Age and founder effect of SOD1 A4V mutation causing ALS

The familial amyotrophic lateral sclerosis-associated A4V SOD1 mutant is not able to regulate aerobic glycolysis

Under certain stress conditions, astrocytes operate in aerobic glycolysis, a process controlled by pyruvate dehydrogenase (PDH) inhibition through its E1 α subunit (Pda1) phosphorylation. This supplies lactate to neurons, which save glucose to obtain NADPH to, among other roles, counteract reactive oxygen species. A failure in this metabolic cooperation causes severe damage to neurons. In this work, using humanized Saccharomyces cerevisiae cells in which its endogenous Cu/Zn Superoxide Dismutase (SOD1) was replaced by human ortholog, we investigated the role of human SOD1 (hSOD1) in aerobic glycolysis regulation and its implications to amyotrophic lateral sclerosis (ALS), a neurodegenerative disease. Yeast cells ferment glucose even in the presence of oxygen and switch to respiratory metabolism after glucose exhaustion. However, like cells of SOD1-knockout strain, cells expressing A4V mutant of hSOD1 growing on glucose showed a respiratory phenotype, i.e., low glucose and high oxygen consumptions and low intracellular oxidation levels in response to peroxide stress, contrary to cells expressing wild-type (WT) SOD1 (yeast or human). The A4V mutation in hSOD1 is linked to ALS. In contrast to WT SOD1 strains, PDH activity of both sod1Δ and A4V hSOD1 cells did not change in response to a metabolic shift toward oxidative metabolism, which was associated to lower Pda1 phosphorylation levels under growth on glucose. Taken together, our results suggest that A4V mutant cannot regulate aerobic glycolysis via Pda1 phosphorylation the same way WT hSOD1, which might be linked to problems observed in the motor neurons of ALS patients with the SOD1 A4V mutation.

Pan-neuronal expression of human mutant SOD1 in Drosophila impairs survival and motor performance, induces early neuroinflammation and chromosome aberrations

Several mutations in the SOD1 gene encoding for the antioxidant enzyme Superoxide Dismutase 1, are associated with amyotrophic lateral sclerosis, a rare and devastating disease characterized by motor neuron degeneration and patients' death within 2-5 years from diagnosis. Motor neuron loss and related symptomatology manifest mostly in adult life and, to date, there is still a gap of knowledge on the precise cellular and molecular events preceding neurodegeneration. To deepen our awareness of the early phases of the disease, we leveraged two Drosophila melanogaster models pan-neuronally expressing either the mutation A4V or G85R of the human gene SOD1 (hSOD1A4V or hSOD1G85R). We demonstrate that pan-neuronal expression of the hSOD1A4V or hSOD1G85R pathogenic construct impairs survival and motor performance in transgenic flies. Moreover, protein and transcript analysis on fly heads indicates that mutant hSOD1 induction stimulates the glial marker Repo, up-regulates the IMD/Toll immune pathways through antimicrobial peptides and interferes with oxidative metabolism. Finally, cytological analysis of larval brains demonstrates hSOD1-induced chromosome aberrations. Of note, these parameters are found modulated in a timeframe when neurodegeneration is not detected. The novelty of our work is twofold: we have expressed for the first time hSOD1 mutations in all neurons of Drosophila and confirmed some ALS-related pathological phenotypes in these flies, confirming the power of SOD1 mutations in generating ALS-like phenotypes. Moreover, we have related SOD1 pathogenesis to chromosome aberrations and antimicrobial peptides up-regulation. These findings were unexplored in the SOD1-ALS field.

Profiling tofersen as a treatment of superoxide dismutase 1 amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive motor neuron disorder with a fatal outcome 3-5 years after disease onset due to respiratory complications. Superoxide dismutase 1 (SOD1) mutations are found in about 2% of all patients. Tofersen is a novel oligonucleotide antisense drug specifically developed to treat SOD1-ALS patients.

AREAS COVERED

Our review covers and discusses tofersen pharmacological properties and its phase I/II and III clinical trials results. Other available drugs and their limitations are also addressed.

EXPERT OPINION

VALOR study failed to meet the primary endpoint (change in the revised Amyotrophic Lateral Sclerosis Functional Rating Scale score from baseline to week 28, tofersen arm vs. placebo), but a significant reduction in plasma neurofilament light chain (NfL) levels was observed in tofersen arm (60% vs. 20%). PrefALS study has proposed plasma NfL has a potential biomarker for presymptomatic treatment, since it increases 6-12 months before phenoconversion. There is probably a delay between plasma NfL reduction and the clinical benefit. ATLAS study will allow more insights regarding tofersen clinical efficacy in disease progression rate, survival, and even disease onset delay in presymptomatic SOD1 carriers.

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.

High-Fidelity Assay Based on Turn-Off Fluorescence to Detect the Perturbations of Cellular Proteostasis

The persistence of neurodegenerative diseases has necessitated the development of new strategies to monitor protein homeostasis (proteostasis). Previous efforts in our laboratory have focused on the development of fluorogenic strategies to observe the onset and progression of proteostatic stress. These works utilized solvatochromic and viscosity sensitive fluorophores to sense protein folded states, enabling stressor screening with an increase in the emission intensity upon aggregation. In this work, we present a novel, high-fidelity assay to detect perturbations of cellular proteostasis, where the fluorescence intensity decreases with the onset of proteostatic stress. Utilizing a fluorogenic, hydroxymethyl silicon-rhodamine probe to differentiate between protein folded states, we establish the validity of this technology in living cells by demonstrating a two-fold difference in fluorescence intensity between unstressed and stressed conditions.

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.

Molecular dynamics analysis of superoxide dismutase 1 mutations suggests decoupling between mechanisms underlying ALS onset and progression

Mutations in the superoxide dismutase 1 (SOD1) gene are the second most common known cause of ALS. SOD1 variants express high phenotypic variability and over 200 have been reported in people with ALS. It was previously proposed that variants can be broadly classified in two groups, 'wild-type like' (WTL) and 'metal binding region' (MBR) variants, based on their structural location and biophysical properties. MBR variants, but not WTL variants, were associated with a reduction of SOD1 enzymatic activity. In this study we used molecular dynamics and large clinical datasets to characterise the differences in the structural and dynamic behaviour of WTL and MBR variants with respect to the wild-type SOD1, and how such differences influence the ALS clinical phenotype. Our study identified marked structural differences, some of which are observed in both variant groups, while others are group specific. Moreover, collecting clinical data of approximately 500 SOD1 ALS patients carrying variants, we showed that the survival time of patients carrying an MBR variant is generally longer (∼6 years median difference, p < 0.001) with respect to patients with a WTL variant. In conclusion, our study highlighted key differences in the dynamic behaviour between WTL and MBR SOD1 variants, and between variants and wild-type SOD1 at an atomic and molecular level, that could be further investigated to explain the associated phenotypic variability. Our results support the hypothesis of a decoupling between mechanisms of onset and progression of SOD1 ALS, and an involvement of loss-of-function of SOD1 with the disease progression.

