Review: Neuropathology of non-tau frontotemporal lobar degeneration

The cerebellum in frontotemporal dementia: From neglected bystander to potential neuromodulatory target. A narrative review

BACKGROUND

Though cortical changes in frontotemporal dementia (FTD) are well-documented, the cerebellum's role, closely linked to these areas, remains unclear.

OBJECTIVES

To provide evidence on cerebellar involvement in FTD across clinical, genetic, imaging, neuropathological, and neurophysiological perspectives. Additionally, we sought evidence supporting the application of cerebellar non-invasive brain stimulation (NIBS) in FTD for both diagnostic and therapeutic purposes.

METHODS

We performed a literature review using MEDLINE (via PubMed), Scopus, and Web of Science databases.

RESULTS

We emphasized the involvement of specific cerebellar regions which differentiate each FTD subtypes and may account for some of the characteristic symptoms. Furthermore, we highlighted peculiarities in FTD genetic alterations. Finally, we outlined neurophysiological evidence supporting a role for the cerebellum in FTD pathogenesis.

CONCLUSION

The cerebellum is critically involved in the FTD spectrum. Moreover, it can be speculated that cerebellar modulation, as already shown in other neurodegenerative disorders, could restore the interneuronal intracortical circuits typically impaired in FTD patients, providing clinical improvements and fundamental outcome measures in clinical trials.

Identification of novel small molecule chaperone activators for neurodegenerative disease treatment

A pathological hallmark of neurodegenerative disease is the accumulation of aberrant protein aggregates which contribute to the cytotoxicity and are therefore a target for therapy development. One key mechanism to manage cellular protein homeostasis is heat shock proteins (HSPs), protein chaperones which are known to target aberrant protein accumulation. Activation of HSPs target aberrant TDP-43, tau and amyloid to rescue neurodegenerative disease. As an attempt to target HSP activation for neurodegeneration therapy, we here develop a drug screening assay to identify compounds that will activate the master regulator of HSPs, the transcription factor heat shock factor 1 (HSF1). As HSF1 is bound by HSP90 which prevents its activation, we developed a NanoBRET assay, which allows us to monitor and quantify the HSF1-HSP90 interaction in living cells to screen for compounds disrupting this interaction and thereby releasing HSF1 for activation. After the optimisation and validation of the assay, a two thousand compound library was screened which produced 10 hits including two known HSP90 inhibitors. Follow-up functional study showed that one of the hits oxyphenbutazone (OPB) significantly reduces the accumulation of insoluble TDP-43 in a cell model, eliciting no signs of stress or toxicity. Overall, this study demonstrates a viable strategy for new drug discovery in targeting aberrant proteins and identifies potential candidates for translation into neurodegenerative disease treatment.

Unlocking Disease-Modifying Treatments for TDP-43-Mediated Neurodegeneration

Neurons degenerate in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), causing progressive and inevitably fatal neurological decline. The best therapeutic strategies target underlying disease mediators, but after decades of intensive research, the causes of these neurodegenerative diseases remain elusive. Recently, coordinated activities of large consortia, increasing open access to large datasets, new methods such as cryo-transmission electron microscopy, and advancements in high-resolution omics technologies have offered new insights into the biology of disease that bring us closer to understanding mechanisms of neurodegeneration. In particular, improved understanding of the roles of the key pathological protein TAR DNA binding protein 43 (TDP-43) in disease has revealed intriguing new opportunities that provide hope for better diagnostic tools and effective treatments for ALS and FTD.

Apraxia phenotypes and frontotemporal lobar degeneration

BACKGROUND

Apraxia has been identified in all clinical forms of frontotemporal lobar degeneration (FTLD). The characteristics of apraxia symptoms and their underlying cognitive/motor basis are not fully understood. This study investigated apraxia in pathological subtypes of FTLD.

METHODS

The study constituted a retrospective review of 115 pathologically confirmed cases of FTLD from a single cognitive neurology centre. Patients in whom apraxia had been documented as a notable clinical characteristic were identified. Apraxia features, demographic, cognitive, neurological, and imaging findings were recorded.

RESULTS

Eighteen patients were identified: 12 with FTLD-tau pathology (7 corticobasal degeneration (CBD), four Pick type and one progressive supranuclear palsy (PSP)) and six with FTLD-TDP pathology, all type A and four linked to progranulin gene mutations. Apraxia as a dominant presenting feature was typically associated with tau pathologies, whereas it emerged in the context of aphasia in TDP pathology. Apraxia typically predominated in one body part (face or limb) in tau but not TDP pathology. Relatively preserved activities in daily life were associated with TDP. Apraxia of speech was associated with tau pathology. Pick-type pathology was linked to symmetrical atrophy and late development of limb rigidity.

CONCLUSION

Apraxia in FTLD subtypes has variable characteristics. Apraxia associated with CBD pathology conformed to criteria for probable corticobasal syndrome (CBS), whereas apraxia with Pick-type pathology did not. Apraxia in patients with TDP-A pathology was interpreted as one manifestation of their generalised communication disorder. Apraxia in FTLD may have distinct cognitive and motor substrates that require prospective investigation.

Non-Alzheimer's amnestic mild cognitive impairment with medial temporal hypometabolism

INTRODUCTION

The increasing use of Alzheimer's disease (AD) biomarkers has led to the recognition of a subgroup of non-AD amnestic mild cognitive impairment (aMCI) patients who have medial temporal hypometabolism on fluorodeoxyglucose-positron emission tomography (FDG-PET).

METHODS

In this academic memory-clinic-based consecutive series, 16 non-AD aMCI patients and 28 AD controls matched for sex, age, and baseline Mini-Mental State Examination (MMSE) were followed for a median duration of 4.5 years. Our primary outcome was the MMSE decline rate over the subsequent years. We also determined the final diagnosis over time.

RESULTS

FDG-PET showed more pronounced medial temporal hypometabolism in non-AD cases and more inferior parietal lobule hypometabolism in AD controls. MMSE decline was slower in non-AD (β = -0.51) than in AD (β = -2.00) patients. Five non-AD cases developed frontotemporal dementia years after symptom onset, and one developed dementia with Lewy bodies.

DISCUSSION

Non-AD aMCI patients with medial temporal hypometabolism show slower cognitive decline.

Highlights

Non-AD aMCI with medial temporal hypometabolism shows slower cognitive decline than AD.FDG-PET revealed distinct metabolic patterns between non-AD aMCI and AD patients.Approximately one-third of non-AD aMCI cases developed frontotemporal dementia.Comprehensive diagnostic biomarkers are crucial for non-AD aMCI characterization.

Genetic spectrum features and diagnostic accuracy of four plasma biomarkers in 248 Chinese patients with frontotemporal dementia

INTRODUCTION

Frontotemporal dementia (FTD) is characterized by phenotypic and genetic heterogeneities. However, reports on the large Chinese FTD cohort are lacking.

METHODS

Two hundred forty-eight patients with FTD were enrolled. All patients and 2010 healthy controls underwent next generation sequencing. Plasma samples were analyzed for glial fibrillary acidic protein (GFAP), α-synuclein (α-syn), neurofilament light chain (NfL), and phosphorylated tau protein 181 (p-tau181).

RESULTS

Gene sequencing identified 48 pathogenic or likely pathogenic mutations in a total of 19.4% of patients with FTD (48/248). The most common mutation was the C9orf72 dynamic mutation (5.2%, 13/248). Significantly increased levels of GFAP, α-syn, NfL, and p-tau181 were detected in patients compared to controls (all p < 0.05). GFAP and α-syn presented better performance for diagnosing FTD.

DISCUSSION

We investigated the characteristics of phenotypic and genetic spectrum in a large Chinese FTD cohort, and highlighted the utility of plasma biomarkers for diagnosing FTD.

