Making connections: pathology and genetics link amyotrophic lateral sclerosis with frontotemporal lobe dementia

A bioinformatic investigation of proteasome and autophagy expression in the central nervous system

The ubiquitin proteasome system (UPS) and autophagy lysosome pathway (ALP) are crucial in the control of protein quality. However, data regarding the relative significance of UPS and ALP in the central nervous system (CNS) are limited. In the present study, using publicly available data, we computed the quantitative expression status of UPS- and ALP-related genes and their products in the CNS as compared with that in other tissues and cells. We obtained human and mouse gene expression datasets from the reference expression dataset (RefEx) and Genevestigator (a tool for handling curated transcriptomic data from public repositories) as well as human proteomics data from the proteomics database (ProteomicsDB). The expression levels of genes and proteins in four categories-ubiquitin, proteasome, autophagy, and lysosome--in the cells and tissues were assessed. Perturbation of the gene expression by drugs was also analyzed for the four categories. Compared with that for ubiquitin, autophagy, and lysosome, gene expression for proteasome was consistently lower in the CNS of mice but was more pronounced in humans. Neural stem cells and neurons showed low proteasome gene expression as compared with embryonic stem cells. Proteomic analyses, however, did not show trends similar to those observed in the gene expression analyses. Perturbation analyses revealed that azithromycin and vitamin D3 upregulated the expression of both UPS and ALP. Gene and proteomic expression data could offer a fresh perspective on CNS pathophysiology. Our results indicate that disproportional expression of UPS and ALP might affect CNS disorders and that this imbalance might be redressed by several therapeutic candidates.

Autophagy Dysfunction in ALS: from Transport to Protein Degradation

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting upper and lower motor neurons (MNs). Since the identification of the first ALS mutation in 1993, more than 40 genes have been associated with the disorder. The most frequent genetic causes of ALS are represented by mutated genes whose products challenge proteostasis, becoming unable to properly fold and consequently aggregating into inclusions that impose proteotoxic stress on affected cells. In this context, increasing evidence supports the central role played by autophagy dysfunctions in the pathogenesis of ALS. Indeed, in early stages of disease, high levels of proteins involved in autophagy are present in ALS MNs; but at the same time, with neurodegeneration progression, autophagy-mediated degradation decreases, often as a result of the accumulation of toxic protein aggregates in affected cells. Autophagy is a complex multistep pathway that has a central role in maintaining cellular homeostasis. Several proteins are involved in its tight regulation, and importantly a relevant fraction of ALS-related genes encodes products that directly take part in autophagy, further underlining the relevance of this key protein degradation system in disease onset and progression. In this review, we report the most relevant findings concerning ALS genes whose products are involved in the several steps of the autophagic pathway, from phagophore formation to autophagosome maturation and transport and finally to substrate degradation.

The Interplay Between Autophagy and RNA Homeostasis: Implications for Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Amyotrophic lateral sclerosis and frontotemporal dementia are neurodegenerative disorders that lie on a disease spectrum, sharing genetic causes and pathology, and both without effective therapeutics. Two pathways that have been shown to play major roles in disease pathogenesis are autophagy and RNA homeostasis. Intriguingly, there is an increasing body of evidence suggesting a critical interplay between these pathways. Autophagy is a multi-stage process for bulk and selective clearance of malfunctional cellular components, with many layers of regulation. Although the majority of autophagy research focuses on protein degradation, it can also mediate RNA catabolism. ALS/FTD-associated proteins are involved in many stages of autophagy and autophagy-mediated RNA degradation, particularly converging on the clearance of persistent pathological stress granules. In this review, we will summarise the progress in understanding the autophagy-RNA homeostasis interplay and how that knowledge contributes to our understanding of the pathobiology of ALS/FTD.

DNA Damage, Defective DNA Repair, and Neurodegeneration in Amyotrophic Lateral Sclerosis

DNA is under constant attack from both endogenous and exogenous sources, and when damaged, specific cellular signalling pathways respond, collectively termed the “DNA damage response.” Efficient DNA repair processes are essential for cellular viability, although they decline significantly during aging. Not surprisingly, DNA damage and defective DNA repair are now increasingly implicated in age-related neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). ALS affects both upper and lower motor neurons in the brain, brainstem and spinal cord, leading to muscle wasting due to denervation. DNA damage is increasingly implicated in the pathophysiology of ALS, and interestingly, the number of DNA damage or repair proteins linked to ALS is steadily growing. This includes TAR DNA binding protein 43 (TDP-43), a DNA/RNA binding protein that is present in a pathological form in almost all (97%) cases of ALS. Hence TDP-43 pathology is central to neurodegeneration in this condition. Fused in Sarcoma (FUS) bears structural and functional similarities to TDP-43 and it also functions in DNA repair. Chromosome 9 open reading frame 72 (C9orf72) is also fundamental to ALS because mutations in C9orf72 are the most frequent genetic cause of both ALS and related condition frontotemporal dementia, in European and North American populations. Genetic variants encoding other proteins involved in the DNA damage response (DDR) have also been described in ALS, including FUS, SOD1, SETX, VCP, CCNF, and NEK1. Here we review recent evidence highlighting DNA damage and defective DNA repair as an important mechanism linked to neurodegeneration in ALS.

Mitochondria Dysfunction in Frontotemporal Dementia/Amyotrophic Lateral Sclerosis: Lessons From Drosophila Models

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative disorders characterized by declining motor and cognitive functions. Even though these diseases present with distinct sets of symptoms, FTD and ALS are two extremes of the same disease spectrum, as they show considerable overlap in genetic, clinical and neuropathological features. Among these overlapping features, mitochondrial dysfunction is associated with both FTD and ALS. Recent studies have shown that cells derived from patients' induced pluripotent stem cells (iPSC)s display mitochondrial abnormalities, and similar abnormalities have been observed in a number of animal disease models. Drosophila models have been widely used to study FTD and ALS because of their rapid generation time and extensive set of genetic tools. A wide array of fly models have been developed to elucidate the molecular mechanisms of toxicity for mutations associated with FTD/ALS. Fly models have been often instrumental in understanding the role of disease associated mutations in mitochondria biology. In this review, we discuss how mutations associated with FTD/ALS disrupt mitochondrial function, and we review how the use of Drosophila models has been pivotal to our current knowledge in this field.

Glutathione in the Nervous System as a Potential Therapeutic Target to Control the Development and Progression of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare neurological disorder that affects the motor neurons responsible for regulating muscle movement. However, the molecular pathogenic mechanisms of ALS remain poorly understood. A deficiency in the antioxidant tripeptide glutathione (GSH) in the nervous system appears to be involved in several neurodegenerative diseases characterized by the loss of neuronal cells. Impaired antioxidant defense systems, and the accumulation of oxidative damage due to increased dysfunction in GSH homeostasis are known to be involved in the development and progression of ALS. Aberrant GSH metabolism and redox status following oxidative damage are also associated with various cellular organelles, including the mitochondria and nucleus, and are crucial factors in neuronal toxicity induced by ALS. In this review, we provide an overview of the implications of imbalanced GSH homeostasis and its molecular characteristics in various experimental models of ALS.

