Sporadic juvenile amyotrophic lateral sclerosis caused by mutant FUS/TLS: possible association of mental retardation with this mutation

Clinical and Genetic Aspects of Juvenile Amyotrophic Lateral Sclerosis: A Promising Era Emerges

Juvenile Amyotrophic Lateral Sclerosis is a genetically heterogeneous neurodegenerative disorder, which is frequently misdiagnosed due to low clinical suspicion and little knowledge about disease characteristics. More than 20 different genetic loci have been associated with both sporadic and familial juvenile Amyotrophic Lateral Sclerosis. Currently, almost 40% of cases have an identifiable monogenic basis; type 6, associated with FUS gene variants, is the most prevalent globally. Despite several upper motor neuron-dominant forms being generally associated with long-standing motor symptoms and slowly progressive course, certain subtypes with lower motor neuron-dominant features and early bulbar compromise lead to rapidly progressive motor handicap. For some monogenic forms, there is a well-established genotypic-phenotypic correlation. There are no specific biochemical and neuroimaging biomarkers for the diagnosis of juvenile Amyotrophic Lateral Sclerosis. There are several inherited neurodegenerative and neurometabolic disorders which can lead to the signs of motor neuron impairment. This review emphasizes the importance of high clinical suspicion, assessment, and proper diagnostic work-up for juvenile Amyotrophic Lateral Sclerosis.

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.

Mutation in the FUS nuclear localisation signal domain causes neurodevelopmental and systemic metabolic alterations

Variants in the ubiquitously expressed DNA/RNA-binding protein FUS cause aggressive juvenile forms of amyotrophic lateral sclerosis (ALS). Most FUS mutation studies have focused on motor neuron degeneration; little is known about wider systemic or developmental effects. We studied pleiotropic phenotypes in a physiological knock-in mouse model carrying the pathogenic FUSDelta14 mutation in homozygosity. RNA sequencing of multiple organs aimed to identify pathways altered by the mutant protein in the systemic transcriptome, including metabolic tissues, given the link between ALS-frontotemporal dementia and altered metabolism. Few genes were commonly altered across all tissues, and most genes and pathways affected were generally tissue specific. Phenotypic assessment of mice revealed systemic metabolic alterations related to the pathway changes identified. Magnetic resonance imaging brain scans and histological characterisation revealed that homozygous FUSDelta14 brains were smaller than heterozygous and wild-type brains and displayed significant morphological alterations, including a thinner cortex, reduced neuronal number and increased gliosis, which correlated with early cognitive impairment and fatal seizures. These findings show that the disease aetiology of FUS variants can include both neurodevelopmental and systemic alterations.

Advantages of routine next-generation sequencing over standard genetic testing in the amyotrophic lateral sclerosis clinic

BACKGROUND

Next-generation sequencing has enhanced our understanding of amyotrophic lateral sclerosis (ALS) and its genetic epidemiology. Outside the research setting, testing is often restricted to those who report a family history. The aim of this study was to explore the added benefit of offering routine genetic testing to all patients in a regional ALS centre.

METHODS

C9ORF72 expansion testing and exome sequencing was offered to consecutive patients (150 with ALS and 12 with primary lateral sclerosis [PLS]) attending the Oxford Motor Neuron Disease Clinic within a defined time period.

RESULTS

A total of 17 (11.3%) highly penetrant pathogenic variants in C9ORF72, SOD1, TARDBP, FUS and TBK1 were detected, of which 10 were also found through standard clinical genetic testing pathways. The systematic approach resulted in five additional diagnoses of a C9ORF72 expansion (number needed to test [NNT] = 28), and two further missense variants in TARDBP and SOD1 (NNT = 69). Additionally, 3 patients were found to carry pathogenic risk variants in NEK1, and 13 patients harboured common missense variants in CFAP410 and KIF5A, also associated with an increased risk of ALS. We report two novel non-coding loss-of-function splice variants in TBK1 and OPTN. No relevant variants were found in the PLS patients. Patients were offered double-blinded participation, but >80% requested disclosure of the results.

CONCLUSIONS

This study provides evidence that expanding genetic testing to all patients with a clinical diagnosis of ALS enhances the potential for recruitment to clinical trials, but will have direct resource implications for genetic counselling.

