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1.  Screening a UK amyotrophic lateral sclerosis cohort provides evidence of multiple origins of the C9orf72 expansion☆ 
Neurobiology of Aging  2015;36(1):546.e1-546.e7.
An expanded hexanucleotide repeat in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia (C9ALS/FTD). Although 0–30 hexanucleotide repeats are present in the general population, expansions >500 repeats are associated with C9ALS/FTD. Large C9ALS/FTD expansions share a common haplotype and whether these expansions derive from a single founder or occur more frequently on a predisposing haplotype is yet to be determined and is relevant to disease pathomechanisms. Furthermore, although cases carrying 50–200 repeats have been described, their role and the pathogenic threshold of the expansions remain to be identified and carry importance for diagnostics and genetic counseling. We present clinical and genetic data from a UK ALS cohort and report the detailed molecular study of an atypical somatically unstable expansion of 90 repeats. Our results across different tissues provide evidence for the pathogenicity of this repeat number by showing they can somatically expand in the central nervous system to the well characterized pathogenic range. Our results support the occurrence of multiple expansion events for C9ALS/FTD.
doi:10.1016/j.neurobiolaging.2014.07.037
PMCID: PMC4270445  PMID: 25179228
Frontotemporal dementia; Somatic instability; Amyotrophic lateral sclerosis
2.  C9orf72 frontotemporal lobar degeneration is characterised by frequent neuronal sense and antisense RNA foci 
Acta Neuropathologica  2013;126(6):845-857.
An expanded GGGGCC repeat in a non-coding region of the C9orf72 gene is a common cause of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis. Non-coding repeat expansions may cause disease by reducing the expression level of the gene they reside in, by producing toxic aggregates of repeat RNA termed RNA foci, or by producing toxic proteins generated by repeat-associated non-ATG translation. We present the first definitive report of C9orf72 repeat sense and antisense RNA foci using a series of C9FTLD cases, and neurodegenerative disease and normal controls. A sensitive and specific fluorescence in situ hybridisation protocol was combined with protein immunostaining to show that both sense and antisense foci were frequent, specific to C9FTLD, and present in neurons of the frontal cortex, hippocampus and cerebellum. High-resolution imaging also allowed accurate analyses of foci number and subcellular localisation. RNA foci were most abundant in the frontal cortex, where 51 % of neurons contained foci. RNA foci also occurred in astrocytes, microglia and oligodendrocytes but to a lesser degree than in neurons. RNA foci were observed in both TDP-43- and p62-inclusion bearing neurons, but not at a greater frequency than expected by chance. RNA foci abundance in the frontal cortex showed a significant inverse correlation with age at onset of disease. These data establish that sense and antisense C9orf72 repeat RNA foci are a consistent and specific feature of C9FTLD, providing new insight into the pathogenesis of C9FTLD.
Electronic supplementary material
The online version of this article (doi:10.1007/s00401-013-1200-z) contains supplementary material, which is available to authorized users.
doi:10.1007/s00401-013-1200-z
PMCID: PMC3830745  PMID: 24170096
FTLD; FTD; ALS; RNA foci; Antisense; C9orf72
3.  Homozygosity for the C9orf72 GGGGCC repeat expansion in frontotemporal dementia 
Acta Neuropathologica  2013;126(3):401-409.
An expanded hexanucleotide repeat in the C9orf72 gene is the most common genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis (c9FTD/ALS). We now report the first description of a homozygous patient and compare it to a series of heterozygous cases. The patient developed early-onset frontotemporal dementia without additional features. Neuropathological analysis showed c9FTD/ALS characteristics, with abundant p62-positive inclusions in the frontal and temporal cortices, hippocampus and cerebellum, as well as less abundant TDP-43-positive inclusions. Overall, the clinical and pathological features were severe, but did not fall outside the usual disease spectrum. Quantification of C9orf72 transcript levels in post-mortem brain demonstrated expression of all known C9orf72 transcript variants, but at a reduced level. The pathogenic mechanisms by which the hexanucleotide repeat expansion causes disease are unclear and both gain- and loss-of-function mechanisms may play a role. Our data support a gain-of-function mechanism as pure homozygous loss of function would be expected to lead to a more severe, or completely different clinical phenotype to the one described here, which falls within the usual range. Our findings have implications for genetic counselling, highlighting the need to use genetic tests that distinguish C9orf72 homozygosity.
Electronic supplementary material
The online version of this article (doi:10.1007/s00401-013-1147-0) contains supplementary material, which is available to authorized users.
doi:10.1007/s00401-013-1147-0
PMCID: PMC3753468  PMID: 23818065
C9orf72; ALS; FTD
4.  C9orf72 amyotrophic lateral sclerosis and frontotemporal dementia: gain or loss of function? 
Current Opinion in Neurology  2014;27(5):515-523.
