of aphasia foreshadowed what are now called the nonfluent/agrammatic and semantic variants of primary progressive aphasia. Moreover, aphasic symptoms may occur with frontal degeneration (what used to be called "Pick's disease") that yields personality changes and behavioral disturbances, now called the behavioral variant of frontotemporal dementia.

Diagnosis of Alzheimer Disease and Tauopathies on Whole-Slide Histopathology Images Using a Weakly Supervised Deep Learning Algorithm

Neuropathologic assessment during autopsy is the gold standard for diagnosing neurodegenerative disorders. Neurodegenerative conditions, such as Alzheimer disease (AD) neuropathological change, are a continuous process from normal aging rather than categorical; therefore, diagnosing neurodegenerative disorders is a complicated task. We aimed to develop a pipeline for diagnosing AD and other tauopathies, including corticobasal degeneration (CBD), globular glial tauopathy, Pick disease, and progressive supranuclear palsy. We used a weakly supervised deep learning-based approach called clustering-constrained-attention multiple-instance learning (CLAM) on the whole-slide images (WSIs) of patients with AD (n = 30), CBD (n = 20), globular glial tauopathy (n = 10), Pick disease (n = 20), and progressive supranuclear palsy (n = 20), as well as nontauopathy controls (n = 21). Three sections (A: motor cortex; B: cingulate gyrus and superior frontal gyrus; and C: corpus striatum) that had been immunostained for phosphorylated tau were scanned and converted to WSIs. We evaluated 3 models (classic multiple-instance learning, single-attention-branch CLAM, and multiattention-branch CLAM) using 5-fold cross-validation. Attention-based interpretation analysis was performed to identify the morphologic features contributing to the classification. Within highly attended regions, we also augmented gradient-weighted class activation mapping to the model to visualize cellular-level evidence of the model's decisions. The multiattention-branch CLAM model using section B achieved the highest area under the curve (0.970 ± 0.037) and diagnostic accuracy (0.873 ± 0.087). A heatmap showed the highest attention in the gray matter of the superior frontal gyrus in patients with AD and the white matter of the cingulate gyrus in patients with CBD. Gradient-weighted class activation mapping showed the highest attention in characteristic tau lesions for each disease (eg, numerous tau-positive threads in the white matter inclusions for CBD). Our findings support the feasibility of deep learning-based approaches for the classification of neurodegenerative disorders on WSIs. Further investigation of this method, focusing on clinicopathologic correlations, is warranted.

Patients with sporadic FTLD exhibit similar increases in lysosomal proteins and storage material as patients with FTD due to GRN mutations

Loss of function progranulin (GRN) mutations are a major autosomal dominant cause of frontotemporal dementia (FTD). Patients with FTD due to GRN mutations (FTD-GRN) develop frontotemporal lobar degeneration with TDP-43 pathology type A (FTLD-TDP type A) and exhibit elevated levels of lysosomal proteins and storage material in frontal cortex, perhaps indicating lysosomal dysfunction as a mechanism of disease. To investigate whether patients with sporadic FTLD exhibit similar signs of lysosomal dysfunction, we compared lysosomal protein levels, transcript levels, and storage material in patients with FTD-GRN or sporadic FTLD-TDP type A. We analyzed samples from frontal cortex, a degenerated brain region, and occipital cortex, a relatively spared brain region. In frontal cortex, patients with sporadic FTLD-TDP type A exhibited similar increases in lysosomal protein levels, transcript levels, and storage material as patients with FTD-GRN. In occipital cortex of both patient groups, most lysosomal measures did not differ from controls. Frontal cortex from a transgenic mouse model of TDP-opathy had similar increases in cathepsin D and lysosomal storage material, showing that TDP-opathy and neurodegeneration can drive these changes independently of progranulin. To investigate these changes in additional FTLD subtypes, we analyzed frontal cortical samples from patients with sporadic FTLD-TDP type C or Pick's disease, an FTLD-tau subtype. All sporadic FTLD groups had similar increases in cathepsin D activity, lysosomal membrane proteins, and storage material as FTD-GRN patients. However, patients with FTLD-TDP type C or Pick's disease did not have similar increases in lysosomal transcripts as patients with FTD-GRN or sporadic FTLD-TDP type A. Based on these data, accumulation of lysosomal proteins and storage material may be a common aspect of end-stage FTLD. However, the unique changes in gene expression in patients with FTD-GRN or sporadic FTLD-TDP type A may indicate distinct underlying lysosomal changes among FTLD subtypes.

Thioflavin S Staining and Amyloid Formation Are Unique to Mixed Tauopathies

Tau phosphorylation, aggregation, and toxicity are the main drivers of neurodegeneration in multiple tauopathies, including Alzheimer's disease (AD) and frontotemporal lobar degeneration with tau. Although aggregation and amyloid formation are often assumed to be synonymous, the ability of tau aggregates in different diseases to form amyloids in vivo has not been systematically studied. We used the amyloid dye Thioflavin S to look at tau aggregates in mixed tauopathies such as AD and primary age-related tauopathy, as well as pure 3R or 4R tauopathies such as Pick's disease, progressive supranuclear palsy, and corticobasal degeneration. We found that aggregates of tau protein only form thioflavin-positive amyloids in mixed (3R/4R), but not pure (3R or 4R), tauopathies. Interestingly, neither astrocytic nor neuronal tau pathology was thioflavin-positive in pure tauopathies. As most current positron emission tomography tracers are based on thioflavin derivatives, this suggests that they may be more useful for differential diagnosis than the identification of a general tauopathy. Our findings also suggest that thioflavin staining may have utility as an alternative to traditional antibody staining for distinguishing between tau aggregates in patients with multiple pathologies and that the mechanisms for tau toxicity may differ between different tauopathies.