Clinical feature difference between juvenile amyotrophic lateral sclerosis with SPTLC1 and FUS mutations

BACKGROUND

Juvenile amyotrophic lateral sclerosis (JALS) is an uncommon form of amyotrophic lateral sclerosis whose age at onset (AAO) is defined as prior to 25 years. FUS mutations are the most common cause of JALS. SPTLC1 was recently identified as a disease-causative gene for JALS, which has rarely been reported in Asian populations. Little is known regarding the difference in clinical features between JALS patients carrying FUS and SPTLC1 mutations. This study aimed to screen mutations in JALS patients and to compare the clinical features between JALS patients with FUS and SPTLC1 mutations.

METHODS

Sixteen JALS patients were enrolled, including three newly recruited patients between July 2015 and August 2018 from the Second Affiliated Hospital, Zhejiang University School of Medicine. Mutations were screened by whole-exome sequencing. In addition, clinical features such as AAO, onset site and disease duration were extracted and compared between JALS patients carrying FUS and SPTLC1 mutations through a literature review.

RESULTS

A novel and de novo SPTLC1 mutation (c.58G>A, p.A20T) was identified in a sporadic patient. Among 16 JALS patients, 7/16 carried FUS mutations and 5/16 carried respective SPTLC1 , SETX , NEFH , DCTN1 , and TARDBP mutations. Compared with FUS mutation patients, those with SPTLC1 mutations had an earlier AAO (7.9 ± 4.6 years vs. 18.1 ± 3.9 years, P  < 0.01), much longer disease duration (512.0 [416.7-607.3] months vs. 33.4 [21.6-45.1] months, P  < 0.01), and no onset of bulbar.

CONCLUSION

Our findings expand the genetic and phenotypic spectrum of JALS and help to better understand the genotype-phenotype correlation of JALS.

Molecular dynamics and protein frustration analysis of human fused in Sarcoma protein variants in Amyotrophic Lateral Sclerosis type 6: An In Silico approach

Amyotrophic lateral sclerosis (ALS) is the most frequent adult-onset motor neuron disorder. The disease is characterized by degeneration of upper and lower motor neurons, leading to death usually within five years after the onset of symptoms. While most cases are sporadic, 5%-10% of cases can be associated with familial inheritance, including ALS type 6, which is associated with mutations in the Fused in Sarcoma (FUS) gene. This work aimed to evaluate how the most frequent ALS-related mutations in FUS, R521C, R521H, and P525L affect the protein structure and function. We used prediction algorithms to analyze the effects of the non-synonymous single nucleotide polymorphisms and performed evolutionary conservation analysis, protein frustration analysis, and molecular dynamics simulations. Most of the prediction algorithms classified the three mutations as deleterious. All three mutations were predicted to reduce protein stability, especially the mutation R521C, which was also predicted to increase chaperone binding tendency. The protein frustration analysis showed an increase in frustration in the interactions involving the mutated residue 521C. Evolutionary conservation analysis showed that residues 521 and 525 of human FUS are highly conserved sites. The molecular dynamics results indicate that protein stability could be compromised in all three mutations. They also affected the exposed surface area and protein compactness. The analyzed mutations also displayed high flexibility in most residues in all variants, most notably in the interaction site with the nuclear import protein of FUS.

Wild-type FUS corrects ALS-like disease induced by cytoplasmic mutant FUS through autoregulation

Mutations in FUS, an RNA-binding protein involved in multiple steps of RNA metabolism, are associated with the most severe forms of amyotrophic lateral sclerosis (ALS). Accumulation of cytoplasmic FUS is likely to be a major culprit in the toxicity of FUS mutations. Thus, preventing cytoplasmic mislocalization of the FUS protein may represent a valuable therapeutic strategy. FUS binds to its own pre-mRNA creating an autoregulatory loop efficiently buffering FUS excess through multiple proposed mechanisms including retention of introns 6 and/or 7. Here, we introduced a wild-type FUS gene allele, retaining all intronic sequences, in mice whose heterozygous or homozygous expression of a cytoplasmically retained FUS protein (Fus^∆NLS) was previously shown to provoke ALS-like disease or postnatal lethality, respectively. Wild-type FUS completely rescued the early lethality caused by the two Fus^∆NLS alleles, and improved the age-dependent motor deficits and reduced lifespan caused by heterozygous expression of mutant FUS^∆NLS. Mechanistically, wild-type FUS decreased the load of cytoplasmic FUS, increased retention of introns 6 and 7 in the endogenous mouse Fus mRNA, and decreased expression of the mutant mRNA. Thus, the wild-type FUS allele activates the homeostatic autoregulatory loop, maintaining constant FUS levels and decreasing the mutant protein in the cytoplasm. These results provide proof of concept that an autoregulatory competent wild-type FUS expression could protect against this devastating, currently intractable, neurodegenerative disease.