The heterozygous deletion c.1509_1510delAG in exon 14 of FUS causes an aggressive childhood-onset ALS with cognitive impairment

We report a case of childhood-onset ALS with a FUS gene mutation presenting cognitive impairment and a rapid clinical progression. The patient, an 11-year-old girl, presented with right distal upper limb weakness and mild intellectual disability at the Griffith Mental Development Scales. The disease rapidly worsened and the patient became tetraplegic and bed-ridden 2 years after symptom onset. A c.1509_1510delAG mutation in exon 14 of the FUS gene was detected, resulting in a predicted truncated protein, p.G504Wfs*12, lacking the nuclear localization signal. The levels of FUS mRNA in the proband were not significantly different compared to controls. Western immunoblot analysis showed that one antibody (500-526) detected in the proband ~50% of the amount of FUS protein compared to controls, while 3 other antibodies (2-27, 400-450 and FUS C-terminal), which recognize both wild type and the mutated FUS, detected 60% to 75% of the amount of the protein. These findings indicate that p.G504Wfs*12 FUS is more prone to undergo post-translational modification respect to wild type FUS.

Genetic Testing for Amyotrophic Lateral Sclerosis and Frontotemporal Dementia: Impact on Clinical Management

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are devastating neurodegenerative disorders that share clinical, pathologic, and genetic features. Persons and families affected by these conditions frequently question why they developed the disease, the expected disease course, treatment options, and the likelihood that family members will be affected. Genetic testing has the potential to answers these important questions. Despite the progress in gene discovery, the offer of genetic testing is not yet "standard of care" in ALS and FTD clinics. The authors review the current genetic landscape and present recommendations for the laboratory genetic evaluation of persons with these conditions.

FUS P525L mutation causing amyotrophic lateral sclerosis and movement disorders

BACKGROUND

Mutations in the fused in sarcoma (FUS) gene have been associated with amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration, and essential tremor. Among the FUS mutations, p.P525L as a hot spot variant has been reported in more than 20 patients with ALS. Apart from the typical ALS phenotype, patients with p.P525L mutation exhibit some atypical symptoms. However, movement disorders related to p.P525L mutation have not been emphasized currently.

METHODS

Two unrelated patients with ALS were evaluated through a set of clinical and laboratory tests. The genetic screening was performed through next-generation sequencing. Muscle biopsies were performed on the 2 patients. Muscle samples were stained according to standard histological and immunohistochemical procedures.

RESULTS

The first patient presented with juvenile-onset neurogenic weakness and wasting and simultaneously had dropped head, ophthalmoplegia, tremor, involuntary movements, and cognitive impairments. The second patient showed a typical ALS phenotype and prominent adventitious movements. Genetic screening disclosed de novo p.P525L FUS mutation in the 2 patients by family cosegregation analysis. Muscle biopsy showed neurogenic patterns and numerous lipid droplets aggregating in the fibers.

CONCLUSION

Apart from the typical ALS phenotype, patients with p.P525L mutation in the FUS gene can present with great clinical heterogeneity including multiple movement disorders. Numerous lipid droplets in muscle fibers indicate that skeletal muscle is likely an important therapeutic target for ALS.

Key role of UBQLN2 in pathogenesis of amyotrophic lateral sclerosis and frontotemporal dementia

Ubiquilin-2 (UBQLN2) is a member of the ubiquilin family, actively implicated in the degradation of misfolded and redundant proteins through the ubiquitin-proteasome system and macroautophagy. UBQLN2 received much attention after the discovery of gene mutations in amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). The abnormal presence of positive UBQLN2 inclusion in the cytosol of degenerating motor neurons of familial and sporadic forms of ALS patients has been newly related to neurodegeneration. Only recently, data have emerged on its role in liquid-liquid phase separation, in stress granule development and in the formation of secondary amyloid structures. Furthermore, several animal models are available to investigate its involvement in TDP-43 pathology and neuroinflammation in ALS. This review addresses the molecular pathogenetic pathways involving UBQLN2 abnormalities which are converging toward defects in clearance mechanisms. UBQLN2.

A proteomic network approach across the ALS-FTD disease spectrum resolves clinical phenotypes and genetic vulnerability in human brain

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative diseases with overlap in clinical presentation, neuropathology, and genetic underpinnings. The molecular basis for the overlap of these disorders is not well established. We performed a comparative unbiased mass spectrometry‐based proteomic analysis of frontal cortical tissues from postmortem cases clinically defined as ALS, FTD, ALS and FTD (ALS/FTD), and controls. We also included a subset of patients with the C9orf72 expansion mutation, the most common genetic cause of both ALS and FTD. Our systems‐level analysis of the brain proteome integrated both differential expression and co‐expression approaches to assess the relationship of these differences to clinical and pathological phenotypes. Weighted co‐expression network analysis revealed 15 modules of co‐expressed proteins, eight of which were significantly different across the ALS‐FTD disease spectrum. These included modules associated with RNA binding proteins, synaptic transmission, and inflammation with cell‐type specificity that showed correlation with TDP‐43 pathology and cognitive dysfunction. Modules were also examined for their overlap with TDP‐43 protein–protein interactions, revealing one module enriched with RNA‐binding proteins and other causal ALS genes that increased in FTD/ALS and FTD cases. A module enriched with astrocyte and microglia proteins was significantly increased in ALS cases carrying the C9orf72 mutation compared to sporadic ALS cases, suggesting that the genetic expansion is associated with inflammation in the brain even without clinical evidence of dementia. Together, these findings highlight the utility of integrative systems‐level proteomic approaches to resolve clinical phenotypes and genetic mechanisms underlying the ALS‐FTD disease spectrum in human brain.

Alzheimer's Disease and Frontotemporal Dementia: The Current State of Genetics and Genetic Testing Since the Advent of Next-Generation Sequencing

The advent of next-generation sequencing has changed genetic diagnostics, allowing clinicians to test concurrently for phenotypically overlapping conditions such as Alzheimer's disease (AD) and frontotemporal dementia (FTD). However, to interpret genetic results, clinicians require an understanding of the benefits and limitations of different genetic technologies, such as the inability to detect large repeat expansions in such diseases as C9orf72-associated FTD and amyotrophic lateral sclerosis. Other types of mutations such as large deletions or duplications and triple repeat expansions may also go undetected. Additionally, the concurrent testing of multiple genes or the whole exome increases the likelihood of discovering variants of unknown significance. Our goal here is to review the current knowledge about the genetics of AD and FTD and suggest up-to-date guidelines for genetic testing for these dementias. Despite the improvements in diagnosis due to biomarkers testing, AD and FTD can have overlapping symptoms. When used appropriately, genetic testing can elucidate the diagnosis and specific etiology of the disease, as well as provide information for the family and determine eligibility for clinical trials. Prior to ordering genetic testing, clinicians must determine the appropriate genes to test, the types of mutations that occur in these genes, and the best type of genetic test to use. Without this analysis, interpretation of genetic results will be difficult. Patients should be counseled about the benefits and limitations of different types of genetic tests so they can make an informed decision about testing.