HIGHLIGHTS

This study used a frontotemporal dementia (FTD) cohort with a large sample size in Asia to update and reveal the clinical and genetic spectrum, and explore the relationship between multiple plasma biomarkers and FTD phenotypes as well as genotypes. We found for the first time that the C9orf72 dynamic mutation frequency ranks first among all mutations, which broke the previous impression that it was rare in Asian patients. Notably, it was the first time the C9orf72 G4C2 repeat expansion had been identified via whole-genome sequencing data, and this was verified using triplet repeat primed polymerase chain reaction (TP-PCR). We analyzed the diagnostic accuracy of four plasma biomarkers (glial fibrillary acidic protein [GFAP], α-synuclein [α-syn], neurofilament light chain [NfL], and phosphorylated tau protein 181 [p-tau181]) at the same time, especially for α-syn being included in the FTD cohort for the first time, and found GFAP and α-syn had the highest diagnostic accuracy for FTD and its varied subtypes.

Patterns of glucose hypometabolism can help differentiate FTLD-FET from other types of FTLD

INTRODUCTION

FTLD-FET is a newly described subtype of frontotemporal lobar degeneration (FTLD characterized by pathologic inclusions of FET proteins: fused in sarcoma (FUS), Ewing sarcoma, and TATA-binding protein-associated factor 2N (TAF15)). Severe caudate volume loss on MRI has been linked to FTLD-FUS, yet glucose hypometabolism in FTLD-FET has not been studied. We assessed [18F] fluorodeoxyglucose PET (FDG-PET) hypometabolism in FTLD-FET subtypes and compared metabolism to FTLD-tau and FTLD-TDP.

METHODS

We retrospectively reviewed medical records of 26 autopsied FTLD patients (six FTLD-FET, ten FTLD-Tau, and ten FTLD-TDP) who had completed antemortem FDG-PET. We evaluated five regions, caudate nucleus, medial frontal cortex, lateral frontal cortex, and medial temporal using a 0-3 visual rating scale and validated our findings quantitatively using CORTEX-ID suite Z scores.

RESULTS

Of the six FTLD-FET cases (three females) with median age at onset = 36, three were atypical FTLD-U (aFTLD-U) and three were neuronal intermediate filament inclusion disease (NIFID). bvFTD was the most common presentation. Four of the six FTLD cases (3 aFTLD-U + 1 NIFID) showed prominent caudate hypometabolism relatively early in the disease course. FTLD-tau and FTLD-TDP did not show early prominent caudate hypometabolism. Hypometabolism in medial and lateral temporal cortex was associated with FTLD-TDP, while FTLD-tau had normal-minimal regional metabolism.

DISCUSSION

Prominent caudate hypometabolism, especially early in the disease course, appears to be a hallmark feature of the aFTLD-U subtype of FTLD-FET. Assessing caudate and temporal hypometabolism on FDG-PET will help to differentiate FTLD-FET from FTLD-tau and FTLD-TDP.

Biomolecular condensates and disease pathogenesis

Biomolecular condensates or membraneless organelles (MLOs) formed by liquid-liquid phase separation (LLPS) divide intracellular spaces into discrete compartments for specific functions. Dysregulation of LLPS or aberrant phase transition that disturbs the formation or material states of MLOs is closely correlated with neurodegeneration, tumorigenesis, and many other pathological processes. Herein, we summarize the recent progress in development of methods to monitor phase separation and we discuss the biogenesis and function of MLOs formed through phase separation. We then present emerging proof-of-concept examples regarding the disruption of phase separation homeostasis in a diverse array of clinical conditions including neurodegenerative disorders, hearing loss, cancers, and immunological diseases. Finally, we describe the emerging discovery of chemical modulators of phase separation.

Serum Beta-Secretase 1 Activity Is a Potential Marker for the Differential Diagnosis between Alzheimer's Disease and Frontotemporal Dementia: A Pilot Study

Alzheimer's disease (AD) and frontotemporal dementia (FTD) are the two major neurodegenerative diseases causing dementia. Due to similar clinical phenotypes, differential diagnosis is challenging without specific biomarkers. Beta-site Amyloid Precursor Protein cleaving enzyme 1 (BACE1) is a β-secretase pivotal in AD pathogenesis. In AD and mild cognitive impairment subjects, BACE1 activity is increased in brain/cerebrospinal fluid, and plasma levels appear to reflect those in the brain. In this study, we aim to evaluate serum BACE1 activity in FTD, since, to date, there is no evidence about its role. The serum of 30 FTD patients and 30 controls was analyzed to evaluate (i) BACE1 activity, using a fluorescent assay, and (ii) Glial Fibrillary Acid Protein (GFAP) and Neurofilament Light chain (NfL) levels, using a Simoa kit. As expected, a significant increase in GFAP and NfL levels was observed in FTD patients compared to controls. Serum BACE1 activity was not altered in FTD patients. A significant increase in serum BACE1 activity was shown in AD vs. FTD and controls. Our results support the hypothesis that serum BACE1 activity is a potential biomarker for the differential diagnosis between AD and FTD.

Biophysical characterization of the phase separation of TDP-43 devoid of the C-terminal domain

BACKGROUND

Frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-TDP), amyotrophic lateral sclerosis (ALS) and limbic-predominant age-related TDP-43 encephalopathy (LATE) are associated with deposition of cytoplasmic inclusions of TAR DNA-binding protein 43 (TDP-43) in neurons. One complexity of this process lies in the ability of TDP-43 to form liquid-phase membraneless organelles in cells. Previous work has shown that the recombinant, purified, prion-like domain (PrLD) forms liquid droplets in vitro, but the behaviour of the complementary fragment is uncertain.

METHODS

We have purified such a construct without the PrLD (PrLD-less TDP-43) and have induced its phase separation using a solution-jump method and an array of biophysical techniques to study the morphology, state of matter and structure of the TDP-43 assemblies.

RESULTS

The fluorescent TMR-labelled protein construct, imaged using confocal fluorescence, formed rapidly (< 1 min) round, homogeneous and 0.5-1.0 µm wide assemblies which then coalesced into larger, yet round, species. When labelled with AlexaFluor488, they initially exhibited fluorescence recovery after photobleaching (FRAP), showing a liquid behaviour distinct from full-length TDP-43 and similar to PrLD. The protein molecules did not undergo major structural changes, as determined with circular dichroism and intrinsic fluorescence spectroscopies. This process had a pH and salt dependence distinct from those of full-length TDP-43 and its PrLD, which can be rationalized on the grounds of electrostatic forces.

CONCLUSIONS

Similarly to PrLD, PrLD-less TDP-43 forms liquid droplets in vitro through liquid-liquid phase separation (LLPS), unlike the full-length protein that rather undergoes liquid-solid phase separation (LSPS). These results offer a rationale of the complex electrostatic forces governing phase separation of full-length TDP-43 and its fragments. On the one hand, PrLD-less TDP-43 has a low pI and oppositively charged domains, and LLPS is inhibited by salts, which attenuate inter-domain electrostatic attractions. On the other hand, PrLD is positively charged due to a high isoionic point (pI) and LLPS is therefore promoted by salts and pH increases as they both reduce electrostatic repulsions. By contrast, full-length TDP-43 undergoes LSPS most favourably at its pI, with positive and negative salt dependences at lower and higher pH, respectively, depending on whether repulsive or attractive forces dominate, respectively.

Unveiling New Genetic Variants Associated with Age at Onset in Alzheimer's Disease and Frontotemporal Lobar Degeneration Due to C9orf72 Repeat Expansions

Alzheimer's disease (AD) and Frontotemporal lobar degeneration (FTLD) represent the most common forms of neurodegenerative dementias with a highly phenotypic variability. Herein, we investigated the role of genetic variants related to the immune system and inflammation as genetic modulators in AD and related dementias. In patients with sporadic AD/FTLD (n = 300) and GRN/C9orf72 mutation carriers (n = 80), we performed a targeted sequencing of 50 genes belonging to the immune system and inflammation, selected based on their high expression in brain regions and low tolerance to genetic variation. The linear regression analyses revealed two genetic variants: (i) the rs1049296 in the transferrin (TF) gene, shown to be significantly associated with age at onset in the sporadic AD group, anticipating the disease onset of 4 years for each SNP allele with respect to the wild-type allele, and (ii) the rs7550295 in the calsyntenin-1 (CLSTN1) gene, which was significantly associated with age at onset in the C9orf72 group, delaying the disease onset of 17 years in patients carrying the SNP allele. In conclusion, our data support the role of genetic variants in iron metabolism (TF) and in the modulation of the calcium signalling/axonal anterograde transport of vesicles (CLSTN1) as genetic modulators in AD and FTLD due to C9orf72 expansions.

