A patient carrying a homozygous p.A382T TARDBP missense mutation shows a syndrome including ALS, extrapyramidal symptoms, and FTD

TDP-43-M323K causes abnormal brain development and progressive cognitive and motor deficits associated with mislocalised and increased levels of TDP-43

TDP-43 pathology is found in several neurodegenerative disorders, collectively referred to as "TDP-43 proteinopathies". Aggregates of TDP-43 are present in the brains and spinal cords of >97% of amyotrophic lateral sclerosis (ALS), and in brains of ∼50% of frontotemporal dementia (FTD) patients. While mutations in the TDP-43 gene (TARDBP) are usually associated with ALS, many clinical reports have linked these mutations to cognitive impairments and/or FTD, but also to other neurodegenerative disorders including Parkinsonism (PD) or progressive supranuclear palsy (PSP). TDP-43 is a ubiquitously expressed, highly conserved RNA-binding protein that is involved in many cellular processes, mainly RNA metabolism. To investigate systemic pathological mechanisms in TDP-43 proteinopathies, aiming to capture the pleiotropic effects of TDP-43 mutations, we have further characterised a mouse model carrying a point mutation (M323K) within the endogenous Tardbp gene. Homozygous mutant mice developed cognitive and behavioural deficits as early as 3 months of age. This was coupled with significant brain structural abnormalities, mainly in the cortex, hippocampus, and white matter fibres, together with progressive cortical interneuron degeneration and neuroinflammation. At the motor level, progressive phenotypes appeared around 6 months of age. Thus, cognitive phenotypes appeared to be of a developmental origin with a mild associated progressive neurodegeneration, while the motor and neuromuscular phenotypes seemed neurodegenerative, underlined by a progressive loss of upper and lower motor neurons as well as distal denervation. This is accompanied by progressive elevated TDP-43 protein and mRNA levels in cortex and spinal cord of homozygous mutant mice from 3 months of age, together with increased cytoplasmic TDP-43 mislocalisation in cortex, hippocampus, hypothalamus, and spinal cord at 12 months of age. In conclusion, we find that Tardbp M323K homozygous mutant mice model many aspects of human TDP-43 proteinopathies, evidencing a dual role for TDP-43 in brain morphogenesis as well as in the maintenance of the motor system, making them an ideal in vivo model system to study the complex biology of TDP-43.

Homozygous ALS-linked mutations in TARDBP/TDP-43 lead to hypoactivity and synaptic abnormalities in human iPSC-derived motor neurons

Cytoplasmic mislocalization and aggregation of the RNA-binding protein TDP-43 is a pathological hallmark of the motor neuron (MN) disease amyotrophic lateral sclerosis (ALS). Furthermore, while mutations in TARDBP (encoding TDP-43) have been associated with ALS, the pathogenic consequences of these mutations remain poorly understood. Using CRISPR-Cas9, we engineered two homozygous knock-in induced pluripotent stem cell lines carrying mutations in TARDBP encoding TDP-43A382T and TDP-43G348C, two common yet understudied ALS TDP-43 variants. Motor neurons (MNs) differentiated from knock-in iPSCs had normal viability and displayed no significant changes in TDP-43 subcellular localization, phosphorylation, solubility, or aggregation compared with isogenic control MNs. However, our results highlight synaptic impairments in both TDP-43A382T and TDP-43G348C MN cultures, as reflected in synapse abnormalities and alterations in spontaneous neuronal activity. Collectively, our findings suggest that MN dysfunction may precede the occurrence of TDP-43 pathology and neurodegeneration in ALS and further implicate synaptic and excitability defects in the pathobiology of this disease.

Disease survival and progression in TARDBP ALS patients from Sardinia, Italy

BACKGROUND

Common genes implicated in amyotrophic lateral sclerosis (ALS) development may also influence its progression rate. The C9orf72 mutations featured a faster progression rate while the European SOD1 mutations were associated with a slower progression. In this study, we assessed the relationship between TARDBP and ALS progression/survival.

METHODS

ALS incident patients (2010-2019) were diagnosed by El Escorial revised criteria and staged over the disease course by the King's staging system. Disease progression was analysed by Kaplan-Meier survival curves and Cox regression models, with survival measured from symptom onset to death/tracheostomy or censor date.

RESULTS

The study population included 76 patients carrying TARDBP mutations (A382T/G295S), 28 patients carrying the C9orf72 GGGGCC expansion, and 158 patients who had no evidence of causative genetic mutations (nmALS group). TARDBP patients reached death/tracheostomy later than C9orf72 and nmALS patients, independently of possible prognostic indicators (sex, age at ALS onset, diagnostic delay, phenotype at onset, and family history of ALS). On King's staging, the time elapsed between disease onset (King's stage 1) and involvement of the second body region (King's stage 2B) was similar in TARDBP and nmALS patients but longer in TARDBP than in C9orf72 patients. TARDBP patients reached King's stages 3 and 4 later than C9orf72 and nmALS patients.

