Transactive response DNA-binding protein of 43 kDa (TDP-43) is an essential regulator of RNA metabolism, playing a pivotal role in splicing, transport, and stability. While its cytoplasmic aggregation is the pathological hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), recent evidence suggests that the earliest pathogenic event is the disruption of its physiological homodimeric structure. Under healthy conditions, TDP-43 forms dimers via its N-terminal domain, a configuration that is crucial for its nuclear solubility and cooperative RNA binding. In this review, we propose the "Molecular Zipper" hypothesis to describe the maintenance of TDP-43 structural homeostasis. In this framework, the N-terminal domain acts as a stabilizing "NTD-mediated anchor" that keeps the protein in a functional, "zipped" dimeric state, effectively sequestering its aggregation-prone C-terminal regions. Pathogenic triggers-including genetic mutations, aberrant post-translational modifications such as phosphorylation and acetylation, and environmental stressors-can "unzip" this structure, leading to the formation of pathogenic monomers. These pathogenic monomers show increased propensity for cytoplasmic mislocalization and recruit wild-type protein into aggregates through a prion-like seeded aggregation mechanism, culminating in nuclear functional loss and cytoplasmic gain-of-toxicity. We further evaluate the emerging diagnostic landscape, focusing on methods to monitor the dimer-to-monomer ratio. Integrating prior biochemical data on TDP-43 dimerization with structural modeling enables a more coherent account of the transition from the physiological dimer to pathological conformers. The Molecular Zipper framework offers a conceptual foundation for reconciling existing experimental findings and for guiding future studies on early structural changes in TDP-43 proteinopathy.
Frontotemporal dementia is a neurodegenerative disorder with a strong heritable component. Frontotemporal lobar degeneration refers to the pathological changes seen in frontotemporal dementia, characterized by atrophy of the frontal and temporal lobes and the presence of abnormal protein inclusions. In the case of frontotemporal lobar degeneration with hyperphosphorylated TDP-43 positive inclusions (FTLD-TDP), five pathological subtypes (A, B, C, D and E) are observed based on the types and distribution of inclusions found in the brain. In all subtypes, there tends to be a large variability in the number of pathological inclusions observed between cases, with limited correlation to clinical manifestations. TDP-43 is an RNA-binding protein belonging to the heterogeneous nuclear ribonucleoprotein (hnRNP) family, which along with other hnRNPs, modulates multiple aspects of RNA processing. HnRNPs other than TDP-43 have been implicated in several neurological diseases, including Amyotrophic Lateral Sclerosis, FTLD-TDP, frontotemporal lobar degeneration with fused in sarcoma (FTLD-FUS) and Alzheimer's disease. Multiple hnRNPs have been found in pathological inclusions in specific subtypes of FTLD-TDP, suggesting potential roles in the disease process. The role of the hnRNP network in frontotemporal lobar degeneration disease pathogenesis, however, has not yet been investigated. This study aimed to comprehensively evaluate the presence and expression of hnRNP proteins in two pathological subtypes of sporadic FTLD-TDP (A and C) as well as the genetic form FTLD-TDP A C9orf72 using immunohistochemistry and gene expression analysis by single-nuclei RNA-sequencing. We found that there was great variability in the frequency of TDP-43 pathology across and within FTLD-TDP pathological subtypes. Our findings suggest that distinct global transcriptomic profiles may underlie the different pathological subtypes of FTLD-TDP. The most prominent transcriptomic changes were observed in oligodendrocytes and astrocytes, involving multiple hnRNPs across frontotemporal lobar degeneration subtypes compared to controls. Transcriptomic co-expression analysis further revealed that glial clusters were more strongly associated with RNA-processing dysfunction and contributed to disease classification. Together, these findings highlight the involvement of the hnRNP network and glial-specific RNA-processing alterations in FTLD-TDP pathophysiology, offering new insight into the molecular distinctions between pathological subtypes and potential targets for future investigation.