Mutational Landscape of Alzheimer's Disease and Frontotemporal Dementia: Regional Variances in Northern, Central, and Southern Italy

Alzheimer's Disease (AD) and Frontotemporal Dementia (FTD) are the two major neurodegenerative diseases with distinct clinical and neuropathological profiles. The aim of this report is to conduct a population-based investigation in well-characterized APP, PSEN1, PSEN2, MAPT, GRN, and C9orf72 mutation carriers/pedigrees from the north, the center, and the south of Italy. We retrospectively analyzed the data of 467 Italian individuals. We identified 21 different GRN mutations, 20 PSEN1, 11 MAPT, 9 PSEN2, and 4 APP. Moreover, we observed geographical variability in mutation frequencies by looking at each cohort of participants, and we observed a significant difference in age at onset among the genetic groups. Our study provides evidence that age at onset is influenced by the genetic group. Further work in identifying both genetic and environmental factors that modify the phenotypes in all groups is needed. Our study reveals Italian regional differences among the most relevant AD/FTD causative genes and emphasizes how the collaborative studies in rare diseases can provide new insights to expand knowledge on genetic/epigenetic modulators of age at onset.

Impaired glymphatic system in genetic frontotemporal dementia: a GENFI study

The glymphatic system is an emerging target in neurodegenerative disorders. Here, we investigated the activity of the glymphatic system in genetic frontotemporal dementia with a diffusion-based technique called diffusion tensor image analysis along the perivascular space. We investigated 291 subjects with symptomatic or presymptomatic frontotemporal dementia (112 with chromosome 9 open reading frame 72 [C9orf72] expansion, 119 with granulin [GRN] mutations and 60 with microtubule-associated protein tau [MAPT] mutations) and 83 non-carriers (including 50 young and 33 old non-carriers). We computed the diffusion tensor image analysis along the perivascular space index by calculating diffusivities in the x-, y- and z-axes of the plane of the lateral ventricle body. Clinical stage and blood-based markers were considered. A subset of 180 participants underwent cognitive follow-ups for a total of 640 evaluations. The diffusion tensor image analysis along the perivascular space index was lower in symptomatic frontotemporal dementia (estimated marginal mean ± standard error, 1.21 ± 0.02) than in old non-carriers (1.29 ± 0.03, P = 0.009) and presymptomatic mutation carriers (1.30 ± 0.01, P < 0.001). In mutation carriers, lower diffusion tensor image analysis along the perivascular space was associated with worse disease severity (β = -1.16, P < 0.001), and a trend towards a significant association between lower diffusion tensor image analysis along the perivascular space and higher plasma neurofilament light chain was reported (β = -0.28, P = 0.063). Analysis of longitudinal data demonstrated that worsening of disease severity was faster in patients with low diffusion tensor image analysis along the perivascular space at baseline than in those with average (P = 0.009) or high (P = 0.006) diffusion tensor image analysis along the perivascular space index. Using a non-invasive imaging approach as a proxy for glymphatic system function, we demonstrated glymphatic system abnormalities in the symptomatic stages of genetic frontotemporal dementia. Such measures of the glymphatic system may elucidate pathophysiological processes in human frontotemporal dementia and facilitate early phase trials of genetic frontotemporal dementia.

Dendritic spine head diameter is reduced in the prefrontal cortex of progranulin haploinsufficient mice

Loss-of-function mutations in the progranulin (GRN) gene are an autosomal dominant cause of Frontotemporal Dementia (FTD). These mutations typically result in haploinsufficiency of the progranulin protein. Grn+/- mice provide a model for progranulin haploinsufficiency and develop FTD-like behavioral abnormalities by 9-10 months of age. In previous work, we demonstrated that Grn+/- mice develop a low dominance phenotype in the tube test that is associated with reduced dendritic arborization of layer II/III pyramidal neurons in the prelimbic region of the medial prefrontal cortex (mPFC), a region key for social dominance behavior in the tube test assay. In this study, we investigated whether progranulin haploinsufficiency induced changes in dendritic spine density and morphology. Individual layer II/III pyramidal neurons in the prelimbic mPFC of 9-10 month old wild-type or Grn+/- mice were targeted for iontophoretic microinjection of fluorescent dye, followed by high-resolution confocal microscopy and 3D reconstruction for morphometry analysis. Dendritic spine density in Grn+/- mice was comparable to wild-type littermates, but the apical dendrites in Grn+/- mice had a shift in the proportion of spine types, with fewer stubby spines and more thin spines. Additionally, apical dendrites of Grn+/- mice had longer spines and smaller thin spine head diameter in comparison to wild-type littermates. These changes in spine morphology may contribute to altered circuit-level activity and social dominance deficits in Grn+/- mice.

A Systematic Review of the Genetics and Pathology of Psychosis in Frontotemporal Dementia

OBJECTIVES

Frontotemporal dementia (FTD) patients frequently present with psychosis, which complicates diagnosis and management. In this study, we aim to examine the relationship between psychosis and the most common genetic mutations predisposing to FTD, and in the different pathological subtypes of FTD.

DESIGN

We conducted a systematic review, searching the literature up to December 2022, and reviewed 50 articles that met our inclusion criteria. From the reviewed articles, we extracted and summarized data regarding the frequency of psychosis and patient characteristics in each major genetic and pathological subtype of FTD.

RESULTS

Among FTD patients with confirmed genetic mutations or pathological diagnosss, the frequency of psychosis was 24.2%. Among the genetic mutation carriers, C9orf72 mutation carriers had the highest frequency of psychosis (31.4%), whereas GRN (15.0%) and MAPT (9.2%) mutation carriers had lower frequencies of psychosis. MAPT mutation carriers notably developed psychosis at a younger age compared to other genetic groups. The most common psychotic symptoms were delusions among C9orf72 carriers and visual hallucinations among GRN mutation carriers. Among the pathological subtypes, 30% of patients with FUS pathology, 25.3% of patients with TDP-43 pathology, and 16.4% of patients with tau pathology developed psychosis. In the TDP-43 group, subtype B pathology was the most common subtype reported in association with psychosis.

CONCLUSION

Our systematic review suggests a high frequency of psychosis in specific subgroups of FTD patients. Further studies are required to understand the structural and biological underpinnings of psychosis in FTD.

Neuroimaging-guided diagnosis of possible FTLD-FUS pathology: a case report

BACKGROUND

This case report presents a patient with progressive memory loss and choreiform movements.

CASE PRESENTATION

Neuropsychological tests indicated multi-domain amnestic mild cognitive impairment (aMCI), and neurological examination revealed asymmetrical involuntary hyperkinetic movements. Imaging studies showed severe left-sided atrophy and hypometabolism in the left frontal and temporoparietal cortex. [18F]Flortaucipir PET exhibited moderately increased tracer uptake in hypometabolic areas. The diagnosis initially considered Alzheimer's disease (AD), frontotemporal degeneration (FTD), and corticobasal degeneration (CBD), cerebral hemiatrophy syndrome, but imaging and cerebrospinal fluid analysis excluded AD and suggested fused-in-sarcoma-associated FTD (FTLD-FUS), a subtype of the behavioural variant of FTD.

CONCLUSIONS

Our case highlights that despite the lack of specific FUS biomarkers the combination of clinical features and neuroimaging biomarkers can guide choosing the most likely differential diagnosis in a complex neurological case. Imaging in particular allowed an accurate measure of the topography and severity of neurodegeneration and the exclusion of AD-related pathology.

