Genotype-phenotype relationships in familial amyotrophic lateral sclerosis with FUS/TLS mutations in Japan

Amyotrophic lateral sclerosis patients with various gene mutations show diverse motor phenotypes and survival in China

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterised by progressive degeneration of motor neurons. Genetic factors have a substantial impact on ALS. Therefore, this study aimed to explore the correlation between genotype (SOD1, TARDBP, FUS, C9orf72) and phenotype in ALS.

METHODS

Genetic analysis was performed on 2038 patients with ALS, among which 1696 patients with sporadic ALS (SALS) as controls for genotype-phenotype analysis, and 1602 SALS as controls for survival analysis. Logistic regression and Cox proportional hazards models were used for statistical analysis.

RESULTS

A total of 172 patients with ALS with the gene mutations were included in the statistical analysis (SOD1, n=65; FUS, n=43; TARDBP, n=27; C9orf72, n=37). SOD1 mutations were more frequent in flail leg phenotype (OR 7.317, p=0.001) and less in bulbar phenotype (OR 0.222, p=0.038). C9orf72 expansions exhibited higher frequency in bulbar phenotype (OR 2.770, p=0.008). SOD1 and FUS mutations were significantly associated with earlier age of onset (HR 2.039, p<0.001; HR 1.762, p=0.001). The patients with SOD1 mutations, C9orf72 expansions and those carrying pathogenic FUS mutations had significantly increased death risk (HR 2.217, p<0.001; HR 1.694, p=0.008; HR 1.652, p=0.036). The increased risk of death in ALS with C9orf72 expansions was significant in females (HR 2.419, p=0.014) but not in males (HR 1.442, p=0.128).

CONCLUSION

Our study revealed distinct motor phenotypic tendencies in patients with ALS with different genotypes, indicating variations in the vulnerability of motor neurons during the disease's progression. Furthermore, we made novel discoveries regarding survival of different gene mutations, warranting further investigation.

Unraveling the Genetic Landscape of Neurological Disorders: Insights into Pathogenesis, Techniques for Variant Identification, and Therapeutic Approaches

Genetic abnormalities play a crucial role in the development of neurodegenerative disorders (NDDs). Genetic exploration has indeed contributed to unraveling the molecular complexities responsible for the etiology and progression of various NDDs. The intricate nature of rare and common variants in NDDs contributes to a limited understanding of the genetic risk factors associated with them. Advancements in next-generation sequencing have made whole-genome sequencing and whole-exome sequencing possible, allowing the identification of rare variants with substantial effects, and improving the understanding of both Mendelian and complex neurological conditions. The resurgence of gene therapy holds the promise of targeting the etiology of diseases and ensuring a sustained correction. This approach is particularly enticing for neurodegenerative diseases, where traditional pharmacological methods have fallen short. In the context of our exploration of the genetic epidemiology of the three most prevalent NDDs-amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease, our primary goal is to underscore the progress made in the development of next-generation sequencing. This progress aims to enhance our understanding of the disease mechanisms and explore gene-based therapies for NDDs. Throughout this review, we focus on genetic variations, methodologies for their identification, the associated pathophysiology, and the promising potential of gene therapy. Ultimately, our objective is to provide a comprehensive and forward-looking perspective on the emerging research arena of NDDs.

Genetics of amyotrophic lateral sclerosis: seeking therapeutic targets in the era of gene therapy