What every neuropathologist needs to know: condensed protocol work-up for clinical dementia syndromes

Concerns about the costs associated with autopsy assessment of Alzheimer disease and related dementias according to 2012 NIA-AA Guidelines have been expressed since the publication of those guidelines. For this reason, we designed and validated a Condensed Protocol for the neuropathologic diagnoses of Alzheimer disease neuropathologic change, Lewy Body disease neuropathologic change, as well as chronic microvascular lesions, hippocampal sclerosis of aging, and cerebral amyloid angiopathy. In this study, the Condensed Protocol is updated to include frontotemporal lobar degeneration [FTLD] tau (corticobasal degeneration, progressive supranuclear palsy, and Pick disease), FTLD-TDP, and limbic-predominant, age-related TDP-43 encephalopathy. The same 20 brain regions are sampled and processed in 5 tissue cassettes, which reduces reagent costs by approximately 65%. Three board-certified neuropathologists were blinded to the original Northwestern University Alzheimer's Disease Research Center Original Protocol neuropathological diagnoses and all clinical history information. The results yielded near uniform agreement with the original comprehensive Alzheimer's Disease Research Center neuropathologic assessments. Diagnostic sensitivity was not impacted. In summary, our recent results show that our updated Condensed Protocol is also an accurate and less expensive alternative to the comprehensive protocols for the additional neuropathologic diagnoses of FTLD Tau and TDP43 proteinopathies.

Longitudinal Brain Atrophy Rates in Presymptomatic Carriers of Genetic Frontotemporal Dementia

BACKGROUND AND OBJECTIVES

It is important to identify at what age brain atrophy rates in genetic frontotemporal dementia (FTD) start to accelerate and deviate from normal aging effects to find the optimal starting point for treatment. We investigated longitudinal brain atrophy rates in the presymptomatic stage of genetic FTD using normative brain volumetry software.

METHODS

Presymptomatic GRN, MAPT, and C9orf72 pathogenic variant carriers underwent longitudinal volumetric T1-weighted magnetic resonance imaging of the brain as part of a prospective cohort study. Images were automatically analyzed with Quantib® ND, which consisted of volume measurements (CSF and sum of gray and white matter) of lobes, cerebellum, and hippocampus. All volumes were compared with reference centile curves based on a large population-derived sample of nondemented individuals (n = 4,951). Mixed-effects models were fitted to analyze atrophy rates of the different gene groups as a function of age.

RESULTS

Thirty-four GRN, 8 MAPT, and 14 C9orf72 pathogenic variant carriers were included (mean age = 52.1, standard deviation = 7.2; 66% female). The mean follow-up duration of the study was 64 ± 33 months (median = 52; range 13-108). GRN pathogenic variant carriers showed a faster decline than the reference centile curves for all brain areas, though relative volumes remained between the 5th and 75th percentiles between the ages of 45 and 70 years. In MAPT pathogenic variant carriers, frontal lobe volume was already at the 5th percentile at age 45 years and showed a further decline between the ages 50 and 60 years. Temporal lobe volume started in the 50th percentile at age 45 years but showed fastest decline over time compared with other brain structures. Frontal, temporal, parietal, and cerebellar volume already started below the 5th percentile compared with the reference centile curves at age 45 years for C9orf72 pathogenic variant carriers, but there was minimal decline over time until the age of 60 years.

DISCUSSION

We provide evidence for longitudinal brain atrophy in the presymptomatic stage of genetic FTD. The affected brain areas and the age after which atrophy rates start to accelerate and diverge from normal aging slopes differed between gene groups. These results highlight the value of normative volumetry software for disease tracking and staging biomarkers in genetic FTD. These techniques could help in identifying the optimal time window for starting treatment and monitoring treatment response.

Finding Common Ground on the Site of Onset of Amyotrophic Lateral Sclerosis

The fundamental origin of amyotrophic lateral sclerosis (ALS) has remained an enigma since its earliest description as a relentlessly progressive degeneration with prominent neuromuscular manifestations that are associated with upper and lower motor neuron dysfunction. Although this remains the hallmark of ALS, a significant proportion of patients will also demonstrate one or more features of frontotemporal dysfunction, including a frontotemporal dementia (FTD). Understanding whether these 2 seemingly disparate syndromes are simply reflective of the co-occurrence of 2 distinct pathologic processes or the clinical manifestations of a common pathophysiologic derangement involving the brain more widely has gripped contemporary ALS researchers. Supporting a commonality of causation, both ALS and FTD show an alteration in the metabolism of TAR DNA-binding protein 43, marked by a shift in nucleocytoplasmic localization alongside a broad range of neuronal cytoplasmic inclusions consisting of pathologic aggregates of RNA-binding proteins. Similarly, several disease-associated or disease-modifying genetic variants that are shared between the 2 disorders suggest shared underlying mechanisms. In both, a prominent glial response has been postulated to contribute to non-cell-autonomous spread. A more contemporary hypothesis, however, suggests that syndromes of cortical and subcortical dysfunction are driven by impairments in discrete neural networks. This postulates that such networks, including networks subserving motor or cognitive function, possess unique and selective vulnerabilities to either single molecular toxicities or combinations thereof. The co-occurrence of one or more network dysfunctions in ALS and FTD is thus a reflection not of unique neuroanatomic correlates but rather of shared molecular vulnerabilities. The basis of such shared vulnerabilities becomes the fulcrum around which the next advances in our understanding of ALS and its possible therapy will develop.

Dissecting the Many Faces of Frontotemporal Dementia: An Imaging Perspective

Frontotemporal dementia (FTD) is a heterogeneous clinical and neuropathological disorder characterized by behavioral abnormalities, executive dysfunctions and language deficits. FTD encompasses a wide range of different pathological entities, associated with the accumulation of proteins, such as tau and TPD-43. A family history of dementia is found in one third of cases, and several genes causing autosomal dominant inherited disease have been identified. The clinical symptoms are preceded by a prodromal phase, which has been mainly studied in cases carrying pathogenetic mutations. New experimental strategies are emerging, in both prodromal and clinical settings, and outcome markers are needed to test their efficacy. In this complex context, in the last few years, advanced neuroimaging techniques have allowed a better characterization of FTD, supporting clinical diagnosis, improving the comprehension of genetic heterogeneity and the earliest stages of the disease, contributing to a more detailed classification of underlying proteinopathies, and developing new outcome markers on clinical grounds. In this review, we briefly discuss the contribution of brain imaging and the most recent techniques in deciphering the different aspects of FTD.

Sensitivity of the Social Behavior Observer Checklist to Early Symptoms of Patients With Frontotemporal Dementia

BACKGROUND AND OBJECTIVES

Changes in social behavior are common symptoms of frontotemporal lobar degeneration (FTLD) and Alzheimer disease syndromes. For early identification of individual patients and differential diagnosis, sensitive clinical measures are required that are able to assess patterns of behaviors and detect syndromic differences in both asymptomatic and symptomatic stages. We investigated whether the examiner-based Social Behavior Observer Checklist (SBOCL) is sensitive to early behavior changes and reflects disease severity within and between neurodegenerative syndromes.