Galectin-3 is upregulated in frontotemporal dementia patients with subtype specificity

INTRODUCTION

Neuroinflammation is a major contributor to the progression of frontotemporal dementia (FTD). Galectin-3 (Gal-3), a microglial activation regulator, holds promise as a therapeutic target and potential biomarker. Our study aimed to investigate Gal-3 levels in patients with FTD and assess its diagnostic potential.

METHODS

We examined Gal-3 levels in brain, serum, and cerebrospinal fluid (CSF) samples of patients with FTD and controls. Multiple linear regressions between Gal-3 levels and other FTD markers were explored.

RESULTS

Gal-3 levels were increased significantly in patients with FTD, mainly across brain tissue and CSF, compared to controls. Remarkably, Gal-3 levels were higher in cases with tau pathology than TAR-DNA Binding Protein 43 (TDP-43) pathology. Only MAPT mutation carriers displayed increased Gal-3 levels in CSF samples, which correlated with total tau and 14-3-3.

DISCUSSION

Our findings underscore the potential of Gal-3 as a diagnostic marker for FTD, particularly in MAPT cases, and highlights the relation of Gal-3 with neuronal injury markers.

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.

Behavioral variant frontotemporal dementia associated with GRN and ErbB4 gene mutations: a case report and literature review

OBJECTIVE

To report the clinical manifestation and genetic characteristics of a patient having frontotemporal dementia (FTD) with abnormal behavior and unstable walking.

METHODS

The clinical and imaging features of a patient who was eventually diagnosed with FTD were analyzed. The patient's neuropsychological, PET-CT, electromyography, and genetic data were collected. Furthermore, the patient's blood samples were examined for FTD-related genes.

RESULTS

The patient was a 52-year-old man with hidden onset. The symptoms progressed gradually, presenting with abnormal behaviors, including repeated shopping, taking away other people's things, constantly eating snacks, and frequently calling friends at night. The patient also exhibited executive dysfunction, such as the inability to cook and multiple driving problems, e.g., constantly deviates from his lane while driving. In addition, the patient showed personality changes such as irritability, indifference, and withdrawal, as well as motor symptoms, including unstable walking and frequent falls when walking. Brain magnetic resonance imaging revealed hippocampal sclerosis along with widening and deepening of the bilateral temporal lobe sulcus. Brain metabolic imaging via PET-CT demonstrated decreased metabolism in the bilateral prefrontal lobe, with the abnormal energy metabolism indicating FTD. Lastly, blood sample analysis detected mutations in the amyotrophic lateral sclerosis (ALS)-related GRN gene c.1352C > T (p.P451L) and ErbB4 gene c.256 T > C (p.Y86H).

CONCLUSION

This is the first case of heterozygous mutations in the GRN and ErbB4 genes in FTD alone. The GRN and ErbB4 genes are likely to be important in the pathogenesis of FTD, expanding the common genetic profile of ALS and FTD.

Autophagy Markers Are Altered in Alzheimer's Disease, Dementia with Lewy Bodies and Frontotemporal Dementia

The accumulation of protein aggregates defines distinct, yet overlapping pathologies such as Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD). In this study, we investigated ATG5, UBQLN2, ULK1, and LC3 concentrations in 66 brain specimens and 120 plasma samples from AD, DLB, FTD, and control subjects (CTRL). Protein concentration was measured with ELISA kits in temporal, frontal, and occipital cortex specimens of 32 AD, 10 DLB, 10 FTD, and 14 CTRL, and in plasma samples of 30 AD, 30 DLB, 30 FTD, and 30 CTRL. We found alterations in ATG5, UBQLN2, ULK1, and LC3 levels in patients; ATG5 and UBQLN2 levels were decreased in both brain specimens and plasma samples of patients compared to those of the CTRL, while LC3 levels were increased in the frontal cortex of DLB and FTD patients. In this study, we demonstrate alterations in different steps related to ATG5, UBQLN2, and LC3 autophagy pathways in DLB and FTD patients. Molecular alterations in the autophagic processes could play a role in a shared pathway involved in the pathogenesis of neurodegeneration, supporting the hypothesis of a common molecular mechanism underlying major neurodegenerative dementias and suggesting different potential therapeutic targets in the autophagy pathway for these disorders.

TAF15 amyloid filaments in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) causes frontotemporal dementia (FTD), the most common form of dementia after Alzheimer's disease, and is often also associated with motor disorders1. The pathological hallmarks of FTLD are neuronal inclusions of specific, abnormally assembled proteins2. In the majority of cases the inclusions contain amyloid filament assemblies of TAR DNA-binding protein 43 (TDP-43) or tau, with distinct filament structures characterizing different FTLD subtypes3,4. The presence of amyloid filaments and their identities and structures in the remaining approximately 10% of FTLD cases are unknown but are widely believed to be composed of the protein fused in sarcoma (FUS, also known as translocated in liposarcoma). As such, these cases are commonly referred to as FTLD-FUS. Here we used cryogenic electron microscopy (cryo-EM) to determine the structures of amyloid filaments extracted from the prefrontal and temporal cortices of four individuals with FTLD-FUS. Surprisingly, we found abundant amyloid filaments of the FUS homologue TATA-binding protein-associated factor 15 (TAF15, also known as TATA-binding protein-associated factor 2N) rather than of FUS itself. The filament fold is formed from residues 7-99 in the low-complexity domain (LCD) of TAF15 and was identical between individuals. Furthermore, we found TAF15 filaments with the same fold in the motor cortex and brainstem of two of the individuals, both showing upper and lower motor neuron pathology. The formation of TAF15 amyloid filaments with a characteristic fold in FTLD establishes TAF15 proteinopathy in neurodegenerative disease. The structure of TAF15 amyloid filaments provides a basis for the development of model systems of neurodegenerative disease, as well as for the design of diagnostic and therapeutic tools targeting TAF15 proteinopathy.

Proteomics elucidating physiological and pathological functions of TDP-43

Trans-activation response DNA binding protein of 43 kDa (TDP-43) regulates a great variety of cellular processes in the nucleus and cytosol. In addition, a defined subset of neurodegenerative diseases is characterized by nuclear depletion of TDP-43 as well as cytosolic mislocalization and aggregation. To perform its diverse functions TDP-43 can associate with different ribonucleoprotein complexes. Combined with transcriptomics, MS interactome studies have unveiled associations between TDP-43 and the spliceosome machinery, polysomes and RNA granules. Moreover, the highly dynamic, low-valency interactions regulated by its low-complexity domain calls for innovative proximity labeling methodologies. In addition to protein partners, the analysis of post-translational modifications showed that they may play a role in the nucleocytoplasmic shuttling, RNA binding, liquid-liquid phase separation and protein aggregation of TDP-43. Here we review the various TDP-43 ribonucleoprotein complexes characterized so far, how they contribute to the diverse functions of TDP-43, and roles of post-translational modifications. Further understanding of the fluid dynamic properties of TDP-43 in ribonucleoprotein complexes, RNA granules, and self-assemblies will advance the understanding of RNA processing in cells and perhaps help to develop novel therapeutic approaches for TDPopathies.

Microglia in neurodegenerative diseases: mechanism and potential therapeutic targets

Microglia activation is observed in various neurodegenerative diseases. Recent advances in single-cell technologies have revealed that these reactive microglia were with high spatial and temporal heterogeneity. Some identified microglia in specific states correlate with pathological hallmarks and are associated with specific functions. Microglia both exert protective function by phagocytosing and clearing pathological protein aggregates and play detrimental roles due to excessive uptake of protein aggregates, which would lead to microglial phagocytic ability impairment, neuroinflammation, and eventually neurodegeneration. In addition, peripheral immune cells infiltration shapes microglia into a pro-inflammatory phenotype and accelerates disease progression. Microglia also act as a mobile vehicle to propagate protein aggregates. Extracellular vesicles released from microglia and autophagy impairment in microglia all contribute to pathological progression and neurodegeneration. Thus, enhancing microglial phagocytosis, reducing microglial-mediated neuroinflammation, inhibiting microglial exosome synthesis and secretion, and promoting microglial conversion into a protective phenotype are considered to be promising strategies for the therapy of neurodegenerative diseases. Here we comprehensively review the biology of microglia and the roles of microglia in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, multiple system atrophy, amyotrophic lateral sclerosis, frontotemporal dementia, progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies and Huntington's disease. We also summarize the possible microglia-targeted interventions and treatments against neurodegenerative diseases with preclinical and clinical evidence in cell experiments, animal studies, and clinical trials.