Studies of Genetic and Proteomic Risk Factors of Amyotrophic Lateral Sclerosis Inspire Biomarker Development and Gene Therapy

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease affecting the upper and lower motor neurons, leading to muscle weakness, motor impairments, disabilities and death. Approximately 5-10% of ALS cases are associated with positive family history (familial ALS or fALS), whilst the remainder are sporadic (sporadic ALS, sALS). At least 50 genes have been identified as causative or risk factors for ALS. Established pathogenic variants include superoxide dismutase type 1 (SOD1), chromosome 9 open reading frame 72 (c9orf72), TAR DNA Binding Protein (TARDBP), and Fused In Sarcoma (FUS); additional ALS-related genes including Charged Multivesicular Body Protein 2B (CHMP2B), Senataxin (SETX), Sequestosome 1 (SQSTM1), TANK Binding Kinase 1 (TBK1) and NIMA Related Kinase 1 (NEK1), have been identified. Mutations in these genes could impair different mechanisms, including vesicle transport, autophagy, and cytoskeletal or mitochondrial functions. So far, there is no effective therapy against ALS. Thus, early diagnosis and disease risk predictions remain one of the best options against ALS symptomologies. Proteomic biomarkers, microRNAs, and extracellular vehicles (EVs) serve as promising tools for disease diagnosis or progression assessment. These markers are relatively easy to obtain from blood or cerebrospinal fluids and can be used to identify potential genetic causative and risk factors even in the preclinical stage before symptoms appear. In addition, antisense oligonucleotides and RNA gene therapies have successfully been employed against other diseases, such as childhood-onset spinal muscular atrophy (SMA), which could also give hope to ALS patients. Therefore, an effective gene and biomarker panel should be generated for potentially "at risk" individuals to provide timely interventions and better treatment outcomes for ALS patients as soon as possible.

Unraveling Molecular and Genetic Insights into Neurodegenerative Diseases: Advances in Understanding Alzheimer's, Parkinson's, and Huntington's Diseases and Amyotrophic Lateral Sclerosis

Neurodegenerative diseases are, according to recent studies, one of the main causes of disability and death worldwide. Interest in molecular genetics has started to experience exponential growth thanks to numerous advancements in technology, shifts in the understanding of the disease as a phenomenon, and the change in the perspective regarding gene editing and the advantages of this action. The aim of this paper is to analyze the newest approaches in genetics and molecular sciences regarding four of the most important neurodegenerative disorders: Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. We intend through this review to focus on the newest treatment, diagnosis, and predictions regarding this large group of diseases, in order to obtain a more accurate analysis and to identify the emerging signs that could lead to a better outcome in order to increase both the quality and the life span of the patient. Moreover, this review could provide evidence of future possible novel therapies that target the specific genes and that could be useful to be taken into consideration when the classical approaches fail to shed light.

The contribution of Neanderthal introgression and natural selection to neurodegenerative diseases

Humans are thought to be more susceptible to neurodegeneration than equivalently-aged primates. It is not known whether this vulnerability is specific to anatomically-modern humans or shared with other hominids. The contribution of introgressed Neanderthal DNA to neurodegenerative disorders remains uncertain. It is also unclear how common variants associated with neurodegenerative disease risk are maintained by natural selection in the population despite their deleterious effects. In this study, we aimed to quantify the genome-wide contribution of Neanderthal introgression and positive selection to the heritability of complex neurodegenerative disorders to address these questions. We used stratified-linkage disequilibrium score regression to investigate the relationship between five SNP-based signatures of natural selection, reflecting different timepoints of evolution, and genome-wide associated variants of the three most prevalent neurodegenerative disorders: Alzheimer's disease, amyotrophic lateral sclerosis and Parkinson's disease. We found no evidence for enrichment of positively-selected SNPs in the heritability of Alzheimer's disease, amyotrophic lateral sclerosis and Parkinson's disease, suggesting that common deleterious disease variants are unlikely to be maintained by positive selection. There was no enrichment of Neanderthal introgression in the SNP-heritability of these disorders, suggesting that Neanderthal admixture is unlikely to have contributed to disease risk. These findings provide insight into the origins of neurodegenerative disorders within the evolution of Homo sapiens and addresses a long-standing debate, showing that Neanderthal admixture is unlikely to have contributed to common genetic risk of neurodegeneration in anatomically-modern humans.

Enhanced axonal regeneration of ALS patient iPSC-derived motor neurons harboring SOD1A4V mutation

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease, characterized by degeneration of upper and lower motor neurons that leads to muscle weakness, paralysis, and death, but the effects of disease-causing mutations on axonal outgrowth of neurons derived from human induced pluripotent stem cells (iPSC)-derived motor neurons (hiPSC-MN) are poorly understood. The use of hiPSC-MN is a promising tool to develop more relevant models for target identification and drug development in ALS research, but questions remain concerning the effects of distinct disease-causing mutations on axon regeneration. Mutations in superoxide dismutase 1 (SOD1) were the first to be discovered in ALS patients. Here, we investigated the effect of the SOD1A4V mutation on axonal regeneration of hiPSC-MNs, utilizing compartmentalized microfluidic devices, which are powerful tools for studying hiPSC-MN distal axons. Surprisingly, SOD1+/A4V hiPSC-MNs regenerated axons more quickly following axotomy than those expressing the native form of SOD1. Though initial axon regrowth was not significantly different following axotomy, enhanced regeneration was apparent at later time points, indicating an increased rate of outgrowth. This regeneration model could be used to identify factors that enhance the rate of human axon regeneration.

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.