Clinical and experimental studies of a novel P525R FUS mutation in amyotrophic lateral sclerosis

Objective:

To describe the clinical features of a novel fused in sarcoma (FUS) mutation in a young adult female amyotrophic lateral sclerosis (ALS) patient with rapid progression of weakness and to experimentally validate the consequences of the P525R mutation in cellular neuronal models.

Methods:

We conducted sequencing of genomic DNA from the index patient and her family members. Immunocytochemistry was performed in various cellular models to determine whether the newly identified P525R mutant FUS protein accumulated in cytoplasmic inclusions. Clinical features of the index patient were compared with 19 other patients with ALS carrying the P525L mutation in the same amino acid position.

Results:

A novel mutation c.1574C>G (p.525P>R) in the FUS gene was identified in the index patient. The clinical symptoms are similar to those in familial ALS patients with the P525L mutation at the same position. The P525R mutant FUS protein showed cytoplasmic localization and formed large stress granule–like cytoplasmic inclusions in multiple cellular models.

Conclusions:

The clinical features of the patient and the cytoplasmic inclusions of the P525R mutant FUS protein strengthen the notion that mutations at position 525 of the FUS protein result in a coherent phenotype characterized by juvenile or young adult onset, rapid progression, variable positive family history, and female preponderance.

The Endoplasmic Reticulum Unfolded Protein Response in Neurodegenerative Disorders and Its Potential Therapeutic Significance

In eukaryotic cells, the endoplasmic reticulum (ER) is the cell compartment involved in secretory protein translocation and quality control of secretory protein folding. Different conditions can alter ER function, resulting in the accumulation of unfolded or misfolded proteins within the ER lumen. Such a condition, known as ER stress, elicits an integrated adaptive response known as the unfolded protein response (UPR) that aims to restore proteostasis within the secretory pathway. Conversely, in prolonged cell stress or insufficient adaptive response, UPR signaling causes cell death. ER dysfunctions are involved and contribute to neuronal degeneration in several human diseases, including Alzheimer, Parkinson and Huntington disease and amyotrophic lateral sclerosis. The correlations between ER stress and its signal transduction pathway known as the UPR with neuropathological changes are well established. In addition, much evidence suggests that genetic or pharmacological modulation of UPR could represent an effective strategy for minimizing the progressive neuronal loss in neurodegenerative diseases. Here, we review recent results describing the main cellular mechanisms linking ER stress and UPR to neurodegeneration. Furthermore, we provide an up-to-date panoramic view of the currently pursued strategies for ameliorating the toxic effects of protein unfolding in disease by targeting the ER UPR pathway.

RNA-binding proteins with prion-like domains in health and disease

Approximately 70 human RNA-binding proteins (RBPs) contain a prion-like domain (PrLD). PrLDs are low-complexity domains that possess a similar amino acid composition to prion domains in yeast, which enable several proteins, including Sup35 and Rnq1, to form infectious conformers, termed prions. In humans, PrLDs contribute to RBP function and enable RBPs to undergo liquid-liquid phase transitions that underlie the biogenesis of various membraneless organelles. However, this activity appears to render RBPs prone to misfolding and aggregation connected to neurodegenerative disease. Indeed, numerous RBPs with PrLDs, including TDP-43 (transactivation response element DNA-binding protein 43), FUS (fused in sarcoma), TAF15 (TATA-binding protein-associated factor 15), EWSR1 (Ewing sarcoma breakpoint region 1), and heterogeneous nuclear ribonucleoproteins A1 and A2 (hnRNPA1 and hnRNPA2), have now been connected via pathology and genetics to the etiology of several neurodegenerative diseases, including amyotrophic lateral sclerosis, frontotemporal dementia, and multisystem proteinopathy. Here, we review the physiological and pathological roles of the most prominent RBPs with PrLDs. We also highlight the potential of protein disaggregases, including Hsp104, as a therapeutic strategy to combat the aberrant phase transitions of RBPs with PrLDs that likely underpin neurodegeneration.

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.

The essential and downstream common proteins of amyotrophic lateral sclerosis: A protein-protein interaction network analysis

Amyotrophic Lateral Sclerosis (ALS) is a devastative neurodegenerative disease characterized by selective loss of motoneurons. While several breakthroughs have been made in identifying ALS genetic defects, the detailed molecular mechanisms are still unclear. These genetic defects involve in numerous biological processes, which converge to a common destiny: motoneuron degeneration. In addition, the common comorbid Frontotemporal Dementia (FTD) further complicates the investigation of ALS etiology. In this study, we aimed to explore the protein-protein interaction network built on known ALS-causative genes to identify essential proteins and common downstream proteins between classical ALS and ALS+FTD (classical ALS + ALS/FTD) groups. The results suggest that classical ALS and ALS+FTD share similar essential protein set (VCP, FUS, TDP-43 and hnRNPA1) but have distinctive functional enrichment profiles. Thus, disruptions to these essential proteins might cause motoneuron susceptible to cellular stresses and eventually vulnerable to proteinopathies. Moreover, we identified a common downstream protein, ubiquitin-C, extensively interconnected with ALS-causative proteins (22 out of 24) which was not linked to ALS previously. Our in silico approach provides the computational background for identifying ALS therapeutic targets, and points out the potential downstream common ground of ALS-causative mutations.

Novel group-based QSAR and combinatorial design of CK-1δ inhibitors as neuroprotective agents

Background

Tar DNA binding protein 43 (TDP-43) hyperphosphorylation, caused by Casein kinase 1 (CK-1) protein isoforms, is associated with the onset and progression of Amyotrophic Lateral Sclerosis (ALS). Among the reported isoforms and splice variants of CK-1 protein superfamily, CK-1δ is known to phosphorylate different serine and threonine sites on TDP-43 protein in vitro and thus qualifies as a potential target for ALS treatment.

Results

The developed GQSAR (group based quantitative structure activity relationship) model displayed satisfactory statistical parameters for the dataset of experimentally reported N-Benzothiazolyl-2-Phenyl Acetamide derivatives. A combinatorial library of molecules was also generated and the activities were predicted using the statistically sound GQSAR model. Compounds with higher predicted inhibitory activity were screened against CK-1δ that resulted in to the potential novel leads for CK-1δ inhibition.

