Clinical phenotypes and radiological findings in frontotemporal dementia related to TARDBP mutations

Cognitive and Behavioral Features of Patients With Amyotrophic Lateral Sclerosis Who Are Carriers of the TARDBP Pathogenic Variant

BACKGROUND AND OBJECTIVES

TARDBP patients are considered particularly prone to cognitive involvement, but no systematic studies of cognitive impairment in TARDBP patients are available. The aim of this article was to depict in depth the cognitive-behavioral characteristics of a cohort of patients with amyotrophic lateral sclerosis (ALS) carrying TARDBP pathogenetic variants followed by an ALS referral center.

METHODS

We enrolled all patients with ALS seen at the Turin ALS expert center in the 2009-2021 period who underwent extensive genetic testing and a neuropsychological battery encompassing executive function, verbal memory, language, visual memory, visuoconstructive abilities, attention/working memory, psychomotor speed, nonverbal intelligence, cognitive flexibility, social cognition, and behavior. Tests were compared with the Mann-Whitney U test on age-corrected, sex-corrected, and education-corrected scores. Cognition was classified as normal (ALS-CN); isolated cognitive impairment (ALSci), that is, evidence of executive and/or language dysfunction; isolated behavioral impairment (ALSbi), that is, identification of apathy; cognitive and behavioral impairment (ALScbi), that is, evidence meeting the criteria for both ALSci and ALSbi; and frontotemporal dementia (ALS-FTD).

RESULTS

This study includes 33 patients with TARDBP pathogenetic variants (TARDBP-ALS) (median age 61 years [interquartile range (IQR) 53-67], 8 female [24.2%]) and 928 patients with ALS not carrying the pathogenic variant (WT-ALS) (median age 67 years [IQR 59-74], 386 female [41.6%]). TARDBP-ALS cases were also compared with 129 matched controls (median age 66 years [IQR 57.5-71.5], 55 female [42.6%]). TARDBP-ALS and WT-ALS patients were cognitively classified as ALS-CN (54% vs 58.8%, respectively), ALSci (21.2% vs 18.3%), ALSci (9.1% vs 9.5%), ALScbi (6.1% vs 6.0%), and ALS-FTD (9.1 vs 6.7%), with no significant difference (p = 0.623). Compared with controls, TARDBP-ALS had a worse performance in executive functions, visual memory, visuoconstructive abilities, verbal fluency, and the apathy behavioral component of FrSBe. The scores of performed tests, including all Edinburgh Cognitive and Behavioral ALS Screen subdomains, were similar in TARDBP-ALS and WT-ALS.

DISCUSSION

TARDBP-ALS patients were significantly more impaired than controls in most examined domains but do not show any specific pattern of cognitive impairment compared with WT-ALS. Our findings are relevant both clinically, considering the effect of cognitive impairment on patients' decision-making and caregivers' burden, and in designing clinical trials for the treatment of patients carrying TARDBP pathogenetic variants.

Symptomatic progression of frontotemporal dementia with the TARDBP I383V variant

We present a longitudinal description of a man with the TARDBP I383V variant of frontotemporal dementia (FTD). His progressive changes in behavior and language resulted in a diagnosis of the right temporal variant of FTD, also called the semantic behavioral variant (sbvFTD). We also present data from a small series of patients with the TARDBP I383V variant who were enrolled in a nationwide FTD research collaboration (ALLFTD). These data support slowly progressive loss of semantic function. While semantic dementia is infrequently considered genetic, the TARDBP I383V variant seems to be an exception. Longitudinal analyses in larger samples are warranted.

Primary progressive aphasia: six questions in search of an answer

Here, we review recent progress in the diagnosis and management of primary progressive aphasia-the language-led dementias. We pose six key unanswered questions that challenge current assumptions and highlight the unresolved difficulties that surround these diseases. How many syndromes of primary progressive aphasia are there-and is syndromic diagnosis even useful? Are these truly 'language-led' dementias? How can we diagnose (and track) primary progressive aphasia better? Can brain pathology be predicted in these diseases? What is their core pathophysiology? In addition, how can primary progressive aphasia best be treated? We propose that pathophysiological mechanisms linking proteinopathies to phenotypes may help resolve the clinical complexity of primary progressive aphasia, and may suggest novel diagnostic tools and markers and guide the deployment of effective therapies.

Novel data-driven subtypes and stages of brain atrophy in the ALS-FTD spectrum

BACKGROUND

TDP-43 proteinopathies represent a spectrum of neurological disorders, anchored clinically on either end by amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD). The ALS-FTD spectrum exhibits a diverse range of clinical presentations with overlapping phenotypes, highlighting its heterogeneity. This study was aimed to use disease progression modeling to identify novel data-driven spatial and temporal subtypes of brain atrophy and its progression in the ALS-FTD spectrum.

METHODS

We used a data-driven procedure to identify 13 anatomic clusters of brain volume for 57 behavioral variant FTD (bvFTD; with either autopsy-confirmed TDP-43 or TDP-43 proteinopathy-associated genetic variants), 103 ALS, and 47 ALS-FTD patients with likely TDP-43. A Subtype and Stage Inference (SuStaIn) model was trained to identify subtypes of individuals along the ALS-FTD spectrum with distinct brain atrophy patterns, and we related subtypes and stages to clinical, genetic, and neuropathological features of disease.

RESULTS

SuStaIn identified three novel subtypes: two disease subtypes with predominant brain atrophy in either prefrontal/somatomotor regions or limbic-related regions, and a normal-appearing group without obvious brain atrophy. The limbic-predominant subtype tended to present with more impaired cognition, higher frequencies of pathogenic variants in TBK1 and TARDBP genes, and a higher proportion of TDP-43 types B, E and C. In contrast, the prefrontal/somatomotor-predominant subtype had higher frequencies of pathogenic variants in C9orf72 and GRN genes and higher proportion of TDP-43 type A. The normal-appearing brain group showed higher frequency of ALS relative to ALS-FTD and bvFTD patients, higher cognitive capacity, higher proportion of lower motor neuron onset, milder motor symptoms, and lower frequencies of genetic pathogenic variants. The overall SuStaIn stages also correlated with evidence for clinical progression including longer disease duration, higher King's stage, and cognitive decline. Additionally, SuStaIn stages differed across clinical phenotypes, genotypes and types of TDP-43 pathology.

CONCLUSIONS

Our findings suggest distinct neurodegenerative subtypes of disease along the ALS-FTD spectrum that can be identified in vivo, each with distinct brain atrophy, clinical, genetic and pathological patterns.

Novel data-driven subtypes and stages of brain atrophy in the ALS-FTD spectrum

Background

TDP-43 proteinopathies represents a spectrum of neurological disorders, anchored clinically on either end by amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD). The ALS-FTD spectrum exhibits a diverse range of clinical presentations with overlapping phenotypes, highlighting its heterogeneity. This study aimed to use disease progression modeling to identify novel data-driven spatial and temporal subtypes of brain atrophy and its progression in the ALS-FTD spectrum.

