Pathophysiological insights into ALS with C9ORF72 expansions

Novel approaches to assessing upper motor neuron dysfunction in motor neuron disease/amyotrophic lateral sclerosis: IFCN handbook chapter

Identifying upper motor neuron (UMN) dysfunction is fundamental to the diagnosis and understanding of disease pathogenesis in motor neuron disease (MND). The clinical assessment of UMN dysfunction may be difficult, particularly in the setting of severe muscle weakness. From a physiological perspective, transcranial magnetic stimulation (TMS) techniques provide objective biomarkers of UMN dysfunction in MND and may also be useful to interrogate cortical and network function. Single, paired- and triple pulse TMS techniques have yielded novel diagnostic and prognostic biomarkers in MND, and have provided important pathogenic insights, particularly pertaining to site of disease onset. Cortical hyperexcitability, as heralded by reduced short interval intracortical inhibition (SICI) and increased short interval intracortical facilitation, has been associated with the onset of lower motor neuron degeneration, along with patterns of disease spread, development of specific clinical features such as the split hand phenomenon, and may provide an indication about the rate of disease progression. Additionally, reduction of SICI has emerged as a potential diagnostic aid in MND. The triple stimulation technique (TST) was shown to enhance the diagnostic utility of conventional TMS measures in detecting UMN dysfunction in MND. Separately, sophisticated brain imaging techniques have uncovered novel biomarkers of neurodegeneration that have bene associated with progression. The present review will discuss the utility of TMS and brain neuroimaging derived biomarkers of UMN dysfunction in MND, focusing on recently developed TMS techniques and advanced neuroimaging modalities that interrogate structural and functional integrity of the corticomotoneuronal system, with an emphasis on pathogenic, diagnostic, and prognostic utility.

Assessment of risk of ALS conferred by the GGGGCC hexanucleotide repeat expansion in C9orf72 among first-degree relatives of patients with ALS carrying the repeat expansion

OBJECTIVES

We aimed to estimate the age-related risk of ALS in first-degree relatives of patients with ALS carrying the C9orf72 repeat expansion.

METHODS

We included all patients with ALS carrying a C9orf72 repeat expansion in The Netherlands. Using structured questionnaires, we determined the number of first-degree relatives, their age at death due to ALS or another cause, or age at time of questionnaire. The cumulative incidence of ALS among first-degree relatives was estimated, while accounting for death from other causes. Variability in ALS risk between families was evaluated using a random effects hazards model. We used a second, distinct approach to estimate the risk of ALS and FTD in the general population, using previously published data.

RESULTS

In total, 214 of the 2,486 (9.2%) patients with ALS carried the C9orf72 repeat expansion. The mean risk of ALS at age 80 for first-degree relatives carrying the repeat expansion was 24.1%, but ranged between individual families from 16.0 to 60.6%. Using the second approach, we found the risk of ALS and FTD combined was 28.7% (95% CI 17.8%-54.3%) for carriers in the general population.

CONCLUSIONS

On average, our estimated risk of ALS in the C9orf72 repeat expansion was lower compared to historical estimates. We showed, however, that the risk of ALS likely varies between families and one overall penetrance estimate may not be sufficient to describe ALS risk. This warrants a tailor-made, patient-specific approach in testing. Further studies are needed to assess the risk of FTD in the C9orf72 repeat expansion.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

An interaction between synapsin and C9orf72 regulates excitatory synapses and is impaired in ALS/FTD

Dysfunction and degeneration of synapses is a common feature of amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). A GGGGCC hexanucleotide repeat expansion in the C9ORF72 gene is the main genetic cause of ALS/FTD (C9ALS/FTD). The repeat expansion leads to reduced expression of the C9orf72 protein. How C9orf72 haploinsufficiency contributes to disease has not been resolved. Here we identify the synapsin family of synaptic vesicle proteins, the most abundant group of synaptic phosphoproteins, as novel interactors of C9orf72 at synapses and show that C9orf72 plays a cell-autonomous role in the regulation of excitatory synapses. We mapped the interaction of C9orf72 and synapsin to the N-terminal longin domain of C9orf72 and the conserved C domain of synapsin, and show interaction of the endogenous proteins in synapses. Functionally, C9orf72 deficiency reduced the number of excitatory synapses and decreased synapsin levels at remaining synapses in vitro in hippocampal neuron cultures and in vivo in the hippocampal mossy fibre system of C9orf72 knockout mice. Consistent with synaptic dysfunction, electrophysiological recordings identified impaired excitatory neurotransmission and network function in hippocampal neuron cultures with reduced C9orf72 expression, which correlated with a severe depletion of synaptic vesicles from excitatory synapses in the hippocampus of C9orf72 knockout mice. Finally, neuropathological analysis of post-mortem sections of C9ALS/FTD patient hippocampus with C9orf72 haploinsufficiency revealed a marked reduction in synapsin, indicating that disruption of the interaction between C9orf72 and synapsin may contribute to ALS/FTD pathobiology. Thus, our data show that C9orf72 plays a cell-autonomous role in the regulation of neurotransmission at excitatory synapses by interaction with synapsin and modulation of synaptic vesicle pools, and identify a novel role for C9orf72 haploinsufficiency in synaptic dysfunction in C9ALS/FTD.

Hyperactivity of Purkinje cell and motor deficits in C9orf72 knockout mice

A hexanucleotide (GGGGCC) repeat expansion in the first intron of the C9ORF72 gene is the most frequently reported genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The cerebellum has not traditionally been thought to be involved in the pathogenesis of C9ORF72-associated ALS/FTD, but recent evidence suggested a potential role. C9ORF72 is highly expressed in the cerebellum. Decreased C9ORF72 transcript and protein levels were detected in the postmortem cerebellum, suggesting a loss-of-function effect of C9ORF72 mutation. This study investigated the role of loss of C9ORF72 function using a C9orf72 knockout mouse line. C9orf72 deficiency led to motor impairment in rotarod, beam-walking, paw-print, open-field, and grip-strength tests. Purkinje cells are the sole output neurons in the cerebellum, and we next determined their involvement in the motor phenotypes. We found hyperactivity of Purkinje cells in the C9orf72 knockout mouse accompanied by a significant increase of the large-conductance calcium-activated potassium channel (BK) protein in the cerebellum. The link between BK and Purkinje cell firing was demonstrated by the acute application of the BK activator that increased the firing frequency of the Purkinje cells ex vivo. In vivo chemogenetic activation of Purkinje cells in wild-type mice led to similar motor deficits in rotarod and beam-walking tests. Our results highlight that C9ORF72 loss alters the activity of the Purkinje cell and potentially the pathogenesis of the disease. Manipulating the Purkinje cell firing or cerebellar output may contribute to C9ORF72-associated ALS/FTD treatment.

Aberrant Neural Activity in Prefrontal Pyramidal Neurons Lacking TDP-43 Precedes Neuron loss

Mislocalization of TAR DNA binding protein 43 kDa (TARDBP, or TDP-43) is a principal pathological hallmark identified in cases of neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). As an RNA binding protein, TDP-43 serves in the nuclear compartment to repress non-conserved cryptic exons to ensure the normal transcriptome. Multiple lines of evidence from animal models and human studies support the view that loss of TDP-43 leads to neuron loss, independent of its cytosolic aggregation. However, the underlying pathogenic pathways driven by the loss-of-function mechanism are still poorly defined. We employed a genetic approach to determine the impact of TDP-43 loss in pyramidal neurons of the prefrontal cortex (PFC). Using a custom-built miniscope imaging system, we performed repetitive in vivo calcium imaging from freely behaving mice for up to 7 months. By comparing calcium activity in PFC pyramidal neurons between TDP-43 depleted and TDP-43 intact mice, we demonstrated remarkably increased numbers of pyramidal neurons exhibiting hyperactive calcium activity after short-term TDP-43 depletion, followed by rapid activity declines prior to neuron loss. Our results suggest aberrant neural activity driven by loss of TDP-43 as the pathogenic pathway at early stage in ALS and FTD.

