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

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.

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.

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.

Genetics of progressive supranuclear palsy in a Chinese population

BACKGROUND

Genetics plays an important role in progressive supranuclear palsy (PSP) and remains poorly understood. A detailed literature search identified 19 PSP-associated genes: MAPT, LRRK2, LRP10, DCTN1, GRN, NPC1, PARK, TARDBP, TBK1, BSN, GBA, STX6, EIF2AK3, MOBP, DUSP10, SLCO1A2, RUNX2, CXCR4, and APOE. To date, genetic studies on PSP have focused on Caucasian population. The gaps in PSP genetic study on East Asian populations need to be filled.

METHODS

Exon and flanking regions of the PSP-associated genes were sequenced in 104 patients with PSP and 488 healthy controls. Common variant-based association analysis and gene-based association tests of rare variants were performed using PLINK 1.9 and the sequence kernel association test-optimal, respectively. Additionally, the association of APOE and MAPT genotypes with PSP was evaluated. The above association analyses were repeated among probable PSP patients. Finally, PLINK 1.9 was used to test variants associated with the onset age of PSP.

RESULTS

A rare non-pathogenic variant of MAPT (c.425C > T,p.A142V) was detected in a PSP patient. No common variants were significantly associated with PSP. In both the rare-variant and the rare-damaging-variant groups, the combined effect for GBA reached statistical significance (p = 1.43 × 10^-3, p = 4.98 × 10^-4). The result between APOE, MAPT genotypes and PSP risk were inconsistent across all PSP group and probably PSP group.

CONCLUSIONS

The pathogenic variant in MAPT were uncommon in PSP patients. Moreover, GBA gene was likely to increase the risk of PSP, and GBA-associated diseases were beyond α-synucleinopathies. The association between APOE, MAPT and PSP is still unclear among the non-Caucasian population.

Parkinsonian Syndromes in Motor Neuron Disease: A Clinical Study

Background

Parkinsonian syndromes may rarely occur in motor neuron disease (MND). However, previous studies are heterogeneous and mostly case reports or small case series. Therefore, we aimed to identify and characterize patients with concurrent parkinsonian syndromes extracted from a cohort of 1,042 consecutive cases diagnosed with MND at a tertiary Italian Center.

Methods

Diagnosis of Parkinson's disease (PD), progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS) was made according to current criteria. Clinical characterization included: upper and lower motor neuron disease features, typical and atypical parkinsonian features, oculomotor disorders, cognitive testing, MRI features, and, when available molecular neuroimaging. Genetic testing was carried out for major MND and PD-associated genes.

Results

Parkinsonian syndromes were diagnosed in 18/1042 (1.7%) of MND patients (7 PD, 6 PSP, 3 CBS, 2 other parkinsonisms). Based on phenotype, patients could be categorized into amyotrophic lateral sclerosis (ALS)-parkinsonism and primary lateral sclerosis (PLS)-parkinsonism clusters. Across the whole database, parkinsonism was significantly more common in PLS than in other MND phenotypes (12.1 vs. 1.1%, p = 5.0 × 10⁻¹⁰). MND patients with parkinsonian features had older age of onset, higher frequency of oculomotor disorders, cognitive impairment, and family history of parkinsonism or dementia. Two patients showed pathogenic mutations in TARDBP and C9orf72 genes.

Conclusion

Specific patterns in MND-parkinsonism were observed, with PLS patients often showing atypical parkinsonian syndromes and ALS patients more frequently showing typical PD. Systematic clinical, genetic, and neuropathologic characterization may provide a better understanding of these phenotypes.

Genotype-Phenotype Correlation in Progressive Supranuclear Palsy Syndromes: Clinical and Radiological Similarities and Specificities

The progressive supranuclear palsy (PSP) syndrome encompasses different entities. PSP disease of sporadic origin is the most frequent presentation, but different genetic mutations can lead either to monogenic variants of PSP disease, or to other conditions with a different pathophysiology that eventually may result in PSP phenotype. PSP syndrome of monogenic origin is poorly understood due to the low prevalence and variable expressivity of some mutations. Through this review, we describe how early age of onset, family history of early dementia, parkinsonism, dystonia, or motor neuron disease among other clinical features, as well as some neuroimaging signatures, may be the important clues to suspect PSP syndrome of monogenic origin. In addition, a diagnostic algorithm is proposed that may be useful to guide the genetic diagnosis once there is clinical suspicion of a monogenic PSP syndrome.