CONCLUSIONS

TARDBP patients have a better survival/prognosis than C9orf72-positive and nmALS patients. King's staging also suggested that the higher survival rate and the slower progression associated with the TARDBP mutation could mainly be attributed to the longer time elapsed between King's stages 2B to 3.

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.

Sensory Involvement in Amyotrophic Lateral Sclerosis

Although amyotrophic lateral sclerosis (ALS) is pre-eminently a motor disease, the existence of non-motor manifestations, including sensory involvement, has been described in the last few years. Although from a clinical perspective, sensory symptoms are overshadowed by their motor manifestations, this does not mean that their pathological significance is not relevant. In this review, we have made an extensive description of the involvement of sensory and autonomic systems described to date in ALS, from clinical, neurophysiological, neuroimaging, neuropathological, functional, and molecular perspectives.

TARDBP mutations in a cohort of Italian patients with Parkinson’s disease and atypical parkinsonisms

Background

Aggregates of TAR DNA-binding protein of 43 kDa (TDP-43) represent the pathological hallmark of most amyotrophic lateral sclerosis (ALS) and of nearly 50% of frontotemporal dementia (FTD) cases but were also observed to occur as secondary neuropathology in the nervous tissue of patients with different neurodegenerative diseases, including Parkinson’s disease (PD) and atypical parkinsonism. Mutations of TARDBP gene, mainly in exon 6 hotspot, have been reported to be causative of some forms of ALS and FTD, with clinical signs of parkinsonism observed in few mutation carriers.

Methods

Direct DNA sequencing of TARDBP exon 6 was performed in a large Italian cohort of 735 patients affected by PD (354 familial and 381 sporadic) and 142 affected by atypical parkinsonism, including 39 corticobasal syndrome (CBS) and 103 progressive sopranuclear palsy (PSP). Sequencing data from 1710 healthy, ethnically matched controls were already available.

Results

Four TARDBP missense variants (p.N267S, p. G294A, p.G295S, p.S393L) were identified in four patients with typical PD and in two individuals with atypical parkinsonism (1 CBS and 1 PSP). None of the detected mutations were found in healthy controls and only the variant p.N267S was previously described in association to idiopathic familial and sporadic PD and to CBS.

Conclusion

In this study we provide further insight into the clinical phenotypic heterogeneity associated with TARDBP mutations, which expands beyond the classical ALS and FTD diseases to include also PD and atypical parkinsonism, although with a low mutational frequency, varying considerably in different Caucasian populations. In addition, our study extends the spectrum of TARDBP pathogenetic mutations found in familial and sporadic PD.

Novel TARDBP missense mutation caused familial amyotrophic lateral sclerosis with frontotemporal dementia and parkinsonism

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that predominately involves the motor neurons in the brain and spinal cord. The TARDBP gene, encoding TAR DNA-binding protein 43 (TDP-43) protein, has been identified as a major causative gene in ALS. In this study, we screened 275 SALS patients and 20 unrelated FALS probands for TARDBP mutations. We identified three TARDBP mutations in three SALS patients and two TARDBP mutations in two FALS probands, including a previously unreported mutation, p.K176I, in FALS patients consistent with frontotemporal dementia (FTD) and parkinsonism. The p.K176I mutation is the first mutation outside exon 6 of the TARDBP gene manifesting parkinsonism and the first TARDBP mutation manifesting parkinsonism identified in the Chinese population. Our results support that TARDBP mutations are one of the most common changes in both FALS and SALS in China. Patients with TARDBP mutations may have a broad phenotype spectrum of ALS, FTD, and parkinsonism. The TARDBP gene should be included in genetic screening for ALS with FTD, and/or parkinsonism.

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).

The first case of the TARDBP p.G294V mutation in a homozygous state: is a single pathogenic allele sufficient to cause ALS?

Here, we described the first amyotrophic lateral sclerosis patient presenting the c.881 G > T p.G294V TARDBP mutation in homozygous status. The patient belongs to a large pedigree from Morocco. Except for one older affected brother his parents and remaining 8 sibs are referred to be healthy and do not show any neurological sign or symptom. The lack of evidence of TARDBP deletions of any sizes, together with the presence of several AOH segments, strongly suggests that the homozygosity status of p.G294V in the proband derived from parental consanguinity. A revision of the literature and our cohorts indicates that the p.G294V mutation has been detected in only 15 additional ALS patients in heterozygosity and, except for one additional Moroccan patient, all were of Italian origin. The analysis of microsatellite markers surrounding the TARDBP gene in 8 individuals carrying the p.G294V mutation showed that the haplotypic context of the Moroccan proband is shared with most patients of European origin indicating that they carry the p.G294V mutation inherited from a common ancestor. The analysis of the 15 ALS pedigrees (from literature data and present study), strongly suggests a reduced penetrance of the p.G294V mutation since for 13 of the 15 described p.G294V ALS cases the parents did not show any neurological symptoms. This result has potentially important implications in genetic counseling, since genetic testing of a reduced penetrance mutation on pre-symptomatic individuals proves very difficult to predict the outcome based on the genotype.