Most individuals with amyotrophic lateral sclerosis (ALS) develop bulbar impairment as their disease progresses. The ALS Functional Rating Scale-Revised (ALSFRS-R) bulbar subscore and neurological examination of upper (UMN) and lower motor neurons (LMN) are routinely used to assess this dysfunction but have inherent limitations. Speech‑derived measures have shown promise for capturing bulbar decline with greater sensitivity, but their neurobiological correlates remain unclear. This study examined the associations between quantitative speech measures and cortical thinning in ALS. Data from the Canadian ALS Neuroimaging Consortium were analyzed. Speech measures were extracted from audio recordings of the standardized "Bamboo Passage". Cortical thickness was calculated from T1‑weighted MRI scans. General linear models first compared cortical thickness between patients with ALS and healthy controls. Associations between the speech measures and cortical thickness were then assessed within the ALS group. Patients with ALS showed cortical thinning across bilateral frontotemporal regions, with the largest clusters in the bilateral motor cortices. Reduced speaking and articulation rates were associated with thinning in both oral motor cortices. In contrast, the ALSFRS-R bulbar subscore and UMN and LMN bulbar burden showed no significant associations. Measures of pausing behavior were negatively associated with frontal cortical regions. Thinning of the oral motor cortex in ALS was linked to reduced oral motor function, supporting speaking and articulation rate as sensitive markers of bulbar motor neuron degeneration. These measures demonstrated neuroanatomical associations that the ALSFRS-R bulbar subscore and neurological examination findings did not, highlighting their potential value for monitoring bulbar dysfunction in ALS.
Primary lateral sclerosis (PLS) is a low incidence motor neuron disease manifesting in progressive limb spasticity, gait impairment, bulbar dysfunction and often in pseudobulbar affect. Varying degree of frontotemporal involvement has also been recently confirmed. Postmortem data is scarce in PLS and disease burden patterns are best characterised in vivo by purpose-designed neuroimaging protocols. A large prospective neuroimaging study has been undertaken to explore cerebral involvement patterns in PLS using a both structural T1-weighted data and diffusion MRI data. Neuroimaging data were complemented by genetic screening and comprehensive clinical profiling. Brain involvement patterns have been first characterised by standard morphometric and diffusivity analyses. Resulting disease burden maps were then correlated to physiological mitochondrial density (MitoD) maps. In an additional, region-of-interest analysis, brain regions with significant topological associations between neurodegeneration and MitoD were ranked based on their r-values. Grey matter degeneration in PLS is not limited to the motor cortex, but also encompasses frontotemporal, caudate, thalamic, cerebellar and cingulate regions. Voxelwise statistics confirm topological associations between atrophy and physiological mitochondrial density. The most significant associations between neurodegeneration and MitoD were detected in the cerebellum, superior temporal lobe, precentral gyrus, inferior operculum, and orbitofrontal gyrus. Similarly, white matter degeneration is not limited to the corticospinal tracts, but includes the corpus callosum, frontotemporal association fibres, the cingulum, cerebellar peduncles, and the fornix. Anatomical associations were also detected between diffusivity alterations and focal MitoD. PLS is associated with a selective disease burden pattern, and our data suggest that brain regions with high baseline metabolic activity are more likely to succumb to neurodegeneration. Cerebral areas showing the most significant anatomical associations between atrophy and mitochondrial density (precentral gyrus, cerebellum, frontotemporal regions) are pathognomonic brain regions of PLS driving its core clinical manifestations.