Superoxide Dismutase 1 Folding Stability as a Target for Molecular Tweezers in SOD1-Related Amyotrophic Lateral Sclerosis

Protein misfolding and aggregation are hallmarks of many severe neurodegenerative diseases including Alzheimer's, Parkinson's and Huntington's disease. As a supramolecular ligand that binds to lysine and arginine residues, the molecular tweezer CLR01 was found to modify the aggregation pathway of disease-relevant proteins in vitro and in vivo with beneficial effects on toxicity. However, the molecular mechanisms of how tweezers exert these effects remain mainly unknown, hampering further drug development. Here, we investigate the modulation mechanism of unfolding and aggregation pathways of SOD1, which are involved in amyotrophic lateral sclerosis (ALS), by CLR01. Using a truncated version of the wildtype SOD1 protein, SOD1_bar , we show that CLR01 acts on the first step of the aggregation pathway, the unfolding of the SOD1 monomer. CLR01 increases, by ∼10 °C, the melting temperatures of the A4V and G41D SOD1 mutants, which are commonly observed mutations in familial ALS. Molecular dynamics simulations and binding free energy calculations as well as native mass spectrometry and mutational studies allowed us to identify K61 and K92 as binding sites for the tweezers to mediate the stability increase. The data suggest that the modulation of SOD1 conformational stability is a promising target for future developments of supramolecular ligands against neurodegenerative diseases.

Identification of TARDBP Gly298Ser as a founder mutation for amyotrophic lateral sclerosis in Southern China

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by predominant impairment of upper and lower motor neurons. Over 50 TARDBP mutations have been reported in both familial (FALS) and sporadic ALS (SALS). Some mutations in TARDBP, e.g. A382T and G294V, have genetic founder effects in certain geographic regions. However, such prevalence and founder effect have not been reported in Chinese.

METHODS

Whole-exome sequencing (WES) was performed in 16 Chinese FALS patients, followed by Sanger sequencing for the TARDBP p.Gly298Ser mutation (G298S) in 798 SALS patients and 1,325 controls. Haplotype analysis using microsatellites flanking TARDBP was conducted in the G298S-carrying patients and noncarriers. The geographic distribution and phenotypic correlation of the TARDBP mutations reported worldwide were reviewed.

RESULTS

WES detected the TARDBP G298S mutation in 8 FALS patients, and Sanger sequencing found additional 8 SALS cases, but no controls, carrying this mutation. All the 16 cases came from Southern China, and 7 of these patients shared the 117-286-257-145-246-270 allele for the D1S2736-D1S1151-D1S2667-D1S489-D1S434-D1S2697 markers, which was not found in the 92 non-carrier patients (0/92) (p < 0.0001) and 65 age-matched and neurologically normal individuals (0/65) (p < 0.0001). The A382T and G298S mutations were prevalent in Europeans and Eastern Asians, respectively. Additionally, carriers for the M337V mutation are dominated by bulbar onset with a long survival, whereas those for G298S are dominated by limb onset with a short survival.

CONCLUSIONS

Some prevalent TARDBP mutations are distributed in a geographic pattern and related to clinical profiles. TARDBP G298S mutation is a founder mutation in the Southern Chinese ALS population.

Toxic SOD1 trimers are off-pathway in the formation of amyloid-like fibrils in ALS

Accumulation of insoluble amyloid fibrils is widely studied as a critical factor in the pathology of multiple neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease. Misfolded Cu, Zn superoxide dismutase (SOD1) was the first protein linked to ALS, and non-native SOD1 trimeric oligomers were recently linked to cytotoxicity, while larger oligomers were protective to cells. The balance between trimers and larger aggregates in the process of SOD1 aggregation is, thus, a critical determinant of potential therapeutic approaches to treat ALS. Yet, it is unknown whether these trimeric oligomers are a necessary intermediate for larger aggregate formation or a distinct off-pathway species competing with fibril formation. Depending on the on- or off-pathway scenario of trimer formation, we expect drastically different therapeutic approaches. Here, we show that the toxic SOD1 trimer is an off-pathway intermediate competing with protective fibril formation. We design mutant SOD1 constructs that remain in a trimeric state (super stable trimers) and show that stabilizing the trimeric SOD1 prevents formation of fibrils in vitro and in a motor neuron like cell model (NSC-34). Using size exclusion chromatography, we track the aggregation kinetics of purified SOD1 and show direct competition of trimeric SOD1 with larger oligomer and fibril formation. Finally, we show the trimer is structurally independent of both larger soluble oligomers and insoluble fibrils using circular dichroism spectroscopy and limited proteolysis.

Short structural variants as informative genetic markers for ALS disease risk and progression

There is considerable variability in disease progression for patients with amyotrophic lateral sclerosis (ALS) including the age of disease onset, site of disease onset, and survival time. There is growing evidence that short structural variations (SSVs) residing in frequently overlooked genomic regions can contribute to complex disease mechanisms and can explain, in part, the phenotypic variability in ALS patients. Here, we discuss SSVs recently characterized by our laboratory and how these discoveries integrate into the current literature on ALS, particularly in the context of application to future clinical trials. These markers may help to identify and differentiate patients for clinical trials that have a similar ALS disease mechanism(s), thereby reducing the impact of participant heterogeneity. As evidence accumulates for the genetic markers discovered in SQSTM1, SCAF4, and STMN2, we hope to improve the outcomes of future ALS clinical trials.

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.

Role of genetics in amyotrophic lateral sclerosis: a large cohort study in Chinese mainland population

Background

A large number of new causative and risk genes for amyotrophic lateral sclerosis (ALS) have been identified mostly in patients of European ancestry. In contrast, we know relatively little regarding the genetics of ALS in other ethnic populations. This study aims to provide a comprehensive analysis of the genetics of ALS in an unprecedented large cohort of Chinese mainland population and correlate with the clinical features of rare variants carriers.

Methods

A total of 1587 patients, including 64 familial ALS (FALS) and 1523 sporadic ALS (SALS), and 1866 in-house controls were analysed by whole-exome sequencing and/or testing for G4C2 repeats in C9orf72. Forty-one ALS-associated genes were analysed.

Findings

155 patients, including 26 (40.6%) FALS and 129 (8.5%) SALS, carrying rare pathogenic/likely pathogenic (P/LP) variants of ALS causative genes were identified. SOD1 was the most common mutated gene, followed by C9orf72, FUS, NEK1, TARDBP and TBK1. By burden analysis, rare variants in SOD1, FUS and TARDBP contributed to the collective risk for ALS (p<2.5e-6) at the gene level, but at the allelic level TARDBP p.Gly294Val and FUS p.Arg521Cys and p.Arg521His were the most important single variants causing ALS. Clinically, P/LP variants in TARDBP and C9orf72 were associated with poor prognosis, in FUS linked with younger age of onset, and C9orf72 repeats tended to affect cognition.

