Mutations in the TARDBP gene are a cause of autosomal dominant amyotrophic lateral sclerosis (ALS) and of frontotemporal lobar degeneration (FTLD), but they have not been found so far in patients with Parkinson’s disease (PD). A founder TARDBP mutation (p.Ala382Thr) was recently identified as the cause of ~30% of ALS cases in Sardinia, a Mediterranean genetic isolate. We studied 327 consecutive Sardinian patients with clinically diagnosed PD (88 familial, 239 sporadic) and 578 Sardinian controls. One family with FTLD and parkinsonism was also included. The p.Ala382Thr heterozygous mutation was detected in eight unrelated PD patients (2.5%). The three patients from the FTLD/parkinsonism family also carried this mutation. Within the control group, there were three heterozygous mutation carriers. During follow-up, one of these individuals developed motoneuron disease and another, a rapidly progressive dementia; the third remains healthy at the age of 79 but two close relatives developed motoneuron disease and dementia. The eight PD patients carrying the p.Ala382Thr mutation had all sporadic disease presentation. Their average onset age was 70.0 years (SD 9.4, range 51–79), which is later but not significantly different from that of the patients who did not carry this mutation. In conclusion, we expand the clinical spectrum associated with TARDBP mutations to FTLD with parkinsonism without motoneuron disease and to clinically definite PD. The TDP-43 protein might be directly involved in a broader neurodegenerative spectrum, including not only motoneuron disease and FTLD but also PD.
Parkinson’s disease; Frontotemporal lobar degeneration; Amyotrophic lateral sclerosis; Sardinia; TARDBP; Mutation
Mutations in the TARDBP gene, which encodes the Tar DNA binding protein, have been shown to causes of both familial amyotrophic lateral sclerosis (FALS) and sporadic ALS (SALS). Recently, several novel TARDBP exon 6 mutants have been reported in patients with ALS in Europe and America but not in Asia. To further examine the spectrum and frequency of TARDBP exon 6 mutations, we investigated their frequency in ethnic Chinese patients with sporadic ALS. TARDBP exon 6 was screened by direct sequencing in 207 non-SOD1 SALS patients and 230 unrelated healthy controls but no mutations were identified. Our data indicate that exon 6 mutations in TARDBP are not a common cause of SALS in Han Chinese population from Southern Mainland China.
Abnormal neuronal inclusions composed of the TAR DNA binding protein 43 (TDP-43) are the characteristic neuropathological lesions in sporadic and familial forms of amyotrophic lateral sclerosis (ALS). This makes TARDBP, the gene encoding for TDP-43, an interesting candidate gene for genetic screening in ALS.
To investigate the presence and frequency of TARDBP mutations in ALS.
One hundred thirty-four patiens with sporadic ALS, 31 patients with familial non-SOD1-ALS, and 400 healthy control subjects.
We identified two missense mutations in TARDBP (G348C and the novel N352S) in two small kindreds with a hereditary form of ALS with early spinal onset resulting in fatal respiratory insufficiency without clinical relevant bulbar symptoms or signs of cognitive impairment. The mutations located in the C-terminus of TDP-43 were absent in 400 Caucasian control individuals. The novel identified N352S mutation is predicted to increase TDP-43 phosphorylation while the G348C mutation might interfere with normal TDP-43 function by forming intermolecular disulfide bridges.
Mutations in TARDBP are a rare cause of familial non-SOD1-ALS. The identification of TARDBP mutations provides strong evidence for a direct link between TDP-43 dysfunction and neurodegeneration in ALS.
TDP-43; ALS; TARDBP
TDP-43 is a major component of the ubiquitinated inclusions that characterise amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) with ubiquitin inclusions (FTLD-U). TDP-43 is an RNA-binding and DNA-binding protein that has many functions and is encoded by the TAR DNA-binding protein gene (TARDBP) on chromosome 1. Our aim was to investigate whether TARDBP is a candidate disease gene for familial ALS that is not associated with mutations in superoxide dismutase 1 (SOD1).
