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Heterozygous truncating loss-of-function (LoF) variants in NEK1 are a known cause of amyotrophic lateral sclerosis (ALS). NEK1 encodes the pleiotropic serine/threonine kinase NIMA-related kinase 1, and prior in vitro studies have implicated kinase dysfunction as the principal pathogenic mechanism underlying NEK1-associated ALS. However, bona fide pathogenic missense variants causally linked to ALS have not previously been reported, leaving this hypothesis unconfirmed. Here, we identify a rare NEK1 missense variant, p.N598S, that co-segregates with disease in a familial ALS pedigree and is enriched in European ALS cohorts. This variant exhibits normal protein expression levels, indicating a functional rather than quantitative defect. Using isogenic human motor neurons, we directly compared the effects of p.N598S with those of the ALS-associated truncating variant p.R812* to delineate disease mechanisms. The p.N598S variant induced pathological phenotypes consistent with NEK1 haploinsufficiency, including increased susceptibility to DNA damage, increased apoptosis, ciliary dysmorphia, and nucleocytoplasmic translocation of TDP-43. Importantly, p.N598S impaired NEK1 kinase activity, and pharmacological inhibition of NEK1 recapitulated the cellular phenotypes observed in both p.N598S- and p.R812*-mutant motor neurons. Collectively, these findings provide strong genetic and functional evidence for a disease-causing role of NEK1 kinase disruption in NEK1-ALS. Our findings provide immediate diagnostic and therapeutic implications, particularly for the functional interpretation of missense variants of uncertain significance and the development of targeted treatment strategies.

Background: Spinobulbar muscular atrophy (SBMA) is an X-linked neuromuscular disorder characterized by adult-onset progressive muscle atrophy, flaccid paresis, and bulbar palsy. In addition, increasing evidence indicates that SBMA is a multisystem disorder with prominent non-motor symptoms, such as sensory neuropathy, androgen insensitivity, and glucose intolerance. This study aimed to further characterize the clinical manifestations and biomarker profile in a large Swedish SBMA cohort.

Methods: 49 genetically confirmed SBMA patients were identified from a motor neuron disease database at Umeå University Hospital, Sweden. CAG repeat length in the androgen receptor (AR) gene was assessed by RP-PCR. Blood samples were analyzed for cardiovascular and muscle biomarkers. Clinical data were collected from medical records and interviews, with autopsy findings reviewed in two cases.

Results: The mean CAG repeat length was 43.1, with a mean age at motor symptom onset of 58.6 years. Notably, 19% of patients initially presented with sensory symptoms. High prevalence of hypertonia (70%), diabetes mellitus (39%), and cardiac disease (38%) was observed. Elevated troponin levels were common, and pNfL (neurofilament light chain in plasma) was elevated in seven patients, likely reflecting combined cerebrovascular and cardiovascular comorbidity. Importantly, two of these seven patients exhibited rapid disease progression, and a concomitant diagnosis of ALS was confirmed histopathologically.

Discussion: This cohort was characterized by a relatively low number of AR gene CAG repeats and a late onset of motor symptoms. Sensory symptoms frequently occurred before motor decline. Cardiovascular disease and diabetes were common comorbidities and, in some cases, preceded neurological symptoms. These findings underscore the need for improved clinical awareness of the heterogeneous presentation of SBMA and support routine cardiovascular monitoring to reduce diagnostic delays and prevent early mortality.

Mutations in the antioxidant enzyme superoxide dismutase-1 (SOD1) are a well-established cause of amyotrophic lateral sclerosis (ALS). The mutations promote SOD1 misfolding, resulting in protein aggregation and motor neuron degeneration. SOD1 is normally a structurally stable enzyme, and the mechanisms underlying SOD1 misfolding remain poorly understood. Approximately one third of SOD1 in cerebrospinal fluid (CSF) exhibits an N-terminal truncation, the biological significance of which remains unclear. This is remarkable given the dramatic effects ALS-linked C-terminal truncations have on the enzyme. In this study, we identified the truncation site and investigated its impact on SOD1 stability and enzymatic activity. Edman degradation revealed the cleavage site between Asn-26 and Gly-27, generating a 26-residue peptide that was confirmed by mass spectrometry. We analyzed postmortem tissues from different parts of the central nervous system (CNS), including the choroid plexus, and found only trace amounts of N-terminally truncated SOD1. Biochemical characterization of the SOD1 in CSF was done by size exclusion chromatography, ion exchange chromatography, and mass spectrometry. Our findings demonstrate that SOD1 in CSF retains full enzymatic activity, that the N-terminally truncated variant is mainly present in heterodimers with native SOD1 subunits, and that the dimer remains folded and active, with both fragments of the truncated SOD1 fixed after proteolysis. Truncated SOD1 was absent in human plasma. In mice, only transgenically expressed human SOD1 underwent truncation in CSF, whereas endogenous murine SOD1 remained intact. Lastly, the N-terminal truncation does not induce misfolding, unlike the destabilizing effects observed with C-terminal truncations. The location where the truncation takes place and the underlying mechanism could not be identified. Whether the N-truncated SOD1 variant contributes to ALS pathogenesis remains to be determined. (Figure presented.).