Emerging Mechanisms Underpinning Neurophysiological Impairments in C9ORF72 Repeat Expansion-Mediated Amyotrophic Lateral Sclerosis/Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by degeneration of upper and lower motor neurons and neurons of the prefrontal cortex. The emergence of the C9ORF72 hexanucleotide repeat expansion mutation as the leading genetic cause of ALS and FTD has led to a progressive understanding of the multiple cellular pathways leading to neuronal degeneration. Disturbances in neuronal function represent a major subset of these mechanisms and because such functional perturbations precede degeneration, it is likely that impaired neuronal function in ALS/FTD plays an active role in pathogenesis. This is supported by the fact that ALS/FTD patients consistently present with neurophysiological impairments prior to any apparent degeneration. In this review we summarize how the discovery of the C9ORF72 repeat expansion mutation has contributed to the current understanding of neuronal dysfunction in ALS/FTD. Here, we discuss the impact of the repeat expansion on neuronal function in relation to intrinsic excitability, synaptic, network and ion channel properties, highlighting evidence of conserved and divergent pathophysiological impacts between cortical and motor neurons and the influence of non-neuronal cells. We further highlight the emerging association between these dysfunctional properties with molecular mechanisms of the C9ORF72 mutation that appear to include roles for both, haploinsufficiency of the C9ORF72 protein and aberrantly generated dipeptide repeat protein species. Finally, we suggest that relating key pathological observations in C9ORF72 repeat expansion ALS/FTD patients to the mechanistic impact of the C9ORF72 repeat expansion on neuronal function will lead to an improved understanding of how neurophysiological dysfunction impacts upon pathogenesis.

Neural mechanisms of psychosis vulnerability and perceptual abnormalities in the ALS-FTD spectrum

OBJECTIVE

The aims of this study were to (i) explore psychotic experiences across the entire amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) spectrum from a clinical and genetic perspective, (ii) determine the rate of abnormal perceptual experiences across the five sensory modalities and (iii) explore the neurobiological factors that lead to psychosis vulnerability in ALS-FTD.

METHODS

In a prospective case-controlled study design, 100 participants were enrolled including ALS (n = 37, 24% satisfied criteria for ALS-Plus), ALS-FTD (n = 11), bvFTD (n = 27) and healthy controls (n = 25). Psychotic experiences, perceptual abnormalities and psychosocial factors were determined by means of the clinical interview and carer and patient reports. Voxel-based morphometry analyses determined atrophy patterns in patients experiencing psychosis-like experiences and other perceptual abnormalities.

RESULTS

The rates of psychotic experiences and abnormalities of perception in each sensory modality were high across the entire ALS-FTD continuum. The rate was highest in those with C9orf72 expansions. Rates were also high in patients with pure ALS including psychosis measured by carer-based reports (18%) and self-report measures of psychotic-like experiences (21%). In an ENTER regression model, social anxiety and ACE-III scores were the best predictors of psychosis proneness, accounting for 44% of the score variance. Psychosis-like experiences and perceptual abnormalities were associated with a predominantly frontal and temporal pattern of atrophy that extended to the cerebellum and centred on the anterior thalamus.

INTERPRETATION

The model for psychosis proneness in ALS-FTD likely includes complex interactions between cognitive, social and neurobiological factors that determine vulnerability to psychosis and that may have relevance for individualised patient management.

Utility of Transcranial Magnetic Simulation in Studying Upper Motor Neuron Dysfunction in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is characterised by progressive dysfunction of the upper and lower motor neurons. The disease can evolve over time from focal limb or bulbar onset to involvement of other regions. There is some clinical heterogeneity in ALS with various phenotypes of the disease described, from primary lateral sclerosis, progressive muscular atrophy and flail arm/leg phenotypes. Whilst the majority of ALS patients are sporadic in nature, recent advances have highlighted genetic forms of the disease. Given the close relationship between ALS and frontotemporal dementia, the importance of cortical dysfunction has gained prominence. Transcranial magnetic stimulation (TMS) is a noninvasive neurophysiological tool to explore the function of the motor cortex and thereby cortical excitability. In this review, we highlight the utility of TMS and explore cortical excitability in ALS diagnosis, pathogenesis and insights gained from genetic and variant forms of the disease.

Cortical hyperexcitability: Diagnostic and pathogenic biomarker of ALS

Cortical hyperexcitability is an early and intrinsic feature of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS).. Importantly, cortical hyperexcitability appears to be associated with motor neuron degeneration, possibly via an anterograde glutamate-mediated excitotoxic process, thereby forming a pathogenic basis for ALS. The presence of cortical hyperexcitability in ALS patients may be readily determined by transcranial magnetic stimulation (TMS), a neurophysiological tool that provides a non-invasive and painless method for assessing cortical function. Utilising the threshold tracking TMS technique, cortical hyperexcitability has been established as a robust diagnostic biomarker that distinguished ALS from mimicking disorders at early stages of the disease process. The present review discusses the pathophysiological and diagnostic utility of cortical hyperexcitability in ALS.

Altered network properties in C9ORF72 repeat expansion cortical neurons are due to synaptic dysfunction

BACKGROUND

Physiological disturbances in cortical network excitability and plasticity are established and widespread in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) patients, including those harbouring the C9ORF72 repeat expansion (C9ORF72RE) mutation - the most common genetic impairment causal to ALS and FTD. Noting that perturbations in cortical function are evidenced pre-symptomatically, and that the cortex is associated with widespread pathology, cortical dysfunction is thought to be an early driver of neurodegenerative disease progression. However, our understanding of how altered network function manifests at the cellular and molecular level is not clear.

METHODS

To address this we have generated cortical neurons from patient-derived iPSCs harbouring C9ORF72RE mutations, as well as from their isogenic expansion-corrected controls. We have established a model of network activity in these neurons using multi-electrode array electrophysiology. We have then mechanistically examined the physiological processes underpinning network dysfunction using a combination of patch-clamp electrophysiology, immunocytochemistry, pharmacology and transcriptomic profiling.

RESULTS

We find that C9ORF72RE causes elevated network burst activity, associated with enhanced synaptic input, yet lower burst duration, attributable to impaired pre-synaptic vesicle dynamics. We also show that the C9ORF72RE is associated with impaired synaptic plasticity. Moreover, RNA-seq analysis revealed dysregulated molecular pathways impacting on synaptic function. All molecular, cellular and network deficits are rescued by CRISPR/Cas9 correction of C9ORF72RE. Our study provides a mechanistic view of the early dysregulated processes that underpin cortical network dysfunction in ALS-FTD.

CONCLUSION

These findings suggest synaptic pathophysiology is widespread in ALS-FTD and has an early and fundamental role in driving altered network function that is thought to contribute to neurodegenerative processes in these patients. The overall importance is the identification of previously unidentified defects in pre and postsynaptic compartments affecting synaptic plasticity, synaptic vesicle stores, and network propagation, which directly impact upon cortical function.

Effect of Ezogabine on Cortical and Spinal Motor Neuron Excitability in Amyotrophic Lateral Sclerosis: A Randomized Clinical Trial

Importance

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of the motor nervous system. Clinical studies have demonstrated cortical and spinal motor neuron hyperexcitability using transcranial magnetic stimulation and threshold tracking nerve conduction studies, respectively, although metrics of excitability have not been used as pharmacodynamic biomarkers in multi-site clinical trials.

Objective

To ascertain whether ezogabine decreases cortical and spinal motor neuron excitability in ALS.

Design, Setting, and Participants

This double-blind, placebo-controlled phase 2 randomized clinical trial sought consent from eligible participants from November 3, 2015, to November 9, 2017, and was conducted at 12 US sites within the Northeast ALS Consortium. Participants were randomized in equal numbers to a higher or lower dose of ezogabine or to an identical matched placebo, and they completed in-person visits at screening, baseline, week 6, and week 8 for clinical assessment and neurophysiological measurements.

Interventions

Participants were randomized to receive 600 mg/d or 900 mg/d of ezogabine or a matched placebo for 10 weeks.