TARDBP was sequenced in 259 patients with ALS, FTLD, or both. We used TaqMan-based SNP genotyping to screen for the identifi ed variants in control groups matched to two kindreds of patients for age and ethnic origin. Additional clinical, genetic, and pathological assessments were made in these two families.
We identified two variants, p.Gly290Ala and p.Gly298Ser, in TARDBP in two familial ALS kindreds and we observed TDP-43 neuropathology in the CNS tissue available from one family. The variants are considered pathogenic mutations because they co-segregate with disease in both families, are absent in ethnically-matched controls, and are associated with TDP-43 neuropathology in several family members.
The p.Gly290Ala and p.Gly298Ser mutations are located in the glycine-rich domain that regulates gene expression and mediates protein-protein interactions; in particular TDP-43 binds to heterogeneous ribonucleoproteins (hnRNPs) via this domain. We postulate that due to the varied and important cellular functions of TDP-43, these mutations may cause neurodegeneration through both gains and losses of function. The finding of TARDBP mutations implicates TDP-43 as an active mediator of neurodegeneration in a novel class of disorders, TDP-43 proteinopathies, a class of disorder that includes ALS and FTLD-U.
The TAR DNA-binding protein 43 (TDP-43) has been identified as the major disease protein in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin inclusions (FTLD-U), defining a novel class of neurodegenerative conditions: the TDP-43 proteinopathies. The first pathogenic mutations in the gene encoding TDP-43 (TARDBP) were recently reported in familial and sporadic ALS patients, supporting a direct role for TDP-43 in neurodegeneration. In this study, we report the identification and functional analyses of two novel and one known mutation in TARDBP that we identified as a result of extensive mutation analyses in a cohort of 296 patients with variable neurodegenerative diseases associated with TDP-43 histopathology. Three different heterozygous missense mutations in exon 6 of TARDBP (p.M337V, p.N345K, and p.I383V) were identified in the analysis of 92 familial ALS patients (3.3%), while no mutations were detected in 24 patients with sporadic ALS or 180 patients with other TDP-43–positive neurodegenerative diseases. The presence of p.M337V, p.N345K, and p.I383V was excluded in 825 controls and 652 additional sporadic ALS patients. All three mutations affect highly conserved amino acid residues in the C-terminal part of TDP-43 known to be involved in protein-protein interactions. Biochemical analysis of TDP-43 in ALS patient cell lines revealed a substantial increase in caspase cleaved fragments, including the ∼25 kDa fragment, compared to control cell lines. Our findings support TARDBP mutations as a cause of ALS. Based on the specific C-terminal location of the mutations and the accumulation of a smaller C-terminal fragment, we speculate that TARDBP mutations may cause a toxic gain of function through novel protein interactions or intracellular accumulation of TDP-43 fragments leading to apoptosis.
The abnormal accumulation of disease proteins in neuronal cells of the brain is a characteristic feature of many neurodegenerative diseases. Rare mutations in the genes that encode the accumulating proteins have been identified in these disorders and are crucial for the development of cell and animal models used to study neurodegeneration. Recently, the TAR DNA-binding protein 43 (TDP-43) was identified as the disease accumulating protein in patients with frontotemporal lobar degeneration with ubiquitin inclusions (FTLD-U) and in amyotrophic lateral sclerosis (ALS). TDP-43 was also found in the brains of 20–30% of patients with Alzheimer's disease (AD). Here, we evaluated whether mutations in TDP-43 cause disease in a cohort of 296 patients presenting with FTLD, ALS or AD. We identified three missense mutations in three out of 92 familial ALS patients (3.3%), and no mutations in AD or FTLD patients. All the identified mutations clustered in exon 6, which codes for a highly conserved region in the C-terminal part of the TDP-43 protein, which is known to be involved in the interaction of TDP-43 with other proteins. We conclude that mutations in TDP-43 are a rare cause of familial ALS, but so far are not found in other neurodegenerative diseases.
TARDBP mutations have been reported in patients with amyotrophic lateral sclerosis (ALS) in different populations except Chinese. The present aim is to investigate the association between TARDBP mutations and Chinese patients with ALS.