The spectrum of involuntary vocalizations in humans: A video atlas

In clinical practice, involuntary vocalizing behaviors are typically associated with Tourette syndrome and other tic disorders. However, they may also be encountered throughout the entire tenor of neuropsychiatry, movement disorders, and neurodevelopmental syndromes. Importantly, involuntary vocalizing behaviors may often constitute a predominant clinical sign, and, therefore, their early recognition and appropriate classification are necessary to guide diagnosis and treatment. Clinical literature and video-documented cases on the topic are surprisingly scarce. Here, we pooled data from 5 expert centers of movement disorders, with instructive video material to cover the entire range of involuntary vocalizations in humans. Medical literature was also reviewed to document the range of possible etiologies associated with the different types of vocalizing behaviors and to explore treatment options. We propose a phenomenological classification of involuntary vocalizations within different categorical domains, including (1) tics and tic-like vocalizations, (2) vocalizations as part of stereotypies, (3) vocalizations as part of dystonia or chorea, (4) continuous vocalizing behaviors such as groaning or grunting, (5) pathological laughter and crying, (6) vocalizations resembling physiological reflexes, and (7) other vocalizations, for example, those associated with exaggerated startle responses, as part of epilepsy and sleep-related phenomena. We provide comprehensive lists of their associated etiologies, including neurodevelopmental, neurodegenerative, neuroimmunological, and structural causes and clinical clues. We then expand on the pathophysiology of the different vocalizing behaviors and comment on available treatment options. Finally, we present an algorithmic approach that covers the wide range of involuntary vocalizations in humans, with the ultimate goal of improving diagnostic accuracy and guiding appropriate treatment. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Frontotemporal Dementia

Frontotemporal dementia (FTD) is a heterogeneous disorder with distinct clinical phenotypes associated with multiple neuropathologic entities. Presently, the term FTD encompasses clinical disorders that include changes in behavior, language, executive control, and often motor symptoms. The core FTD spectrum disorders include behavioral variant FTD, nonfluent/agrammatic variant primary progressive aphasia, and semantic variant PPA. Related FTD disorders include frontotemporal dementia with motor neuron disease, progressive supranuclear palsy syndrome, and corticobasal syndrome. In this article, the authors discuss the clinical presentation, diagnostic criteria, neuropathology, genetics, and treatments of these disorders.

Genetic Counseling Dilemmas for a Patient with Sporadic Amyotrophic Lateral Sclerosis, Frontotemporal Degeneration & Parkinson's Disease

Amyotrophic lateral sclerosis (ALS), frontotemporal degeneration and Parkinson's disease may be different expressions of the same neurodegenerative disease. However, association between ALS and parkinsonism-dementia complex (ALS-PDC) has only rarely been reported apart from the cluster detected in Guam. We report a patient presenting with ALS-PDC in whom pathological mutations/expansions were investigated. No other family members were reported to have any symptoms of a neurological condition. Our case demonstrates that ALS-PDC can occur as a sporadic disorder, even though the coexistence of the three clinical features in one patient suggests a single underlying genetic cause. It is known that genetic testing should be preferentially offered to patients with ALS who have affected first or second-degree relatives. However, this case illustrates the importance of genetic counseling for family members of patients with sporadic ALC-PDC in order to provide education on the low recurrence risk. Here, we dicuss the ethical, psychological and practical consequences for patients and their relatives.

Extra-motor abnormalities in amyotrophic lateral sclerosis: another layer of heterogeneity

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease defined by the presence of muscle weakness. The motor features of disease are heterogeneous in site of onset and progression. There are also extra-motor features in some patients. The genetic basis for extra-motor features is uncertain. The heterogeneity of ALS is an issue for clinical trials. Areas covered: This paper reviews the range and prevalence of extra-motor features associated with ALS, and highlights the current information about genetic associations with extra-motor features. Expert commentary: There are extra-motor features of ALS, but these are not found in all patients. The most common is cognitive abnormality. More data is required to ascertain whether extra-motor features arise with progression of disease. Extra-motor features are reported in patients with a range of causative genetic mutations, but are not found in all patients with these mutations. Further studies are required of the heterogeneity of ALS, and genotype/phenotype correlations are required, taking note of extra-motor features.

