Sporadic Amyotrophic Lateral Sclerosis Cases Research Articles

Repetitive element transcripts are elevated in the brain of C9orf72 ALS/FTLD patients.

Significant transcriptome alterations are detected in the brain of patients with amyotrophic lateral sclerosis (ALS), including carriers of the C9orf72 repeat expansion and C9orf72-negative sporadic cases. Recently, the expression of repetitive element transcripts has been associated with toxicity and, while increased repetitive element expression has been observed in several neurodegenerative diseases, little is known about their contribution to ALS. To assess whether aberrant expression of repetitive element sequences are observed in ALS, we analysed RNA sequencing data from C9orf72-positive and sporadic ALS cases, as well as healthy controls. Transcripts from multiple classes and subclasses of repetitive elements (LINEs, endogenous retroviruses, DNA transposons, simple repeats, etc.) were significantly increased in the frontal cortex of C9orf72 ALS patients. A large collection of patient samples, representing both C9orf72 positive and negative ALS, ALS/FTLD, and FTLD cases, was used to validate the levels of several repetitive element transcripts. These analyses confirmed that repetitive element expression was significantly increased in C9orf72-positive compared to C9orf72-negative or control cases. While previous studies suggest an important link between TDP-43 and repetitive element biology, our data indicate that TDP-43 pathology alone is insufficient to account for the observed changes in repetitive elements in ALS/FTLD. Instead, we found that repetitive element expression positively correlated with RNA polymerase II activity in postmortem brain, and pharmacologic modulation of RNA polymerase II activity altered repetitive element expression in vitro. We conclude that increased RNA polymerase II activity in ALS/FTLD may lead to increased repetitive element transcript expression, a novel pathological feature of ALS/FTLD.

Retrotransposon activation contributes to neurodegeneration in a Drosophila TDP-43 model of ALS.

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are two incurable neurodegenerative disorders that exist on a symptomological spectrum and share both genetic underpinnings and pathophysiological hallmarks. Functional abnormality of TAR DNA-binding protein 43 (TDP-43), an aggregation-prone RNA and DNA binding protein, is observed in the vast majority of both familial and sporadic ALS cases and in ~40% of FTLD cases, but the cascade of events leading to cell death are not understood. We have expressed human TDP-43 (hTDP-43) in Drosophila neurons and glia, a model that recapitulates many of the characteristics of TDP-43-linked human disease including protein aggregation pathology, locomotor impairment, and premature death. We report that such expression of hTDP-43 impairs small interfering RNA (siRNA) silencing, which is the major post-transcriptional mechanism of retrotransposable element (RTE) control in somatic tissue. This is accompanied by de-repression of a panel of both LINE and LTR families of RTEs, with somewhat different elements being active in response to hTDP-43 expression in glia versus neurons. hTDP-43 expression in glia causes an early and severe loss of control of a specific RTE, the endogenous retrovirus (ERV) gypsy. We demonstrate that gypsy causes the degenerative phenotypes in these flies because we are able to rescue the toxicity of glial hTDP-43 either by genetically blocking expression of this RTE or by pharmacologically inhibiting RTE reverse transcriptase activity. Moreover, we provide evidence that activation of DNA damage-mediated programmed cell death underlies both neuronal and glial hTDP-43 toxicity, consistent with RTE-mediated effects in both cell types. Our findings suggest a novel mechanism in which RTE activity contributes to neurodegeneration in TDP-43-mediated diseases such as ALS and FTLD.