People living with ALS (plwALS) and/or FTD (plwFTD) often experience cognitive and behavioural changes. However, detection can be confounded due to factors like fatigue and testing anxiety. Cumulus neuroscience developed NeuLogiq(R), a multi-modal neurocognitive platform that can be used in clinic or at home, providing an ecologically valid measure of cognition. This study examined the feasibility and usability of NeuLogiq in plwALS, plwFTD, and controls, and compared performance on gold standard neuropsychological assessments with corresponding NeuLogiq digital assessments. Over 8 months, plwALS (n = 11), plwFTD (n = 7), and matched healthy controls (n = 10) completed longitudinal full neuropsychological assessment, as well as three 25-minute NeuLogiq Platform sessions every 2 weeks in their homes. Participants adhered well to the study schedule, conducting over 32/54 sessions on average. All groups rated usability in the 'good' or 'excellent' range and had > 80% complete data. Baseline group differences were detectable on both NeuLogiq digital assessments and benchmark neuropsychological assessments of similar cognitive domains. Longitudinal mixed effects models found that the ALS group showed decline on NeuLogiq measures of emotion recognition and speech fluency. These findings suggest that the NeuLogiq platform is feasible and usable for plwALS and plwFTD, and can identify cognitive deficits to a similar extent as benchmark assessments over time.
A hexanucleotide (GGGGCC) repeat expansion in C9orf72 gene represents the most frequent genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), resulting in reduced C9orf72 mRNA and protein expression. C9orf72 is highly expressed in the cerebellum and growing evidence implicates C9orf72-associated cerebellar pathology across neurodegenerative disorders including ALS/FTD, yet the pathogenic mechanisms remain unresolved. Here, we demonstrate in vivo C9orf72 loss of function leads to cerebellar atrophy, loss of GABAergic interneurons, and depletion of Purkinje and Granule cells. Additionally, we demonstrate that these cerebellar anomalies precede motor defects. Single-cell transcriptomics of the C9orf72-zebrafish brain revealed the downregulation of a purine biosynthetic gene paics in Purkinje cells. Furthermore, we demonstrate the reduced expression of PAICS in the human post-mortem cerebellar sections and iPSC-derived motor neurons from C9orf72 and sporadic ALS patients. Knockout of paics in zebrafish recapitulates cerebellar neuronal loss, neuromuscular junction disruption, motor impairment and widespread DNA damage and repair (DDR) defects including suppression of key DNA repair pathways. Restoring paics expression in C9orf72 zebrafish resolves DNA damage and preserves Purkinje cells and Granule cells, revealing PAICS as a critical mediator of cerebellar degeneration and a promising therapeutic avenue for C9orf72-associated ALS and FTD.
This study aimed at identifying neuropsychological sub-phenotypes in amyotrophic lateral sclerosis (ALS) within the mild cognitive impairment (MCI) and mild behavioral impairment (MBI) frameworks. We used individual task-/item-level data from the cognitive and behavioral sections of the Edinburgh Cognitive and Behavioral ALS Screen (ECAS) from 901 non-demented ALS to derive neuropsychological sub-phenotypes pursuant to classical MCI and MBI frameworks and in accordance with an expanded version of Strong's criteria, which also addressed memory and visuo-spatial measures. The prevalence of MCI and MBI was 39% and 37%, respectively in this retrospective review. The following MCI sub-phenotypes were identified: dysexecutive MCI-single- and multiple-domain (dMCI-sd: 63%; dMCI-md: 24%, respectively); non-dysexecutive MCI-single- and multiple-domain (ndMCI-sd: 12%; ndMCI-md: 1%, respectively). MBI was classified as follows: apathetic MBI-single- and multiple-domain (aMBI-sd: 40%; aMBI-md: 20%, respectively); apathetic-disinihibited/perseverative MBI-multiple domain (ad/pMBI-md: 21%); disinihibited/perseverative MBI-multiple domain (d/pMBI-md: 7%); psychotic MBI-single- and multiple-domain (psyMBI-sd: 2%; psyMBI-md: 3%, respectively); unclassifiable MBI-multiple domain (uMBI-md: 1%). 143 (16%) of patients exhibited mild cognitive and behavioral impairment (MCBI). This study delivers a provisional, ECAS-based classification for the neuropsychological sub-phenotyping of non-demented ALS patients, which, with further validation, might be useful for both research and clinical purposes.
