SPATACSIN mutations cause autosomal recessive juvenile amyotrophic lateral sclerosis

The changing scene of amyotrophic lateral sclerosis

Several recent breakthroughs have provided notable insights into the pathogenesis of amyotrophic lateral sclerosis (ALS), with some even shifting our thinking about this neurodegenerative disease and raising the question as to whether this disorder is a proteinopathy, a ribonucleopathy or both. In addition, these breakthroughs have revealed mechanistic links between ALS and frontotemporal dementia, as well as between ALS and other neurodegenerative diseases, such as the cerebellar atrophies, myotonic dystrophy and inclusion body myositis. Here, we summarize the new findings in ALS research, discuss what they have taught us about this disease and examine issues that are still outstanding.

Rapidly deteriorating course in Dutch hereditary spastic paraplegia type 11 patients

Although SPG11 is the most common complicated hereditary spastic paraplegia, our knowledge of the long-term prognosis and life expectancy is limited. We therefore studied the disease course of all patients with a proven SPG11 mutation as tested in our laboratory, the single Dutch laboratory providing SPG11 mutation analysis, between 1 January 2009 and 1 January 2011. We identified nine different SPG11 mutations, four of which are novel, in nine index patients. Eighteen SPG11 patients from these nine families were studied by means of a retrospective chart analysis and additional interview/examination. Ages at onset were between 4 months and 14 years; 39% started with learning difficulties rather than gait impairment. Brain magnetic resonance imaging showed a thin corpus callosum and typical periventricular white matter changes in the frontal horn region (known as the 'ears-of the lynx'-sign) in all. Most patients became wheelchair bound after a disease duration of 1 to 2 decades. End-stage disease consisted of loss of spontaneous speech, severe dysphagia, spastic tetraplegia with peripheral nerve involvement and contractures. Several patients died of complications between ages 30 and 48 years, 3-4 decades after onset of gait impairment. Other relevant features during the disease were urinary and fecal incontinence, obesity and psychosis. Our study of 18 Dutch SPG11-patients shows the potential serious long-term consequences of SPG11 including a possibly restricted life span.

Protein SUMOylation, an emerging pathway in amyotrophic lateral sclerosis

The covalent attachment of SUMO proteins (small ubiquitin-like modifier) to specific proteins or SUMOylation regulates their functional properties in the nucleus and cytoplasm of neurons. Recent studies reported dysfunction of the SUMO pathway in molecular and cellular abnormalities associated with amyotrophic lateral sclerosis (ALS). Furthermore, several observations support a direct role for SUMOylation in diverse pathogenic mechanisms involved in ALS, such as response to hypoxia, oxidative stress, glutamate excitotoxicity and proteasome impairment. Recent results also suggest that SUMO modifications of superoxide dismutase 1, transactive response DNA-binding protein 43, CTE (COOH terminus of EAAT2) (proteolytic C-terminal fragment of the glutamate transporter excitatory amino acid transporter 2, EAAT2) and proteins regulating the turnover of ALS-related proteins can participate in the pathogenesis of ALS. Moreover, the fused in sarcoma (FUS) gene, mutated in ALS, encodes a protein with a SUMO E3 ligase activity. In this review, we summarize the functioning of the SUMO pathway in normal conditions and in response to stresses, its action on ALS-related proteins and discuss the need for further research on this pathway in ALS.

Amyotrophic lateral sclerosis: new insights into underlying molecular mechanisms and opportunities for therapeutic intervention

Recent years have witnessed a renewed interest in the pathogenic mechanisms of amyotrophic lateral sclerosis (ALS), a late-onset progressive degeneration of motor neurons. The discovery of new genes associated with the familial form of the disease, along with a deeper insight into pathways already described for this disease, has led scientists to reconsider previous postulates. While protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, and excitotoxicity have not been dismissed, they need to be re-examined as contributors to the onset or progression of ALS in the light of the current knowledge that the mutations of proteins involved in RNA processing, apparently unrelated to the previous "old partners," are causative of the same phenotype. Thus, newly envisaged models and tools may offer unforeseen clues on the etiology of this disease and hopefully provide the key to treatment.