Sporadic Amyotrophic Lateral Sclerosis Due to a FUS P525L Mutation with Asymmetric Muscle Weakness and Anti-ganglioside Antibodies

Amyotrophic lateral sclerosis (ALS) due to a fused in sarcoma (FUS) P525L mutation is characterized by a rapidly progressive course. Multifocal motor neuropathy (MMN) may resemble ALS in early stage and is associated with anti-ganglioside antibodies. A 38-year-old woman was admitted to our hospital because of progressive muscle weakness in the right limbs. She had mild mental retardation and minor deformities. Initially, we suspected MMN given the asymmetric muscle weakness and detection of anti-ganglioside antibodies. However, physical and electrophysiological tests did not support MMN, instead suggesting ALS. We confirmed a heterozygous P525L mutation and finally diagnosed this case as ALS due to an FUS mutation.

Cytoplasmic FUS triggers early behavioral alterations linked to cortical neuronal hyperactivity and inhibitory synaptic defects

Gene mutations causing cytoplasmic mislocalization of the RNA-binding protein FUS lead to severe forms of amyotrophic lateral sclerosis (ALS). Cytoplasmic accumulation of FUS is also observed in other diseases, with unknown consequences. Here, we show that cytoplasmic mislocalization of FUS drives behavioral abnormalities in knock-in mice, including locomotor hyperactivity and alterations in social interactions, in the absence of widespread neuronal loss. Mechanistically, we identified a progressive increase in neuronal activity in the frontal cortex of Fus knock-in mice in vivo, associated with altered synaptic gene expression. Synaptic ultrastructural and morphological defects were more pronounced in inhibitory than excitatory synapses and associated with increased synaptosomal levels of FUS and its RNA targets. Thus, cytoplasmic FUS triggers synaptic deficits, which is leading to increased neuronal activity in frontal cortex and causing related behavioral phenotypes. These results indicate that FUS mislocalization may trigger deleterious phenotypes beyond motor neuron impairment in ALS, likely relevant also for other neurodegenerative diseases characterized by FUS mislocalization.

FUS mutation is probably the most common pathogenic gene for JALS, especially sporadic JALS

Juvenile amyotrophic lateral sclerosis (JALS) is a rare and severe form of ALS. The development of gene sequencing methods has resulted in increased reports of JALS cases in recent years, and additional gene mutations in FUS have been identified. Fused in sarcoma (FUS) mutations, appeared rarely in classical ALS but indeed were the most frequent pathogenic mutations in JALS, especially in sporadic JALS. After studied the reports in the last 10 years about JALS cases, the case characteristics caused by FUS mutations and the commonality of the mutation sites were summarized in this review. FUS mutation associated with more than half of JALS and the very majority of sporadic JALS. It's worth noting that almost all of the mutations occur in nuclear localization signal (NLS) of FUS in sporadic JALS. This discovery emphasized a new perspective focus on NLS for the diagnosis and etiology of sporadic JALS as well as for further study about new treatment.