Main Outcomes and Measures

The primary outcome was change in short-interval intracortical inhibition (SICI; SICI-1 was used in analysis to reflect stronger inhibition from an increase in amplitude) from pretreatment mean at screening and baseline to the full-dose treatment mean at weeks 6 and 8. The secondary outcomes included levels of cortical motor neuron excitability (including resting motor threshold) measured by transcranial magnetic stimulation and spinal motor neuron excitability (including strength-duration time constant) measured by threshold tracking nerve conduction studies.

Results

A total of 65 participants were randomized to placebo (23), 600 mg/d of ezogabine (23), and 900 mg/d of ezogabine (19 participants); 45 were men (69.2%) and the mean (SD) age was 58.3 (8.8) years. The SICI-1 increased by 53% (mean ratio, 1.53; 95% CI, 1.12-2.09; P = .009) in the 900-mg/d ezogabine group vs placebo group. The SICI-1 did not change in the 600-mg/d ezogabine group vs placebo group (mean ratio, 1.15; 95% CI, 0.87-1.52; P = .31). The resting motor threshold increased in the 600-mg/d ezogabine group vs placebo group (mean ratio, 4.61; 95% CI, 0.21-9.01; P = .04) but not in the 900-mg/d ezogabine group vs placebo group (mean ratio, 1.95; 95% CI, -2.64 to 6.54; P = .40). Ezogabine caused a dose-dependent decrease in excitability by several other metrics, including strength-duration time constant in the 900-mg/d ezogabine group vs placebo group (mean ratio, 0.73; 95% CI, 0.60 to 0.87; P < .001).

Conclusions and Relevance

Ezogabine decreased cortical and spinal motor neuron excitability in participants with ALS, suggesting that such neurophysiological metrics may be used as pharmacodynamic biomarkers in multisite clinical trials.

Trial Registration

ClinicalTrials.gov Identifier: NCT02450552.

Structural and functional underpinnings of precentral abnormalities in amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by the loss of both upper and lower motor neurons. Studies using various magnetic resonance imaging (MRI) analytical approaches have consistently identified significant precentral abnormalities in ALS, whereas their structural and functional underpinnings remain poorly understood.

METHODS

Using cortical thickness, fractional anisotropy (FA), and effective connectivity, we performed a multimodal MRI study to examine the structural and functional alterations associated with precentral abnormalities in patients with ALS (n = 60) compared with healthy controls (n = 60).

RESULTS

Cortical thickness analysis revealed significant cortical thinning in the right precentral gyrus (PCG), superior frontal gyrus, and superior temporal gyrus in patients with ALS. Tractwise white matter microstructure analyses revealed decreased FA in the tracts connected to the PCG cluster in patients with ALS involving the right corticospinal tract and the middle posterior body of the corpus callosum. Additionally, the cortical thickness of the PCG cluster was found to be positively correlated with FA of the tracts connected to the PCG cluster, suggesting that these two structural features are tightly coupled. Using spectral dynamic causal modelling, effective connectivity analysis among the three regions with cortical thinning revealed decreased self-inhibitory influence in the PCG cluster in patients with ALS, which might be an endophenotypic manifestation of an imbalance in inhibitory and excitatory neurotransmitters in this region.

CONCLUSIONS

The present data shed new light on the structural and functional underpinnings of precentral abnormalities in ALS.

Improving clinical trial outcomes in amyotrophic lateral sclerosis

Individuals who are diagnosed with amyotrophic lateral sclerosis (ALS) today face the same historically intransigent problem that has existed since the initial description of the disease in the 1860s - a lack of effective therapies. In part, the development of new treatments has been hampered by an imperfect understanding of the biological processes that trigger ALS and promote disease progression. Advances in our understanding of these biological processes, including the causative genetic mutations, and of the influence of environmental factors have deepened our appreciation of disease pathophysiology. The consequent identification of pathogenic targets means that the introduction of effective therapies is becoming a realistic prospect. Progress in precision medicine, including genetically targeted therapies, will undoubtedly change the natural history of ALS. The evolution of clinical trial designs combined with improved methods for patient stratification will facilitate the translation of novel therapies into the clinic. In addition, the refinement of emerging biomarkers of therapeutic benefits is critical to the streamlining of care for individuals. In this Review, we synthesize these developments in ALS and discuss the further developments and refinements needed to accelerate the introduction of effective therapeutic approaches.

SQSTM1 variant in disorders of the frontotemporal dementia-amyotrophic lateral sclerosis spectrum: identification of a novel heterozygous variant and a review of the literature

INTRODUCTION

Accumulating evidence shows that SQSTM1 plays a vital role in the pathogenesis of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), which represent a neurodegenerative disease continuum. Here, we report a novel SQSTM1 variant in a patient presenting with progressive nonfluent aphasia (PNFA) and progressive bulbar palsy (PBP). Relevant literature about FTD and FTD-ALS caused by SQSTM1 mutation was reviewed to better understand its clinical features.

METHODS

We collected data from a 66-year-old male patient with a novel heterozygous variant (c.995C > G, p.S332X) in the SQSTM1 gene who was diagnosed with PNFA and PBP and performed a PubMed literature search using the advanced research criteria: [("frontotemporal lobar degeneration") OR ("frontotemporal dementia") OR ("amyotrophic lateral sclerosis") OR ("motor neuron disease")] AND ("SQSTM1"). The clinical features of FTD and FTD-ALS related to SQSTM1 mutation were summarized based on previous cases and our new case.

RESULTS

The initial symptom of the current patient was progressive verb finding difficulties and effortful speech output, which developed into dysarthria and dysphagia in subsequent months. The results, including tongue atrophy, fasciculations, neurogenic changes, and mild left dominant hypometabolism of 18F-fluorodeoxyglucose PET in the frontal cortex, suggest the possibility of PNFA and PBP. A novel likely pathogenic heterozygous variant (c.995C > G, p.S332X) in the SQSTM1 gene was identified. The literature search revealed a total of 33 FTD and FTD-ALS cases related to the SQSTM1 mutation with detailed clinical information. The mean age of onset (including our patient) was 63.5 ± 9.7 years. bvFTD was the most common clinical phenotype. The missense mutation in the SQSTM1 gene coding region and the UBA domain involvement are its main genetic characteristics.

CONCLUSION

Although rare, mutations in SQSTM1 can lead to various clinical subtypes of FTD and FTD-ALS, including the rare combination of PNFA and PBP. Exon missense mutation is the main type of mutation, which is common in the UBA domain.

Modelling frontotemporal dementia using patient-derived induced pluripotent stem cells

Frontotemporal dementia (FTD) describes a group of clinically heterogeneous conditions that frequently affect people under the age of 65 (Le Ber et al., 2013). There are multiple genetic causes of FTD, including coding or splice-site mutations in MAPT, GRN mutations that lead to haploinsufficiency of progranulin protein, and a hexanucleotide GGGGCC repeat expansion in C9ORF72. Pathologically, FTD is characterised by abnormal protein accumulations in neurons and glia. These aggregates can be composed of the microtubule-associated protein tau (observed in FTD with MAPT mutations), the DNA/RNA-binding protein TDP-43 (seen in FTD with mutations in GRN or C9ORF72 repeat expansions) or dipeptide proteins generated by repeat associated non-ATG translation of the C9ORF72 repeat expansion. There are currently no disease-modifying therapies for FTD and the availability of in vitro models that recapitulate pathologies in a disease-relevant cell type would accelerate the development of novel therapeutics. It is now possible to generate patient-specific stem cells through the reprogramming of somatic cells from a patient with a genotype/phenotype of interest into induced pluripotent stem cells (iPSCs). iPSCs can subsequently be differentiated into a plethora of cell types including neurons, astrocytes and microglia. Using this approach has allowed researchers to generate in vitro models of genetic FTD in human cell types that are largely inaccessible during life. In this review we explore the recent progress in the use of iPSCs to model FTD, and consider the merits, limitations and future prospects of this approach.