Amyotrophic lateral sclerosis (ALS) is an intractable disease that causes respiratory failure leading to mortality. The main locus of ALS is motor neurons. The success of antisense oligonucleotide (ASO) therapy in spinal muscular atrophy (SMA), a motor neuron disease, has triggered a paradigm shift in developing ALS therapies. The causative genes of ALS and disease-modifying genes, including those of sporadic ALS, have been identified one after another. Thus, the freedom of target choice for gene therapy has expanded by ASO strategy, leading to new avenues for therapeutic development. Tofersen for superoxide dismutase 1 (SOD1) was a pioneer in developing ASO for ALS. Improving protocols and devising early interventions for the disease are vital. In this review, we updated the knowledge of causative genes in ALS. We summarized the genetic mutations identified in familial ALS and their clinical features, focusing on SOD1, fused in sarcoma (FUS), and transacting response DNA-binding protein. The frequency of the C9ORF72 mutation is low in Japan, unlike in Europe and the United States, while SOD1 and FUS are more common, indicating that the target mutations for gene therapy vary by ethnicity. A genome-wide association study has revealed disease-modifying genes, which could be the novel target of gene therapy. The current status and prospects of gene therapy development were discussed, including ethical issues. Furthermore, we discussed the potential of axonal pathology as new therapeutic targets of ALS from the perspective of early intervention, including intra-axonal transcription factors, neuromuscular junction disconnection, dysregulated local translation, abnormal protein degradation, mitochondrial pathology, impaired axonal transport, aberrant cytoskeleton, and axon branching. We simultaneously discuss important pathological states of cell bodies: persistent stress granules, disrupted nucleocytoplasmic transport, and cryptic splicing. The development of gene therapy based on the elucidation of disease-modifying genes and early intervention in molecular pathology is expected to become an important therapeutic strategy in ALS.

Phenotype Analysis of Fused in Sarcoma Mutations in Amyotrophic Lateral Sclerosis

Background and Objectives

Pathogenic variations in fused in sarcoma (FUS) are among the most common genetic causes of amyotrophic lateral sclerosis (ALS) worldwide. They are supposedly characterized by a homogeneous pure motor phenotype with early-onset and short disease duration. However, a few FUS-mutated cases with a very late disease onset and slow progression have been reported. To analyze genotype-phenotype correlations and identify the prognostic factors in FUS-ALS cases.

Methods

We identified and cross-sectionally analyzed 22 FUS-ALS patient histories from a single-center cohort of 2,615 genetically tested patients and reviewed 289 previously published FUS-ALS cases. Survival analysis was performed by Kaplan-Meier survival curves, followed by the log-rank test and multivariate Cox analysis.

Results

Survival of FUS-ALS is age-dependent: In our cohort, early-onset cases had a rapid disease progression and short survival (p = 0.000003) while the outcome of FUS-mutated patients with mid-to-late onset did not differ from non–FUS-ALS patients (p = 0.437). Meta-analysis of literature data confirmed this trend (p = 0.00003). This survival pattern is not observed in other ALS-related genes in our series. We clustered FUS-ALS patients in 3 phenotypes: (1) axial ALS, with upper cervical and dropped-head onset in mid-to-late adulthood; (2) benign ALS, usually with a late-onset and slow disease progression; and (3) juvenile ALS, often with bulbar onset and preceded by learning disability or mild mental retardation. Those phenotypes arise from different mutations.

Discussion

We observed specific genotype-phenotype correlations of FUS-ALS and identified age at onset as the most critical prognostic factor. Our results demonstrated that FUS mutations underlie a specific subtype of ALS and enable a careful stratification of newly diagnosed FUS-ALS cases for clinical course and potential therapeutic windows. This will be crucial in the light of incoming gene-specific therapy.

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.

Neuroimaging in genetic frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) have a strong clinical, genetic and pathological overlap. This review focuses on the current understanding of structural, functional and molecular neuroimaging signatures of genetic FTD and ALS. We overview quantitative neuroimaging studies on the most common genes associated with FTD (MAPT, GRN), ALS (SOD1), and both (C9orf72), and summarize visual observations of images reported in the rarer genes (CHMP2B, TARDBP, FUS, OPTN, VCP, UBQLN2, SQSTM1, TREM2, CHCHD10, TBK1).

Phenotypes and malignancy risk of different FUS mutations in genetic amyotrophic lateral sclerosis

OBJECTIVE

Mutations in Fused in Sarcoma (FUS or TLS) are the fourth most prevalent in Western European familial amyotrophic lateral sclerosis (ALS) populations and have been associated with causing both early and very late disease onset. FUS aggregation, DNA repair deficiency, and genomic instability are contributors to the pathophysiology of FUS-ALS, but their clinical significance per se and their influence on the clinical variability have yet to be sufficiently investigated. The aim of this study was to analyze genotype-phenotype correlations and malignancy rates in a newly compiled FUS-ALS cohort.

