Phenotypic variability in amyotrophic lateral sclerosis

Copper homeostasis and neurodegenerative diseases

Copper, one of the most prolific transition metals in the body, is required for normal brain physiological activity and allows various functions to work normally through its range of concentrations. Copper homeostasis is meticulously maintained through a complex network of copper-dependent proteins, including copper transporters (CTR1 and CTR2), the two copper ion transporters the Cu -transporting ATPase 1 (ATP7A) and Cu-transporting beta (ATP7B), and the three copper chaperones ATOX1, CCS, and COX17. Disruptions in copper homeostasis can lead to either the deficiency or accumulation of copper in brain tissue. Emerging evidence suggests that abnormal copper metabolism or copper binding to various proteins, including ceruloplasmin and metallothionein, is involved in the pathogenesis of neurodegenerative disorders. However, the exact mechanisms underlying these processes are not known. Copper is a potent oxidant that increases reactive oxygen species production and promotes oxidative stress. Elevated reactive oxygen species levels may further compromise mitochondrial integrity and cause mitochondrial dysfunction. Reactive oxygen species serve as key signaling molecules in copper-induced neuroinflammation, with elevated levels activating several critical inflammatory pathways. Additionally, copper can bind aberrantly to several neuronal proteins, including alpha-synuclein, tau, superoxide dismutase 1, and huntingtin, thereby inducing neurotoxicity and ultimately cell death. This study focuses on the latest literature evaluating the role of copper in neurodegenerative diseases, with a particular focus on copper-containing metalloenzymes and copper-binding proteins in the regulation of copper homeostasis and their involvement in neurodegenerative disease pathogenesis. By synthesizing the current findings on the functions of copper in oxidative stress, neuroinflammation, mitochondrial dysfunction, and protein misfolding, we aim to elucidate the mechanisms by which copper contributes to a wide range of hereditary and neuronal disorders, such as Wilson's disease, Menkes' disease, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis. Potential clinically significant therapeutic targets, including superoxide dismutase 1, D-penicillamine, and 5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline, along with their associated therapeutic agents, are further discussed. Ultimately, we collate evidence that copper homeostasis may function in the underlying etiology of several neurodegenerative diseases and offer novel insights into the potential prevention and treatment of these diseases based on copper homeostasis.

Resting-State EEG Oscillations in Amyotrophic Lateral Sclerosis (ALS): Toward Mechanistic Insights and Clinical Markers

Introduction: Amyotrophic lateral sclerosis (ALS) is a complex, progressive neurodegenerative disorder characterized by the degeneration of motor neurons in the brain, brainstem, and spinal cord. Several neuroimaging techniques can help reveal the pathophysiology of ALS. One of these is the electroencephalogram (EEG), a noninvasive and relatively inexpensive tool for examining electrical activity of the brain with excellent temporal precision. Methods: This mechanistic review examines the pattern of resting-state EEG activity. With a focus on publications published between January 1995 and October 2024, we carried out a comprehensive search in October 2024 across a number of databases, including PubMed/Medline, Research Gate, Google Scholar, and Cochrane. Results: The literature search yielded 17 studies included in this review. The studies varied significantly in their methodology and patient characteristics. Despite this, a common biomarker typical of ALS was found-reduced alpha power. Regarding other oscillations, the findings are less consistent and sometimes contradictory. As this is a mechanistic review, three possible explanations for this biomarker are provided. The main and most important one is increased cortical excitability. In addition, due to the limitations of the studies, recommendations for future research on this topic are outlined to enable a further and better understanding of EEG patterns in ALS. Conclusions: Most studies included in this review showed alpha power deficits in ALS patients, reflecting pathological hyperexcitability of the cerebral cortex. Future studies should address the methodological limitations identified in this review, including small sample sizes, inconsistent frequency-band definitions, and insufficient functional outcome measures, to solidify and extend current findings.

Dysfunctional mitochondria in age-related neurodegeneration: Utility of melatonin as an antioxidant treatment

Mitochondria functionally degrade as neurons age. Degenerative changes cause inefficient oxidative phosphorylation (OXPHOS) and elevated electron leakage from the electron transport chain (ETC) promoting increased intramitochondrial generation of damaging reactive oxygen and reactive nitrogen species (ROS and RNS). The associated progressive accumulation of molecular damage causes an increasingly rapid decline in mitochondrial physiology contributing to aging. Melatonin, a multifunctional free radical scavenger and indirect antioxidant, is synthesized in the mitochondrial matrix of neurons. Melatonin reduces electron leakage from the ETC and elevates ATP production; it also detoxifies ROS/RNS and via the SIRT3/FOXO pathway it upregulates activities of superoxide dismutase 2 and glutathione peroxidase. Melatonin also influences glucose processing by neurons. In neurogenerative diseases, neurons often adopt Warburg-type metabolism which excludes pyruvate from the mitochondria causing reduced intramitochondrial acetyl coenzyme A production. Acetyl coenzyme A supports the citric acid cycle and OXPHOS. Additionally, acetyl coenzyme A is a required co-substrate for arylalkylamine-N-acetyl transferase, which rate limits melatonin synthesis; therefore, melatonin production is diminished in cells that experience Warburg-type metabolism making mitochondria more vulnerable to oxidative stress. Moreover, endogenously produced melatonin diminishes during aging, further increasing oxidative damage to mitochondrial components. More normal mitochondrial physiology is preserved in aging neurons with melatonin supplementation.