Mutations of CCNF gene is rare in patients with amyotrophic lateral sclerosis and frontotemporal dementia from Mainland China

Objective: Mutations of the cyclin F (CCNF) gene were recently identified to be associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) in Western and Japanese populations. The rare protein-altering variants frequency is 0.6 to 3.3% in ALS and FTD from these diverse geographic populations while no systematic analysis of CCNF variants were conducted in the Chinese population.Methods: We screened all exons of CCNF in a cohort of 269 cases (including 181 ALS and 88 FTD) from Mainland China using Sanger sequencing.Results: A rare heterozygous variant (c.481G > A, p.G161R) was detected in a sporadic ALS case with a frequency of 0.6%, while no mutation was identified in patients with FTD. The same variant was also found in a sporadic ALS patient from America.Conclusions: Our result indicates that the mutation of CCNF is rare in patients with ALS and FTD from Mainland China.

New Therapeutic Avenue for ALS: Avoiding a Fatal Encounter of TDP-43 at the Mitochondria

Amyotrophic lateral sclerosis (ALS) is the most common fatal neuromuscular disease in adults, and very limited options for clinical improvement are currently available.1 The etiology of ALS is complex and heterogeneous, with multiple genetic associations reported so far.2 Among these, the gene coding for TAR DNA-binding protein 43 (TDP-43) RNA/DNA binding protein was identified as the principal component of ubiquitinated cytoplasmic inclusions, which are one of the main pathological hallmarks observed in most familial and sporadic cases of ALS as well as in frontotemporal dementia with ubiquitin inclusions (FTD-U).

Cortical synaptic and dendritic spine abnormalities in a presymptomatic TDP-43 model of amyotrophic lateral sclerosis.

Layer V pyramidal neurons (LVPNs) within the motor cortex integrate sensory cues and co-ordinate voluntary control of motor output. In amyotrophic lateral sclerosis (ALS) LVPNs and spinal motor neurons degenerate. The pathogenesis of neural degeneration is unknown in ALS; 10% of cases have a genetic cause, whereas 90% are sporadic, with most of the latter showing TDP-43 inclusions. Clinical and experimental evidence implicate excitotoxicity as a prime aetiological candidate. Using patch clamp and dye-filling techniques in brain slices, combined with high-resolution confocal microscopy, we report increased excitatory synaptic inputs and dendritic spine densities in early presymptomatic mice carrying a TDP-43Q331K mutation. These findings demonstrate substantive alterations in the motor cortex neural network, long before an overt degenerative phenotype has been reported. We conclude that increased excitatory neurotransmission is a common pathophysiology amongst differing genetic cases of ALS and may be of relevance to the 95% of sporadic ALS cases that exhibit TDP-43 inclusions.

Neuronal overexpression of human VAPB slows motor impairment and neuromuscular denervation in a mouse model of ALS.

Four mutations in the VAMP/synaptobrevin-associated protein B (VAPB) gene have been linked to amyotrophic lateral sclerosis (ALS) type 8. The mechanism by which VAPB mutations cause motor neuron disease is unclear, but studies of the most common P56S variant suggest both loss of function and dominant-negative sequestration of wild-type protein. Diminished levels of VAPB and its proteolytic cleavage fragment have also been reported in sporadic ALS cases, suggesting that VAPB loss of function may be a common mechanism of disease. Here, we tested whether neuronal overexpression of wild-type human VAPB would attenuate disease in a mouse model of familial ALS1. We used neonatal intraventricular viral injections to express VAPB or YFP throughout the brain and spinal cord of superoxide dismutase (SOD1) G93A transgenic mice. Lifelong elevation of neuronal VAPB slowed the decline of neurological impairment, delayed denervation of hindlimb muscles, and prolonged survival of spinal motor neurons. Collectively, these changes produced a slight but significant extension in lifespan, even in this highly aggressive model of disease. Our findings lend support for a protective role of VAPB in neuromuscular health.