METHODS

We cross-sectionally reviewed FUS-ALS patient histories in a multicenter cohort with 36 novel cases and did a meta-analysis of published FUS-ALS cases reporting the largest genotype-phenotype correlation of FUS-ALS.

RESULTS

The age of onset (median 39 years, range 11-80) was positively correlated with the disease duration. C-terminal domain mutations were found in 90%. Among all, P525L and truncating/ frameshift mutations most frequently caused juvenile onset, rapid disease progression, and atypical ALS often associated with negative family history while the R521 mutation site was associated with late disease onset and pure spinal phenotype. Malignancies were found in one of 40 patients.

INTERPRETATION

We report the largest genotype-phenotype correlation of FUS-ALS, which enables a careful prediction of the clinical course in newly diagnosed patients. In this cohort, FUS-ALS patients did not have an increased risk for malignant diseases.

Aberrant axon branching via Fos-B dysregulation in FUS-ALS motor neurons

Background

The characteristic structure of motor neurons (MNs), particularly of the long axons, becomes damaged in the early stages of amyotrophic lateral sclerosis (ALS). However, the molecular pathophysiology of axonal degeneration remains to be fully elucidated.

Method

Two sets of isogenic human-induced pluripotent stem cell (hiPSCs)-derived MNs possessing the single amino acid difference (p.H517D) in the fused in sarcoma (FUS) were constructed. By combining MN reporter lentivirus, MN specific phenotype was analyzed. Moreover, RNA profiling of isolated axons were conducted by applying the microfluidic devices that enable axon bundles to be produced for omics analysis. The relationship between the target gene, which was identified as a pathological candidate in ALS with RNA-sequencing, and the MN phenotype was confirmed by intervention with si-RNA or overexpression to hiPSCs-derived MNs and even in vivo. The commonality was further confirmed with other ALS-causative mutant hiPSCs-derived MNs and human pathology.

Findings

We identified aberrant increasing of axon branchings in FUS-mutant hiPSCs-derived MN axons compared with isogenic controls as a novel phenotype. We identified increased level of Fos-B mRNA, the binding target of FUS, in FUS-mutant MNs. While Fos-B reduction using si-RNA or an inhibitor ameliorated the observed aberrant axon branching, Fos-B overexpression resulted in aberrant axon branching even in vivo. The commonality of those phenotypes was further confirmed with other ALS causative mutation than FUS.

Interpretation

Analyzing the axonal fraction of hiPSC-derived MNs using microfluidic devices revealed that Fos-B is a key regulator of FUS-mutant axon branching.

Fund

Japan Agency for Medical Research and development; Japanese Ministry of Education, Culture, Sports, Science and Technology Clinical Research, Innovation and Education Center, Tohoku University Hospital; Japan Intractable Diseases (Nanbyo) Research Foundation; the Kanae Foundation for the Promotion of Medical Science; and “Inochi-no-Iro” ALS research grant.

Safety, Tolerability, and Pharmacodynamics of Intrathecal Injection of Recombinant Human HGF (KP-100) in Subjects With Amyotrophic Lateral Sclerosis: A Phase I Trial