Mutations in the antioxidant enzyme superoxide dismutase-1 (SOD1) are a well-established cause of amyotrophic lateral sclerosis (ALS). The mutations promote SOD1 misfolding, resulting in protein aggregation and motor neuron degeneration. SOD1 is normally a structurally stable enzyme, and the mechanisms underlying SOD1 misfolding remain poorly understood. Approximately one third of SOD1 in cerebrospinal fluid (CSF) exhibits an N-terminal truncation, the biological significance of which remains unclear. This is remarkable given the dramatic effects ALS-linked C-terminal truncations have on the enzyme. In this study, we identified the truncation site and investigated its impact on SOD1 stability and enzymatic activity. Edman degradation revealed the cleavage site between Asn-26 and Gly-27, generating a 26-residue peptide that was confirmed by mass spectrometry. We analyzed postmortem tissues from different parts of the central nervous system (CNS), including the choroid plexus, and found only trace amounts of N-terminally truncated SOD1. Biochemical characterization of the SOD1 in CSF was done by size exclusion chromatography, ion exchange chromatography, and mass spectrometry. Our findings demonstrate that SOD1 in CSF retains full enzymatic activity, that the N-terminally truncated variant is mainly present in heterodimers with native SOD1 subunits, and that the dimer remains folded and active, with both fragments of the truncated SOD1 fixed after proteolysis. Truncated SOD1 was absent in human plasma. In mice, only transgenically expressed human SOD1 underwent truncation in CSF, whereas endogenous murine SOD1 remained intact. Lastly, the N-terminal truncation does not induce misfolding, unlike the destabilizing effects observed with C-terminal truncations. The location where the truncation takes place and the underlying mechanism could not be identified. Whether the N-truncated SOD1 variant contributes to ALS pathogenesis remains to be determined. 

Mutations in superoxide dismutase−1 (SOD1) are a common cause of amyotrophic lateral sclerosis (ALS). Inheritance is as a rule dominant, but in carriers of the most prevalent mutation, D90A, disease primarily develops in homozygotes. Increasing evidence suggests that prion-like propagation of SOD1 aggregation is the central pathogenic mechanism. Two structurally different strains of aggregates have been found to arise in human SOD1 (hSOD1) transgenic (Tg) mouse models of ALS. Strain A is formed by most mutants including hSOD1^G85R and homozygous hSOD1^WT Tg mice, whereas homozygous hSOD1^D90A Tg mice form a distinct strain B, but also A. Inoculation of strain A and B seed preparations from Tg mice into lumbar spinal cord of adult hSOD1^G85R mice induced templated spreading hSOD1 aggregation and premature ALS-like disease. Seeds from an ALS patient carrying the hSOD1^G127X truncation mutation likewise transmitted strain A aggregation and disease. In the present study, we investigated whether seeds prepared from spinal ventral horns from six patients homozygous for the hSOD1^D90A mutation could transmit aggregation and disease to adult hSOD1^G85R Tg mice. Despite the extensive degeneration and loss of motor neurons in the long-lived D90A patients, two of the seeds significantly shortened the survival of the Tg mice, one transmitting A and the other B-pattern hSOD1 aggregation. Nine different preparations from four human controls lacked effects. The results demonstrate that two distinct aggregate strains can arise and propagate in homozygous hSOD1^D90A ALS patients, further supporting the hypothesis that prion-like transmission of hSOD1 aggregation is the primary pathogenic mechanism in SOD1-linked ALS.

