Automatic classification of AD pathology in FTD phenotypes using natural speech

INTRODUCTION

Screening for Alzheimer's disease neuropathologic change (ADNC) in individuals with atypical presentations is challenging but essential for clinical management. We trained automatic speech-based classifiers to distinguish frontotemporal dementia (FTD) patients with ADNC from those with frontotemporal lobar degeneration (FTLD).

METHODS

We trained automatic classifiers with 99 speech features from 1 minute speech samples of 179 participants (ADNC = 36, FTLD = 60, healthy controls [HC] = 89). Patients' pathology was assigned based on autopsy or cerebrospinal fluid analytes. Structural network-based magnetic resonance imaging analyses identified anatomical correlates of distinct speech features.

RESULTS

Our classifier showed 0.88 ± $ \pm $ 0.03 area under the curve (AUC) for ADNC versus FTLD and 0.93 ± $ \pm $ 0.04 AUC for patients versus HC. Noun frequency and pause rate correlated with gray matter volume loss in the limbic and salience networks, respectively.

DISCUSSION

Brief naturalistic speech samples can be used for screening FTD patients for underlying ADNC in vivo. This work supports the future development of digital assessment tools for FTD.

HIGHLIGHTS

We trained machine learning classifiers for frontotemporal dementia patients using natural speech. We grouped participants by neuropathological diagnosis (autopsy) or cerebrospinal fluid biomarkers. Classifiers well distinguished underlying pathology (Alzheimer's disease vs. frontotemporal lobar degeneration) in patients. We identified important features through an explainable artificial intelligence approach. This work lays the groundwork for a speech-based neuropathology screening tool.

Disfluency patterns in Alzheimer's disease and frontotemporal lobar degeneration

Disfluencies may reflect various mechanisms: word-finding difficulties, planning strategies, inter-individual cognitive variability, etc. In the current paper, we examined disfluency production in patients with a behavioural variant of Frontotemporal lobar degeneration (bvFTLD), compared to patients with Alzheimer's disease (AD) and healthy older adults. We showed that bvFTLD participants have lower speech rate and produce more incomplete utterances. However, those measures were not correlated with naming and fluency tasks. On the contrary, AD participants did not differ from healthy controls on disfluency production, but discourse measures were correlated with the participants' lexical-semantic impairment. This provides evidence for different causes of disfluency in AD and FTLD, and a distinct role of each disfluency phenomenon.

Atypical TDP-43 proteinopathy clinically presenting with progressive nonfluent aphasia: A case report

Progressive nonfluent aphasia (PNFA) is a form of frontotemporal lobar degeneration (FTLD) caused by tau and transactive response DNA-binding protein of 43 kDa (TDP-43) accumulation. Here we report the autopsy findings of a 64-year-old right-handed man with an atypical TDP-43 proteinopathy who presented with difficulties with speech, verbal paraphasia, and dysphagia that progressed over the 36 months prior to his death. He did not show pyramidal tract signs until his death. At autopsy, macroscopic brain examination revealed atrophy of the left dominant precentral, superior, and middle frontal gyri and discoloration of the putamen. Spongiform change and neuronal loss were severe on the cortical surfaces of the precentral, superior frontal, and middle frontal gyri and the temporal tip. Immunostaining with anti-phosphorylated TDP-43 revealed neuronal cytoplasmic inclusions and long and short dystrophic neurites in the frontal cortex, predominantly in layers II, V, and VI of the temporal tip, amygdala, and transentorhinal cortex. Immunoblot analysis of the sarkosyl-insoluble fractions showed hyperphosphorylated TDP-43 bands at 45 kDa and phosphorylated C-terminal fragments at approximately 25 kDa. The pathological distribution and immunoblot band pattern differ from the major TDP-43 subtype and therefore may represent a new FTLD-TDP phenotype.

Data stewardship in FTLD research: Investigator and research participant views

INTRODUCTION

Federal policies and guidelines have expanded the return of individual results to participants and expectations for data sharing between investigators and through repositories. Here, we report investigators' and study participants' views and experiences with data stewardship practices within frontotemporal lobal degeneration (FTLD) research, which reveal unique ethical challenges.

METHODS

Semi-structured interviews with (1) investigators conducting FTLD research that includes genetic data collection and/or analysis and (2) participants enrolled in a single site longitudinal FTLD study.

RESULTS

Analysis of the interviews identified three meta themes: perspectives on data sharing, experiences with enrollment and participation, and data management and security as mechanisms for participant protections.

DISCUSSION

This study identified a set of preliminary gaps and needs regarding data stewardship within FTLD research. The results offer initial insights on ethical challenges to data stewardship aimed at informing future guidelines and policies.

Pathology-specific patterns of cerebellar atrophy in neurodegenerative disorders

INTRODUCTION

Associations of cerebellar atrophy with specific neuropathologies in Alzheimer's disease and related dementias (ADRD) have not been systematically analyzed. This study examined cerebellar gray matter volume across major pathological subtypes of ADRD.

METHODS

Cerebellar gray matter volume was examined using voxel-based morphometry in 309 autopsy-proven ADRD cases and 80 healthy controls. ADRD subtypes included AD, mixed Lewy body disease and AD (LBD-AD), and frontotemporal lobar degeneration (FTLD). Clinical function was assessed using the Clinical Dementia Rating (CDR) scale.

RESULTS

Distinct patterns of cerebellar atrophy were observed in all ADRD subtypes. Significant cerebellar gray matter changes appeared in the early stages of most subtypes and the very early stages of AD, LBD-AD, FTLD-TDP type A, and progressive supranuclear palsy. Cortical atrophy positively predicted cerebellar atrophy across all subtypes.

DISCUSSION

Our findings establish pathology-specific profiles of cerebellar atrophy in ADRD and propose cerebellar neuroimaging as a non-invasive biomarker for differential diagnosis and disease monitoring.

HIGHLIGHTS

Cerebellar atrophy was examined in 309 patients with autopsy-proven neurodegeneration. Distinct patterns of cerebellar atrophy are found in all pathological subtypes of Alzheimer's disease and related dementias (ADRD). Cerebellar atrophy is seen in early-stage (Clinical Dementia Rating [CDR] ≤1) AD, Lewy body dementia (LBD), frontotemporal lobar degeneration with tau-positive inclusion (FTLD-tau), and FTLD-transactive response DNA binding protein (FTLD-TDP). Cortical atrophy positively predicts cerebellar atrophy across all neuropathologies.

Utility of the Japanese version of the Clinical Dementia Rating® plus National Alzheimer's Coordinating Centre Behaviour and Language Domains for sporadic cases of frontotemporal dementia in Japan

BACKGROUND

We aimed to validate the Clinical Dementia Rating (CDR®) dementia staging instrument plus the National Alzheimer's Coordinating Centre Behaviour and Language Domains (CDR® plus NACC FTLD) for use in clinical settings in Japan and in the Japanese language.

METHODS

This prospective observational study enrolled 29 patients with frontotemporal dementia (FTD) and 21 patients with Alzheimer's disease (AD) dementia from the Departments of Psychiatry at Osaka University Hospital and Asakayama General Hospital and the Brain Function Centre at Nippon Life Hospital. CDR® plus NACC FTLD, CDR®, Mini-Mental State Examination (MMSE), Western Aphasia Battery (WAB), Neuropsychiatric Inventory-plus (NPI-plus), Stereotypy Rating Inventory (SRI), and frontal behavioural symptom scores obtained from items of NPI-plus and SRI, were conducted to assess inter- and intra-rater reliability, validity, and responsiveness. We performed receiver operating characteristic (ROC) curve analysis to evaluate the discriminating power of the Behaviour/Comportment/Personality (BEHAV) and Language (LANG) domains of the CDR® plus NACC FTLD and the MEMORY domain of the CDR® in patients AD dementia and FTD.

RESULTS

The CDR® plus NACC FTLD showed good inter- and intra-rater reliabilities. In patients with FTD, the BEHAV domain of the CDR® plus NACC FTLD was significantly correlated with all clinical measures except for the SRI total score, while the LANG domain of the CDR® plus NACC FTLD was significantly correlated with the MMSE and the WAB-Aphasia quotient. In addition, the CDR® plus NACC FTLD sum of boxes significantly changed after 6 months and after 1 year. ROC curve analysis showed that the BEHAV and LANG domains of the CDR® plus NACC FTLD distinguished between patients with AD dementia and FTD better than the MEMORY domain of the CDR®.

CONCLUSIONS

This study validated the Japanese version of the CDR® plus NACC FTLD with good reliability, validity, and responsiveness.