Altered serum protein levels in frontotemporal dementia and amyotrophic lateral sclerosis indicate calcium and immunity dysregulation

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that are considered to be on the same disease spectrum because of overlapping genetic, pathological and clinical traits. Changes in serum proteins in FTD and ALS are poorly understood, and currently no definitive biomarkers exist for diagnosing or monitoring disease progression for either disease. Here we applied quantitative discovery proteomics to analyze protein changes in FTD (N = 72) and ALS (N = 28) patient serum compared to controls (N = 22). Twenty three proteins were significantly altered in FTD compared to controls (increased-APOL1, C3, CTSH, EIF5A, MYH2, S100A8, SUSD5, WDR1; decreased-C1S, C7, CILP2, COMP, CRTAC1, EFEMP1, FBLN1, GSN, HSPG2, IGHV1, ITIH2, PROS1, SHBG, UMOD, VASN) and 14 proteins were significantly altered in ALS compared to controls (increased-APOL1, CKM, CTSH, IGHG1, IGKC, MYH2; decreased-C7, COMP, CRTAC1, EFEMP1, FBLN1, GSN, HSPG2, SHBG). There was substantial overlap in the proteins that were altered in FTD and ALS. These results were validated using western blotting. Gene ontology tools were used to assess functional pathways potentially dysregulated in the two diseases, and calcium ion binding and innate immunity pathways were altered in both diseases. When put together, these results suggest significant overlap in pathophysiological peripheral changes in FTD and ALS. This study represents the first proteomics side-by-side comparison of serum changes in FTD and ALS, providing new insights into under-recognized perturbed pathways and an avenue for biomarker development for FTD and ALS.

Human salivary Raman fingerprint as biomarker for the diagnosis of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease leading to progressive and irreversible muscle atrophy. The diagnosis of ALS is time-consuming and complex, with the clinical and neurophysiological evaluation accompanied by monitoring of progression and a long procedure for the discrimination of similar neurodegenerative diseases. The delayed diagnosis strongly slows the potential development of adequate therapies and the time frame for a prompt intervention. The discovery of new biomarkers could improve the disease diagnosis, as well as the therapeutic and rehabilitative effectiveness and monitoring of the pathological progression. In this work saliva collected from 19 patients with ALS, 10 affected by Parkinson’s disease, 10 affected by Alzheimer’s disease and 10 healthy subjects, was analysed using Raman spectroscopy, optimizing the parameters for detailed and reproducible spectra. The statistical multivariate analysis of the data revealed a significant difference between the groups, allowing the discrimination of the disease onset. Correlation of Raman data revealed a direct relationship with paraclinical scores, identifying multifactorial biochemical modifications related to the pathology. The proposed approach showed a promising accuracy in ALS onset discrimination, using a fast and sensitive procedure that can make more efficient the diagnostic procedure and the monitoring of therapeutic and rehabilitative processes in ALS.

Genetics and Sex in the Pathogenesis of Amyotrophic Lateral Sclerosis (ALS): Is There a Link?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with no known cure. Approximately 90% of ALS cases are sporadic, although multiple genetic risk factors have been recently revealed also in sporadic ALS (SALS). The pathological expansion of a hexanucleotide repeat in chromosome 9 open reading frame 72 (C9orf72) is the most common genetic mutation identified in familial ALS, detected also in 5–10% of SALS patients. C9orf72-related ALS phenotype appears to be dependent on several modifiers, including demographic factors. Sex has been reported as an independent factor influencing ALS development, with men found to be more susceptible than women. Exposure to both female and male sex hormones have been shown to influence disease risk or progression. Moreover, interplay between genetics and sex has been widely investigated in ALS preclinical models and in large populations of ALS patients carrying C9orf72 repeat expansion. In light of the current need for reclassifying ALS patients into pathologically homogenous subgroups potentially responsive to targeted personalized therapies, we aimed to review the recent literature on the role of genetics and sex as both independent and synergic factors, in the pathophysiology, clinical presentation, and prognosis of ALS. Sex-dependent outcomes may lead to optimizing clinical trials for developing patient-specific therapies for ALS.

Evidence for polygenic and oligogenic basis of Australian sporadic amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with phenotypic and genetic heterogeneity. Approximately 10% of cases are familial, while remaining cases are classified as sporadic. To date, >30 genes and several hundred genetic variants have been implicated in ALS.

METHODS

Seven hundred and fifty-seven sporadic ALS cases were recruited from Australian neurology clinics. Detailed clinical data and whole genome sequencing (WGS) data were available from 567 and 616 cases, respectively, of which 426 cases had both datasets available. As part of a comprehensive genetic analysis, 853 genetic variants previously reported as ALS-linked mutations or disease-associated alleles were interrogated in sporadic ALS WGS data. Statistical analyses were performed to identify correlation between clinical variables, and between phenotype and the number of ALS-implicated variants carried by an individual. Relatedness between individuals carrying identical variants was assessed using identity-by-descent analysis.

RESULTS

Forty-three ALS-implicated variants from 18 genes, including C9orf72, ATXN2, TARDBP, SOD1, SQSTM1 and SETX, were identified in Australian sporadic ALS cases. One-third of cases carried at least one variant and 6.82% carried two or more variants, implicating a potential oligogenic or polygenic basis of ALS. Relatedness was detected between two sporadic ALS cases carrying a SOD1 p.I114T mutation, and among three cases carrying a SQSTM1 p.K238E mutation. Oligogenic/polygenic sporadic ALS cases showed earlier age of onset than those with no reported variant.

CONCLUSION

We confirm phenotypic associations among ALS cases, and highlight the contribution of genetic variation to all forms of ALS.

Interrogating interneurone function using threshold tracking of the H reflex in healthy subjects and patients with motor neurone disease

OBJECTIVE

The excitability of the lower motoneurone pool is traditionally tested using the H reflex and a constant-stimulus paradigm, which measures changes in the amplitude of the reflex response. This technique has limitations because reflex responses of different size must involve the recruitment or inhibition of different motoneurones. The threshold-tracking technique ensures that the changes in excitability occur for an identical population of motoneurones. We aimed to assess this technique and then apply it in patients with motor neurone disease (MND).

METHODS

The threshold-tracking approach was assessed in 17 healthy subjects and 11 patients with MND. The soleus H reflex was conditioned by deep peroneal nerve stimulation producing reciprocal Ia and so-called D1 and D2 inhibitions, which are believed to reflect presynaptic inhibition of soleus Ia afferents.

RESULTS

Threshold tracking was quicker than the constant-stimulus technique and reliable, properties that may be advantageous for clinical studies. D1 inhibition was significantly reduced in patients with MND.

CONCLUSIONS

Threshold tracking is useful and may be preferable under some conditions for studying the excitability of the motoneurone pool. The decreased D1 inhibition in the patients suggests that presynaptic inhibition may be reduced in MND.

SIGNIFICANCE

Reduced presynaptic inhibition could be evidence of an interneuronopathy in MND. It is possible that the hyperreflexia is a spinal pre-motoneuronal disorder, and not definitive evidence of corticospinal involvement in MND.

Electrical impedance myography (EIM) in a natural history study of C9ORF72 mutation carriers

Objective: Electrical Impedance Myography (EIM) was used to evaluate disease progression in subjects with C9ORF72 expansion mutations and to assess correlations with Medical Research Council (MRC) Scale and revised ALS Functional Rating Scale (ALSFRS-R) measurements. Four types of clinical presentations were assessed; Amyotrophic Lateral Sclerosis (ALS), Frontotemporal dementia (FTD) or other dementia, ALS-FTD, and asymptomatic (ASYMP). Methods: Subjects were divided into an ALS Group (ALS/ALS-FTD) and non-ALS Group (FTD/ASYMP) based on initial visit and evaluated at 0, 6, 18, and 30 months with EIM of 4 arm and 4 leg muscles, ALSFRS-R, and MRC scales. The change in EIM from baseline and correlation with the functional scale and strength testing were analyzed. Results: EIM 50kHz phase values significantly declined over time in the ALS group (n = 31) compared to the non-ALS group (FTD/ASYMP) (n = 19). In the ALS group, the decline in EIM was correlated with decline in the ALSFRS-R and MRC scores using within-subject correlations. Conclusion: In clinical trials with small populations of genetically associated ALS such as C9ORF-related ALS, EIM may be a useful quantitative biomarker. We did not detect decline in asymptomatic subjects, but longer term studies may detect early changes in this group.

