Loss of GDE2 leads to complex behavioral changes including memory impairment.

BACKGROUND: Alzheimer's disease (AD) and amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) are debilitating neurodegenerative diseases for which there are currently no cures. Familial cases with known genetic causes make up less than 10% of these diseases, and little is known about the underlying mechanisms that contribute to sporadic disease. Accordingly, it is important to expand investigations into possible pathways that may contribute to disease pathophysiology. Glycerophosphodiester phosphodiesterase 2 (GDE2 or GDPD5) is a membrane-bound enzyme that acts at the cell surface to cleave the glycosylphosphatidylinositol (GPI)-anchor that tethers distinct proteins to the membrane. GDE2 abnormally accumulates in intracellular compartments in the brain of patients with AD, ALS, and ALS/FTD, indicative of GDE2 dysfunction. Mice lacking GDE2 (Gde2KO) show neurodegenerative changes such as neuronal loss, reduced synaptic proteins and synapse loss, and increased Aß deposition, raising the possibility that GDE2 disruption in disease might contribute to disease pathophysiology. However, the effect of GDE2 loss on behavioral function and learning/memory has not been characterized. RESULTS: Here, we show that GDE2 is expressed throughout the adult mouse brain in areas including the cortex, hippocampus, habenula, thalamus, and amygdala. Gde2KO and WT mice were tested in a set of behavioral tasks between 7 and 16 months of age. Compared to WT, Gde2KO mice display moderate hyperactivity that becomes more pronounced with age across a variety of behavioral tests assessing novelty-induced exploratory activity. Additionally, Gde2KO mice show reduced startle response, with females showing additional defects in prepulse inhibition. No changes in anxiety-associated behaviors were found, but Gde2KOs show reduced sociability. Notably, aged Gde2KO mice demonstrate impaired short/long-term spatial memory and cued fear memory/secondary contextual fear acquisition. CONCLUSIONS: Taken together, these observations suggest that loss of GDE2 leads to behavioral deficits, some of which are seen in neurodegenerative disease models, implying that loss of GDE2 may be an important contributor to phenotypes associated with neurodegeneration.

14-3-3θ, a novel player in TDP-43 pathophysiology: Implications for ALS/FTD.

In this issue of Neuron, Ke et al.1 report a novel non-canonical interaction between 14-3-3θ and TDP-43 that impacts loss-of-function and gain-of-toxic pathology in TDP-43 proteinopathies. The authors further provide proof of principle for a 14-3-3θ-targeted gene therapy to reduce TDP-43-induced deficits in transgenic TDP-43 mutant mice.

Epigenetic modulation through BET bromodomain inhibitors as a novel therapeutic strategy for progranulin-deficient frontotemporal dementia.

Frontotemporal dementia (FTD) is a debilitating neurodegenerative disorder with currently no disease-modifying treatment options available. Mutations in GRN are one of the most common genetic causes of FTD, near ubiquitously resulting in progranulin (PGRN) haploinsufficiency. Small molecules that can restore PGRN protein to healthy levels in individuals bearing a heterozygous GRN mutation may thus have therapeutic value. Here, we show that epigenetic modulation through bromodomain and extra-terminal domain (BET) inhibitors (BETi) potently enhance PGRN protein levels, both intracellularly and secreted forms, in human central nervous system (CNS)-relevant cell types, including in microglia-like cells. In terms of potential for disease modification, we show BETi treatment effectively restores PGRN levels in neural cells with a GRN mutation known to cause PGRN haploinsufficiency and FTD. We demonstrate that BETi can rapidly and durably enhance PGRN in neural progenitor cells (NPCs) in a manner dependent upon BET protein expression, suggesting a gain-of-function mechanism. We further describe a CNS-optimized BETi chemotype that potently engages endogenous BRD4 and enhances PGRN expression in neuronal cells. Our results reveal a new epigenetic target for treating PGRN-deficient forms of FTD and provide mechanistic insight to aid in translating this discovery into therapeutics.

A TBK1 variant causes autophagolysosomal and motoneuron pathology without neuroinflammation in mice.