Conclusions

Our data provide essential information for understanding the genetic and clinical features of ALS in China and for optimal design of genetic testing and evaluation of disease prognosis.

Dysregulations of Expression of Genes of the Ubiquitin/SUMO Pathways in an In Vitro Model of Amyotrophic Lateral Sclerosis Combining Oxidative Stress and SOD1 Gene Mutation

Protein aggregates in affected motor neurons are a hallmark of amyotrophic lateral sclerosis (ALS), but the molecular pathways leading to their formation remain incompletely understood. Oxidative stress associated with age, the major risk factor in ALS, contributes to this neurodegeneration in ALS. We show that several genes coding for enzymes of the ubiquitin and small ubiquitin-related modifier (SUMO) pathways exhibit altered expression in motor neuronal cells exposed to oxidative stress, such as the CCNF gene mutated in ALS patients. Eleven of these genes were further studied in conditions combining oxidative stress and the expression of an ALS related mutant of the superoxide dismutase 1 (SOD1) gene. We observed a combined effect of these two environmental and genetic factors on the expression of genes, such as Uhrf2, Rbx1, Kdm2b, Ube2d2, Xaf1, and Senp1. Overall, we identified dysregulations in the expression of enzymes of the ubiquitin and SUMO pathways that may be of interest to better understand the pathophysiology of ALS and to protect motor neurons from oxidative stress and genetic alterations.

A specific biomarker for amyotrophic lateral sclerosis: Quantitative susceptibility mapping

OBJECTIVE

Accurate and timely diagnosis of amyotrophic lateral sclerosis (ALS) is a diagnostic challenge given the lack of specific diagnostic and imaging biomarkers as well as the significant clinic overlap with mimic syndromes. We hypothesize that MR quantitative susceptibility mapping (QSM) can help differentiate ALS from mimic diagnoses.

METHODS

In a blinded retrospective study of MRIs with QSM from 2015 to 2018, we compared motor cortex susceptibility along the hand and face homunculi in ALS patients and patients with similar clinical presentations. Inclusion required a confirmed ALS or a mimic diagnosis. Comparative groups included age-matched patients with MRIs performed for non-motor neuron symptoms that were reported as normal or demonstrated leukoaraiosis. Quantitative susceptibility values were compared with ANOVA and Tukey-Kramer (post-hoc). ROC analysis and Youden's index were used to identify optimal cutoff values.

RESULTS

Fifty ALS, 35 mimic, and 70 non-motor neuron symptom patients (35 normal, 35 leukoaraiosis) were included. Hand and face homunculus mean susceptibility values were significantly higher in the ALS group compared to the mimic (p=0.001, p=0.004), leukoaraiosis (p<0.001, p=0.003), and normal (p<0.001, p<0.001) groups. ROC curve analysis comparing ALS to mimics resulted in an area under the curve of 0.71 and 0.67 for the hand and face homunculus measurements, respectively. In differentiating ALS from mimics, Youden's index showed 100% specificity and 36% sensitivity for hand homunculus measurements.

CONCLUSIONS

QSM has diagnostic potential in the assessment of suspected ALS patients, demonstrating very high specificity in differentiating ALS from mimic diagnoses.

Fractal genomics of SOD1 evolution

To understand the fundamental processes of gene evolution such as the impact of point mutations and segmental duplications on statistical topography, superoxide dismutase-1 (SOD1) orthologous sequences (n = 50) are studied. These demonstrate scale invariant self-similarity patterns and long-range correlations (LRCs) indicating fractal organization. Phylogenetic hierarchies change when SOD1 orthologs are grouped according to fractal measures, indicating that statistical topographies can be used to study gene evolution. Sliding window k-mer analysis show that majority of k-mers across all SOD1 orthologs are unique, with very few duplications. Orthologs from simpler species contribute minimally (< 1% of k-mers) to more complex species. Both simple and complex random processes fail to produce significant matching k-mer sequences for SOD1 orthologs. Point mutations causing amyotrophic lateral sclerosis do not impact the fractal organization of human SOD1. Hence, SOD1 did not evolve by a patchwork of repetitive sequences modified by point mutations. Moreover, fractal and other methods described here can be used to study the origin and evolution of genomes.

Putative founder effect in the Polish, Iranian and United States populations for the L144S SOD1 mutation associated with slowly uniform phenotype of amyotrophic lateral sclerosis

Mutations in SOD1 cause approximately 12-25% of familial ALS and ≈2% of apparently sporadic ALS cases. Clinical phenotypes linked to SOD1 mutations are heterogeneous and intra-familial variability of the clinical phenotype is frequently observed. SOD1 L144S mutation, identified also in Brazil, Iran and United States, is the second most frequent mutation among ALS patients in Poland. So far, 10 FALS pedigrees with SOD1 L144S mutation have been reported worldwide. The aim of the study was to establish the origin of SOD1 L144S mutation in geographically distinct populations. The clinical presentation of the Polish patients was compared with those from the previously reported populations (26 ever-reported patients). Clinically, L144S mutation is associated with both sporadic and familial ALS of relatively slow uniform course, a prevalent onset in the lower limbs, either classic or PMA presentation and a long survival time. Like in the case of other previously described SOD1 mutations, there was an intra-familial heterogeneity and reduced penetrance for ALS was observed. We propose that the L144S SOD1 mutation in the three studied populations has a common founder most likely of Polish origin.

Identity by descent analysis identifies founder events and links SOD1 familial and sporadic ALS cases

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterised by the loss of upper and lower motor neurons resulting in paralysis and eventual death. Approximately 10% of ALS cases have a family history of disease, while the remainder present as apparently sporadic cases. Heritability studies suggest a significant genetic component to sporadic ALS, and although most sporadic cases have an unknown genetic aetiology, some familial ALS mutations have also been found in sporadic cases. This suggests that some sporadic cases may be unrecognised familial cases with reduced disease penetrance in their ancestors. A powerful strategy to uncover a familial link is identity-by-descent (IBD) analysis, which detects genomic regions that have been inherited from a common ancestor. IBD analysis was performed on 83 Australian familial ALS cases from 25 families and three sporadic ALS cases, each of whom carried one of three SOD1 mutations (p.I114T, p.V149G and p.E101G). We defined five unique 350-SNP haplotypes that carry these mutations in our cohort, indicative of five founder events. This included two founder haplotypes that carry SOD1 p.I114T; linking familial and sporadic cases. We found that SOD1 p.E101G arose independently in each family that carries this mutation and linked two families that carry SOD1 p.V149G. The age of disease onset varied between cases that carried each SOD1 p.I114T haplotype. Linking families with identical ALS mutations allows for larger sample sizes and increased statistical power to identify putative phenotypic modifiers.