IN VITRO AND IN VIVO MODELS OF AMYOTROPHIC LATERAL SCLEROSIS: AN UPDATED OVERVIEW

Amyotrophic Lateral Sclerosis (ALS) is a progressive, neurodegenerative disease characterized by loss of upper motor neurons (UMN) and lower motor neurons (LMN). Disease affects people all over the world and is more prevalent in men. Patients with ALS develop extensive muscle wasting, paralysis and ultimately death, with a median survival of usually fewer than five years after disease onset. ALS may be sporadic (sALS, 90%) or familial (fALS, 10%). The large majority of fALS cases are associated with genetic alterations, which are mainly related to the genes SOD1, TDP-43, FUS, and C9ORF72. In vitro and in vivo models have helped elucidate ALS etiology and pathogenesis, as well as its molecular, cellular, and physiological mechanisms. Many studies in cell cultures and animal models, such as Caenorhabditis elegans, Drosophila melanogaster, zebrafish, rodents, and non-human primates have been performed to clarify the relationship of these genes to ALS disease. However, there are inherent limitations to consider when using experimental models. In this review, we provide an updated overview of the most used in vitro and in vivo studies that have contributed to a better understanding of the different ALS pathogenic mechanisms.

On-chip 3D neuromuscular model for drug screening and precision medicine in neuromuscular disease

This protocol describes the design, fabrication and use of a 3D physiological and pathophysiological motor unit model consisting of motor neurons coupled to skeletal muscles interacting via the neuromuscular junction (NMJ) within a microfluidic device. This model facilitates imaging and quantitative functional assessment. The 'NMJ chip' enables real-time, live imaging of axonal outgrowth, NMJ formation and muscle maturation, as well as synchronization of motor neuron activity and muscle contraction under optogenetic control for the study of normal physiological events. The proposed protocol takes ~2-3 months to be implemented. Pathological behaviors associated with various neuromuscular diseases, such as regression of motor neuron axons, motor neuron death, and muscle degradation and atrophy can also be recapitulated in this system. Disease models can be created by the use of patient-derived induced pluripotent stem cells to generate both the motor neurons and skeletal muscle cells used. This is demonstrated by the use of cells from a patient with sporadic amyotrophic lateral sclerosis but can be applied more generally to models of neuromuscular disease, such as spinal muscular atrophy, NMJ disorder and muscular dystrophy. Models such as this hold considerable potential for applications in precision medicine, drug screening and disease risk assessment.

Pre-symptomatic diagnosis in ALS

Pathophysiology of amyotrophic lateral sclerosis (ALS) remains partially understood even though it is accepted worldwide that motor neuron death results from a pluri-factorial process with a variable role of genetic factors. Although not distinguishable from a clinical point of view, familial forms of ALS (fALS, 10% of cases) and sporadic forms (sALS, 90% of cases) can be described. Since the identification of superoxide dismutase 1 gene (SOD1) mutations, more than 30 genes have been linked to fALS. Among these genes, five (C9ORF72, SOD1, TARDBP, FUS, TBK1) seem predominant with mutation frequencies of 40%, 20%, 5%, <5%, <5% in fALS and 6%, 3%, and <1% for the last three in sALS, respectively. The situation that classically leads to request genetic screening is the presence of a familial history of motor neuron disorders (MND) or fronto-temporal lobar dementia (FTLD). However, this dichotomy between fALS and sALS based on familial history can lead to mistakes since illegitimacy, ignorance of MND, FTD or psychiatric disorders within the family due to a familial censorship or lack of familial relationship, or a recessive autosomal inheritance could wrongly lead to failing to recognize a familial form. The significant development of genetic research and easier access to genetic tests in fALS increase the number of situations for which gene mutations are identified. The consequence is an increase in genetic requests from relatives of ALS patients who are eager to know their own genetic status and their own individual risk to develop ALS. Pre-symptomatic testing is thus becoming a daily issue in ALS Centers. This led us to propose a framework for such pre-symptomatic genetic testing for people at risk for developing ALS.

Circuit Mechanisms of Neurodegenerative Diseases: A New Frontier With Miniature Fluorescence Microscopy

Neurodegenerative diseases (NDDs), such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD), are devastating age-associated brain disorders. Significant efforts have been made to uncover the molecular and cellular pathogenic mechanisms that underlie NDDs. However, our understanding of the neural circuit mechanisms that mediate NDDs and associated symptomatic features have been hindered by technological limitations. Our inability to identify and track individual neurons longitudinally in subcortical brain regions that are preferentially targeted in NDDs has left gaping holes in our knowledge of NDDs. Recent development and advancement of the miniature fluorescence microscope (miniscope) has opened up new avenues for examining spatially and temporally coordinated activity from hundreds of cells in deep brain structures in freely moving rodents. In the present mini-review, we examine the capabilities of current and future miniscope tools and discuss the innovative applications of miniscope imaging techniques that can push the boundaries of our understanding of neural circuit mechanisms of NDDs into new territories.

TDP-43 levels in the brain tissue of ALS cases with and without C9ORF72 or ATXN2 gene expansions

OBJECTIVE

To assess the amount of phosphorylated and nonphosphorylated TAR DNA-binding protein 43 (TDP-43) in the motor brain regions of cases of amyotrophic lateral sclerosis (ALS) with and without repeat expansions in the ATXN2 or C9ORF72 genes.

METHODS

The 45-kDa phosphorylated form of TDP-43 and 43-kDa nonphosphorylated form of TDP-43 were quantified by immunoblot in postmortem brain tissue from the motor cortex, spinal cord, and cerebellar vermis of 23 cases with ALS with repeat expansions in the ATXN2 or C9ORF72 genes and sporadic disease and 10 controls.

RESULTS

Significantly greater levels of phosphorylated TDP-43 were identified in the motor cortex of cases with ALS with C9ORF72 expansions, and significantly greater amounts of phosphorylated TDP-43 were found in the spinal cord of cases with ALS with intermediate ATXN2 expansions. In contrast, however, similar levels of nonphosphorylated TDP-43 were found in all 3 regions between ALS groups.

CONCLUSION

Despite its central role in the pathogenesis of ALS and the emergence of potential targets to modify its aggregation, TDP-43 levels have not been quantified in pathologically confirmed cases with ALS. The present results demonstrating significant differences in phosphorylated but not nonphosphorylated TDP-43 levels suggest that different posttranslational modifications are involved in the generation of greater pathologic TDP-43 levels identified here in our cohort of cases with genetic expansions. These findings are consistent with emerging studies implicating distinct pathomechanisms in the generation of pathologic TDP-43 in cases with ALS with C9ORF72 or ATXN2 expansions and are of relevance to therapeutic research aimed at reducing pathologic TDP-43 in all or a subset of patients with ALS.

C9orf72-mediated ALS and FTD: multiple pathways to disease

The discovery that repeat expansions in the C9orf72 gene are a frequent cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) has revolutionized our understanding of these diseases. Substantial headway has been made in characterizing C9orf72-mediated disease and unravelling its underlying aetiopathogenesis. Three main disease mechanisms have been proposed: loss of function of the C9orf72 protein and toxic gain of function from C9orf72 repeat RNA or from dipeptide repeat proteins produced by repeat-associated non-ATG translation. Several downstream processes across a range of cellular functions have also been implicated. In this article, we review the pathological and mechanistic features of C9orf72-associated FTD and ALS (collectively termed C9FTD/ALS), the model systems used to study these conditions, and the probable initiators of downstream disease mechanisms. We suggest that a combination of upstream mechanisms involving both loss and gain of function and downstream cellular pathways involving both cell-autonomous and non-cell-autonomous effects contributes to disease progression.