Cryptic exon detection and transcriptomic changes revealed in single-nuclei RNA sequencing of C9ORF72 patients spanning the ALS-FTD spectrum

The C9ORF72-linked diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by the nuclear depletion and cytoplasmic accumulation of TAR DNA-binding protein 43 (TDP-43). Recent studies have shown that the loss of TDP-43 function leads to the inclusion of cryptic exons (CE) in several RNA transcript targets of TDP-43. Here, we show for the first time the detection of CEs in a single-nuclei RNA sequencing (snRNA-seq) dataset obtained from frontal and occipital cortices of C9ORF72 patients that phenotypically span the ALS-FTD disease spectrum. We assessed each cellular cluster for detection of recently described TDP-43-induced CEs. Transcripts containing CEs in the genes STMN2 and KALRN were detected in the frontal cortex of all C9ORF72 disease groups with the highest frequency in excitatory neurons in the C9ORF72-FTD group. Within the excitatory neurons, the cluster with the highest proportion of cells containing a CE had transcriptomic similarities to von Economo neurons, which are known to be vulnerable to TDP-43 pathology and selectively lost in C9ORF72-FTD. Differential gene expression and pathway analysis of CE-containing neurons revealed multiple dysregulated metabolic processes. Our findings reveal novel insights into the transcriptomic changes of neurons vulnerable to TDP-43 pathology.

Insights into the pathological basis of dementia from population-based neuropathology studies

The epidemiological neuropathology perspective of population and community-based studies allows unbiased assessment of the prevalence of various pathologies and their relationships to late-life dementia. In addition, this approach provides complementary insights to conventional case-control studies, which tend to be more representative of a younger clinical cohort. The Cognitive Function and Ageing Study (CFAS) is a longitudinal study of cognitive impairment and frailty in the general United Kingdom population. In this review, we provide an overview of the major findings from CFAS, alongside other studies, which have demonstrated a high prevalence of pathology in the ageing brain, particularly Alzheimer's disease neuropathological change and vascular pathology. Increasing burdens of these pathologies are the major correlates of dementia, especially neurofibrillary tangles, but there is substantial overlap in pathology between those with and without dementia, particularly at intermediate burdens of pathology and also at the oldest ages. Furthermore, additional pathologies such as limbic-predominant age-related TDP-43 encephalopathy, ageing-related tau astrogliopathy and primary age-related tauopathies contribute to late-life dementia. Findings from ageing population-representative studies have implications for the understanding of dementia pathology in the community. The high prevalence of pathology and variable relationship to dementia status has implications for disease definition and indicate a role for modulating factors on cognitive outcome. The complexity of late-life dementia, with mixed pathologies, indicates a need for a better understanding of these processes across the life-course to direct the best research for reducing risk in later life of avoidable clinical dementia syndromes.

Psychotic symptoms in frontotemporal dementia with TDP-43 tend to be associated with type B pathology

AIMS

Psychotic symptoms are increasingly recognized as a distinguishing clinical feature in patients with dementia due to frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP). Within this group, carriers of the C9orf72 repeat expansion are particularly prone to develop delusions and hallucinations.

METHODS

The present retrospective study sought to provide novel details about the relationship between FTLD-TDP pathology and the presence of psychotic symptoms during life.

RESULTS

We found that FTLD-TDP subtype B was more frequent in patients with psychotic symptoms than in those without. This relationship was present even when corrected for the presence of C9orf72 mutation, suggesting that pathophysiological processes leading to the development of subtype B pathology may increase the risk of psychotic symptoms. Within the group of FTLD-TDP cases with subtype B pathology, psychotic symptoms tended to be associated with a greater burden of TDP-43 pathology in the white matter and a lower burden in lower motor neurons. When present, pathological involvement of motor neurons was more likely to be asymptomatic in patients with psychosis.

CONCLUSIONS

This work suggests that psychotic symptoms in patients with FTLD-TDP tend to be associated with subtype B pathology. This relationship is not completely explained by the effects of the C9orf72 mutation and raises the possibility of a direct link between psychotic symptoms and this particular pattern of TDP-43 pathology.

TANK-Binding Kinase 1 Mutation as a Rare Cause of Frontotemporal Dementia in a Mexican Patient: The First Case Report in a Tertiary Referral Hospital in Mexico

Frontotemporal dementia (FTD) is a heterogeneous condition characterized by changes in behavior, personality, and language resulting from degeneration of the frontal and/or temporal lobes. A wide spectrum of clinical syndromes and an overlap with different motor disorders make this entity challenging for clinicians, both in achieving a correct diagnosis and providing proper treatment. Despite the majority of cases being sporadic, FTD has a hereditary component, and more than 10 disease-causing genes have been identified. We present the case of a Mexican patient with a positive family history of neurocognitive disorders who developed early-onset behavioral symptoms, cognitive alterations, and motor disturbances. After a comprehensive study and multiple assessments by various medical services, a molecular diagnosis was achieved by documenting a loss-of-function mutation in the TANK-binding kinase 1 (TBK1) gene, an extremely rare cause of FTD. Genetic diagnosis is crucial in these situations, as this mutation has been associated with rapid disease progression and the potential development of motor syndromes during its course. Our case underscores the challenges involved in reaching an accurate diagnosis, highlighting the importance of molecular testing. A thorough family history, past medical records, and a detailed description of symptom onset and progression are imperative, as they can significantly influence both treatment approaches and prognosis. Diagnostic errors, combined with their subsequent inappropriate treatment, can further deteriorate patients' quality of life.

Frontotemporal Dementia, Where Do We Stand? A Narrative Review

Frontotemporal dementia (FTD) is a neurodegenerative disease of growing interest, since it accounts for up to 10% of middle-age-onset dementias and entails a social, economic, and emotional burden for the patients and caregivers. It is characterised by a (at least initially) selective degeneration of the frontal and/or temporal lobe, generally leading to behavioural alterations, speech disorders, and psychiatric symptoms. Despite the recent advances, given its extreme heterogeneity, an overview that can bring together all the data currently available is still lacking. Here, we aim to provide a state of the art on the pathogenesis of this disease, starting with established findings and integrating them with more recent ones. In particular, advances in the genetics field will be examined, assessing them in relation to both the clinical manifestations and histopathological findings, as well as considering the link with other diseases, such as amyotrophic lateral sclerosis (ALS). Furthermore, the current diagnostic criteria will be explored, including neuroimaging methods, nuclear medicine investigations, and biomarkers on biological fluids. Of note, the promising information provided by neurophysiological investigations, i.e., electroencephalography and non-invasive brain stimulation techniques, concerning the alterations in brain networks and neurotransmitter systems will be reviewed. Finally, current and experimental therapies will be considered.

CGG repeat expansion in LRP12 in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the degeneration of motor neurons. Although repeat expansion in C9orf72 is its most common cause, the pathogenesis of ALS isn't fully clear. In this study, we show that repeat expansion in LRP12, a causative variant of oculopharyngodistal myopathy type 1 (OPDM1), is a cause of ALS. We identify CGG repeat expansion in LRP12 in five families and two simplex individuals. These ALS individuals (LRP12-ALS) have 61-100 repeats, which contrasts with most OPDM individuals with repeat expansion in LRP12 (LRP12-OPDM), who have 100-200 repeats. Phosphorylated TDP-43 is present in the cytoplasm of iPS cell-derived motor neurons (iPSMNs) in LRP12-ALS, a finding that reproduces the pathological hallmark of ALS. RNA foci are more prominent in muscle and iPSMNs in LRP12-ALS than in LRP12-OPDM. Muscleblind-like 1 aggregates are observed only in OPDM muscle. In conclusion, CGG repeat expansions in LRP12 cause ALS and OPDM, depending on the length of the repeat. Our findings provide insight into the repeat length-dependent switching of phenotypes.