Identification of a novel loss-of-function C9orf72 splice site mutation in a patient with amyotrophic lateral sclerosis

Abnormal expansion of a hexanucleotide GGGGCC repeat in the C9orf72 gene is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia in Caucasians. However, the underlying pathologic mechanisms remain controversial, and both loss-of-function and gain-of-function models have been proposed. To gain further insight into these mechanisms, we performed mutation analysis of C9orf72 in 276 Han Chinese patients with ALS. We identified GGGGCC expansions in 2 cases of sporadic ALS with 38 and 63 repeats, as well as a novel splice site mutation (c.601-2A>G) in a third case. These genetic alterations were not detected in 332 control patients without neurological disease. Intriguingly, functional analysis revealed that the splice site mutation disrupted the reading frame, creating a premature stop codon (p.I201fsX235). Decreased levels of the mutant messenger RNA were detected in patient cells, suggesting that it may undergo nonsense-mediated messenger RNA decay. Taken together, these results demonstrate that C9orf72 mutation is infrequently associated with ALS in Han Chinese patients and suggest that a splice site mutation in C9orf72 may lead to loss of function due to haploinsufficiency of the resulting protein.

Heterogeneity of cerebral TDP-43 pathology in sporadic amyotrophic lateral sclerosis: Evidence for clinico-pathologic subtypes.

Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are types of major TDP-43 (43-kDa TAR DNA-binding protein) proteinopathy. Cortical TDP-43 pathology has been analyzed in detail in cases of FTLD-TDP, but is still unclear in cases of ALS. We attempted to clarify the cortical and subcortical TDP-43 pathology in Japanese cases of sporadic ALS (n = 96) using an antibody specific to phosphorylated TDP-43 (pTDP-43). The cases were divided into two groups: those without pTDP-43-positive neuronal cytoplasmic inclusions in the hippocampal dentate granule cells (Type 1, n = 63), and those with such inclusions (Type 2, n = 33). Furthermore, the Type 2 cases were divided into two subgroups based on semi-quantitative estimation of pTDP-43-positive dystrophic neurites (DNs) in the temporal neocortex: Type 2a (accompanied by no or few DNs, n = 22) and Type 2b (accompanied by abundant DNs, n = 11). Clinico-pathologic analysis revealed that cognitive impairment was a feature in patients with Type 2a and Type 2b, but not in those with Type 1, and that importantly, Type 2b is a distinct subtype characterized by a poor prognosis despite the less severe loss of lower motor neurons, the unusual subcortical dendrospinal pTDP-43 pathology, and more prominent glial involvement in cortical pTDP-43 pathology than other two groups. Considering the patient survival time and severity of motor neuron loss in each group, transition from Type 1 to Type 2, or from Type 2a to Type 2b during the disease course appeared unlikely. Therefore, each of these three groups was regarded as an independent subtype.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0335-2) contains supplementary material, which is available to authorized users.

Enhancing NAD+ Salvage Pathway Reverts the Toxicity of Primary Astrocytes Expressing Amyotrophic Lateral Sclerosis-linked Mutant Superoxide Dismutase 1 (SOD1)

Nicotinamide adenine dinucleotide (NAD(+)) participates in redox reactions and NAD(+)-dependent signaling pathways. Although the redox reactions are critical for efficient mitochondrial metabolism, they are not accompanied by any net consumption of the nucleotide. On the contrary, NAD(+)-dependent signaling processes lead to its degradation. Three distinct families of enzymes consume NAD(+) as substrate: poly(ADP-ribose) polymerases, ADP-ribosyl cyclases (CD38 and CD157), and sirtuins (SIRT1-7). Because all of the above enzymes generate nicotinamide as a byproduct, mammalian cells have evolved an NAD(+) salvage pathway capable of resynthesizing NAD(+) from nicotinamide. Overexpression of the rate-limiting enzyme in this pathway, nicotinamide phosphoribosyltransferase, increases total and mitochondrial NAD(+) levels in astrocytes. Moreover, targeting nicotinamide phosphoribosyltransferase to the mitochondria also enhances NAD(+) salvage pathway in astrocytes. Supplementation with the NAD(+) precursors nicotinamide mononucleotide and nicotinamide riboside also increases NAD(+) levels in astrocytes. Amyotrophic lateral sclerosis (ALS) is caused by the progressive degeneration of motor neurons in the spinal cord, brain stem, and motor cortex. Superoxide dismutase 1 (SOD1) mutations account for up to 20% of familial ALS and 1-2% of apparently sporadic ALS cases. Primary astrocytes isolated from mutant human superoxide dismutase 1-overexpressing mice as well as human post-mortem ALS spinal cord-derived astrocytes induce motor neuron death in co-culture. Increasing total and mitochondrial NAD(+) content in ALS astrocytes increases oxidative stress resistance and reverts their toxicity toward co-cultured motor neurons. Taken together, our results suggest that enhancing the NAD(+) salvage pathway in astrocytes could be a potential therapeutic target to prevent astrocyte-mediated motor neuron death in ALS.