Network Analysis Identifies Disease-Specific Pathways for Parkinson's Disease

Neurodegenerative diseases are characterized by the progressive loss of specific neurons in selected regions of the central nervous system. The main clinical manifestation (movement disorders, cognitive impairment, and/or psychiatric disturbances) depends on the neuron population being primarily affected. Parkinson's disease is a common movement disorder, whose etiology remains mostly unknown. Progressive loss of dopaminergic neurons in the substantia nigra causes an impairment of the motor control. Some of the pathogenetic mechanisms causing the progressive deterioration of these neurons are not specific for Parkinson's disease but are shared by other neurodegenerative diseases, like Alzheimer's disease and amyotrophic lateral sclerosis. Here, we performed a meta-analysis of the literature of all the quantitative proteomic investigations of neuronal alterations in different models of Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis to distinguish between general and Parkinson's disease-specific pattern of neurodegeneration. Then, we merged proteomics data with genetics information from the DisGeNET database. The comparison of gene and protein information allowed us to identify 25 proteins involved uniquely in Parkinson's disease and we verified the alteration of one of them, i.e., transaldolase 1 (TALDO1), in the substantia nigra of 5 patients. By using open-source bioinformatics tools, we identified the biological processes specifically affected in Parkinson's disease, i.e., proteolysis, mitochondrion organization, and mitophagy. Eventually, we highlighted four cellular component complexes mostly involved in the pathogenesis: the proteasome complex, the protein phosphatase 2A, the chaperonins CCT complex, and the complex III of the respiratory chain.

TDP-43/FUS in motor neuron disease: Complexity and challenges

Amyotrophic lateral sclerosis (ALS), a common motor neuron disease affecting two per 100,000 people worldwide, encompasses at least five distinct pathological subtypes, including, ALS-SOD1, ALS-C9orf72, ALS-TDP-43, ALS-FUS and Guam-ALS. The etiology of a major subset of ALS involves toxicity of the TAR DNA-binding protein-43 (TDP-43). A second RNA/DNA binding protein, fused in sarcoma/translocated in liposarcoma (FUS/TLS) has been subsequently associated with about 1% of ALS patients. While mutations in TDP-43 and FUS have been linked to ALS, the key contributing molecular mechanism(s) leading to cell death are still unclear. One unique feature of TDP-43 and FUS pathogenesis in ALS is their nuclear clearance and simultaneous cytoplasmic aggregation in affected motor neurons. Since the discoveries in the last decade implicating TDP-43 and FUS toxicity in ALS, a majority of studies have focused on their cytoplasmic aggregation and disruption of their RNA-binding functions. However, TDP-43 and FUS also bind to DNA, although the significance of their DNA binding in disease-affected neurons has been less investigated. A recent observation of accumulated genomic damage in TDP-43 and FUS-linked ALS and association of FUS with neuronal DNA damage repair pathways indicate a possible role of deregulated DNA binding function of TDP-43 and FUS in ALS. In this review, we discuss the different ALS disease subtypes, crosstalk of etiopathologies in disease progression, available animal models and their limitations, and recent advances in understanding the specific involvement of RNA/DNA binding proteins, TDP-43 and FUS, in motor neuron diseases.

Monocytes of patients with amyotrophic lateral sclerosis linked to gene mutations display altered TDP-43 subcellular distribution

AIMS

Cytoplasmic accumulation of the nuclear protein transactive response DNA-binding protein 43 (TDP-43) is an early determinant of motor neuron degeneration in most amyotrophic lateral sclerosis (ALS) cases. We previously disclosed this accumulation in circulating lymphomonocytes (CLM) of ALS patients with mutant TARDBP, the TDP-43-coding gene, as well as of a healthy individual carrying the parental TARDBP mutation. Here, we investigate TDP-43 subcellular localization in CLM and in the constituent cells, lymphocytes and monocytes, of patients with various ALS-linked mutant genes.

METHODS

TDP-43 subcellular localization was analysed with western immunoblotting and immunocytofluorescence in CLM of healthy controls (n = 10), patients with mutant TARDBP (n = 4, 1 homozygous), valosin-containing protein (VCP; n = 2), fused in sarcoma/translocated in liposarcoma (FUS; n = 2), Cu/Zn superoxide dismutase 1 (SOD1; n = 6), chromosome 9 open reading frame 72 (C9ORF72; n = 4), without mutations (n = 5) and neurologically unaffected subjects with mutant TARDBP (n = 2).

RESULTS

TDP-43 cytoplasmic accumulation was found (P < 0.05 vs. controls) in CLM of patients with mutant TARDBP or VCP, but not FUS, in line with TDP-43 subcellular localization described for motor neurons of corresponding groups. Accumulation also characterized CLM of the healthy individuals with mutant TARDBP and of some patients with mutant SOD1 or C9ORF72. In 5 patients, belonging to categories described to carry TDP-43 mislocalization in motor neurons (3 C9ORF72, 1 TARDBP and 1 without mutations), TDP-43 cytoplasmic accumulation was not detected in CLM or in lymphocytes but was in monocytes.

CONCLUSIONS

In ALS forms characterized by TDP-43 mislocalization in motor neurons, monocytes display this alteration, even when not manifest in CLM. Monocytes may be used to support diagnosis, as well as to identify subjects at risk, of ALS and to develop/monitor targeted treatments.