71 SALS patients and 5 FALS families with non-SOD1 mutations were screened for TARDBP mutations via direct sequencing.
A novel heterozygous variation, Ser292Asn (875G>A), was identified in the proband and 4 asymptomatic relatives including the children of the dead patient from a FALS family. Thus the dead patient, the proband's brother, was speculated to carry Ser292Asn though his sample was unavailable to the detection. This variation was not found in 200 unrelated control subjects. A homology search of the TDP-43 protein in different species demonstrated that it was highly conserved. Also, it was predicted to be deleterious to protein function with SIFT-calculated probabilities of 0.00. Therefore, Ser292Asn is predicted to be a pathogenic mutation. In addition, we have found two silent mutations (Gly40Gly and Ala366Ala) and one novel polymorphism (239-18t>c).
The present data have extended the spectrum of TARDBP mutations and polymorphisms, and supported the pathological role of TDP-43 in Chinese ALS patients.
Neurodegenerative diseases are often characterized by the presence of aggregates of misfolded proteins. TDP-43 is a major component of these aggregates in Amyotrophic Lateral Sclerosis (ALS), but has also been observed in Alzheimer's (AD) and Parkinson's Diseases (PD). In addition, mutations in the TARDBP gene, encoding TDP-43, have been found to be a significant cause of familial ALS (FALS). All mutations, except for one, have been found in exon 6. To confirm this observation in ALS and to investigate whether TARDBP may play a role in the pathogenesis of AD and PD, we screened for mutations in exon 6 of the TARDBP gene in three cohorts composed of 376 AD, 463 PD (18% familial PD) and 376 ALS patients (50% FALS). We found mutations in ∼7% of FALS and ∼0.5% of sporadic ALS (SALS) patients, including two novel mutations, p.N352T and p.G384R. In contrast, we did not find TARDBP mutations in our cohort of AD and PD patients. These results suggest that mutations in TARDBP are not a significant cause of AD and PD.
TAR DNA-binding protein 43, encoded by the TARDBP gene, has been identified as the major pathological protein of frontotemporal lobar dementia (FTLD) with or without amyotrophic lateral sclerosis (ALS) and sporadic ALS. Subsequently, mutations in the TARDBP gene have been detected in 2% to 3% of patients with ALS (both familial and sporadic ALS). However, to our knowledge, there is only 1 description of 2 patients with FTLD and TARDBP gene mutations who later developed motor neuron disease.
To describe cognitive abnormalities in 3 Italian families with familial ALS and TARDBP gene mutations.
Design, Setting, and Participants
Genetic, neuropsychological, and neuroimaging analyses in 36 patients with familial non–superoxide dismutase 1 gene (SOD1) ALS and 280 healthy controls.
Main Outcome Measure
We identified 3 index cases of familial ALS carrying the p.Ala382Thr missense mutation of the TARDBP gene and with clinical, neuroimaging, and neuropsychological features of FTLD.
The p.Ala382Thr missense mutation of the TARDBP gene was absent in the 280 controls. It was present in all affected members of the 3 families for whom DNA was available. All affected members of the 3 families developed FTLD after the onset of ALS, confirmed by neuropsychological testing and hypometabolism in frontal associative areas assessed with fludeoxyglucose F 18 positron emission tomography and computed tomography.
Three apparently unrelated families with familial ALS carrying the p.Ala382Thr TARDBP missense mutation developed FTLD. In these families, FTLD co-segregates with ALS. Patients with ALS carrying TARDBP mutations may develop FTLD.
Mutations in the transactive response DNA binding protein-43 (TARDBP/TDP-43) gene, which regulates transcription and splicing, causes a familial form of amyotrophic lateral sclerosis (ALS). Here, we characterize and report the first tardbp mutation in zebrafish, which introduces a premature stop codon (Y220X), eliminating expression of the Tardbp protein. Another TARDBP ortholog, tardbpl, in zebrafish is shown to encode a Tardbp-like protein which is truncated compared with Tardbp itself and lacks part of the C-terminal glycine-rich domain (GRD). Here, we show that tardbp mutation leads to the generation of a novel tardbpl splice form (tardbpl-FL) capable of making a full-length Tardbp protein (Tardbpl-FL), which compensates for the loss of Tardbp. This finding provides a novel in vivo model to study TDP-43-mediated splicing regulation. Additionally, we show that elimination of both zebrafish TARDBP orthologs results in a severe motor phenotype with shortened motor axons, locomotion defects and death at around 10 days post fertilization. The Tardbp/Tardbpl knockout model generated in this study provides an excellent in vivo system to study the role of the functional loss of Tardbp and its involvement in ALS pathogenesis.