Purpose of review
The molecular mechanisms that underlie chromosome 9 open reading frame 72 (C9orf72)-associated amyotrophic lateral sclerosis and frontotemporal dementia are rapidly emerging. Two potential disease mechanisms have been postulated – gain or loss of function. We provide an overview of recent advances that support or oppose gain-of-function and loss-of-function mechanisms.
Recent findings
Since the discovery that a noncoding repeat expansion in C9orf72 was responsible for chromosome 9-linked amyotrophic lateral sclerosis and frontotemporal dementia in 2011, a plethora of studies have investigated clinical, pathological and mechanistic aspects of the disease. Loss of function is supported by reduced levels of C9orf72 in patient brain and functional work, revealing a role of the C9orf72 protein in endocytic and autophagic pathways and motor function. Gain of function is supported by the presence in patient brain of both repeat RNA and protein aggregates. Repeat RNA aggregates termed RNA foci, a hallmark of noncoding repeat expansion diseases, have been shown to sequester proteins involved in RNA splicing, editing, nuclear export and nucleolar function. Repeat-associated non-ATG dependent translation gives rise to toxic dipeptide repeat proteins that form inclusions in patient tissue. Antisense oligonucleotides targeting C9orf72 have shown promise for combating gain-of-function toxicity.
Summary
Rapid progress is being made towards understanding this common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. Overall, the weight of data currently sits in favour of gain of function as the most important disease mechanism, which has important implications for the development of effective and targeted therapies.
doi:10.1097/WCO.0000000000000130
PMCID: PMC4165481  PMID: 25188012
amyotrophic lateral sclerosis; C9orf72; frontotemporal dementia; gain or loss of function
5.  C9orf72 hexanucleotide repeat associated with amyotrophic lateral sclerosis and frontotemporal dementia forms RNA G-quadruplexes 
Scientific Reports  2012;2:1016.
Large expansions of a non-coding GGGGCC-repeat in the first intron of the C9orf72 gene are a common cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). G-rich sequences have a propensity for forming highly stable quadruplex structures in both RNA and DNA termed G-quadruplexes. G-quadruplexes have been shown to be involved in a range of processes including telomere stability and RNA transcription, splicing, translation and transport. Here we show using NMR and CD spectroscopy that the C9orf72 hexanucleotide expansion can form a stable G-quadruplex, which has profound implications for disease mechanism in ALS and FTD.
doi:10.1038/srep01016
PMCID: PMC3527825  PMID: 23264878
6.  A comparative clinical, pathological, biochemical and genetic study of fused in sarcoma proteinopathies 
Brain  2011;134(9):2548-2564.
Neuronal intermediate filament inclusion disease and atypical frontotemporal lobar degeneration are rare diseases characterized by ubiquitin-positive inclusions lacking transactive response DNA-binding protein-43 and tau. Recently, mutations in the fused in sarcoma gene have been shown to cause familial amyotrophic lateral sclerosis and fused in sarcoma-positive neuronal inclusions have subsequently been demonstrated in neuronal intermediate filament inclusion disease and atypical frontotemporal lobar degeneration with ubiquitinated inclusions. Here we provide clinical, imaging, morphological findings, as well as genetic and biochemical data in 14 fused in sarcoma proteinopathy cases. In this cohort, the age of onset was variable but included cases of young-onset disease. Patients with atypical frontotemporal lobar degeneration with ubiquitinated inclusions all presented with behavioural variant frontotemporal dementia, while the clinical presentation in neuronal intermediate filament inclusion disease was more heterogeneous, including cases with motor neuron disease and extrapyramidal syndromes. Neuroimaging revealed atrophy of the frontal and anterior temporal lobes as well as the caudate in the cases with atypical frontotemporal lobar degeneration with ubiquitinated inclusions, but was more heterogeneous in the cases with neuronal intermediate filament inclusion disease, often being normal to visual inspection early on in the disease. The distribution and severity of fused in sarcoma-positive neuronal cytoplasmic inclusions, neuronal intranuclear inclusions and neurites were recorded and fused in sarcoma was biochemically analysed in both subgroups. Fused in sarcoma-positive neuronal cytoplasmic and intranuclear inclusions were found in the hippocampal granule cell layer in variable numbers. Cortical fused in sarcoma-positive neuronal cytoplasmic inclusions were often ‘Pick body-like’ in neuronal intermediate filament inclusion disease, and annular and crescent-shaped inclusions were seen in both conditions. Motor neurons contained variable numbers of compact, granular or skein-like cytoplasmic inclusions in all fused in sarcoma-positive cases in which brainstem and spinal cord motor neurons were available for study (five and four cases, respectively). No fused in sarcoma mutations were found in any cases. Biochemically, two major fused in sarcoma species were found and shown to be more insoluble in the atypical frontotemporal lobar degeneration with ubiquitinated inclusions subgroup compared with neuronal intermediate filament inclusion disease. There is considerable overlap and also significant differences in fused in sarcoma-positive pathology between the two subgroups, suggesting they may represent a spectrum of the same disease. The co-existence of fused in sarcoma-positive inclusions in both motor neurons and extramotor cerebral structures is a characteristic finding in sporadic fused in sarcoma proteinopathies, indicating a multisystem disorder.