Heterozygous mutations in the TBK1 gene can cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The majority of TBK1-ALS/FTD patients carry deleterious loss-of-expression mutations, and it is still unclear which TBK1 function leads to neurodegeneration. We investigated the impact of the pathogenic TBK1 missense variant p.E696K, which does not abolish protein expression, but leads to a selective loss of TBK1 binding to the autophagy adaptor protein and TBK1 substrate optineurin. Using organelle-specific proteomics, we found that in a knock-in mouse model and human iPSC-derived motor neurons, the p.E696K mutation causes presymptomatic onset of autophagolysosomal dysfunction in neurons precipitating the accumulation of damaged lysosomes. This is followed by a progressive, age-dependent motor neuron disease. Contrary to the phenotype of mice with full Tbk1 knock-out, RIPK/TNF-α-dependent hepatic, neuronal necroptosis, and overt autoinflammation were not detected. Our in vivo results indicate autophagolysosomal dysfunction as a trigger for neurodegeneration and a promising therapeutic target in TBK1-ALS/FTD.

Bone scan findings of Paget's disease of bone in patients with VCP Multisystem Proteinopathy 1.

Multisystem Proteinopathy 1 (MSP1) disease is a rare genetic disorder caused by mutations in the Valosin-Containing Protein (VCP) gene with clinical features of inclusion body myopathy (IBM), frontotemporal dementia (FTD), and Paget's disease of bone (PDB). We performed bone scan imaging in twelve patients (6 females, 6 males) with confirmed VCP gene mutation six (50%) of which has myopathy alone, four (33%) with both PDB and myopathy, and two (15%) were presymptomatic carriers. We aim to characterize the PDB in diagnosed individuals, and potentially identify PDB in the myopathy and presymptomatic groups. Interestingly, two patients with previously undiagnosed PDB had positive diagnostic findings on the bone scan and subsequent radiograph imaging. Among the individuals with PDB, increased radiotracer uptake of the affected bones were of typical distribution as seen in conventional PDB and those reported in other MSP1 cohorts which are the thoracic spine and ribs (75%), pelvis (75%), shoulder (75%) and calvarium (15%). Overall, we show that technetium-99m bone scans done at regular intervals are a sensitive screening tool in patients with MSP1 associated VCP variants at risk for PDB. However, diagnostic confirmation should be coupled with clinical history, biochemical analysis, and skeletal radiographs to facilitate early treatment and prevention complications, acknowledging its limited specificity.

Pathogenic mutations in UBQLN2 exhibit diverse aggregation propensity and neurotoxicity.

The ubiquitin-adaptor protein UBQLN2 promotes degradation of several aggregate-prone proteins implicated in neurodegenerative diseases. Missense UBQLN2 mutations also cause X-linked amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Previously we demonstrated that the liquid-like properties of UBQLN2 molecular assemblies are altered by a specific pathogenic mutation, P506T, and that the propensity of UBQLN2 to aggregate correlated with neurotoxicity. Here, we systematically assess the effects of multiple, spatially distinct ALS/FTD-linked missense mutations on UBQLN2 aggregation propensity, neurotoxicity, phase separation, and autophagic flux. In contrast to what we observed for the P506T mutation, no other tested pathogenic mutant exhibited a clear correlation between aggregation propensity and neurotoxicity. These results emphasize the unique nature of pathogenic UBQLN2 mutations and argue against a generalizable link between aggregation propensity and neurodegeneration in UBQLN2-linked ALS/FTD.

Neuronal STING activation in amyotrophic lateral sclerosis and frontotemporal dementia.

The stimulator of interferon genes (STING) pathway has been implicated in neurodegenerative diseases, including Parkinson's disease and amyotrophic lateral sclerosis (ALS). While prior studies have focused on STING within immune cells, little is known about STING within neurons. Here, we document neuronal activation of the STING pathway in human postmortem cortical and spinal motor neurons from individuals affected by familial or sporadic ALS. This process takes place selectively in the most vulnerable cortical and spinal motor neurons but not in neurons that are less affected by the disease. Concordant STING activation in layer V cortical motor neurons occurs in a mouse model of C9orf72 repeat-associated ALS and frontotemporal dementia (FTD). To establish that STING activation occurs in a neuron-autonomous manner, we demonstrate the integrity of the STING signaling pathway, including both upstream activators and downstream innate immune response effectors, in dissociated mouse cortical neurons and neurons derived from control human induced pluripotent stem cells (iPSCs). Human iPSC-derived neurons harboring different familial ALS-causing mutations exhibit increased STING signaling with DNA damage as a main driver. The elevated downstream inflammatory markers present in ALS iPSC-derived neurons can be suppressed with a STING inhibitor. Our results reveal an immunophenotype that consists of innate immune signaling driven by the STING pathway and occurs specifically within vulnerable neurons in ALS/FTD.