Five to 10% of cases of amyotrophic lateral sclerosis are familial, with the most common genetic causes being mutations in the C9ORF72, SOD1, TARDBP and FUS genes. Mutations in the angiogenin gene, ANG, have been identified in both familial and sporadic patients in several populations within Europe and North America. The aim of this study was to establish the incidence of ANG mutations in a large cohort of 517 patients from Northern England and establish the neuropathology associated with these cases.
The single exon ANG gene was amplified, sequenced and analysed for mutations. Pathological examination of brain, spinal cord and skeletal muscle included conventional histology and immunohistochemistry.
Mutation screening identified a single sporadic amyotrophic lateral sclerosis case with a p.K54E mutation, which is absent from 278 neurologically normal control samples. The clinical presentation was of limb onset amyotrophic lateral sclerosis, with rapid disease progression and no evidence of cognitive impairment. Neuropathological examination established the presence of characteristic ubiquitinated and TDP-43-positive neuronal and glial inclusions, but no abnormality in the distribution of angiogenin protein.
There is only one previous report describing the neuropathology in a single case with a p.K17I ANG mutation which highlighted the presence of eosinophilic neuronal intranuclear inclusions in the hippocampus. The absence of this feature in the present case indicates that patients with ANG mutations do not always have pathological changes distinguishable from those of sporadic amyotrophic lateral sclerosis.
amyotrophic lateral sclerosis; angiogenin; glial inclusions; intranuclear inclusions; neuronal inclusions; neuropathology
TAR DNA binding protein, encoded by TARDBP, was shown to be a central component of ubiquitin-positive, tau-negative inclusions in frontotemporal lobar degeneration (FTLD-U) and amyotrophic lateral sclerosis (ALS). Recently, mutations in TARDBP have been linked to familial and sporadic ALS.
To further examine the frequency of mutations in TARDBP in sporadic ALS, 279 ALS cases and 806 neurologically normal control individuals of European descent were screened for sequence variants, copy number variants, genetic and haplotype association with disease. An additional 173 African samples from the Human Gene Diversity Panel were sequenced as this population had the highest likelihood of finding changes. No mutations were found in the ALS cases. Several genetic variants were identified in controls, which were considered as non-pathogenic changes. Furthermore, pathogenic structural variants were not observed in the cases and there was no genetic or haplotype association with disease status across the TARDBP locus.
Our data indicate that genetic variation in TARDBP is not a common cause of sporadic ALS in North American.
Mutations in the SOD1 and TARDBP genes have been commonly identified in Amyotrophic Lateral Sclerosis (ALS). Recently, mutations in the Fused in sarcoma gene (FUS) were identified in familial (FALS) ALS cases and sporadic (SALS) patients. Similarly to TDP-43 (coded by TARDBP gene), FUS is an RNA binding protein. Using the zebrafish (Danio rerio), we examined the consequences of expressing human wild-type (WT) FUS and three ALS–related mutations, as well as their interactions with TARDBP and SOD1. Knockdown of zebrafish Fus yielded a motor phenotype that could be rescued upon co-expression of wild-type human FUS. In contrast, the two most frequent ALS–related FUS mutations, R521H and R521C, unlike S57Δ, failed to rescue the knockdown phenotype, indicating loss of function. The R521H mutation caused a toxic gain of function when expressed alone, similar to the phenotype observed upon knockdown of zebrafish Fus. This phenotype was not aggravated by co-expression of both mutant human TARDBP (G348C) and FUS (R521H) or by knockdown of both zebrafish Tardbp and Fus, consistent with a common pathogenic mechanism. We also observed that WT FUS rescued the Tardbp knockdown phenotype, but not vice versa, suggesting that TARDBP acts upstream of FUS in this pathway. In addition we observed that WT SOD1 failed to rescue the phenotype observed upon overexpression of mutant TARDBP or FUS or upon knockdown of Tardbp or Fus; similarly, WT TARDBP or FUS also failed to rescue the phenotype induced by mutant SOD1 (G93A). Finally, overexpression of mutant SOD1 exacerbated the motor phenotype caused by overexpression of mutant FUS. Together our results indicate that TARDBP and FUS act in a pathogenic pathway that is independent of SOD1.