Modified age-dependent expression of NaV1.6 in an ALS model correlates with motor cortex excitability alterations

Cortical hyperexcitability is an early and intrinsic feature of Amyotrophic Lateral Sclerosis (ALS), but the mechanisms underlying this critical neuronal dysfunction are poorly understood. Recently, we have demonstrated that layer V pyramidal neurons (PNs) in the primary motor cortex (M1) of one-month old (P30) G93A ALS mice display an early hyperexcitability status compared to Control mice. In order to investigate the time-dependent evolution of the cortical excitability in the G93A ALS model, here we have performed an electrophysiological and immunohistochemical study at three different mouse ages. M1 PNs from 14-days old (P14) G93A mice have shown no excitability alterations, while M1 PNs from 3-months old (P90) G93A mice have shown a hypoexcitability status, compared to Control mice. These age-dependent cortical excitability dysfunctions correlate with a similar time-dependent trend of the persistent sodium current (INa_P) amplitude alterations, suggesting that INa_P may play a crucial role in the G93A cortical excitability aberrations. Specifically, immunohistochemistry experiments have indicated that the expression level of the NaV1.6 channel, one of the voltage-gated Na⁺ channels mainly distributed within the central nervous system, varies in G93A primary motor cortex during disease progression, according to the excitability and INa_P alterations, but not in other cortical areas. Microfluorometry experiments, combined with electrophysiological recordings, have verified that P30 G93A PNs hyperexcitability is associated to a greater accumulation of intracellular calcium ([Ca²⁺]_i) compared to Control PNs, and that this difference is still present when G93A and Control PNs fire action potentials at the same frequency. These results suggest that [Ca²⁺]_i de-regulation in G93A PNs may contribute to neuronal demise and that the NaV1.6 channels could be a potential therapeutic target to ameliorate ALS disease progression.

Augmentation of spinal cord glutamatergic synaptic currents in zebrafish primary motoneurons expressing mutant human TARDBP (TDP-43)

Though there is compelling evidence that de-innervation of neuromuscular junctions (NMJ) occurs early in amyotrophic lateral sclerosis (ALS), defects arising at synapses in the spinal cord remain incompletely understood. To investigate spinal cord synaptic dysfunction, we took advantage of a zebrafish larval model and expressed either wild type human TARDBP (wtTARDBP) or the ALS-causing G348C variant (mutTARDBP). The larval zebrafish is ideally suited to examine synaptic connectivity between descending populations of neurons and spinal cord motoneurons as a fully intact spinal cord is preserved during experimentation. Here we provide evidence that the tail-beat motor pattern is reduced in both frequency and duration in larvae expressing mutTARDBP. In addition, we report that motor-related synaptic depolarizations in primary motoneurons of the spinal cord are shorter in duration and fewer action potentials are evoked in larvae expressing mutTARDBP. To more thoroughly examine spinal cord synaptic dysfunction in our ALS model, we isolated AMPA/kainate-mediated glutamatergic miniature excitatory post-synaptic currents in primary motoneurons and found that in addition to displaying a larger amplitude, the frequency of quantal events was higher in larvae expressing mutTARDBP when compared to larvae expressing wtTARDBP. In a final series of experiments, we optogenetically drove neuronal activity in the hindbrain and spinal cord population of descending ipsilateral glutamatergic interneurons (expressing Chx10) using the Gal4-UAS system and found that larvae expressing mutTARDBP displayed abnormal tail-beat patterns in response to optogenetic stimuli and augmented synaptic connectivity with motoneurons. These findings indicate that expression of mutTARDBP results in functionally altered glutamatergic synapses in the spinal cord.

Pathophysiology and Diagnosis of ALS: Insights from Advances in Neurophysiological Techniques

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disorder of the motor neurons, characterized by focal onset of muscle weakness and incessant disease progression. While the presence of concomitant upper and lower motor neuron signs has been recognized as a pathognomonic feature of ALS, the pathogenic importance of upper motor neuron dysfunction has only been recently described. Specifically, transcranial magnetic stimulation (TMS) techniques have established cortical hyperexcitability as an important pathogenic mechanism in ALS, correlating with neurodegeneration and disease spread. Separately, ALS exhibits a heterogeneous clinical phenotype that may lead to misdiagnosis, particularly in the early stages of the disease process. Cortical hyperexcitability was shown to be a robust diagnostic biomarker if ALS, reliably differentiating ALS from neuromuscular mimicking disorders. The present review will provide an overview of key advances in the understanding of ALS pathophysiology and diagnosis, focusing on the importance of cortical hyperexcitability and its relationship to advances in genetic and molecular processes implicated in ALS pathogenesis.

Neurophysiological biomarkers in amyotrophic lateral sclerosis

PURPOSE OF REVIEW

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons, characterized by upper motor neuron (UMN) and lower motor neuron (LMN) dysfunction. There have been significant technological advances in the development of neurophysiological biomarkers of UMN and LMN dysfunction in ALS. In this review, we discuss major advances in development of neurophysiological biomarkers in ALS, critiquing their potential in diagnosis and prognosis of ALS, as well as utility in monitoring treatment effects.

RECENT FINDINGS

The threshold tracking transcranial magnetic stimulation (TMS) technique has established cortical hyperexcitability as an early and specific biomarker of UMN dysfunction in ALS, and associated with neurodegeneration. In addition to establishing cortical hyperexcitability as a pathophysiological mechanism, threshold tracking TMS has enabled an earlier diagnosis of ALS and provided a means of monitoring effects of therapeutic agents. Biomarkers of LMN dysfunction, including motor unit number estimation, the neurophysiological index, electrical impedance myography and axonal excitability techniques, have all exhibited utility in monitoring disease progression.

SUMMARY

In addition to enhancing ALS diagnosis, the development of novel neurophysiological biomarkers has implications for clinical trials research and drug development, enabling the assessment of biological efficacy of agents in early stages of drug development.

Frontotemporal dementia

Frontotemporal dementia (FTD) is the second commonest cause of young onset dementia. Our understanding of FTD and its related syndromes has advanced significantly in recent years. Among the most prominent areas of progress is the overlap between FTD, MND, and other neurodegenerative conditions at a clinicopathologic and genetic level. In parallel major advances in neuroimaging techniques, the discovery of new genetic mutations as well as the development of potential biomarkers may serve to further expand knowledge of the biologic processes at play in FTD and may in turn propel research toward identifying curative and preventative pharmacologic therapies. The aim of this chapter is to discuss the clinical, pathologic, and genetic complexities of FTD and related disorders.

Biomarkers for Amyotrophic Lateral Sclerosis and Frontotemporal Dementia Associated With Hexanucleotide Expansion Mutations in C9orf72

Now that genetic testing can identify persons at risk for developing amyotrophic lateral sclerosis (ALS) many decades before symptoms begin, there is a critical need for biomarkers that signal the onset and progression of degeneration. The search for candidate disease biomarkers in patients with mutations in the gene C9orf72 has included imaging, physiology, and biofluid measurements. In cross-sectional imaging studies, C9+ ALS patients display diffuse reductions of gray and white matter integrity compared to ALS patients without mutations. This structural imaging signature overlaps with frontotemporal dementia (FTD), reflecting the frequent co-occurrence of cognitive impairment, even frank FTD, in C9+ ALS patients. Changes in functional connectivity occur as critical components of the networks associated with cognition and behavior degenerate. In presymptomatic C9+carriers, subtle differences in volumes of subcortical structures and functional connectivity can be detected, often decades before the typical family age of symptom onset. Dipeptide repeat proteins produced by the repeat expansion mutation are also measurable in the cerebrospinal fluid (CSF) of presymptomatic gene carriers, possibly throughout their lives. In contrast, a rise in the level of neurofilament proteins in the CSF appears to presage the onset of degeneration in presymptomatic carriers in one longitudinal study. Cross-sectional studies indicate that neurofilament protein levels may provide prognostic information for survival in C9+ ALS patients. Longitudinal studies will be needed to validate the candidate biomarkers discussed here. Understanding how these candidate biomarkers change over time is critical if they are to be used in future therapeutic decisions.