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of cortical and spinal motor neurons. Mendelian germline mutations often cause familial ALS (fALS) but only approximately 10% of sporadic ALS cases (sALS). We leveraged DNA and single-cell RNA sequencing data from autopsy tissue to explore the presence of somatic mosaic variants in sALS cases. Deep targeted panel sequencing of known ALS disease genes in motor cortex tissue revealed an enrichment of low allele frequency variants in sALS, but not in fALS with an identified monogenic cause. In silico analysis predicted increased pathogenicity of mosaic mutations in various known ALS mutational hot-spots. In particular, we identified the somatic FUS variant p.E516X, located in an established hotspot for germline ALS mutations, which leads to nucleo-cytoplasmic mislocalization and aggregation typical for ALS FUS pathology. Additionally, we performed somatic variant calling on single-cell RNA-sequencing data from sALS tissue and revealed a specific accumulation of somatic variants in excitatory neurons, reinforcing a neuron-autonomous disease initiation. Collectively, this study indicates that somatic mutations within the motor cortex, especially in excitatory neurons, may contribute to sALS development.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder. We describe four patients with hereditary ALS caused by the p.Gly94Ser SOD1 mutation who were treated monthly with the intrathecal antisense oligonucleotide tofersen in a clinical setting at Landspitali University Hospital of Iceland. After initiating treatment 15–26 months ago, no significant clinical deterioration was observed, and three patients showed signs of clinical improvement, with some recovery of motor function. All four patients currently present with chronic nonprogressive ALS, a phenotype not previously observed or documented. Concomitantly, the concentration of neurofilament light chain (Nf-L) in the cerebrospinal fluid decreased to the normal range. This clinical benefit and decrease in Nf-L levels were detected regardless of the patient’s initial ALSFRS-R score. No serious adverse events were observed. Notably, we observed a clinically meaningful effect in two patients who had been ill for several years before treatment was instituted, raising questions about who should receive treatment and the biology of paresis and motor neuron cell loss in patients with ALS. Although only a minority of ALS patients carry a SOD1 mutation, the advent of this new precision medicine has profound implications for ALS management.

INTRODUCTION: We evaluated differences in p-tau levels between Alzheimer's disease (AD), a condition with brain-specific changes in p-tau, and amyotrophic lateral sclerosis (ALS), a condition associated with increases in peripheral p-tau levels.

METHODS: Cerebrospinal fluid and plasma from 668 participants were analyzed using immunoassays specific for the low-molecular-weight (LMW) tau isoforms present in the brain (i.e., p-tau217Lilly, p-tau181Lilly) and those that detect both LMW- and high-molecular-weight (HMW) tau expressed in the peripheral nervous system (i.e., p-tau217AlzPath, p-tau181UGOT).

RESULTS: Increases in plasma p-tau in ALS versus controls were significantly smaller for the LMW-specific p-tau assays (15.9%–20.5%) compared with non-specific assays (92.0%–121.3%). The LMW-specific p-tau assays showed significantly larger plasma p-tau increases in AD versus ALS, discriminating AD from ALS with areas under the curve (AUCs; 0.890.93) higher than the AUCs of the non-specific assays (0.54–0.74).

DISCUSSION: LMW-specific p-tau assays could be more useful in the diagnostic workup of AD, especially in population-based communities where conditions causing peripheral neuropathy are frequent. 

Pathogenic variants in the superoxide dismutase 1 (SOD1) gene were the first identified genetic cause of amyotrophic lateral sclerosis (ALS), in 1993. This discovery enabled the development of transgenic rodent models for studying the biology of SOD1 ALS. The understanding that SOD1 ALS is driven by a toxic gain-of-function mutation has led to therapeutic strategies that aim to lower concentrations of SOD1 protein, an endeavour that has been complicated by the phenotypic heterogeneity of SOD1 ALS. The successful development of genetically targeted therapies to reduce SOD1 expression, together with a better understanding of pre-symptomatic disease and the discovery of neurofilament light protein as a susceptibility/risk biomarker that predicts phenoconversion, has ushered in a new era of trials that aim to prevent clinically manifest SOD1 ALS. The 30-year journey from gene discovery to gene therapy has not only uncovered the pathophysiology of SOD1 ALS, but has also facilitated the development of biomarkers that should aid therapy development for all forms of ALS.

Mutations in superoxide dismutase-1 (SOD1) are a common cause of amyotrophic lateral sclerosis (ALS). Inheritance is as a rule dominant, but in carriers of the most common mutation, D90A, disease can develop in both homozygous and, more rarely, in heterozygous individuals with unexplained differences in clinical presentation. There is mounting evidence that prion-like spread of SOD1 aggregation is the primary cause of the disease. Two different strains of aggregates have been found to arise in human SOD1 (hSOD1) transgenic mouse models of ALS. Strain A is formed by most mutants including hSOD1G85R and hSOD1WT, whereas hSOD1D90A transgenic mice form a distinct strain B in addition to A. To explore the effects of aggregate strain propensities when hSOD1 variants are coexpressed, we generated digenic hSOD1G85R/WT and hSOD1G85R/D90A mice. Coexpression of hSOD1WT considerably shortened the lifespan of hSOD1G85R mice to the extent expected from the neurotoxicities of the variants alone. In contrast, coexpression of hSOD1D90A had a minimal effect on survival, far smaller than expected. Moreover, time from onset to the end stage was markedly prolonged in the hSOD1G85R/D90A mice. Aggregation of hSOD1 developed concomitantly with motor neuron disease, and the aggregates contained large amounts of both coexpressed variants in both digenic models. Our findings suggest that hSOD1WT has high a capacity to coaggregate with mutants and enhance neurotoxicity. Such interactions may be restricted by differences in strain propensities, which may contribute to the primarily recessive inheritance associated with the hSOD1D90A mutation.