Screening of SOD1, FUS and TARDBP genes in patients with amyotrophic lateral sclerosis in central-southern China

Protein Structure-based FUS Mutational Subtypes Are Associated With Protein Mislocalization in Amyotrophic Lateral Sclerosis Patients

The mislocalization of RNA-binding proteins (RBPs) from nucleus to cytoplasm and the formation of aggregates are hallmarks of neurodegeneration. Amyotrophic lateral sclerosis (ALS) disease-causing mutations in the fused in sarcoma (FUS) gene, encoding an RNA-binding protein, cluster at the C-terminal proline/tyrosine-nuclear localization signal (PY-NLS) domain, which is crucial for mediating nucleus-cytoplasm translocation by binding to Transportin-1. However, the mechanisms underlying heterogeneous protein mislocalization and age at onset (AAO) of ALS cases carrying FUS PY-NLS mutations remain unclear. Here, we screened FUS mutations in 416 ALS patients, and identified 12 patients carrying four FUS mutations at the p.R521 locus of PY-NLS domain (p.R521P, p.R521C, p.R521G, p.R521H), exhibiting highly variable AAO (20-56 years). AlphaFold-2 predicted protein structures classified FUS p.R521 mutants into alpha-helix containing (p.R521C, p.R521H) and alpha-helix disrupted (p.R521P, p.R521G) subgroups. Isothermal titration calorimetry experiment showed that the FUS alpha-helix disrupted subgroup had a reduced binding affinity with transportin-1, which is essential for mediating the nucleus-cytoplasm translocation. Furthermore, immunofluorescence in HEK-293 T and SH-SY5Y cells revealed more protein mislocalization in the FUS alpha-helix disrupted subgroup compared to the alpha-helix containing subgroup. FUS mislocalization status is also significantly associated with ALS AAO. Finally, the alpha-helix structure based FUS-ALS subgroups exhibited significantly different AAO (P = 0.036) in our cohort, but not in a Chinese cohort including published dataset. In summary, we showed highly diverse phenotypes in ALS patients with FUS R521 mutants, and implicated a link between genetic mutation related C-terminal structure with the status of FUS protein mislocalization.

Adenosine diphosphate-ribosylation greatly affects proteins function: a focus on neurodegenerative diseases

Adenosine diphosphate-ribosylation (ADPRylation) is a reversible posttranslational modification that plays a crucial role in cellular homeostasis and disease development. ADPRylation is produced via nicotinamide adenine dinucleotide hydrolysis and modifies proteins via corresponding transferases, mainly poly(ADP-ribose) polymerases (PARPs), the inhibitors of which have been used in the clinical treatment of cancer. ADPRylation is involved in various physiological processes, including pathogen infection, inflammation, DNA repair, and neurological disorders. In neurodegenerative diseases (NDs), dysregulated ADPRylation contributes to protein aggregation, neuroinflammation, and metabolic disturbances, while targeted modulation shows therapeutic potential. ADPRylation differentially regulates neurodegenerative processes, and PARP inhibitors can reduce neuroinflammation, oxidative stress, and metabolic dysfunction. However, challenges such as poor blood-brain barrier penetration and cell type-specific responses limit clinical translation. This review summarizes recent findings on the role of ADPRylation and PARPs in NDs, highlighting their involvement in protein aggregation and cellular signaling. It emphasizes the importance of ADPRylation in neuronal cells and supports the development of precision therapies targeting this pathway to address current treatment challenges in NDs.

Clinical characterization and founder effect analysis in Chinese amyotrophic lateral sclerosis patients with SOD1 common variants

OBJECTIVE

In the Asian population, SOD1 variants are the most common cause of amyotrophic lateral sclerosis (ALS). To date, more than 200 variants have been reported in SOD1. This study aimed to summarize the genotype-phenotype correlation and determine whether the patients carrying common variants derive from a common ancestor.

METHODS

A total of 103 sporadic ALS (SALS) and 11 familial ALS (FALS) probands were included and variants were screened by whole exome sequencing. Functional analyses were performed on fibroblasts derived from patients with SOD1 p.V48A and control. Haplotype analysis was performed in the probands with p.H47R or p.V48A and their familial members.

RESULTS

A total of 25 SOD1 variants were identified in 44 probands, in which p.H47R, p.V48A and p.C112Y variants were the most common variants. 94.3% and 60% of patients with p.H47R or p.V48A had lower limb onset with predominant lower motor neurons (LMNs) involvement. Patients with p.H47R had a slow progression and prolonged survival time, while patients with p.V48A exhibited a duration of 2-5 years. Patients with p.C112Y variant showed remarkable phenotypic variation in age at onset and disease course. SOD1V48A fibroblasts showed mutant SOD1 aggregate formation, enhanced intracellular reactive oxygen species level, and decreased mitochondrial membrane potential compared to the control fibroblast. Haplotype analysis showed that seven families had two different haplotypes. p.H47R and p.V48A variants did not originate from a common founder.