Utility of threshold tracking transcranial magnetic stimulation in ALS

Upper motor neuron [UMN] and lower motor neuron [LMN] dysfunction, in the absence of sensory features, is a pathognomonic feature of amyotrophic lateral sclerosis [ALS]. Although the precise mechanisms have yet to be elucidated, one leading hypothesis is that UMN precede LMN dysfunction, which is induced by anterograde glutamatergic excitotoxicity. Transcranial magnetic stimulation (TMS) is a neurophysiological tool that provides a non-invasive and painless assessment of cortical function. Threshold tracking methodologies have been recently adopted for TMS, whereby changes in threshold rather than motor evoked potential (MEP) amplitude serve as outcome measures. This technique is reliable and provides a rapid assessment of cortical function in ALS. Utilisng the threshold tracking TMS technique, cortical hyperexcitability was demonstrated as an early feature in sporadic ALS preceding the onset of LMN dysfunction and possibly contributing to disease spread. Separately, cortical hyperexcitability was reported to precede the clinical onset of familial ALS. Of further relevance, the threshold tracking TMS technique was proven to reliably distinguish ALS from mimicking disorders, even in the presence of a comparable degree of LMN dysfunction, suggesting a diagnostic utility of TMS. Taken in total, threshold tracking TMS has provided support for a cortical involvement at the earliest detectable stages of ALS, underscoring the utility of the technique for probing the underlying pathophysiology. The present review will discuss the physiological processes underlying TMS parameters, while further evaluating the pathophysiological and diagnostic utility of threshold tracking TMS in ALS.

Modeling the C9ORF72 repeat expansion mutation using human induced pluripotent stem cells

C9ORF72 repeat expansion is the most frequent causal genetic mutation giving rise to amyotrophic lateral sclerosis (ALS) and fronto‐temporal dementia (FTD). The relatively recent discovery of the C9ORF72 repeat expansion in 2011 and the complexity of the mutation have meant that animal models that successfully recapitulate human C9ORF72 repeat expansion‐mediated disease are only now emerging. Concurrent advances in the use of patient‐derived induced pluripotent stem cells (iPSCs) to model aspects of neurological disease offers an additional approach for the study of C9ORF72 mutation. This review focuses on the opportunities of human C9ORF72 iPSC platforms to model pathological aspects of disease and how findings compare with other existing models of disease and post mortem data.

Amyotrophic lateral sclerosis-A case report and mechanistic review of the association with toluene and other volatile organic compounds

Unmasking of latent neurodegenerative disease has been reported following exposure to chemicals that share one or more mechanisms of action in common with those implicated in the specific disease. For example, unmasking of latent Parkinson's disease (PD) has been associated with exposure to anti-dopaminergic agents, while the progression of pre-existing mild cognitive impairment and unmasking of latent Alzheimer's disease has been associated with exposure to general anesthetic agents which promote Aβ protein aggregation. This literature review and clinical case report about a 45-year-old man with no family history of motor neuron disease who developed overt symptoms of a neuromuscular disorder in close temporal association with his unwitting occupational exposure to volatile organic compounds (VOCs) puts forth the hypothesis that exposure to VOCs such as toluene, which disrupt motor function and increase oxidative stress, can unmask latent ALS type neuromuscular disorder in susceptible individuals.

The frequency of the C9orf72 expansion in a Brazilian population

G₄C₂ hexanucleotide repeat expansions in the C9orf72 gene seem to be the cause of numerous cases of amyotrophic lateral sclerosis (ALS) and/or frontotemporal dementia (FTD). In this study, we investigated the presence of the G₄C₂ repeat expansion in 463 Brazilian probands, of whom 404 had ALS/motor neuron disease and 67 FTD, and in 63 healthy controls in the southeastern region of Brazil. The highest frequencies of the C9orf72 mutation were in the ALS-FTD group (50% of familial and 17.6% of sporadic cases), although it was also present in 5% of pure ALS/motor neuron disease patients (11.8% of familial and 3.6% of sporadic cases) and in 7.1% of pure familial FTD. Among G₄C₂ repeat mutation carriers, 68.8% of the subjects who developed dementia symptoms were females. This frequency was significantly higher than the percentage reached by men with C9orf72 expansion who had this phenotype (p = 0.047). No abnormal repeat expansion was found in control groups. Inclusion of the C9orf72 genetic test in the molecular panels for Brazilian populations with these neurodegenerative diseases should be strongly considered.

Unaffected mosaic C9orf72 case: RNA foci, dipeptide proteins, but upregulated C9orf72 expression

Objective

Suggested C9orf72 disease mechanisms for amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration include C9orf72 haploinsufficiency, G₄C₂/C₄G₂ RNA foci, and dipeptide repeat (DPR) proteins translated from the G₄C₂ expansion; however, the role of small expansions (e.g., 30–90 repeats) is unknown and was investigated here.

Methods

We conducted a molecular and pathology study of a family in which the father (unaffected at age 90) carried a 70-repeat allele in blood DNA that expanded to ≈1,750 repeats in his children, causing ALS.

Results

Southern blotting revealed different degrees of mosaicism of small and large expansions in the father's tissues from the CNS. Surprisingly, in each mosaic tissue, C9orf72 mRNA levels were significantly increased compared to an ALS-affected daughter with a large expansion. Increased expression correlated with higher levels of the 70-repeat allele (the upregulation was also evident at the protein level). Remarkably, RNA foci and DPR burdens were similar or even significantly increased (in cerebellum) in the unaffected father compared to the daughter with ALS. However, the father did not display TDP-43 pathology and signs of neurodegeneration.

Conclusion

The presence of RNA foci and DPR pathology was insufficient for disease manifestation and TDP-43 pathology in the mosaic C9orf72 carrier with upregulated C9orf72 expression. It is important to conduct an investigation of similar cases, which could be found among unaffected parents of sporadic C9orf72 patients (e.g., 21% among Finnish patients with ALS). Caution should be taken when consulting carriers of small expansions because disease manifestation could be dependent on the extent of the somatic instability in disease-relevant tissues.

Poly(GP) proteins are a useful pharmacodynamic marker for C9ORF72-associated amyotrophic lateral sclerosis

There is no effective treatment for amyotrophic lateral sclerosis (ALS), a devastating motor neuron disease. However, discovery of a G₄C₂ repeat expansion in the C9ORF72 gene as the most common genetic cause of ALS has opened up new avenues for therapeutic intervention for this form of ALS. G₄C₂ repeat expansion RNAs and proteins of repeating dipeptides synthesized from these transcripts are believed to play a key role in C9ORF72-associated ALS (c9ALS). Therapeutics that target G₄C₂ RNA, such as antisense oligonucleotides (ASOs) and small molecules, are thus being actively investigated. A limitation in moving such treatments from bench to bedside is a lack of pharmacodynamic markers for use in clinical trials. We explored whether poly(GP) proteins translated from G₄C₂ RNA could serve such a purpose. Poly(GP) proteins were detected in cerebrospinal fluid (CSF) and in peripheral blood mononuclear cells from c9ALS patients and, notably, from asymptomatic C9ORF72 mutation carriers. Moreover, CSF poly(GP) proteins remained relatively constant over time, boding well for their use in gauging biochemical responses to potential treatments. Treating c9ALS patient cells or a mouse model of c9ALS with ASOs that target G₄C₂ RNA resulted in decreased intracellular and extracellular poly(GP) proteins. This decrease paralleled reductions in G₄C₂ RNA and downstream G₄C₂ RNA-mediated events. These findings indicate that tracking poly(GP) proteins in CSF could provide a means to assess target engagement of G₄C₂ RNA-based therapies in symptomatic C9ORF72 repeat expansion carriers and presymptomatic individuals who are expected to benefit from early therapeutic intervention.

Current Advances and Limitations in Modeling ALS/FTD in a Dish Using Induced Pluripotent Stem Cells

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two age-dependent multifactorial neurodegenerative disorders, which are typically characterized by the selective death of motor neurons and cerebral cortex neurons, respectively. These two diseases share many clinical, genetic and pathological aspects. During the past decade, cell reprogramming technologies enabled researchers to generate human induced pluripotent stem cells (iPSCs) from somatic cells. This resulted in the unique opportunity to obtain specific neuronal and non-neuronal cell types from patients which could be used for basic research. Moreover, these in vitro models can mimic not only the familial forms of ALS/FTD, but also sporadic cases without known genetic cause. At present, there have been extensive technical advances in the generation of iPSCs, as well as in the differentiation procedures to obtain iPSC-derived motor neurons, cortical neurons and non-neuronal cells. The major challenge at this moment is to determine whether these iPSC-derived cells show relevant phenotypes that recapitulate complex diseases. In this review, we will summarize the work related to iPSC models of ALS and FTD. In addition, we will discuss potential drawbacks and solutions for establishing more trustworthy iPSC models for both ALS and FTD.