doi:10.1093/brain/awr160
PMCID: PMC3170529  PMID: 21752791
frontotemporal lobar degeneration; FUS; clinical presentation; neuropathology; biochemistry
7.  Clinical and neuroanatomical signatures of tissue pathology in frontotemporal lobar degeneration 
Brain  2011;134(9):2565-2581.
Relating clinical symptoms to neuroanatomical profiles of brain damage and ultimately to tissue pathology is a key challenge in the field of neurodegenerative disease and particularly relevant to the heterogeneous disorders that comprise the frontotemporal lobar degeneration spectrum. Here we present a retrospective analysis of clinical, neuropsychological and neuroimaging (volumetric and voxel-based morphometric) features in a pathologically ascertained cohort of 95 cases of frontotemporal lobar degeneration classified according to contemporary neuropathological criteria. Forty-eight cases (51%) had TDP-43 pathology, 42 (44%) had tau pathology and five (5%) had fused-in-sarcoma pathology. Certain relatively specific clinicopathological associations were identified. Semantic dementia was predominantly associated with TDP-43 type C pathology; frontotemporal dementia and motoneuron disease with TDP-43 type B pathology; young-onset behavioural variant frontotemporal dementia with FUS pathology; and the progressive supranuclear palsy syndrome with progressive supranuclear palsy pathology. Progressive non-fluent aphasia was most commonly associated with tau pathology. However, the most common clinical syndrome (behavioural variant frontotemporal dementia) was pathologically heterogeneous; while pathologically proven Pick's disease and corticobasal degeneration were clinically heterogeneous, and TDP-43 type A pathology was associated with similar clinical features in cases with and without progranulin mutations. Volumetric magnetic resonance imaging, voxel-based morphometry and cluster analyses of the pathological groups here suggested a neuroanatomical framework underpinning this clinical and pathological diversity. Frontotemporal lobar degeneration-associated pathologies segregated based on their cerebral atrophy profiles, according to the following scheme: asymmetric, relatively localized (predominantly temporal lobe) atrophy (TDP-43 type C); relatively symmetric, relatively localized (predominantly temporal lobe) atrophy (microtubule-associated protein tau mutations); strongly asymmetric, distributed atrophy (Pick's disease); relatively symmetric, predominantly extratemporal atrophy (corticobasal degeneration, fused-in-sarcoma pathology). TDP-43 type A pathology was associated with substantial individual variation; however, within this group progranulin mutations were associated with strongly asymmetric, distributed hemispheric atrophy. We interpret the findings in terms of emerging network models of neurodegenerative disease: the neuroanatomical specificity of particular frontotemporal lobar degeneration pathologies may depend on an interaction of disease-specific and network-specific factors.
doi:10.1093/brain/awr198
PMCID: PMC3170537  PMID: 21908872
frontotemporal dementia; frontotemporal lobar degeneration; voxel-based morphometry; MRI; neural network
8.  FUS pathology defines the majority of tau- and TDP-43-negative frontotemporal lobar degeneration 
Acta neuropathologica  2010;120(1):33-41.
Through an international consortium, we have collected 37 tau- and TAR DNA-binding protein 43 (TDP-43)-negative frontotemporal lobar degeneration (FTLD) cases, and present here the first comprehensive analysis of these cases in terms of neuropathology, genetics, demographics and clinical data. 92% (34/37) had fused in sarcoma (FUS) protein pathology, indicating that FTLD-FUS is an important FTLD subtype. This FTLD-FUS collection specifically focussed on aFTLD-U cases, one of three recently defined subtypes of FTLD-FUS. The aFTLD-U subtype of FTLD-FUS is characterised clinically by behavioural variant frontotemporal dementia (bvFTD) and has a particularly young age of onset with a mean of 41 years. Further, this subtype had a high prevalence of psychotic symptoms (36% of cases) and low prevalence of motor symptoms (3% of cases). We did not find FUS mutations in any aFTLD-U case. To date, the only subtype of cases reported to have ubiquitin-positive but tau-, TDP-43- and FUS-negative pathology, termed FTLD-UPS, is the result of charged multivesicular body protein 2B gene (CHMP2B) mutation. We identified three FTLD-UPS cases, which are negative for CHMP2B mutation, suggesting that the full complement of FTLD pathologies is yet to be elucidated.
doi:10.1007/s00401-010-0698-6
PMCID: PMC2887939  PMID: 20490813
FTLD; FUS; FTLD-UPS; Frontotemporal; FTD
9.  FUS pathology defines the majority of tau- and TDP-43-negative frontotemporal lobar degeneration 
Acta Neuropathologica  2010;120(1):33-41.