CONCLUSIONS

Our study expanded the understanding of the genotype-phenotype correlation of ALS with SOD1 variants and revealed that the common p.H47R or p.V48A variant did not have a founder effect.

Glycolic acid and D-lactate-putative products of DJ-1-restore neurodegeneration in FUS - and SOD1-ALS

Amyotrophic lateral sclerosis (ALS) leads to death within 2-5 yr. Currently, available drugs only slightly prolong survival. We present novel insights into the pathophysiology of Superoxide Dismutase 1 (SOD1)- and in particular Fused In Sarcoma (FUS)-ALS by revealing a supposedly central role of glycolic acid (GA) and D-lactic acid (DL)-both putative products of the Parkinson's disease associated glyoxylase DJ-1. Combined, not single, treatment with GA/DL restored axonal organelle phenotypes of mitochondria and lysosomes in FUS- and SOD1-ALS patient-derived motoneurons (MNs). This was not only accompanied by restoration of mitochondrial membrane potential but even dependent on it. Despite presenting an axonal transport deficiency as well, TDP43 patient-derived MNs did not share mitochondrial depolarization and did not respond to GA/DL treatment. GA and DL also restored cytoplasmic mislocalization of FUS and FUS recruitment to DNA damage sites, recently reported being upstream of the mitochondrial phenotypes in FUS-ALS. Whereas these data point towards the necessity of individualized (gene-) specific therapy stratification, it also suggests common therapeutic targets across different neurodegenerative diseases characterized by mitochondrial depolarization.

Variability in SOD1-associated amyotrophic lateral sclerosis: geographic patterns, clinical heterogeneity, molecular alterations, and therapeutic implications

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of motor neurons, resulting in global health burden and limited post-diagnosis life expectancy. Although primarily sporadic, familial ALS (fALS) cases suggest a genetic basis. This review focuses on SOD1, the first gene found to be associated with fALS, which has been more recently confirmed by genome sequencing. While informative, databases such as ALSoD and STRENGTH exhibit regional biases. Through a systematic global examination of SOD1 mutations from 1993 to 2023, we found different geographic distributions and clinical presentations. Even though different SOD1 variants are expressed at different protein levels and have different half-lives and dismutase activities, these alterations lead to loss of function that is not consistently correlated with disease severity. Gain of function of toxic aggregates of SOD1 resulting from mutated SOD1 has emerged as one of the key contributors to ALS. Therapeutic interventions specifically targeting toxic gain of function of mutant SOD1, including RNA interference and antibodies, show promise, but a cure remains elusive. This review provides a comprehensive perspective on SOD1-associated ALS and describes molecular features and the complex genetic landscape of SOD1, highlighting its importance in determining diverse clinical manifestations observed in ALS patients and emphasizing the need for personalized therapeutic strategies.

Unveiling the SOD1-mediated ALS phenotype: insights from a comprehensive meta-analysis

BACKGROUND AND OBJECTIVES

Amyotrophic lateral sclerosis associated with mutations in SOD1 (SOD1-ALS) might be susceptible to specific treatment. The aim of the study is to outline the clinical features of SOD1-ALS patients by comparing them to patients without ALS major gene variants and patients with variants in other major ALS genes. Defining SOD1-ALS phenotype may assist clinicians in identifying patients who should be prioritized for genetic testing.

METHODS

We performed an extensive literature research including original studies which reported the clinical features of SOD1-ALS and at least one of the following patient groups: C9ORF72 hexanucleotide repeat expansion (C9-ALS), TARDBP (TARDBP-ALS), FUS (FUS-ALS) or patients without a positive test for a major-ALS gene (N-ALS). A random effects meta-analytic model was applied to clinical data extracted encompassing sex, site and age of onset. To reconstruct individual patient survival data, the published Kaplan-Meier curves were digitized. Data were measured as odds ratio (OR) or standardized mean difference (SMD) as appropriate. Median survival was compared between groups.

RESULTS

Twenty studies met the inclusion criteria. We identified 721 SOD1-ALS, 470 C9-ALS, 183 TARDBP-ALS, 113 FUS-ALS and 2824 N-ALS. SOD1-ALS showed a higher rate of spinal onset compared with N-ALS and C9-ALS (OR = 4.85, 95% CI = 3.04-7.76; OR = 10.47, 95% CI = 4.32-27.87) and an earlier onset compared with N-ALS (SMD = - 0.45, 95% CI = - 0.72 to - 0.18). SOD1-ALS had a similar survival compared with N-ALS (p = 0.14), a longer survival compared with C9-ALS (p < 0.01) and FUS-ALS (p = 0.019) and a shorter survival compared with TARDBP-ALS (p < 0.01).

DISCUSSION

This study indicates the presence of a specific SOD1-ALS phenotype. Insights in SOD1-ALS clinical features are important in genetic counseling, disease prognosis and support patients' stratification in clinical trials.