Advances in the treatment and management of frontotemporal dementia

INTRODUCTION

Frontotemporal dementia (FTD) is a complex neurodegenerative disorder, characterized by a wide range of pathological conditions associated with the buildup of proteins such as tau and TDP-43. With a strong hereditary component, FTD often results from genetic variants in three genes - MAPT, GRN, and C9orf72.

AREAS COVERED

In this review, the authors explore abnormal protein accumulation in FTD and forthcoming treatments, providing a detailed analysis of new diagnostic advancements, including innovative markers. They analyze how these discoveries have influenced therapeutic strategies, particularly disease-modifying treatments, which could potentially transform FTD management. This comprehensive exploration of FTD from its molecular underpinnings to its therapeutic prospects offers a compelling overview of the current state of FTD research.

EXPERT OPINION

Notable challenges in FTD management involve identifying reliable biomarkers for early diagnosis and response monitoring. Genetic forms of FTD, particularly those linked to C9orf72 and GRN, show promise, with targeted therapies resulting in substantial progress in disease-modifying strategies. The potential of neuromodulation techniques, like tDCS and rTMS, is being explored, requiring further study. Ongoing trials and multi-disciplinary care highlight the continued push toward effective FTD treatments. With increasing understanding of FTD's molecular and clinical intricacies, the hope for developing effective interventions grows.

Proteomics of the dentate gyrus reveals semantic dementia specific molecular pathology

Semantic dementia (SD) is a clinical subtype of frontotemporal dementia consistent with the neuropathological diagnosis frontotemporal lobar degeneration (FTLD) TDP type C, with characteristic round TDP-43 protein inclusions in the dentate gyrus. Despite this striking clinicopathological concordance, the pathogenic mechanisms are largely unexplained forestalling the development of targeted therapeutics. To address this, we carried out laser capture microdissection of the dentate gyrus of 15 SD patients and 17 non-demented controls, and assessed relative protein abundance changes by label-free quantitative mass spectrometry. To identify SD specific proteins, we compared our results to eight other FTLD and Alzheimer's disease (AD) proteomic datasets of cortical brain tissue, parallel with functional enrichment analyses and protein-protein interactions (PPI). Of the total 5,354 quantified proteins, 151 showed differential abundance in SD patients (adjusted P-value < 0.01). Seventy-nine proteins were considered potentially SD specific as these were not detected, or demonstrated insignificant or opposite change in FTLD/AD. Functional enrichment indicated an overrepresentation of pathways related to the immune response, metabolic processes, and cell-junction assembly. PPI analysis highlighted a cluster of interacting proteins associated with adherens junction and cadherin binding, the cadherin-catenin complex. Multiple proteins in this complex showed significant upregulation in SD, including β-catenin (CTNNB1), γ-catenin (JUP), and N-cadherin (CDH2), which were not observed in other neurodegenerative proteomic studies, and hence may resemble SD specific involvement. A trend of upregulation of all three proteins was observed by immunoblotting of whole hippocampus tissue, albeit only significant for N-cadherin. In summary, we discovered a specific increase of cell adhesion proteins in SD constituting the cadherin-catenin complex at the synaptic membrane, essential for synaptic signaling. Although further investigation and validation are warranted, we anticipate that these findings will help unravel the disease processes underlying SD.

Very early-onset behavioral variant frontotemporal dementia in a patient with a variant of uncertain significance of a FUS gene mutation

The behavioral variant of Frontotemporal dementia (bvFTD) has typically a progressive course with cognitive and behavioral changes that manifests between 50 and 70 years. Very early-onset bvFTD with rapid progression is a rare syndrome under the frontotemporal lobar degeneration (FTLD) umbrella that has been associated with a variety of protein deposition and genetic mutations. We present a case of a 24-year-old man who developed behavioral symptoms and progressed with severe cognitive impairment and functional loss within months.   Genetic testing identified a variant of uncertain significance (VUS) mutation in the FUS gene.

Distinct cell type-specific protein signatures in GRN and MAPT genetic subtypes of frontotemporal dementia

Frontotemporal dementia is characterized by progressive atrophy of frontal and/or temporal cortices at an early age of onset. The disorder shows considerable clinical, pathological, and genetic heterogeneity. Here we investigated the proteomic signatures of frontal and temporal cortex from brains with frontotemporal dementia due to GRN and MAPT mutations to identify the key cell types and molecular pathways in their pathophysiology. We compared patients with mutations in the GRN gene (n = 9) or with mutations in the MAPT gene (n = 13) with non-demented controls (n = 11). Using quantitative proteomic analysis on laser-dissected tissues we identified brain region-specific protein signatures for both genetic subtypes. Using published single cell RNA expression data resources we deduced the involvement of major brain cell types in driving these different protein signatures. Subsequent gene ontology analysis identified distinct genetic subtype- and cell type-specific biological processes. For the GRN subtype, we observed a distinct role for immune processes related to endothelial cells and for mitochondrial dysregulation in neurons. For the MAPT subtype, we observed distinct involvement of dysregulated RNA processing, oligodendrocyte dysfunction, and axonal impairments. Comparison with an in-house protein signature of Alzheimer’s disease brains indicated that the observed alterations in RNA processing and oligodendrocyte function are distinct for the frontotemporal dementia MAPT subtype. Taken together, our results indicate the involvement of different brain cell types and biological mechanisms in genetic subtypes of frontotemporal dementia. Furthermore, we demonstrate that comparison of proteomic profiles of different disease entities can separate general neurodegenerative processes from disease-specific pathways, which may aid the development of disease subtype-specific treatment strategies.

Proximity-based labeling reveals DNA damage-induced phosphorylation of fused in sarcoma (FUS) causes distinct changes in the FUS protein interactome

Accumulation of cytoplasmic inclusions containing fused in sarcoma (FUS), an RNA/DNA-binding protein, is a common hallmark of frontotemporal lobar degeneration and amyotrophic lateral sclerosis neuropathology. We have previously shown that DNA damage can trigger the cytoplasmic accumulation of N-terminally phosphorylated FUS. However, the functional consequences of N-terminal FUS phosphorylation are unknown. To gain insight into this question, we utilized proximity-dependent biotin labeling via ascorbate peroxidase 2 aired with mass spectrometry to investigate whether N-terminal phosphorylation alters the FUS protein-protein interaction network (interactome), and subsequently, FUS function. We report the first analysis comparing the interactomes of three FUS variants: homeostatic wildtype FUS (FUS WT), phosphomimetic FUS (FUS PM; a proxy for N-terminally phosphorylated FUS), and the toxic FUS proline 525 to leucine mutant (FUS P525L) that causes juvenile amyotrophic lateral sclerosis. We found that the phosphomimetic FUS interactome is uniquely enriched for a group of cytoplasmic proteins that mediate mRNA metabolism and translation, as well as nuclear proteins involved in the spliceosome and DNA repair functions. Furthermore, we identified and validated the RNA-induced silencing complex RNA helicase MOV10 as a novel interacting partner of FUS. Finally, we provide functional evidence that N-terminally phosphorylated FUS may disrupt homeostatic translation and steady-state levels of specific mRNA transcripts. Taken together, these results highlight phosphorylation as a unique modulator of the interactome and function of FUS.

Behavioral Variant Frontotemporal Dementia

PURPOSE OF REVIEW

This article reviews many of the complex facets of behavioral variant frontotemporal dementia (bvFTD) and frontotemporal lobar degeneration (FTLD). A particular focus is on improving diagnostic accuracy to reduce the arduous diagnostic odyssey that so many patients and families endure. Strategies to promote diagnostic accuracy and approach the management of problematic symptoms are also discussed.

