Aims and background:Mutations in the TARDBP gene, which encodes the TAR DNA binding protein (TDP-43), have been described in individuals with familial and sporadic amyotrophic lateral sclerosis ...(ALS). We screened the TARDBP gene in 285 French sporadic ALS patients to assess the frequency of TARDBP mutations in ALS.Results:Six individuals had potentially deleterious mutations of which three were novel including a Y374X truncating mutation and P363A and A382P missense mutations. This suggests that TARDBP mutations may predispose to ALS in approximately 2% of the individuals followed in this study.Conclusion:Our findings, combined with those from other collections, brings the total number of mutations in unrelated ALS patients to 17, further suggesting that mutations in the TARDBP gene have an important role in the pathogenesis of ALS.
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.
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.
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.
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.
ABSTRACT
Mutations in the TAR DNA Binding Protein gene (TARDBP), encoding the protein TDP‐43, were identified in amyotrophic lateral sclerosis (ALS) patients. Interestingly, TDP‐43 positive inclusion ...bodies were first discovered in ubiquitin‐positive, tau‐negative ALS and frontotemporal dementia (FTD) inclusion bodies, and subsequently observed in the majority of neurodegenerative disorders. To date, 47 missense and one truncating mutations have been described in a large number of familial (FALS) and sporadic (SALS) patients. Fused in sarcoma (FUS) was found to be responsible for a previously identified ALS6 locus, being mutated in both FALS and SALS patients. TARDBP and FUS have a structural and functional similarity and most of mutations in both genes are also clustered in the C‐terminus of the proteins. The molecular mechanisms through which mutant TDP‐43 and FUS may cause motor neuron degeneration are not well understood. Both proteins play an important role in mRNA transport, axonal maintenance, and motor neuron development. Functional characterization of these mutations in in vitro and in vivo systems is helping to better understand how motor neuron degeneration occurs. This report summarizes the biological and clinical relevance of TARDBP and FUS mutations in ALS. All the data reviewed here have been submitted to a database based on the Leiden Open (source) Variation Database (LOVD) and is accessible online at www.lovd.nl/TARDBP, www.lovd.nl/FUS.
Amyotrophic Lateral Sclerosis is a progressive and devastating disorder of motor neurons. A number of genes have been found commonly mutated in ALS patients. Among these, TARDBP and FUS play an important role. Both proteins are involved in mRNA transport, axonal maintenance and motor neuron development but the exact molecular mechanisms through which they cause motor neuron degeneration, when mutated, are not well understood. This report summarizes the genetic, biological and clinical relevance of TARDBP and FUS mutations in ALS.
The paraoxonase gene cluster on chromosome 7 comprising the PON1-3 genes is an attractive candidate for association in amyotrophic lateral sclerosis (ALS) given the role of paraoxonase genes during ...the response to oxidative stress and their contribution to the enzymatic break down of nerve toxins. Oxidative stress is considered one of the mechanisms involved in ALS pathogenesis. Evidence for this includes the fact that mutations of SOD1, which normally reduce the production of toxic superoxide anion, account for 12% to 23% of familial cases in ALS. In addition, PON variants were shown to be associated with susceptibility to ALS in several North American and European populations.
We extended this analysis to examine 20 single nucleotide polymorphisms (SNPs) across the PON gene cluster in a set of patients from France (480 cases, 475 controls), Quebec (159 cases, 95 controls), and Sweden (558 cases, 506 controls).
Although individual SNPs were not considered associated on their own, a haplotype of SNPs at the C-terminal portion of PON2 that includes the PON2 C311S amino acid change was significant in the French (p value 0.0075) and Quebec (p value 0.026) populations as well as all three populations combined (p value 1.69 x 10(-6)). Stratification of the samples showed that this variation was pertinent to ALS susceptibility as a whole, and not to a particular subset of patients.
These findings contribute to the increasing weight of evidence that genetic variants in the paraoxonase gene cluster are associated with amyotrophic lateral sclerosis.
Amyotrophic lateral sclerosis (ALS) is a rapidly progressing, fatal disorder with no effective treatment. We used simple genetic models of ALS to screen phenotypically for potential therapeutic ...compounds. We screened libraries of compounds in C. elegans, validated hits in zebrafish, and tested the most potent molecule in mice and in a small clinical trial. We identified a class of neuroleptics that restored motility in C. elegans and in zebrafish, and the most potent was pimozide, which blocked T-type Ca2+ channels in these simple models and stabilized neuromuscular transmission in zebrafish and enhanced it in mice. Finally, a short randomized controlled trial of sporadic ALS subjects demonstrated stabilization of motility and evidence of target engagement at the neuromuscular junction. Simple genetic models are, thus, useful in identifying promising compounds for the treatment of ALS, such as neuroleptics, which may stabilize neuromuscular transmission and prolong survival in this disease.
Mutations in the Cu/Zn‐superoxide dismutase (SOD‐1) gene are responsible for a familial form of amyotrophic lateral sclerosis (fALS). The present study demonstrated impaired proteasomal function in ...the lumbar spinal cord of transgenic mice expressing human SOD‐1 with the ALS‐causing mutation G93A (SOD‐1G93A) compared to non‐transgenic littermates (LM) and SOD‐1WT transgenic mice. Chymotrypsin‐like activity was decreased as early as 45 days of age. By 75 days, chymotrypsin‐, trypsin‐, and caspase‐like activities of the proteasome were impaired, at about 50% of control activity in lumbar spinal cord, but unchanged in thoracic spinal cord and liver. Both total and specific activities of the proteasome were reduced to a similar extent, indicating that a change in proteasome function, rather than a decrease in proteasome levels, had occurred. Similar decreases of total and specific activities of the proteasome were observed in NIH 3T3 cell lines expressing fALS mutants SOD‐1G93A and SOD‐1G41S, but not in SOD‐1WT controls. Although overall levels of proteasome were maintained in spinal cord of SOD‐1G93A transgenic mice, the level of 20S proteasome was substantially reduced in lumbar spinal motor neurons relative to the surrounding neuropil. It is concluded that impairment of the proteasome is an early event and contributes to ALS pathogenesis.
In amyotrophic lateral sclerosis caused by mutations in Cu/Zn-superoxide dismutase (SOD1), altered solubility and aggregation of the mutant protein implicates failure of pathways for detecting and ...catabolizing misfolded proteins. Our previous studies demonstrated early reduction of proteasome-mediated proteolytic activity in lumbar spinal cord of SOD1G⁹³A transgenic mice, tissue particularly vulnerable to disease. The purpose of this study was to identify any underlying abnormalities in proteasomal structure. In lumbar spinal cord of pre-symptomatic mice postnatal day 45 (P45) and P75, normal levels of structural 20S α subunits were incorporated into 20S/26S proteasomes; however, proteasomal complexes separated by native gel electrophoresis showed decreased immunoreactivity with antibodies to β3, a structural subunit of the 20S proteasome core, and β5, the subunit with chymotrypsin-like activity. This occurred prior to increase in β5i immunoproteasomal subunit. mRNA levels were maintained and no association of mutant SOD1 with proteasomes was identified, implicating post-transcriptional mechanisms. mRNAs also were maintained in laser captured motor neurons at a later stage of disease (P100) in which multiple 20S proteins are reduced relative to the surrounding neuropil. Increase in detergent-insoluble, ubiquitinated proteins at P75 provided further evidence of stress on mechanisms of protein quality control in multiple cell types prior to significant motor neuron death.
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