Association of TRMT2B gene variants with juvenile amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive degeneration of motor neurons, and it demonstrates high clinical heterogeneity and complex genetic architecture. A variation within TRMT2B (c.1356G>T; p.K452N) was identified to be associated with ALS in a family comprising two patients with juvenile ALS (JALS). Two missense variations and one splicing variation were identified in 10 patients with ALS in a cohort with 910 patients with ALS, and three more variants were identified in a public ALS database including 3317 patients with ALS. A decreased number of mitochondria, swollen mitochondria, lower expression of ND1, decreased mitochondrial complex I activities, lower mitochondrial aerobic respiration, and a high level of ROS were observed functionally in patient-originated lymphoblastoid cell lines and TRMT2B interfering HEK293 cells. Further, TRMT2B variations overexpression cells also displayed decreased ND1. In conclusion, a novel JALS-associated gene called TRMT2B was identified, thus broadening the clinical and genetic spectrum of ALS.

FUS gene mutation in amyotrophic lateral sclerosis: a new case report and systematic review

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease associated with upper and lower motor neuron degeneration and necrosis, characterized by progressive muscle weakness, atrophy, and paralysis. The FUS mutation-associated ALS has been classified as ALS6. We reported a case of ALS6 with de novo mutation and investigated retrospectively the characteristics of cases with FUS mutation.

METHODS

We reported a male patient with a new heterozygous variant of the FUS gene and comprehensively reviewed 173 ALS cases with FUS mutation. The literature was reviewed from the PubMed MEDLINE electronic database (https://www.ncbi.nlm.nih.gov/pubmed) using "Amyotrophic Lateral Sclerosis and Fus mutation" or "Fus mutation" as key words from 1 January 2009 to 1 January 2022.

RESULTS

We report a case of ALS6 with a new mutation point (c.1225-1227delGGA) and comprehensively review 173 ALS cases with FUS mutation. Though ALS6 is all with FUS mutation, it is still a highly heterogenous subtype. The average onset age of ALS6 is 35.2 ± 1.3 years, which is much lower than the average onset age of ALS (60 years old). Juvenile FUS mutations have an aggressive progression of disease, with an average time from onset to death or tracheostomy of 18.2 ± 0.5 months. FUS gene has the characteristics of early onset, faster progress, and shorter survival, especially in deletion mutation p.G504Wfs *12 and missense mutation of p.P525L.

CONCLUSIONS

ALS6 is a highly heterogenous subtype. Our study could allow clinicians to better understand the non-ALS typical symptoms, phenotypes, and pathophysiology of ALS6.

Impaired RNA Binding Does Not Prevent Histone Modification Changes in a FUS ALS/FTD Yeast Model

Mutations in the RNA-binding protein FUS are linked to amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). FUS mutants mislocalize and aggregate in dying neurons. We previously established that FUS proteinopathy is linked to changes in the histone modification landscape in a yeast ALS/FTD model. Here, we examine whether FUS' RNA binding is necessary for this connection. We find that overexpression of a FUS mutant unable to bind RNA is still associated with reduced levels of H3S10ph, H3K14ac and H3K56ac. Hence, FUS' ability to bind RNA is not required in the mechanism connecting FUS proteinopathy to altered histone post-translational modifications.

Amyotrophic lateral sclerosis: translating genetic discoveries into therapies

Recent advances in sequencing technologies and collaborative efforts have led to substantial progress in identifying the genetic causes of amyotrophic lateral sclerosis (ALS). This momentum has, in turn, fostered the development of putative molecular therapies. In this Review, we outline the current genetic knowledge, emphasizing recent discoveries and emerging concepts such as the implication of distinct types of mutation, variability in mutated genes in diverse genetic ancestries and gene-environment interactions. We also propose a high-level model to synthesize the interdependent effects of genetics, environmental and lifestyle factors, and ageing into a unified theory of ALS. Furthermore, we summarize the current status of therapies developed on the basis of genetic knowledge established for ALS over the past 30 years, and we discuss how developing treatments for ALS will advance our understanding of targeting other neurological diseases.

Genetic Interaction of tRNA-Dependent Mistranslation with Fused in Sarcoma Protein Aggregates