In vivo PET classification of tau pathologies in patients with frontotemporal dementia

Frontotemporal dementia refers to a group of neurodegenerative disorders with diverse clinical and neuropathological features. In vivo neuropathological assessments of frontotemporal dementia at an individual level have hitherto not been successful. In this study, we aim to classify patients with frontotemporal dementia based on topologies of tau protein aggregates captured by PET with 18F-florzolotau (aka 18F-APN-1607 and 18F-PM-PBB3), which allows high-contrast imaging of diverse tau fibrils in Alzheimer's disease as well as in non-Alzheimer's disease tauopathies. Twenty-six patients with frontotemporal dementia, 15 with behavioural variant frontotemporal dementia and 11 with other frontotemporal dementia phenotypes, and 20 age- and sex-matched healthy controls were included in this study. They underwent PET imaging of amyloid and tau depositions with 11C-PiB and 18F-florzolotau, respectively. By combining visual and quantitative analyses of PET images, the patients with behavioural variant frontotemporal dementia were classified into the following subgroups: (i) predominant tau accumulations in frontotemporal and frontolimbic cortices resembling three-repeat tauopathies (n = 3), (ii) predominant tau accumulations in posterior cortical and subcortical structures indicative of four-repeat tauopathies (n = 4); (iii) amyloid and tau accumulations consistent with Alzheimer's disease (n = 4); and (iv) no overt amyloid and tau pathologies (n = 4). Despite these distinctions, clinical symptoms and localizations of brain atrophy did not significantly differ among the identified behavioural variant frontotemporal dementia subgroups. The patients with other frontotemporal dementia phenotypes were also classified into similar subgroups. The results suggest that PET with 18F-florzolotau potentially allows the classification of each individual with frontotemporal dementia on a neuropathological basis, which might not be possible by symptomatic and volumetric assessments.

Plasminogen activator inhibitor-1 serum levels in frontotemporal lobar degeneration

Plasminogen activator inhibitor-1 (PAI-1) impedes brain plasmin synthesis. Reduced plasmin activity facilitates cumulation of amyloid beta (Aβ) in Alzheimer's disease (AD). Since plasmin also regulates the synaptic activity, it is possible that altered PAI-1 is present in other neurodegenerative disorders. We investigated whether PAI-1 and its counter-regulatory tissue plasminogen activator (tPA) are altered in serum of patients with dementia due to frontotemporal lobar degeneration (FTLD). Thirty five FTLD patients (21 in mild cognitive impairment stage (MCI) and 14 in dementia stage) and 10 cognitively healthy controls were recruited. Serum tPA and PAI-1 protein levels were measured by anova. Correlation between biochemical and demographic data were explored by measuring Pearson correlation coefficient. Serum PAI-1 levels were elevated in the FTLD dementia group as compared to FTLD MCI and controls. tPA serum levels and PAI-1/tPA ratio did not significantly differ among groups. There was a negative correlation between PAI-1 serum levels and disease severity measured by MMSE score. No correlations of tPA serum levels and PAI-1/tPA ratio with MMSE were found. Increased PAI-1 serum levels may serve as a marker of dementia in FTLD, suggesting that, besides Aβ pathway, the plasmin system may affect cognition through synaptic activity.

Detection of TDP-43 seeding activity in the olfactory mucosa from patients with frontotemporal dementia

INTRODUCTION

We assessed TAR DNA-binding protein 43 (TDP-43) seeding activity and aggregates detection in olfactory mucosa of patients with frontotemporal lobar degeneration with TDP-43-immunoreactive pathology (FTLD-TDP) by TDP-43 seeding amplification assay (TDP43-SAA) and immunocytochemical analysis.

METHODS

The TDP43-SAA was optimized using frontal cortex samples from 16 post mortem cases with FTLD-TDP, FTLD with tau inclusions, and controls. Subsequently, olfactory mucosa samples were collected from 17 patients with FTLD-TDP, 15 healthy controls, and three patients carrying MAPT variants.

RESULTS

TDP43-SAA discriminated with 100% accuracy post mortem cases presenting or lacking TDP-43 neuropathology. TDP-43 seeding activity was detectable in the olfactory mucosa, and 82.4% of patients with FTLD-TDP tested positive, whereas 86.7% of controls tested negative (P < 0.001). Two out of three patients with MAPT mutations tested negative. In TDP43-SAA positive samples, cytoplasmatic deposits of phosphorylated TDP-43 in the olfactory neural cells were detected.

DISCUSSION

TDP-43 aggregates can be detectable in olfactory mucosa, suggesting that TDP43-SAA might be useful for identifying and monitoring FTLD-TDP in living patients.

Neurodegenerative Disease Tauopathies

Tauopathies are a diverse group of progressive and fatal neurodegenerative diseases characterized by aberrant tau inclusions in the central nervous system. Tau protein forms pathologic fibrillar aggregates that are typically closely associated with neuronal cell death, leading to varied clinical phenotypes including dementia, movement disorders, and motor neuron disease. In this review, we describe the clinicopathologic features of tauopathies and highlight recent advances in understanding the mechanisms that lead to spread of pathologic aggregates through interconnected neuronal pathways. The cell-to-cell propagation of tauopathy is then linked to posttranslational modifications, tau fibril structural variants, and the breakdown of cellular protein quality control.

Simple models to understand complex disease: 10 years of progress from Caenorhabditis elegans models of amyotrophic lateral sclerosis and frontotemporal lobar degeneration

The nematode Caenorhabditis elegans are a powerful model system to study human disease, with numerous experimental advantages including significant genetic and cellular homology to vertebrate animals, a short lifespan, and tractable behavioral, molecular biology and imaging assays. Beginning with the identification of SOD1 as a genetic cause of amyotrophic lateral sclerosis (ALS), C. elegans have contributed to a deeper understanding of the mechanistic underpinnings of this devastating neurodegenerative disease. More recently this work has expanded to encompass models of other types of ALS and the related disease frontotemporal lobar degeneration (FTLD-TDP), including those characterized by mutation or accumulation of the proteins TDP-43, C9orf72, FUS, HnRNPA2B1, ALS2, DCTN1, CHCHD10, ELP3, TUBA4A, CAV1, UBQLN2, ATXN3, TIA1, KIF5A, VAPB, GRN, and RAB38. In this review we summarize these models and the progress and insights from the last ten years of using C. elegans to study the neurodegenerative diseases ALS and FTLD-TDP.

Truncated TDP-43 proteoforms diagnostic of frontotemporal dementia with TDP-43 pathology

INTRODUCTION

Biomarkers of TDP-43 pathology are needed to distinguish frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP) from phenotypically related disorders. While normal physiological TDP-43 is not a promising biomarker, low-resolution techniques have suggested truncated forms of TDP-43 may be specific to TDP-43 pathology. To advance biomarker efforts for FTLD-TDP, we employed a high-resolution structural technique to characterize TDP-43 post-translational modifications in FTLD-TDP.

METHODS

High-resolution mass spectrometry was used to characterize TDP-43 proteoforms in brain tissue from FTLD-TDP, non-TDP-43 dementias and neuropathologically unaffected cases. Findings were then verified in a larger cohort of FTLD-TDP and non-TDP-43 dementias via targeted quantitative mass spectrometry.

RESULTS

In the discovery phase, truncated TDP-43 identified FTLD-TDP with 85% sensitivity and 100% specificity. The verification phase revealed similar findings, with 83% sensitivity and 89% specificity.

DISCUSSION

The concentration of truncated TDP-43 proteoforms-in particular, in vivo generated C-terminal fragments-have high diagnostic accuracy for FTLD-TDP.

HIGHLIGHTS

Discovery: Truncated TDP-43 differentiates FTLD-TDP from related dementias. Verification: Truncated TDP-43 concentration has high accuracy for FTLD-TDP. TDP-43 proteoforms <28 kDa have highest discriminatory power for TDP-43 pathology.

2024 United States Elections: Air Pollution, Neurodegeneration, Neuropsychiatric, and Neurodevelopmental Disorders. Who Cares?

Air pollution exposures ought to be of significant interest for the United States (US) public as health issues will play a role in the 2024 elections. Citizens are not aware of the harmful brain impact of exposures to ubiquitous anthropogenic combustion emissions and friction-derived nanoparticles, industrial nanoplastics, the growing risk of wildfires, and the smoke plumes of soot. Ample consideration of pediatric and early adulthood hallmarks of Alzheimer's disease, Parkinson's disease, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis and associations with neuropsychiatric and neurodevelopmental disorders in the process of setting, reviewing, and implementing standards for particulate matter (PM)2.5, ultrafine PM, and industrial nanoparticles must be of interest to US citizens.

An in situ and in vitro investigation of cytoplasmic TDP-43 inclusions reveals the absence of a clear amyloid signature

Introduction: Several neurodegenerative conditions are associated with a common histopathology within neurons of the central nervous system, consisting of the deposition of cytoplasmic inclusions of TAR DNA-binding protein 43 (TDP-43). Such inclusions have variably been described as morphologically and molecularly ordered aggregates having amyloid properties, as filaments without the cross-β-structure and dye binding specific for amyloid, or as amorphous aggregates with no defined structure and fibrillar morphology.Aims and Methods: Here we have expressed human full-length TDP-43 in neuroblastoma x spinal cord 34 (NSC-34) cells to investigate the morphological, structural, and tinctorial properties of TDP-43 inclusions in situ. We have used last-generation amyloid diagnostic probes able to cross the cell membrane and detect amyloid in the cytoplasm and have adopted Raman and Fourier transform infrared microspectroscopies to study in situ the secondary structure of the TDP-43 protein in the inclusions. We have then used transmission electron microscopy to study the morphology of the TDP-43 inclusions.Results: The results show the absence of amyloid dye binding, the lack of an enrichment of cross-β structure in the inclusions, and of a fibrillar texture in the round inclusions. The aggregates formed in vitro from the purified protein under conditions in which it is initially native also lack all these characteristics, ruling out a clear amyloid-like signature.Conclusions: These findings indicate a low propensity of TDP-43 to form amyloid fibrils and even non-amyloid filaments, under conditions in which the protein is initially native and undergoes its typical nucleus-to-cell mislocalization. It cannot be excluded that filaments emerge on the long time scale from such inclusions, but the high propensity of the protein to form initially other types of inclusions appear to be an essential characteristic of TDP-43 proteinopathies.KEY MESSAGESCytoplasmic inclusions of TDP-43 formed in NSC-34 cells do not stain with amyloid-diagnostic dyes, are not enriched with cross-β structure, and do not show a fibrillar morphology.TDP-43 assemblies formed in vitro from pure TDP-43 do not have any hallmarks of amyloid.