Amyotrophic lateral sclerosis (ALS) is a heritable disorder where rare variants with low-to-moderate penetrance are thought to dominate genetic risk. To identify such rare variants, we harmonized and analyzed exome data from 22 cohorts, totaling 17,919 individuals with ALS and 200,703 controls across discovery and replication phases. Rare variant analyses identified several new risk genes, with replication confirming association of YKT6 and supporting HTR3C, GBGT1 and KNTC1. We also provide strong, independent validation for genes with limited previous evidence: ARPP21, DNAJC7 and CFAP410. Notably, in ARPP21, we identified a new high-effect variant (p.P747L) and confirmed that p.P563L is an ALS-associated variant leading to an aggressive disease course. Beyond new discoveries, our analyses largely recapitulated the known genetic architecture of ALS, identifying risk variants in over 20% of cases and supporting a cumulative oligogenic risk model. These findings highlight new translational targets and show that rare variant analyses capture substantially more genetic risk than common variant genome-wide association studies.
This study aimed to compare different algorithms based on the Edinburgh Cognitive and Behavioural ALS Screen (ECAS) to classify patients with amyotrophic lateral sclerosis (ALS) according to their neuropsychological phenotype to identify possible discrepancies among these systems. ECAS-Cognitive and -Carer Interview (ECAS-C/-CI) scores of N = 901 patients with ALS without a formal diagnosis of dementia were retrospectively retrieved. Patients were classified, pursuant to Strong et al.'s criteria, as cognitively and behaviourally normal (ALScbn), cognitively and/or behaviourally impaired (ALSci/bi/cbi), or Possible ALS-FTD, according the following ECAS-based algorithms: (1) Abrahams', solely addressing ECAS-C total and ALS-Specific subtotals; (2) Poletti et al.'s, addressing single task-level ECAS-C scores; (3) "Subscale", addressing ECAS-C subscales (i.e., Language, Executive, Fluency, Memory and Visuospatial). All algorithms relied on single-item-level ECAS-CI scores for behavioural classifications. Whilst agreement rates among these classifications were moderate to high (84-86%; Cohen's k = 0.78-0.81), and some discrepancies emerged: (1) "ALScbn-to-ALSci" and "ALSci-to-ALScbn" re-classifications occurred across the three comparisons, ranging from ~ 11% to ~ 24%; (2) the most classificatory disagreements (~ 43%) occurred for the ALScbi category when comparing single task-level (Poletti) to total-level (Abrahams) algorithms, with patients being re-classified as either ALSbi or Possible ALS-FTD; (3) ~ 24% of Abraham's Possible ALS-FTD cases were re-classified as either ALScbi or ALSbi by the Subscale approach. Different ECAS-based algorithms for deriving Strong's phenotypes might yield slight discrepancies that could under- or overestimate a given classification.
Frontotemporal lobar degeneration (FTLD) refers to a spectrum of neuropathology preferentially affecting the frontal and temporal lobes manifesting with progressive behavioral, language, and motor impairment. These clinical symptoms linked to FTLD are collectively referred to as frontotemporal spectrum disorders (FTSD) and include behavioral-variant frontotemporal dementia, nonfluent/agrammatic primary progressive aphasia, semantic variant primary progressive aphasia, right temporal variant frontotemporal dementia, corticobasal syndrome, progressive supranuclear palsy, and amyotrophic lateral sclerosis-frontotemporal spectrum disorders. While some patients with FTLD present with a single, well-defined syndrome, others exhibit features of multiple syndromes, and clinical phenotypes frequently evolve over time. Moreover, there is substantial phenotypic overlap between FTSD and other neurological disorders, contributing to frequent misdiagnosis and diagnostic delays. To address these challenges, we provide a practical, clinically oriented framework for the diagnosis of FTSD. We review common and nuanced clinical features, pertinent diagnostic testing, and the role of genetic testing in the context of current understanding of neuropathological correlates. Despite the absence of disease-modifying therapies, we also outline evidence-informed strategies for the symptomatic management of FTSD.