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.

SPG11 Presenting with Tremor

BACKGROUND

Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurological diseases, which typically present with progressive lower extremity weakness and spasticity causing progressive walking difficulties. Complicating neurological or extraneurological features may be present.

CASE REPORT

We describe a 19-year-old male who was referred because of an action tremor of the hands; he later developed walking difficulties. Callosal atrophy was present on his cerebral magnetic resonance imaging scan, prompting genetic testing for SPG11, which revealed homozygous mutations.

DISCUSSION

The clinical features, differential diagnosis and management of SPG11, the most common form of autosomal recessive complicated HSP with a thin corpus callosum are discussed.

The genetics and neuropathology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motor neurons leading to death from respiratory failure within about 3 years of symptom onset. A family history of ALS is obtained in about 5 % but the distinction between familial and apparently sporadic ALS is artificial and genetic factors play a role in all types. For several years, only one gene was known to have a role in ALS pathogenesis, SOD1. In the last few years there has been a rapid advance in our genetic knowledge of the causes of ALS, and the relationship of the genetic subtypes with pathological subtypes and clinical phenotype. Mutations in the gene for TDP-43 protein, TARDBP, highlight this, with pathology mimicking closely that found in other types of ALS, and a phenotypic spectrum that includes frontotemporal dementia. Mutations in the FUS gene, closely related to TDP-43, lead to a similar clinical phenotype but distinct pathology, so that the three pathological groups represented by SOD1, TARDBP, and FUS are distinct. In this review, we explore the genetic architecture of ALS, highlight some of the genes implicated in pathogenesis, and describe their phenotypic range and overlap with other diseases.

TDP-43 pathology in a case of hereditary spastic paraplegia with a NIPA1/SPG6 mutation

Mutations in NIPA1 (non-imprinted in Prader-Willi/Angelman syndrome) have been described as a cause of autosomal dominant hereditary spastic paraplegia (HSP) known as SPG6 (spastic paraplegia-6). We present the first neuropathological description of a patient with a NIPA1 mutation, and clinical phenotype of complicated HSP with motor neuron disease-like syndrome and cognitive decline. Postmortem examination revealed degeneration of lateral corticospinal tracts and dorsal columns with motor neuron loss. TDP-43 immunostaining showed widespread spinal cord and cerebral skein-like and round neuronal cytoplasmic inclusions. We ruled out NIPA1 mutations in 419 additional cases of motor neuron disease. These findings suggest that hereditary spastic paraplegia due to NIPA1 mutations could represent a TDP-43 proteinopathy.

Spatacsin and spastizin act in the same pathway required for proper spinal motor neuron axon outgrowth in zebrafish

Hereditary spastic paraplegias (HSPs) are rare neurological conditions caused by degeneration of the long axons of the cerebrospinal tracts, leading to locomotor impairment and additional neurological symptoms. There are more than 40 different causative genes, 24 of which have been identified, including SPG11 and SPG15 mutated in complex clinical forms. Since the vast majority of the causative mutations lead to loss of function of the corresponding proteins, we made use of morpholino-oligonucleotide (MO)-mediated gene knock-down to generate zebrafish models of both SPG11 and SPG15 and determine how invalidation of the causative genes (zspg11 and zspg15) during development might contribute to the disease. Micro-injection of MOs targeting each gene caused locomotor impairment and abnormal branching of spinal cord motor neurons at the neuromuscular junction. More severe phenotypes with abnormal tail developments were also seen. Moreover, partial depletion of both proteins at sub-phenotypic levels resulted in the same phenotypes, suggesting for the first time, in vivo, a genetic interaction between these genes. In conclusion, the zebrafish orthologues of the SPG11 and SPG15 genes are important for proper development of the axons of spinal motor neurons and likely act in a common pathway to promote their proper path finding towards the neuromuscular junction.