Transcranial direct current stimulation in semantic variant of primary progressive aphasia: a state-of-the-art review

The semantic variant of primary progressive aphasia (svPPA), known also as "semantic dementia (SD)," is a neurodegenerative disorder that pertains to the frontotemporal lobar degeneration clinical syndromes. There is currently no approved pharmacological therapy for all frontotemporal dementia variants. Transcranial direct current stimulation (tDCS) is a promising non-invasive brain stimulation technique capable of modulating cortical excitability through a sub-threshold shift in neuronal resting potential. This technique has previously been applied as adjunct treatment in Alzheimer's disease, while data for frontotemporal dementia are controversial. In this scoped review, we summarize and critically appraise the currently available evidence regarding the use of tDCS for improving performance in naming and/or matching tasks in patients with svPPA. Clinical trials addressing this topic were identified through MEDLINE (accessed by PubMed) and Web of Science, as of November 2022, week 3. Clinical trials have been unable to show a significant benefit of tDCS in enhancing semantic performance in svPPA patients. The heterogeneity of the studies available in the literature might be a possible explanation. Nevertheless, the results of these studies are promising and may offer valuable insights into methodological differences and overlaps, raising interest among researchers in identifying new non-pharmacological strategies for treating svPPA patients. Further studies are therefore warranted to investigate the potential therapeutic role of tDCS in svPPA.

Dysregulation of the progranulin-driven autophagy-lysosomal pathway mediates secretion of the nuclear protein TDP-43

The cytoplasmic accumulation of the nuclear protein transactive response DNA-binding protein 43 kDa (TDP-43) has been linked to the progression of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. TDP-43 secreted into the extracellular space has been suggested to contribute to the cell-to-cell spread of the cytoplasmic accumulation of TDP-43 throughout the brain; however, the underlying mechanisms remain unknown. We herein demonstrated that the secretion of TDP-43 was stimulated by the inhibition of the autophagy-lysosomal pathway driven by progranulin (PGRN), a causal protein of frontotemporal lobar degeneration. Among modulators of autophagy, only vacuolar-ATPase inhibitors, such as bafilomycin A1 (Baf), increased the levels of the full-length and cleaved forms of TDP-43 and the autophagosome marker LC3-II (microtubule-associated proteins 1A/1B light chain 3B) in extracellular vesicle fractions prepared from the culture media of HeLa, SH-SY5Y, or NSC-34 cells, whereas vacuolin-1, MG132, chloroquine, rapamycin, and serum starvation did not. The C-terminal fragment of TDP-43 was required for Baf-induced TDP-43 secretion. The Baf treatment induced the translocation of the aggregate-prone GFP-tagged C-terminal fragment of TDP-43 and mCherry-tagged LC3 to the plasma membrane. The Baf-induced secretion of TDP-43 was attenuated in autophagy-deficient ATG16L1 knockout HeLa cells. The knockdown of PGRN induced the secretion of cleaved TDP-43 in an autophagy-dependent manner in HeLa cells. The KO of PGRN in mouse embryonic fibroblasts increased the secretion of the cleaved forms of TDP-43 and LC3-II. The treatment inducing TDP-43 secretion increased the nuclear translocation of GFP-tagged transcription factor EB, a master regulator of the autophagy-lysosomal pathway in SH-SY5Y cells. These results suggest that the secretion of TDP-43 is promoted by dysregulation of the PGRN-driven autophagy-lysosomal pathway.

Factors affecting progression of non-Alzheimer dementia: a retrospective analysis with long-term follow-up

Background

Non-Alzheimer's dementias, including vascular dementia (VaD), frontotemporal dementia (FTD), Lewy body dementia (LBD), and Parkinson's disease dementia (PDD), possess unique characteristics and prognostic factors that remain poorly understood. This study aims to investigate the temporal course of these subtypes and identify the impact of functional, neuropsychiatric, and comorbid medical conditions on prognosis. Additionally, the relationship between hippocampal atrophy, white matter intensities, and disease progression will be examined, along with the identification of key covariates influencing slow or fast progression in non-Alzheimer's dementias.

Methods

A total of 196 patients with non-Alzheimer's dementias who underwent at least three comprehensive evaluations were included, with proportions of VaD, FTD, LBD, and PDD being 50, 19.39, 19.90, and 10.71%, respectively. Patient demographics, comorbidities, neuropsychiatric and neuroimaging parameters, and global evaluation were analyzed using appropriate statistical methods. The study followed patients for a mean duration of 62.57 ± 33.45 months (ranging from 11 to 198 months).

Results

The results from three different visits for each non-AD dementia case demonstrated significant differences in various measures across visits, including functional capacity (BDLAS), cognition (MMSE), and other neuropsychological tests. Notably, certain genotypes and hippocampal atrophy grades were more prevalent in specific subtypes. The results indicate that Fazekas grading and hippocampal atrophy were significant predictors of disease progression, while epilepsy, extrapyramidal symptoms, thyroid dysfunction, coronary artery disease, diabetes mellitus, hypertension, stroke, hyperlipidemia, sleep disorders, smoking, and family history of dementia were not significant predictors. BDLAS and EDLAS scores at the first and second visits showed significant associations with disease progression, while scores at the third visit did not. Group-based trajectory analysis revealed that non-AD cases separated into two reliable subgroups with slow/fast prognosis, showing high reliability (Entropy = 0.790, 51.8 vs. 48.2%).

Conclusion

This study provides valuable insights into the temporal course and prognostic factors of non-Alzheimer's dementias. The findings underscore the importance of considering functional, neuropsychological, and comorbid medical conditions in understanding disease progression. The significant associations between hippocampal atrophy, white matter intensities, and prognosis highlight potential avenues for further research and therapeutic interventions.

Frontotemporal-TDP and LATE Neurocognitive Disorders: A Pathophysiological and Genetic Approach

Frontotemporal lobar degeneration (FTLD) belongs to a heterogeneous group of highly complex neurodegenerative diseases and represents the second cause of presenile dementia in individuals under 65. Frontotemporal-TDP is a subgroup of frontotemporal dementia characterized by the aggregation of abnormal protein deposits, predominantly transactive response DNA-binding protein 43 (TDP-43), in the frontal and temporal brain regions. These deposits lead to progressive degeneration of neurons resulting in cognitive and behavioral impairments. Limbic age-related encephalopathy (LATE) pertains to age-related cognitive decline primarily affecting the limbic system, which is crucial for memory, emotions, and learning. However, distinct, emerging research suggests a potential overlap in pathogenic processes, with some cases of limbic encephalopathy displaying TDP-43 pathology. Genetic factors play a pivotal role in both disorders. Mutations in various genes, such as progranulin (GRN) and chromosome 9 open reading frame 72 (C9orf72), have been identified as causative in frontotemporal-TDP. Similarly, specific genetic variants have been associated with an increased risk of developing LATE. Understanding these genetic links provides crucial insights into disease mechanisms and the potential for targeted therapies.

Epigenetic Age Acceleration in Frontotemporal Lobar Degeneration: A Comprehensive Analysis in the Blood and Brain

Frontotemporal lobar degeneration (FTLD) includes a heterogeneous group of disorders pathologically characterized by the degeneration of the frontal and temporal lobes. In addition to major genetic contributors of FTLD such as mutations in MAPT, GRN, and C9orf72, recent work has identified several epigenetic modifications including significant differential DNA methylation in DLX1, and OTUD4 loci. As aging remains one of the major risk factors for FTLD, we investigated the presence of accelerated epigenetic aging in FTLD compared to controls. We calculated epigenetic age in both peripheral blood and brain tissues of multiple FTLD subtypes using several DNA methylation clocks, i.e., DNAmClockMulti, DNAmClockHannum, DNAmClockCortical, GrimAge, and PhenoAge, and determined age acceleration and its association with different cellular proportions and clinical traits. Significant epigenetic age acceleration was observed in the peripheral blood of both frontotemporal dementia (FTD) and progressive supranuclear palsy (PSP) patients compared to controls with DNAmClockHannum, even after accounting for confounding factors. A similar trend was observed with both DNAmClockMulti and DNAmClockCortical in post-mortem frontal cortex tissue of PSP patients and in FTLD cases harboring GRN mutations. Our findings support that increased epigenetic age acceleration in the peripheral blood could be an indicator for PSP and to a smaller extent, FTD.