Methods

We used a data-driven procedure to identify 13 anatomic clusters of brain volumes for 57 behavioral variant FTD (bvFTD; with either autopsy-confirmed TDP-43 or TDP-43 proteinopathy-associated genetic variants), 103 ALS, and 47 ALS-FTD patients with likely TDP-43. A Subtype and Stage Inference (SuStaIn) model was trained to identify subtypes of individuals along the ALS-FTD spectrum with distinct brain atrophy patterns, and we related subtypes and stages to clinical, genetic, and neuropathological features of disease.

Results

SuStaIn identified three novel subtypes: two disease subtypes with predominant brain atrophy either in prefrontal/somatomotor regions or limbic-related regions, and a normal-appearing group without obvious brain atrophy. The Limbic-predominant subtype tended to present with more impaired cognition, higher frequencies of pathogenic variants in TBK1 and TARDBP genes, and a higher proportion of TDP-43 type B, E and C. In contrast, the Prefrontal/Somatomotor-predominant subtype had higher frequencies of pathogenic variants in C9orf72 and GRN genes and higher proportion of TDP-43 type A. The normal-appearing brain group showed higher frequency of ALS relative to ALS-FTD and bvFTD patients, higher cognitive capacity, higher proportion of lower motor neuron onset, milder motor symptoms, and lower frequencies of genetic pathogenic variants. Overall SuStaIn stages also correlated with evidence for clinical progression including longer disease duration, higher King's stage, and cognitive decline. Additionally, SuStaIn stages differed across clinical phenotypes, genotypes and types of TDP-43 pathology.

Conclusions

Our findings suggest distinct neurodegenerative subtypes of disease along the ALS-FTD spectrum that can be identified in vivo, each with distinct brain atrophy, clinical, genetic and pathological patterns.

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.

The landscape of cognitive impairment in superoxide dismutase 1-amyotrophic lateral sclerosis

Although mutations in the superoxide dismutase 1 gene account for only a minority of total amyotrophic lateral sclerosis cases, the discovery of this gene has been crucial for amyotrophic lateral sclerosis research. Since the identification of superoxide dismutase 1 in 1993, the field of amyotrophic lateral sclerosis genetics has considerably widened, improving our understanding of the diverse pathogenic basis of amyotrophic lateral sclerosis. In this review, we focus on cognitive impairment in superoxide dismutase 1-amyotrophic lateral sclerosis patients. Literature has mostly reported that cognition remains intact in superoxide dismutase 1-amyotrophic lateral sclerosis patients, but recent reports highlight frontal lobe function frailty in patients carrying different superoxide dismutase 1-amyotrophic lateral sclerosis mutations. We thoroughly reviewed all the various mutations reported in the literature to contribute to a comprehensive database of superoxide dismutase 1-amyotrophic lateral sclerosis genotype-phenotype correlation. Such a resource could ultimately improve our mechanistic understanding of amyotrophic lateral sclerosis, enabling a more robust assessment of how the amyotrophic lateral sclerosis phenotype responds to different variants across genes, which is important for the therapeutic strategy targeting genetic mutations. Cognition in superoxide dismutase 1-amyotrophic lateral sclerosis deserves further longitudinal research since this peculiar frailty in patients with similar mutations can be conditioned by external factors, including environment and other unidentified agents including modifier genes.

Study of Alzheimer's disease- and frontotemporal dementia-associated genes in the Cretan Aging Cohort

Using exome sequencing, we analyzed 196 participants of the Cretan Aging Cohort (CAC; 95 with Alzheimer's disease [AD], 20 with mild cognitive impairment [MCI], and 81 cognitively normal controls). The APOE ε4 allele was more common in AD patients (23.2%) than in controls (7.4%; p < 0.01) and the PSEN2 p.Arg29His and p.Cys391Arg variants were found in 3 AD and 1 MCI patient, respectively. Also, we found the frontotemporal dementia (FTD)-associated TARDBP gene p.Ile383Val variant in 2 elderly patients diagnosed with AD and in 2 patients, non CAC members, with the amyotrophic lateral sclerosis/FTD phenotype. Furthermore, the p.Ser498Ala variant in the positively selected GLUD2 gene was less frequent in AD patients (2.11%) than in controls (16%; p < 0.01), suggesting a possible protective effect. While the same trend was found in another local replication cohort (n = 406) and in section of the ADNI cohort (n = 808), this finding did not reach statistical significance and therefore it should be considered preliminary. Our results attest to the value of genetic testing to study aged adults with AD phenotype.

Genotype-phenotype correlation in the spectrum of frontotemporal dementia-parkinsonian syndromes and advanced diagnostic approaches

The term frontotemporal dementia (FTD) refers to a group of progressive neurodegenerative disorders characterized mainly by atrophy of the frontal and anterior temporal lobes. Based on clinical presentation, three main clinical syndromes have traditionally been described: behavioral variant frontotemporal dementia (bvFTD), non-fluent/agrammatic primary progressive aphasia (nfPPA), and semantic variant PPA (svPPA). However, over the last 20 years, it has been recognized that cognitive phenotypes often overlap with motor phenotypes, either motor neuron diseases or parkinsonian signs and/or syndromes like progressive supranuclear palsy (PSP) and cortico-basal syndrome (CBS). Furthermore, FTD-related genes are characterized by genetic pleiotropy and can cause, even in the same family, pure motor phenotypes, findings that underlie the clinical continuum of the spectrum, which has pure cognitive and pure motor phenotypes as the extremes. The genotype-phenotype correlation of the spectrum, FTD-motor neuron disease, has been well defined and extensively investigated, while the continuum, FTD-parkinsonism, lacks a comprehensive review. In this narrative review, we describe the current knowledge about the genotype-phenotype correlation of the spectrum, FTD-parkinsonism, focusing on the phenotypes that are less frequent than bvFTD, namely nfPPA, svPPA, PSP, CBS, and cognitive-motor overlapping phenotypes (i.e. PPA + PSP). From a pathological point of view, they are characterized mainly by the presence of phosphorylated-tau inclusions, either 4 R or 3 R. The genetic correlate of the spectrum can be heterogeneous, although some variants seem to lead preferentially to specific clinical syndromes. Furthermore, we critically review the contribution of genome-wide association studies (GWAS) and next-generation sequencing (NGS) in disentangling the complex heritability of the FTD-parkinsonism spectrum and in defining the genotype-phenotype correlation of the entire clinical scenario, owing to the ability of these techniques to test multiple genes, and so to allow detailed investigations of the overlapping phenotypes. Finally, we conclude with the importance of a detailed genetic characterization and we offer to patients and families the chance to be included in future randomized clinical trials focused on autosomal dominant forms of FTLD.

Neurocognitive patterns across genetic levels in behavioral variant frontotemporal dementia: a multiple single cases study

BACKGROUND

Behavioral variant frontotemporal dementia (bvFTD) has been related to different genetic factors. Identifying multimodal phenotypic heterogeneity triggered by various genetic influences is critical for improving diagnosis, prognosis, and treatments. However, the specific impact of different genetic levels (mutations vs. risk variants vs. sporadic presentations) on clinical and neurocognitive phenotypes is not entirely understood, specially in patites from underrepresented regions such as Colombia.