METHODS

Asymptomatic individuals and patients with neurodegenerative disease were selected from the multisite ALLFTD cohort study. In a sample of participants with at least 1 time point of SBOCL data, we investigated whether the Disorganized, Reactive, and Insensitive subscales of the SBOCL change as a function of disease stage within and between these syndromes. In a longitudinal subsample with both SBOCL and neuroimaging data, we examined whether change over time on each subscale corresponds to progressive gray matter atrophy.

RESULTS

A total of 1,082 FTLD pathogenic variant carriers and noncarriers were enrolled (282 asymptomatic, 341 behavioral variant frontotemporal dementia, 114 semantic and 95 nonfluent variant primary progressive aphasia, 137 progressive supranuclear palsy, and 113 Alzheimer disease syndrome). The Disorganized score increased between asymptomatic to very mild (p = 0.016, estimate = -1.10, 95% CI = -1.99 to -0.22), very mild to mild (p = 0.013, estimate = -1.17, 95% CI = -2.08 to -0.26), and mild to moderate/severe (p < 0.001, estimate = -2.00, 95% CI = -2.55 to -1.45) disease stages in behavioral variant frontotemporal dementia regardless of pathogenic variant status. Asymptomatic GRN pathogenic gene variant carriers showed more reactive behaviors (preoccupation with time: p = 0.001, estimate = 1.11, 95% CI = 1.06 to 1.16; self-consciousness: p = 0.003, estimate = 1.77, 95% CI = 1.52 to 2.01) than asymptomatic noncarriers (estimate = 1.01, 95% CI = 0.98 to 1.03; estimate = 1.31, 95% CI = 1.20 to 1.41). The Insensitive score increased to a clinically abnormal level in advanced stages of behavioral variant frontotemporal dementia (p = 0.003, estimate = -0.73, 95% CI = -1.18 to -0.29). Higher scores on each subscale corresponded with higher caregiver burden (p < 0.001). Greater change over time corresponded to greater fronto-subcortical atrophy in the semantic-appraisal and fronto-parietal intrinsically connected networks.

DISCUSSION

The SBOCL is sensitive to early symptoms and reflects disease severity, with some evidence for progression across asymptomatic and symptomatic stages of FTLD syndromes; thus, it may hold promise for early measurement and monitoring of behavioral symptoms in clinical practice and treatment trials.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that the SBOCL is sensitive to early behavioral changes in FTLD pathogenic variants and early symptomatic individuals in a highly educated patient cohort.

Clinical, radiologic, and pathologic features of the globular glial tauopathy subtype of frontotemporal lobar degeneration in right temporal variant frontotemporal dementia with salient features of Geschwind syndrome

Globular Glial Tauopathy (GGT) is a rare form of Frontotemporal Lobar Degeneration (FTLD) consisting of 4-repeat tau globular inclusions in astrocytes and oligodendrocytes. We present the pathological findings of GGT in a previously published case of a 73-year-old woman with behavioral symptoms concerning for right temporal variant frontotemporal dementia with initial and salient features of Geschwind syndrome. Clinically, she lacked motor abnormalities otherwise common in previously published GGT cases. Brain MRI showed focal right anterior temporal atrophy (indistinguishable from five FTLD-TDP cases) and subtle ipsilateral white matter signal abnormalities. Brain autopsy showed GGT type III and Alzheimer's neuropathologic changes. .

Structural brain splitting is a hallmark of Granulin-related frontotemporal dementia

Frontotemporal dementia associated with granulin (GRN) mutations presents asymmetric brain atrophy. We applied a Minimum Spanning Tree plus an Efficiency Cost Optimization approach to cortical thickness data in order to test whether graph theory measures could identify global or local impairment of connectivity in the presymptomatic phase of pathology, where other techniques failed in demonstrating changes. We included 52 symptomatic GRN mutation carriers (SC), 161 presymptomatic GRN mutation carriers (PSC) and 341 non-carriers relatives from the Genetic Frontotemporal dementia research Initiative cohort. Group differences of global, nodal and edge connectivity in (Minimum Spanning Tree plus an Efficiency Cost Optimization) graph were tested via Structural Equation Models. Global graph perturbation was selectively impaired in SC compared to non-carriers, with no changes in PSC. At the local level, only SC exhibited perturbation of frontotemporal nodes, but edge connectivity revealed a characteristic pattern of interhemispheric disconnection, involving homologous parietal regions, in PSC. Our results suggest that GRN-related frontotemporal dementia resembles a disconnection syndrome, with interhemispheric disconnection between parietal regions in presymptomatic phases that progresses to frontotemporal areas as symptoms emerge.

Downstream effects of polypathology on neurodegeneration of medial temporal lobe subregions

The medial temporal lobe (MTL) is a nidus for neurodegenerative pathologies and therefore an important region in which to study polypathology. We investigated associations between neurodegenerative pathologies and the thickness of different MTL subregions measured using high-resolution post-mortem MRI. Tau, TAR DNA-binding protein 43 (TDP-43), amyloid-β and α-synuclein pathology were rated on a scale of 0 (absent)-3 (severe) in the hippocampus and entorhinal cortex (ERC) of 58 individuals with and without neurodegenerative diseases (median age 75.0 years, 60.3% male). Thickness measurements in ERC, Brodmann Area (BA) 35 and 36, parahippocampal cortex, subiculum, cornu ammonis (CA)1 and the stratum radiatum lacunosum moleculare (SRLM) were derived from 0.2 × 0.2 × 0.2 mm3 post-mortem MRI scans of excised MTL specimens from the contralateral hemisphere using a semi-automated approach. Spearman's rank correlations were performed between neurodegenerative pathologies and thickness, correcting for age, sex and hemisphere, including all four proteinopathies in the model. We found significant associations of (1) TDP-43 with thickness in all subregions (r =  - 0.27 to r =  - 0.46), and (2) tau with BA35 (r =  - 0.31) and SRLM thickness (r =  - 0.33). In amyloid-β and TDP-43 negative cases, we found strong significant associations of tau with ERC (r =  - 0.40), BA35 (r =  - 0.55), subiculum (r =  - 0.42) and CA1 thickness (r =  - 0.47). This unique dataset shows widespread MTL atrophy in relation to TDP-43 pathology and atrophy in regions affected early in Braak stageing and tau pathology. Moreover, the strong association of tau with thickness in early Braak regions in the absence of amyloid-β suggests a role of Primary Age-Related Tauopathy in neurodegeneration.