Conclusions

In this study, a robust fragment based QSAR model was developed on a congeneric set of experimentally reported molecules and using combinatorial library approach, a series of molecules were generated from which we report two top scoring, CK-1δ inhibitors i.e., CHC (6-benzyl-2-cyclopropyl-4-{[(4-cyclopropyl-6-ethyl-1,3-benzothiazol-2-yl)carbamoyl]methyl}j-3-fluorophenyl hydrogen carbonate) and DHC (6-benzyl-4-{[(4-cyclopropyl-6-ethyl-1,3-benzothiazol-2-yl)carbamoyl]methyl}-2-(decahydronaphthalen-1-yl)-3-hydroxyphenyl hydrogen carbonate) with binding energy of −6.11 and −6.01 kcal/mol, respectively.

Linear ubiquitination is involved in the pathogenesis of optineurin-associated amyotrophic lateral sclerosis

Optineurin (OPTN) mutations cause neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and glaucoma. Although the ALS-associated E478G mutation in the UBAN domain of OPTN reportedly abolishes its NF-κB suppressive activity, the precise molecular basis in ALS pathogenesis still remains unclear. Here we report that the OPTN-UBAN domain is crucial for NF-κB suppression. Our crystal structure analysis reveals that OPTN-UBAN binds linear ubiquitin with homology to NEMO. TNF-α-mediated NF-κB activation is enhanced in OPTN-knockout cells, through increased ubiquitination and association of TNF receptor (TNFR) complex I components. Furthermore, OPTN binds caspase 8, and OPTN deficiency accelerates TNF-α-induced apoptosis by enhancing complex II formation. Immunohistochemical analyses of motor neurons from OPTN-associated ALS patients reveal that linear ubiquitin and activated NF-κB are partially co-localized with cytoplasmic inclusions, and that activation of caspases is elevated. Taken together, OPTN regulates both NF-κB activation and apoptosis via linear ubiquitin binding, and the loss of this ability may lead to ALS.

Mutations in optineurin are associated with neurodegenerative diseases, including amyotrophic lateral sclerosis. Here, the authors report the structure of the ubiquitin binding domain of optineurin, which binds linear ubiquitin with homology to NEMO, and explore the function of this domain.

Defective recognition of LC3B by mutant SQSTM1/p62 implicates impairment of autophagy as a pathogenic mechanism in ALS-FTLD

Growing evidence implicates impairment of autophagy as a candidate pathogenic mechanism in the spectrum of neurodegenerative disorders which includes amyotrophic lateral sclerosis and frontotemporal lobar degeneration (ALS-FTLD). SQSTM1, which encodes the autophagy receptor SQSTM1/p62, is genetically associated with ALS-FTLD, although to date autophagy-relevant functional defects in disease-associated variants have not been described. A key protein-protein interaction in autophagy is the recognition of a lipid-anchored form of LC3 (LC3-II) within the phagophore membrane by SQSTM1, mediated through its LC3-interacting region (LIR), and notably some ALS-FTLD mutations map to this region. Here we show that although representing a conservative substitution and predicted to be benign, the ALS-associated L341V mutation of SQSTM1 is defective in recognition of LC3B. We place our observations on a firm quantitative footing by showing the L341V-mutant LIR is associated with a ∼3-fold reduction in LC3B binding affinity and using protein NMR we rationalize the structural basis for the effect. This functional deficit is realized in motor neuron-like cells, with the L341V mutant EGFP-mCherry-SQSTM1 less readily incorporated into acidic autophagic vesicles than the wild type. Our data supports a model in which the L341V mutation limits the critical step of SQSTM1 recruitment to the phagophore. The oligomeric nature of SQSTM1, which presents multiple LIRs to template growth of the phagophore, potentially gives rise to avidity effects which amplify the relatively modest impact of any single mutation on LC3B binding. Over the lifetime of a neuron, impaired autophagy could expose a vulnerability, which ultimately tips the balance from cell survival toward cell death.

Juvenile-onset Sporadic Amyotrophic Lateral Sclerosis with a Frameshift FUS Gene Mutation Presenting Unique Neuroradiological Findings and Cognitive Impairment

A 24-year-old Japanese woman developed anterocollis, weakness of the proximal arms, and subsequent cognitive impairment. A neurological examination revealed amyotrophic lateral sclerosis (ALS) without a family history. Systemic muscle atrophy progressed rapidly. Cerebral MRI clearly exhibited high signal intensities along the bilateral pyramidal tracts. An analysis of the FUS gene revealed a heterozygous two-base pair deletion, c.1507-1508delAG (p.G504WfsX515). A subset of juvenile-onset familial/sporadic ALS cases with FUS gene mutations reportedly demonstrates mental retardation or learning difficulty. Our study emphasizes the importance of conducting a FUS gene analysis in juvenile-onset ALS cases, even when no family occurrence is confirmed.

Viral expression of ALS-linked ubiquilin-2 mutants causes inclusion pathology and behavioral deficits in mice

Background

UBQLN2 mutations have recently been associated with familial forms of amyotrophic lateral sclerosis (ALS) and ALS-dementia. UBQLN2 encodes for ubiquilin-2, a member of the ubiquitin-like protein family which facilitates delivery of ubiquitinated proteins to the proteasome for degradation. To study the potential role of ubiquilin-2 in ALS, we used recombinant adeno-associated viral (rAAV) vectors to express UBQLN2 and three of the identified ALS-linked mutants (P497H, P497S, and P506T) in primary neuroglial cultures and in developing neonatal mouse brains.

Results

In primary cultures rAAV2/8-mediated expression of UBQLN2 mutants resulted in inclusion bodies and insoluble aggregates. Intracerebroventricular injection of FVB mice at post-natal day 0 with rAAV2/8 expressing wild type or mutant UBQLN2 resulted in widespread, sustained expression of ubiquilin-2 in brain. In contrast to wild type, mutant UBQLN2 expression induced significant pathology with large neuronal, cytoplasmic inclusions and ubiquilin-2-positive aggregates in surrounding neuropil. Ubiquilin-2 inclusions co-localized with ubiquitin, p62/SQSTM, optineurin, and occasionally TDP-43, but were negative for α-synuclein, neurofilament, tau, and FUS. Mutant UBLQN2 expression also resulted in Thioflavin-S-positive inclusions/aggregates. Mice expressing mutant forms of UBQLN2 variably developed a motor phenotype at 3–4 months, including nonspecific clasping and rotarod deficits.

Conclusions

These findings demonstrate that UBQLN2 mutants (P497H, P497S, and P506T) induce proteinopathy and cause behavioral deficits, supporting a “toxic” gain-of-function, which may contribute to ALS pathology. These data establish also that our rAAV model can be used to rapidly assess the pathological consequences of various UBQLN2 mutations and provides an agile system to further interrogate the molecular mechanisms of ubiquilins in neurodegeneration.