The Chronic Effects of a Single Low-Intensity Blast Exposure on Phosphoproteome Networks and Cognitive Function Influenced by Mutant Tau Overexpression.

Blast-induced neurotrauma (BINT) is a pressing concern for veterans and civilians exposed to explosive devices. Affected personnel may have increased risk for long-term cognitive decline and developing tauopathies including Alzheimer's disease-related disorders (ADRD) or frontal-temporal dementia (FTD). The goal of this study was to identify the effect of BINT on molecular networks and their modulation by mutant tau in transgenic (Tg) mice overexpressing the human tau P301L mutation (rTg4510) linked to FTD or non-carriers. The primary focus was on the phosphoproteome because of the prominent role of hyperphosphorylation in neurological disorders. Discrimination learning was assessed following injury in the subsequent 6 weeks, using the automated home-cage monitoring CognitionWall platform. At 40 days post injury, label-free phosphoproteomics was used to evaluate molecular networks in the frontal cortex of mice. Utilizing a weighted peptide co-expression network analysis (WpCNA) approach, we identified phosphopeptide networks tied to associative learning and mossy-fiber pathways and those which predicted learning outcomes. Phosphorylation levels in these networks were inversely related to learning and linked to synaptic dysfunction, cognitive decline, and dementia including Atp6v1a and Itsn1. Low-intensity blast (LIB) selectively increased pSer262tau in rTg4510, a site implicated in initiating tauopathy. Additionally, individual and group level analyses identified the Arhgap33 phosphopeptide as an indicator of BINT-induced cognitive impairment predominantly in rTg4510 mice. This study unveils novel interactions between ADRD genetic susceptibility, BINT, and cognitive decline, thus identifying dysregulated pathways as targets in potential precision-medicine focused therapeutics to alleviate the disease burden among those affected by BINT.

Single-cell dissection of the human motor and prefrontal cortices in ALS and FTLD.

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) share many clinical, pathological, and genetic features, but a detailed understanding of their associated transcriptional alterations across vulnerable cortical cell types is lacking. Here, we report a high-resolution, comparative single-cell molecular atlas of the human primary motor and dorsolateral prefrontal cortices and their transcriptional alterations in sporadic and familial ALS and FTLD. By integrating transcriptional and genetic information, we identify known and previously unidentified vulnerable populations in cortical layer 5 and show that ALS- and FTLD-implicated motor and spindle neurons possess a virtually indistinguishable molecular identity. We implicate potential disease mechanisms affecting these cell types as well as non-neuronal drivers of pathogenesis. Finally, we show that neuron loss in cortical layer 5 tracks more closely with transcriptional identity rather than cellular morphology and extends beyond previously reported vulnerable cell types.

The relationship between major depressive disorder and dementia: A bidirectional two-sample Mendelian randomization study.

BACKGROUND: Major depressive disorder (MDD) and dementia psychiatric and neurological diseases that are clinically widespread, but whether there is a causal link between them is still unclear. In this study, bidirectional two-sample Mendelian randomization (MR) was used to investigate the potential causal relationship between MDD and dementia via a genome-wide association study (GWAS) database, containing samples from the European population. METHOD: We collected data on MDD and common clinical dementia subtypes from GWAS, including Alzheimer's disease (AD), frontotemporal dementia (FTD), dementia with Lewy bodies (DLB), Parkinson's disease with dementia (PDD), and vascular dementia (VaD). A series of bidirectional two-sample MR studies and correlation sensitivity analysis were carried out. RESULTS: In the study of the effect of MDD on dementia subtypes, no causal relationship was found between MDD and dementia subtypes other than VaD, inverse variance weighted (IVW) method: odds ratio (OR), 2.131; 95 % confidence interval (CI), 1.249-3.639, P = 0.006; MDD-AD: OR, 1.000; 95 % CI, 0.999-1.001, P = 0.537; MDD-FTD: OR, 1.476; 95 % CI, 0.471-4.627, P = 0.505; MDD-PDD: OR, 0.592; 95 % CI, 0.204-1.718, P = 0.335; MR-Egger method: MDD-DLB: OR, 0.582; 95 % CI, 0.021-15.962, P = 0.751. In reverse MR analyses, no dementia subtype was found to be a risk factor for MDD. LIMITATIONS: The results of this study may not be generalizable to non-European populations. CONCLUSION: MDD was identified as a potential risk factor for VaD, but no dementia subtype was found to be a risk factor for MDD. These results suggest a new avenue for the prevention of VaD.