RECENT FINDINGS

Although the International Consensus Criteria for bvFTD were published more than a decade ago and clinicopathologic studies have confirmed their utility, diagnostic confusion continues. This article presents updated data along with illustrative cases to emphasize the clinical pearls that are most useful for clinicians. Although accurate prediction of the underlying proteinopathy remains a challenge, the ability to differentiate bvFTD from atypical Alzheimer disease, psychiatric disorders, and other mimickers has improved. Knowledge about the genetic underpinnings in a significant minority of individuals with familial FTLD is enabling early and accurate diagnosis. Therapeutic optimism has also increased, particularly in familial FTLD, with a few clinical trials in progress and several more planned, some of which are designed to slow progression or delay the onset of symptoms, or both.

SUMMARY

The diagnosis and management of bvFTD is challenging for clinicians and particularly for patients and their families. Although much progress has been gained over recent years, several key research questions persist. Treatments that significantly improve symptoms or alter the course of FTLD remain elusive, but optimism is increasing as pathobiology is better understood and novel therapies are being developed.

Phases of volume loss in patients with known frontotemporal lobar degeneration spectrum pathology

Frontotemporal lobar degeneration (FTLD) includes clinically similar FTLD-tau or FTLD-TDP proteinopathies which lack in vivo markers for accurate antemortem diagnosis. To identify early distinguishing sites of cortical atrophy between groups, we retrospectively analyzed in vivo volumetric MRI from 42 FTLD-Tau and 21 FTLD-TDP patients and validated these findings with postmortem measures of pathological burden. Our frequency-based staging model revealed distinct loci of maximal early cortical atrophy in each group, including dorsolateral and medial frontal regions in FTLD-Tau and ventral frontal and anterior temporal regions in FTLD-TDP. Sørenson-Dice calculations between proteinopathy groups showed little overlap of phases. Conversely, within-group subtypes showed good overlap between 3R- and 4R-tauopathies, and between TDP-43 Types A and C for early regions with subtle divergence between subtypes in subsequent phases of atrophy. Postmortem validation found an association of imaging phases with pathologic burden within FTLD-tau (F(4, 238) = 17.44, p < 0.001) and FTLD-TDP (F(4,245) = 42.32, p < 0.001). These results suggest that relatively early, distinct markers of atrophy may distinguish FTLD proteinopathies during life.

Current concepts of mixed pathologies in neurodegenerative diseases

Neurodegenerative diseases are a pathologically, clinically and genetically diverse group of disorders without effective disease-modifying therapies. Pathologically, these disorders are characterised by disease-specific protein aggregates in neurons and/or glia and referred to as proteinopathies. Many neurodegenerative diseases show pathological overlap with the same abnormally deposited protein occurring in anatomically distinct regions, which give rise to specific patterns of cognitive and motor clinical phenotypes. Sequential distribution patterns of protein inclusions throughout the brain have been described. Rather than occurring in isolation, it is increasingly recognised that combinations of one or more proteinopathies with or without cerebrovascular disease frequently occur in individuals with neurodegenerative diseases. In addition, complex constellations of ageing-related and incidental pathologies associated with tau, TDP-43, Aβ, α-synuclein deposition have been commonly reported in longitudinal ageing studies. This review provides an overview of current classification of neurodegenerative and age-related pathologies and presents the spectrum and complexity of mixed pathologies in community-based, longitudinal ageing studies, in major proteinopathies, and genetic conditions. Mixed pathologies are commonly reported in individuals >65 years with and without cognitive impairment; however, they are increasingly recognised in younger individuals (<65 years). Mixed pathologies are thought to lower the threshold for developing cognitive impairment and dementia. Hereditary neurodegenerative diseases also show a diverse range of mixed pathologies beyond the proteinopathy primarily linked to the genetic abnormality. Cases with mixed pathologies might show a different clinical course, which has prognostic relevance and obvious implications for biomarker and therapy development, and stratifying patients for clinical trials.

The role of inflammation in neurodegeneration: novel insights into the role of the immune system in C9orf72 HRE-mediated ALS/FTD

Neuroinflammation is an important hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). An inflammatory reaction to neuronal injury is deemed vital for neuronal health and homeostasis. However, a continued activation of the inflammatory response can be detrimental to remaining neurons and aggravate the disease process. Apart from a disease modifying role, some evidence suggests that neuroinflammation may also contribute to the upstream cause of the disease. In this review, we will first focus on the role of neuroinflammation in the pathogenesis of chromosome 9 open reading frame 72 gene (C9orf72) hexanucleotide repeat expansions (HRE)-mediated ALS/FTD (C9-ALS/FTD). Additionally, we will discuss evidence from ex vivo and in vivo studies and finally, we briefly summarize the trials and progress of anti-inflammatory therapies.

A postzygotic de novo NCDN mutation identified in a sporadic FTLD patient results in neurochondrin haploinsufficiency and altered FUS granule dynamics

Frontotemporal dementia (FTD) is a heterogeneous clinical disorder characterized by progressive abnormalities in behavior, executive functions, personality, language and/or motricity. A neuropathological subtype of FTD, frontotemporal lobar degeneration (FTLD)-FET, is characterized by protein aggregates consisting of the RNA-binding protein fused in sarcoma (FUS). The cause of FTLD-FET is not well understood and there is a lack of genetic evidence to aid in the investigation of mechanisms of the disease. The goal of this study was to identify genetic variants contributing to FTLD-FET and to investigate their effects on FUS pathology. We performed whole-exome sequencing on a 50-year-old FTLD patient with ubiquitin and FUS-positive neuronal inclusions and unaffected parents, and identified a de novo postzygotic nonsense variant in the NCDN gene encoding Neurochondrin (NCDN), NM_014284.3:c.1206G > A, p.(Trp402*). The variant was associated with a ~ 31% reduction in full-length protein levels in the patient’s brain, suggesting that this mutation leads to NCDN haploinsufficiency. We examined the effects of NCDN haploinsufficiency on FUS and found that depleting primary cortical neurons of NCDN causes a reduction in the total number of FUS-positive cytoplasmic granules. Moreover, we found that these granules were significantly larger and more highly enriched with FUS. We then examined the effects of a loss of FUS function on NCDN in neurons and found that depleting cells of FUS leads to a decrease in NCDN protein and mRNA levels. Our study identifies the NCDN protein as a likely contributor of FTLD-FET pathophysiology. Moreover, we provide evidence for a negative feedback loop of toxicity between NCDN and FUS, where loss of NCDN alters FUS cytoplasmic dynamics, which in turn has an impact on NCDN expression.

Cardiac Autonomic Modulation in Subjects with Amyotrophic Lateral Sclerosis (ALS) during an Upper Limb Virtual Reality Task: A Prospective Control Trial

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease. As a result of the rapid progression and severity of the disease, people with ALS experience loss of functionality and independence. Furthermore, it has already been described presence of autonomic dysfunction. Despite the increasing use of virtual reality (VR) in the treatment of different diseases, the use of virtual reality environment as an intervention program for ALS patients is innovative. The benefits and limitations have not yet been proven. Our objective was to evaluate the autonomic function of individuals with amyotrophic lateral sclerosis throughout the virtual reality task. The analysis of autonomic function was completed before, during, and after the virtual reality task using the upper limbs; also, all steps lasted ten minutes in a sitting position. Heart rate variability (HRV) was taken via the Polar® RS800CX cardiofrequencymeter. The following questionnaire was enforced: Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS) and Fatigue Severity Scale (FSS). Different types of HRV were revealed for the groups, indicating that the ALS group has reduced HRV, with most of the representative indices of the sympathetic nervous system. Besides, the physiological process of reducing parasympathetic activity from rest to VR activity (vagal withdrawal), with reduction in HF (ms²) and an increase in HR from rest to activity, and a further increase throughout recovery, with withdrawal of sympathetic nervous system, occurs just for the control group (CG), with no alterations between rest, activity, and recovery in individuals with ALS. We could conclude that patients with ALS have the reduction of HRV with the sympathetic predominance when equated to the healthy CG. Besides that, the ALS individuals have no capability to adapt the autonomic nervous system when likened to the CG during therapy based on VR and their recovery.