Identification of pharmacological targets in amyotrophic lateral sclerosis through genomic analysis of deregulated genes and pathways

Amyotrophic Lateral Sclerosis (ALS) is a progressive and disabling neurodegenerative disorder characterized by upper and lower motor neuron loss, leading to respiratory insufficiency and death after 3-5 years. Riluzole is currently the only FDA approved drug for ALS, but it has only modest effects on survival. The majority of ALS cases are sporadic and probably associated to a multifactorial etiology. With the completion of genome sequencing in humans and model organisms, together with the advent of DNA microarray technology, the transcriptional cascades and networks underlying neurodegeneration in ALS are being elucidated providing new potential pharmacological targets. The main challenge now is the effective screening of the myriad of targets to identify those with the most therapeutic utility. The present review will illustrate how the identification, prioritization and validation of preclinical therapeutics can be achieved through genomic analysis of critical pathways and networks deregulated in ALS pathology.

Young-onset amyotrophic lateral sclerosis: historical and other observations

There is a wide range of age at initial symptom onset in amyotrophic lateral sclerosis despite a mean age of 65 years in population-based studies. 'Young-onset' amyotrophic lateral sclerosis typically refers to patients younger than ∼45 years and accounts for about 10% of cases in contemporary series. A review of published cases of amyotrophic lateral sclerosis from 1850 to 1950 revealed a far higher proportion of cases with young onset (>50%), with a steady decline to the contemporary figure. It is possible that this is not solely explained by increases in life expectancy. While there is still a rich variation in phenotypes among cases of young-onset amyotrophic lateral sclerosis, bulbar onset was found to be significantly under-represented in analysis of a large patient database, with implications for age-related vulnerabilities pertaining to focality of symptom onset. The timing of initiating pathological processes in relation to the emergence of symptoms is discussed, including the potential role of very early development and the interaction of epigenetic and environmental factors.

The use of next-generation sequencing in movement disorders

New advances in genomic technology are being introduced at a greater speed and are revolutionizing the field of genetics for both complex and Mendelian diseases. For instance, during the past few years, genome-wide association studies (GWAS) have identified a large number of significant associations between genomic loci and movement disorders such as Parkinson's disease and progressive supranuclear palsy. GWAS are carried out through the use of high-throughput SNP genotyping arrays, which are also used to perform linkage analyses in families previously considered statistically underpowered for genetic analyses. In inherited movement disorders, using this latter technology, it has repeatedly been shown that mutations in a single gene can lead to different phenotypes, while the same clinical entity can be caused by mutations in different genes. This is being highlighted with the use of next-generation sequencing technologies and leads to the search for genes or genetic modifiers that contribute to the phenotypic expression of movement disorders. Establishing an accurate genome-epigenome-phenotype relationship is becoming a major challenge in the post-genomic research that should be facilitated through the implementation of both functional and cellular analyses.

Hereditary spastic paraplegias with autosomal dominant, recessive, X-linked, or maternal trait of inheritance

Hereditary spastic paraplegia (SPG) is a clinically and genetically heterogeneous group of neurodegenerative disorders that are clinically characterised by progressive spasticity and weakness of the lower-limbs (pure SPG) and, majoritorian, additional more extensive neurological or non-neurological manifestations (complex or complicated SPG). Pure SPG is characterised by progressive spasticity and weakness of the lower-limbs, and occasionally sensory disturbances or bladder dysfunction. Complex SPGs additionally include cognitive impairment, dementia, epilepsy, extrapyramidal disturbances, cerebellar involvement, retinopathy, optic atrophy, deafness, polyneuropathy, or skin lesions in the absence of coexisting disorders. Nineteen SPGs follow an autosomal-dominant (AD-SPG), 27 an autosomal-recessive (AR-SPG), 5 X-linked (XL-SPG), and one a maternal trait of inheritance. SPGs are due to mutations in genes encoding for proteins involved in the maintenance of corticospinal tract neurons. Among the AD-SPGs, 40-45% of patients carry mutations in the SPAST-gene (SPG4) and 10% in the ATL1-gene (SPG3), while the other 9 genes are more rarely involved (NIPA1 (SPG6), KIAA0196 (SPG8), KIF5A (SPG10), RNT2 (SPG12), SPGD1 (SPG13), BSCL2 (SPG17), REEP1 (SPG31), ZFYVE27 (SPG33, debated), and SLC33A1 (SPG42, debated)). Among the AR-SPGs, ~20% of the patients carry mutations in the KIAA1840 (SPG11) gene whereas the 15 other genes are rarely mutated and account for SPGs in single families yet (CYP7B1 (SPG5), SPG7 (SPG7), ZFYVE26 (SPG15), ERLIN2 (SPG18), SPG20 (SPG20), ACP33 (SPG21), KIF1A (SPG30), FA2H (SPG35), NTE (SPG39), GJA12/GJC2 (SPG44), KIAA0415 (SPG48) and 4 genes encoding for the AP4-complex (SPG47)). Among the XL-SPGs, 3 causative genes have been identified (L1CAM (SPG1), PLP1 (SPG2), and SLC16A2 (SPG22)). The diagnosis of SPGs is based on clinical, instrumental and genetic investigations. Treatment is exclusively symptomatic.