Long-term physical activity: an exogenous risk factor for sporadic amyotrophic lateral sclerosis?

Objectives: To conduct a geographically defined, UK-based case-control study, to examine any association between physical activity (PA) and amyotrophic lateral sclerosis (ALS). Methods: A novel historical PA questionnaire was designed, validated, and subsequently administered in individual face-to-face interviews of 175 newly diagnosed sporadic ALS cases and 317 age- and sex-matched community controls. Historical PA energy expenditure and time spent in vigorous-intensity PA were derived from questionnaire data and compared between cases and controls. Results: Participation in an extra 10kJ/kg/day of PA (equivalent to approximately 45minutes brisk walking) was consistently associated with an increased risk of ALS, with the strongest association observed for adulthood exercise-related PA (OR 1.47, 95% CI 1.10-1.97). An extra 10mins/day of vigorous PA was also associated with the odds of ALS (OR 1.03, 95% CI 1·01-1·05). Results were slightly attenuated following adjustment for smoking and educational attainment. Conclusions: To our knowledge this is the first study to demonstrate a positive association between ALS and PA participation using a specifically designed and validated historical PA questionnaire. Despite the well-established health benefits of PA, a high activity lifestyle may also be associated with elevated risk of ALS. Large-scale prospective studies in the future may help to confirm this association.

Analysis of C9orf72 in patients with frontotemporal dementia and amyotrophic lateral sclerosis from Argentina

Pathologic expansion of the G4C2 repeat in C9orf72 is the main genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). To evaluate the frequency of the G4C2 expansion in a Latin American cohort of FTD and ALS patients, we used a 2-step genotyping strategy. For FTD, we observed an overall expansion frequency of 18.2% (6 of 33 unrelated cases). Moreover, the C9orf72 expansion accounted for 37.5% of all familial FTD cases (6 of 16 families). The expansion frequency in sporadic ALS cases was 2% (1 of 47 unrelated patients), whereas we observed the expansion in 1 of 3 families with a positive history for ALS. Overall, the expansion frequency in our FTD group was similar to that reported for patients in Europe and North America, whereas the frequency in our sporadic ALS group was significantly lower. To our knowledge, this is the first report on the frequency of the C9orf72 expansion in a Latin American population.

Cerebellar neuronal loss in amyotrophic lateral sclerosis cases with ATXN2 intermediate repeat expansions

Despite evidence suggesting that the cerebellum may be targeted in amyotrophic lateral sclerosis (ALS), particularly in cases with repeat expansions in the ATXN2 and C9ORF72 genes, the integrity of cerebellar neurons has yet to be examined. The present study undertakes a histopathological analysis to assess the impact of these repeat expansions on cerebellar neurons and determine whether similar cerebellar pathology occurs in sporadic disease. Purkinje and granule cells were quantified in the vermis and lateral cerebellar hemispheres of ALS cases with repeat expansions in the ATXN2 and C9ORF72 genes, sporadic disease, and sporadic progressive muscular atrophy with only lower motor neuron degeneration. ALS cases with intermediate repeat expansions in the ATXN2 gene demonstrate a significant loss in Purkinje cells in the cerebellar vermis only. Despite ALS cases with expansions in the C9ORF72 gene having the highest burden of inclusion pathology, no neuronal loss was observed in this group. Neuronal numbers were also unchanged in sporadic ALS and sporadic PMA cases. The present study has established a selective loss of Purkinje cells in the cerebellar vermis of ALS cases with intermediate repeat expansions in the ATXN2 gene, suggesting a divergent pathogenic mechanism independent of upper and lower motor neuron degeneration in ALS. We discuss these findings in the context of large repeat expansions in ATXN2 and spinocerebellar ataxia type 2, providing evidence that intermediate repeats in ATXN2 cause significant, albeit less substantial, spinocerebellar damage compared with longer repeats in ATXN2.