RNautophagy/DNautophagy possesses selectivity for RNA/DNA substrates

Lysosomes can degrade various biological macromolecules, including nucleic acids, proteins and lipids. Recently, we identified novel nucleic acid-degradation systems termed RNautophagy/DNautophagy (abbreviated as RDA), in which RNA and DNA are directly taken up by lysosomes in an ATP-dependent manner and degraded. We also found that a lysosomal membrane protein, LAMP2C, the cytoplasmic region of which binds to RNA and DNA, functions, at least in part, as an RNA/DNA receptor in the process of RDA. However, it has been unclear whether RDA possesses selectivity for RNA/DNA substrates and the RNA/DNA sequences that are recognized by LAMP2C have not been determined. In the present study, we found that the cytosolic region of LAMP2C binds to poly-G/dG, but not to poly-A/dA, poly-C/dC, poly-dT or poly-U. Consistent with this binding activity, poly-G/dG was transported into isolated lysosomes via RDA, while poly-A/dA, poly-C/dC, poly-dT and poly-U were not. GGGGGG or d(GGGG) sequences are essential for the interaction between poly-G/dG and LAMP2C. In addition to poly-G/dG, G/dG-rich sequences, such as a repeated GGGGCC sequence, interacted with the cytosolic region of LAMP2C. Our findings indicate that RDA does possess selectivity for RNA/DNA substrates and that at least some consecutive G/dG sequence(s) can mediate RDA.

Autophagy receptor defects and ALS-FTLD

Various pathophysiological mechanisms have been implicated in the ALS-FTLD clinicopathological spectrum of neurodegenerative disorders. Here we focus on the role of autophagy, an intracellular catabolic pathway, in these conditions. Growing evidence suggests that the autophagic process can be disturbed in ALS-FTLD, including by genetic mutations affecting autophagy receptor proteins (ubiquilin-2, optineurin, SQSTM1/p62) and regulators (VCP). Such mutations may impair clearance of autophagy substrates with pathological consequences. Recent studies have also uncovered a direct connection between autophagy and RNA processing, supporting an integrated model connecting several ALS-FTLD associated gene products. This article is part of a Special Issue entitled 'Neuronal Protein'.

Substantially elevating the levels of αB-crystallin in spinal motor neurons of mutant SOD1 mice does not significantly delay paralysis or attenuate mutant protein aggregation

There has been great interest in enhancing endogenous protein maintenance pathways such as the heat-shock chaperone response, as it is postulated that enhancing clearance of misfolded proteins could have beneficial disease modifying effects in amyotrophic lateral sclerosis and other neurodegenerative disorders. In cultured cell models of mutant SOD1 aggregation, co-expression of αB-crystallin (αB-crys) has been shown to inhibit the formation of detergent-insoluble forms of mutant protein. Here, we describe the generation of a new line of transgenic mice that express αB-crys at > 6-fold the normal level in spinal cord, with robust increases in immunoreactivity throughout the spinal cord grey matter and, specifically, in spinal motor neurons. Surprisingly, spinal cords of mice expressing αB-crys alone contained 20% more motor neurons per section than littermate controls. Raising αB-crys by these levels in mice transgenic for either G93A or L126Z mutant SOD1 had no effect on the age at which paralysis developed. In the G93A mice, which showed the most robust degree of motor neuron loss, the number of these cells declined by the same proportion as in mice expressing the mutant SOD1 alone. In paralyzed bigenic mice, the levels of detergent-insoluble, misfolded, mutant SOD1 were similar to those of mice expressing mutant SOD1 alone. These findings indicate that raising the levels of αB-crys in spinal motor neurons by 6-fold does not produce the therapeutic effects predicted by cell culture models of mutant SOD1 aggregation. Enhancing the protein chaperone function may present a therapeutic approach to amyotrophic lateral sclerosis caused by mutations in SOD1, and other neurodegenerative disorders characterized by cytosolic protein aggregation. Previous studies in cell models suggested that the chaperone known as αB-crystallin (αB-crys) can prevent mutant SOD1 aggregation. We report that transgenic expression of αB-crys at > 6-fold the normal level in spinal cords of mice expressing mutant SOD1 produces no therapeutic benefit.

VCP mutations are not a major cause of familial amyotrophic lateral sclerosis in the UK

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease causing loss of motor neurons in the spinal cord, brain stem and cerebral cortex. Mutations in the Valosin containing protein (VCP) gene have recently been identified in Familial ALS (FALS) patients, accounting for ~1% of all FALS cases. In order to study the frequency of VCP mutations in UK FALS patients, we have screened the exons known to harbour mutations together with 3' and 5' UTR sequences. No coding changes were identified in this UK cohort and no common polymorphisms were associated with FALS. However, we identified an imperfect hexanucleotide expansion (8 repeats), c.-221_-220insCTGCCACTGCCACTGCCG, in the 5'UTR of a FALS case and a 7-repeat hexanucleotide repeat in a Sporadic ALS case (SALS) that were not present in 219 UK controls. Subsequent screening of sequence data from 1844 controls (1000 genomes Phase 3) revealed the presence of the 7-repeat (0.3%) and a single individual with an 8-repeat containing a homogeneous insert [CTGCCG]3 but no individuals with the heterogeneous insert found in FALS ([CTGCCA]2[CTGCCG]). Two novel single base pair substitutions, c.-360G>C and c.2421+94C>T, were found in FALS cases in the 5' and 3' UTRs respectively. The hexanucleotide expansion and c.-360G>C were predicted to be pathogenic and were found in FALS cases harbouring C9orf72 expansions. The SALS case with a 7 repeat lacked a C9orf72 expansion. We conclude that VCP mutations are not a major cause of FALS in the UK population although novel rare variations in the 5' UTR of the VCP gene may be pathogenic.

Dendritic spinopathy in transgenic mice expressing ALS/dementia-linked mutant UBQLN2

Mutations in the gene encoding ubiquilin2 (UBQLN2) cause amyotrophic lateral sclerosis (ALS), frontotemporal type of dementia, or both. However, the molecular mechanisms are unknown. Here, we show that ALS/dementia-linked UBQLN2(P497H) transgenic mice develop neuronal pathology with ubiquilin2/ubiquitin/p62-positive inclusions in the brain, especially in the hippocampus, recapitulating several key pathological features of dementia observed in human patients with UBQLN2 mutations. A major feature of the ubiquilin2-related pathology in these mice, and reminiscent of human disease, is a dendritic spinopathy with protein aggregation in the dendritic spines and an associated decrease in dendritic spine density and synaptic dysfunction. Finally, we show that the protein inclusions in the dendritic spines are composed of several components of the proteasome machinery, including Ub(G76V)-GFP, a representative ubiquitinated protein substrate that is accumulated in the transgenic mice. Our data, therefore, directly link impaired protein degradation to inclusion formation that is associated with synaptic dysfunction and cognitive deficits. These data imply a convergent molecular pathway involving synaptic protein recycling that may also be involved in other neurodegenerative disorders, with implications for development of widely applicable rational therapeutics.

Clinical neurogenetics: amyotrophic lateral sclerosis

Our understanding of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease, is expanding rapidly as its genetic causes are uncovered. The pace of new gene discovery over the last 5 years has accelerated, providing new insights into the pathogenesis of disease and highlighting biological pathways as targets for therapeutic development. This article reviews our current understanding of the heritability of ALS and provides an overview of each of the major ALS genes, highlighting their phenotypic characteristics and frequencies as a guide for clinicians evaluating patients with ALS.