The Occurrence of FUS Mutations in Pediatric Amyotrophic Lateral Sclerosis: A Case Report and Review of the Literature

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease affecting both upper and lower motor neurons and leading to progressive paralysis. Most cases are sporadic, and the symptoms generally begin in the sixth or seventh decade. Juvenile ALS appears in a rare subgroup of patients with onset before the age of 25 years old. Contrary to the classical adult phenotype where 90% of cases are sporadic, most cases of juvenile ALS are caused by a genetic mutation in either SOD1 (superoxide dismutase one), SETX (senataxin), or FUS (fused in sarcoma). In the pediatric population, ALS is more infrequent and rarely considered in the differential diagnosis. There are few reports of ALS in children. Here, we describe a 14-year-old boy with a very fast progressing classical ALS phenotype and tremor caused by a c.1554_1557delACAG mutation in FUS. Our review of the literature advocates that pediatric ALS is highly suggestive of FUS mutations and that gene should be tested in children presenting with symptoms of ALS. The children with FUS-related ALS may have no family history and present initially with learning disabilities, tremor, and mild motor developmental delay.

Frameshift peptides alter the properties of truncated FUS proteins in ALS-FUS

Mutations in the FUS gene cause a subset of ALS cases (ALS-FUS). The majority of FUS mutations are missense mutations affecting the nuclear localisation signal (NLS) of FUS. In addition, a number of frameshift mutations which result in complete NLS deletion have been described. Patients bearing frameshift mutations usually present with more aggressive disease, characterised by an early onset and rapid progression. Both missense mutations in the NLS coding sequence and complete loss of the NLS are known to result in cytoplasmic mislocalisation of FUS protein. However, in addition to the removal of FUS functional domains, frameshift mutations in most cases lead to the attachment of a "tail" of novel amino acids at the FUS C-terminus - a frameshift peptide. It is not clear whether these peptide tails would affect the properties of truncated FUS proteins. In the current study, we compared intracellular behaviour of disease-associated truncated FUS proteins with and without the corresponding frameshift peptides. We demonstrate that some of these peptides can affect subcellular distribution and/or increase aggregation capacity and stability of the truncated FUS protein. Our study suggests that frameshift peptides can alter the properties of truncated FUS variants which may modulate FUS pathogenicity and contribute to the variability of the disease course in ALS-FUS.

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.

Importance of Functional Loss of FUS in FTLD/ALS

Fused in sarcoma (FUS) is an RNA binding protein that regulates RNA metabolism including alternative splicing, transcription, and RNA transportation. FUS is genetically and pathologically involved in frontotemporal lobar degeneration (FTLD)/amyotrophic lateral sclerosis (ALS). Multiple lines of evidence across diverse models suggest that functional loss of FUS can lead to neuronal dysfunction and/or neuronal cell death. Loss of FUS in the nucleus can impair alternative splicing and/or transcription, whereas dysfunction of FUS in the cytoplasm, especially in the dendritic spines of neurons, can cause mRNA destabilization. Alternative splicing of the MAPT gene at exon 10, which generates 4-repeat Tau (4R-Tau) and 3-repeat Tau (3R-Tau), is one of the most impactful targets regulated by FUS. Additionally, loss of FUS function can affect dendritic spine maturations by destabilizing mRNAs such as Glutamate receptor 1 (GluA1), a major AMPA receptor, and Synaptic Ras GTPase-activating protein 1 (SynGAP1). Moreover, FUS is involved in axonal transport and morphological maintenance of neurons. These findings indicate that a biological link between loss of FUS function, Tau isoform alteration, aberrant post-synaptic function, and phenotypic expression might lead to the sequential cascade culminating in FTLD. Thus, to facilitate development of early disease markers and/or therapeutic targets of FTLD/ALS it is critical that the functions of FUS and its downstream pathways are unraveled.

Inherited Paediatric Motor Neuron Disorders: Beyond Spinal Muscular Atrophy

Paediatric motor neuron diseases encompass a group of neurodegenerative diseases characterised by the onset of muscle weakness and atrophy before the age of 18 years, attributable to motor neuron loss across various neuronal networks in the brain and spinal cord. While the genetic underpinnings are diverse, advances in next generation sequencing have transformed diagnostic paradigms. This has reinforced the clinical phenotyping and molecular genetic expertise required to navigate the complexities of such diagnoses. In turn, improved genetic technology and subsequent gene identification have enabled further insights into the mechanisms of motor neuron degeneration and how these diseases form part of a neurodegenerative disorder spectrum. Common pathophysiologies include abnormalities in axonal architecture and function, RNA processing, and protein quality control. This review incorporates an overview of the clinical manifestations, genetics, and pathophysiology of inherited paediatric motor neuron disorders beyond classic SMN1-related spinal muscular atrophy and describes recent advances in next generation sequencing and its clinical application. Specific disease-modifying treatment is becoming a clinical reality in some disorders of the motor neuron highlighting the importance of a timely and specific diagnosis.