The AD tau core spontaneously self-assembles and recruits full-length tau to filaments

Tau accumulation is a major pathological hallmark of Alzheimer's disease (AD) and other tauopathies, but the mechanism(s) of tau aggregation remains unclear. Taking advantage of the identification of tau filament cores by cryoelectron microscopy, we demonstrate that the AD tau core possesses the intrinsic ability to spontaneously aggregate in the absence of an inducer, with antibodies generated against AD tau core filaments detecting AD tau pathology. The AD tau core also drives aggregation of full-length wild-type tau, increases seeding potential, and templates abnormal forms of tau present in brain homogenates and antemortem cerebrospinal fluid (CSF) from patients with AD in an ultrasensitive real-time quaking-induced conversion (QuIC) assay. Finally, we show that the filament cores in corticobasal degeneration (CBD) and Pick's disease (PiD) similarly assemble into filaments under physiological conditions. These results document an approach to modeling tau aggregation and have significant implications for in vivo investigation of tau transmission and biomarker development.

Diagnostic Accuracy of Amyloid versus 18 F-Fluorodeoxyglucose Positron Emission Tomography in Autopsy-Confirmed Dementia

OBJECTIVE

The purpose of this study was to compare the diagnostic accuracy of antemortem 11 C-Pittsburgh compound B (PIB) and 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET) versus autopsy diagnosis in a heterogenous sample of patients.

METHODS

One hundred one participants underwent PIB and FDG PET during life and neuropathological assessment. PET scans were visually interpreted by 3 raters blinded to clinical information. PIB PET was rated as positive or negative for cortical retention, whereas FDG scans were read as showing an Alzheimer disease (AD) or non-AD pattern. Neuropathological diagnoses were assigned using research criteria. Majority visual reads were compared to intermediate-high AD neuropathological change (ADNC).

RESULTS

One hundred one participants were included (mean age = 67.2 years, 41 females, Mini-Mental State Examination = 21.9, PET-to-autopsy interval = 4.4 years). At autopsy, 32 patients showed primary AD, 56 showed non-AD neuropathology (primarily frontotemporal lobar degeneration [FTLD]), and 13 showed mixed AD/FTLD pathology. PIB showed higher sensitivity than FDG for detecting intermediate-high ADNC (96%, 95% confidence interval [CI] = 89-100% vs 80%, 95% CI = 68-92%, p = 0.02), but equivalent specificity (86%, 95% CI = 76-95% vs 84%, 95% CI = 74-93%, p = 0.80). In patients with congruent PIB and FDG reads (77/101), combined sensitivity was 97% (95% CI = 92-100%) and specificity was 98% (95% CI = 93-100%). Nine of 24 patients with incongruent reads were found to have co-occurrence of AD and non-AD pathologies.

INTERPRETATION

In our sample enriched for younger onset cognitive impairment, PIB-PET had higher sensitivity than FDG-PET for intermediate-high ADNC, with similar specificity. When both modalities are congruent, sensitivity and specificity approach 100%, whereas mixed pathology should be considered when PIB and FDG are incongruent. ANN NEUROL 2021;89:389-401.

Clusterin ameliorates tau pathology in vivo by inhibiting fibril formation

The molecular chaperone Clusterin (CLU) impacts the amyloid pathway in Alzheimer's disease (AD) but its role in tau pathology is unknown. We observed CLU co-localization with tau aggregates in AD and primary tauopathies and CLU levels were upregulated in response to tau accumulation. To further elucidate the effect of CLU on tau pathology, we utilized a gene delivery approach in CLU knock-out (CLU KO) mice to drive expression of tau bearing the P301L mutation. We found that loss of CLU was associated with exacerbated tau pathology and anxiety-like behaviors in our mouse model of tauopathy. Additionally, we found that CLU dramatically inhibited tau fibrilization using an in vitro assay. Together, these results demonstrate that CLU plays a major role in both amyloid and tau pathologies in AD.

Hoarding and obsessive-compulsive behaviours in frontotemporal dementia: Clinical and neuroanatomic associations

BACKGROUND

Hoarding and obsessive-compulsive behaviours (OCB) are well documented symptoms in frontotemporal dementia (FTD). While contemporary models consider hoarding and obsessive-compulsive disorder distinct, the related behaviours have not been separately examined in patients with FTD, and the neuroanatomical correlates of hoarding in patients with FTD have not been previously examined (American Psychiatric Association, 2013; Grisham and Baldwin, 2015; Mataix-Cols et al., 2010).

METHODS

Patients with FTD who were evaluated between 2004 and 2018 at our centre were included. Cortical thickness and subcortical volumetric analyses were completed on available T1 high resolution anatomic scans using FreeSurfer.

RESULTS

Eighty-seven patients met inclusion criteria, and 49 had scans available for quantitative MRI volumetric analysis. New hoarding behaviours were present in 29% of patients and were more common in the semantic variant subtype of FTD, while 49% of individuals had new or increased OCB. Hoarding behaviours were associated with decreased thickness in a factor comprised of left temporal, insular and anterior cingulate cortices. The presence of OCB was predicted by reduced cortical thickness and volumes in a factor comprised of the anterior cingulate and subcortical volumes in the bilateral amygdala and hippocampus. OCB were associated with greater right temporal cortical thickness in comparison to patients with hoarding.

DISCUSSION

The association of the semantic variant with hoarding, together with the observed associations between left temporal atrophy and hoarding indicate that degeneration of the left temporal lobe has a role in the emergence of hoarding in FTD. As in current models of Hoarding disorder and Obsessive-Compulsive disorder, our results suggest that in patients with FTD, hoarding and OCB are clinically and anatomically partially dissociable phenomenon. The results may also help to further elucidate the cognitive processes and neural networks contributing to Hoarding disorder and Obsessive-Compulsive disorder in persons without dementia.