METHODS

Here, in a multiple single cases study, we provide systematic comparisons regarding cognitive, neuropsychiatric, brain atrophy, and gene expression-atrophy overlap in a novel cohort of FTD patients (n = 42) from Colombia with different genetic levels, including patients with known genetic influences (G-FTD) such as those with genetic mutations (GR1) in particular genes (MAPT, TARDBP, and TREM2); patients with risk variants (GR2) in genes associated with FTD (tau Haplotypes H1 and H2 and APOE variants including ε2, ε3, ε4); and sporadic FTD patients (S-FTD (GR3)).

RESULTS

We found that patients from GR1 and GR2 exhibited earlier disease onset, pervasive cognitive impairments (cognitive screening, executive functioning, ToM), and increased brain atrophy (prefrontal areas, cingulated cortices, basal ganglia, and inferior temporal gyrus) than S-FTD patients (GR3). No differences in disease duration were observed across groups. Additionally, significant neuropsychiatric symptoms were observed in the GR1. The GR1 also presented more clinical and neurocognitive compromise than GR2 patients; these groups, however, did not display differences in disease onset or duration. APOE and tau patients showed more neuropsychiatric symptoms and primary atrophy in parietal and temporal cortices than GR1 patients. The gene-atrophy overlap analysis revealed atrophy in regions with specific genetic overexpression in all G-FTD patients. A differential family presentation did not explain the results.

CONCLUSIONS

Our results support the existence of genetic levels affecting the clinical, neurocognitive, and, to a lesser extent, neuropsychiatric presentation of bvFTD in the present underrepresented sample. These results support tailored assessments characterization based on the parallels of genetic levels and neurocognitive profiles in bvFTD.

Synaptic dysfunction in ALS and FTD: anatomical and molecular changes provide insights into mechanisms of disease

Synaptic loss is a pathological feature of all neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). ALS is a disease of the cortical and spinal motor neurons resulting in fatal paralysis due to denervation of muscles. FTD is a form of dementia that primarily affects brain regions controlling cognition, language and behavior. Once classified as two distinct diseases, ALS and FTD are now considered as part of a common disease spectrum based on overlapping clinical, pathological and genetic evidence. At the cellular level, aggregation of common proteins and overlapping gene susceptibilities are shared in both ALS and FTD. Despite the convergence of these two fields of research, the underlying disease mechanisms remain elusive. However, recent discovers from ALS and FTD patient studies and models of ALS/FTD strongly suggests that synaptic dysfunction is an early event in the disease process and a unifying hallmark of these diseases. This review provides a summary of the reported anatomical and cellular changes that occur in cortical and spinal motor neurons in ALS and FTD tissues and models of disease. We also highlight studies that identify changes in the proteome and transcriptome of ALS and FTD models and provide a conceptual overview of the processes that contribute to synaptic dysfunction in these diseases. Due to space limitations and the vast number of publications in the ALS and FTD fields, many articles have not been discussed in this review. As such, this review focuses on the three most common shared mutations in ALS and FTD, the hexanucleuotide repeat expansion within intron 1 of chromosome 9 open reading frame 72 (C9ORF72), transactive response DNA binding protein 43 (TARDBP or TDP-43) and fused in sarcoma (FUS), with the intention of highlighting common pathways that promote synaptic dysfunction in the ALS-FTD disease spectrum.

Primary progressive aphasia and motor neuron disease: A review

Background

This study aims at reviewing, within the framework of motor neuron disease-frontotemporal degeneration (MND-FTD)-spectrum disorders, evidence on the co-occurrence between primary progressive aphasia (PPA) and MND in order to profile such a complex at pathological, genetic and clinical levels.

Methods

This review was pre-registered (osf.io/ds8m4) and performed in accordance with the 2020 PRISMA guidelines. Case reports/series and group studies were included if addressing (1) progressive non-fluent aphasia (PNFA) or semantic dementia (SD) with MND or (2) MND patients with co-morbid PNFA/SD.

Results

Out of 546 initial records, 56 studies were included. As to case reports/series (N = 35), which included 61 PPA-MND patients, the following findings yielded: (1) PNFA is more frequent than SD in PPA-MND; (2) in PPA-MND, the most prevalent motor phenotypes are amyotrophic lateral sclerosis and predominant-upper MND, with bulbar involvement being ubiquitous; (3) extrapyramidal features are moderately frequent in PPA-MND; (4) PPA-MND patients usually display frontotemporal, left-greater-than-right involvement; (5) TDP-43-B is the typical pathological substrate of PPA-MND; (6) TBK1 mutations represent the most frequent genetic risk factors for PPA-MND.

As to group studies, including 121 patients, proportional meta-analytic procedures revealed that: (1) the lifetime prevalence of MND in PPA is 6%; (2) PPA occurs in 19% of patients with co-morbid MND and FTD; (3) MND is more frequent in PNFA (10%) than in SD patients (3%).

Discussion

Insights herewith delivered into the clinical, neuropathological and genetic features of PPA-MND patients prompt further investigations aimed at improving clinical practice within the MND-FTD spectrum.

Biological basis and psychiatric symptoms in frontotemporal dementia

Frontotemporal dementia is a neurodegenerative disease characterized by focal degeneration of the frontal and temporal lobes, clinically presenting with disinhibited behavior, personality changes, progressive non-fluent aphasia and/or impaired semantic memory. Research progress has been made in re-organizing the clinical concept of frontotemporal dementia and neuropathological classification based on multiple accumulating proteins. Alongside this progress a list of genetic mutations or variants that are causative or increase the risk of frontotemporal dementia have been identified and some of these gene products are extensively studied. However, there are still a lot of points that need to be overcome, including lack of specific diagnostic biomarker which enable antemortem diagnosis of underlying neurodegenerative process, and lack of disease modifying therapy which could prevent disease progression. Early and precise diagnosis of frontotemporal dementia is urgently required. In this context, how to define prodromal frontotemporal dementia and early differential diagnosis from primary psychiatric disorders are also important issues. In this review we will summarize and discuss current understanding of biological basis and psychiatric symptoms in frontotemporal dementia.

Profiling morphologic MRI features of motor neuron disease caused by TARDBP mutations

Objective

Mutations in the TARDBP gene are a rare cause of genetic motor neuron disease (MND). Morphologic MRI characteristics of MND patients carrying this mutation have been poorly described. Our objective was to investigate distinctive clinical and MRI features of a relatively large sample of MND patients carrying TARDBP mutations.

Methods

Eleven MND patients carrying a TARDBP mutation were enrolled. Eleven patients with sporadic MND (sMND) and no genetic mutations were also selected and individually matched by age, sex, clinical presentation and disease severity, along with 22 healthy controls. Patients underwent clinical and cognitive evaluations, as well as 3D T1-weighted and diffusion tensor (DT) MRI on a 3 Tesla scanner. Gray matter (GM) atrophy was first investigated at a whole-brain level using voxel-based morphometry (VBM). GM volumes and DT MRI metrics of the main white matter (WM) tracts were also obtained. Clinical, cognitive and MRI features were compared between groups.