High-fidelity protein synthesis requires properly aminoacylated transfer RNAs (tRNAs), yet diverse cell types, from bacteria to humans, show a surprising ability to tolerate errors in translation resulting from mutations in tRNAs, aminoacyl-tRNA synthetases, and other components of protein synthesis. Recently, we characterized a tRNASerAGA G35A mutant (tRNASerAAA) that occurs in 2% of the human population. The mutant tRNA decodes phenylalanine codons with serine, inhibits protein synthesis, and is defective in protein and aggregate degradation. Here, we used cell culture models to test our hypothesis that tRNA-dependent mistranslation will exacerbate toxicity caused by amyotrophic lateral sclerosis (ALS)-associated protein aggregation. Relative to wild-type tRNA, we found cells expressing tRNASerAAA showed slower but effective aggregation of the fused in sarcoma (FUS) protein. Despite reduced levels in mistranslating cells, wild-type FUS aggregates showed similar toxicity in mistranslating cells and normal cells. The aggregation kinetics of the ALS-causative FUS R521C variant were distinct and more toxic in mistranslating cells, where rapid FUS aggregation caused cells to rupture. We observed synthetic toxicity in neuroblastoma cells co-expressing the mistranslating tRNA mutant and the ALS-causative FUS R521C variant. Our data demonstrate that a naturally occurring human tRNA variant enhances cellular toxicity associated with a known causative allele for neurodegenerative disease.

Analysis of SOD1 Variants in Chinese Patients with Familial Amyotrophic Lateral Sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease, and genetic contributors exert a significant role in the complicated pathogenesis. Identification of the genetic causes in ALS families could be valuable for early diagnosis and management. The development of potential drugs for patients with genetic defects will shed new light on ALS therapy.

AIM

To identify causative variants in three Chinese families with familial ALS (FALS), reveal the pathogenic mechanism, and look for the targeted drug for ALS.

DESIGN AND METHODS

Whole-exome sequencing and bioinformatics were used to perform genetic analysis of the ALS families. Functional analysis was performed to study the variants' function and search for potential drug targets.

RESULTS

Three heterozygous missense variants of the SOD1 gene were identified in families with FALS. The clinical manifestations of these patients include spinal onset, predominant lower motor neurons presentation, and absence of cognitive involvement. Functional analysis showed that all three SOD1 variants led to increased reactive oxygen species (ROS) levels, reduced cell viability, and formation of cytoplasmic aggregates. Remarkably, the decreased cell viability induced by variants was rescued after treatment with the ROS inhibitor N-acetylcysteine.

CONCLUSIONS

This study identified three SOD1 variants in three families with FALS. The variant SOD1 toxicity was associated with oxidative damage and aggregation, and N-acetylcysteine could rescue the decreased cell viability induced by these variants. Our findings support a pathogenic role for ROS in SOD1 deficiencies, and provide a potential drug N-acetylcysteine for ALS therapy, especially in SOD1-patients with limb onset.

Potential roles of the endoplasmic reticulum stress pathway in amyotrophic lateral sclerosis

The endoplasmic reticulum (ER) is a major organelle involved in protein quality control and cellular homeostasis. ER stress results from structural and functional dysfunction of the organelle, along with the accumulation of misfolded proteins and changes in calcium homeostasis, it leads to ER stress response pathway such as unfolded protein response (UPR). Neurons are particularly sensitive to the accumulation of misfolded proteins. Thus, the ER stress is involved in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, prion disease and motor neuron disease (MND). Recently, the complex involvement of ER stress pathways has been demonstrated in experimental models of amyotrophic lateral sclerosis (ALS)/MND using pharmacological and genetic manipulation of the unfolded protein response (UPR), an adaptive response to ER stress. Here, we aim to provide recent evidence demonstrating that the ER stress pathway is an essential pathological mechanism of ALS. In addition, we also provide therapeutic strategies that can help treat diseases by targeting the ER stress pathway.

Genotype-phenotype association of TARDBP mutations in Chinese patients with amyotrophic lateral sclerosis: a single-center study and systematic review of published literature

BACKGROUND

This study aims to determine the genetic and clinical features of TARDBP-mutated patients in our cohort of Chinese patients with amyotrophic lateral sclerosis (ALS) combined with data in the literature.

METHODS

We performed TARDBP mutation screening in 1258 Chinese ALS patients, including 1204 sporadic ALS (sALS) and 54 familial ALS (fALS) patients. A systematic literature review was conducted by searching TARDBP-mutated patients from China in the online databases.

RESULTS

In our cohort, the mutant frequency of TARDBP variants was 0.3% (4/1258), with two recurrent variants (p.G294V, p.G298V) and one novel variant (p.S332G) identified. Combining with data in the literature review, the TARDBP-mutant frequency in the Chinese population was 1.4% (83/5998), with 0.8% (46/5470) in sALS and 7.0% (37/528) in fALS. Most patients had limb onset (63.0%), with an average life expectancy of 4.3 years (range 0.5-13). Disease durations significantly differed (p = 0.002), with p.M337V showing the longest duration (80 months) and p.N378D showing the shortest duration (16.7 months).

CONCLUSION

Our study found that TARDBP mutation was not rare in Chinese fALS patients. Different TARDBP mutations were associated with specific features in phenotypes.