Preferential tau aggregation in von Economo neurons and fork cells in frontotemporal lobar degeneration with specific MAPT variants

Tau aggregation is a hallmark feature in a subset of patients with frontotemporal dementia (FTD). Early and selective loss of von Economo neurons (VENs) and fork cells within the frontoinsular (FI) and anterior cingulate cortices (ACC) is observed in patients with sporadic behavioral variant FTD (bvFTD) due to frontotemporal lobar degeneration (FTLD), including FTLD with tau inclusions (FTLD-tau). Recently, we further showed that these specialized neurons show preferential aggregation of TDP-43 in FTLD-TDP. Whether VENs and fork cells are prone to tau accumulation in FTLD-tau remains unclear, and no previous studies of these neurons have focused on patients with pathogenic variants in the gene encoding microtubule-associated protein tau (FTLD-tau/MAPT). Here, we examined regional profiles of tau aggregation and neurodegeneration in 40 brain regions in 8 patients with FTLD-tau/MAPT and 7 with Pick's disease (PiD), a sporadic form of FTLD-tau that often presents with bvFTD. We further qualitatively assessed the cellular patterns of frontoinsular tau aggregation in FTLD-tau/MAPT using antibodies specific for tau hyperphosphorylation, acetylation, or conformational change. ACC and mid-insula were among the regions most affected by neurodegeneration and tau aggregation in FTLD-tau/MAPT and PiD. In these two forms of FTLD-tau, severity of regional neurodegeneration and tau protein aggregation were highly correlated across regions. In FTLD-tau/MAPT, VENs and fork cells showed disproportionate tau protein aggregation in patients with V337 M, A152T, and IVS10 + 16 variants, but not in patients with the P301L variant. As seen in FTLD-TDP, our data suggest that VENs and fork cells represent preferentially vulnerable neuron types in most, but not all of the MAPT variants we studied.

Astrocytic ceramide as possible indicator of neuroinflammation

BACKGROUND

Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease dementia (PDD), and frontotemporal lobar dementia (FTLD) are characterized by progressive neuronal loss but differ in their underlying pathological mechanisms. However, neuroinflammation is commonly observed within these different forms of dementia. Recently, it has been suggested that an altered sphingolipid metabolism may contribute to the pathogenesis of a variety of neurodegenerative conditions. Especially ceramide, the precursor of all complex sphingolipids, is thought to be associated with pro-apoptotic cellular processes, thereby propagating neurodegeneration and neuroinflammation, although it remains unclear to what extent. The current pathological study therefore investigates whether increased levels of ceramide are associated with the degree of neuroinflammation in various neurodegenerative disorders.

METHODS

Immunohistochemistry was performed on human post-mortem tissue of PDD and FTLD Pick's disease cases, which are well-characterized cases of dementia subtypes differing in their neuroinflammatory status, to assess the expression and localization of ceramide, acid sphingomyelinase, and ceramide synthase 2 and 5. In addition, we determined the concentration of sphingosine, sphingosine-1-phosphate (S1P), and ceramide species differing in their chain-length in brain homogenates of the post-mortem tissue using HPLC-MS/MS.

RESULTS

Our immunohistochemical analysis reveals that neuroinflammation is associated with increased ceramide levels in astrocytes in FTLD Pick's disease. Moreover, the observed increase in ceramide in astrocytes correlates with the expression of ceramide synthase 5. In addition, HPLC-MS/MS analysis shows a shift in ceramide species under neuroinflammatory conditions, favoring pro-apoptotic ceramide.

CONCLUSIONS

Together, these findings suggest that detected increased levels of pro-apoptotic ceramide might be a common denominator of neuroinflammation in different neurodegenerative diseases.

Neurons selectively targeted in frontotemporal dementia reveal early stage TDP-43 pathobiology

TAR DNA-binding protein 43 (TDP-43) aggregation is the most common pathological hallmark in frontotemporal dementia (FTD) and characterizes nearly all patients with motor neuron disease (MND). The earliest stages of TDP-43 pathobiology are not well-characterized, and whether neurodegeneration results from TDP-43 loss-of-function or aggregation remains unclear. In the behavioral variant of FTD (bvFTD), patients undergo selective dropout of von Economo neurons (VENs) and fork cells within the frontoinsular (FI) and anterior cingulate cortices. Here, we examined TDP-43 pathobiology within these vulnerable neurons in the FI across a clinical spectrum including 17 patients with sporadic bvFTD, MND, or both. In an exploratory analysis based on our initial observations, we further assessed ten patients with C9orf72-associated bvFTD/MND. VENs and fork cells showed early, disproportionate TDP-43 aggregation that correlated with anatomical and clinical severity, including loss of emotional empathy. The presence of a TDP-43 inclusion was associated with striking nuclear and somatodendritic atrophy. An intriguing minority of neurons lacked detectable nuclear TDP-43 despite the apparent absence of a cytoplasmic TDP-43 inclusion. These cells showed neuronal atrophy comparable to inclusion-bearing neurons, suggesting that the loss of nuclear TDP-43 function promotes neurodegeneration, even when TDP-43 aggregation is inconspicuous or absent.

Structures of filaments from Pick's disease reveal a novel tau protein fold

The ordered assembly of tau protein into abnormal filamentous inclusions underlies many human neurodegenerative diseases1. Tau assemblies seem to spread through specific neural networks in each disease2, with short filaments having the greatest seeding activity3. The abundance of tau inclusions strongly correlates with disease symptoms4. Six tau isoforms are expressed in the normal adult human brain-three isoforms with four microtubule-binding repeats each (4R tau) and three isoforms that lack the second repeat (3R tau)1. In various diseases, tau filaments can be composed of either 3R or 4R tau, or of both. Tau filaments have distinct cellular and neuroanatomical distributions5, with morphological and biochemical differences suggesting that they may be able to adopt disease-specific molecular conformations6,7. Such conformers may give rise to different neuropathological phenotypes8,9, reminiscent of prion strains10. However, the underlying structures are not known. Using electron cryo-microscopy, we recently reported the structures of tau filaments from patients with Alzheimer's disease, which contain both 3R and 4R tau11. Here we determine the structures of tau filaments from patients with Pick's disease, a neurodegenerative disorder characterized by frontotemporal dementia. The filaments consist of residues Lys254-Phe378 of 3R tau, which are folded differently from the tau filaments in Alzheimer's disease, establishing the existence of conformers of assembled tau. The observed tau fold in the filaments of patients with Pick's disease explains the selective incorporation of 3R tau in Pick bodies, and the differences in phosphorylation relative to the tau filaments of Alzheimer's disease. Our findings show how tau can adopt distinct folds in the human brain in different diseases, an essential step for understanding the formation and propagation of molecular conformers.