Large-scale screening in sporadic amyotrophic lateral sclerosis identifies genetic modifiers in C9orf72 repeat carriers

Sporadic amyotrophic lateral sclerosis (ALS) is considered to be a complex disease with multiple genetic risk factors contributing to the pathogenesis. Identification of genetic risk factors that co-occur frequently could provide relevant insight into underlying mechanisms of motor neuron degeneration. To dissect the genetic architecture of sporadic ALS, we undertook a large sequencing study in 755 apparently sporadic ALS cases and 959 controls, analyzing 10 ALS genes: SOD1, C9orf72, TARDBP, FUS, ANG, CHMP2B, ATXN2, NIPA1, SMN1, and UNC13A. We observed sporadic cases with multiple genetic risk variants in 4.1% compared with 1.3% in controls. The overall difference was not in excess of what is to be expected by chance (binomial test, p = 0.59). We did, however, observe a higher frequency than expected of C9orf72 repeat carriers with co-occurring susceptibility variants (ATXN2, NIPA1, and SMN1; p = 0.001), which is mainly because of the co-occurrence of NIPA1 repeats in 15% of C9orf72 repeat carriers (p = 0.006).

Aberrant association of misfolded SOD1 with Na(+)/K(+)ATPase-α3 impairs its activity and contributes to motor neuron vulnerability in ALS.

Amyotrophic lateral sclerosis (ALS) is an adult onset progressive motor neuron disease with no cure. Transgenic mice overexpressing familial ALS associated human mutant SOD1 are a commonly used model for examining disease mechanisms. Presently, it is well accepted that alterations in motor neuron excitability and spinal circuits are pathological hallmarks of ALS, but the underlying molecular mechanisms remain unresolved. Here, we sought to understand whether the expression of mutant SOD1 protein could contribute to altering processes governing motor neuron excitability. We used the conformation specific antibody B8H10 which recognizes a misfolded state of SOD1 (misfSOD1) to longitudinally identify its interactome during early disease stage in SOD1G93A mice. This strategy identified a direct isozyme-specific association of misfSOD1 with Na(+)/K(+)ATPase-α3 leading to the premature impairment of its ATPase activity. Pharmacological inhibition of Na(+)/K(+)ATPase-α3 altered glutamate receptor 2 expression, modified cholinergic inputs and accelerated diseasepathology. After mapping the site of direct association of misfSOD1 with Na(+)/K(+)ATPase-α3 onto a 10 amino acid stretch that is unique to Na(+)/K(+)ATPase-α3 but not found in the closely related Na(+)/K(+)ATPase-α1 isozyme, we generated a misfSOD1 binding deficient, but fully functional Na(+)/K(+)ATPase-α3 pump. Adeno associated virus (AAV)-mediated expression of this chimeric Na(+)/K(+)ATPase-α3 restored Na(+)/K(+)ATPase-α3 activity in the spinal cord, delayed pathological alterations and prolonged survival of SOD1G93A mice. Additionally, altered Na(+)/K(+)ATPase-α3 expression was observed in the spinal cord of individuals with sporadic and familial ALS. A fraction of sporadic ALS cases also presented B8H10 positive misfSOD1 immunoreactivity, suggesting that similar mechanism might contribute to the pathology.