Bradykinesia in motoneuron diseases

OBJECTIVE

Only few studies investigated voluntary movement abnormalities in patients with motoneuron diseases (MNDs) or their neurophysiological correlates. We aimed to kinematically assess finger tapping abnormalities in patients with amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS), as compared to healthy controls (HCs), and their relationship with motoneuron involvement.

METHODS

Fourteen ALS and 5 PLS patients were enrolled. Finger tapping was assessed by a motion analysis system. Patients underwent a central motor conduction time assessment, a motor nerve conduction study, and needle electromyography. Data were compared to those of 79 HCs using non-parametric tests. Possible relationships between clinical, kinematic, and neurophysiological data were assessed in patients.

RESULTS

As a major finding, ALS and PLS patients performed finger tapping slower than HCs. In both conditions, movement slowness correlated with muscle strength. In ALS, movement slowness also correlated with the amplitude of the compound muscle action potential recorded from the muscles involved in the task and with denervation activity. No correlations were found between slowness, measures of upper motoneuron involvement, and other clinical and neurophysiological data.

CONCLUSIONS

This study provides novel information on voluntary movement abnormalities in MNDs.

SIGNIFICANCE

The results highlight the pathophysiological role of motoneurons in generating movement slowness.

Genetics of Progressive Supranuclear Palsy: A Review

Progressive supranuclear palsy (PSP) is an atypical parkinsonism with prominent 4R-tau neuropathology, and the classical clinical phenotype is characterized by vertical supranuclear gaze palsy, unprovoked falls, akinetic-rigid syndrome and cognitive decline. Though PSP is generally regarded as sporadic, there is increasing evidence suggesting that a series of common and rare genetic variants impact on sporadic and familial forms of PSP. To date, more than 10 genes have been reported to show a potential association with PSP. Among these genes, the microtubule-associated protein tau (MAPT) is the risk locus with the strongest effect size on sporadic PSP in the case-control genome-wide association studies (GWAS). Additionally, MAPT mutations are the most common cause of familial PSP while the leucine-rich repeat kinase 2 (LRRK2) is a rare monogenic cause of PSP, and several other gene mutations may mimic the PSP phenotype, like the dynactin subunit 1 (DCTN1). In total, 15 MAPT mutations have been identified in cases with PSP, and the mean age at onset is much earlier than in cases carrying LRRK2 or DCTN1 mutations. GWAS have further identified several risk loci of PSP, proposing molecular pathways related to PSP. The present review focused on genetic studies on PSP and summarized genetic factors of PSP, which may help to elucidate the underlying pathogenesis and provide new perspectives for therapeutic strategies.

Is it accurate to classify ALS as a neuromuscular disorder?

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a fatal disorder characterized by the progressive loss of upper and lower motor neurons. ALS has traditionally been classified within the domain of neuromuscular diseases, which are a unique spectrum of disorders that predominantly affect the peripheral nervous system. However, over the past decades compounding evidence has emerged that there is extensive involvement of the central nervous system. Therefore, one can question whether it remains accurate to classify ALS as a neuromuscular disorder.

AREAS COVERED

In this review, the authors sought to discuss current approaches toward disease classification and how we should classify ALS based on novel insights from clinical, imaging, pathophysiological, neuropathological and genetic studies.

EXPERT OPINION

ALS exhibits the cardinal features of a neurodegenerative disease. Therefore, classifying ALS as a neuromuscular disease in the strict sense has become untenable. Diagnosing ALS however does require significant neuromuscular expertise and therefore neuromuscular specialists remain best equipped to evaluate this category of patients. Designating motor neuron diseases as a separate category in the ICD-11 is justified and adequately deals with this issue. However, to drive effective therapy development the fields of motor neuron disease and neurodegenerative disorders must come together.