Results

MND with TARDBP mutations was associated with all possible clinical phenotypes, including isolated upper/lower motor neuron involvement, with no predilection for bulbar or limb involvement at presentation. Greater impairment at naming tasks was found in TARDBP mutation carriers compared with sMND. VBM analysis showed significant atrophy of the right lateral parietal cortex in TARDBP patients, compared with controls. A distinctive reduction of GM volumes was found in the left precuneus and right angular gyrus of TARDBP patients compared to controls. WM microstructural damage of the corticospinal tract (CST) and inferior longitudinal fasciculi (ILF) was found in both sMND and TARDBP patients, compared with controls, although decreased fractional anisotropy of the right CST and increased axial diffusivity of the left ILF (p = 0.017) was detected only in TARDBP mutation carriers.

Conclusions

TARDBP patients showed a distinctive parietal pattern of cortical atrophy and greater damage of motor and extra-motor WM tracts compared with controls, which sMND patients matched for disease severity and clinical presentation were lacking. Our findings suggest that TDP-43 pathology due to TARDBP mutations may cause deeper morphologic alterations in both GM and WM.

The Role of VCP Mutations in the Spectrum of Amyotrophic Lateral Sclerosis-Frontotemporal Dementia

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are two neurological diseases which, respectively, and primarily affect motor neurons and frontotemporal lobes. Although they can lead to different signs and symptoms, it is now evident that these two pathologies form a continuum and that hallmarks of both diseases can be present within the same person in the so-called ALS-FTD spectrum. Many studies have focused on the genetic overlap of these pathologies and it is now clear that different genes, such as C9orf72, TARDBP, SQSTM1, FUS, and p97/VCP can be mutated in both the diseases. VCP was one of the first genes associated with both FTD and ALS representing an early example of gene overlapping. VCP belongs to the type II AAA (ATPases Associated with diverse cellular activities) family and is involved in ubiquitinated proteins degradation, autophagy, lysosomal clearance and mitochondrial quality control. Since its numerous roles, mutations in this gene lead to different pathological features, first and foremost TDP-43 mislocalization. This review aims to outline recent findings on VCP roles and on how its mutations are linked to the neuropathology of ALS and FTD.

Frontotemporal dementia: A unique window on the functional role of the temporal lobes

Frontotemporal dementia (FTD) is an umbrella term covering a plethora of progressive changes in executive functions, motor abilities, behavior, and/or language. Different clinical syndromes have been described in relation to localized atrophy, informing on the functional networks that underlie these specific cognitive, emotional, and behavioral processes. These functional declines are linked with the underlying neurodegeneration of frontal and/or temporal lobes due to diverse molecular pathologies. Initially, the accumulation of misfolded proteins targets specifically susceptible cell assemblies, leading to relatively focal neurodegeneration that later spreads throughout large-scale cortical networks. Here, we discuss the most recent clinical, neuropathological, imaging, and genetics findings in FTD-spectrum syndromes affecting the temporal lobe. We focus on the semantic variant of primary progressive aphasia and its mirror image, the right temporal variant of FTD. Incipient focal atrophy of the left anterior temporal lobe (ATL) manifests with predominant naming, word comprehension, reading, and object semantic deficits, while cases of predominantly right ATL atrophy present with impairments of socioemotional, nonverbal semantic, and person-specific knowledge. Overall, the observations in FTD allow for crucial clinical-anatomic inferences, shedding light on the role of the temporal lobes in both cognition and complex behaviors. The concerted activity of both ATLs is critical to ensure that percepts are translated into concepts, yet important hemispheric differences should be acknowledged. On one hand, the left ATL attributes meaning to linguistic, external stimuli, thus supporting goal-oriented, action-related behaviors (e.g., integrating sounds and letters into words). On the other hand, the right ATL assigns meaning to emotional, visceral stimuli, thus guiding socially relevant behaviors (e.g., integrating body sensations into feelings of familiarity).

The Essential Role of Epigenetic Modifications in Neurodegenerative Diseases with Dyskinesia

Epigenetics play an essential role in the occurrence and improvement of many diseases. Evidence shows that epigenetic modifications are crucial to the regulation of gene expression. DNA methylation is closely linked to embryonic development in mammalian. In recent years, epigenetic drugs have shown unexpected therapeutic effects on neurological diseases, leading to the study of the epigenetic mechanism in neurodegenerative diseases. Unlike genetics, epigenetics modify the genome without changing the DNA sequence. Research shows that epigenetics is involved in all aspects of neurodegenerative diseases. The study of epigenetic will provide valuable insights into the molecular mechanism of neurodegenerative diseases, which may lead to new treatments and diagnoses. This article reviews the role of epigenetic modifications neurodegenerative diseases with dyskinesia, and discusses the therapeutic potential of epigenetic drugs in neurodegenerative diseases.

Genetic and clinical features of Chinese sporadic amyotrophic lateral sclerosis patients with TARDBP mutations

OBJECTIVES

To investigate the genetic and clinical features of Chinese sporadic amyotrophic lateral sclerosis (SALS) patients with TARDBP mutations, we carried out a genetic analysis in a cohort of 391 SALS patients and explored the clinical manifestations of patients with TARDBP variants.

MATERIALS AND METHODS

The coding region of all five coding exons of TARDBP, exons 2-6, were sequenced for mutations in 391 Chinese SALS patients. The clinical features of patients with TARDBP mutations were described and compared with cases in literatures.

RESULTS

Two missense mutations in TARDBP gene, c.1132A > G (p.N378D) and c.1147A > G (p.I383V), were detected in three cases, showing a low frequency (0.77%, 3/391) of TARDBP missense mutations in Chinese SALS patients. Based on a retrospective analysis of literatures, p.N378D mutation mainly presents a phenotype of early onset, whereas p.I383V mutation presents pure ALS or ALS alongside semantic variant primary progressive aphasia (svPPA), a type of frontotemporal dementia (FTD).

CONCLUSIONS

Our results demonstrate that TARDBP mutation is a rare cause of Chinese SALS patients and expand the spectrum of phenotype. It is implied that genetic analysis of SALS patients plays a crucial role in uncovering the cause of disease, especially for cases developing early onset or alongside FTD.

Experimental Disease-Modifying Agents for Frontotemporal Lobar Degeneration

Frontotemporal dementia is a clinically, genetically and pathologically heterogeneous neurodegenerative disorder, enclosing a wide range of different pathological entities, associated with the accumulation of proteins such as tau and TPD-43. Characterized by a high hereditability, mutations in three main genes, MAPT, GRN and C9orf72, can drive the neurodegenerative process. The connection between different genes and proteinopathies through specific mechanisms has shed light on the pathophysiology of the disease, leading to the identification of potential pharmacological targets. New experimental strategies are emerging, in both preclinical and clinical settings, which focus on small molecules rather than gene therapy. In this review, we provide an insight into the aberrant mechanisms leading to FTLD-related proteinopathies and discuss recent therapies with the potential to ameliorate neurodegeneration and disease progression.