Parkinsonism, movement disorders and genetics in frontotemporal dementia

Frontotemporal dementia (FTD) refers to a group of clinically and genetically heterogeneous neurodegenerative disorders that are a common cause of adult-onset behavioural and cognitive impairment. FTD often presents in combination with various hyperkinetic or hypokinetic movement disorders, and evidence suggests that various genetic mutations underlie these different presentations. Here, we review the known syndromatic-genetic correlations in FTD. Although no direct genotype-phenotype correlations have been identified, mutations in multiple genes have been associated with various presentations. Mutations in the genes that encode microtubule-associated protein tau (MAPT) and progranulin (PGRN) can manifest as symmetrical parkinsonism, including the phenotypes of Richardson syndrome and corticobasal syndrome (CBS). Expansions in the C9orf72 gene are most frequently associated with familial FTD, typically combined with motor neuron disease, but other manifestations, such as symmetrical parkinsonism, CBS and multiple system atrophy-like presentations, have been described in patients with these mutations. Less common gene mutations, such as those in TARDBP, CHMP2B, VCP, FUS and TREM2, can also present as atypical parkinsonism. The most common hyperkinetic movement disorders in FTD are motor and vocal stereotypies, which have been observed in up to 78% of patients with autopsy-proven FTD. Other hyperkinetic movements, such as chorea, orofacial dyskinesias, myoclonus and dystonia, are also observed in some patients with FTD.

Phenotypic Heterogeneity of Monogenic Frontotemporal Dementia

Frontotemporal dementia (FTD) is a genetically and pathologically heterogeneous disorder characterized by personality changes, language impairment, and deficits of executive functions associated with frontal and temporal lobe degeneration. Different phenotypes have been defined on the basis of presenting clinical symptoms, i.e., the behavioral variant of FTD, the agrammatic variant of primary progressive aphasia, and the semantic variant of PPA. Some patients have an associated movement disorder, either parkinsonism, as in progressive supranuclear palsy and corticobasal syndrome, or motor neuron disease (FTD-MND). A family history of dementia is found in 40% of cases of FTD and about 10% have a clear autosomal-dominant inheritance. Genetic studies have identified several genes associated with monogenic FTD: microtubule-associated protein tau, progranulin, TAR DNA-binding protein 43, valosin-containing protein, charged multivesicular body protein 2B, fused in sarcoma, and the hexanucleotide repeat expansion in intron 1 of the chromosome 9 open reading frame 72. Patients often present with an extensive phenotypic variability, even among different members of the same kindred carrying an identical disease mutation. The objective of the present work is to review and evaluate available literature data in order to highlight recent advances in clinical, biological, and neuroimaging features of monogenic frontotemporal lobar degeneration and try to identify different mechanisms underlying the extreme phenotypic heterogeneity that characterizes this disease.

ALS mutant FUS proteins are recruited into stress granules in induced pluripotent stem cell-derived motoneurons

Patient-derived induced pluripotent stem cells (iPSCs) provide an opportunity to study human diseases mainly in those cases for which no suitable model systems are available. Here, we have taken advantage of in vitro iPSCs derived from patients affected by amyotrophic lateral sclerosis (ALS) and carrying mutations in the RNA-binding protein FUS to study the cellular behavior of the mutant proteins in the appropriate genetic background. Moreover, the ability to differentiate iPSCs into spinal cord neural cells provides an in vitro model mimicking the physiological conditions. iPSCs were derived from FUS^R514S and FUS^R521C patient fibroblasts, whereas in the case of the severe FUS^P525L mutation, in which fibroblasts were not available, a heterozygous and a homozygous iPSC line were raised by TALEN-directed mutagenesis. We show that aberrant localization and recruitment of FUS into stress granules (SGs) is a prerogative of the FUS mutant proteins and occurs only upon induction of stress in both undifferentiated iPSCs and spinal cord neural cells. Moreover, we show that the incorporation into SGs is proportional to the amount of cytoplasmic FUS, strongly correlating with the cytoplasmic delocalization phenotype of the different mutants. Therefore, the available iPSCs represent a very powerful system for understanding the correlation between FUS mutations, the molecular mechanisms of SG formation and ALS ethiopathogenesis.

Summary: Mutated FUS protein is aberrantly delocalized and recruited into stress granules in iPSC-derived motoneurons, which provide a new model system for amyotrophic lateral sclerosis.

A novel mutation P112H in the TARDBP gene associated with frontotemporal lobar degeneration without motor neuron disease and abundant neuritic amyloid plaques

Introduction

Although TDP-43 is the main constituent of the ubiquitinated cytoplasmic inclusions in the most common forms of frontotemporal lobar degeneration, TARDBP mutations are not a common cause of familial frontotemporal dementia, especially in the absence of motor neuron disease.