Angiogenin and tRNA fragments in Parkinson's disease and neurodegeneration

In this review, we summarise the evidence for a role of the ribonuclease angiogenin in the pathophysiology of neurodegenerative disorders, with a specific focus on Parkinson’s disease (PD). Angiogenin is a stress-induced, secreted ribonuclease with both nuclear and cytosolic activities. Loss-of-function mutations in the angiogenin gene (ANG) have been initially discovered in familial cases of amyotrophic lateral sclerosis (ALS), however, variants in ANG have subsequently been identified in PD and Alzheimer’s disease. Delivery of angiogenin protein reduces neurodegeneration and delays disease progression in in vitro and in vivo models of ALS and in vitro models of PD. In the nucleus, angiogenin promotes ribosomal RNA transcription. Under stress conditions, angiogenin also translocates to the cytosol where it cleaves non-coding RNA into RNA fragments, in particular transfer RNAs (tRNAs). Stress-induced tRNA fragments have been proposed to have multiple cellular functions, including inhibition of ribosome biogenesis, inhibition of protein translation and inhibition of apoptosis. We will discuss recent evidence of tRNA fragment accumulation in PD, as well as their potential neuroprotective activities.

Genetics and molecular mechanisms of frontotemporal lobar degeneration: an update and future avenues

Frontotemporal lobar degeneration (FTLD) is the second most common form of dementia after Alzheimer's disease. The study and the dissection of FTLD is complex due to its clinical, pathological, and genetic heterogeneity. In this review, we survey the state-of-the-art genetics of familial FTLD and recapitulate our current understanding of the genetic architecture of sporadic FTLD by summarizing results of genome-wide association studies performed in FTLD to date. We then discuss the challenges of translating these heterogeneous genetic features into the understanding of the molecular underpinnings of FTLD pathogenesis. We particularly highlight a number of susceptibility processes that appear to be conserved across familial and sporadic cases (e.g., and the cellular waste disposal pathways, and immune system signaling) and finally describe cutting-edge approaches, based on mathematical prediction tools, highlighting novel intriguing risk pathways such as DNA damage response as an emerging theme in FTLD.

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.

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.

Phenotypic variability related to C9orf72 mutation in a large Sardinian kindred

We investigated intrafamilial phenotypic variability in carriers of the C9orf72 mutation, analysing clinical, neuropsychological and imaging characteristics of various members from a large Sardinian kindred with FTD or ALS. We compared these with those of C9 + patients in our ALS and FTD cohorts. Results showed that three patients carried the C9orf72 mutation: two with ALS and one with FTD and Parkinsonism. C9 + patients in our bvFTD Sardinian cohort had a higher frequency of Parkinsonism than non-mutated patients (75% vs. 36.3%, p <0.02). Parkinsonism was present in 2.7% of our ALS cohort and 3.3% of the C9 + patients. The prevalence of Parkinsonism in C9 + patients in the bvFTD and ALS cohorts showed a statistically significant difference (p <0.006). In conclusion, Parkinsonism was frequently associated with FTD but not ALS in a large Sardinian family, a finding reflected in the wider C9orf72 associated Sardinian ALS and FTD populations.

Genetics Underlying Atypical Parkinsonism and Related Neurodegenerative Disorders

Atypical parkinsonism syndromes, such as dementia with Lewy bodies, multiple system atrophy, progressive supranuclear palsy and corticobasal degeneration, are neurodegenerative diseases with complex clinical and pathological features. Heterogeneity in clinical presentations, possible secondary determinants as well as mimic syndromes pose a major challenge to accurately diagnose patients suffering from these devastating conditions. Over the last two decades, significant advancements in genomic technologies have provided us with increasing insights into the molecular pathogenesis of atypical parkinsonism and their intriguing relationships to related neurodegenerative diseases, fueling new hopes to incorporate molecular knowledge into our diagnostic, prognostic and therapeutic approaches towards managing these conditions. In this review article, we summarize the current understanding of genetic mechanisms implicated in atypical parkinsonism syndromes. We further highlight mimic syndromes relevant to differential considerations and possible future directions.

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.