Research advances in gene therapy approaches for the treatment of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease of motor neurons that causes progressive muscle weakness, paralysis, and premature death. No effective therapy is available. Research in the motor neuron field continues to grow, and recent breakthroughs have demonstrated the possibility of completely achieving rescue in animal models of spinal muscular atrophy, a genetic motor neuron disease. With adeno-associated virus (AAV) vectors, gene transfer can be achieved with systemic non-invasive injection and minimal toxicity. In the context of this success, we review gene therapy approaches for ALS, considering what has been done and the possible future directions for effective application of the latest generation of vectors for clinical translation. We focus on recent developments in the areas of RNA/antisense-mediated silencing of specific ALS causative genes like superoxide dismutase-1 and other molecular pathogenetic targets, as well as the administration of neuroprotective factors with viral vectors. We argue that gene therapy offers new opportunities to open the path for clinical progress in treating ALS.

Molecular pathways of motor neuron injury in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a genetically diverse disease. At least 15 ALS-associated gene loci have so far been identified, and the causative gene is known in approximately 30% of familial ALS cases. Less is known about the factors underlying the sporadic form of the disease. The molecular mechanisms of motor neuron degeneration are best understood in the subtype of disease caused by mutations in superoxide dismutase 1, with a current consensus that motor neuron injury is caused by a complex interplay between multiple pathogenic processes. A key recent finding is that mutated TAR DNA-binding protein 43 is a major constituent of the ubiquitinated protein inclusions in ALS, providing a possible link between the genetic mutation and the cellular pathology. New insights have also indicated the importance of dysregulated glial cell-motor neuron crosstalk, and have highlighted the vulnerability of the distal axonal compartment early in the disease course. In addition, recent studies have suggested that disordered RNA processing is likely to represent a major contributing factor to motor neuron disease. Ongoing research on the cellular pathways highlighted in this Review is predicted to open the door to new therapeutic interventions to slow disease progression in ALS.

FUS-related proteinopathies: lessons from animal models

The recent identification of ALS-linked mutations in FUS and TDP-43 has led to a major shift in our thinking in regard to the potential molecular mechanisms of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). RNA-mediated proteinopathy is increasingly being recognized as a potential cause of neurodegenerative disorders. FUS and TDP-43 are structurally and functionally similar proteins. FUS is a DNA/RNA binding protein that may regulate aspects of RNA metabolism, including splicing, mRNA processing, and micro RNA biogenesis. It is unclear how ALS-linked mutations perturb the functions of FUS. This review highlights recent advances in understanding the functions of FUS and discusses findings from FUS animal models that provide several key insights into understanding the molecular mechanisms that might contribute to ALS pathogenesis.

Exome sequencing reveals SPG11 mutations causing juvenile ALS

We report here the description of a nonconsanguineous family with 2 affected individuals with a recessively inherited juvenile motor neuron disease. Exome sequencing of these 2 affected individuals led us to identify 2 compound heterozygous deletions leading to a frameshift and a premature stop codon in the SPG11 gene. One of these deletions, c.5199delA in exon 30, has not been previously reported. Interestingly, these deletions are associated with an intrafamilial phenotypic heterogeneity as one affected has atypical juvenile amyotrophic lateral sclerosis (ALS) and the other has classical hereditary spastic paraplegia with thin corpus callosum. Our findings confirm SPG11 as a genetic cause of juvenile amyotrophic lateral sclerosis and indicate that SPG11 mutations could be associated with 2 different clinical phenotypes within the same family.