Designing an Internationally Accessible Web-Based Questionnaire to Discover Risk Factors for Amyotrophic Lateral Sclerosis: A Case-Control Study.

BackgroundAmyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease with a typical survival of three to five years. Epidemiological studies using paper-based questionnaires in individual countries or continents have failed to find widely accepted risk factors for the disease. The advantages of online versus paper-based questionnaires have been extensively reviewed, but few online epidemiological studies into human neurodegenerative diseases have so far been undertaken.ObjectiveTo design a Web-based questionnaire to identify environmental risk factors for ALS and enable international comparisons of these risk factors.MethodsA Web-based epidemiological questionnaire for ALS has been developed based on experience gained from administering a previous continent-wide paper-based questionnaire for this disease. New and modified questions have been added from our previous paper-based questionnaire, from literature searches, and from validated ALS questionnaires supplied by other investigators. New criteria to allow the separation of familial and sporadic ALS cases have been included. The questionnaire addresses many risk factors that have already been proposed for ALS, as well as a number that have not yet been rigorously examined. To encourage participation, responses are collected anonymously and no personally identifiable information is requested. The survey is being translated into a number of languages which will allow many people around the world to read and answer it in their own language.ResultsAfter the questionnaire had been online for 4 months, it had 379 respondents compared to only 46 respondents for the same initial period using a paper-based questionnaire. The average age of the first 379 web questionnaire respondents was 54 years compared to the average age of 60 years for the first 379 paper questionnaire respondents. The questionnaire is soon to be promoted in a number of countries through ALS associations and disease registries.ConclusionsWeb-based questionnaires are a time- and resource-efficient method for performing large epidemiological studies of neurodegenerative diseases such as ALS. The ability to compare risk factors between different countries using the same analysis tool will be of particular value for finding robust risk factors that underlie ALS.

Altered age-related changes in bioenergetic properties and mitochondrial morphology in fibroblasts from sporadic amyotrophic lateral sclerosis patients

Mitochondria play a key role in aging, which is a well-established risk factor in amyotrophic lateral sclerosis (ALS). We have previously modeled metabolic dysregulation in ALS using fibroblasts isolated from sporadic ALS (SALS) and familial ALS patients. In the present study, we show that fibroblasts from SALS patients have an altered metabolic response to aging. Control fibroblasts demonstrated increased mitochondrial network complexity and spare respiratory capacity with age which was not seen in the SALS cases. SALS cases displayed an increase in uncoupled mitochondrial respiration, which was not evident in control cases. Unlike SALS cases, controls showed a decrease in glycolysis and an increase in the oxygen consumption rate/extracellular acidification rate ratio, indicating an increased reliance on mitochondrial function. Switching to a more oxidative state by removing glucose with in the culture media resulted in a loss of the mitochondrial interconnectivity and spare respiratory capacity increases observed in controls grown in glucose. Glucose removal also led to an age-independent increase in glycolysis in the SALS cases. This study is, to the best our knowledge, the first to assess the effect of aging on both mitochondrial and glycolytic function simultaneously in intact human fibroblasts and demonstrates that the SALS disease state shifts the cellular metabolic response to aging to a more glycolytic state compared with age-matched control fibroblasts. This work highlights that ALS alters the metabolic equilibrium even in peripheral tissues outside the central nervous system. Elucidating at a molecular level how this occurs and at what stage in the disease process is crucial to understanding why ALS affects cellular energy metabolism and how the disease alters the natural cellular response to aging.

C9ORF72 hexanucleotide repeat expansion in ALS patients from the Central European Russia population

Cohorts of amyotrophic lateral sclerosis (ALS) patients and control individuals of Caucasian origin from the Central European Russia (Moscow city and region) were analyzed for the presence of hexanucleotide repeat GGGGCC expansion within the first intron of the C9ORF72 gene. The presence of a large (>40) repeat expansion was found in 15% of familial ALS cases (3 of 20 unrelated familial cases) and 2.5% of sporadic ALS cases (6 of 238) but in none of control cases. These results suggest that the frequency of C9ORF72 hexanucleotide repeats expansions in the Central European Russian ALS patients is significantly lower than in Western European or Northern American ALS patients of Caucasian origin but higher than in Asian ALS patients.