Defective Lysosomal Lipid Catabolism as a Common Pathogenic Mechanism for Dementia

Dementia poses an ever-growing burden to health care and social services as life expectancies have grown across the world and populations age. The most common forms of dementia are Alzheimer's disease (AD), vascular dementia, frontotemporal dementia (FTD), and Lewy body dementia, which includes Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB). Genomic studies over the past 3 decades have identified variants in genes regulating lipid transporters and endosomal processes as major risk determinants for AD, with the most significant being inheritance of the ε4 allele of the APOE gene, encoding apolipoprotein E. A recent surge in research on lipid handling and metabolism in glia and neurons has established defective lipid clearance from endolysosomes as a central driver of AD pathogenesis. The most prevalent genetic risk factors for DLB are the APOE ε4 allele, and heterozygous loss of function mutations in the GBA gene, encoding the lysosomal catabolic enzyme glucocerebrosidase; whilst heterozygous mutations in the GRN gene, required for lysosomal catabolism of sphingolipids, are responsible for a significant proportion of FTD cases. Homozygous mutations in the GBA or GRN genes produce the lysosomal storage diseases Gaucher disease and neuronal ceroid lipofuscinosis. Research from mouse and cell culture models, and neuropathological evidence from lysosomal storage diseases, has established that impaired cholesterol or sphingolipid catabolism is sufficient to produce the pathological hallmarks of dementia, indicating that defective lipid catabolism is a common mechanism in the etiology of dementia.

The Right Temporal Variant of Frontotemporal Dementia Is Not Genetically Sporadic: A Case Series

Background:

Right temporal variant frontotemporal dementia (rtvFTD) has been generally considered as a right sided variant of semantic variant primary progressive aphasia (svPPA), which is a genetically sporadic disorder. Recently, we have shown that rtvFTD has a unique clinical syndrome compared to svPPA and behavioral variant frontotemporal dementia.

Objective:

We challenge the assumption that rtvFTD is a sporadic, non-familial variant of FTD by identifying potential autosomal dominant inheritance and related genes in rtvFTD.

Methods:

We collected all subjects with a diagnosis of FTD or primary progressive aphasia who had undergone genetic screening (n = 284) and subsequently who had a genetic variant (n = 48) with a diagnosis of rtvFTD (n = 6) in 2 specialized memory clinics.

Results:

Genetic variants in FTD related genes were found in 33% of genetically screened rtvFTD cases; including MAPT (n = 4), GRN (n = 1), and TARDBP (n = 1) genes, whereas only one svPPA case had a genetic variant in our combined cohorts. Additionally, 4 out of 6 rtvFTD subjects had a strong family history for dementia.

Conclusion:

Our results demonstrate that rtvFTD, unlike svPPA, is not a pure sporadic, but a heterogeneous potential genetic variant of FTD, and screening for genetic causes for FTD should be performed in patients with rtvFTD.

Temporal variant of frontotemporal dementia in C9orf72 repeat expansion carriers: two case studies

The temporal variant of frontotemporal dementia (tv-FTD) is a progressive neurodegenerative disease with a complex clinical picture mainly characterized by behavioral and language disorders. In this work, we describe clinical, genetic, neuroanatomical and neuropathological (only in one case) features of two patients with tv-FTD carrying C9orf72 repeat expansion. The first patient (AB) presented with a 1-year disease duration showing focal right anterior temporal lobe (ATL) atrophy on magnetic resonance imaging (MRI). The second patient (BC) came to medical attention 13 years after disease onset and showed a prominent bilateral ATL involvement. Both patients showed naming deficits, impairment in identifying known faces and proper names, and personality changes with new onset behavioral rigidity, and progressing language difficulties to single-word and sentence comprehension difficulties. They were classified as tv-FTD. Clinical, cognitive and MRI follow-up were performed. As cognitive impairment progressed, MRI atrophy worsened in ATL and frontotemporal areas in both patients. Both cases had clear family histories of neurological and/or psychiatric disease. Genetic testing revealed a C9orf72 hexanucleotide repeat expansion in both cases. BC passed away after 15 years of disease and autopsy showed the expected TDP-type B pathology. These genetic cases of tv-FTD highlight the susceptibility of ATL to C9orf72-related pathology and emphasize the importance of genetical testing in FTD-spectrum disorders, regardless of the clinical phenotype.

Frontotemporal dementia-linked P112H mutation of TDP-43 induces protein structural change and impairs its RNA binding function

TDP‐43 forms the primary constituents of the cytoplasmic inclusions contributing to various neurodegenerative diseases, including amyotrophic lateral sclerosis and frontotemporal dementia (FTD). Over 60 TDP‐43 mutations have been identified in patients suffering from these two diseases, but most variations are located in the protein's disordered C‐terminal glycine‐rich region. P112H mutation of TDP‐43 has been uniquely linked to FTD, and is located in the first RNA recognition motif (RRM1). This mutation is thought to be pathogenic, but its impact on TDP‐43 at the protein level remains unclear. Here, we compare the biochemical and biophysical properties of TDP‐43 truncated proteins with or without P112H mutation. We show that P112H‐mutated TDP‐43 proteins exhibit higher thermal stability, impaired RNA‐binding activity, and a reduced tendency to aggregate relative to wild‐type proteins. Near‐UV CD, 2D‐nuclear‐magnetic resonance, and intrinsic fluorescence spectrometry further reveal that the P112H mutation in RRM1 generates local conformational changes surrounding the mutational site that disrupt the stacking interactions of the W113 side chain with nucleic acids. Together, these results support the notion that P112H mutation of TDP‐43 contributes to FTD through functional impairment of RNA metabolism and/or structural changes that curtail protein clearance.

Diagnostic Assessment in Primary Progressive Aphasia: An Illustrative Case Example

Purpose Diagnosis and classification of primary progressive aphasia (PPA) requires confirmation of specific speech and language symptoms, highlighting the important role of speech-language pathologists in the evaluation process. The purpose of this case report is to inform speech-language pathologists regarding current practices for diagnostic assessment in PPA, describing standard approaches as well as complementary, state-of-the-art procedures that may improve diagnostic precision. Method We describe the diagnostic evaluation of a 49-year-old woman with complaints of progressive word-finding difficulty. She completed standard neurological, neuropsychological, and speech-language evaluations, as well as magnetic resonance and positron emission tomography imaging of her brain. In addition, a history of developmental speech, language, and learning abilities was obtained, as well as genetic testing and assessment of cerebrospinal fluid biomarkers. We discuss the evaluation results in the context of the most current research related to PPA diagnosis. Conclusion Detailed behavioral assessment, thorough intake of symptom history and neurodevelopmental differences, multimodal neuroimaging, and comprehensive examination of genes and biomarkers are of paramount importance for detecting and characterizing PPA, with ramifications for early behavioral and/or pharmacological intervention. Supplemental Material https://doi.org/10.23641/asha.12771113.