Disease-modifying effects of an SCAF4 structural variant in a predominantly SOD1 ALS cohort

OBJECTIVE

To test the hypothesis that rs573116164 will have disease-modifying effects in patients with superoxide dismutase 1 (SOD1) familial amyotrophic lateral sclerosis (fALS), we characterized rs573116164 within a cohort of 190 patients with fALS and 560 healthy age-matched controls to assess the variant for association with various measures of disease.

METHODS

Using a previously described bioinformatics evaluation algorithm, a polymorphic short structural variant associated with SOD1 was identified according to its theoretical effect on gene expression. An 12-18 poly-T repeat (rs573116164) within the 3' untranslated region of serine and arginine rich proteins-related carboxy terminal domain associated factor 4 (SCAF4), a gene that is adjacent to SOD1, was assessed for disease association and influence on survival and age at onset in an fALS cohort using PCR, Sanger sequencing, and capillary separation techniques for allele detection.

RESULTS

In a North American cohort of predominantly SOD1 fALS patients (n =190) and age-matched healthy controls (n = 560), we showed that carriage of an 18T SCAF4 allele was associated with disease within this cohort (odds ratio [OR] 6.6; 95% confidence interval [CI] 3.9-11.2; p = 4.0e-11), but also within non-SOD1 cases (n = 27; OR 5.3; 95% CI 1.9-14.5; p = 0.0014). This finding suggests genetically SOD1-independent effects of SCAF4 on fALS susceptibility. Furthermore, carriage of an 18T allele was associated with a 26-month reduction in survival time (95% CI 6.6-40.8; p = 0.014), but did not affect age at onset of disease.

CONCLUSIONS

The findings in this fALS cohort suggest that rs573116164 could have SOD1-independent and broader relevance in ALS, warranting further investigation in other fALS and sporadic ALS cohorts, as well as studies of functional effects of the 18T variant on gene expression.

The Cysteine (Cys) Residues Cys-6 and Cys-111 in Mutant Superoxide Dismutase 1 (SOD1) A4V Are Required for Induction of Endoplasmic Reticulum Stress in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the degeneration of motor neurons. Between 12 and 20% of inherited cases and approximately 1-2% of all cases are caused by mutations in the gene encoding dismutase 1 (SOD1). Mutant SOD1 A4V (alanine to valine) induces endoplasmic reticulum (ER) stress, which is increasingly implicated as a pathway to motor neuron degeneration and death in ALS. However, it remains unclear how ER stress is induced by mutant SOD1 A4V. Previous studies have established that it is induced early in pathophysiology and it precedes the formation of mutant SOD1 inclusions. SOD1 contains four cysteine residues, two of which form an intra-subunit disulphide bond involving Cys-57 and Cys-146. The remaining two cysteines, Cys-6 and Cys-111, remain unpaired and have been implicated in mutant SOD1 aggregation. In this study, we examined the relationship between the SOD1 A4V cysteine residues and aggregation, ER stress induction and toxicity. We report here that mutation of Cys-6 and Cys-111 in mutant SOD1 A4V, but not Cys-57 or Cys-146, ameliorates ER stress, inclusion formation and apoptosis in neuronal cell lines. These results imply that protein misfolding, induced by Cys-6 and Cys-111, is required for these pathological events in neuronal cells.

Ebselen as template for stabilization of A4V mutant dimer for motor neuron disease therapy

Mutations to the gene encoding superoxide dismutase-1 (SOD1) were the first genetic elements discovered that cause motor neuron disease (MND). These mutations result in compromised SOD1 dimer stability, with one of the severest and most common mutations Ala4Val (A4V) displaying a propensity to monomerise and aggregate leading to neuronal death. We show that the clinically used ebselen and related analogues promote thermal stability of A4V SOD1 when binding to Cys111 only. We have developed a A4V SOD1 differential scanning fluorescence-based assay on a C6S mutation background that is effective in assessing suitability of compounds. Crystallographic data show that the selenium atom of these compounds binds covalently to A4V SOD1 at Cys111 at the dimer interface, resulting in stabilisation. This together with chemical amenability for hit expansion of ebselen and its on-target SOD1 pharmacological chaperone activity holds remarkable promise for structure-based therapeutics for MND using ebselen as a template.

Mutations in Superoxide Dismutase 1 (Sod1) Linked to Familial Amyotrophic Lateral Sclerosis Can Disrupt High-Affinity Zinc-Binding Promoted by the Copper Chaperone for Sod1 (Ccs)

Zinc (II) ions (hereafter simplified as zinc) are important for the structural and functional activity of many proteins. For Cu, Zn superoxide dismutase (Sod1), zinc stabilizes the native structure of each Sod1 monomer, promotes homo-dimerization and plays an important role in activity by "softening" the active site so that copper cycling between Cu(I) and Cu(II) can rapidly occur. Previously, we have reported that binding of Sod1 by its copper chaperone (Ccs) stabilizes a conformation of Sod1 that promotes site-specific high-affinity zinc binding. While there are a multitude of Sod1 mutations linked to the familial form of amyotrophic lateral sclerosis (fALS), characterizations by multiple research groups have been unable to realize strong commonalities among mutants. Here, we examine a set of fALS-linked Sod1 mutations that have been well-characterized and are known to possess variation in their biophysical characteristics. The zinc affinities of these mutants are evaluated here for the first time and then compared with the previously established value for wild-type Sod1 zinc affinity. Ccs does not have the same ability to promote zinc binding to these mutants as it does for the wild-type version of Sod1. Our data provides a deeper look into how (non)productive Sod1 maturation by Ccs may link a diverse set of fALS-Sod1 mutations.

Haplotype Analysis of the First A4V-SOD1 Spanish Family: Two Separate Founders or a Single Common Founder?