Neurodegenerative disease concomitant proteinopathies are prevalent, age-related and APOE4-associated

Lewy bodies commonly occur in Alzheimer's disease, and Alzheimer's disease pathology is frequent in Lewy body diseases, but the burden of co-pathologies across neurodegenerative diseases is unknown. We assessed the extent of tau, amyloid-β, α-synuclein and TDP-43 proteinopathies in 766 autopsied individuals representing a broad spectrum of clinical neurodegenerative disease. We interrogated pathological Alzheimer's disease (n = 247); other tauopathies (n = 95) including Pick's disease, corticobasal disease and progressive supranuclear palsy; the synucleinopathies (n = 164) including multiple system atrophy and Lewy body disease; the TDP-43 proteinopathies (n = 188) including frontotemporal lobar degeneration with TDP-43 inclusions and amyotrophic lateral sclerosis; and a minimal pathology group (n = 72). Each group was divided into subgroups without or with co-pathologies. Age and sex matched logistic regression models compared co-pathology prevalence between groups. Co-pathology prevalence was similar between the minimal pathology group and most neurodegenerative diseases for each proteinopathy: tau was nearly universal (92-100%), amyloid-β common (20-57%); α-synuclein less common (4-16%); and TDP-43 the rarest (0-16%). In several neurodegenerative diseases, co-pathology increased: in Alzheimer's disease, α-synuclein (41-55%) and TDP-43 (33-40%) increased; in progressive supranuclear palsy, α-synuclein increased (22%); in corticobasal disease, TDP-43 increased (24%); and in neocortical Lewy body disease, amyloid-β (80%) and TDP-43 (22%) increased. Total co-pathology prevalence varied across groups (27-68%), and was increased in high Alzheimer's disease, progressive supranuclear palsy, and neocortical Lewy body disease (70-81%). Increased age at death was observed in the minimal pathology group, amyotrophic lateral sclerosis, and multiple system atrophy cases with co-pathologies. In amyotrophic lateral sclerosis and neocortical Lewy body disease, co-pathologies associated with APOE ɛ4. Lewy body disease cases with Alzheimer's disease co-pathology had substantially lower Mini-Mental State Examination scores than pure Lewy body disease. Our data imply that increased age and APOE ɛ4 status are risk factors for co-pathologies independent of neurodegenerative disease; that neurodegenerative disease severity influences co-pathology as evidenced by the prevalence of co-pathology in high Alzheimer's disease and neocortical Lewy body disease, but not intermediate Alzheimer's disease or limbic Lewy body disease; and that tau and α-synuclein strains may also modify co-pathologies since tauopathies and synucleinopathies had differing co-pathologies and burdens. These findings have implications for clinical trials that focus on monotherapies targeting tau, amyloid-β, α-synuclein and TDP-43.

[Pick's disease]

Pick's disease is a type of frontotemporal lobar degeneration(FTLD) with circumscribed atrophy in the frontotemporal lobe. The terminology for Pick's disease has evolved over time. Pick's disease was a term formerly used to define a disorder with symptoms caused by frontal and temporal lobe dysfunction. Therefore, the diagnosis was previously based on clinical features and the distribution of brain atrophy. Pick's disease is currently defined by the presence of tau-positive Pick bodies, and thus can be diagnosed only pathologically. The clinical phenotypes of Pick's disease include behavioral variant FTD (bvFTD), progressive nonfluent aphasia (PNFA) and semantic dementia (SD).

A novel triple repeat mutant tau transgenic model that mimics aspects of pick's disease and fronto-temporal tauopathies

Tauopathies are a group of disorders leading to cognitive and behavioral impairment in the aging population. While four-repeat (4R) Tau is more abundant in corticobasal degeneration, progressive supranuclear palsy, and Alzheimer’s disease, three-repeat (3R) Tau is the most abundant splice, in Pick's disease. A number of transgenic models expressing wild-type and mutant forms of the 4R Tau have been developed. However, few models of three-repeat Tau are available. A transgenic mouse model expressing three-repeat Tau was developed bearing the mutations associated with familial forms of Pick's disease (L266V and G272V mutations). Two lines expressing high (Line 13) and low (Line 2) levels of the three-repeat mutant Tau were analyzed. By Western blot, using antibodies specific to three-repeat Tau, Line 13 expressed 5-times more Tau than Line 2. The Tau expressed by these mice was most abundant in the frontal-temporal cortex and limbic system and was phosphorylated at residues detected by the PHF-1, AT8, CP9 and CP13 antibodies. The higher-expressing mice displayed hyperactivity, memory deficits in the water maze and alterations in the round beam. The behavioral deficits started at 6-8 months of age and were associated with a progressive increase in the accumulation of 3R Tau. By immunocytochemistry, mice from Line 13 displayed extensive accumulation of 3R Tau in neuronal cells bodies in the pyramidal neurons of the neocortex, CA1-3 regions, and dentate gyrus of the hippocampus. Aggregates in the granular cells had a globus appearance and mimic Pick’s-like inclusions. There were abundant dystrophic neurites, astrogliosis and synapto-dendritic damage in the neocortex and hippocampus of the higher expresser line. The hippocampal lesions were moderately argyrophilic and Thioflavin-S negative. By electron microscopy, discrete straight filament aggregates were detected in some neurons in the hippocampus. This model holds promise for better understanding the natural history and progression of 3R tauopathies and their relationship with mitochondrial alterations and might be suitable for therapeutical testing.

Immunolocalization of an amino-terminal fragment of apolipoprotein E in the Pick's disease brain

Although the risk factor for apolipoprotein E (apoE) polymorphism in Alzheimer's disease (AD) has been well described, the role that apoE plays in other neurodegenerative diseases, including Pick's disease, is not well established. To examine a possible role of apoE in Pick's disease, an immunohistochemical analysis was performed utilizing a novel site-directed antibody that is specific for an amino-terminal fragment of apoE. Application of this antibody, termed the amino-terminal apoE cleavage fragment (nApoECF) antibody, consistently labeled Pick bodies within area CA1 of the hippocampus in 4 of the 5 cases examined. Co-localization of the nApoECF antibody with PHF-1, a general marker for Pick bodies, as well as with an antibody to caspase-cleaved tau (TauC3) was evident within the hippocampus. While staining of the nApoECF antibody was robust in area CA1, little co-localization with PHF-1 in Pick bodies within the dentate gyrus was observed. A quantitative analysis indicated that approximately 86% of the Pick bodies identified in area CA1 labeled with the nApoECF antibody. The presence of truncated apoE within Pick bodies suggests a broader role of apoE beyond AD and raises the question as to whether this protein contributes to pathogenesis associated with Pick's disease.