Increased copy-number variant load of associated risk genes in sporadic cases of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an age-related neurodegenerative disease characterized by selective loss of motor neurons in the brainstem and spinal cord. Several genetic factors have been associated to ALS, ranging from causal genes and potential risk factors to disease modifiers. The search for pathogenic variants in these genes has mostly focused on single nucleotide variants (SNVs) while relatively understudied and not fully elucidated is the contribution of structural variants, such as copy number variations (CNVs). Here, we applied an exon-centric aCGH method to investigate, in sporadic ALS patients, the load of CNVs in 131 genes previously associated to ALS. Our approach revealed that CNV load, defined as the total number of CNVs or their size, was significantly higher in ALS cases than controls. About 87% of patients harbored multiple CNVs in ALS-related genes, and 75% structural variants compromised genes directly implicated in ALS pathogenesis (C9orf72, CHCHD10, EPHA4, FUS, HNRNPA1, KIF5A, NEK1, OPTN, PFN1, SOD1, TARDBP, TBK1, UBQLN2, UNC13A, VAPB, VCP). CNV load was also associated to higher onset age and disease progression rate. Although the contribution of individual CNVs in ALS is still unknown, their extensive load in disease-related genes may have relevant implications for the diagnostic, prognostic and therapeutical management of this devastating disorder.

Protein aggregation and therapeutic strategies in SOD1- and TDP-43- linked ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with severe socio-economic impact. A hallmark of ALS pathology is the presence of aberrant cytoplasmic inclusions composed of misfolded and aggregated proteins, including both wild-type and mutant forms. This review highlights the critical role of misfolded protein species in ALS pathogenesis, particularly focusing on Cu/Zn superoxide dismutase (SOD1) and TAR DNA-binding protein 43 (TDP-43), and emphasizes the urgent need for innovative therapeutic strategies targeting these misfolded proteins directly. Despite significant advancements in understanding ALS mechanisms, the disease remains incurable, with current treatments offering limited clinical benefits. Through a comprehensive analysis, the review focuses on the direct modulation of the misfolded proteins and presents recent discoveries in small molecules and peptides that inhibit SOD1 and TDP-43 aggregation, underscoring their potential as effective treatments to modify disease progression and improve clinical outcomes.

Unsupervised machine learning identifies distinct ALS molecular subtypes in post-mortem motor cortex and blood expression data

Amyotrophic lateral sclerosis (ALS) displays considerable clinical and genetic heterogeneity. Machine learning approaches have previously been utilised for patient stratification in ALS as they can disentangle complex disease landscapes. However, lack of independent validation in different populations and tissue samples have greatly limited their use in clinical and research settings. We overcame these issues by performing hierarchical clustering on the 5000 most variably expressed autosomal genes from motor cortex expression data of people with sporadic ALS from the KCL BrainBank (N = 112). Three molecular phenotypes linked to ALS pathogenesis were identified: synaptic and neuropeptide signalling, oxidative stress and apoptosis, and neuroinflammation. Cluster validation was achieved by applying linear discriminant analysis models to cases from TargetALS US motor cortex (N = 93), as well as Italian (N = 15) and Dutch (N = 397) blood expression datasets, for which there was a high assignment probability (80-90%) for each molecular subtype. The ALS and motor cortex specificity of the expression signatures were tested by mapping KCL BrainBank controls (N = 59), and occipital cortex (N = 45) and cerebellum (N = 123) samples from TargetALS to each cluster, before constructing case-control and motor cortex-region logistic regression classifiers. We found that the signatures were not only able to distinguish people with ALS from controls (AUC 0.88 ± 0.10), but also reflect the motor cortex-based disease process, as there was perfect discrimination between motor cortex and the other brain regions. Cell types known to be involved in the biological processes of each molecular phenotype were found in higher proportions, reinforcing their biological interpretation. Phenotype analysis revealed distinct cluster-related outcomes in both motor cortex datasets, relating to disease onset and progression-related measures. Our results support the hypothesis that different mechanisms underpin ALS pathogenesis in subgroups of patients and demonstrate potential for the development of personalised treatment approaches. Our method is available for the scientific and clinical community at https://alsgeclustering.er.kcl.ac.uk .