Data-driven neuropathological staging and subtyping of TDP-43 proteinopathies

TAR DNA-binding protein-43 (TDP-43) accumulation is the primary pathology underlying several neurodegenerative diseases. Charting the progression and heterogeneity of TDP-43 accumulation is necessary to better characterize TDP-43 proteinopathies, but current TDP-43 staging systems are heuristic and assume each syndrome is homogeneous. Here, we use data-driven disease progression modelling to derive a fine-grained empirical staging system for the classification and differentiation of frontotemporal lobar degeneration due to TDP-43 (FTLD-TDP, n = 126), amyotrophic lateral sclerosis (ALS, n = 141) and limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) with and without Alzheimer's disease (n = 304). The data-driven staging of ALS and FTLD-TDP complement and extend previously described human-defined staging schema for ALS and behavioural variant frontotemporal dementia. In LATE-NC individuals, progression along data-driven stages was positively associated with age, but negatively associated with age in individuals with FTLD-TDP. Using only regional TDP-43 severity, our data driven model distinguished individuals diagnosed with ALS, FTLD-TDP or LATE-NC with a cross-validated accuracy of 85.9%, with misclassifications associated with mixed pathological diagnosis, age and genetic mutations. Adding age and SuStaIn stage to this model increased accuracy to 92.3%. Our model differentiates LATE-NC from FTLD-TDP, though some overlap was observed between late-stage LATE-NC and early-stage FTLD-TDP. We further tested for the presence of subtypes with distinct regional TDP-43 progression patterns within each diagnostic group, identifying two distinct cortical-predominant and brainstem-predominant subtypes within FTLD-TDP and a further two subcortical-predominant and corticolimbic-predominant subtypes within ALS. The FTLD-TDP subtypes exhibited differing proportions of TDP-43 type, while there was a trend for age differing between ALS subtypes. Interestingly, a negative relationship between age and SuStaIn stage was seen in the brainstem/subcortical-predominant subtype of each proteinopathy. No subtypes were observed for the LATE-NC group, despite aggregating individuals with and without Alzheimer's disease and a larger sample size for this group. Overall, we provide an empirical pathological TDP-43 staging system for ALS, FTLD-TDP and LATE-NC, which yielded accurate classification. We further demonstrate that there is substantial heterogeneity amongst ALS and FTLD-TDP progression patterns that warrants further investigation in larger cross-cohort studies.

HnRNP Pathologies in Frontotemporal Lobar Degeneration

Frontotemporal dementia (FTD) is the second most common form of young-onset (<65 years) dementia. Clinically, it primarily manifests as a disorder of behavioural, executive, and/or language functions. Pathologically, frontotemporal lobar degeneration (FTLD) is the predominant cause of FTD. FTLD is a proteinopathy, and the main pathological proteins identified so far are tau, TAR DNA-binding protein 43 (TDP-43), and fused in sarcoma (FUS). As TDP-43 and FUS are members of the heterogeneous ribonucleic acid protein (hnRNP) family, many studies in recent years have expanded the research on the relationship between other hnRNPs and FTLD pathology. Indeed, these studies provide evidence for an association between hnRNP abnormalities and FTLD. In particular, several studies have shown that multiple hnRNPs may exhibit nuclear depletion and cytoplasmic mislocalisation within neurons in FTLD cases. However, due to the diversity and complex association of hnRNPs, most studies are still at the stage of histological discovery of different hnRNP abnormalities in FTLD. We herein review the latest studies relating hnRNPs to FTLD. Together, these studies outline an important role of multiple hnRNPs in the pathogenesis of FTLD and suggest that future research into FTLD should include the whole spectrum of this protein family.

Distinct and shared neuropsychiatric phenotypes in FTLD-tauopathies

Frontotemporal lobar degeneration (FTLD) with tau pathology (FTLD-tau) commonly causes dementia syndromes that include primary progressive aphasia (PPA) and behavioral variant frontotemporal dementia (bvFTD). Cognitive decline in PPA and bvFTD is often accompanied by debilitating neuropsychiatric symptoms. In 44 participants with PPA or bvFTD due to autopsy-confirmed FTLD-tau, we characterized neuropsychiatric symptoms at early and late disease stages and determined whether the presence of certain symptoms predicted a specific underlying FTLD-tauopathy. Participants completed annual research visits at the Northwestern University Alzheimer's Disease Research Center. All participants had an initial Global Clinical Dementia Rating (CDR) Scale score ≤ 2, and neuropsychiatric symptoms were evaluated via the Neuropsychiatric Inventory-Questionnaire (NPI-Q). We assessed the frequency of neuropsychiatric symptoms across all participants at their initial and final visits and performed logistic regression to determine whether symptoms predicted a specific FTLD-tau pathologic diagnosis. Across the FTLD-tau cohort, irritability and apathy were most frequently endorsed at initial and final visits, respectively, whereas psychosis was highly uncommon at both timepoints. Irritability at initial visit predicted greater odds of a 4-repeat compared to a 3-repeat tauopathy (OR = 3.95, 95% CI = 1.10-15.83, p < 0.05). Initial sleep disturbance predicted greater odds of progressive supranuclear palsy (PSP) compared to other FTLD-tau subtypes (OR = 10.68, 95% CI = 2.05-72.40, p < 0.01). Appetite disturbance at final evaluation predicted lower odds of PSP (OR = 0.15, 95% CI = 0.02-0.74, p < 0.05). Our findings suggest that characterization of neuropsychiatric symptoms can aid in the prediction of underlying FTLD-tauopathies. Given considerable pathologic heterogeneity underlying dementias, neuropsychiatric symptoms may be useful for differential diagnosis and treatment planning.

Aspects of degradation and translation of the expanded C9orf72 hexanucleotide repeat RNA

An hexanucleotide repeat expansion mutation in the non-coding region of C9orf72 gene causes frontotemporal dementia and amyotrophic lateral sclerosis. This mutation is estimated to be the most frequent genetic cause of these currently incurable diseases. Since the mutation causes autosomal dominantly inherited diseases, disease cascade essentially starts from the expanded DNA repeats. However, molecular disease mechanism is inevitably complex because possible toxic entity for the disease is not just functional loss of translated C9ORF72 protein, if any, but potentially includes bidirectionally transcribed expanded repeat containing RNA and their unconventional repeat-associated non-AUG translation products in all possible reading frames. Although the field learned so much about the disease since the identification of the mutation in 2011, how the expanded repeat causes a particular type of fronto-temporal lobe dominant neurodegeneration and/or motor neuron degeneration is not yet clear. In this review, we summarize and discuss the current understandings of molecular mechanism of this repeat expansion mutation with focuses on the degradation and translation of the repeat containing RNA transcripts.

Cortical iron accumulation in MAPT- and C9orf 72-associated frontotemporal lobar degeneration

Neuroinflammation has been implicated in frontotemporal lobar degeneration (FTLD) pathophysiology, including in genetic forms with microtubule-associated protein tau (MAPT) mutations (FTLD-MAPT) or chromosome 9 open reading frame 72 (C9orf72) repeat expansions (FTLD-C9orf72). Iron accumulation as a marker of neuroinflammation has, however, been understudied in genetic FTLD to date. To investigate the occurrence of cortical iron accumulation in FTLD-MAPT and FTLD-C9orf72, iron histopathology was performed on the frontal and temporal cortex of 22 cases (11 FTLD-MAPT and 11 FTLD-C9orf72). We studied patterns of cortical iron accumulation and its colocalization with the corresponding underlying pathologies (tau and TDP-43), brain cells (microglia and astrocytes), and myelination. Further, with ultrahigh field ex vivo MRI on a subset (four FTLD-MAPT and two FTLD-C9orf72), we examined the sensitivity of T2*-weighted MRI for iron in FTLD. Histopathology showed that cortical iron accumulation occurs in both FTLD-MAPT and FTLD-C9orf72 in frontal and temporal cortices, characterized by a diffuse mid-cortical iron-rich band, and by a superficial cortical iron band in some cases. Cortical iron accumulation was associated with the severity of proteinopathy (tau or TDP-43) and neuronal degeneration, in part with clinical severity, and with the presence of activated microglia, reactive astrocytes and myelin loss. Ultra-high field T2*-weighted MRI showed a good correspondence between hypointense changes on MRI and cortical iron observed on histology. We conclude that iron accumulation is a feature of both FTLD-MAPT and FTLD-C9orf72 and is associated with pathological severity. Therefore, in vivo iron imaging using T2*-weighted MRI or quantitative susceptibility mapping may potentially be used as a noninvasive imaging marker to localize pathology in FTLD.

Analysis of positron emission tomography hypometabolic patterns and neuropsychiatric symptoms in patients with dementia syndromes

AIMS

To estimate the proportions of specific hypometabolic patterns and their association with neuropsychiatric symptoms (NPS) in patients with cognitive impairment (CI).

METHODS

This multicenter study with 1037 consecutive patients was conducted from December 2012 to December 2019. ¹⁸ F-FDG PET and clinical/demographic information, NPS assessments were recorded and analyzed to explore the associations between hypometabolic patterns and clinical features by correlation analysis and multivariable logistic regression models.

RESULTS

Patients with clinical Alzheimer's disease (AD, 81.6%, 605/741) and dementia with Lewy bodies (67.9%, 19/28) mostly had AD-pattern hypometabolism, and 76/137 (55.5%) of patients with frontotemporal lobar degeneration showed frontal and anterior temporal pattern (FT-P) hypometabolism. Besides corticobasal degeneration, patients with behavioral variant frontotemporal dementia (36/58), semantic dementia (7/10), progressive non-fluent aphasia (6/9), frontotemporal lobar degeneration and amyotrophic lateral sclerosis (3/5), and progressive supranuclear palsy (21/37) also mostly showed FT-P hypometabolism. The proportion of FT-P hypometabolism was associated with the presence of hallucinations (R = 0.171, p = 0.04), anxiety (R = 0.182, p = 0.03), and appetite and eating abnormalities (R = 0.200, p = 0.01) in AD.