Sex differences in the prevalence of genetic mutations in FTD and ALS: A meta-analysis

OBJECTIVE

To conduct a meta-analysis that investigates sex differences in the prevalence of mutations in the 3 most common genes that cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD)-chromosome 9 open reading frame 72 (C9orf72), progranulin (GRN), or microtubule-associated protein tau (MAPT)-in patients clinically diagnosed with these conditions.

METHODS

MEDLINE, EMBASE, and PsycINFO databases were searched (inception to June 30, 2016). Studies of patients with FTD or ALS that reported the number of men and women with and without mutations of interest were selected. Female to male pooled risk ratios (RR) and 95% confidence intervals (CI) for each mutation were calculated using random-effects models.

RESULTS

Thirty-two articles reporting 12,784 patients with ALS (including 1,244 C9orf72 mutation carriers) revealed a higher prevalence of female patients with C9orf72-related ALS (RR 1.16, 95% CI 1.04-1.29). Twenty-three articles reporting 5,320 patients with FTD (including 488 C9orf72 mutation carriers) revealed no sex differences in C9orf72-related FTD (RR 0.95, 95% CI 0.81-1.12). Thirty-six articles reporting 3,857 patients with FTD (including 369 GRN mutation carriers) revealed a higher prevalence of female patients with GRN-related FTD (RR 1.33, 95% CI 1.09-1.62). Finally, 21 articles reporting 2,377 patients with FTD (including 215 MAPT mutation carriers) revealed no sex difference in MAPT-related FTD (RR 1.21, 95% CI 0.95-1.55).

CONCLUSIONS

Higher female prevalence of C9orf72 hexanucleotide repeat expansions in ALS and GRN mutations in FTD suggest that sex-related risk factors might moderate C9orf72 and GRN-mediated phenotypic expression.

Changes in the Excitability of Neocortical Neurons in a Mouse Model of Amyotrophic Lateral Sclerosis Are Not Specific to Corticospinal Neurons and Are Modulated by Advancing Disease

Cell type-specific changes in neuronal excitability have been proposed to contribute to the selective degeneration of corticospinal neurons in amyotrophic lateral sclerosis (ALS) and to neocortical hyperexcitability, a prominent feature of both inherited and sporadic variants of the disease, but the mechanisms underlying selective loss of specific cell types in ALS are not known. We analyzed the physiological properties of distinct classes of cortical neurons in the motor cortex of hSOD1^G93A mice of both sexes and found that they all exhibit increases in intrinsic excitability that depend on disease stage. Targeted recordings and in vivo calcium imaging further revealed that neurons adapt their functional properties to normalize cortical excitability as the disease progresses. Although different neuron classes all exhibited increases in intrinsic excitability, transcriptional profiling indicated that the molecular mechanisms underlying these changes are cell type specific. The increases in excitability in both excitatory and inhibitory cortical neurons show that selective dysfunction of neuronal cell types cannot account for the specific vulnerability of corticospinal motor neurons in ALS. Furthermore, the stage-dependent alterations in neuronal function highlight the ability of cortical circuits to adapt as disease progresses. These findings show that both disease stage and cell type must be considered when developing therapeutic strategies for treating ALS.SIGNIFICANCE STATEMENT It is not known why certain classes of neurons preferentially die in different neurodegenerative diseases. It has been proposed that the enhanced excitability of affected neurons is a major contributor to their selective loss. We show using a mouse model of amyotrophic lateral sclerosis (ALS), a disease in which corticospinal neurons exhibit selective vulnerability, that changes in excitability are not restricted to this neuronal class and that excitability does not increase monotonically with disease progression. Moreover, although all neuronal cell types tested exhibited abnormal functional properties, analysis of their gene expression demonstrated cell type-specific responses to the ALS-causing mutation. These findings suggest that therapies for ALS may need to be tailored for different cell types and stages of disease.

Mouse Models of C9orf72 Hexanucleotide Repeat Expansion in Amyotrophic Lateral Sclerosis/ Frontotemporal Dementia

The presence of hexanucleotide repeat expansion (HRE) in the first intron of the human C9orf72 gene is the most common genetic cause underlying both familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Studies aimed at elucidating the pathogenic mechanisms associated of C9orf72 FTD and ALS (C9FTD/ALS) have focused on the hypothesis of RNA and protein toxic gain-of-function models, including formation of nuclear RNA foci containing GGGGCC (G₄C₂) HRE, inclusions containing dipeptide repeat proteins through a non-canonical repeat associated non-ATG (RAN) translation mechanism, and on loss-of-function of the C9orf72 protein. Immense effort to elucidate these mechanisms has been put forth and toxic gain-of-function models have especially gained attention. Various mouse models that recapitulate distinct disease-related pathological, functional, and behavioral phenotypes have been generated and characterized. Although these models express the C9orf72 HRE mutation, there are numerous differences among them, including the transgenesis approach to introduce G₄C₂-repeat DNA, genomic coverage of C9orf72 features in the transgene, G₄C₂-repeat length after genomic stabilization, spatiotemporal expression profiles of RNA foci and RAN protein aggregates, neuropathological features, and neurodegeneration-related clinical symptoms. This review aims to (1) provide an overview of the key characteristics; (2) provide insights into potential pathological factors contributing to neurotoxicity and clinical phenotypes through systematic comparison of these models.

Predictive genetic testing for amyotrophic lateral sclerosis and frontotemporal dementia: genetic counselling considerations

Once a gene mutation that is causal of amyotrophic lateral sclerosis (ALS) and/or frontotemporal dementia (FTD) is identified in a family, relatives may decide to undergo predictive genetic testing to determine whether they are at risk of developing disease. Recent advances in gene discovery have led to a pressing need to better understand the implications of predictive genetic testing. Here we review the uptake of genetic counselling, predictive and reproductive testing, and the factors that impact the decision to undergo testing, for consideration in clinical practice. The literature suggests that the factors impacting the decision to undergo testing are complex due to the nature of these diseases, absence of available preventative medical treatment and variable age of onset in mutation carriers. Gaining further insight into the decision-making process and the impact of testing is critical as we seek to develop best-practice guidelines for predictive testing for familial ALS and FTD.

The genotype-phenotype landscape of familial amyotrophic lateral sclerosis in Australia

Amyotrophic lateral sclerosis (ALS) is a clinically and genetically heterogeneous fatal neurodegenerative disease. Around 10% of ALS cases are hereditary. ALS gene discoveries have provided most of our understanding of disease pathogenesis. We aimed to describe the genetic landscape of ALS in Australia by assessing 1013 Australian ALS patients for known ALS mutations by direct sequencing, whole exome sequencing or repeat primed polymerase chain reaction. Age of disease onset and disease duration were used for genotype-phenotype correlations. We report 60.8% of Australian ALS families in this cohort harbour a known ALS mutation. Hexanucleotide repeat expansions in C9orf72 accounted for 40.6% of families and 2.9% of sporadic patients. We also report ALS families with mutations in SOD1 (13.7%), FUS (2.4%), TARDBP (1.9%), UBQLN2 (.9%), OPTN (.5%), TBK1 (.5%) and CCNF (.5%). We present genotype-phenotype correlations between these genes as well as between gene mutations. Notably, C9orf72 hexanucleotide repeat expansion positive patients experienced significantly later disease onset than ALS mutation patients. Among SOD1 families, p.I114T positive patients had significantly later onset and longer survival. Our report highlights a unique spectrum of ALS gene frequencies among patients from the Australian population, and further, provides correlations between specific ALS mutations with disease onset and/or duration.