Symptoms of amyotrophic lateral sclerosis (ALS) may present as adverse events (AEs) in ALS clinical trials. Identifying anticipated AEs independent of investigational drug is crucial for trial design and required by the FDA for safety reporting and assessment in drug development. This study describes anticipated AEs and their predicted incidence in ALS trials, leveraging data from the Pooled Resource Open-Access ALS Clinical Trials (PRO-ACT) database. Placebo-treated people living with ALS (age ≥18 years, disease duration ≤36 months, ≥50% of predicted vital capacity at screening) were included. A confirmed diagnosis per the El Escorial criteria was required for a sensitivity analysis. Reported AEs were grouped based on pathophysiology and implications in clinical management and safety monitoring. AEs were further consolidated, with seven anticipated groups pre-specified for analysis. AE incidence proportions (IPs) and rates in person-years were estimated. The analysis included 1,388 participants (mean [SD] age: 56.8 [11.3] years; mean [SD] disease duration: 1.4 [0.6] years). IP was ≥5% for 24 AE groups, highest for falls and injuries (18.8%), headaches (13.5%), muscle weakness (13.1%), and gastrointestinal signs and symptoms (13.1%). Of seven pre-specified AE groups, falls, injuries, and fractures were the most frequent (23.0%), followed by severe respiratory failure and disorders including dyspnea (19.1%) and dysphagia (10.5%). Sensitivity analysis results were comparable (n = 931), although IPs were generally lower. These new findings will facilitate a systematic approach for safety monitoring and reporting in ALS trials, enable detection of true safety signals that may be obscured by these events, and support clinical development.
Clinically relevant anxiety can be detected in patients with amyotrophic lateral sclerosis (ALS), but its prevalence and determinants have not yet been fully assessed. This study aimed at assessing the prevalence and clinical underpinnings of anxiety in ALS. Non-demented ALS patients (N = 433) and healthy controls (N = 313) were administered the State- and Trait-Anxiety Inventory - Form Y (STAI-Y1 for state-anxiety and STAI-Y2 for trait-anxiety) and the Beck Depression Inventory (BDI). Patients were further assessed for cognition (Edinburgh Cognitive and Behavioural ALS Screen), behaviour (Frontal Behavioural Inventory) and motor status (disease duration, ALS Functional Rating Scale-Revised and progression rate). The prevalence of clinically significant state- and trait-anxiety were estimated by applying age-stratified cut-offs to STAI-Y1/-Y2 t-scores. Linear and logistic regressions were run to test the determinants of STAI-Y1/-Y2 scores. STAI-Y1 and -Y2 scores above cut-off were detected in 18.2 and 13.9% of patients, respectively - with proportions being higher in cases versus controls (ps < 0.001). BDI, but neither cognitive/behavioural nor motor variables, was identified as a significant predictor of STAI-Y1/-Y2 scores (ps < 0.003). The cognitive-affective subscale of BDI was the sole predictor of scores above cut-off on both STAI-Y1 and STAI-Y2 (ps < 0.001). Clinically significant levels of state- and trait-anxiety occur in ∼18 and ∼14% of non-demented ALS patients, respectively, mostly driven by cognitive and affective facets of depression, and are independent of motor and cognitive/behavioural features.