Mutations in the SOD1, TARDBP, and FUS genes have been commonly identified in Amyotrophic Lateral Sclerosis (ALS). However, possible interactions between these ALS–causative genetic mutations have not been examined. Here we expressed each of three human FUS mutations (R521H, R521C, and S57Δ) in zebrafish embryos, with or without knocking down the zebrafish homolog Fus, and observed a motor phenotype consisting of significant behavioral (touch-evoked escape response) and cellular (shortened axonal projections from motor neurons) deficits due to loss of function for the R521H and R521C mutations and/or toxic gain of function solely for the R521H mutation. Wild-type FUS could rescue the Tardbp knockdown phenotype, but not vice versa, suggesting that TARDBP is upstream of FUS in this pathway responsible for motor neuron disorder. Furthermore, neither TARDBP nor FUS were able to modify and/or rescue the motor phenotype caused by mutant SOD1, and likewise SOD1 failed to rescue the phenotype of zebrafish expressing mutant TARDBP or FUS. Our results indicate that TARDBP acts upstream of FUS in a pathogenic pathway that is distinct from that of SOD1.
To assess the frequency and clinical characteristics of patients with mutations of major amyotrophic lateral sclerosis (ALS) genes in a prospectively ascertained, population-based epidemiologic series of cases.
The study population includes all ALS cases diagnosed in Piemonte, Italy, from January 2007 to June 2011. Mutations of SOD1, TARDBP, ANG, FUS, OPTN, and C9ORF72 have been assessed.
Out of the 475 patients included in the study, 51 (10.7%) carried a mutation of an ALS-related gene (C9ORF72, 32; SOD1, 10; TARDBP, 7; FUS, 1; OPTN, 1; ANG, none). A positive family history for ALS or frontotemporal dementia (FTD) was found in 46 (9.7%) patients. Thirty-one (67.4%) of the 46 familial cases and 20 (4.7%) of the 429 sporadic cases had a genetic mutation. According to logistic regression modeling, besides a positive family history for ALS or FTD, the chance to carry a genetic mutation was related to the presence of comorbid FTD (odds ratio 3.5; p = 0.001), and age at onset ≤54 years (odds ratio 1.79; p = 0.012).
We have found that ∼11% of patients with ALS carry a genetic mutation, with C9ORF72 being the commonest genetic alteration. Comorbid FTD or a young age at onset are strong indicators of a possible genetic origin of the disease.
Background: The identification of mutations in the TARDBP and more recently the identification of mutations in the FUS gene as the cause of amyotrophic lateral sclerosis (ALS) is providing the field with new insight about the mechanisms involved in this severe neurodegenerative disease.
Methods: To extend these recent genetic reports, we screened the entire gene in a cohort of 200 patients with ALS. An additional 285 patients with sporadic ALS were screened for variants in exon 15 for which mutations were previously reported.
Results: In total, 3 different mutations were identified in 4 different patients, including 1 3-bp deletion in exon 3 of a patient with sporadic ALS and 2 missense mutations in exon 15 of 1 patient with familial ALS and 2 patients with sporadic ALS.
Conclusions: Our study identified sporadic patients with mutations in the FUS gene. The accumulation and description of different genes and mutations helps to develop a more comprehensive picture of the genetic events underlying amyotrophic lateral sclerosis.