Energy Homeostasis and Abnormal RNA Metabolism in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease that is clinically characterized by progressive muscle weakness and impaired voluntary movement due to the loss of motor neurons in the brain, brain stem and spinal cord. To date, no effective treatment is available. Ample evidence suggests that impaired RNA homeostasis and abnormal energy status are two major pathogenesis pathways in ALS. In the present review article, we focus on recent studies that report molecular insights of both pathways, and discuss the possibility that energy dysfunction might negatively regulate RNA homeostasis via the impairment of cytoplasmic-nuclear shuttling in motor neurons and subsequently contribute to the development of ALS.

The investigation of genetic and clinical features in Chinese patients with juvenile amyotrophic lateral sclerosis

Juvenile amyotrophic lateral sclerosis (JALS) occurs at an age of onset below 25 years with a heterogeneous disease onset location, variable progression and survival time. To investigate whether an ALS gene profile could resolve any aspects of clinical symptom heterogeneity, we have used targeted sequencing technology in a cohort of 12 JALS patients of Chinese descent. We detected 5 likely pathogenic mutations, 2 in familial probands and 3 in sporadic patients. One was a known TARDBP mutation (p.G348V) and 4 were FUS frameshift mutations including a known p.Gln519Ilefs*9 mutation and 3 novel mutations, p.Gly515Valfs*14, p.Gly486Profs*30, and p.Arg498Alafs*32. Of the 4 FUS mutations, 2 were able to be confirmed as de novo mutations. The TARDBP mutation carrier showed a classic ALS phenotype. All patients with FUS mutations experienced limb weakness at an early age and developed bulbar symptoms during the disease course. FUS mutations have previously been associated with increased JALS disease progression, however, we found a large range 12 to 84 months in disease survival (mean 58.2 months). Our results justify future screening for variants in FUS as it remains the most frequent genetic determinant of early onset, JALS (found in 30% of our patients).

Cognitive dysfunction in hereditary spastic paraplegias and other motor neuron disorders

Hereditary spastic paraplegia (HSP) is a diverse group of single-gene disorders that share the predominant clinical feature of progressive lower limb spasticity and weakness. More than 70 different genetic subtypes have been described and all modes of inheritance are possible. Intellectual dysfunction in HSP is frequent in recessive forms but rare in dominant families. It may manifest by either mental retardation and/or cognitive decline. The latter may be subtle, restricted to executive dysfunction or may evolve to severe dementia. The cognitive profile is thought to depend largely on the genetic subtype of HSP, although wide phenotypic variability within the same genetic subtype and also within the same family can be found.

R521C and R521H mutations in FUS result in weak binding with Karyopherinβ2 leading to Amyotrophic lateral sclerosis: a molecular docking and dynamics study

Fused in sarcoma (FUS) gene encodes the RNA binding protein FUS. This gene is mapped to chromosome 16p11.2. The FUS protein binds with karyopherineβ2 (Kapβ2) through its proline/tyrosine nuclear localization signal (PY-NLS) that helps in the localization of FUS protein within the nucleus. Arginine residue in 521 position (R521) of PY-NLS plays a vital role in the binding of FUS protein with Kapβ2. Mutations in this position (R521C and R521H) are the most predominant mutations associated with amyotrophic lateral sclerosis (ALS). However, the mechanism by which these mutations lead to ALS is poorly understood. We examined the binding behaviour of the mutants FUS (R521C) and FUS (R521H) with Kapβ2 through protein-protein docking and molecular dynamics simulation. The binding patterns of mutants were compared with the binding behaviour of wild FUS-Kapβ2. Our results suggest that these mutants have relatively weak binding affinity with Kapβ2 when compared with wild FUS-Kapβ2 as indicated by the lesser number of interactions found between the mutant FUS and Kapβ2. Hence, these mutations weakens the binding and this results in the cytoplasmic mislocalization of mutant FUS; and thereby it increases the severity of ALS.