There are no FDA-approved diagnostic biomarkers for amyotrophic lateral sclerosis (ALS). TDP-43 is a known cofactor in the cleavage of long premature microRNAs (miRNAs) into their short, mature products. isomiRs are miRNA variants that differ in their 5' and 3' end points and regulate distinct mRNA targets. In this study, we tested the hypotheses that circulating isomiR profiles differ in the context of TAR DNA-binding Protein pathology and that isomiRs are superior to miRNAs for classification of ALS. We obtained RNA from plasma samples of 14 patients with ALS and 14 age-matched and sex-matched controls for sequencing on a NextSeq 2000. Data were processed using Unique Molecular Identifier tools and a custom pipeline designed to match miRNA variant sequences without mismatches. Differential expression (DE) was identified using DEseq2 at FDR ≤ 0.1. XGBoost classifiers were built using a subset of (Model 1) isomiRs or (Model 2) miRNAs that were present above a median threshold in all sequencing batches. Parameters were tuned using grid search and 10-fold cross-validation while training to distinguish ALS samples from controls among a single large public data set. Models were then validated on in-house samples and 1 publicly available holdout data set. Fourteen (0.2%), 355 (2.7%), and 14 (0.7%) isomiRs were differentially expressed in in-house plasma, public ALS plasma, and public ALS serum, respectively. One (0.1%), 94 (5.5%), and 13 (2.4%) miRNAs were differentially expressed, respectively. Model 1 accurately classified in-house ALS plasma and public ALS serum (area under the curve [AUC] = 0.87) and did not distinguish 40 of 41 Alzheimer disease samples from control plasma (GSE215789; AUC = 0.47) or 60 of 77 Parkinson disease samples from control whole blood (GSE180193; AUC = 0.55). In comparison, Model 2 using miRNAs performed worse on in-house plasma (AUC = 0.49). Analyzing individual isomiRs may improve the performance of circulating noncoding RNAs as diagnostic biomarkers of ALS.
The temporal sequence of clinical, imaging, and biological changes in sporadic frontotemporal lobar degeneration (FTLD)-associated syndromes remains poorly characterized, and a comprehensive biomarker cascade model is lacking. We developed a data-driven biomarker cascade model in 489 patients across the FTLD spectrum (211 behaviorial variant frontotemporal dementia [bvFTD], 129 primary progressive aphasia [PPA], 71 corticobasal syndrome [CBS], 66 progressive supranuclear palsy [PSP], and 12 FTD associated with amyotrophic lateral sclerosis [FTD-ALS]; 1904 patient-visit observations). Plasma, magnetic resonance imaging (MRI), and clinical biomarkers were modeled using sigmoid trajectories fitted to covariate-adjusted longitudinal data. Plasma glial fibrillary acidic protein departed from normality earliest, followed by Trail Making Test Part B (TMT-B), white matter lesion volume, and neurofilament light chain. Insular atrophy showed the steepest transition among MRI measures; clinical dementia rating dementia staging instrument plus National Alzheimer's Coordinating Center behavior and language domains sum of boxes declined most steeply overall. TMT-B inflected earliest in bvFTD, whereas insula atrophy dominated in PPA. This first data-driven temporal cascade of multimodal biomarkers in sporadic FTLD-associated syndromes offers a framework for disease staging and stage-specific clinical trial design.
We report an autopsy case of frontotemporal lobar degeneration (FTLD)-TDP type C with severe striatal involvement and annexin A11- and phosphorylated TDP-43-positive glial cytoplasmic inclusions. The patient developed progressive asymmetric rigidity accompanied by marked striatal atrophy and showed both upper and lower motor neuron involvement. These findings expand the clinicopathological spectrum of FTLD-TDP type C and may support the concept of an annexin A11-associated pathogenic continuum linking FTLD and amyotrophic lateral sclerosis.
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Astrocytes have traditionally been cast as supportive glia, but they are increasingly recognized as metabolic hubs that regulate cholesterol synthesis, fatty acid detoxification, lipid droplet dynamics and redox homeostasis in the CNS. Neurons have a limited intrinsic capacity for lipid storage and detoxification and rely heavily on astrocytes to maintain a safe lipid environment. Emerging evidence indicates that dysregulation of astrocytic lipid homeostasis precedes overt neuronal degeneration in a range of neurodegenerative diseases, including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, frontotemporal dementia and Huntington disease. Perturbations in astrocytic lipid handling can drive maladaptive reactive states, promote oxidative stress, impair lysosomal and mitochondrial function and disrupt neuron-glia lipid exchange, collectively creating an environment that leads to neurodegeneration. Therefore, lipid dysregulation within astrocytes could trigger or amplify neuronal vulnerability. In this Review, we assess evidence that astrocytic lipid metabolism is not solely protective or pathological but has instructive physiological roles and that astrocytic lipid dysregulation is an early driver of neurodegeneration. We critically evaluate disease-specific evidence, distinguishing correlative observations from causal mechanisms. We propose that targeting of astrocytic lipid homeostasis represents a promising strategy for preventing or minimizing neurodegeneration and opens new avenues for early detection and biomarker development.