Clinical genetics of amyotrophic lateral sclerosis: what do we really know?

Hereditary amyotrophic lateral sclerosis (ALS) encompasses a group of genetic disorders characterized by adult-onset loss of the lower and upper motor neuron systems, often with involvement of other parts of the nervous system. Cases of hereditary ALS have been attributed to mutations in 12 different genes, the most common being SOD1, FUS and TARDBP-mutations in the other genes are rare. The identified genes explain 25-35% of cases of familial ALS, but identifying the remaining genes has proved difficult. Only a few genes seem to account for significant numbers of ALS cases, with many others causing a few cases each. Hereditary ALS can be inherited in an autosomal dominant, autosomal recessive or X-linked manner, and families with low disease penetrance are frequently observed. In such families, the genetic predisposition may remain unnoticed, so many patients carry a diagnosis of isolated or sporadic ALS. The only clinical feature that distinguishes recognized hereditary from apparently sporadic ALS is a lower mean age of onset in the former. All the clinical features reported in hereditary cases (including signs of extrapyramidal, cerebellar or cognitive involvement) have also been observed in sporadic cases. Genetic counseling and risk assessment in relatives depend on establishing the specific gene defect and the disease penetrance in the particular family.

New considerations in the design of clinical trials for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a devastating neurodegenerative disease caused by loss of motor neurons. Its pathophysiology remains unknown, but progress has been made in understanding its genetic and biochemical basis. Clinical trialists are working to translate basic science successes into human trials with more efficiency, in the hope of finding successful treatments. In the future, new preclinical models, including patient-derived stem cells may augment transgenic animal models as preclinical tools. Biomarker discovery projects aim to identify markers of disease onset and progression for use in clinical trials. New trial designs are reducing study time, improving efficiency and helping to keep pace with the increasing rate of basic and translational discoveries. Ongoing trials with novel designs are paving the way for amyotrophic lateral sclerosis clinical research.

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

Over the last couple of decades, there has been a growing body of clinical, genetic, and histopathological evidence that similar pathological processes underlie amyotrophic lateral sclerosis (ALS) and some types of frontotemporal lobe dementia (FTD). Even though there is great diversity in the genetic causes of these disorders, there is a high degree of overlap in their histopathology. Genes linked to rare cases of familial ALS and/or FTD, like FUS, TARDBP, OPTN, and UBQLN2 may converge onto a unifying pathogenic pathway and thereby provide novel therapeutic targets common to a spectrum of etiologically diverse forms of ALS and ALS-FTD. Additionally, there are major loci for ALS-FTD on chromosomes 9p and 15q. Identification of causative genetic alterations at those loci will be an important step in understanding the pathogenesis of juvenile- and adult-onset ALS and ALS-FTD. Interactions between TDP-43, FUS, optineurin, and ubiquilin 2 need to be studied to understand their common molecular pathways. Future efforts should also be directed towards generation and characterization of in vivo models to dissect the pathogenic mechanisms of these diseases. Such efforts will rapidly accelerate the discovery of new drugs that regulate accumulation of pathogenic proteins and their downstream consequences.

Thinning of the corpus callosum and cerebellar atrophy is correlated with phenotypic severity in a family with spastic paraplegia type 11

Background

Mutations in the spatacsin gene are associated with spastic paraplegia type 11 (SPG11), which is the most-common cause of autosomal recessive hereditary spastic paraplegia. Although SPG11 has diverse phenotypes, thinning of the corpus callosum is an important feature.

Case Report

Clinical, genetic, and radiological evaluations were undertaken in a large family from Gujarat in North India with hereditary spastic paraplegia, whose affected members presented with varying degrees of spasticity, ataxia, and cognitive impairment. The clinical severity and the degree of corpus callosum and cerebellar atrophy varied among the four affected individuals in the family. Genetic testing of the affected members revealed recessive mutations in the spatacsin gene, consistent with a diagnosis of SPG11.