Complexities of Genetic Counseling for ALS: A Case of Two Siblings with Discordant Genetic Test Results

Rapid advances in the genetics of amyotrophic lateral sclerosis (ALS) have dramatically changed the approach of clinicians and researchers to the motor neuron diseases. We report two siblings in whom the genetic study provided conflicting results, hence raising a number of issues which deserve to be considered by clinicians involved in genetic testing for ALS. The first patient died within 2 years of ALS onset, while her brother still manages to walk unaided, 7 years into onset. Genetic analyses, performed on the first patient as part of a research protocol, and as clinical genetic testing on the brother, provided different results. Results for Patient 1 were negative for all investigated genes, thus suggesting that her disease may be a phenocopy, while her brother carried an autosomal dominant TARDBP mutation (p.A382T). A multidisciplinary approach may help patients and clinicians face the emerging dilemmas in such a complex field. Sharing and updating of advances, not to mention uncertainties inherent to current knowledge, with patients and families may prove to be an effective way to support them and to make them aware of the present limits of our knowledge and of the blurred border between research and clinical practice.

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.

Constructional apraxia in frontotemporal dementia associated with the C9orf72 mutation: broadening the clinical and neuropsychological phenotype

In our study we analysed clinical and neuropsychological data in a cohort of 57 Sardinian patients with FTD (55 apparently unrelated and two belonging to the same family), who underwent genetic screening for the C9orf72 mutation. Eight out of 56 patients were found positive for the C9orf72 mutation representing 14% of the entire cohort and 31.6% of the familial cases (6/19). C9orf72 mutated patients differed from the other FTD cases of the cohort for a younger age of onset, higher frequency of familial history for FTD and higher prevalence of delusional psychotic symptoms and hallucinations. In the neuropsychological assessment, C9orf72 mutated patients differed from non-mutated for the high frequency of visuospatial dysfunction regarding constructional apraxia (p = 0.02). In conclusion, our study confirms that Sardinian FTD patients have peculiar genetic characteristics and that C9orf72 mutated patients have a distinctive clinical and neuropsychological profile that could help differentiate them from other FTD patients. In our cohort we found that constructional apraxia, rarely reported in FTD, can properly discriminate between C9orf72 mutated and non-mutated patients and contribute to broaden the neuropsychological profile in frontotemporal dementia associated with this mutation.

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.

The neurogenetics of atypical parkinsonian disorders

Although classic Parkinson disease is the disorder most commonly associated with the clinical feature of parkinsonism, there is in fact a broader spectrum of disease represented by a collection of phenotypically similar neurodegenerative conditions that mimic many of its core features. These atypical parkinsonian disorders most commonly include progressive supranuclear palsy and corticobasal degeneration, disorders both associated with frontotemporal dementia, as well as multiple system atrophy and dementia with Lewy bodies. Although the clinical distinction of these disorders still remains a challenge to physicians, recent advances in genetics are poised to tease apart the differences. Insights into the molecular etiologies underlying these conditions will improve diagnosis, yield a better understanding of the underlying disease pathology, and ultimately lend stimulation to the development of potential treatments. At the same time, the wide range of phenotypes observed from mutations in a single gene warrants broad testing facilitated by advances in DNA sequencing. These expanding genomic approaches, ranging from the use of next-generation sequencing to identify causative or risk-associated gene variations to the study of epigenetic modification linking human genetics to environmental factors, are poised to lead the field into a new age of discovery.

Advances in the Genetics of Parkinson's Disease: A Guide for the Clinician

Over the last 16 years, insights in clinical and genetic characteristics of Parkinson's disease (PD) have increased substantially. We summarize the clinical, genetic, and pathological findings of autosomal dominant PD linked to mutations in SNCA, leucine-rich repeat kinase 2, vacuolar protein sorting-35, and eukaryotic translation initiation factor 4 gamma 1 and autosomal recessive PD linked to parkin,PINK1, and DJ-1, as well as autosomal recessive complicated parkinsonian syndromes caused by mutations in ATP13A2,FBXO7,PLA2G6,SYNJ1, and DNAJC6. We also review the advances in high- and low-risk genetic susceptibility factors and present multisystem disorders that may present with parkinsonism as the major clinical feature and provide recommendations for prioritization of genetic testing. Finally, we consider the challenges of future genetic research in PD.