Amyotrophic lateral sclerosis (ALS) is a progressive paralytic disorder caused by degeneration of motor neurons. Mutations in the FUS gene were identified in patients with familial ALS (FALS) and patients with sporadic ALS (SALS) from a variety of genetic backgrounds. This work further explores the spectrum of FUS mutations in patients with FALS and patients with FALS with features of frontotemporal dementia (FALS/FTD) or parkinsonism and dementia (FALS/PD/DE).
All exons of the FUS gene were sequenced in 476 FALS index cases negative for mutations in SOD1 and TARDBP. A total of 561–726 controls were analyzed for genetic variants observed. Clinical data from patients with FUS mutations were compared to those of patients with known SOD1 and TARDBP mutations.
We identified 17 FUS mutations in 22 FALS families, 2 FALS/FTD families, and 1 FALS/PD/DE family from diverse genetic backgrounds; 11 mutations were novel. There were 4 frameshift, 1 nonsense, and 1 possible alternate splicing mutation. Patients with FUS mutations appeared to have earlier symptom onset, a higher rate of bulbar onset, and shorter duration of symptoms than those with SOD1 mutations.
FUS gene mutations are not an uncommon cause in patients with FALS from diverse genetic backgrounds, and have a prevalence of 5.6% in non-SOD1 and non-TARDBP FALS, and ∼4.79% in all FALS. The pathogenicity of some of these novel mutations awaits further studies. Patients with FUS mutations manifest earlier symptom onset, a higher rate of bulbar onset, and shorter duration of symptoms.
= amyotrophic lateral sclerosis;
= familial amyotrophic lateral sclerosis;
= familial amyotrophic lateral sclerosis with features of frontotemporal dementia;
= familial amyotrophic lateral sclerosis with features of parkinsonism and dementia;
= sporadic amyotrophic lateral sclerosis.
Mutations in the Cu/Zn superoxide dismutase (SOD1), transactive response (TAR)-DNA binding protein (TARDBP) and fused in sarcoma (FUS) genes account for approximately one third of familial amyotrophic lateral sclerosis (ALS) cases. Mutations in these genes have been found in 1 to 2% of apparently sporadic cases. We present the first case of an ALS patient carrying a de novo missense mutation of the FUS gene (c.1561C>T, p.R521C). This report highlights the importance of screening ALS patients, both familial and sporadic, for FUS mutations and also suggests that de novo mutations is a relevant mechanism underlying sporadic neurodegenerative disease.
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.
Mutations in the gene encoding fused in sarcoma (FUS) were recently identified as a novel cause of amyotrophic lateral sclerosis (ALS), emphasizing the genetic heterogeneity of ALS. We sequenced the genes encoding superoxide dismutase (SOD1), TAR DNA-binding protein 43 (TARDBP) and FUS in 99 sporadic and 17 familial ALS patients ascertained at Mayo Clinic. We identified two novel mutations in FUS in two out of 99 (2.0%) sporadic ALS patients and established the de novo occurrence of one FUS mutation. In familial patients, we identified three (17.6%) SOD1 mutations, while FUS and TARDBP mutations were excluded. The de novo FUS mutation (g.10747A>G; IVS13-2A>G) affects the splice-acceptor site of FUS intron 13 and was shown to induce skipping of FUS exon 14 leading to the C-terminal truncation of FUS (p.G466VfsX14). Subcellular localization studies showed a dramatic increase in the cytoplasmic localization of FUS and a reduction of normal nuclear expression in cells transfected with truncated compared to wild-type FUS. We further identified a novel in-frame insertion/deletion mutation in FUS exon 12 (p.S402 P411delinsGGGG) which is predicted to expand a conserved poly-glycine motif. Our findings extend the mutation spectrum in FUS leading to ALS and describe the first de novo mutation in FUS.