FUS mutations in Asian amyotrophic lateral sclerosis patients: a case report and literature review of genotype-phenotype correlations

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive weakness and muscular atrophy in the upper or lower limbs, ultimately leading to paralysis and death. Genetic studies have demonstrated that mutation in the gene encoding fused in sarcoma (FUS) is an uncommon cause of ALS. Here, we report a case of a 31-year-old Asian man with ALS with rare onset of dropped-head syndrome. Symptoms, including asymmetric proximal weakness of the upper limbs, hoarseness, dysphagia, and nocturnal dyspnea, emerged over a period of 5 months. After genetic testing, the patient was confirmed to harbor a novel pathogenic heterozygous mutation, c.1558C > T (p.R520C). We summarize the genotype-clinical phenotype relationships in 42 Asian patients with ALS-FUS.

SOD1 mutations associated with amyotrophic lateral sclerosis analysis of variant severity

Mutations in superoxide dismutase 1 gene (SOD1) are linked to amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder predominantly affecting upper and lower motor neurons. The clinical phenotype of ALS shows inter- and intrafamilial heterogeneity. The aim of the study was to analyze the relations between individual SOD1 mutations and the clinical presentation using in silico methods to assess the SOD1 mutations severity. We identified SOD1 causative variants in a group of 915 prospectively tested consecutive Polish ALS patients from a neuromuscular clinical center, performed molecular modeling of mutated SOD1 proteins and in silico analysis of mutation impact on clinical phenotype and survival analysis of associations between mutations and hazard of clinical end-points. Fifteen SOD1 mutations were identified in 21.1% familial and 2.3% sporadic ALS cases. Their effects on SOD1 protein structure and functioning inferred from molecular modeling and in silico analyses correlate well with the clinical data. Molecular modeling results support the hypothesis that folding intermediates rather than mature SOD1 protein give rise to the source of cytotoxic conformations in ALS. Significant associations between type of mutation and clinical end-points were found.

Genetic analysis in Chinese patients with familial or young-onset amyotrophic lateral sclerosis

OBJECTIVE

The aim of our study was to investigate the genetic characteristics in patients with familial or young-onset amyotrophic lateral sclerosis (ALS) in a Chinese center.

METHODS

Patients with familial or young-onset (age of onset < 45 years old) ALS were reviewed. The clinical data was collected. Whole-exome sequencing was performed to identify the disease-associated variants. Single-nucleotide variants and small insertions/deletions were further predicted with silico tools and compared to the Single Nucleotide Polymorphism Database, Exome Aggregation Consortium, and the 1000 Genomes Project. The evolutionary conservations were estimated, and the structures of proteins were constructed by Swiss-Model server. Immunohistochemistry was used to confirm the misfolded SOD1 protein.

RESULTS

Three familial ALS and 5 young-onset ALS were enrolled. Genetic analysis identified related variants of SOD1 (4/6, 66.7%), FUS (1/6, 16.7%), and NEK1 (1/6, 16.7%) in 6 patients. Three of them were familial probands (3/3, 100%), and the others were sporadic young-onset patients (3/5, 60%). NEK1 c.290G > A mutation (NM_012224.2 exon4) in a patient with familial ALS and SOD1 c.362A > G mutation (NM_000454 exon5) in a young-onset ALS patient were novel. The novel mutations were predicted to be deleterious, affected evolutionarily highly conserved amino acid residue and the formation of hydrogen bonds between the mutated site and its surrounding amino acid residues. Misfolded SOD1 protein was identified in patient with SOD1 c.362A > G mutation.

CONCLUSIONS

Two novel mutations were detected in our patients. Patients with familial or young-onset ALS often carried related gene mutations, and genetic sequencing should be thus routinely performed.

Circulating Biomarkers in Neuromuscular Disorders: What Is Known, What Is New

The urgent need for new therapies for some devastating neuromuscular diseases (NMDs), such as Duchenne muscular dystrophy or amyotrophic lateral sclerosis, has led to an intense search for new potential biomarkers. Biomarkers can be classified based on their clinical value into different categories: diagnostic biomarkers confirm the presence of a specific disease, prognostic biomarkers provide information about disease course, and therapeutic biomarkers are designed to predict or measure treatment response. Circulating biomarkers, as opposed to instrumental/invasive ones (e.g., muscle MRI or nerve ultrasound, muscle or nerve biopsy), are generally easier to access and less “time-consuming”. In addition to well-known creatine kinase, other promising molecules seem to be candidate biomarkers to improve the diagnosis, prognosis and prediction of therapeutic response, such as antibodies, neurofilaments, and microRNAs. However, there are some criticalities that can complicate their application: variability during the day, stability, and reliable performance metrics (e.g., accuracy, precision and reproducibility) across laboratories. In the present review, we discuss the application of biochemical biomarkers (both validated and emerging) in the most common NMDs with a focus on their diagnostic, prognostic/predictive and therapeutic application, and finally, we address the critical issues in the introduction of new biomarkers.