Network analysis of the progranulin-deficient mouse brain proteome reveals pathogenic mechanisms shared in human frontotemporal dementia caused by GRN mutations

Heterozygous, loss-of-function mutations in the granulin gene (GRN) encoding progranulin (PGRN) are a common cause of frontotemporal dementia (FTD). Homozygous GRN mutations cause neuronal ceroid lipofuscinosis-11 (CLN11), a lysosome storage disease. PGRN is a secreted glycoprotein that can be proteolytically cleaved into seven bioactive 6 kDa granulins. However, it is unclear how deficiency of PGRN and granulins causes neurodegeneration. To gain insight into the mechanisms of FTD pathogenesis, we utilized Tandem Mass Tag isobaric labeling mass spectrometry to perform an unbiased quantitative proteomic analysis of whole-brain tissue from wild type (Grn^+/+) and Grn knockout (Grn^-/-) mice at 3- and 19-months of age. At 3-months lysosomal proteins (i.e. Gns, Scarb2, Hexb) are selectively increased indicating lysosomal dysfunction is an early consequence of PGRN deficiency. Additionally, proteins involved in lipid metabolism (Acly, Apoc3, Asah1, Gpld1, Ppt1, and Naaa) are decreased; suggesting lysosomal degradation of lipids may be impaired in the Grn^-/- brain. Systems biology using weighted correlation network analysis (WGCNA) of the Grn^-/- brain proteome identified 26 modules of highly co-expressed proteins. Three modules strongly correlated to Grn deficiency and were enriched with lysosomal proteins (Gpnmb, CtsD, CtsZ, and Tpp1) and inflammatory proteins (Lgals3, GFAP, CD44, S100a, and C1qa). We find that lysosomal dysregulation is exacerbated with age in the Grn^-/- mouse brain leading to neuroinflammation, synaptic loss, and decreased markers of oligodendrocytes, myelin, and neurons. In particular, GPNMB and LGALS3 (galectin-3) were upregulated by microglia and elevated in FTD-GRN brain samples, indicating common pathogenic pathways are dysregulated in human FTD cases and Grn^-/- mice. GPNMB levels were significantly increased in the cerebrospinal fluid of FTD-GRN patients, but not in MAPT or C9orf72 carriers, suggesting GPNMB could be a biomarker specific to FTD-GRN to monitor disease onset, progression, and drug response. Our findings support the idea that insufficiency of PGRN and granulins in humans causes neurodegeneration through lysosomal dysfunction, defects in autophagy, and neuroinflammation, which could be targeted to develop effective therapies.

Modelling frontotemporal dementia using patient-derived induced pluripotent stem cells

Frontotemporal dementia (FTD) describes a group of clinically heterogeneous conditions that frequently affect people under the age of 65 (Le Ber et al., 2013). There are multiple genetic causes of FTD, including coding or splice-site mutations in MAPT, GRN mutations that lead to haploinsufficiency of progranulin protein, and a hexanucleotide GGGGCC repeat expansion in C9ORF72. Pathologically, FTD is characterised by abnormal protein accumulations in neurons and glia. These aggregates can be composed of the microtubule-associated protein tau (observed in FTD with MAPT mutations), the DNA/RNA-binding protein TDP-43 (seen in FTD with mutations in GRN or C9ORF72 repeat expansions) or dipeptide proteins generated by repeat associated non-ATG translation of the C9ORF72 repeat expansion. There are currently no disease-modifying therapies for FTD and the availability of in vitro models that recapitulate pathologies in a disease-relevant cell type would accelerate the development of novel therapeutics. It is now possible to generate patient-specific stem cells through the reprogramming of somatic cells from a patient with a genotype/phenotype of interest into induced pluripotent stem cells (iPSCs). iPSCs can subsequently be differentiated into a plethora of cell types including neurons, astrocytes and microglia. Using this approach has allowed researchers to generate in vitro models of genetic FTD in human cell types that are largely inaccessible during life. In this review we explore the recent progress in the use of iPSCs to model FTD, and consider the merits, limitations and future prospects of this approach.

Neuroimaging in genetic frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) have a strong clinical, genetic and pathological overlap. This review focuses on the current understanding of structural, functional and molecular neuroimaging signatures of genetic FTD and ALS. We overview quantitative neuroimaging studies on the most common genes associated with FTD (MAPT, GRN), ALS (SOD1), and both (C9orf72), and summarize visual observations of images reported in the rarer genes (CHMP2B, TARDBP, FUS, OPTN, VCP, UBQLN2, SQSTM1, TREM2, CHCHD10, TBK1).

TDP-43, a protein central to amyotrophic lateral sclerosis, is destabilized by tankyrase-1 and -2

In >95% of cases of amyotrophic lateral sclerosis (ALS) and ∼45% of frontotemporal degeneration (FTD), the RNA/DNA-binding protein TDP-43 is cleared from the nucleus and abnormally accumulates in the cytoplasm of affected brain cells. Although the cellular triggers of disease pathology remain enigmatic, mounting evidence implicates the poly(ADP-ribose) polymerases (PARPs) in TDP-43 neurotoxicity. Here we show that inhibition of the PARP enzymes tankyrase 1 and tankyrase 2 (referred to as Tnks-1/2) protect primary rodent neurons from TDP-43-associated neurotoxicity. We demonstrate that Tnks-1/2 interacts with TDP-43 via a newly defined tankyrase-binding domain. Upon investigating the functional effect, we find that interaction with Tnks-1/2 inhibits the ubiquitination and proteasomal turnover of TDP-43, leading to its stabilization. We further show that proteasomal turnover of TDP-43 occurs preferentially in the nucleus; our data indicate that Tnks-1/2 stabilizes TDP-43 by promoting cytoplasmic accumulation, which sequesters the protein from nuclear proteasome degradation. Thus, Tnks-1/2 activity modulates TDP-43 and is a potential therapeutic target in diseases associated with TDP-43, such as ALS and FTD.This article has an associated First Person interview with the first author of the paper.