Progress in Primary Progressive Aphasia: A Review.

We present a review of the definition, classification, and epidemiology of primary progressive aphasia (PPA); an update of the taxonomy of the clinical syndrome of PPA; and recent advances in the neuroanatomy, pathology, and genetics of PPA, as well as the search for biomarkers and treatment. PPA studies that have contributed to concepts of language organization and disease propagation in neurodegeneration are also reviewed. In addition, the issues of heterogeneity versus the relationships of the clinical phenotypes and their relationship to biological, pathological, and genetic advances are discussed, as is PPA's relationship to other conditions such as frontotemporal dementia, corticobasal degeneration, progressive supranuclear palsy, Pick disease, and amyotrophic lateral sclerosis. Arguments are presented in favor of considering these conditions as one entity versus many.

The nuclear import receptor Kapß2 modifies neurotoxicity mediated by poly(GR) in C9orf72-linked ALS/FTD.

Expanded intronic G4C2 repeats in the C9ORF72 gene cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). These intronic repeats are translated through a non-AUG-dependent mechanism into five different dipeptide repeat proteins (DPRs), including poly-glycine-arginine (GR), which is aggregation-prone and neurotoxic. Here, we report that Kapß2 and GR interact, co-aggregating, in cultured neurons in-vitro and CNS tissue in-vivo. Importantly, this interaction significantly decreased the risk of death of cultured GR-expressing neurons. Downregulation of Kapß2 is detrimental to their survival, whereas increased Kapß2 levels mitigated GR-mediated neurotoxicity. As expected, GR-expressing neurons displayed TDP-43 nuclear loss. Raising Kapß2 levels did not restore TDP-43 into the nucleus, nor did alter the dynamic properties of GR aggregates. Overall, our findings support the design of therapeutic strategies aimed at up-regulating Kapß2 expression levels as a potential new avenue for contrasting neurodegeneration in C9orf72-ALS/FTD.

Loss of TMEM106B exacerbates Tau pathology and neurodegeneration in PS19 mice.

TMEM106B, a gene encoding a lysosome membrane protein, is tightly associated with brain aging, hypomyelinating leukodystrophy, and multiple neurodegenerative diseases, including frontotemporal lobar degeneration with TDP-43 aggregates (FTLD-TDP). Recently, TMEM106B polymorphisms have been associated with tauopathy in chronic traumatic encephalopathy (CTE) and FTLD-TDP patients. However, how TMEM106B influences Tau pathology and its associated neurodegeneration, is unclear. Here we show that loss of TMEM106B enhances the accumulation of pathological Tau, especially in the neuronal soma in the hippocampus, resulting in severe neuronal loss in the PS19 Tau transgenic mice. Moreover, Tmem106b-/- PS19 mice develop significantly increased abnormalities in the neuronal cytoskeleton, autophagy-lysosome activities, as well as glial activation, compared with PS19 and Tmem106b-/- mice. Together, our findings demonstrate that loss of TMEM106B drastically exacerbates Tau pathology and its associated disease phenotypes, and provide new insights into the roles of TMEM106B in neurodegenerative diseases.

Neuromuscular organoids model spinal neuromuscular pathologies in C9orf72 amyotrophic lateral sclerosis.