Despite the genetic heterogeneity reported in familial amyotrophic lateral sclerosis (ALS) (fALS), Cu/Zn superoxide-dismutase (SOD1) gene mutations are the second most common cause of the disease, accounting for around 20% of all families (ALS1) and isolated sporadic cases (sALS). At least 186 different mutations in the SOD1 gene have been reported to date. The possibility of a single founder and separate founders have been investigated for D90A (p.D91A) and A4V (p.A5V), the most common mutations worldwide. High-throughput single nucleotide polymorphism genotyping studies have suggested two founders for A4V (one for the Amerindian population and another for the European population) although the possibility that the two populations are descended from a single ancient founder cannot be ruled out. We used 15 genetic variants spanning the human chromosome 21 from the SOD1 gene to the SCAF4 gene, comparing them with the population reference panels, to demonstrate that the first A4V Spanish pedigree shared the genetic background reported in the European population.

Genotype-phenotype correlation and evidence for a common ancestor in two Italian ALS patients with the D124G SOD1 mutation

Objective: To describe the phenotypic and genotypic features of two unrelated Italian amyotrophic lateral sclerosis (ALS) patients, a FALS case and an apparently sporadic case, carrying the same D124G SOD1 mutation. Since this mutation is very rare, previously reported in only one patient of unknown geographical origin, to look for a founder effect. Methods: Cases were classified based on the El Escorial revised criteria. Genomic DNA was isolated from whole blood samples and the coding region of the SOD1 gene was analyzed by polymerase chain reaction (PCR) and sequencing. For the haplotype analysis, genotyping was carried out using eight polymorphic markers flanking the SOD1 gene. Results: Both patients had a spinal onset in the lower limbs and progressive muscular atrophy (PMA) phenotype. The progression of the disease in our cases differed from that reported for PMA patients, characterized by a longer survival than the majority of ALS phenotypes, being more aggressive, in particular in the sporadic case (survival less than 1 year). Genotyping showed a shared haplotype for the D124G allele and the estimate of the mutation dating revealed that the mutation originated approximately 400 years ago. Conclusions: We have defined for the first time the clinical profile associated with the D124G mutation in SOD1 gene and provided evidence that this mutation in Italy originates from a common founder.

Emerging Developments in Targeting Proteotoxicity in Neurodegenerative Diseases

The most common neurodegenerative diseases are Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease, frontotemporal lobar degeneration, and the motor neuron diseases, with AD affecting approximately 6% of people aged 65 years and older, and PD affecting approximately 1% of people aged over 60 years. Specific proteins are associated with these neurodegenerative diseases, as determined by both immunohistochemical studies on post-mortem tissue and genetic screening, where protein misfolding and aggregation are key hallmarks. Many of these proteins are shown to misfold and aggregate into soluble non-native oligomers and large insoluble protein deposits (fibrils and plaques), both of which may exert a toxic gain of function. Proteotoxicity has been examined intensively in cell culture and in in vivo models, and clinical trials of methods to attenuate proteotoxicity are relatively new. Therapies to enhance cellular protein quality control mechanisms such as upregulation of chaperones and clearance/degradation pathways, as well as immunotherapies against toxic protein conformations, are being actively pursued. In this article, we summarize the common pathophysiology of neurodegenerative disease, and review therapies in early-phase clinical trials that target the proteotoxic component of several neurodegenerative diseases.

Locus and gene-based GWAS meta-analysis identifies new diabetic nephropathy genes

Objective Assimilation of SNPs Interacting in Synchrony (OASIS) is a locus-based clustering algorithm recently described that can potentially address false positives and negatives in genome-wide association studies (GWAS) of complex disorders. Diabetic nephropathy (DN) is incompletely understood due to a paucity of genes identified despite several GWAS. OASIS was applied to three DN dbGAP GWAS datasets (4725 subjects; 1.06 million SNPs). OASIS identified 19 DN genes which were verified using single variant replication in a standard association study and gene-based analysis using GATES. CARS and FRMD3 were confirmed as DN genes, and five known diabetes-associated genes, viz. NLRP3, INPPL1, PIK3C2G, NRXN3, and TBC1D4, not previously identified using these datasets were discovered. Furthermore, three additional novel DN genes were found which replicated in two sets of analysis, viz. NTN1, EBF2, and DNAH11. Hence, composite analysis with OASIS, gene-based, and single variant association testing can be universally applied to existing GWAS datasets for the identification of new genes.

Identification of an A4V SOD1 mutation in a Chinese patient with amyotrophic lateral sclerosis without the A4V founder effect common in North America

We identified a missense alanine to valine mutation at codon 4 (A4V) in the Cu/Zn superoxide dismutase (SOD1) gene in a 51-year-old male of Chinese origin with familial amyotrophic lateral sclerosis (ALS). The patient displayed a typical A4V-related phenotype that included rapid progression and predominant lower motor neuron involvement. This patient is the first such carrier reported outside Caucasian ALS patients, despite the fact that A4V mutations account for up to 50% of all SOD1 mutations in North America. Further SNP analyses showed that the A4V patient of Chinese origin did not share the common founder effect observed in North America.

A Case-Control Study of the Genetic Variability in Reactive Oxygen Species-Metabolizing Enzymes in Melanoma Risk

Recent studies have shown that ultraviolet (UV)-induced chemiexcitation of melanin fragments leads to DNA damage; and chemiexcitation of melanin fragments requires reactive oxygen species (ROS), as ROS excite an electron in the melanin fragments. In addition, ROS also cause DNA damages on their own. We hypothesized that ROS producing and metabolizing enzymes were major contributors in UV-driven melanomas. In this case-control study of 349 participants, we genotyped 23 prioritized single nucleotide polymorphisms (SNPs) in nicotinamide adenine dinucleotide phosphate (NADPH) oxidases 1 and 4 (NOX1 and NOX4, respectively), CYBA, RAC1, superoxide dismutases (SOD1, SOD2, and SOD3) and catalase (CAT), and analyzed their associated melanoma risk. Five SNPs, namely rs1049255 (CYBA), rs4673 (CYBA), rs10951982 (RAC1), rs8031 (SOD2), and rs2536512 (SOD3), exhibited significant genotypic frequency differences between melanoma cases and healthy controls. In simple logistic regression, RAC1 rs10951982 (odds ratio (OR) 8.98, 95% confidence interval (CI): 5.08 to 16.44; p < 0.001) reached universal significance (p = 0.002) and the minor alleles were associated with increased risk of melanoma. In contrast, minor alleles in SOD2 rs8031 (OR 0.16, 95% CI: 0.06 to 0.39; p < 0.001) and SOD3 rs2536512 (OR 0.08, 95% CI: 0.01 to 0.31; p = 0.001) were associated with reduced risk of melanoma. In multivariate logistic regression, RAC1 rs10951982 (OR 6.15, 95% CI: 2.98 to 13.41; p < 0.001) remained significantly associated with increased risk of melanoma. Our results highlighted the importance of RAC1, SOD2, and SOD3 variants in the risk of melanoma.