An update on genetic frontotemporal dementia

Frontotemporal dementia (FTD) is a highly heritable group of neurodegenerative disorders, with around 30% of patients having a strong family history. The majority of that heritability is accounted for by autosomal dominant mutations in the chromosome 9 open reading frame 72 (C9orf72), progranulin (GRN), and microtubule-associated protein tau (MAPT) genes, with mutations more rarely seen in a number of other genes. This review will discuss the recent updates in the field of genetic FTD. Age at symptom onset in genetic FTD is variable with recently identified genetic modifiers including TMEM106B (in GRN carriers particularly) and a polymorphism at a locus containing two overlapping genes LOC101929163 and C6orf10 (in C9orf72 carriers). Behavioural variant FTD (bvFTD) is the most common diagnosis in each of the genetic groups, although in C9orf72 carriers amyotrophic lateral sclerosis either alone, or with bvFTD, is also common. An atypical neuropsychiatric presentation is also seen in C9orf72 carriers and family members of carriers are at greater risk of psychiatric disorders including schizophrenia and autistic spectrum disorders. Large natural history studies of presymptomatic genetic FTD are now underway both in Europe/Canada (GENFI—the Genetic FTD Initiative) and in the US (ARTFL/LEFFTDS study), collaborating together under the banner of the FTD Prevention Initiative (FPI). These studies are taking forward the validation of cognitive, imaging and fluid biomarkers that aim to robustly measure disease onset, staging and progression in genetic FTD. Grey matter changes on MRI and hypometabolism on FDG-PET are seen at least 10 years before symptom onset with white matter abnormalities seen earlier, but the pattern and exact timing of changes differ between different genetic groups. In contrast, tau PET has yet to show promise in genetic FTD. Three key fluid biomarkers have been identified so far that are likely to be helpful in clinical trials—CSF or blood neurofilament light chain levels (in all groups), CSF or blood progranulin levels (in GRN carriers) and CSF poly(GP) dipeptide repeat protein levels (in C9orf72 carriers). Increased knowledge about genetic FTD has led to more clinical presymptomatic genetic testing but this has not yet been mirrored in the development of either an accepted FTD-specific testing protocol or provision of appropriate psychological support mechanisms for those living through the at-risk phase. This will become even more relevant as disease-modifying therapy trials start in each of the genetic groups over the next few years.

Fluorescence in-situ hybridization method reveals that carboxyl-terminal fragments of transactive response DNA-binding protein-43 truncated at the amino acid residue 218 reduce poly(A)+ RNA expression

Transactive response (TAR) DNA-binding protein 43 (TDP-43) has emerged as an important contributor to amyotrophic lateral sclerosis and frontotemporal lobar degeneration. To understand the association of TDP-43 with complex RNA processing in disease pathogenesis, we performed fluorescence in-situ hybridization using HeLa cells transfected with a series of deleted TDP-43 constructs and investigated the effect of truncation of TDP-43 on the expression of poly(A) RNA. Endogenous and overexpressed full-length TDP-43 localized to the perichromatin region and interchromatin space adjacent to poly(A) RNA. Deleted variants of TDP-43 containing RNA recognition motif 1 and truncating N-terminal region induced cytoplasmic inclusions in which poly(A) RNA was recruited. Carboxyl-terminal TDP-43 truncated at residue 202 or 218 was distributed in the cytoplasm as punctate structures. Carboxyl-terminal TDP-43 truncated at residue 218, but not at 202, significantly decreased poly(A) RNA expression by ∼24% compared with the level in control cells. Our results suggest that the disturbance of RNA metabolism induced by pathogenic fragments plays central roles in the pathogenesis of amyotrophic lateral sclerosis and frontotemporal lobar degeneration.

MAPT (Tau) expression is a biomarker for an increased rate of survival in pediatric neuroblastoma

Although the impact of MAPT (Tau) expression has been well documented for neuronal cells in the context of tauopathies and neurodegenerative diseases, the impact and role of Tau expression in cancer, and specifically cancers of neuronal origin, is in its infancy. To determine the correlation between MAPT expression and survival in pediatric neuroblastoma, MAPT gene expression for samples from the TARGET pediatric neuroblastoma dataset was assessed. Initial analyses indicated that increased MAPT expression correlated with increased overall survival in neuroblastoma but not in ovarian cancer. Expression of apoptosis- and proliferation-effector genes in the neuroblastoma samples was consistent with the MAPT related survival result. Furthermore, we determined that higher neuroblastoma expression of APP also associated with neurodegeneration, correlated with better neuroblastoma survival rates. In sum, Gene expression associated with neuronal degenerative diseases was associated with a better neuroblastoma outcome. Abbreviations: ALS: Amyotrophic Lateral Sclerosis; APP: Amyloid Precursor Protein gene; CASP3: Caspase 3 gene; CASP9: Caspase 9 gene; H2AFX: H2A histone family, member X gene; HIST1H2AL: Histone H2A type 1 gene; HIST1H2BK: Histone H2B type 1-K gene; HIST1H3J: Histone H3J gene; HIST1H4B: Histone H4B gene; HIST2H2BE: Histone H2B type 2-E gene; HUGO: human genome organization; KM: Kaplan-Meier survival curve; MAPT: Tau gene; OV: Ovarian cancer; SNCA: alpha-syneculin gene; TARDBP: Transactive response DNA binding protein 43 kDa; TCGA: the cancer genome atlas.

Reduced stress granule formation and cell death in fibroblasts with the A382T mutation of TARDBP gene: evidence for loss of TDP-43 nuclear function

TAR deoxyribonucleic acid-binding protein 43 (TDP-43) is a key protein in the pathogenesis of amyoptrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Recent studies suggest that mutations in the TDP-43 coding gene, TARDBP, as well as variations in TDP-43 protein expression levels may disrupt the dynamics of stress granules (SGs). However, it remains unclear whether the pathogenetic effect of the TDP-43 protein is exerted at the cytoplasmic level, through direct participation to SG composition, or at nuclear level, through control of proteins essential to SG assembly. To clarify this point, we investigated the dynamics of SG formation in primary skin fibroblast cultures from the patients with ALS together with the A382T mutation and the patients with ALS and healthy controls with wild-type TDP-43. Under stress conditions induced by sodium arsenite, we found that in human fibroblasts TDP-43 did not translocate to the SGs but instead contributed to the SG formation through a regulatory effect on the G3BP1 core protein. We found that the A382T mutation caused a significant reduction in the number of SGs per cell (P < 0.01) as well as the percentage of cells that form SGs (P < 0.00001). Following stress stimuli, a significant decrease of viability was observed for cells with the TDP-43 A382T mutation (P < 0.0005). We can therefore conclude that the A382T mutation caused a reduction in the ability of cells to respond to stress through loss of TDP-43 function in SG nucleation. The pathogenetic action revealed in our study model does not seem to be mediated by changes in the localization of the TDP-43 protein.

Frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by progressive changes in behavior, personality, and language with involvement of the frontal and temporal regions of the brain. About 40% of FTD cases have a positive family history, and about 10% of these cases are inherited in an autosomal-dominant pattern. These gene defects present with distinct clinical phenotypes. As the diagnosis of FTD becomes more recognizable, it will become increasingly important to keep these gene mutations in mind. In this chapter, we review the genes with known associations to FTD. We discuss protein functions, mutation frequencies, clinical phenotypes, imaging characteristics, and pathology associated with these genes.

Genetics of Frontotemporal Dementia

Frontotemporal dementia (FTD) is the second most common cause of dementia following Alzheimer's disease (AD). Between 20 and 50% of cases are familial. Mutations in MAPT, GRN and C9orf72 are found in 60% of familial FTD cases. C9orf72 mutations are the most common and account for 25%. Rarer mutations (<5%) occur in other genes such as VPC, CHMP2B, TARDP, FUS, ITM2B, TBK1 and TBP. The diagnosis is often challenging due to symptom overlap with AD and other conditions. We review the genetics, clinical presentations, neuroimaging, neuropathology, animal studies and therapeutic trials in FTD. We describe clinical scenarios including the original family with the tau stem loop mutation (+14) and also the recently discovered 'missing tau' mutation +15 that 'closed the loop' in 2015.