Hexanucleotide repeat expansions in the C9orf72 gene are the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Due to the lack of trunk neuromuscular organoids (NMOs) from ALS patients' induced pluripotent stem cells (iPSCs), an organoid system was missing to model the trunk spinal neuromuscular neurodegeneration. With the C9orf72 ALS patient-derived iPSCs and isogenic controls, we used an NMO system containing trunk spinal cord neural and peripheral muscular tissues to show that the ALS NMOs could model peripheral defects in ALS, including contraction weakness, neural denervation, and loss of Schwann cells. The neurons and astrocytes in ALS NMOs manifested the RNA foci and dipeptide repeat proteins. Acute treatment with the unfolded protein response inhibitor GSK2606414 increased the glutamatergic muscular contraction 2-fold and reduced the dipeptide repeat protein aggregation and autophagy. This study provides an organoid system for spinal neuromuscular pathologies in ALS and its application for drug testing.

Detecting and Validating MAPT Mutations in Neurodegeneration Patients and Analysis of Exon Splicing Consequences.

Mutation of MAPT has been observed in patients with parkinsonism, progressive supranuclear palsy, and corticobasal degeneration and is a significant cause of frontotemporal dementia. In this chapter, we discuss considerations for next-generation sequencing analysis to identify MAPT mutations in patient genomic DNA and describe the validation of these mutations by Sanger sequencing. One of the most common effects of MAPT mutations is differential splicing of exon 10, which leads to an imbalance in the proportion of 3-repeat and 4-repeat tau isoforms. We describe how to investigate the effect of novel DNA variants on the splicing efficiency of this exon in vitro using the exon-trapping technique, also known as the splicing reporter minigene assay.

Mutations in human prion-like domains: pathogenic but not always amyloidogenic.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are multifunctional proteins with integral roles in RNA metabolism and the regulation of alternative splicing. These proteins typically contain prion-like domains of low complexity (PrLDs or LCDs) that govern their assembly into either functional or pathological amyloid fibrils. To date, over 60 mutations targeting the LCDs of hnRNPs have been identified and associated with a spectrum of neurodegenerative diseases including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer's disease (AD). The cryo-EM structures of pathological and functional fibrils formed by different hnRNPs have been recently elucidated, including those of hnRNPA1, hnRNPA2, hnRNPDL-2, TDP-43, and FUS. In this review, we discuss the structural features of these amyloid assemblies, placing particular emphasis on scrutinizing the impact of prevalent disease-associated mutations mapping within their LCDs. By performing systematic energy calculations, we reveal a prevailing trend of destabilizing effects induced by these mutations in the amyloid structure, challenging the traditionally assumed correlation between pathogenicity and amyloidogenic propensity. Understanding the molecular basis of this discrepancy might provide insights for developing targeted therapeutic strategies to combat hnRNP-associated diseases.

A systematic review of progranulin concentrations in biofluids in over 7,000 people-assessing the pathogenicity of GRN mutations and other influencing factors.

BACKGROUND: Pathogenic heterozygous mutations in the progranulin gene (GRN) are a key cause of frontotemporal dementia (FTD), leading to significantly reduced biofluid concentrations of the progranulin protein (PGRN). This has led to a number of ongoing therapeutic trials aiming to treat this form of FTD by increasing PGRN levels in mutation carriers. However, we currently lack a complete understanding of factors that affect PGRN levels and potential variation in measurement methods. Here, we aimed to address this gap in knowledge by systematically reviewing published literature on biofluid PGRN concentrations. METHODS: Published data including biofluid PGRN concentration, age, sex, diagnosis and GRN mutation were collected for 7071 individuals from 75 publications. The majority of analyses (72%) had focused on plasma PGRN concentrations, with many of these (56%) measured with a single assay type (Adipogen) and so the influence of mutation type, age at onset, sex, and diagnosis were investigated in this subset of the data. RESULTS: We established a plasma PGRN concentration cut-off between pathogenic mutation carriers and non-carriers of 74.8 ng/mL using the Adipogen assay based on 3301 individuals, with a CSF concentration cut-off of 3.43 ng/mL. Plasma PGRN concentration varied by GRN mutation type as well as by clinical diagnosis in those without a GRN mutation. Plasma PGRN concentration was significantly higher in women than men in GRN mutation carriers (p = 0.007) with a trend in non-carriers (p = 0.062), and there was a significant but weak positive correlation with age in both GRN mutation carriers and non-carriers. No significant association was seen with weight or with TMEM106B rs1990622 genotype. However, higher plasma PGRN levels were seen in those with the GRN rs5848 CC genotype in both GRN mutation carriers and non-carriers. CONCLUSIONS: These results further support the usefulness of PGRN concentration for the identification of the large majority of pathogenic mutations in the GRN gene. Furthermore, these results highlight the importance of considering additional factors, such as mutation type, sex and age when interpreting PGRN concentrations. This will be particularly important as we enter the era of trials for progranulin-associated FTD.