CONCLUSION

Specific hypometabolic patterns in FDG-PET are associated with NPS and beneficial for the early identification and management of NPS in patients with CI.

Pathological combinations in neurodegenerative disease are heterogeneous and disease-associated

Pathologies that are causative for neurodegenerative disease (ND) are also frequently present in unimpaired, older individuals. In this retrospective study of 1,647 autopsied individuals, we report the incidence of ten pathologies across ND and normal ageing in attempt to clarify which pathological combinations are disease-associated and which are ageing-related. Eight clinically defined groups were examined including unimpaired individuals and those with clinical Alzheimer's disease, mixed dementia, amyotrophic lateral sclerosis, frontotemporal degeneration, multiple system atrophy, probable Lewy body disease, or probable tauopathies. Up to seven pathologies were observed concurrently resulting in a heterogenous mix of 161 pathological combinations. The presence of multiple, additive pathologies associated with older age, increasing disease duration, APOE e4 allele, and presence of dementia across the clinical groups. 15-67 combinations occurred in each group with the unimpaired group defined by 35 combinations. Most combinations occurred at a < 5% prevalence included 86 that were present in only 1-2 individuals. To better understand this heterogeneity, we organized the pathologic combinations into five broad categories based on their age-related frequency: 1) Ageing only for the unimpaired group combinations, 2) ND only if only the expected pathology for that individual's clinical phenotype was present, 3) Other ND if the expected pathology was not present, 4) ND + ageing if the expected pathology was present together with aging-related pathologies at a similar prevalence as the unimpaired group, and 5) ND + associated if the expected pathology was present together with other pathologies either not observed in the unimpaired group or observed at a greater frequency. ND only cases comprised a minority of cases (19-45%) except in the amyotrophic lateral sclerosis (56%) and multiple system atrophy (65%) groups. The ND + ageing category represented 9-28% of each group, but was rare in Alzheimer's disease (1%). ND + associated combinations were common in Alzheimer's disease (58%) and Lewy body disease (37%) and were observed in all groups. The Ageing only and Other ND categories accounted for a minority of individuals in each group. This observed heterogeneity indicates that the total pathological burden in ND is frequently more than a primary expected clinicopathological correlation with a high frequency of additional disease- or age-associated pathologies.

Combining Neuropsychological Assessment with Neuroimaging to Distinguish Early-Stage Alzheimer's Disease from Frontotemporal Lobar Degeneration in Non-Western Tonal Native Language-Speaking Individuals Living in Taiwan: A Case Series

Neuropsychological tests (NPTs), which are routinely used in clinical practice for assessment of dementia, are also considered to be essential for differential diagnosis of Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD), especially the behavioral variants of frontotemporal dementia (bvFTD) and primary progressive aphasia (PPA) at their initial clinical presentations. However, the heterogeneous features of these diseases, which have many overlapping signs, make differentiation between AD and FTLD highly challenging. Moreover, NPTs were primarily developed in Western countries and for native speakers of non-tonal languages. Hence, there is an ongoing dispute over the validity and reliability of these tests in culturally different and typologically diverse language populations. The purpose of this case series was to examine which of the NPTs adjusted for Taiwanese society may be used to distinguish these two diseases. Since AD and FTLD have different effects on individuals' brain, we combined NPTs with neuroimaging. We found that participants diagnosed with FTLD had lower scores in NPTs assessing language or social cognition than AD participants. PPA participants also had lower measures in the Free and Cued Selective Reminding Test than those diagnosed with bvFTD, while bvFTD participants showed poorer performances in the behavioral measures than PPA participants. In addition, the initial diagnosis was supported by the standard one-year clinical follow-up.

Mortality Risks and Causes of Death by Dementia Types in a Japanese Cohort with Dementia: NCGG-Stories

BACKGROUND

Prognosis-related information regarding dementia needs to be updated, as changes in medical and long-term care environments for patients with dementia in recent decades may be improving the prognosis of the disease.

OBJECTIVE

We aimed to investigate the mortality, cause of death, and prognostic factors by types of dementia in a Japanese clinic-based cohort.

METHODS

The National Center for Geriatrics and Gerontology-Life Stories of People with Dementia consists of clinical records and prognostic data of patients who visited the Memory Clinic in Japan. Patients who attended the clinic between July 2010 and September 2018, or their close relatives, were asked about death information via a postal survey. A cohort of 3,229 patients (mean age, 76.9; female, 1,953) was classified into six groups: normal cognition (NC), mild cognitive impairment (MCI), Alzheimer's disease (AD), vascular dementia, dementia with Lewy bodies (DLB), and frontotemporal lobar degeneration. A Cox proportional hazards model was employed to compare the mortality of each type of dementia, MCI, and NC.

RESULTS

Patients with all types of dementia and MCI had higher mortality rates than those with NC (hazard risks: 2.61-5.20). The most common cause of death was pneumonia, followed by cancer. In the MCI, AD, and DLB groups, older age, male sex, and low cognitive function were common prognostic factors but not presence of apolipoprotein E ɛ4 allele.

CONCLUSION

Our findings suggest important differences in the mortality risk and cause of death among patients with dementia, which will be useful in advanced care planning and policymaking.

Application of the AT(N) and Other CSF Classification Systems in Behavioral Variant Frontotemporal Dementia

BACKGROUND

Patients with a frontotemporal lobar degeneration (FTLD) usually manifest with behavioral variant frontotemporal dementia (bvFTD). Alzheimer's disease (AD) may also manifest with a predominant behavioral-dysexecutive syndrome, similar to bvFTD. Cerebrospinal fluid (CSF) biomarkers, such as total tau (τ_T), phosphorylated tau (τ_P-181) and amyloid beta with 42 amino-acids (Aβ₄₂), can predict AD pathology in vivo. The aim of this study was to compare the τ_T/Aβ₄₂ and τ_P-181/Aβ₄₂ ratios, the BIOMARKAPD/ABSI criteria and the AT(N) classification system in a cohort of bvFTD patients.

METHODS

A total of 105 bvFTD patients (21 possible bvFTD; 20%) with CSF data, examined from 2008 to 2022, were included. Seventy-eight AD patients and 62 control subjects were included. The CSF biomarkers were measured with Innotest (2008-2017 subcohort) and EUROIMMUN (2017-2022 subcohort) ELISAs.

RESULTS

Depending on the classification system, 7.6 to 28.6% of bvFTD had an AD biochemical profile. The τ_T/Aβ₄₂ and τ_P-181/Aβ₄₂ ratios classified more patients as AD compared to the BIOMARKAPD/ABSI and AT(N) systems. The patients with possible bvFTD had higher frequencies of AD compared to the probable bvFTD patients.

CONCLUSIONS

The four classification criteria of CSF AD biomarkers resulted in differences in AD allocation in this bvFTD cohort. A consensus on the optimal classification criteria of CSF AD biomarkers is pivotal.

RNA Dysmetabolism and Repeat-Associated Non-AUG Translation in Frontotemporal Lobar Degeneration/Amyotrophic Lateral Sclerosis due to C9orf72 Hexanucleotide Repeat Expansion

Neuropathological features of frontotemporal dementia and amyotrophic lateral sclerosis (ALS) due to C9orf72 GGGGCC hexanucleotide repeat expansion include early dipeptide repeats, repeat RNA foci, and subsequent TDP-43 pathologies. Since the discovery of the repeat expansion, extensive studies have elucidated the disease mechanism of how the repeat causes neurodegeneration. In this review, we summarize our current understanding of abnormal repeat RNA metabolism and repeat-associated non-AUG translation in C9orf72 frontotemporal lobar degeneration/ALS. For repeat RNA metabolism, we specifically focus on the role of hnRNPA3, the repeat RNA-binding protein, and the EXOSC10/RNA exosome complex, an intracellular RNA-degrading enzyme. In addition, the mechanism of repeat-associated non-AUG translation inhibition via TMPyP4, a repeat RNA-binding compound, is discussed.

A caregiver's perspective on clinically relevant symptoms in behavioural variant frontotemporal dementia: tools for disease management and trial design

BACKGROUND

Adequate detection of symptoms and disease progression in behavioural variant frontotemporal dementia (bvFTD) is complex. Dementia cohorts usually utilize cognitive and functional measures, which fail to detect dominant behavioural and social cognitive deficits in bvFTD. Moreover, since patients typically have a loss of insight, caregivers are important informants. This is the first qualitative study to investigate caregiver relevant symptoms during the disease course of bvFTD, aiming to improve tools for diagnosis, progression, and future clinical trials.

METHODS

Informal caregivers of patients in different disease stages of bvFTD (N = 20) were recruited from the neurology outpatient clinic of the Amsterdam UMC and a patient organization for peer support in the Netherlands. Their perspectives on clinical relevance were thoroughly explored during individual semi-structured interviews. Inductive content analysis with open coding was performed by two researchers independently to establish overarching themes and patterns.

RESULTS

Caregivers reported a variety of symptoms, in which (i) loss of emotional connection, (ii) preoccupation and restlessness, and (iii) apathy and dependency compose major themes of relevance for diagnosis and treatment. Within heterogeneous disease trajectories, symptom presence differed between stages and among individuals, which is relevant in the context of progression and outcome measures. Significant socio-emotional changes dominated in early stages, while severe cognitive, behavioural, and physical deterioration shifted focus from predominant personality change to quality of life in later stages.