Locus and gene-based GWAS meta-analysis identifies new diabetic nephropathy genes

Objective Assimilation of SNPs Interacting in Synchrony (OASIS) is a locus-based clustering algorithm recently described that can potentially address false positives and negatives in genome-wide association studies (GWAS) of complex disorders. Diabetic nephropathy (DN) is incompletely understood due to a paucity of genes identified despite several GWAS. OASIS was applied to three DN dbGAP GWAS datasets (4725 subjects; 1.06 million SNPs). OASIS identified 19 DN genes which were verified using single variant replication in a standard association study and gene-based analysis using GATES. CARS and FRMD3 were confirmed as DN genes, and five known diabetes-associated genes, viz. NLRP3, INPPL1, PIK3C2G, NRXN3, and TBC1D4, not previously identified using these datasets were discovered. Furthermore, three additional novel DN genes were found which replicated in two sets of analysis, viz. NTN1, EBF2, and DNAH11. Hence, composite analysis with OASIS, gene-based, and single variant association testing can be universally applied to existing GWAS datasets for the identification of new genes.

Amyotrophic lateral sclerosis patient iPSC-derived astrocytes impair autophagy via non-cell autonomous mechanisms

Amyotrophic lateral sclerosis, a devastating neurodegenerative disease, is characterized by the progressive loss of motor neurons and the accumulation of misfolded protein aggregates. The latter suggests impaired proteostasis may be a key factor in disease pathogenesis, though the underlying mechanisms leading to the accumulation of aggregates is unclear. Further, recent studies have indicated that motor neuron cell death may be mediated by astrocytes. Herein we demonstrate that ALS patient iPSC-derived astrocytes modulate the autophagy pathway in a non-cell autonomous manner. We demonstrate cells treated with patient derived astrocyte conditioned medium demonstrate decreased expression of LC3-II, a key adapter protein required for the selective degradation of p62 and ubiquitinated proteins targeted for degradation. We observed an increased accumulation of p62 in cells treated with patient conditioned medium, with a concomitant increase in the expression of SOD1, a protein associated with the development of ALS. Activation of autophagic mechanisms with Rapamycin reduces the accumulation of p62 puncta in cells treated with patient conditioned medium. These data suggest that patient astrocytes may modulate motor neuron cell death by impairing autophagic mechanisms, and the autophagy pathway may be a useful target in the development of novel therapeutics.

Novel linkage disequilibrium clustering algorithm identifies new lupus genes on meta-analysis of GWAS datasets

Systemic lupus erythematosus (SLE) is a complex disorder. Genetic association studies of complex disorders suffer from the following three major issues: phenotypic heterogeneity, false positive (type I error), and false negative (type II error) results. Hence, genes with low to moderate effects are missed in standard analyses, especially after statistical corrections. OASIS is a novel linkage disequilibrium clustering algorithm that can potentially address false positives and negatives in genome-wide association studies (GWAS) of complex disorders such as SLE. OASIS was applied to two SLE dbGAP GWAS datasets (6077 subjects; ∼0.75 million single-nucleotide polymorphisms). OASIS identified three known SLE genes viz. IFIH1, TNIP1, and CD44, not previously reported using these GWAS datasets. In addition, 22 novel loci for SLE were identified and the 5 SLE genes previously reported using these datasets were verified. OASIS methodology was validated using single-variant replication and gene-based analysis with GATES. This led to the verification of 60% of OASIS loci. New SLE genes that OASIS identified and were further verified include TNFAIP6, DNAJB3, TTF1, GRIN2B, MON2, LATS2, SNX6, RBFOX1, NCOA3, and CHAF1B. This study presents the OASIS algorithm, software, and the meta-analyses of two publicly available SLE GWAS datasets along with the novel SLE genes. Hence, OASIS is a novel linkage disequilibrium clustering method that can be universally applied to existing GWAS datasets for the identification of new genes.

Locomotor analysis identifies early compensatory changes during disease progression and subgroup classification in a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a motoneuron degenerative disease that is challenging to diagnose and presents with considerable variability in survival. Early identification and enhanced understanding of symptomatic patterns could aid in diagnosis and provide an avenue for monitoring disease progression. Use of the mSOD1G93A mouse model provides control of the confounding environmental factors and genetic heterogeneity seen in amyotrophic lateral sclerosis patients, while investigating underlying disease-induced changes. In the present study, we performed a longitudinal behavioral assessment paradigm and identified an early hindlimb symptom, resembling the common gait abnormality foot drop, along with an accompanying forelimb compensatory mechanism in the mSOD1G93A mouse. Following these initial changes, mSOD1 mice displayed a temporary hindlimb compensatory mechanism resembling an exaggerated steppage gait. As the disease progressed, these compensatory mechanisms were not sufficient to sustain fundamental locomotor parameters and more severe deficits appeared. We next applied these initial findings to investigate the inherent variability in B6SJL mSOD1G93A survival. We identified four behavioral variables that, when combined in a cluster analysis, identified two subpopulations with different disease progression rates: a fast progression group and a slow progression group. This behavioral assessment paradigm, with its analytical approaches, provides a method for monitoring disease progression and detecting mSOD1 subgroups with different disease severities. This affords researchers an opportunity to search for genetic modifiers or other factors that likely enhance or slow disease progression. Such factors are possible therapeutic targets with the potential to slow disease progression and provide insight into the underlying pathology and disease mechanisms.

Ethical issues in the evaluation of adults with suspected genetic neuromuscular disorders

Genetic testing is rapidly becoming an increasingly significant part of the diagnostic armamentarium of neuromuscular clinicians. Although technically easy to order, the results of such testing, whether positive or negative, have potentially enormous consequences for the individual tested and for family members. As a result, ethical considerations must be in the forefront of the physician's agenda when obtaining genetic testing. Informed consent is an important starting point for discussions between physicians and patients, but the counseling embedded in the informed consent process must be an ongoing part of subsequent interactions, including return of results and follow-up. Patient autonomy, including the right to know and right not-to-know results, must be respected. Considerations of capacity, physician beneficence and nonmaleficence, and privacy all play roles in the process. Muscle Nerve 54: 997-1006, 2016.