Intrathecal infusion of BMAA induces selective motor neuron damage and astrogliosis in the ventral horn of the spinal cord

The neurotoxin beta-N-methylamino-l-alanine (BMAA) was first identified as a "toxin of interest" in regard to the amyotrophic lateral sclerosis-Parkinsonism Dementia Complex of Guam (ALS/PDC); studies in recent years highlighting widespread environmental sources of BMAA exposure and providing new clues to toxic mechanisms have suggested possible relevance to sporadic ALS as well. However, despite clear evidence of uptake into tissues and a range of toxic effects in cells and animals, an animal model in which BMAA induces a neurodegenerative picture resembling ALS is lacking, possibly in part reflecting limited understanding of critical factors pertaining to its absorption, biodistribution and metabolism. To bypass some of these issues and ensure delivery to a key site of disease pathology, we examined effects of prolonged (30day) intrathecal infusion in wild type (WT) rats, and rats harboring the familial ALS associated G93A SOD1 mutation, over an age range (80±2 to 110±2days) during which the G93A rats are developing disease pathology yet remain asymptomatic. The BMAA exposures induced changes that in many ways resemble those seen in the G93A rats, with degenerative changes in ventral horn motor neurons (MNs) with relatively little dorsal horn pathology, marked ventral horn astrogliosis and increased 3-nitrotyrosine labeling in and surrounding MNs, a loss of labeling for the astrocytic glutamate transporter, GLT-1, surrounding MNs, and mild accumulation and aggregation of TDP-43 in the cytosol of some injured and degenerating MNs. Thus, prolonged intrathecal infusion of BMAA can reproduce a picture in spinal cord incorporating many of the pathological hallmarks of diverse forms of human ALS, including substantial restriction of overt pathological changes to the ventral horn, consistent with the possibility that environmental BMAA exposure could be a risk factor and/or contributor to some human disease.

Protein recycling pathways in neurodegenerative diseases

Many progressive neurodegenerative diseases, including Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis, and frontotemporal lobe dementia, are associated with the formation of insoluble intracellular proteinaceous inclusions. It is therefore imperative to understand the factors that regulate normal, as well as abnormal, protein recycling in neurons. Dysfunction of the ubiquitin-proteasome or autophagy pathways might contribute to the pathology of various neurodegenerative diseases. Induction of these pathways may offer a rational therapeutic strategy for a number of these diseases.

[Development of neurology in Germany after 1960]

The still continuing accelerated development of neurology in Germany is described in this article by a contemporary witness who was active in this field from 1965 to 2005. The personal experiences of the author are obviously only reflected over these 40 years so that the glorious antecedents in the period up to 1933, the era in which our predecessors were the world leaders in neurology, is not sufficiently covered. This dominance was lost by the anti-Semitism during the era of National Socialism and the sequelae of World War II. As a result of the war, German neurologists became effectively isolated and their participation in international congresses was forbidden so that a gradual reestablishment of alignment only became possible after 1960. In this brief description no attempt at completeness has been made and only subjectivity and brevity have been considered. An attempt is made to retrospectively convey what essentially happened. An exact dating of advances over the period was sometimes difficult. The readership will have the opportunity to share the surprise of the author on how meagre the neurological knowledge and diagnostic methods were 50 years ago, how rapidly the subsequent development happened, how rapidly things became obvious which 20 years ago nobody was aware of and despite the progress how pleased we were to find ourselves at the most recent state of error and probably still find ourselves nowadays. In particular, how powerless and untested the therapeutic efforts were at that time. The progress can only be measured by a comparison between then, 50 years ago and the present. A projection of the future based on these experiences is not attempted but it seems to be certain that many conceptions, diagnostic advances and therapy options are still undiscovered and that further exciting times can be expected.

The Department of Veterans Affairs Biorepository Brain Bank: a national resource for amyotrophic lateral sclerosis research

Our objective was to describe a unique national resource to facilitate amyotrophic lateral sclerosis (ALS) research, the Department of Veterans Affairs Biorepository Brain Bank. Enrolled veterans receive biannual telephone follow-up to collect clinical data until death including the ALS Functional Rating Scale-Revised (ALSFRS-R). A comprehensive post mortem examination is performed and a wide range of fixed and frozen brain and spinal cord samples are banked. As of December 2012, 240 veterans were enrolled from 47 states and post mortem tissue recoveries were performed on 100 veterans from 37 states. Average disease duration was 13.5 (range 3-45) years. Average follow-up for living subjects was 3.1 years and average ALSFRS-R score was 23.5 compared to 25.9 (12-24 months earlier), indicating slow disease progression. ALS was confirmed by post mortem examination in 97% of cases. Eighty-six percent of cases were TDP-43-positive. Additional neuropathological diagnoses include Lewy body disease (13%), frontotemporal lobar degeneration (6.3%), chronic traumatic encephalopathy with motor neuron disease (3.2%), and Alzheimer's disease (2.1%). Tissue RIN values were ≥ 4.0 in 88% of cases. In conclusion, the availability of high quality fixed and frozen CNS tissue from this well characterized cohort is an important resource to facilitate research into genetic and environmental risk factors and clinical pathological relationships in ALS.

Sequestosome-1 (SQSTM1) sequence variants in ALS cases in the UK: prevalence and coexistence of SQSTM1 mutations in ALS kindred with PDB

Mutations in the SQSTM1 gene have been reported to be associated with amyotrophic lateral sclerosis (ALS). We sought to determine the frequency of these mutations in a UK familial ALS (FALS) cohort. Sequences of all eight exons of the SQSTM1 gene were analysed in index cases from 61 different FALS kindred lacking known FALS mutations. Six exonic variants c.463G>A, p.(Glu155Lys), c.822G>C, p.(Glu274Asp), c.888G>T, p.(=), c.954C>T, p.(=), c.1038G>A, p.(=) and c.1175C>T, p.(Pro392Leu) were identified in five FALS index cases, three of which were non-synonymous and three were synonymous. One index case harboured three variants (c.822G>C, c.888G>T and c.954C>T), and a second index case harboured two variants (c.822G>C and c.954C>T). Only the p.(Pro392Leu) and p.(Glu155Lys) mutations were predicted to be pathogenic. In one p.(Pro392Leu) kindred, the carrier developed both ALS and Paget's disease of bone (PDB), and, in the p.(Glu155Lys) kindred, the father of the proband developed PDB. All p.(Pro392Leu) carriers were heterozygous for a previously reported founder haplotype for PDB, where this mutation has an established causal effect. The frequency of the p.(Pro392Leu) mutation in this UK FALS cohort was 2.3% and 0.97% overall including three previously screened FALS cohorts. Our results confirm the presence of the p.(Pro392Leu) SQSTM1 mutation in FALS. This mutation is the most common SQSTM1 mutation found in ALS to date, and a likely pathogenicity is supported by having an established causal role in PDB. The occurrence of the same mutation in ALS and PDB is indicative of a common pathogenic pathway that converges on protein homeostasis.