FUS/TLS; fused in sarcoma; amyotrophic lateral sclerosis; de novo mutation; FUS splice-site mutation; FUS truncating mutation
Mutations in TARDBP, encoding Tar DNA binding protein-43 (TDP43), cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Attempts to model TDP43 dysfunction in mice have used knockouts or transgenic overexpressors, which have revealed the difficulties of manipulating TDP43, whose level is tightly controlled by auto-regulation. In a complementary approach, to create useful mouse models for the dissection of TDP43 function and pathology, we have identified a nonsense mutation in the endogenous mouse Tardbp gene through screening an N-ethyl-N-nitrosourea (ENU) mutant mouse archive. The mutation is predicted to cause a Q101X truncation in TDP43. We have characterised TardbpQ101X mice to investigate this mutation in perturbing TDP43 biology at endogenous expression levels. We found the TardbpQ101X mutation is homozygous embryonic lethal, highlighting the importance of TDP43 in early development. Heterozygotes (Tardbp+/Q101X) have abnormal levels of mutant transcript, but we find no evidence of the truncated protein and mice have similar full-length TDP43 protein levels as wildtype littermates. Nevertheless, Tardbp+/Q101X mice have abnormal alternative splicing of downstream gene targets, and limb-clasp and body tone phenotypes. Thus the nonsense mutation in Tardbp causes a mild loss-of-function phenotype and behavioural assessment suggests underlying neurological abnormalities. Due to the role of TDP43 in ALS, we investigated potential interactions with another known causative gene, mutant superoxide dismutase 1 (SOD1). Tardbp+/Q101X mice were crossed with the SOD1G93Adl transgenic mouse model of ALS. Behavioural and physiological assessment did not reveal modifying effects on the progression of ALS-like symptoms in the double mutant progeny from this cross. In summary, the TardbpQ101X mutant mice are a useful tool for the dissection of TDP43 protein regulation, effects on splicing, embryonic development and neuromuscular phenotypes. These mice are freely available to the community.
The identification of TAR DNA-binding protein 43 (TDP-43) as the major disease protein in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin inclusions (FTLD-U) has defined a new class of neurodegenerative conditions: the TDP-43 proteinopathies. This breakthrough was quickly followed by mutation analysis of TARDBP, the gene encoding TDP-43. Herein, we provide a review of our previously published efforts that led to the identification of 3 TARDBP mutations (p.M337V, p.N345K, and p.I383V) in familial ALS patients, 2 of which were novel. With over 40 TARDBP mutations now discovered, there exists conclusive evidence that TDP-43 plays a direct role in neurodegeneration. The onus is now on researchers to elucidate the mechanisms by which mutant TDP-43 confers toxicity, and to exploit these findings to gain a better understanding of how TDP-43 contributes to the pathogenesis of disease. Our biochemical analysis of TDP-43 in ALS patient lymphoblastoid cell lines revealed a substantial increase in TDP-43 truncation products, including a ~25 kDa fragment, compared to control lymphoblastoid cell lines. We discuss the putative harmful consequence of abnormal TDP-43 fragmentation, as well as highlight additional mechanisms of toxicity associated with mutant TDP-43.
TDP-43; TARDBP; mutation; neurodegeneration; amyotrophic lateral sclerosis; frontotemporal lobar degeneration
Recently, fused in sarcoma/translated in liposarcoma (FUS/TLS) gene, located on chromosome 16p11.2, has been identified as a disease gene in familial amyotrophic lateral sclerosis (FALS). We have analyzed FUS/TLS in a cohort of 52 index cases from seven Italian regions with non-SOD1 and non-TARDBP FALS. We identified a heterozygous c.G1542C missense mutation in a family of northern Italian origin, and a heterozygous c.C1574T missense mutation in a family of Sicilian origin. Both variants are located in exon 15 encoding the RNA-recognition motif, and result in a substitution of an arginine with a serine in position 514 (p.R514S) and substitution of a proline with a leucine at position 525 (p.P525L) respectively. Overall, the two mutations accounted for 3.8% of 52 non-SOD1 and non-TDP43 index cases of FALS. The clinical phenotype was similar within each of the families, with a predominantly upper limb onset in the family carrying the p.R514S mutation and bulbar onset, with very young age and a rapid course in the family carrying the p.P525L mutation.
amyotrophic lateral sclerosis; genetics; FUS gene; family pedigrees
We have recently published data showing that a founder mutation of the TARDBP gene (p.A382T) accounts for approximately one third of ALS cases on the Mediterranean island of Sardinia (Chiò et al, 2011). In that report, we identified 53 years-old man carrying a homozygous A382T missense mutation of the TARDBP gene with a complex neurological syndrome including ALS, parkinsonian features, motor and vocal tics, and frontotemporal dementia (FTD). Due to the uniqueness of this case, here we provide a detailed clinical description, as well as neurophysiological, neuropsychological and neuroimaging data for that case and his extended family.