Results

We describe a pedigree presenting with a complex autosomal dominant disease, with a heterogeneous clinical phenotype, comprising unspecified dementia, parkinsonism, frontotemporal dementia and motor neuron disease. Genetic analyses identified a novel P112H TARDBP double variation located in exon 3 coding for the first RNA recognition motif of the protein (RRM1). This double mutation is probably pathogenic based on neuropathological findings, in silico prediction analysis and exome sequencing. The two autopsied siblings described here presented with frontotemporal dementia involving multiple cognitive domains and behavior but lacking symptoms of motor neuron disease throughout the disease course. The siblings presented with strikingly similar, although atypical, neuropathological features, including an unclassifiable TDP-43 inclusion pattern, a high burden of tau-negative β-amyloid neuritic plaques with an AD-like biochemical profile, and an unclassifiable 4-repeat tauopathy. The co-occurrence of multiple protein inclusions points to a pathogenic mechanism that facilitates misfolded protein interaction and aggregation or a loss of TDP-43 function that somehow impairs protein clearance.

Conclusions

TARDBP mutation screening should be considered in familial frontotemporal dementia cases, even without signs or symptoms of motor neuron disease, especially when other more frequent causes of genetic frontotemporal dementia (i.e. GRN, C9ORF72, MAPT) have been excluded and when family history is complex and includes parkinsonism, motor neuron disease and frontotemporal dementia. Further investigations in this family may provide insight into the physiological functions of TARDBP.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0190-6) contains supplementary material, which is available to authorized users.

Frontotemporal dementia: a bridge between dementia and neuromuscular disease

The concept that frontotemporal dementia (FTD) is a purely cortical dementia has largely been refuted by the recognition of its close association with motor neuron disease, and the identification of transactive response DNA-binding protein 43 (TDP-43) as a major pathological substrate underlying both diseases. Genetic findings have transformed this field and revealed connections between disorders that were previous thought clinically unrelated. The discovery that the C9ORF72 locus is responsible for the majority of hereditary FTD, amyotrophic lateral sclerosis (ALS), and FTD-ALS cases and the understanding that repeat-containing RNA plays a crucial role in pathogenesis of both disorders has paved the way for the development of potential biomarkers and therapeutic targets for these devastating diseases. In this review, we summarize the historical aspects leading up to our current understanding of the genetic, clinical, and neuropathological overlap between FTD and ALS, and include brief discussions on chronic traumatic encephalopathy (CTE), given its association with TDP-43 pathology, its associated increased dementia risk, and reports of ALS in CTE patients. In addition, we describe other genetic associations between dementia and neuromuscular disease, such as inclusion body myositis with Paget's disease and FTD.

Genetic architecture of ALS in Sardinia

Conserved populations, such as Sardinians, displaying elevated rates of familial or sporadic amyotrophic lateral sclerosis (ALS) provide unique information on the genetics of the disease. Our aim was to describe the genetic profile of a consecutive series of ALS patients of Sardinian ancestry. All ALS patients of Sardinian ancestry, identified between 2008 and 2013 through the Italian ALS Genetic Consortium, were eligible to be included in the study. Patients and controls underwent the analysis of TARDBP, C9ORF72, SOD1, and FUS genes. Genetic mutations were identified in 155 out of 375 Sardinian ALS cases (41.3%), more commonly the p.A382T and p.G295S mutations of TARDBP and the GGGGCC hexanucleotide repeat expansion of C9ORF72. One patient had both p.G295S and p.A382T mutations of TARDBP and 8 carried both the heterozygous p.A382T mutation of TARDBP and a repeat expansion of C9ORF72. Patients carrying the p.A382T and the p.G295S mutations of TARDBP and the C9ORF72 repeat expansion shared distinct haplotypes across these loci. Patients with cooccurrence of C9ORF72 and TARDBP p.A382T missense mutation had a significantly lower age at onset and shorter survival. More than 40% of all cases on the island of Sardinia carry a mutation of an ALS-related gene, representing the highest percentage of ALS cases genetically explained outside of Scandinavia. Clinical phenotypes associated with different genetic mutations show some distinctive characteristics, but the heterogeneity between and among families carrying the same mutations implies that ALS manifestation is influenced by other genetic and nongenetic factors.

Protein aggregation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the aggregation of ubiquitinated proteins in affected motor neurons. Recent studies have identified several new molecular constituents of ALS-linked cellular aggregates, including FUS, TDP-43, OPTN, UBQLN2 and the translational product of intronic repeats in the gene C9ORF72. Mutations in the genes encoding these proteins are found in a subgroup of ALS patients and segregate with disease in familial cases, indicating a causal relationship with disease pathogenesis. Furthermore, these proteins are often detected in aggregates of non-mutation carriers and those observed in other neurodegenerative disorders, supporting a widespread role in neuronal degeneration. The molecular characteristics and distribution of different types of protein aggregates in ALS can be linked to specific genetic alterations and shows a remarkable overlap hinting at a convergence of underlying cellular processes and pathological effects. Thus far, self-aggregating properties of prion-like domains, altered RNA granule formation and dysfunction of the protein quality control system have been suggested to contribute to protein aggregation in ALS. The precise pathological effects of protein aggregation remain largely unknown, but experimental evidence hints at both gain- and loss-of-function mechanisms. Here, we discuss recent advances in our understanding of the molecular make-up, formation, and mechanism-of-action of protein aggregates in ALS. Further insight into protein aggregation will not only deepen our understanding of ALS pathogenesis but also may provide novel avenues for therapeutic intervention.