Protein aggregation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the aggregation of ubiquitinated proteins in affected motor neurons. Recent studies have identified several new molecular constituents of ALS-linked cellular aggregates, including FUS, TDP-43, OPTN, UBQLN2 and the translational product of intronic repeats in the gene C9ORF72. Mutations in the genes encoding these proteins are found in a subgroup of ALS patients and segregate with disease in familial cases, indicating a causal relationship with disease pathogenesis. Furthermore, these proteins are often detected in aggregates of non-mutation carriers and those observed in other neurodegenerative disorders, supporting a widespread role in neuronal degeneration. The molecular characteristics and distribution of different types of protein aggregates in ALS can be linked to specific genetic alterations and shows a remarkable overlap hinting at a convergence of underlying cellular processes and pathological effects. Thus far, self-aggregating properties of prion-like domains, altered RNA granule formation and dysfunction of the protein quality control system have been suggested to contribute to protein aggregation in ALS. The precise pathological effects of protein aggregation remain largely unknown, but experimental evidence hints at both gain- and loss-of-function mechanisms. Here, we discuss recent advances in our understanding of the molecular make-up, formation, and mechanism-of-action of protein aggregates in ALS. Further insight into protein aggregation will not only deepen our understanding of ALS pathogenesis but also may provide novel avenues for therapeutic intervention.

How do C9ORF72 repeat expansions cause amyotrophic lateral sclerosis and frontotemporal dementia: can we learn from other noncoding repeat expansion disorders?

PURPOSE OF REVIEW

The aim of this review is to describe disease mechanisms by which chromosome 9 open reading frame 72 (C9ORF72) repeat expansions could lead to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) and to discuss these diseases in relation to other noncoding repeat expansion disorders.

RECENT FINDINGS

ALS and FTD are complex neurodegenerative disorders with a considerable clinical and pathological overlap, and this overlap is further substantiated by the recent discovery of C9ORF72 repeat expansions. These repeat expansions are currently the most important genetic cause of familial ALS and FTD, accounting for approximately 34.2 and 25.9% of the cases. Clinical phenotypes associated with these repeat expansions are highly variable, and combinations with mutations in other ALS-associated and/or FTD-associated genes may contribute to this pleiotropy. It is challenging, however, to diagnose patients with C9ORF72 expansions, not only because of large repeat sizes, but also due to somatic heterogeneity. Most other noncoding repeat expansion disorders share an RNA gain-of-function disease mechanism, a mechanism that could underlie the development of ALS and/or FTD as well.

SUMMARY

The discovery of C9ORF72 repeat expansions provides novel insights into the pathogenesis of ALS and FTD and highlights the importance of noncoding repeat expansions and RNA toxicity in neurodegenerative diseases.

Expanded GGGGCC repeat RNA associated with amyotrophic lateral sclerosis and frontotemporal dementia causes neurodegeneration

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) share phenotypic and pathologic overlap. Recently, an expansion of GGGGCC repeats in the first intron of C9orf72 was found to be a common cause of both illnesses; however, the molecular pathogenesis of this expanded repeat is unknown. Here we developed both Drosophila and mammalian models of this expanded hexanucleotide repeat and showed that expression of the expanded GGGGCC repeat RNA (rGGGGCC) is sufficient to cause neurodegeneration. We further identified Pur α as the RNA-binding protein of rGGGGCC repeats and discovered that Pur α and rGGGGCC repeats interact in vitro and in vivo in a sequence-specific fashion that is conserved between mammals and Drosophila. Furthermore, overexpression of Pur α in mouse neuronal cells and Drosophila mitigates rGGGGCC repeat-mediated neurodegeneration, and Pur α forms inclusions in the fly eye expressing expanded rGGGGCC repeats, as well as in cerebellum of human carriers of expanded GGGGCC repeats. These data suggest that expanded rGGGGCC repeats could sequester specific RNA-binding protein from their normal functions, ultimately leading to cell death. Taken together, these findings suggest that the expanded rGGGGCC repeats could cause neurodegeneration, and that Pur α may play a role in the pathogenesis of amyotrophic lateral sclerosis and frontotemporal dementia.

Frontotemporal dementia in a Brazilian kindred with the c9orf72 mutation

OBJECTIVES

To describe the clinical features of a Brazilian kindred with C9orf72 frontotemporal dementia-amyotrophic lateral sclerosis and compare them with other described families with C9orf72 and frontotemporal dementia-amyotrophic lateral sclerosis-causing mutations.

DESIGN

Report of a kindred.

SETTING

Dementia center at a university hospital.

PATIENTS

One kindred encompassing 3 generations.

RESULTS

The presence of a hexanucleotide (GGGGCC) expansion in C9orf72 was confirmed by repeat-primed polymerase chain reaction and Southern blot. The observed phenotypes were behavioral variant frontotemporal dementia and amyotrophic lateral sclerosis with dementia, with significant variability in age at onset and duration of disease. Parkinsonian features with focal dystonia, visual hallucinations, and more posterior atrophy on neuroimaging than is typical for frontotemporal dementia were seen.

CONCLUSIONS

Behavioral variant frontotemporal dementia due to C9orf72 expansion displays some phenotypic heterogeneity and may be associated with hallucinations, parkinsonism, focal dystonia, and posterior brain atrophy. Personality changes may precede the diagnosis of dementia by many years and may be a distinguishing feature of this mutation.

Investigation of c9orf72 in 4 neurodegenerative disorders

OBJECTIVE To estimate the allele frequency of C9orf72 (G4C2) repeats in amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), Alzheimer disease (AD), and Parkinson disease (PD). DESIGN The number of repeats was estimated by a 2-step genotyping strategy. For expansion carriers, we sequenced the repeat flanking regions and obtained APOE genotypes and MAPT H1/H2 haplotypes. SETTING Hospitals specializing in neurodegenerative disorders. SUBJECTS We analyzed 520 patients with FTLD, 389 patients with ALS, 424 patients with AD, 289 patients with PD, 602 controls, 18 families, and 29 patients with PD with the LRRK2 G2019S mutation. MAIN OUTCOME MEASURE The expansion frequency. RESULTS Based on a prior cutoff (>30 repeats), the expansion was detected in 9.3% of patients with ALS, 5.2% of patients with FTLD, and 0.7% of patients with PD but not in controls or patients with AD. It was significantly associated with family history of ALS or FTLD and age at onset of FTLD. Phenotype variation (ALS vs FTLD) was not associated with MAPT, APOE, or variability in the repeat flanking regions. Two patients with PD were carriers of 39 and 32 repeats with questionable pathological significance, since the 39-repeat allele does not segregate with PD. No expansion or intermediate alleles (20-29 repeats) were found among the G2019S carriers and AD cases with TAR DNA-binding protein 43-positive inclusions. Surprisingly, the frequency of the 10-repeat allele was marginally increased in all 4 neurodegenerative diseases compared with controls, indicating the presence of an unknown risk variation in the C9orf72 locus. CONCLUSIONS The C9orf72 expansion is a common cause of ALS and FTLD, but not of AD or PD. Our study raises concern about a reliable cutoff for the pathological repeat number, which is important in the utility of genetic screening.