Motor neurone disease/amyotrophic lateral sclerosis associated with intermediate-length CAG repeat expansions in Ataxin-2 does not have 1C2-positive polyglutamine inclusions.

Intermediate-length cytosine-adenine-guanine repeat expansions in the ATXN2 gene (which encodes for Ataxin-2 protein) have been linked to increased risk for motor neurone disease/amyotrophic lateral sclerosis (ALS). We screened DNA from cases for which we had post-mortem brain tissue to enable characterization of the neuropathology associated with this mutation. Polymerase chain reaction and sequencing of DNA from frozen brain tissue on a cohort of 178 amyotrophic lateral sclerosis (ALS) autopsy cases from the north of England and 159 controls was performed. This was followed by tinctorial staining and immunohistochemistry (including for Ataxin-2) on selected blocks from ALS cases with intermediate-length expansions (ATXN2-ALS), sporadic ALS cases and neurologically healthy controls. Four ALS cases with intermediate-length CAG repeat expansions within ATXN2 were identified. One such case also had a mutation of the C9ORF72 gene. All had lower motor neurone depletion, and three out of four cases had transactive response DNA binding protein 43 (TDP-43)-positive neuronal cytoplasmic inclusions (predominantly skein-like). No inclusions of aggregated polyglutamine proteins were identified. Ataxin-2 protein expression was largely granular and cytoplasmic with the most prominent staining observed in larger neurones. Ataxin-2 staining was variable both within and between cases, but no staining pattern that was specific for cases with ATXN2 mutations was seen. Intermediate expansions of the CAG repeat in ATXN2 are associated with ALS. They are mostly associated with TDP-43 proteinopathy, but not with 1C2-positive polyglutamine inclusions. In the nervous system, Ataxin-2 protein expression is predominantly seen in large neurones. There is no consistent histopathological hallmark that is unique to ATXN2-ALS.

Exome sequencing uncovers hidden pathways in familial and sporadic ALS.

Amyotrophic lateral sclerosis (ALS) is a complex and as yet untreatable neurodegenerative disorder. We discuss two examples of exome sequencing in large international collections of familial and sporadic ALS cases that are revealing new and potentially treatable pathways, such as those involving autophagy and neuroinflammation.

Identification of rare protein disulfide isomerase gene variants in amyotrophic lateral sclerosis patients

Disruption of endoplasmic reticulum (ER) proteostasis is a salient feature of amyotrophic lateral sclerosis (ALS). Upregulation of ER foldases of the protein disulfide isomerase (PDI) family has been reported in ALS mouse models and spinal cord tissue and body fluids derived from sporadic ALS cases. Although in vitro studies suggest a neuroprotective role of PDIs in ALS, the possible contribution of genetic mutations of these ER foldases in the disease process remains unknown. Interestingly, intronic variants of the PDIA1 gene were recently reported as a risk factor for ALS. Here, we initially screened for mutations in two major PDI genes (PDIA1/P4HB and PDIA3/ERp57) in a US cohort of 96 familial and 96 sporadic ALS patients using direct DNA sequencing. Then, 463 familial and 445 sporadic ALS patients from two independent cohorts were also screened for mutations in these two genes using whole exome sequencing. A total of nine PDIA1 missense variants and seven PDIA3 missense variants were identified in 16 ALS patients. We have identified several novel and rare single nucleotide polymorphisms (SNPs) in both genes that are enriched in ALS cases compared with a large group of control subjects showing a frequency of around 1% in ALS cases. The possible biological and structural impact of these ALS-linked PDI variants is also discussed.