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Mutation analysis of SOD1, C9orf72, TARDBP and FUS genes in ethnically-diverse Malaysian patients with amyotrophic lateral sclerosis (ALS)

Recent studies have identified SOD1, FUS, TARDBP and C9orf72 as major ALS-related genes in both European and Asian populations. However, significant differences exist in the mutation frequencies of these genes between various ancestral backgrounds. This study aims to identify the frequency of mutations in the common causative ALS genes in a multi-ethnic Malaysian cohort. We screened 101 Malaysian ALS patients including 3 familial and 98 sporadic cases for mutations in the coding regions of SOD1, FUS, and TARDBP by Sanger sequencing. The C9orf72 hexanucleotide repeat expansion was screened using the repeat-primed polymerase chain reaction assay. Mutations were found in 5.9% (6 of 101) of patients including 3.0% (3 of 101) of patients with the previously reported SOD1 missense mutations (p.V48A and p.N87S) and 3.0% (3 of 101) of patients with the C9orf72 repeat expansion. No mutations were found in the FUS and TARDBP genes. This study is the first to report the mutation frequency in an ethnically diverse Malaysian ALS population and warrants further investigation to reveal novel genes and disease pathways.

Mutation spectrum of amyotrophic lateral sclerosis in Central South China

To analyze the mutational spectrum of known ALS causative genes in China ALS patients. We comprehensively analyzed 51 ALS causative genes by combining different sequencing technologies in 753 unrelated ALS patients from Central South China. The mean age at onset (AAO) was 53.7±11.4 years. The AAO was earlier in the autosomal dominant (AD) ALS patients than in the sporadic ALS (sALS) patients. Bulbar onset was more frequent in females than in males. SOD1 was the most frequently mutated gene in the AD-ALS and the sALS patients, followed by the ATXN2 and FUS genes in the AD-ALS patients and the NEK1 and CACNA1H genes in the sALS patients. Patients with RDVs in the SOD1 or FUS genes had an earlier AAO than the mean AAO of all the patients, while the patients with RDVs in the NEK1 gene showed later onset. SOD1 gene was the most commonly mutated gene in ALS patients in China, followed by ATXN2 and NEK1. The phenotype might be determined synergistically by sex and genetic variants.

Spreading of pathological TDP-43 along corticospinal tract axons induces ALS-like phenotypes in Atg5+/- mice

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease, characterized by phosphorylated TDP-43 (pTDP-43)-positive inclusions in neurons and glial cells. However, the pathogenic mechanism that underlies ALS remains largely unknown. To investigate the effects of autophagy deficiency in the formation and spreading of pathological TDP-43 along corticospinal tract axons, TDP-43 preformed fibrils (PFFs) were prepared and unilaterally injected into the fifth layer of the left primary motor cortex (M1) or the left anterior horn of the seventh cervical spinal cord segment (C7) of Atg5+/- mice. After the injection of TDP-43 PFFs, the elevated levels of pTDP-43 were present in several pyramidal tract-associated regions of Atg5+/- mice. Additionally, the occurrence of spontaneous potentials detected by electromyography demonstrates evidence of lower motor neuron dysfunction in M1-TDP-43 PFFs-injected Atg5+/- mice, and prolonged central motor conduction time detected by motor evoked potentials provides evidence of upper motor neuron dysfunction in C7-TDP-43 PFFs-injected Atg5+/- mice. These results show that injection of TDP-43 PFFs into the M1 or C7 of Atg5+/- mice induces the spreading of pathological TDP-43 along corticospinal tract axons in both an anterograde and retrograde manner. Importantly, TDP-43 PFFs-injected Atg5+/- mice also display ALS-like motor dysfunction. Taken together, our findings provide direct evidence that TDP-43 PFFs-injected Atg5+/- mice exhibited ALS-like neuropathology and motor phenotypes, suggesting that autophagy deficiency promotes the formation and spreading of pathological TDP-43 in vivo.

Identification of novel FUS and TARDBP gene mutations in Chinese amyotrophic lateral sclerosis patients with HRM analysis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of motor neurons. More than 30 genes have been linked to ALS to date, including FUS and TARDBP, which exhibit similar roles in RNA metabolism. This study explored the use of high-resolution melting (HRM) analysis to screen for FUS and TARDBP mutation hotspot regions in 146 Chinese ALS patients, which achieved 100% detection. Two FUS mutations were observed in two different familial ALS probands, a missense mutation (p.R521H) and a novel splicing mutation (c.1541+1G>A). Five TARDBP mutations were identified in six ALS patients, including a novel 3'UTR mutation (c.*731A>G) and four missense mutations (p.G294V, p.M337V, p.G348V, and p.I383V). We found that FUS mutations were present in 1.4% of Chinese ALS patients, whereas TARDBP mutations were responsible for 4.1% of Chinese ALS cases. Here, we describe the accuracy of using highly sensitive HRM analysis to identify two novel FUS and TARDBP mutations in Chinese sporadic and familial ALS cases. Our study contributes to the further understanding of the genetic and phenotypic diversity of ALS.