How do the RNA-binding proteins TDP-43 and FUS relate to amyotrophic lateral sclerosis and frontotemporal degeneration, and to each other?

PURPOSE OF REVIEW

This review examines the recent research developments aimed at defining the role of RNA-binding proteins (TDP-43 and FUS) in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD).

RECENT FINDINGS

TAR DNA-binding protein 43 kDa (TDP-43) and fused in sarcoma (FUS) are RNA-binding proteins that form aggregates in ALS and FTLD, and when mutated can drive the pathogenesis of these disorders. However, fundamental questions remain as to the relationship between TDP-43 and FUS aggregation and disease, their normal and pathologic function, and where they converge on the same cellular pathways. Autopsy series point to distinct molecular actions as TDP-43 and FUS neuronal inclusions do not overlap, with FUS inclusions being present in only a small subgroup of patients. By contrast, modeling experiments in lower organisms support a genetic interaction between TDP-43 and FUS, although it is likely indirect. Regardless, the recent finding that additional RNA-binding proteins may also cause ALS, and the observation that TDP-43 aggregation remains a core feature in all of the recently identified genetic forms of ALS (C9ORF72, VCP, UBQLN2, and PFN1), underscores the central role of TDP-43 and RNA metabolism in ALS and FTLD.

SUMMARY

Recent discoveries point to an unprecedented convergence of molecular pathways in ALS and FTLD involving RNA metabolism. Defining the exact points of convergence will likely be key to advancing therapeutics development in the coming years.

The p.A382T TARDBP gene mutation in Sardinian patients affected by Parkinson's disease and other degenerative parkinsonisms

Based on our previous finding of the p.A382T founder mutation in ALS patients with concomitant parkinsonism in the Sardinian population, we hypothesized that the same variant may underlie Parkinson's disease (PD) and/or other forms of degenerative parkinsonism on this Mediterranean island. We screened a cohort of 611 patients with PD (544 cases) and other forms of degenerative parkinsonism (67 cases) and 604 unrelated controls for the c.1144G > A (p.A382T) missense mutation of the TARDBP gene. The p.A382T mutation was identified in nine patients with parkinsonism. Of these, five (0.9 % of PD patients) presented a typical PD (two with familiar forms), while four patients (6.0 % of all other forms of parkinsonism) presented a peculiar clinical presentation quite different from classical atypical parkinsonism with an overlap of extrapyramidal-pyramidal-cognitive clinical signs. The mutation was found in eight Sardinian controls (1.3 %) consistent with a founder mutation in the island population. Our findings suggest that the clinical presentation of the p.A382T TARDBP gene mutation may include forms of parkinsonism in which the extrapyramidal signs are the crucial core of the disease at onset. These forms can present PSP or CBD-like clinical signs, with bulbar and/or extrabulbar pyramidal signs and cognitive impairment. No evidence of association has been found between TARDBP gene mutation and typical PD.

Frontotemporal dementia in a Brazilian kindred with the c9orf72 mutation

OBJECTIVES

To describe the clinical features of a Brazilian kindred with C9orf72 frontotemporal dementia-amyotrophic lateral sclerosis and compare them with other described families with C9orf72 and frontotemporal dementia-amyotrophic lateral sclerosis-causing mutations.

DESIGN

Report of a kindred.

SETTING

Dementia center at a university hospital.

PATIENTS

One kindred encompassing 3 generations.

RESULTS

The presence of a hexanucleotide (GGGGCC) expansion in C9orf72 was confirmed by repeat-primed polymerase chain reaction and Southern blot. The observed phenotypes were behavioral variant frontotemporal dementia and amyotrophic lateral sclerosis with dementia, with significant variability in age at onset and duration of disease. Parkinsonian features with focal dystonia, visual hallucinations, and more posterior atrophy on neuroimaging than is typical for frontotemporal dementia were seen.

CONCLUSIONS

Behavioral variant frontotemporal dementia due to C9orf72 expansion displays some phenotypic heterogeneity and may be associated with hallucinations, parkinsonism, focal dystonia, and posterior brain atrophy. Personality changes may precede the diagnosis of dementia by many years and may be a distinguishing feature of this mutation.

TARDBP mutations in Parkinson's disease

Mutations of the TARDBP gene encoding TDP-43 protein have been shown to cause amyotrophic lateral sclerosis and have been reported to present with clinical heterogeneity including parkinsonism. In addition, TDP-43 pathology has been observed across a spectrum of neurodegenerative disorders, including Alzheimer's and Parkinson's disease. Herein we report the presence of a TDP-43 mutation in a patient with a clinical diagnosis of Parkinson's disease. The TDP-43 p.N267S substitution has been previously implicated in both amyotrophic lateral sclerosis and behavioral variant frontotemporal dementia. Our findings widen the phenotypic presentation for the TDP-43 p.N267S substitution and support a possible role for rare TDP-43 mutations presenting with Parkinson's disease.