CONCLUSIONS

Caregiver perspectives on target symptoms in bvFTD differ according to clinical stage and patient-caregiver characteristics, with significant socio-emotional changes characterizing early stages. These findings call for more appropriate tools and symptomatic treatments, as well as a personalized approach in treatment of bvFTD and a focus on early stage interventions in clinical trial design.

The role of neurofilament light in genetic frontotemporal lobar degeneration

Genetic frontotemporal lobar degeneration caused by autosomal dominant gene mutations provides an opportunity for targeted drug development in a highly complex and clinically heterogeneous dementia. These neurodegenerative disorders can affect adults in their middle years, progress quickly relative to other dementias, are uniformly fatal and have no approved disease-modifying treatments. Frontotemporal dementia, caused by mutations in the GRN gene which encodes the protein progranulin, is an active area of interventional drug trials that are testing multiple strategies to restore progranulin protein deficiency. These and other trials are also examining neurofilament light as a potential biomarker of disease activity and disease progression and as a therapeutic endpoint based on the assumption that cerebrospinal fluid and blood neurofilament light levels are a surrogate for neuroaxonal damage. Reports from genetic frontotemporal dementia longitudinal studies indicate that elevated concentrations of blood neurofilament light reflect disease severity and are associated with faster brain atrophy. To better inform patient stratification and treatment response in current and upcoming clinical trials, a more nuanced interpretation of neurofilament light as a biomarker of neurodegeneration is now required, one that takes into account its relationship to other pathophysiological and topographic biomarkers of disease progression from early presymptomatic to later clinically symptomatic stages.

Asymmetric Cerebral Peduncle Atrophy: A Simple Diagnostic Clue for Distinguishing Frontotemporal Lobar Degeneration from Alzheimer's Disease

BACKGROUND

Due to confusing clinicoradiological features such as amnestic symptoms and hippocampal atrophy in frontotemporal lobar degeneration (FTLD), antemortem differentiation between FTLD and Alzheimer's disease (AD) can be challenging. Although asymmetric atrophy of the cerebral peduncle is regarded as a representative imaging finding in some disorders of the FTLD spectrum, the utility of this finding has not been sufficiently evaluated for differentiating between FTLD and AD.

OBJECTIVE

This study aimed to explore the diagnostic performance of asymmetric cerebral peduncle atrophy on axial magnetic resonance imaging as a simple radiological discriminator between FTLD and AD.

METHODS

Seventeen patients with pathologically confirmed FTLD, including six with progressive supranuclear palsy, three with corticobasal degeneration, eight with TAR DNA-binding protein 43 (FTLD-TDP), and 11 with pathologically confirmed AD, were investigated. Quantitative indices representing the difference between the volumes of the bilateral cerebral peduncles (i.e., cerebral peduncular asymmetry index [CPAI]), the voxel-based specific regional analysis system for Alzheimer's disease (VSRAD) Z-score representing the degree of hippocampal atrophy, and semiquantitative visual analysis to evaluate the asymmetry of the cerebral peduncle (visual assessment of cerebral peduncular asymmetry: VACPA) were compared between the two groups.

RESULTS

Contrary to the VSRAD Z-score, the CPAI and VACPA scores demonstrated higher diagnostic performance in differentiating patients with FTLD from those with AD (areas under the receiver operating characteristic curve of 0.88, 082, and 0.60, respectively).

CONCLUSIONS

Quantitative and visual analytical techniques can differentiate between FTLD and AD. These simple methods may be useful in daily clinical practice.

Is the pathology of posterior cortical atrophy clinically predictable?

Posterior cortical atrophy (PCA) is a neurodegenerative disorder characterized by an early prominent deficit of visual functions associated with signs and symptoms that are the expression of dysfunction of posterior brain regions. Although PCA is commonly associated with Alzheimer's disease (AD), in recent years new pathological substrates have emerged. Among them, frontotemporal lobar degeneration (FTLD) is the most commonly reported but, to date, little is known about the clinical features of PCA due to FTLD. We conducted a systematic search in the main biomedical database MEDLINE. We searched for all clinical PCA reports that assessed the pathological basis of such syndrome with at least one of the following: (1) neuropathological examination, (2) cerebrospinal fluid biomarkers, (3) amyloid-PET imaging and (4) genetic testing. Of 369 potentially eligible studies, 40 fulfilled the inclusion criteria with an overall number of 144 patients (127 PCA-AD vs. 17 PCA-FTD/non-AD). We found that hallucinations/illusions were present in none of the probable PCA-FTD/non-AD subjects while were reported in 15 out of 97 PCA-AD individuals. Optic ataxia and Parkinsonism showed a significantly greater prevalence in probable PCA FTD/non-AD than in PCA-AD whereas myoclonus and disorientation in time and space were significantly more frequent in PCA-AD than in probable PCA FTD/non-AD. We also found a predominance of a left-side pattern of atrophy/hypometabolism in the probable PCA FTD/non-AD. Clinical features such as optic ataxia, Parkinsonism, myoclonus, hallucinations and disorientation in time and space suggest the underlying pathological basis of PCA and help in leading the diagnostic protocol consequently.

Blood Biomarkers for the Diagnosis of Neurodegenerative Dementia: A Systematic Review

IMPORTANCE

Accurately diagnosing neurodegenerative dementia is often challenging due to overlapping clinical features. Disease specific biomarkers could enhance diagnostic accuracy. However, CSF analysis procedures and advanced imaging modalities are either invasive or high-priced, and routinely unavailable. Easily accessible disease biomarkers would be of utmost value for accurate differential diagnosis of dementia subtypes.

OBJECTIVE

To assess the diagnostic accuracy of blood-based biomarkers for the differential diagnosis of AD from Frontotemporal Lobar Degeneration (FTLD), or AD from Dementia with Lewy Bodies (DLB).

METHODS

Systematic review. Three databases (PubMed, Scopus, and Web of Science) were searched. Studies assessing blood-based biomarkers levels in AD versus FTLD, or AD versus DLB, and its diagnostic accuracy, were selected. When the same biomarker was assessed in three or more studies, a meta-analysis was performed. QUADAS-2 criteria were used for quality assessment.

RESULTS

Twenty studies were included in this analysis. Collectively, 905 AD patients were compared to 1262 FTLD patients, and 209 AD patients were compared to 246 DLB patients. Regarding biomarkers for AD versus FTLD, excellent discriminative accuracy (AUC >0.9) was found for p-tau181, p-tau217, synaptophysin, synaptopodin, GAP43 and calmodulin. Other biomarkers also demonstrated good accuracy (AUC = 0.8-0.9). For AD versus DLB distinction, only miR-21-5p and miR-451a achieved excellent accuracy (AUC >0.9).

CONCLUSION

Encouraging results were found for several biomarkers, alone or in combination. Prospective longitudinal designs and consensual protocols, comprising larger cohorts and homogeneous testing modalities across centres, are essential to validate the clinical value of blood biomarkers for the precise etiological diagnosis of dementia.

Longitudinal changes in behaviour, mood and functional capacity in the primary progressive aphasia variants

Primary progressive aphasia (PPA) is a neurodegenerative clinical syndrome characterised by a progressive decline in speech and language functions. Deficits in behaviour, mood and functional capacity are reported in PPA but are less well understood. This study examined the PPA variants' profiles on these domains at initial presentation and over time and evaluated their relations to overall cognitive ability. Behaviour, mood and functional capacity were measured annually (over ~6 years) in 145 individuals diagnosed with PPA (41 logopenic [lv-PPA], 44 non-fluent [nfv-PPA] and 60 semantic variants [sv-PPA]) using the Cambridge Behavioural Inventory-Revised (CBI-R) carer questionnaire. Overall cognition was assessed annually with the Addenbrooke's Cognitive Examination-III. Distinct profiles were observed across PPA syndromes. Notably, sv-PPA carers reported greater behavioural, eating and motivational disturbances than the other PPA variants throughout the disease course. Reported memory problems were also greater in sv-PPA and lv-PPA than in nfv-PPA across all time points. These disturbances occurred in the context of the sv-PPA group demonstrating a slower rate of cognitive decline than the lv-PPA group and a parallel rate to that found in the nfv-PPA group. Associations between overall cognition and the CBI-R domains were trivial at baseline assessment; however, distinct profiles emerged when mapping each syndrome's overall cognitive decline with their behavioural, mood and functional trajectories. Our findings demonstrate that the evolving behaviour, mood and functional capacity profiles of the PPA variants are distinct and extend beyond the primary disorder of language. These findings have important implications for clinical management and caregiver education in PPA.

Early-stage differentiation between Alzheimer's disease and frontotemporal lobe degeneration: Clinical, neuropsychology, and neuroimaging features

BACKGROUND

Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) are the two most common forms of neurodegenerative dementia. Although both of them have well-established diagnostic criteria, achieving early diagnosis remains challenging. Here, we aimed to make the differential diagnosis of AD and FTLD from clinical, neuropsychological, and neuroimaging features.

MATERIALS AND METHODS

In this retrospective study, we selected 95 patients with PET-CT defined AD and 106 patients with PET-CT/biomarker-defined FTLD. We performed structured chart examination to collect clinical data and ascertain clinical features. A series of neuropsychological scales were used to assess the neuropsychological characteristics of patients. Automatic tissue segmentation of brain by Dr. Brain tool was used to collect multi-parameter volumetric measurements from different brain areas. All patients' structural neuroimage data were analyzed to obtain brain structure and white matter hyperintensities (WMH) quantitative data.