Common mutations of interest in the diagnosis of amyotrophic lateral sclerosis: how common are common mutations in ALS genes?

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disease predominantly affecting upper and lower motor neurons. Diagnosis of this devastating pathology is very difficult because the high degree of clinical heterogeneity with which it occurs and until now, no truly effective treatment exists.

AREAS COVERED

Molecular diagnosis may be a valuable tool for dissecting out ALS complex heterogeneity and for identifying new molecular mechanisms underlying the characteristic selective degeneration and death of motor neurons. To date, pathogenic variants in ALS genes are known to be present in up to 70% of familial and 10% of apparently sporadic ALS cases and can be associated with risks for ALS only or risks for other neurodegenerative diseases. This paper shows the procedure currently used in diagnostic laboratories to investigate most frequent mutations in ALS and evaluating the utility of involved molecular techniques as potential tools to discriminate 'common mutations' in ALS patients.

EXPERT OPINION

Genetic testing may allow for establishing an accurate pathological diagnosis and a more precise stratification of patient groups in future drug trials.

Genetic Spectrum and Variability in Chinese Patients with Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disease characterized by selective impairment of upper and lower motor neurons. We aimed to investigate the genetic spectrum and variability in Chinese patients with ALS. A total of 24 familial ALS (FALS) and 21 early-onset sporadic ALS (SALS) of Chinese ancestry were enrolled. Targeted next-generation sequencing (NGS) was performed in the probands, followed by verification by Sanger sequencing and co-segregation analysis. Clinical features of patients with pathogenic or likely pathogenic variants were present. The mutation frequency of ALS-related genes was then analyzed in Chinese population. In this cohort, 17 known mutations (9 SOD1, 5 FUS, 2 TARDBP and one SETX) were identified in 14 FALS and 6 early-onset SALS. Moreover, 7 novel variants (SOD1 c.112G>C, OPTN c.811C>T, ERBB4 c.965T>A, DCTN1 c.1915C>T, NEFH c.2602G>A, NEK1 c.3622G>A, and TAF15 c.1535G>A) were identified. In southeastern Chinese FALS, the mutation frequency of SOD1, FUS, and TARDBP was 52.9%, 8.8%, 8.8% respectively. In early-onset SALS, FUS mutations were the most common (22.6%). In Chinese ALS cases, p.H47R is most frequent SOD1 mutations, while p.R521 is most common FUS mutation and p.M337V is most common TARDBP mutation. Our results revealed that mutations in SOD1, FUS and TARDBP are the most common cause of Chinese FALS, while FUS mutations are the most common cause of early-onset SALS. The genetic spectrum is different between Chinese ALS and Caucasian ALS.

Fused in Sarcoma: Properties, Self-Assembly and Correlation with Neurodegenerative Diseases

Fused in sarcoma (FUS) is a DNA/RNA binding protein that is involved in RNA metabolism and DNA repair. Numerous reports have demonstrated by pathological and genetic analysis that FUS is associated with a variety of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), and polyglutamine diseases. Traditionally, the fibrillar aggregation of FUS was considered to be the cause of those diseases, especially via its prion-like domains (PrLDs), which are rich in glutamine and asparagine residues. Lately, a nonfibrillar self-assembling phenomenon, liquid–liquid phase separation (LLPS), was observed in FUS, and studies of its functions, mechanism, and mutual transformation with pathogenic amyloid have been emerging. This review summarizes recent studies on FUS self-assembling, including both aggregation and LLPS as well as their relationship with the pathology of ALS, FTLD, and other neurodegenerative diseases.

Biomarkers in Motor Neuron Disease: A State of the Art Review

Motor neuron disease can be viewed as an umbrella term describing a heterogeneous group of conditions, all of which are relentlessly progressive and ultimately fatal. The average life expectancy is 2 years, but with a broad range of months to decades. Biomarker research deepens disease understanding through exploration of pathophysiological mechanisms which, in turn, highlights targets for novel therapies. It also allows differentiation of the disease population into sub-groups, which serves two general purposes: (a) provides clinicians with information to better guide their patients in terms of disease progression, and (b) guides clinical trial design so that an intervention may be shown to be effective if population variation is controlled for. Biomarkers also have the potential to provide monitoring during clinical trials to ensure target engagement. This review highlights biomarkers that have emerged from the fields of systemic measurements including biochemistry (blood, cerebrospinal fluid, and urine analysis); imaging and electrophysiology, and gives examples of how a combinatorial approach may yield the best results. We emphasize the importance of systematic sample collection and analysis, and the need to correlate biomarker findings with detailed phenotype and genotype data.