Genetic overlap between apparently sporadic motor neuron diseases

Progressive muscular atrophy (PMA) and amyotrophic lateral sclerosis (ALS) are devastating motor neuron diseases (MNDs), which result in muscle weakness and/or spasticity. We compared mutation frequencies in genes known to be associated with MNDs between patients with apparently sporadic PMA and ALS. A total of 261 patients with adult-onset sporadic PMA, patients with sporadic ALS, and control subjects of Dutch descent were obtained at national referral centers for neuromuscular diseases in The Netherlands. Sanger sequencing was used to screen these subjects for mutations in the coding regions of superoxide dismutase-1 (SOD1), angiogenin (ANG), fused in sarcoma/translated in liposarcoma (FUS/TLS), TAR DNA-binding protein 43 (TARDBP), and multivesicular body protein 2B (CHMP2B). In our cohort of PMA patients we identified two SOD1 mutations (p.D90A, p.I113T), one ANG mutation (p.K17I), one FUS/TLS mutation (p.R521H), one TARDBP mutation (p.N352S), and one novel CHMP2B mutation (p.R69Q). The mutation frequency of these genes was similar in sporadic PMA (2.7%) and ALS (2.0%) patients, and therefore, our findings demonstrate a genetic overlap between apparently sporadic PMA and ALS.

Amyotrophic lateral sclerosis in Sardinia, insular Italy, 1995-2009

Recent genetic studies suggest a Sardinian type of amyotrophic lateral sclerosis (ALS). Thus, ALS incidence, prevalence and survival were investigated in a large population of Sardinians aimed to disclose population-specific patterns and their temporal changes. This is a population-based incidence and prevalence study in northern and central Sardinia, insular Italy (over 700,000 population). Incidence rates were computed for the time interval 1995-2009 and by quinquennia. Prevalence was computed for prevalence days 31 December 2004 and 2009. Onset-based survival for 1995-2009 is also reported. All ALS patients (El Escorial Criteria) in the study area were retrospectively included. The ALS crude incidence from 2005-2009 was 2.5 (95 % CIs: 0.1, 4.9), 3.4 in men and 1.6 in women. Onset occurred most often between the age of 65-74 years in men and 55-64 years in women. The ALS incidence tended to increase over the period 1995-2009. The mean age at onset was 61.7 years with no difference based on gender, varying significantly from 59.9 years in 1995-1999 to 63.9 years in 2005-2009. On December 31, 2009, the ALS crude prevalence was 10.8 per 100,000 (95 % CIs: 8.6, 13.1), 13.8 in men and 8.0 in women, whereas it was 6.3 per 100,000 (95 % CIs: 4.1, 8.6) on December 31, 2004 (M:F ratio of 0.95). Mean survival from onset was 37.0 months, with no difference based on gender, and a tendency to decrease during the period 1995-2009, in relation to type and age of onset. The population-based incidence and prevalence data of ALS in Sardinians indicate an increase of the disease occurrence over the past 40 years, providing support for a population-specific variant of ALS in Sardinia.

Wide phenotypic spectrum of the TARDBP gene: homozygosity of A382T mutation in a patient presenting with amyotrophic lateral sclerosis, Parkinson's disease, and frontotemporal lobar degeneration, and in neurologically healthy subject

Mutations in the TARDBP gene are described as a cause of autosomal dominant amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD) with or without motor neuron involvement, and, recently, Parkinson's disease (PD). We hereby describe a family presenting the A382T mutation; two subjects were in the homozygous state, and two were in the heterozygous state. The index case, carrying the A382T mutation in the homozygous state, had an 8-year history of sporadic PD and 6 years later developed ALS and FTLD; his brother, carrying the same mutation in the homozygous state, and the other two family member carriers of the same mutation in the heterozygous state were without neurological signs and symptoms. This family confirms that mutation in transactive response (TAR)-DNA-binding protein 43 (TDP43), both the homozygous and the heterozygous state, may be found in subjects with different clinical conditions ranging from neurological disease to non-neurological disease. In addition, the aforementioned findings add to the debate for the ethical and psychological dilemmas about genetic counseling.

Identifying potential risk factors for developing amyotrophic lateral sclerosis

SUMMARY Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder of adult life, characterized by the progressive loss of upper motor neurons in the primary motor cortex and of the spinal and bulbar lower motor neurons. The cause of sporadic cases and of the majority of hereditary cases remains elusive. So far a total of 17 genes or genetic loci of familial ALS have been identified, related to DNA/RNA processing, protein aggregation, membrane trafficking and axonal transport and mitochondrial dysfunction. A large range of environmental factors have also been studied, with inconclusive results, with the possible exception of cigarette smoking. ALS is now considered a complex multifactorial neurodegenerative disorder, but studies analyzing genetic and environmental factors together are still underway.