Mutations in FUS are the most frequent genetic cause in juvenile sporadic ALS patients of Chinese origin

Juvenile onset ALS is a very rare form of motor neuron disease, with the first symptoms of motor neuron degeneration manifested before 25 years of age. Mutations in the alsin (ALS2), senataxin (SETX), and spatacsin (SPG11) genes have been associated with familial ALS with juvenile onset and slow progression, whereas the genetic architecture of sporadic juvenile ALS remains unclear. We screened mutations in C9orf72, SOD1, FUS, TARDBP, ANG, VCP and PFN1 in 16 juvenile sporadic ALS patients. Four cases (25%) carrying FUS mutations and one individual (6%) harbouring a SOD1 mutation were identified. All cases had an aggressive disease course. Our results suggest that FUS mutations are the most frequent genetic cause in early-onset sporadic ALS patients of Chinese origin. Genetic testing of FUS should be performed in early-onset ALS patients especially those with an aggressive disease course.

Juvenile-onset Sporadic Amyotrophic Lateral Sclerosis with a Frameshift FUS Gene Mutation Presenting Unique Neuroradiological Findings and Cognitive Impairment

A 24-year-old Japanese woman developed anterocollis, weakness of the proximal arms, and subsequent cognitive impairment. A neurological examination revealed amyotrophic lateral sclerosis (ALS) without a family history. Systemic muscle atrophy progressed rapidly. Cerebral MRI clearly exhibited high signal intensities along the bilateral pyramidal tracts. An analysis of the FUS gene revealed a heterozygous two-base pair deletion, c.1507-1508delAG (p.G504WfsX515). A subset of juvenile-onset familial/sporadic ALS cases with FUS gene mutations reportedly demonstrates mental retardation or learning difficulty. Our study emphasizes the importance of conducting a FUS gene analysis in juvenile-onset ALS cases, even when no family occurrence is confirmed.

Mutations in SOD1 and FUS caused juvenile-onset sporadic amyotrophic lateral sclerosis with aggressive progression

Juvenile onset amyotrophic lateral sclerosis (ALS) is a very rare form of motor neuron disease, with the first symptoms of motor neuron degeneration manifested before 25 years of age. Juvenile ALS is more frequently familial in nature than the adult-onset forms. Mutations in the alsin (ALS2), senataxin (SETX), and Spatacsin (SPG11) have been associated with familial ALS with juvenile onset and slowly progression. Here we reported two apparently sporadic ALS with juvenile onset and aggressive progression caused by mutations in the SOD1 and FUS gene. We also reviewed juvenile-onset ALS in publications. Our findings, together with other researches, confirms that both SOD1 and FUS mutations can lead to juvenile-onset malignant form of ALS and should be screened in ALS patients with an earlier age of onset, aggressive progression, even if there is no apparent family history.

Genotype-phenotype relationship in hereditary amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disease. It is characterized by neuronal loss and degeneration of the upper motor neurons (UMNs) and lower motor neurons (LMNs), and is usually fatal due to respiratory failure within 3–5 years of onset. Although approximately 5–10 % of patients with ALS have an inherited form of the disease, the distinction between hereditary and apparently sporadic ALS (SALS) seems to be artificial. Thus, genetic factors play a role in all types of ALS, to a greater or lesser extent. During the decade of upheaval, the evolution of molecular genetics technology has rapidly advanced our genetic knowledge about the causes of ALS, and the relationship between the genetic subtypes and clinical phenotype. In this review, we will focus on the possible genotype-phenotype correlation in hereditary ALS. Uncovering the identity of the genetic factors in ALS will not only improve the accuracy of ALS diagnosis, but may also provide new approaches for preventing and treating the disease.