RESULTS

The prevalence of vascular disease associated factors was higher in AD patients than that in FTLD group. 56.84% of patients with AD carried at least one APOE ε4 allele, which is much high than that in FTLD patients. The first symptoms of AD patients were mostly cognitive impairment rather than behavioral abnormalities. In contrast, behavioral abnormalities were the prominent early manifestations of FTLD, and few patients may be accompanied by memory impairment and motor symptoms. In direct comparison, patients with AD had slightly more posterior lesions and less frontal atrophy, whereas patients with FTLD had more frontotemporal atrophy and less posterior lesions. The WMH burden of AD was significantly higher, especially in cortical areas, while the WMH burden of FTLD was higher in periventricular areas.

CONCLUSION

These results indicate that dynamic evaluation of cognitive function, behavioral and psychological symptoms, and multimodal neuroimaging are helpful for the early diagnosis and differentiation between AD and FTLD.

Cerebrospinal fluid biomarker panel of synaptic dysfunction in Alzheimer's disease and other neurodegenerative disorders

INTRODUCTION

Synaptic degeneration is a key part of the pathophysiology of neurodegenerative diseases, and biomarkers reflecting the pathological alterations are greatly needed.

METHOD

Seventeen synaptic proteins were quantified in a pathology-confirmed cerebrospinal fluid cohort of patients with Alzheimer's disease (AD; n = 63), frontotemporal lobar degeneration (FTLD; n = 53), and Lewy body spectrum of disorders (LBD; n = 21), as well as healthy controls (HC; n = 48).

RESULTS

Comparisons revealed four distinct patterns: markers decreased across all neurodegenerative conditions compared to HC (the neuronal pentraxins), markers increased across all neurodegenerative conditions (14-3-3 zeta/delta), markers selectively increased in AD compared to other neurodegenerative conditions (neurogranin and beta-synuclein), and markers selectively decreased in LBD and FTLD compared to HC and AD (AP2B1 and syntaxin-1B).

DISCUSSION

Several of the synaptic proteins may serve as biomarkers for synaptic dysfunction in AD, LBD, and FTLD. Additionally, differential patterns of synaptic protein alterations seem to be present across neurodegenerative diseases.

HIGHLIGHTS

A panel of synaptic proteins were quantified in the cerebrospinal fluid using mass spectrometry. We compared Alzheimer's disease, frontotemporal degeneration, and Lewy body spectrum of disorders. Pathology was confirmed by autopsy or familial mutations. We discovered synaptic biomarkers for synaptic degeneration and cognitive decline. We found differential patterns of synaptic proteins across neurodegenerative diseases.

Temporal order of clinical and biomarker changes in familial frontotemporal dementia

Unlike familial Alzheimer's disease, we have been unable to accurately predict symptom onset in presymptomatic familial frontotemporal dementia (f-FTD) mutation carriers, which is a major hurdle to designing disease prevention trials. We developed multimodal models for f-FTD disease progression and estimated clinical trial sample sizes in C9orf72, GRN and MAPT mutation carriers. Models included longitudinal clinical and neuropsychological scores, regional brain volumes and plasma neurofilament light chain (NfL) in 796 carriers and 412 noncarrier controls. We found that the temporal ordering of clinical and biomarker progression differed by genotype. In prevention-trial simulations using model-based patient selection, atrophy and NfL were the best endpoints, whereas clinical measures were potential endpoints in early symptomatic trials. f-FTD prevention trials are feasible but will likely require global recruitment efforts. These disease progression models will facilitate the planning of f-FTD clinical trials, including the selection of optimal endpoints and enrollment criteria to maximize power to detect treatment effects.

Cognitive and behavioural but not motor impairment increases brain age in amyotrophic lateral sclerosis

Age is the most important single risk factor of sporadic amyotrophic lateral sclerosis. Neuroimaging together with machine-learning algorithms allows estimating individuals' brain age. Deviations from normal brain-ageing trajectories (so called predicted brain age difference) were reported for a number of neuropsychiatric disorders. While all of them showed increased predicted brain-age difference, there is surprisingly few data yet on it in motor neurodegenerative diseases. In this observational study, we made use of previously trained algorithms of 3377 healthy individuals and derived predicted brain age differences from volumetric MRI scans of 112 amyotrophic lateral sclerosis patients and 70 healthy controls. We correlated predicted brain age difference scores with voxel-based morphometry data and multiple different motoric disease characteristics as well as cognitive/behavioural changes categorized according to Strong and Rascovsky. Against our primary hypothesis, there was no higher predicted brain-age difference in the amyotrophic lateral sclerosis patients as a group. None of the motoric phenotypes/characteristics influenced predicted brain-age difference. However, cognitive/behavioural impairment led to significantly increased predicted brain-age difference, while slowly progressive as well as cognitive/behavioural normal amyotrophic lateral sclerosis patients had even younger brain ages than healthy controls. Of note, the cognitive/behavioural normal amyotrophic lateral sclerosis patients were identified to have increased cerebellar brain volume as potential resilience factor. Younger brain age was associated with longer survival. Our results raise the question whether younger brain age in amyotrophic lateral sclerosis with only motor impairment provides a cerebral reserve against cognitive and/or behavioural impairment and faster disease progression. This new conclusion needs to be tested in subsequent samples. In addition, it will be interesting to test whether a potential effect of cerebral reserve is specific for amyotrophic lateral sclerosis or can also be found in other neurodegenerative diseases with primary motor impairment.

Relationship of serum beta-synuclein with blood biomarkers and brain atrophy

BACKGROUND

Recent data support beta-synuclein as a blood biomarker to study synaptic degeneration in Alzheimer's disease (AD).

METHODS

We provide a detailed comparison of serum beta-synuclein immunoprecipitation - mass spectrometry (IP-MS) with the established blood markers phosphorylated tau 181 (p-tau181) (Simoa) and neurofilament light (NfL) (Ella) in the German FTLD consortium cohort (n = 374) and its relation to brain atrophy (magnetic resonance imaging) and cognitive scores.

RESULTS

Serum beta-synuclein was increased in AD but not in frontotemporal lobar degeneration (FTLD) syndromes. Beta-synuclein correlated with atrophy in temporal brain structures and was associated with cognitive impairment. Serum p-tau181 showed the most specific changes in AD but the lowest correlation with structural alterations. NfL was elevated in all diseases and correlated with frontal and temporal brain atrophy.

DISCUSSION

Serum beta-synuclein changes differ from those of NfL and p-tau181 and are strongly related to AD, most likely reflecting temporal synaptic degeneration. Beta-synuclein can complement the existing panel of blood markers, thereby providing information on synaptic alterations.

HIGHLIGHTS

Blood beta-synuclein is increased in Alzheimer's disease (AD) but not in frontotemporal lobar degeneration (FTLD) syndromes. Blood beta-synuclein correlates with temporal brain atrophy in AD. Blood beta-synuclein correlates with cognitive impairment in AD. The pattern of blood beta-synuclein changes in the investigated diseases is different to phosphorylated tau 181 (p-tau181) and neurofilament light (NfL).

The contribution of behavioral features to caregiver burden in FTLD spectrum disorders

INTRODUCTION

Caregivers of patients with frontotemporal lobar degeneration (FTLD) spectrum disorders experience tremendous burden, which has been associated with the neuropsychiatric and behavioral features of the disorders.

METHODS

In a sample of 558 participants with FTLD spectrum disorders, we performed multiple-variable regressions to identify the behavioral features that were most strongly associated with caregiver burden, as measured by the Zarit Burden Interview, at each stage of disease.

RESULTS

Apathy and disinhibition, as rated by both clinicians and caregivers, as well as clinician-rated psychosis, showed the strongest associations with caregiver burden, a pattern that was consistent when participants were separated cross-sectionally by disease stage. In addition, behavioral features appeared to contribute most to caregiver burden in patients with early dementia.

DISCUSSION

Caregivers should be provided with early education on the management of the behavioral features of FTLD spectrum disorders. Interventions targeting apathy, disinhibition, and psychosis may be most useful to reduce caregiver burden.

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. .

MicroRNA biomarkers in frontotemporal dementia and to distinguish from Alzheimer's disease and amyotrophic lateral sclerosis

Frontotemporal lobar degeneration describes a group of progressive brain disorders that primarily are associated with atrophy of the prefrontal and anterior temporal lobes. Frontotemporal lobar degeneration is considered to be equivalent to frontotemporal dementia. Frontotemporal dementia is characterized by progressive impairments in behavior, executive function, and language. There are two main clinical subtypes: behavioral-variant frontotemporal dementia and primary progressive aphasia. The early diagnosis of frontotemporal dementia is critical for developing management strategies and interventions for these patients. Without validated biomarkers, the clinical diagnosis depends on recognizing all the core or necessary neuropsychiatric features, but misdiagnosis often occurs due to overlap with a range of neurologic and psychiatric disorders. In the studies reviewed a very large number of microRNAs were found to be dysregulated but with limited overlap between individual studies. Measurement of specific miRNAs singly or in combination, or as miRNA pairs (as a ratio) in blood plasma, serum, or cerebrospinal fluid enabled frontotemporal dementia to be discriminated from healthy controls, Alzheimer's disease, and amyotrophic lateral sclerosis. Furthermore, upregulation of miR-223-3p and downregulation of miR-15a-5p, which occurred both in blood serum and cerebrospinal fluid, distinguished behavioral-variant frontotemporal dementia from healthy controls. Downregulation of miR-132-3p in frontal and temporal cortical tissue distinguished frontotemporal lobar degeneration and frontotemporal dementia, respectively, from healthy controls. Possible strong miRNA biofluid biomarker contenders for behavioral-variant frontotemporal dementia are miR-223-3p, miR-15a-5p, miR-22-3p in blood serum and cerebrospinal fluid, and miR-124 in cerebrospinal fluid. No miRNAs were identified able to distinguish between behavioral-variant frontotemporal dementia and primary progressive aphasia subtypes. Further studies are warranted on investigating miRNA expression in biofluids and frontal/temporal cortical tissue to validate and extend these findings.