Conclusions

We believe that the extent of corpus callosum thinning and cerebellar atrophy is correlated with disease severity in affected patients. The addition of extrapyramidal features in the most-affected members suggests that SPG11 exhibits considerable phenotypic heterogeneity.

Research advances in amyotrophic lateral sclerosis, 2009 to 2010

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of upper and lower motor neurons that causes progressive weakness and death. The breadth of research in ALS continues to grow with exciting new discoveries in disease pathogenesis and potential future therapeutics. There is a growing list of identified mutations in familial ALS, including those in genes encoding TDP-43 and FUS/TLS, which are expanding our understanding of the role of RNA modulation in ALS pathogenesis. There is a greater appreciation for the role of glial cells in motor neuron disease. Mitochondrial dysfunction is also being shown to be critical for motor neuron degeneration. In addition to pharmacotherapy, there are promising early developments with therapeutic implications in the areas of RNA interference, stem cell therapies, viral vector-mediated gene therapy, and immunotherapy. With greater understanding of ALS pathogenesis and exciting new therapeutic technologies, there is hope for future progress in treating this disease.

Novel mutations in SPG11 cause hereditary spastic paraplegia associated with early-onset levodopa-responsive Parkinsonism

BACKGROUND

Autosomal recessive hereditary spastic paraplegia with thin corpus callosum is a neurodegenerative disorder characterized by spastic paraparesis, cognitive impairment, and peripheral neuropathy. The neuroradiologic hallmarks are thin corpus callosum and periventricular white matter changes. Mutations in the SPG11 gene have been identified to be a major cause of autosomal recessive hereditary spastic paraplegia with thin corpus callosum and recently also proven to be responsible for juvenile parkinsonism associated with spastic paraplegia.

METHODS

We describe one Italian autosomal recessive hereditary spastic paraplegia with thin corpus callosum patient who unusually presented at onset, 16 years, with parkinsonism-like features, responsive to dopaminergic therapy. Then the clinical picture evolved and became more complex. A brain magnetic resonance imaging scan showed thin corpus callosum and hyperintense T(2)-weighted lesions in periventricular regions, and the (123)I-ioflupane single-photon emission coupled tomography was abnormal.

RESULTS

Genetic analysis detected two novel mutations, a c.3664insT variant in compound heterozygosity with a c.6331insG mutation, in SPG11.

DISCUSSION

This case confirms the high genetic and clinical heterogeneity associated with SPG11 mutations. It also offers further evidence that parkinsonism may initiate autosomal recessive hereditary spastic paraplegia with thin corpus callosum and that parkinsonian symptoms can have variable dopaminergic response in these patients.

Genetic rodent models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the selective death of motor neurons in the motor cortex, brainstem, and spinal cord. A large number of rodent models are available that show motor neuron death and a progressive motor phenotype that is more or less reminiscent of what occurs in patients. These rodent models contain genes with spontaneous or induced mutations or (over) express different (mutant) genes. Some of these models have been of great value to delineate potential pathogenic mechanisms that cause and/or modulate selective motor neuron degeneration. In addition, these genetic rodent models play a crucial role in testing and selecting potential therapeutics that can be used to treat ALS and/or other motor neuron disorders. In this paper, we give a systematic overview of the most important genetic rodent models that show motor neuron degeneration and/or develop a motor phenotype. In addition, we discuss the value and limitations of the different models and conclude that it remains a challenge to find more and better rodent models based on mutations in new genes causing ALS.

Expanding the clinical spectrum of SPG11 gene mutations in recessive hereditary spastic paraplegia with thin corpus callosum

Hereditary spastic paraplegia (HSP) represents a large group of neurological disorders characterized by progressive spasticity of the lower limbs. One subtype of HSP shows an autosomal recessive form of inheritance with thin corpus callosum (ARHSP-TCC), and displays genetic heterogeneity with four known loci. We identified a consanguineous Egyptian family with five affected individuals with ARHSP-TCC. We found linkage to the SPG11 locus and identified a novel homozygous p.Q498X stop codon mutation in exon 7 in the SPG11 gene encoding Spatacsin. Cognitive impairment and polyneuropathy, reported as frequent in SPG11, were not evident. This family supports the importance of SPG11 as a frequent cause for ARHSP-TCC, and expands the clinical SPG11 spectrum.