Autosomal dominant inheritance of rapidly progressive amyotrophic lateral sclerosis due to a truncation mutation in the fused in sarcoma (FUS) gene

Mutations in the gene encoding the RNA-binding protein fused in sarcoma (FUS) account for 4 - 5% of familial cases of amyotrophic lateral sclerosis (ALS). We describe the identification and in vitro cellular characterization of a genetic mutation in a family in which the index case, and subsequently her two children, each developed rapidly progressive ALS at a young age and died within a year of onset. Exome capture and sequencing revealed a mutation in the FUS gene consisting of a 2-bp deletion, c.1509_1510delAG, resulting in a predicted truncated protein, p.G504Wfs * 12, lacking the nuclear localization signal. Expression of this mutation in HEK293 and NSC-34 cells demonstrated severe cytoplasmic mislocalization of mutant FUS, and colocalization with stress granules when compared to wild-type, R521C and P525L mutant FUS. This study provides further evidence of a broad correlation between clinical severity of FUS-related ALS and mislocalization of the protein to the cytoplasm.

The phenotypic variability of amyotrophic lateral sclerosis

Classic textbook neurology teaches that amyotrophic lateral sclerosis (ALS) is a degenerative disease that selectively affects upper and lower motor neurons and is fatal 3-5 years after onset--a description which suggests that the clinical presentation of ALS is very homogenous. However, clinical and postmortem observations, as well as genetic studies, demonstrate that there is considerable variability in the phenotypic expression of ALS. Here, we review the phenotypic variability of ALS and how it is reflected in familial and sporadic ALS, in the degree of upper and lower motor neuron involvement, in motor and extramotor involvement, and in the spectrum of ALS and frontotemporal dementia. Furthermore, we discuss some unusual clinical characteristics regarding presentation, age at onset and disease progression. Finally, we address the importance of this variability for understanding the pathogenesis of ALS and for the development of therapeutic strategies.

Converging mechanisms in ALS and FTD: disrupted RNA and protein homeostasis

Breakthrough discoveries identifying common genetic causes for amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) have transformed our view of these disorders. They share unexpectedly similar signatures, including dysregulation in common molecular players including TDP-43, FUS/TLS, ubiquilin-2, VCP, and expanded hexanucleotide repeats within the C9ORF72 gene. Dysfunction in RNA processing and protein homeostasis is an emerging theme. We present the case here that these two processes are intimately linked, with disease-initiated perturbation of either leading to further deviation of both protein and RNA homeostasis through a feedforward loop including cell-to-cell prion-like spread that may represent the mechanism for relentless disease progression.

Amyotrophic lateral sclerosis: an update on recent genetic insights

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease affecting both upper and lower motor neurons. The prognosis for ALS is extremely poor, but there is a limited course of treatment with only one approved medication. A most striking recent discovery is that TDP-43 is identified as a key molecule that is associated with both sporadic and familial forms of ALS. TDP-43 is not only a pathological hallmark, but also a genetic cause for ALS. Subsequently, a number of ALS-causative genes have been found. Above all, the RNA-binding protein, such as FUS, TAF15, EWSR1 and hnRNPA1, have structural and functional similarities to TDP-43, and physiological functions of some molecules, including VCP, UBQLN2, OPTN, FIG4 and SQSTM1, are involved in a protein degradation system. These discoveries provide valuable insight into the pathogenesis of ALS, and open doors for developing an effective disease-modifying therapy.

Abundant FUS-immunoreactive pathology in the skin of sporadic amyotrophic lateral sclerosis

OBJECTIVES

The fused in sarcoma (FUS) protein is a 526 amino acid and its expression is ubiquitous. Recently, mutations in a gene coding FUS have been identified in familial amyotrophic lateral sclerosis (ALS). Also, FUS has been found in neuronal cytoplasmic inclusions in sporadic forms of ALS, suggesting that FUS has an important role in the neurodegeneration occurring in sporadic disease. However, there has been no study of FUS in ALS skin.

MATERIAL AND METHODS

We made a quantitative immunohistochemical study of the expression of FUS in the skin from patients with sporadic ALS and controls.

RESULTS

The proportion of FUS-immunoreactive (ir) cells in the epidermis in ALS patients was significantly higher (P < 0.001) than in controls. There was a significant positive relationship (r = 0.78, P < 0.001) between the proportion and duration of illness in ALS patients. The optical density of FUS-ir cells in the epidermis in ALS patients is markedly stronger (P < 0.001) than in controls. There was a significant positive relation (r = 0.49, P < 0.05) between the immunoreactivity and duration of illness in ALS patients.

CONCLUSIONS

These data suggest that changes of FUS in ALS skin are related to the disease process, and that metabolic alterations of FUS may take place in the skin of patients with ALS.