Abnormal TDP-43 aggregation is a prominent feature in the neuropathology of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. Mutations in TARDBP, the gene encoding TDP-43, cause some cases of ALS. The normal function of TDP-43 remains incompletely understood. To better understand TDP-43 biology, we generated mutant mice carrying a genetrap disruption of Tardbp. Mice homozygous for loss of TDP-43 are not viable. TDP-43 deficient embryos die about day 7.5 of embryonic development thereby demonstrating that TDP-43 protein is essential for normal prenatal development and survival. However, heterozygous Tardbp mutant mice exhibit signs of motor disturbance and muscle weakness. Compared with wild type control littermates, Tardbp+/− animals have significantly decreased forelimb grip strength and display deficits in a standard inverted grid test despite no evidence of pathologic changes in motor neurons. Thus, TDP-43 is essential for viability, and mild reduction in TDP-43 function is sufficient to cause motor deficits without degeneration of motor neurons.
Amyotrophic lateral sclerosis (ALS) is the most common motor neuron diseases (MND), while frontotemporal lobar degeneration (FTLD) is the second most common cause of early-onset dementia. Many ALS families segregating FTLD have been reported, particularly over the last decade. Recently, mutations in TARDBP, FUS/TLS, and C9ORF72 have been identified in both ALS and FTLD patients, while mutations in VCP, a FTLD associated gene, have been found in ALS families. Distinct variants located in the 3′-untranslated region (UTR) of the SIGMAR1 gene were previously reported in three unrelated FTLD or FTLD–MND families. We directly sequenced the coding and UTR regions of the SIGMAR1 gene in a targeted cohort of 25 individual familial ALS cases of Caucasian origin with a history of cognitive impairments. This screening identified one variant in the 3′-UTR of the SIGMAR1 gene in one ALS patient, but the same variant was also observed in 1 out of 380 control chromosomes. Subsequently, we screened the same samples for a C9ORF72 repeat expansion: 52% of this cohort was found expanded, including the sample with the SIGMAR1 3′-UTR variant. Consequently, coding and noncoding variants located in the 3′-UTR region of the SIGMAR1 gene are not the cause of FTLD–MND in our cohort, and more than half of this targeted cohort is genetically explained by C9ORF72 repeat expansions.
amyotrophic lateral sclerosis; frontotemporal lobar degeneration; motor neuron disease; dementia
There is increasing evidence that frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) represent a continuum of neurodegenerative diseases. FTLD is complicated by ALS in a significant proportion of patients, and neuropsychological studies have demonstrated frontotemporal dysfunction in up to 50% of ALS patients. More recently, advances in neuropathology and molecular genetics have started to disclose the biological basis for the observed clinical concurrence. TDP-43 and FUS have been discovered as key pathological proteins in both FTLD and ALS. The most recent discovery of a pathological hexanucleotide repeat expansion in the gene C9orf72 as a frequent cause of both FTLD and ALS has eventually confirmed the association of these two at first sight distinct neurodegenerative diseases. Mutations in the TARDBP, FUS, and VCP genes had previously been associated with different phenotypes of the FTLD-ALS spectrum, although in these cases one end of the spectrum predominates. Whilst on the one hand providing evidence for overlap, these discoveries have also highlighted that FTLD and ALS are etiologically diverse. In this review, we review the recent advances that support the existence of an FTLD-ALS spectrum, with particular emphasis on the molecular genetic aspect.
Amyotrophic lateral sclerosis; C9orf72; frontotemporal lobar degeneration; genotype–phenotype correlations; molecular genetics; pathology