Genotype-phenotype correlations of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by progressive neuronal loss and degeneration of upper motor neuron (UMN) and lower motor neuron (LMN). The clinical presentations of ALS are heterogeneous and there is no single test or procedure to establish the diagnosis of ALS. Most cases are diagnosed based on symptoms, physical signs, progression, EMG, and tests to exclude the overlapping conditions. Familial ALS represents about 5 ~ 10 % of ALS cases, whereas the vast majority of patients are sporadic. To date, more than 20 causative genes have been identified in hereditary ALS. Detecting the pathogenic mutations or risk variants for each ALS individual is challenging. However, ALS patients carrying some specific mutations or variant may exhibit subtly distinct clinical features. Unraveling the respective genotype-phenotype correlation has important implications for the genetic explanations. In this review, we will delineate the clinical features of ALS, outline the major ALS-related genes, and summarize the possible genotype-phenotype correlations of ALS.

A comprehensive review of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset fatal neurodegenerative disease affecting motor neurons with an incidence of about 1/100,000. Most ALS cases are sporadic, but 5–10% of the cases are familial ALS. Both sporadic and familial ALS (FALS) are associated with degeneration of cortical and spinal motor neurons. The etiology of ALS remains unknown. However, mutations of superoxide dismutase 1 have been known as the most common cause of FALS. In this study, we provide a comprehensive review of ALS. We cover all aspects of the disease including epidemiology, comorbidities, environmental risk factor, molecular mechanism, genetic factors, symptoms, diagnostic, treatment, and even the available supplement and management of ALS. This will provide the reader with an advantage of receiving a broad range of information about the disease.

Voltage-Induced Misfolding of Zinc-Replete ALS Mutant Superoxide Dismutase-1

The monomerization of Cu, Zn superoxide dismutase (SOD1) is an early step along pathways of misfolding linked to amyotrophic lateral sclerosis (ALS). Monomerization requires the reversal of two post-translational modifications that are thermodynamically favorable: (i) dissociation of active-site metal ions and (ii) reduction of intramolecular disulfide bonds. This study found, using amide hydrogen/deuterium (H/D) exchange, capillary electrophoresis, and lysine-acetyl protein charge ladders, that ALS-linked A4V SOD1 rapidly monomerizes and partially unfolds in an external electric field (of physiological strength), without loss of metal ions, exposure to disulfide-reducing agents, or Joule heating. Voltage-induced monomerization was not observed for metal-free A4V SOD1, metal-free WT SOD1, or metal-loaded WT SOD1. Computational modeling suggested a mechanism for this counterintuitive effect: subunit macrodipoles of dimeric SOD1 are antiparallel and amplified 2-fold by metal coordination, which increases torque at the dimer interface as subunits rotate to align with the electric field.

Identification of B6SJL mSOD1(G93A) mouse subgroups with different disease progression rates

Disease progression rates among patients with amyotrophic lateral sclerosis (ALS) vary greatly. Although the majority of affected individuals survive 3-5 years following diagnosis, some subgroups experience a more rapidly progressing form, surviving less than 1 year, and other subgroups experience slowly progressing forms, surviving nearly 50 years. Genetic heterogeneity and environmental factors pose significant barriers in investigating patient progression rates. Similar to the case for humans, variation in survival within the mSOD1 mouse has been well documented, but different progression rates have not been investigated. The present study identifies two subgroups of B6SJL mSOD1(G93A) mice with different disease progression rates, a fast progression group (FPG) and slow progression group, as evidenced by differences in the rate of motor function decline. In addition, increased disease-associated gene expression within the FPG facial motor nucleus confirmed the presence of a more severe phenotype. We hypothesize that a more severe disease phenotype could be the result of 1) an earlier onset of axonal disconnection with a consistent degeneration rate or 2) a more severe or accelerated degenerative process. We performed a facial nerve transection axotomy in both mSOD1 subgroups prior to disease onset as a method to standardize the axonal disconnection. Instead of leading to comparable gene expression in both subgroups, this standardization did not eliminate the severe phenotype in the FPG facial nucleus, suggesting that the FPG phenotype is the result of a more severe or accelerated degenerative process. We theorize that these mSOD1 subgroups are representative of the rapid and slow disease phenotypes often experienced in ALS.

ACTH (Acthar Gel) Reduces Toxic SOD1 Protein Linked to Amyotrophic Lateral Sclerosis in Transgenic Mice: A Novel Observation

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with a complex etiology and pathology that makes the development of new therapies difficult. ACTH has neurotrophic and myotrophic effects, but has not been tested in an ALS mouse model. The G93A-SOD1 mouse model of ALS was used to test the ability of this drug to delay ALS-like symptoms. We showed that within a specific dose range, ACTH significantly postponed the disease onset and paralysis in the mouse model. To our surprise and of greater significance is that ACTH significantly reduced the levels of soluble SOD1 in the spinal cord and CNS tissues of G93A-SOD1 treated mice as well as cultured fibroblasts.

Axotomy-induced target disconnection promotes an additional death mechanism involved in motoneuron degeneration in amyotrophic lateral sclerosis transgenic mice

The target disconnection theory of amyotrophic lateral sclerosis (ALS) pathogenesis suggests that disease onset is initiated by a peripheral pathological event resulting in neuromuscular junction loss and motoneuron (MN) degeneration. Presymptomatic mSOD1(G93A) mouse facial MN (FMN) are more susceptible to axotomy-induced cell death than wild-type (WT) FMN, which suggests additional CNS pathology. We have previously determined that the mSOD1 molecular response to facial nerve axotomy is phenotypically regenerative and indistinguishable from WT, whereas the surrounding microenvironment shows significant dysregulation in the mSOD1 facial nucleus. To elucidate the mechanisms underlying the enhanced mSOD1 FMN loss after axotomy, we superimposed the facial nerve axotomy model on presymptomatic mSOD1 mice and investigated gene expression for death receptor pathways after target disconnection by axotomy vs. disease progression. We determined that the TNFR1 death receptor pathway is involved in axotomy-induced FMN death in WT and is partially responsible for the mSOD1 FMN death. In contrast, an inherent mSOD1 CNS pathology resulted in a suppressed glial reaction and an upregulation in the Fas death pathway after target disconnection. We propose that the dysregulated mSOD1 glia fail to provide support the injured MN, leading to Fas-induced FMN death. Finally, we demonstrate that, during disease progression, the mSOD1 facial nucleus displays target disconnection-induced gene expression changes that mirror those induced by axotomy. This validates the use of axotomy as an investigative tool in understanding the role of peripheral target disconnection in the pathogenesis of ALS.