Hepatocyte growth factor is an endogenous pleiotropic factor shown to act as a potent neuroprotectant against disease progression in animal models of amyotrophic lateral sclerosis, which is a devastating, adult-onset motor neuron disease. To evaluate the safety, tolerability, and pharmacokinetics of recombinant 5-residue-deleted human hepatocyte growth factor (KP-100) injected intrathecally through an implantable catheter connected to a subcutaneous port, we conducted a first-in-human phase I trial of intrathecal KP-100 in 15 Japanese patients with amyotrophic lateral sclerosis. The regimen was a single injection of 3 escalating doses (0.2, 0.6, and 2.0 mg/body) in 9 subjects followed by 2 doses (0.6 and 2.0 mg/body) repeated 5 times at 1-week intervals in 6 subjects (3 subjects/group). With single-dose administration, the mean half-life of KP-100 in the cerebrospinal fluid was 1.2 to 1.4 days, with its maximum concentration increasing in a dose-dependent manner. With multiple-dose administration, the trough KP-100 concentrations in the cerebrospinal fluid generally remained constant for any dose, despite multiple dosing. There were no deaths, serious adverse events, or device malfunctions leading to discontinuation. In all subjects, plasma KP-100 concentrations were <1 ng/mL, or below the lower limit of detection at all time points of measurement. Anti-KP-100 antibody was not detected in the cerebrospinal fluid or plasma specimens from any of the subjects throughout the KP-100 dosing period. These results suggest that KP-100, as well as the device used to administer it, is safe and tolerable. A phase II trial is warranted in patients with various central nervous system diseases such as amyotrophic lateral sclerosis.

Rostrocaudal Areal Patterning of Human PSC-Derived Cortical Neurons by FGF8 Signaling

The cerebral cortex is subdivided into distinct areas that have particular functions. The rostrocaudal (R-C) gradient of fibroblast growth factor 8 (FGF8) signaling defines this areal identity during neural development. In this study, we recapitulated cortical R-C patterning in human pluripotent stem cell (PSC) cultures. Modulation of FGF8 signaling appropriately regulated the R-C markers, and the patterns of global gene expression resembled those of the corresponding areas of human fetal brains. Furthermore, we demonstrated the utility of this culture system in modeling the area-specific forebrain phenotypes [presumptive upper motor neuron (UMN) phenotypes] of amyotrophic lateral sclerosis (ALS). We anticipate that our culture system will contribute to studies of human neurodevelopment and neurological disease modeling.

Comprehensive targeted next-generation sequencing in Japanese familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by loss of motor neurons. We have recently identified SOD1 and FUS mutations as the most common causes in a consecutive series of 111 familial ALS pedigrees in Japan. To reveal possible genetic causes for the remaining 51 patients with familial ALS (45 pedigrees), we performed targeted next-generation sequencing of 35 known ALS/motor neuron diseases-related genes. Known variants in ANG, OPTN, SETX, and TARDBP were identified in 6 patients. A novel likely pathogenic homozygous variant in ALS2 was identified in 1 patient. In addition, 18 patients harbored 1-3 novel variants of uncertain significance, whereas hexanucleotide repeat expansions in C9ORF72 were not detected using repeat-primed polymerase chain reaction. Collectively, in our Japanese cohort, the frequencies of SOD1, FUS, SETX, TARDBP, ANG, and OPTN variants were 32%, 11%, 2%, 2%, 1%, and 1%, respectively. These findings indicate considerable differences in the genetic variations associated with familial ALS across populations. Further genetic analyses and functional studies of novel variants are warranted.

Establishment of In Vitro FUS-Associated Familial Amyotrophic Lateral Sclerosis Model Using Human Induced Pluripotent Stem Cells

Amyotrophic lateral sclerosis (ALS) is a late-onset motor neuron disorder. Although its neuropathology is well understood, the cellular and molecular mechanisms are yet to be elucidated due to limitations in the currently available human genetic data. In this study, we generated induced pluripotent stem cells (iPSC) from two familial ALS (FALS) patients with a missense mutation in the fused-in sarcoma (FUS) gene carrying the heterozygous FUS H517D mutation, and isogenic iPSCs with the homozygous FUS H517D mutation by genome editing technology. These cell-derived motor neurons mimicked several neurodegenerative phenotypes including mis-localization of FUS into cytosolic and stress granules under stress conditions, and cellular vulnerability. Moreover, exon array analysis using motor neuron precursor cells (MPCs) combined with CLIP-seq datasets revealed aberrant gene expression and/or splicing pattern in FALS MPCs. These results suggest that iPSC-derived motor neurons are a useful tool for analyzing the pathogenesis of human motor neuron disorders.