A large genome scan for rare CNVs in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease selectively affecting motor neurons in the brain and spinal cord. Recent genome-wide association studies (GWASs) have identified several common variants which increase disease susceptibility. In contrast, rare copy-number variants (CNVs), which have been associated with several neuropsychiatric traits, have not been studied for ALS in well-powered study populations. To examine the role of rare CNVs in ALS susceptibility, we conducted a CNV association study including over 19,000 individuals. In a genome-wide screen of 1875 cases and 8731 controls, we did not find evidence for a difference in global CNV burden between cases and controls. In our association analyses, we identified two loci that met our criteria for follow-up: the DPP6 locus (OR = 3.59, P = 6.6 × 10(-3)), which has already been implicated in ALS pathogenesis, and the 15q11.2 locus, containing NIPA1 (OR = 12.46, P = 9.3 × 10(-5)), the gene causing hereditary spastic paraparesis type 6 (HSP 6). We tested these loci in a replication cohort of 2559 cases and 5887 controls. Again, results were suggestive of association, but did not meet our criteria for independent replication: DPP6 locus: OR = 1.92, P = 0.097, pooled results: OR = 2.64, P = 1.4 × 10(-3); NIPA1: OR = 3.23, P = 0.041, pooled results: OR = 6.20, P = 2.2 × 10(-5)). Our results highlight DPP6 and NIPA1 as candidates for more in-depth studies. Unlike other complex neurological and psychiatric traits, rare CNVs with high effect size do not play a major role in ALS pathogenesis.

Loss of ALS2/Alsin exacerbates motor dysfunction in a SOD1-expressing mouse ALS model by disturbing endolysosomal trafficking

Background

ALS2/alsin is a guanine nucleotide exchange factor for the small GTPase Rab5 and involved in macropinocytosis-associated endosome fusion and trafficking, and neurite outgrowth. ALS2 deficiency accounts for a number of juvenile recessive motor neuron diseases (MNDs). Recently, it has been shown that ALS2 plays a role in neuroprotection against MND-associated pathological insults, such as toxicity induced by mutant Cu/Zn superoxide dismutase (SOD1). However, molecular mechanisms underlying the relationship between ALS2-associated cellular function and its neuroprotective role remain unclear.

Methodology/Principal Findings

To address this issue, we investigated the molecular and pathological basis for the phenotypic modification of mutant SOD1-expressing mice by ALS2 loss. Genetic ablation of Als2 in SOD1^H46R, but not SOD1^G93A, transgenic mice aggravated the mutant SOD1-associated disease symptoms such as body weight loss and motor dysfunction, leading to the earlier death. Light and electron microscopic examinations revealed the presence of degenerating and/or swollen spinal axons accumulating granular aggregates and autophagosome-like vesicles in early- and even pre-symptomatic SOD1^H46R mice. Further, enhanced accumulation of insoluble high molecular weight SOD1, poly-ubiquitinated proteins, and macroautophagy-associated proteins such as polyubiquitin-binding protein p62/SQSTM1 and a lipidated form of light chain 3 (LC3-II), emerged in ALS2-deficient SOD1^H46R mice. Intriguingly, ALS2 was colocalized with LC3 and p62, and partly with SOD1 on autophagosome/endosome hybrid compartments, and loss of ALS2 significantly lowered the lysosome-dependent clearance of LC3 and p62 in cultured cells.

Conclusions/Significance

Based on these observations, although molecular basis for the distinctive susceptibilities to ALS2 loss in different mutant SOD1-expressing ALS models is still elusive, disturbance of the endolysosomal system by ALS2 loss may exacerbate the SOD1^H46R-mediated neurotoxicity by accelerating the accumulation of immature vesicles and misfolded proteins in the spinal cord. We propose that ALS2 is implicated in endolysosomal trafficking through the fusion between endosomes and autophagosomes, thereby regulating endolysosomal protein degradation in vivo.