ALS mutant FUS disrupts nuclear localization and sequesters wild-type FUS within cytoplasmic stress granules

Mutations in the gene encoding Fused in Sarcoma (FUS) cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. FUS is a predominantly nuclear DNA- and RNA-binding protein that is involved in RNA processing. Large FUS-immunoreactive inclusions fill the perikaryon of surviving motor neurons of ALS patients carrying mutations at post-mortem. This sequestration of FUS is predicted to disrupt RNA processing and initiate neurodegeneration. Here, we demonstrate that C-terminal ALS mutations disrupt the nuclear localizing signal (NLS) of FUS resulting in cytoplasmic accumulation in transfected cells and patient fibroblasts. FUS mislocalization is rescued by the addition of the wild-type FUS NLS to mutant proteins. We also show that oxidative stress recruits mutant FUS to cytoplasmic stress granules where it is able to bind and sequester wild-type FUS. While FUS interacts with itself directly by protein-protein interaction, the recruitment of FUS to stress granules and interaction with PABP are RNA dependent. These findings support a two-hit hypothesis, whereby cytoplasmic mislocalization of FUS protein, followed by cellular stress, contributes to the formation of cytoplasmic aggregates that may sequester FUS, disrupt RNA processing and initiate motor neuron degeneration.

ALS-associated mutations in FUS disrupt the axonal distribution and function of SMN

Mutations in the RNA binding protein fused in sarcoma/translated in liposarcoma (FUS/TLS) cause amyotrophic lateral sclerosis (ALS). Although ALS-linked mutations in FUS often lead to a cytosolic mislocalization of the protein, the pathogenic mechanisms underlying these mutations remain poorly understood. To gain insight into these mechanisms, we examined the biochemical, cell biological and functional properties of mutant FUS in neurons. Expression of different FUS mutants (R521C, R521H, P525L) in neurons caused axonal defects. A protein interaction screen performed to explain these phenotypes identified numerous FUS interactors including the spinal muscular atrophy (SMA) causing protein survival motor neuron (SMN). Biochemical experiments showed that FUS and SMN interact directly and endogenously, and that this interaction can be regulated by FUS mutations. Immunostaining revealed co-localization of mutant FUS aggregates and SMN in primary neurons. This redistribution of SMN to cytosolic FUS accumulations led to a decrease in axonal SMN. Finally, cell biological experiments showed that overexpression of SMN rescued the axonal defects induced by mutant FUS, suggesting that FUS mutations cause axonal defects through SMN. This study shows that neuronal aggregates formed by mutant FUS protein may aberrantly sequester SMN and concomitantly cause a reduction of SMN levels in the axon, leading to axonal defects. These data provide a functional link between ALS-linked FUS mutations, SMN and neuronal connectivity and support the idea that different motor neuron disorders such as SMA and ALS may be caused, in part, by defects in shared molecular pathways.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Balanced translocation t(3;18)(p13;q22.3) and points mutation in the ZNF407 gene detected in patients with both moderate non-syndromic intellectual disability and autism

Intellectual disability (ID) is a common disease. While the etiology remains incompletely understood, genetic defects are a major contributor, which include mutations in genes encoding zinc finger proteins. These proteins modulate gene expression via binding to DNA. Consistent with this knowledge, we report here the identification of mutations in the ZNF407 gene in ID/autistic patients. In our study of an ID patient with autism, a reciprocal translocation 46,XY,t(3;18)(p13;q22.3) was detected. By using FISH and long-range PCR approaches, we have precisely mapped the breakpoints associated with this translocation in a gene-free region in chromosome 3 and in the third intron of the ZNF407 gene in chromosome18. The latter reduces ZNF407 expression. Consistent with this observation, in our subsequent investigation of 105 ID/autism patients with similar clinical presentations, two missense mutations Y460C and P1195A were identified. These mutations cause non-conservative amino acid substitutions in the linker regions between individual finger structures. In line with the linker regions being critical for the integrity of zinc finger motifs, both mutations may result in loss of ZNF407 function. Taken together, we demonstrate that mutations in the ZNF407 gene contribute to the pathogenesis of a group of ID patients with autism.