New insights and therapeutic opportunities for progranulin-deficient frontotemporal dementia

Frontotemporal dementia (FTD) is the second most common form of dementia. It affects the frontal and temporal lobes of the brain and has a highly heterogeneous clinical representation with patients presenting with a wide range of behavioral, language, and executive dysfunctions. Etiology of FTD is complex and consists of both familial and sporadic cases. Heterozygous mutations in the GRN gene, resulting in GRN haploinsufficiency, cause progranulin (PGRN)-deficient FTD characterized with cytoplasmic mislocalization of TAR DNA-binding protein 43 kDa (TDP-43) aggregates. GRN codes for PGRN, a secreted protein that is also localized in the endolysosomes and plays a critical role in regulating lysosomal homeostasis. How PGRN deficiency modulates immunity and causes TDP-43 pathology and FTD-related neurodegeneration remains an active area of intense investigation. In the current review, we discuss some of the significant progress made in the past two years that links PGRN deficiency with microglial-associated neuroinflammation, TDP-43 pathology, and lysosomal dysfunction. We also review the opportunities and challenges toward developing therapies and biomarkers to treat PGRN-deficient FTD.

Cerebrospinal Fluid EV Concentration and Size Are Altered in Alzheimer’s Disease and Dementia with Lewy Bodies

Alzheimer’s disease (AD), dementia with Lewy bodies (DLB) and frontotemporal dementia (FTD) represent the three major neurodegenerative dementias characterized by abnormal brain protein accumulation. In this study, we investigated extracellular vesicles (EVs) and neurotrophic factors in the cerebrospinal fluid (CSF) of 120 subjects: 36 with AD, 30 with DLB, 34 with FTD and 20 controls. Specifically, CSF EVs were analyzed by Nanoparticle Tracking Analysis and neurotrophic factors were measured with ELISA. We found higher EV concentration and lower EV size in AD and DLB groups compared to the controls. Classification tree analysis demonstrated EV size as the best parameter able to discriminate the patients from the controls (96.7% vs. 3.3%, respectively). The diagnostic performance of the EV concentration/size ratio resulted in a fair discrimination level with an area under the curve of 0.74. Moreover, the EV concentration/size ratio was associated with the p-Tau181/Aβ42 ratio in AD patients. In addition, we described altered levels of cystatin C and progranulin in the DLB and AD groups. We did not find any correlation between neurotrophic factors and EV parameters. In conclusion, the results of this study suggest a common involvement of the endosomal pathway in neurodegenerative dementias, giving important insight into the molecular mechanisms underlying these pathologies.

Utility of the Repeat and Point Test for Subtyping Patients With Primary Progressive Aphasia

BACKGROUND

Primary progressive aphasia (PPA) may present with three distinct clinical sybtypes: semantic variant PPA (svPPA), nonfluent/agrammatic variant PPA (nfvPPA), and logopenic variant PPA (lvPPA).

OBJECTIVE

The aim was to examine the utility of the German version of the Repeat and Point (R&P) Test for subtyping patients with PPA.

METHOD

During the R&P Test, the examiner reads out aloud a noun and the participants are asked to repeat the word and subsequently point to the corresponding picture. Data from 204 patients (68 svPPA, 85 nfvPPA, and 51 lvPPA) and 33 healthy controls were analyzed.

RESULTS

Controls completed both tasks with >90% accuracy. Patients with svPPA had high scores in repetition (mean=9.2±1.32) but low scores in pointing (mean=6±2.52). In contrast, patients with nfvPPA and lvPPA performed comparably in both tasks with lower scores in repetition (mean=7.4±2.7 for nfvPPA and 8.2±2.34 for lvPPA) but higher scores in pointing (mean=8.9±1.41 for nfvPPA and 8.6±1.62 for lvPPA). The R&P Test had high accuracy discriminating svPPA from nfvPPA (83% accuracy) and lvPPA (79% accuracy). However, there was low accuracy discriminating nfvPPA from lvPPA (<60%).

CONCLUSION

The R&P Test helps to differentiate svPPA from 2 nonsemantic variants (nfvPPA and lvPPA). However, additional tests are required for the differentiation of nfvPPA and lvPPA.

Investigating the Endo-Lysosomal System in Major Neurocognitive Disorders Due to Alzheimer's Disease, Frontotemporal Lobar Degeneration and Lewy Body Disease: Evidence for SORL1 as a Cross-Disease Gene

Dysfunctions in the endo-lysosomal system have been hypothesized to underlie neurodegeneration in major neurocognitive disorders due to Alzheimer's disease (AD), Frontotemporal Lobar Degeneration (FTLD), and Lewy body disease (DLB). The aim of this study is to investigate whether these diseases share genetic variability in the endo-lysosomal pathway. In AD, DLB, and FTLD patients and in controls (948 subjects), we performed a targeted sequencing of the top 50 genes belonging to the endo-lysosomal pathway. Genetic analyses revealed (i) four previously reported disease-associated variants in the SORL1 (p.N1246K, p.N371T, p.D2065V) and DNAJC6 genes (p.M133L) in AD, FTLD, and DLB, extending the previous knowledge attesting SORL1 and DNAJC6 as AD- and PD-related genes, respectively; (ii) three predicted null variants in AD patients in the SORL1 (p.R985X in early onset familial AD, p.R1207X) and PPT1 (p.R48X in early onset familial AD) genes, where loss of function is a known disease mechanism. A single variant and gene burden analysis revealed some nominally significant results of potential interest for SORL1 and DNAJC6 genes. Our data highlight that genes controlling key endo-lysosomal processes (i.e., protein sorting/transport, clathrin-coated vesicle uncoating, lysosomal enzymatic activity regulation) might be involved in AD, FTLD and DLB pathogenesis, thus suggesting an etiological link behind these diseases.

Role of Autoantibodies in Neurodegenerative Dementia: An Emerging Association

OBJECTIVE

In the background of an emerging role for immune dysregulation in neurodegenerative dementias, this study aimed to investigate the relationship between systemic autoimmunity and dementia. The objective was to study the frequency and profile of disease-specific autoantibodies in Alzheimer's dementia (AD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB).

METHODS

Immunological testing was performed in a large cohort of neurodegenerative dementia diagnosed based on standard clinical and imaging criteria. Patients were evaluated for the presence of autoantibodies specific for systemic autoimmune diseases that included anti-extractable nuclear antibody profile, rheumatoid factor antibody (RA), perinuclear anti-neutrophil cytoplasmic antibody (p-ANCA), and cytoplasmic anti-neutrophil cytoplasmic antibody (c-ANCA) in serum.

RESULTS

Of 174 patients with degenerative dementia (FTD = 114, AD = 53, and DLB = 7) evaluated with immunological testing, 18.9% (n = 33) were seropositive for autoantibodies. The common antibodies detected were anti-Scl-70 (25%), anti-Ro-52 (18.7%), anti-nRNP-Sm (12.5%), and anti-CENP-B (9.3%). There were no significant systemic complaints in the majority of patients. A wider range of antibodies were positive in FTD compared to AD and DLB. While no difference was observed in the mean age, sex, or duration of illness between seropositive and negative patients, family history of dementia was more frequent among seronegative patients.

CONCLUSION

Our findings indicate an emerging role for immune dysregulation in patients with classical neurodegenerative dementias, especially those with FTD. These autoantibodies could play a role in immune degradation of protein aggregates that characterize neurodegeneration. Study findings emphasize the need to explore the complex relationship between systemic autoimmunity and neurodegenerative dementia.

Conceptual framework for the definition of preclinical and prodromal frontotemporal dementia

The presymptomatic stages of frontotemporal dementia (FTD) are still poorly defined and encompass a long accrual of progressive biological (preclinical) and then clinical (prodromal) changes, antedating the onset of dementia. The heterogeneity of clinical presentations and the different neuropathological phenotypes have prevented a prior clear description of either preclinical or prodromal FTD. Recent advances in therapeutic approaches, at least in monogenic disease, demand a proper definition of these predementia stages. It has become clear that a consensus lexicon is needed to comprehensively describe the stages that anticipate dementia. The goal of the present work is to review existing literature on the preclinical and prodromal phases of FTD, providing recommendations to address the unmet questions, therefore laying out a strategy for operationalizing and better characterizing these presymptomatic disease stages.