[Neuropathology of tauopathy]

Microtubules are key cytoskeletal elements found in all eukaryotic cells. Tau was identified as microtubule associated protein and was implicated in microtubule initiation as well as assembly. Its expression is increased expression in neurons and has a specific association with axonal microtubules. Neurodegenerative disorders associated with abundant tau inclusions are collectively described as tauopathies. Pathological inclusions in neurons and glial cells containing fibrillary aggregates of abnormally hyperphosphorylated tau protein are characteristic features of tauopathies. We outlined the pathological features of major tauopathies, including neurofibrillary tangle formation diseases, Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and argyrophilic grain disease (AGD). Disease specific isoform compositions of tau are identified in these tauopathies. Neurofibrillary tangles (NFTs) in Alzheimer's disease contain both three repeat (3R)- and four repeat (4R)-tau. Pick bodies in PiD are immunopositive for 3R-tau. In PSP NFTs, tufted astrocytes, coiled bodies and threads contain 4R-tau and in CBD, pretangles, astrocytic plaques, coiled bodies and threads also demonstrate 4R-tau. Argyrophilic grains are immunopositive for 4R-tau. Although PSP and CBD sometimes share certain pathological distribution, which makes clinical diagnosis difficult, cellular tau pathology and aggregation patterns in neurons and glia are different between the two diseases.

Behavioral variant frontotemporal dementia with corticobasal degeneration pathology: phenotypic comparison to bvFTD with Pick's disease

Patients with corticobasal degeneration (CBD) pathology present with diverse clinical syndromes also associated with other neuropathologies, including corticobasal syndrome, progressive nonfluent aphasia, and an Alzheimer's-type dementia. Some present with behavioral variant frontotemporal dementia (bvFTD), though this subtype still requires more detailed clinical characterization. All patients with CBD pathology and clinical assessment were reviewed (N = 17) and selected if they initially met criteria for bvFTD [bvFTD(CBD), N = 5]. Available bvFTD patients with Pick's [bvFTD(Pick's), N = 5] were selected as controls. Patients were also compared to healthy older controls [N = 53] on neuropsychological and neuroimaging measures. At initial presentation, bvFTD(CBD) showed few neuropsychological or motor differences from bvFTD(Pick's). Neuropsychiatrically, they were predominantly apathetic with less florid social disinhibition and eating disturbances, and were more anxious than bvFTD(Pick's) patients. Voxel-based morphometry revealed similar patterns of predominantly frontal atrophy between bvFTD groups, though overall degree of atrophy was less severe in bvFTD(CBD), who also showed comparative preservation of the frontoinsular rim, with dorsal > ventral frontal atrophy, and sparing of temporal and parietal structures relative to bvFTD(Pick's) patients. Despite a remarkable overlap between the two patient types, bvFTD patients with underlying CBD pathology show subtle clinical features that may distinguish them from patients with Pick's disease neuropathology.

Clinical and neuroanatomical signatures of tissue pathology in frontotemporal lobar degeneration

Relating clinical symptoms to neuroanatomical profiles of brain damage and ultimately to tissue pathology is a key challenge in the field of neurodegenerative disease and particularly relevant to the heterogeneous disorders that comprise the frontotemporal lobar degeneration spectrum. Here we present a retrospective analysis of clinical, neuropsychological and neuroimaging (volumetric and voxel-based morphometric) features in a pathologically ascertained cohort of 95 cases of frontotemporal lobar degeneration classified according to contemporary neuropathological criteria. Forty-eight cases (51%) had TDP-43 pathology, 42 (44%) had tau pathology and five (5%) had fused-in-sarcoma pathology. Certain relatively specific clinicopathological associations were identified. Semantic dementia was predominantly associated with TDP-43 type C pathology; frontotemporal dementia and motoneuron disease with TDP-43 type B pathology; young-onset behavioural variant frontotemporal dementia with FUS pathology; and the progressive supranuclear palsy syndrome with progressive supranuclear palsy pathology. Progressive non-fluent aphasia was most commonly associated with tau pathology. However, the most common clinical syndrome (behavioural variant frontotemporal dementia) was pathologically heterogeneous; while pathologically proven Pick's disease and corticobasal degeneration were clinically heterogeneous, and TDP-43 type A pathology was associated with similar clinical features in cases with and without progranulin mutations. Volumetric magnetic resonance imaging, voxel-based morphometry and cluster analyses of the pathological groups here suggested a neuroanatomical framework underpinning this clinical and pathological diversity. Frontotemporal lobar degeneration-associated pathologies segregated based on their cerebral atrophy profiles, according to the following scheme: asymmetric, relatively localized (predominantly temporal lobe) atrophy (TDP-43 type C); relatively symmetric, relatively localized (predominantly temporal lobe) atrophy (microtubule-associated protein tau mutations); strongly asymmetric, distributed atrophy (Pick's disease); relatively symmetric, predominantly extratemporal atrophy (corticobasal degeneration, fused-in-sarcoma pathology). TDP-43 type A pathology was associated with substantial individual variation; however, within this group progranulin mutations were associated with strongly asymmetric, distributed hemispheric atrophy. We interpret the findings in terms of emerging network models of neurodegenerative disease: the neuroanatomical specificity of particular frontotemporal lobar degeneration pathologies may depend on an interaction of disease-specific and network-specific factors.