De novo FUS gene mutations are associated with juvenile-onset sporadic amyotrophic lateral sclerosis in China

Juvenile amyotrophic lateral sclerosis (ALS) is a rare form of motor neuron disease and occurs before 25 years of age. Only very few sporadic cases of juvenile-onset ALS have been reported. Rare SOD1 mutations and several FUS mutations have been identified in juvenile-onset ALS patients. To define the genetics of juvenile-onset sporadic ALS (SALS) of Chinese origin, we sequenced all 5 exons of SOD1, exons 3-6 and 12-15 of FUS in 11 juvenile-onset SALS patients, 105 adult-onset ALS patients (including 6 familial ALS [FALS] pedigrees), and 245 healthy controls. For the 11 juvenile-onset SALS and 6 FALS cases, the other 7 exons of FUS were also screened. A heterozygous de novo missense mutation c.1574C>T (p.P525L), a heterozygous de novo 2-base pair deletion c.1509_1510delAG (p.G504Wfs*12), and a nonsense mutation c.1483C>T (p.R495X) was each identified in 1 juvenile SALS patient. A heterozygous missense mutation c.1561C>G (p.R521G) was identified in a FALS proband. In the Chinese population, the frequency of FUS mutation in FALS is 11.4% (95% confidence interval [CI], 0.9%-22.0%), higher than the Japanese (10%; 95% CI, 0.7%-19.3%), and Caucasians (4.9%; 95% CI, 3.9%-6.0%). The frequency of FUS mutation in SALS patients is 1.5% (95% CI, 0.2%-2.9%), which is similar to Koreans (1.6%; 95% CI, 0%-3.2%), but higher than in Caucasians (0.6%; 95% CI, 0.4%-0.8%). Our findings suggest that de novo FUS mutations are associated with juvenile-onset SALS of Chinese origin and that this gene should be screened in ALS patients with a young age of onset, aggressive progression, and sporadic occurrence.

Genetics of dementia: update and guidelines for the clinician

With increased frequency, clinical geneticists are asked for genetic advice on the heredity of dementia in families. Alzheimer's disease is in most cases a complex disease, but may be autosomal dominant inherited. Mutations in the PSEN1 gene are the most common genetic cause of early onset Alzheimer's disease, whereas APP and PSEN2 gene mutations are less frequent. Familial frontotemporal dementia may be associated with a mutation in the MAPT or GRN gene, or with a repeat expansion in the C9orf72 gene. All these genes show autosomal dominant inheritance with a high penetrance. Although Alzheimer's disease and frontotemporal dementia are clinically distinguishable entities, phenotypical overlap may occur. Rarely, dementia is caused by mutations in other autosomal dominant genes or by genetic defects with autosomal recessive, X-linked dominant or mitochondrial inheritance. The inherited forms of frontotemporal dementia and Alzheimer's disease show a large phenotypic variability also within families, resulting in many remaining uncertainties for mutation carriers. Therefore, genetic counseling before performing genetic testing is essential in both symptomatic individuals and healthy at risk relatives. This review provides an overview of the genetic causes of dementia and discusses all aspects relevant for genetic counseling and testing. Furthermore, based on current knowledge, we provide algorithms for genetic testing in patients with early onset Alzheimer's disease or frontotemporal dementia.

Slow development of ALS-like spinal cord pathology in mutant valosin-containing protein gene knock-in mice

Pathological features of amyotrophic lateral sclerosis (ALS) include, in addition to selective motor neuron (MN) degeneration, the occurrence of protein aggregates, mitochondrial dysfunction and astrogliosis. SOD1 mutations cause rare familial forms of ALS and have provided the most widely studied animal models. Relatively recent studies implicating another protein, TDP-43, in familial and sporadic forms of ALS have led to the development of new animal models. More recently, mutations in the valosin-containing protein (VCP) gene linked to the human genetic disease, Inclusion Body Myopathy associated with Paget's disease of bone and frontotemporal dementia (IBMPFD), were found also to be associated with ALS in some patients. A heterozygous knock-in VCP mouse model of IBMPFD (VCP^R155H/+) exhibited muscle, bone and brain pathology characteristic of the human disease. We have undertaken studies of spinal cord pathology in VCP^R155H/+ mice and find age-dependent degeneration of ventral horn MNs, TDP-43-positive cytosolic inclusions, mitochondrial aggregation and progressive astrogliosis. Aged animals (∼24–27 months) show electromyography evidence of denervation consistent with the observed MN loss. Although these animals do not develop rapidly progressive fatal ALS-like disease during their lifespans, they recapitulate key pathological features of both human disease and other animal models of ALS, and may provide a valuable new model for studying events preceding onset of catastrophic disease.

External and Internal Influences on Muscle Pathology

Three cases of different types of neuromuscular diseases demonstrate different muscle responses to external stress or intrinsic muscle abnormalities. The first muscle biopsy shows stenosis of its vessels causing acute muscle ischemia, stress from an external vascular disease. The muscle response is similar to the cellular necrosis seen in primary muscle diseases (myopathies), but the histologic pattern is more focal than most myopathies. The second muscle biopsy demonstrates the effects of external motor nerve injury or disease causing groups of muscle fibers to atrophy. If a nerve reinnervates the muscle, it changes the fiber types in distinct patterns. The third muscle biopsy shows an intrinsic muscle abnormality causes chronic failure of the muscle fibers to thrive and repeated attempts by the fibers to regenerate, stimulating other tissue repair processes, like fibrosis, to change the muscle. Depending on the etiologic factor, muscle will respond to internal and external influences in different manners.

Rapidly progressive frontotemporal dementia and bulbar amyotrophic lateral sclerosis in Portuguese patients with C9orf72 mutation

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) form a spectrum of clinically, pathologically, and genetically overlapping disorders, as confirmed by the recent report that it can be caused by a hexanucleotide repeat expansion in C9orf72. One hundred and fourteen Portuguese cases diagnosed as probable or possible familial FTLD, as part of the EOD consortium study, and nine further Portuguese cases with familial ALS were tested for the presence of this mutation. Results showed that six Portuguese patients from unrelated families had the mutation, five (4.4%) patients from the FTLD group and one (11.1%) from the ALS sample. Of these, three patients had FTLD and rapidly progressive bulbar ALS. Electromyography confirmed diffuse loss of motor units with marked bulbar involvement. In conclusion, the cases now reported showed a very rapid progression, suggesting bulbar ALS could be particularly common and aggressive in patients with the C9orf72 hexanucleotide repeat expansion, in the Portuguese population.