FUS-ALS presenting with myoclonic jerks in a 17-year-old man

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.

Advances in the Structure of GGGGCC Repeat RNA Sequence and Its Interaction with Small Molecules and Protein Partners

The aberrant expansion of GGGGCC hexanucleotide repeats within the first intron of the C9orf72 gene represent the predominant genetic etiology underlying amyotrophic lateral sclerosis (ALS) and frontal temporal dementia (FTD). The transcribed r(GGGGCC)n RNA repeats form RNA foci, which recruit RNA binding proteins and impede their normal cellular functions, ultimately resulting in fatal neurodegenerative disorders. Furthermore, the non-canonical translation of the r(GGGGCC)n sequence can generate dipeptide repeats, which have been postulated as pathological causes. Comprehensive structural analyses of r(GGGGCC)n have unveiled its polymorphic nature, exhibiting the propensity to adopt dimeric, hairpin, or G-quadruplex conformations, all of which possess the capacity to interact with RNA binding proteins. Small molecules capable of binding to r(GGGGCC)n have been discovered and proposed as potential lead compounds for the treatment of ALS and FTD. Some of these molecules function in preventing RNA-protein interactions or impeding the phase transition of r(GGGGCC)n. In this review, we present a comprehensive summary of the recent advancements in the structural characterization of r(GGGGCC)n, its propensity to form RNA foci, and its interactions with small molecules and proteins. Specifically, we emphasize the structural diversity of r(GGGGCC)n and its influence on partner binding. Given the crucial role of r(GGGGCC)n in the pathogenesis of ALS and FTD, the primary objective of this review is to facilitate the development of therapeutic interventions targeting r(GGGGCC)n RNA.

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.

Very early-onset behavioral variant frontotemporal dementia in a patient with a variant of uncertain significance of a FUS gene mutation

The behavioral variant of Frontotemporal dementia (bvFTD) has typically a progressive course with cognitive and behavioral changes that manifests between 50 and 70 years. Very early-onset bvFTD with rapid progression is a rare syndrome under the frontotemporal lobar degeneration (FTLD) umbrella that has been associated with a variety of protein deposition and genetic mutations. We present a case of a 24-year-old man who developed behavioral symptoms and progressed with severe cognitive impairment and functional loss within months.   Genetic testing identified a variant of uncertain significance (VUS) mutation in the FUS gene.

Juvenile Amyotrophic Lateral Sclerosis: A Review

Juvenile amyotrophic lateral sclerosis (JALS) is a rare group of motor neuron disorders with gene association in 40% of cases. JALS is defined as onset before age 25. We conducted a literature review of JALS and gene mutations associated with JALS. Results of the literature review show that the most common gene mutations associated with JALS are FUS, SETX, and ALS2. In familial cases, the gene mutations are mostly inherited in an autosomal recessive pattern and mutations in SETX are inherited in an autosomal dominant fashion. Disease prognosis varies from rapidly progressive to an indolent course. Distinct clinical features may emerge with specific gene mutations in addition to the clinical finding of combined upper and lower motor neuron degeneration. In conclusion, patients presenting with combined upper and lower motor neuron disorders before age 25 should be carefully examined for genetic mutations. Hereditary patterns and coexisting features may be useful in determining prognosis.

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.

FUS P525L mutation causing amyotrophic lateral sclerosis and movement disorders

BACKGROUND

Mutations in the fused in sarcoma (FUS) gene have been associated with amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration, and essential tremor. Among the FUS mutations, p.P525L as a hot spot variant has been reported in more than 20 patients with ALS. Apart from the typical ALS phenotype, patients with p.P525L mutation exhibit some atypical symptoms. However, movement disorders related to p.P525L mutation have not been emphasized currently.

METHODS

Two unrelated patients with ALS were evaluated through a set of clinical and laboratory tests. The genetic screening was performed through next-generation sequencing. Muscle biopsies were performed on the 2 patients. Muscle samples were stained according to standard histological and immunohistochemical procedures.

RESULTS

The first patient presented with juvenile-onset neurogenic weakness and wasting and simultaneously had dropped head, ophthalmoplegia, tremor, involuntary movements, and cognitive impairments. The second patient showed a typical ALS phenotype and prominent adventitious movements. Genetic screening disclosed de novo p.P525L FUS mutation in the 2 patients by family cosegregation analysis. Muscle biopsy showed neurogenic patterns and numerous lipid droplets aggregating in the fibers.

CONCLUSION

Apart from the typical ALS phenotype, patients with p.P525L mutation in the FUS gene can present with great clinical heterogeneity including multiple movement disorders. Numerous lipid droplets in muscle fibers indicate that skeletal muscle is likely an important therapeutic target for ALS.