[FTLD-U and Pick disease without Pick bodies--a clinical and pathological review]

Circumscribed cerebral lobar atrophy is observed in Pick disease with or without Pick bodies (conventional Pick disease) show circumscribed cerebral lobar atrophy. Pick disease with Pick bodies was initially termed as 3-repeat tauopathy to distinguish this disease from the conventional Pick disease. Case of Pick disease without Pick bodies formed a heterogeneous group. In all cases of Pick disease without Pick bodies, except for rare cases without any type of inclusions [dementia lacking distinctive histology (DLDH)] the presence of ubiquitinated inclusions was confirmed, which were broadly termed as frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). In Japan, the number of cases of Pick disease with Pick bodies and those with FTLD-U appears to be almost the same. The patterns of cerebral and subcortical nuclear degeneration are quite simillar in cases of Pick disease with Pick bodies and in cases of Pick disease with FLTD-U. Investigation of the motor neuron system in FTLD-U cases revealed that approximately two-third patients had mild to severe degeneration in the upper motor neural system (pyramidal tract). These cases of FTLD-U with motor neuron involvement formed an important group, namely, FTLD with motor neuron disease (FTLD-MND). Amyotrophic lateral sclerosis with dementia (ALS-D) in which degeneration of the lower motor neurons was generally prominent in comparison to the mild pyramidal tract degeneration in the case of FTLD-MND, is also a type of FTLD-MND. Thus, conventional Pick disease was further classified into Pick disease, FTLD-MND, FTLD-U (in a narrow sense), and DLDH.

[The complexes of degenerative dementias: an evolution from disease to spectrum]

INTRODUCTION

Everyone has a particular combination of risk polymorphisms and occasionally determinant mutations, related to molecular items which are pathogenetic in degenerative dementias. If we add other epigenetic factors to this, we can generate a very heterogeneous base, which explains why these diseases manifest through varied clinical and neuropathological phenotypes, distributed in <<complexes>> (groups of entities with symptomatic, neurochemical, histopathologic and proteinopathic affinities).

METHOD

A review of the current knowledge about phenotype variants of degenerative dementias has been carried out, detecting overlapping and divergent aspects between them and generating groups (complexes) which are more operative to work with, instead of using the current independent entities (diseases).

RESULTS

Besides the known Pick complex, there are sufficient data to propose the recognition of the Lewy complex, Alzheimer complex, multisystemic atrophy complex, and polyglutamine complex. Each one of them contains phenotypic variants that overlap with other complex variants, creating links between all the complexes and forming a spectrum in which almost all degenerative dementias can be included.

CONCLUSIONS

The progression of medical knowledge has made it more appropriate to locate each patient at a specific point in a complex, in the degenerative dementia spectrum, instead of diagnosing a generic disease. This change makes it recommendable to adjust the diagnostic criteria, and the therapeutic decisions should be designed individually according to their specific location in a complex. Researchers should also take into account this diversity when establishing both the criteria for selecting participants and the objectives of their therapeutic trials.

[Rivastigmine in a case of autopsy proved frontotemporal dementia (Pick's disease)]

INTRODUCTION

Cholinesterase inhibitors are useful in the treatment of behavioural and psychological symptoms in Alzheimer's disease. Their effectiveness in frontotemporal dementia has not been proved, since such a claim has only been backed by the publication of one open-label trial in which the behavioural and psychological symptoms of the patients treated with rivastigmine over a 12-month period improved significantly with respect to those belonging to a group that were given a placebo. We report a case of frontotemporal dementia, Pick's disease, which improved with rivastigmine treatment.

CASE REPORT

A 61-year-old male who presented a progressive clinical picture of behavioural disorders and executive-cognitive impairment that had begun two years earlier. Magnetic resonance imaging of the head revealed severe frontotemporal atrophy. Neuropsychological Inventory (NPI). Overall score 36/144 (6/12: anxiety, disinhibition and aberrant motor behaviour, 4/12: agitation, irritability and apathy; 3/12: sleep and eating disorders. After three months' treatment with rivastigmine, the overall score on the NPI was 10/144. This improvement remained stable over the months that followed. The patient died eight months later after developing liver cancer with metastasis. The microscopic study of the brain showed tau-positive neuronal inclusions, gliosis and neuronal loss. The inclusions were well-circumscribed Pick bodies, which were present in the frontal and temporal cortices and in the dentate gyrus of the hippocampus.

CONCLUSIONS

This case confirms the idea that treatment with cholinesterase inhibitors can be effective in the behavioural and psychological symptoms of frontotemporal dementia.

Tauopathies with parkinsonism: clinical spectrum, neuropathologic basis, biological markers, and treatment options

Tauopathies with parkinsonism represent a spectrum of disease entities unified by the pathologic accumulation of hyperphosphorylated tau protein fragments within the central nervous system. These pathologic characteristics suggest shared pathogenetic pathways and possible molecular targets for disease-modifying therapeutic interventions. Natural history studies, for instance, in progressive supranuclear palsy, frontotemporal dementia with parkinsonism linked to chromosome 17, corticobasal degeneration, and Niemann-Pick disease type C as well as in amyotrophic lateral sclerosis/Parkinson-dementia complex permit clinical characterization of the disease phenotypes and are crucial to the development and validation of biological markers for differential diagnostics and disease monitoring, for example, by use of neuroimaging or proteomic approaches. The wide pathologic and clinical spectrum of the tauopathies with parkinsonism is reviewed in this article, and perspectives on future advances in the understanding of the pathogenesis are given, together with potential therapeutic strategies.

[Clinical and biomolecular classification of the frontotemporal dementias. A review of the literature]

INTRODUCTION

The term 'frontotemporal lobar dementia' (FTLD) covers a group of neurodegenerative diseases that are very heterogeneous in their clinical expression, genetic component and histopathological features, and this has traditionally made it difficult to study and classify them. Patients usually present a progressive change in their behaviour associated with language disorders and loss of memory, which constitutes the second most important cause of dementia in persons under the age of 65. The most significant characteristic at the histopathological level is the presence of abnormal aggregates or accumulations of proteins in neurons or glial cells; their identification has, on the one hand, helped further our knowledge of the pathogenic mechanisms and, on the other hand, has allowed this type of dementia to be classified.

DEVELOPMENT AND CONCLUSIONS

In the last two decades a remarkable amount of progress has been made in our knowledge of this group of diseases, thanks to the genetic advances related to the discovery of the MAPT gene and the progranulin gene, as well as their mutations, which are responsible for a high percentage of cases of hereditary FTLD. Likewise, the development of new immunohistochemical techniques has made it possible to characterise some abnormal proteins, such as the protein TDP-43, as the main component of the neuronal inclusions in tau-negative FTLD. All this has led to a new classification of the FTLD. This work includes a thorough review of said advances and the possible clinical, histological, genetic and biomolecular correlations of the different subtypes of FTLD are also considered.