Casein kinase 1δ/ε phosphorylates fused in sarcoma (FUS) and ameliorates FUS-mediated neurodegeneration

Aberrant cytoplasmic accumulation of an RNA-binding protein, fused in sarcoma (FUS), characterizes the neuropathology of subtypes of ALS and frontotemporal lobar degeneration, although the effects of post-translational modifications of FUS, especially phosphorylation, on its neurotoxicity have not been fully characterized. Here, we show that casein kinase 1δ (CK1δ) phosphorylates FUS at 10 serine/threonine residues in vitro using mass spectrometric analyses. We also show that phosphorylation by CK1δ or CK1ε significantly increased the solubility of FUS in human embryonic kidney 293 cells. In transgenic Drosophila that overexpress wt or P525L ALS-mutant human FUS in the retina or in neurons, we found coexpression of human CK1δ or its Drosophila isologue Dco in the photoreceptor neurons significantly ameliorated the observed retinal degeneration, and neuronal coexpression of human CK1δ extended fly life span. Taken together, our data suggest a novel regulatory mechanism of the assembly and toxicity of FUS through CK1δ/CK1ε-mediated phosphorylation, which could represent a potential therapeutic target in FUS proteinopathies.

A pathologically confirmed case of combined amyotrophic lateral sclerosis with C9orf72 mutation and multiple system atrophy

Hexanucleotide repeat expansions in C9orf72 account for a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. There have been occasional reported cases associated with this expansion but also additional extrapyramidal clinical features. However, only very rarely has there been pathological confirmation of a parkinsonian syndrome associated with a C9orf72 repeat expansion. To date, as far as we are aware, there have been no reported pathologically confirmed cases of ALS with C9orf72 mutation and multiple system atrophy (MSA). We report a case of a man who initially presented with extrapyramidal features, including cogwheel rigidity, and, therefore, was clinically considered likely to have Parkinson's disease or a parkinsonian syndrome. Subsequent examination six months later revealed additional abnormal upper and lower motor neuron signs, raising the strong possibility of ALS. He had a rapid clinical decline and died 16 months after the first presentation. It was noted that his father also had ALS, and that his mother had a parkinsonian syndrome, suggestive of progressive supranuclear palsy. The macroscopic and microscopic examination of the brain and spinal cord revealed ALS pathology with neuronal loss, especially of the anterior horns of the cord and the motor cortex. This was associated with numerous neuronal cytoplasmic inclusions immunoreactive for phosphorylated transactivation response DNA‐binding protein of 43 Da (TDP43). There were additional pathological features, including p62‐immunoreactive cerebellar neuronal cytoplasmic inclusions, fully in keeping with a C9orf72 repeat expansion, and this was confirmed on molecular analysis. However, there was also α‐synuclein pathology in the form of oligodendroglial cytoplasmic inclusions in the basal ganglia, cerebellum, and brainstem, indicative of MSA. To our knowledge, this is the first reported case of pathologically confirmed combined ALS‐C9orf72 and MSA.

The Diagnostic Patterns of Referring Physicians and Hospital Expert Psychiatrists Regarding Particular Frontotemporal Lobar Degeneration Clinical and Neuropathological Subtypes

BACKGROUND

It is important to make accurate clinical diagnosis of frontotemporal lobar degeneration (FTLD), which in turn, leads to future therapic approaches. The FTLD cases are frequently inaccurately identified, but the frequency of this misidentification according to the underlying pathological subtypes is still unclear.

OBJECTIVE

We aimed to quantify the accuracy of behavioral variant frontotemporal dementia (bvFTD) and semantic variant primary progressive aphasia (svPPA) diagnoses by both the patients' referring physicians and hospital expert psychiatrists, and we investigated whether the physicians' and psychiatrists' diagnostic patterns are associated with a specific neuropathology.

METHODS

We retrospectively analyzed the cases of a series of Japanese patients with pathologically diagnosed FTLD (n = 55): the bvFTD group (n = 47) consisted of patients with FTLD-tau (n = 20), FTLD-TDP (TAR DNA-binding protein of 43-kDA) (n = 19), and FTLD-FUS (fused in sarcoma) (n = 8). The svPPA patients (n = 8) all had FTLD-TDP.

RESULTS

Only 31% of the patients' referring physicians mentioned FTD syndrome. The referring psychiatrists and neurologists showed similar diagnostic accuracy. High diagnostic accuracy was observed for the TDP pathology group (mainly svPPA patients). The FTLD-FUS patients were more likely to be diagnosed as having a psychiatric disorder by referring physicians. The hospital expert psychiatrists' accuracy for identifying FTLD-tau pathology was low.

CONCLUSION

The results of our analyses revealed a specific diagnostic pattern associated with particular FTLD pathological subtypes, which will help to improve non-specialists' diagnostic ability.

Divergent Histopathological Networks of Frontotemporal Degeneration Proteinopathy Subytpes

Network analyses inform complex systems such as human brain connectivity, but this approach is seldom applied to gold-standard histopathology. Here, we use two complimentary computational approaches to model microscopic progression of the main subtypes of tauopathy versus TDP-43 proteinopathy in the human brain. Digital histopathology measures were obtained in up to 13 gray matter (GM) and adjacent white matter (WM) cortical brain regions sampled from 53 tauopathy and 66 TDP-43 proteinopathy autopsy patients. First, we constructed a weighted non-directed graph for each group, where nodes are defined as GM and WM regions sampled and edges in the graph are weighted using the group-level Pearson's correlation coefficient for each pairwise node comparison. Additionally, we performed mediation analyses to test mediation effects of WM pathology between anterior frontotemporal and posterior parietal GM nodes. We find greater correlation (i.e., edges) between GM and WM node pairs in tauopathies compared with TDP-43 proteinopathies. Moreover, WM pathology strongly correlated with a graph metric of pathology spread (i.e., node-strength) in tauopathies (r = 0.60, p < 0.03) but not in TDP-43 proteinopathies (r = 0.03, p = 0.9). Finally, we found mediation effects for WM pathology on the association between anterior and posterior GM pathology in FTLD-Tau but not in FTLD-TDP. These data suggest distinct tau and TDP-43 proteinopathies may have divergent patterns of cellular propagation in GM and WM. More specifically, axonal spread may be more influential in FTLD-Tau progression. Network analyses of digital histopathological measurements can inform models of disease progression of cellular degeneration in the human brain.SIGNIFICANCE STATEMENT In this study, we uniquely perform two complimentary computational approaches to model and contrast microscopic disease progression between common frontotemporal lobar degeneration (FTLD) proteinopathy subtypes with similar clinical syndromes during life. Our models suggest white matter (WM) pathology influences cortical spread of disease in tauopathies that is less evident in TDP-43 proteinopathies. These data support the hypothesis that there are neuropathologic signatures of cellular degeneration within neurocognitive networks for specific protienopathies. These distinctive patterns of cellular pathology can guide future efforts to develop tissue-sensitive imaging and biological markers with diagnostic and prognostic utility for FTLD. Moreover, our novel computational approach can be used in future work to model various neurodegenerative disorders with mixed proteinopathy within the human brain connectome.

Pathogenic Mutation of TDP-43 Impairs RNA Processing in a Cell Type-Specific Manner: Implications for the Pathogenesis of ALS/FTLD

Transactivating response element DNA-binding protein of 43 kDa (TDP-43), which is encoded by the TARDBP gene, is an RNA-binding protein with fundamental RNA processing activities, and its loss-of-function (LOF) has a central role in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). TARDBP mutations are postulated to inactivate TDP-43 functions, leading to impaired RNA processing. However, it has not been fully examined how mutant TDP-43 affects global RNA regulation, especially in human cell models. Here, we examined global RNA processing in forebrain cortical neurons derived from human induced pluripotent stem cells (iPSCs) with a pathogenic TARDBP mutation encoding the TDP-43^K263E protein. In neurons expressing mutant TDP-43, we detected disrupted RNA regulation, including global changes in gene expression, missplicing, and aberrant polyadenylation, all of which were highly similar to those induced by TDP-43 knock-down. This mutation-induced TDP-43 LOF was not because of the cytoplasmic mislocalization of TDP-43. Intriguingly, in nonneuronal cells, including iPSCs and neural progenitor cells (NPCs), we did not observe impairments in RNA processing, thus indicating that the K263E mutation results in neuron-specific LOF of TDP-43. This study characterizes global RNA processing impairments induced by mutant TDP-43 and reveals the unprecedented cell type specificity of TDP-43 LOF in ALS/FTLD pathogenesis.