RNA-binding proteins with prion-like domains in health and disease

Approximately 70 human RNA-binding proteins (RBPs) contain a prion-like domain (PrLD). PrLDs are low-complexity domains that possess a similar amino acid composition to prion domains in yeast, which enable several proteins, including Sup35 and Rnq1, to form infectious conformers, termed prions. In humans, PrLDs contribute to RBP function and enable RBPs to undergo liquid-liquid phase transitions that underlie the biogenesis of various membraneless organelles. However, this activity appears to render RBPs prone to misfolding and aggregation connected to neurodegenerative disease. Indeed, numerous RBPs with PrLDs, including TDP-43 (transactivation response element DNA-binding protein 43), FUS (fused in sarcoma), TAF15 (TATA-binding protein-associated factor 15), EWSR1 (Ewing sarcoma breakpoint region 1), and heterogeneous nuclear ribonucleoproteins A1 and A2 (hnRNPA1 and hnRNPA2), have now been connected via pathology and genetics to the etiology of several neurodegenerative diseases, including amyotrophic lateral sclerosis, frontotemporal dementia, and multisystem proteinopathy. Here, we review the physiological and pathological roles of the most prominent RBPs with PrLDs. We also highlight the potential of protein disaggregases, including Hsp104, as a therapeutic strategy to combat the aberrant phase transitions of RBPs with PrLDs that likely underpin neurodegeneration.

From animal models to human disease: a genetic approach for personalized medicine in ALS

Amyotrophic Lateral Sclerosis (ALS) is the most frequent motor neuron disease in adults. Classical ALS is characterized by the death of upper and lower motor neurons leading to progressive paralysis. Approximately 10 % of ALS patients have familial form of the disease. Numerous different gene mutations have been found in familial cases of ALS, such as mutations in superoxide dismutase 1 (SOD1), TAR DNA-binding protein 43 (TDP-43), fused in sarcoma (FUS), C9ORF72, ubiquilin-2 (UBQLN2), optineurin (OPTN) and others. Multiple animal models were generated to mimic the disease and to test future treatments. However, no animal model fully replicates the spectrum of phenotypes in the human disease and it is difficult to assess how a therapeutic effect in disease models can predict efficacy in humans. Importantly, the genetic and phenotypic heterogeneity of ALS leads to a variety of responses to similar treatment regimens. From this has emerged the concept of personalized medicine (PM), which is a medical scheme that combines study of genetic, environmental and clinical diagnostic testing, including biomarkers, to individualized patient care. In this perspective, we used subgroups of specific ALS-linked gene mutations to go through existing animal models and to provide a comprehensive profile of the differences and similarities between animal models of disease and human disease. Finally, we reviewed application of biomarkers and gene therapies relevant in personalized medicine approach. For instance, this includes viral delivering of antisense oligonucleotide and small interfering RNA in SOD1, TDP-43 and C9orf72 mice models. Promising gene therapies raised possibilities for treating differently the major mutations in familial ALS cases.

Molecular neuropathology of frontotemporal dementia: insights into disease mechanisms from postmortem studies

Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. The past decade has seen the discovery of several new FTD-causing genetic mutations and the identification of many of the relevant pathological proteins. The current neuropathological classification is based on the predominant protein abnormality and allows most cases of FTD to be placed into one of three broad molecular subgroups; frontotemporal lobar degeneration with tau, TDP-43 or FET protein accumulation. This review will describe our current understanding of the molecular basis of FTD, focusing on insights gained from the study of human postmortem tissue, as well as some of the current controversies. Most cases of FTD can be subclassified into one of three broad molecular subgroups based on the predominant protein that accumulates as pathological cellular inclusions. Understanding the associated pathogenic mechanisms and recognizing these FTD molecular subtypes in vivo will likely be crucial for the development and use of targeted therapies. This article is part of the Frontotemporal Dementia special issue.

Recent advances in amyotrophic lateral sclerosis

ALS is a relentlessly progressive and fatal disease, with no curative therapies available to date. Symptomatic and palliative care, provided in a multidisciplinary context, still remains the cornerstone of ALS management. However, our understanding of the molecular mechanisms underlying the disease has advanced greatly over the past years, giving new hope for the development of novel diagnostic and therapeutic approaches. Here, we have reviewed the most recent studies that have contributed to improving both clinical management and our understanding of ALS pathogenesis.

Defining the spectrum of frontotemporal dementias associated with TARDBP mutations

OBJECTIVES

We describe the largest series of patients with TARDBP mutations presenting with frontotemporal dementia (FTD) and review the cases in the literature to precisely characterize FTD diseases associated with this genotype.

METHODS

The phenotypic characteristics of 29 TARDBP patients, including 10 new French and Dutch cases and 19 reviewed from the literature, were evaluated.

RESULTS

The most frequent phenotype was a behavioral variant frontotemporal dementia (bvFTD), but a significant proportion (40%) of our patients had semantic (svFTD) or nonfluent variants (nfvFTD) at onset; and svFTD was significantly more frequent in TARDBP carriers than in other FTD genotypes (p < 0.001). Remarkably, only a minority (40%) of our patients secondarily developed amyotrophic lateral sclerosis (ALS). Two patients carried a homozygous mutation but strikingly different phenotypes (bvFTD and ALS) indicating that homozygosity does not result in a specific phenotype. Earlier age at onset in children than parent's generations, mimicking an apparent "anticipation" (21.8 ± 9.3 years, p = 0.001), and possible reduced penetrance were present in most families.

CONCLUSIONS

This study enlarges the phenotypic spectrum of TARDBP and will have important clinical implications: (1) FTD can be the only clinical manifestation of TARDBP mutations; (2) Initial language or semantic disorders might be indicative of a specific genotype; (3) Mutations should be searched in all FTD phenotypes after exclusion of major genes, even in the absence of ALS in the proband or in family history; (4) reduced penetrance and clinical variability should be considered to deliver appropriate genetic counseling.

The Genetics of Monogenic Frontotemporal Dementia

Around 10-15% of patients diagnosed with frontotemporal dementia (FTD) have a positive family history for FTD with an autosomal dominant pattern of inheritance. Since the identification of mutations in MAPT (microtubule-associated protein tau gene) in 1998, over 10 other genes have been associated with FTD spectrum disorders, discussed in this review. Along with MAPT, mutations in GRN (progranulin) and C9orf72 (chromosome 9 open reading frame 72) are the most commonly identified in FTD cohorts. The association of FTD and motor neuron disease (MND) can be caused by mutations in C9orf72 and other genes, such as TARDBP (TAR DNA-binding protein), FUS (fused in sarcoma), UBQLN2 (ubiquilin 2). Multisystem proteinopathy is a complex phenotype that includes FTD, Paget disease of the bone, inclusion body myopathy and MND, and can be due to mutations in VCP (valosing containing protein) and other recently identified genes.