Annexin A11 (ANXA11) is a Ca2⁺-dependent phospholipid-binding protein that has recently emerged as a key player in neurodegeneration. Rare pathogenic ANXA11 variants were initially identified in cases of amyotrophic lateral sclerosis (ALS). Since then, ANXA11 has been linked to a broader spectrum of related neurodegenerative diseases. Two independent studies demonstrated that ANXA11 co-aggregates with TDP-43 in all cases of frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP) type C, with cryo-EM revealing heteromeric ANXA11-TDP-43 filaments. These discoveries support the direct pathological interaction between the two proteins as an important feature of FTLD-TDP type C. We also described secondary ANXA11 pathology in related neurodegenerative diseases, including limbic-predominant age-related TDP-43 encephalopathy (LATE), and more rarely in ALS and FTLD-TDP types A and B. ANXA11 and TDP-43 co-aggregates are also a feature of a FTLD-TDP associated with primary lateral sclerosis. These advances have renewed interest in ANXA11 as a major player in ALS/FTLD pathogenesis in both genetic and sporadic neurodegenerative diseases. In this review, we summarize ANXA11 pathology across genetic and sporadic cases, highlighting its heterogeneous overlap with TDP-43 pathology. We synthesize current knowledge of ANXA11's physiological roles in phase separation, membrane repair, and RNA granule dynamics, integrating emerging evidence on how disruption of these processes may promote pathological aggregation and toxicity. Finally, we outline priorities for future research, with particular emphasis on elucidating ANXA11's mechanistic connection to TDP-43.
Neurodegenerative diseases are characterized by protein misfolding and the selective vulnerability of specific neuronal subtypes. This selective vulnerability presents a paradox; most neurodegenerative disease genes are expressed broadly throughout the brain, and some ubiquitously, but only certain types of neurons are lost while others are resistant. The molecular basis for selective neuronal vulnerability has remained a mystery, but recent genomics technological innovations are starting to provide mechanistic insights. Here, we review how single-cell genomics techniques - single-cell transcriptomics, single-cell epigenomics, and spatial transcriptomics - advance our molecular understanding of selective vulnerability and neurodegeneration across Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, frontotemporal dementia, and Huntington disease. Together, these approaches reveal the cell types affected in disease, define disease-associated molecular states, nominate candidate determinants of vulnerability and degeneration, and situate degenerating neurons within their local tissue context. Continued development and application of these techniques, including single-cell perturbation screens, will expand descriptive atlases of relevant cell types in health and disease and identify causal mechanisms, revealing the molecular basis of vulnerability and degeneration and informing therapeutic development.
Although mutations in many genes cause familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), most cases are sporadic (sALS and sFTD) with unclear etiology. Here we tested whether somatic mutations contribute to sALS and sFTD by deep targeted sequencing of 88 neurodegeneration-related genes in postmortem brain and spinal cord samples from 399 sporadic cases and 144 controls. Predicted deleterious somatic variants in ALS/FTD genes were observed in 2.1% of sporadic cases lacking deleterious germline variants. These variants occurred at very low allele fractions (typically <2%) and were often focal and enriched in disease-affected regions. Analysis of bulk RNA-sequencing data from an additional cohort identified deleterious somatic variants in DYNC1H1 and LMNA, genes associated with pediatric motor neuron degeneration. Targeted long-read sequencing further identified one sFTD case with de novo somatic C9orf72 repeat expansions. Together, these findings suggest that rare, focal somatic variants can contribute to sALS and sFTD and drive widespread neurodegeneration.