Identification of CHCHD2 mutations in patients with Alzheimer's disease, amyotrophic lateral sclerosis and frontotemporal dementia in China

Recently, the coiled‑coil‑helix‑coiled‑coil‑helix domain 2 (CHCHD2) gene was identified as a possible causative gene for Parkinson's disease (PD). Three other neurodegenerative diseases, Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), share significant overlaps with PD in clinical phenotypes, pathological features and genetic heredities, and it is still unclear whether CHCHD2 variants could explain these three diseases. The present study screened all exons of the CHCHD2 gene in a total of 780 patients (511 AD, 181 ALS and 88 FTD) and 500 healthy controls from the Chinese Han population. Two missense variants, 5C>T (Pro2Leu) and 238A>G (Ile80Val), were identified in five unrelated patients with AD while no mutations were observed in patients with ALS or FTD. These mutations have been reported as low‑frequency variants in the ExAC database with frequencies of 0.0075 and 0.000025. Pro2 Leu, however, was also detected in controls and was confirmed to have no significant association with the risk for AD; Ile80Val was not detected in any normal controls, suggesting that the CHCHD2 gene may be associated with AD in the Chinese Han population.

High frequency of the TARDBP p.M337 V mutation among south-eastern Chinese patients with familial amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron disease characterized by substantial clinical and genetic heterogeneity. Thus far, only a few TARDBP-ALS families have been reported in China, and no mutation analysis has been reported in south-eastern China.

Methods

Seven index cases from ALS families negative for SOD1 and FUS mutations were screened by Sanger sequencing for TARDBP gene exons 2-6. TARDBP exon 6 was analysed in 215 sporadic ALS patients.

Results

Two TARDBP mutations in exon 6 (p.M337 V and p.G348C) were identified in 5 unrelated families. Four of these 5 families carried the same p.M337 V mutation (family 1II3, family 2II6, family 3II4, and family 4II4), and the p.G348C mutation was identified in family 5 (II5). Among the 215 sporadic patients, only a single nucleotide polymorphism (p.A366A) was detected in 5 patients, and no responsible mutation was identified. Among the TARDBP-linked familial ALS patients, the average age of onset was 57.0 ± 4.7 years, and a trend towards higher rates of bulbar (50.0%, 6/12) onset and upper limb (41.7%, 5/12) onset than lower rates of limb onset (8.3%, 1/12) was observed. Furthermore, ALS patients with TARDBP mutations showed a benign disease course, and the average survival was 106.5 ± 41.8 months (n = 8).

Conclusions

We found a high frequency of the TARDBP p.M337 V mutation in familial ALS in south-eastern China. The TARDBP-linked ALS patients showed a benign disease course and prolonged survival.

Electronic supplementary material

The online version of this article (10.1186/s12883-018-1028-1) contains supplementary material, which is available to authorized users.

Protein Quality Control and the Amyotrophic Lateral Sclerosis/Frontotemporal Dementia Continuum

Protein homeostasis, or proteostasis, has an important regulatory role in cellular function. Protein quality control mechanisms, including protein folding and protein degradation processes, have a crucial function in post-mitotic neurons. Cellular protein quality control relies on multiple strategies, including molecular chaperones, autophagy, the ubiquitin proteasome system, endoplasmic reticulum (ER)-associated degradation (ERAD) and the formation of stress granules (SGs), to regulate proteostasis. Neurodegenerative diseases are characterized by the presence of misfolded protein aggregates, implying that protein quality control mechanisms are dysfunctional in these conditions. Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative diseases that are now recognized to overlap clinically and pathologically, forming a continuous disease spectrum. In this review article, we detail the evidence for dysregulation of protein quality control mechanisms across the whole ALS-FTD continuum, by discussing the major proteins implicated in ALS and/or FTD. We also discuss possible ways in which protein quality mechanisms could be targeted therapeutically in these disorders and highlight promising protein quality control-based therapeutics for clinical trials.

Analysis of SOD1 mutations in a Chinese population with amyotrophic lateral sclerosis: a case-control study and literature review

Although the copper/zinc superoxide dismutase-1 (SOD1) gene has been identified in both familial ALS (FALS) and sporadic ALS (SALS), it has rarely been studied in Chinese patients with ALS, and there are few studies with large samples. This study sought to assess the prevalence of SOD1 mutations in Chinese ALS patients. We screened a cohort of 499 ALS patients (487 SALS and 12 FALS) from the Department of Neurology at the West China Hospital of Sichuan University and analyzed all coding exons of SOD1 by Sanger sequencing. In addition, we reviewed the mutation frequencies of common ALS causative genes in Chinese populations. Eight missense mutations in SOD1 were found in 8 ALS individuals: two novel mutations (p.G73D and p.V120F) and six previously reported mutations. The frequencies of SOD1 mutations were 1.03% (5/487) in SALS and 25% (3/12) in FALS from Southwest China. A literature review indicated that the mutation rates of major ALS causative genes were 53.55% in FALS and 6.29% in SALS. In Chinese SALS and FALS, the highest mutation frequency was in the SOD1 gene. Our results suggest that SOD1 mutation is the most common cause of ALS in Chinese populations and that the mutation spectrum of ALS varies among different ethnic populations.