Understanding age-related pathologic changes in TDP-43 functions and the consequence on RNA splicing and signalling in health and disease.

TAR DNA binding protein-43 (TDP-43) is a key component in RNA splicing which plays a crucial role in the aging process. In neurodegenerative diseases such as amyotrophic lateral sclerosis, frontotemporal dementia and limbic-predominant age-related TDP-43 encephalopathy, TDP-43 can be mutated, mislocalised out of the nucleus of neurons and glial cells and form cytoplasmic inclusions. These TDP-43 alterations can lead to its RNA splicing dysregulation and contribute to mis-splicing of various types of RNA, such as mRNA, microRNA, and circular RNA. These changes can result in the generation of an altered transcriptome and proteome within cells, ultimately changing the diversity and quantity of gene products. In this review, we summarise the findings of novel atypical RNAs resulting from TDP-43 dysfunction and their potential as biomarkers or targets for therapeutic development.

Narcissistic Personality Disorder as Prodromal Feature of Early-Onset, GRN-Positive bvFTD: A Case Report.

Background: Behavioral variant frontotemporal dementia (bvFTD) typically involves subtle changes in personality that can delay a timely diagnosis. Objective: Here, we report the case of a patient diagnosed of GRN-positive bvFTD at the age of 52 presenting with a 7-year history of narcissistic personality disorder, accordingly to DSM-5 criteria. Methods: The patient was referred to neurological and neuropsychological examination. She underwent 3 Tesla magnetic resonance imaging (MRI) and genetic studies. Results: The neuropsychological examination revealed profound deficits in all cognitive domains and 3T brain MRI showed marked fronto-temporal atrophy. A mutation in the GRN gene further confirmed the diagnosis. Conclusions: The present case documents an unusual onset of bvFTD and highlights the problematic nature of the differential diagnosis between prodromal psychiatric features of the disease and primary psychiatric disorders. Early recognition and diagnosis of bvFTD can lead to appropriate management and support for patients and their families. This case highlights the importance of considering neurodegenerative diseases, such as bvFTD, in the differential diagnosis of psychiatric disorders, especially when exacerbations of behavioral traits manifest in adults.

SPTLC2 variants are associated with early-onset ALS and FTD due to aberrant sphingolipid synthesis.

OBJECTIVE: Amyotrophic lateral sclerosis (ALS) is a devastating, incurable neurodegenerative disease. A subset of ALS patients manifests with early-onset and complex clinical phenotypes. We aimed to elucidate the genetic basis of these cases to enhance our understanding of disease etiology and facilitate the development of targeted therapies. METHODS: Our research commenced with an in-depth genetic and biochemical investigation of two specific families, each with a member diagnosed with early-onset ALS (onset age of <40 years). This involved whole-exome sequencing, trio analysis, protein structure analysis, and sphingolipid measurements. Subsequently, we expanded our analysis to 62 probands with early-onset ALS and further included 440 patients with adult-onset ALS and 1163 healthy controls to assess the prevalence of identified genetic variants. RESULTS: We identified heterozygous variants in the serine palmitoyltransferase long chain base subunit 2 (SPTLC2) gene in patients with early-onset ALS. These variants, located in a region closely adjacent to ORMDL3, bear similarities to SPTLC1 variants previously implicated in early-onset ALS. Patients with ALS carrying these SPTLC2 variants displayed elevated plasma ceramide levels, indicative of increased serine palmitoyltransferase (SPT) activity leading to sphingolipid overproduction. INTERPRETATION: Our study revealed novel SPTLC2 variants in patients with early-onset ALS exhibiting frontotemporal dementia. The combination of genetic evidence and the observed elevation in plasma ceramide levels establishes a crucial link between dysregulated sphingolipid metabolism and ALS pathogenesis. These findings expand our understanding of ALS's genetic diversity and highlight the distinct roles of gene defects within SPT subunits in its development.