Role of Oxidative Stress on the Etiology and Pathophysiology of Amyotrophic Lateral Sclerosis (ALS) and Its Relation with the Enteric Nervous System

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting motor neurons in the spinal cord, cerebral cortex, and medulla oblongata. Most patients present a clinical phenotype of classic ALS-with predominant atrophy, muscle weakness, and fasciculations-and survival of 3 to 5 years following diagnosis. In the present review, we performed a literature search to provide an update on the etiology and pathophysiological mechanisms involved in ALS. There are two types of ALS: the familial form with genetic involvement, and the sporadic form with a multifactorial origin. ALS pathophysiology is characterized by involvement of multiple processes, including oxidative stress, glutamate excitotoxicity, and neuroinflammation. Moreover, it is proposed that conditioning risk factors affect ALS development, such as susceptibility to neurodegeneration in motor neurons, the intensity of performed physical activity, and intestinal dysbiosis with involvement of the enteric nervous system, which supports the existing theories of disease generation. To improve patients' prognosis and survival, it is necessary to further deepen our understanding of the etiopathogenesis of ALS.

Clinical heterogeneity in a family with flail arm syndrome and review of hnRNPA1-related spectrum

OBJECTIVE

Flail arm syndrome (FAS) is one of the atypical subtypes of amyotrophic lateral sclerosis (ALS). Mutations in hnRNPA1 encoding heterogeneous nuclear ribonucleoprotein (hnRNP) A1 are a rare genetic cause of ALS. Herein, marked clinical heterogeneity of FAS in a pedigree with a known hnRNPA1 variant was described to raise early awareness of the ALS variant. Furtherly, a literature review of the hnRNPA1-related spectrum was made to summarize the clinical and genetic characteristics.

METHODS

Detailed clinical evaluation, muscle pathology, and whole-exome sequencing were performed. The sequence and co-segregation of the mutation among the family members were confirmed by Sanger sequencing.

RESULTS

The great clinical variability was found in a FAS pedigree. Muscle pathology revealed a cluster distribution of angulated or rounded atrophic fibers, accompanied by significant multi-nucleus aggregation. Immunohistochemical staining showed that mutant hnRNPA1 proteins accumulated in muscle fiber cytoplasm. Exome sequencing identified a documented variant in hnRNPA1 gene c.1018C > T (p.P340S), which co-segregated with disease in the family. Besides, highly phenotypic heterogeneity was also found in other hnRNPA1-related diseases.

INTERPRETATION

We described a Chinese pedigree with hnRNPA1-related FAS, which showed significant clinical variability among the intrafamilial members. FAS is a relatively milder variant of ALS, due to the highly heterogeneous clinical spectrum, early observation is of paramount importance. In addition, the highly phenotypic heterogeneity and molecular genetic mechanism of the hnRNPA1-related spectrum are still beyond fully understood. Further, the detailed molecular mechanism underlying the clinical diversity is warranted to be explored.

Investigating the Genetic Profile of the Amyotrophic Lateral Sclerosis/Frontotemporal Dementia (ALS-FTD) Continuum in Patients of Diverse Race, Ethnicity and Ancestry

Preliminary evidence suggests that commonly used genetic tests may be less likely to identify a genetic etiology for ALS-FTD in patients of underrepresented race, ethnicity, and ancestry (REA), as compared to European REA. Patients of underrepresented REA may therefore be less likely to receive accurate and specific genetic counseling information and less likely to have access to gene-targeted therapies currently in clinical trials. We compiled outcome data from 1911 ALS-FTD patients tested at a commercial laboratory over a seven-year period for C9orf72 hexanucleotide repeat expansion (HRE) alone or C9orf72 and multigene sequencing panel testing. We compared the incidence of pathogenic (P), likely pathogenic (LP), and uncertain variants in C9orf72 and other ALS-FTD genes, as well as age at testing, in patients of different REA. The diagnostic rate in patients of European REA (377/1595, 23.64%) was significantly higher than in patients of underrepresented REA (44/316, 13.92%) (p < 0.001). Patients of European REA were more likely to have the C9orf72 HRE (21.3%) than patients of underrepresented REA (10.4%) (p < 0.001). The overall distribution of positive test outcomes in all tested genes was significantly different between the two groups, with relatively more P and LP variants in genes other than C9orf72 identified in patients of underrepresented REA. The incidence of uncertain test outcomes was not significantly different between patients of European and underrepresented REA. Patients with positive test outcomes were more likely to be younger than those with negative or uncertain outcomes. Although C9orf72 HRE assay has been advocated as the first, and in some cases, only genetic test offered to patients with ALS-FTD in the clinical setting, this practice may result in the reduced ascertainment of genetic ALS-FTD in patients of diverse REA.