Through an international consortium, we have collected 37 tau- and TAR DNA-binding protein 43 (TDP-43)-negative frontotemporal lobar degeneration (FTLD) cases, and present here the first comprehensive analysis of these cases in terms of neuropathology, genetics, demographics and clinical data. 92% (34/37) had fused in sarcoma (FUS) protein pathology, indicating that FTLD-FUS is an important FTLD subtype. This FTLD-FUS collection specifically focussed on aFTLD-U cases, one of three recently defined subtypes of FTLD-FUS. The aFTLD-U subtype of FTLD-FUS is characterised clinically by behavioural variant frontotemporal dementia (bvFTD) and has a particularly young age of onset with a mean of 41 years. Further, this subtype had a high prevalence of psychotic symptoms (36% of cases) and low prevalence of motor symptoms (3% of cases). We did not find FUS mutations in any aFTLD-U case. To date, the only subtype of cases reported to have ubiquitin-positive but tau-, TDP-43- and FUS-negative pathology, termed FTLD-UPS, is the result of charged multivesicular body protein 2B gene (CHMP2B) mutation. We identified three FTLD-UPS cases, which are negative for CHMP2B mutation, suggesting that the full complement of FTLD pathologies is yet to be elucidated.
doi:10.1007/s00401-010-0698-6
PMCID: PMC2887939  PMID: 20490813
FTLD; FUS; FTLD-UPS; Frontotemporal; FTD
10.  Disruption of endocytic trafficking in frontotemporal dementia with CHMP2B mutations 
Human Molecular Genetics  2010;19(11):2228-2238.
Mutations in CHMP2B cause frontotemporal dementia (FTD) in a large Danish pedigree, which is termed FTD linked to chromosome 3 (FTD-3), and also in an unrelated familial FTD patient. CHMP2B is a component of the ESCRT-III complex, which is required for function of the multivesicular body (MVB), an endosomal structure that fuses with the lysosome to degrade endocytosed proteins. We report a novel endosomal pathology in CHMP2B mutation-positive patient brains and also identify and characterize abnormal endosomes in patient fibroblasts. Functional studies demonstrate a specific disruption of endosome–lysosome fusion but not protein sorting by the MVB. We provide evidence for a mechanism for impaired endosome–lysosome fusion whereby mutant CHMP2B constitutively binds to MVBs and prevents recruitment of proteins necessary for fusion to occur, such as Rab7. The fusion of endosomes with lysosomes is required for neuronal function and the data presented therefore suggest a pathogenic mechanism for FTD caused by CHMP2B mutations.
doi:10.1093/hmg/ddq100
PMCID: PMC2865375  PMID: 20223751
11.  TDP-43 is a culprit in human neurodegeneration, and not just an innocent bystander 
Mammalian Genome  2008;19(5):299-305.
In 2006 the protein TDP-43 was identified as the major ubiquitinated component deposited in the inclusion bodies found in two human neurodegenerative diseases, amyotrophic lateral sclerosis and frontotemporal lobar degeneration. The pathogenesis of both disorders is unclear, although they are related by having some overlap of symptoms and now by the shared histopathology of TDP-43 deposition. Now, in 2008, several papers have been published in quick succession describing mutations in the TDP-43 gene, showing they can be a primary cause of amyotrophic lateral sclerosis. There are many precedents in neurodegenerative disease in which rare single-gene mutations have given great insight into understanding disease processes, which is why the TDP-43 mutations are potentially very important.
doi:10.1007/s00335-008-9117-x
PMCID: PMC2515551  PMID: 18592312
12.  Acceleration of Amyloid β-Peptide Aggregation by Physiological Concentrations of Calcium 
The Journal of biological chemistry  2006;281(38):27916-27923.
Alzheimer’s Disease (AD) is characterized by the accumulation of aggregated amyloid β-peptide (Aβ) in the brain. The physiological mechanisms and factors that predispose to Aβ aggregation and deposition are not well understood. In this report, we show that calcium can predispose to Aβ aggregation and fibril formation. Calcium increased the aggregation of early forming protofibrillar structures and markedly increased conversion of protofibrils to mature amyloid fibrils. This occurred at levels 20-fold below the calcium concentration in the extracellular space of the brain, the site at which amyloid plaque deposition occurs. In the absence of calcium, protofibrils can remain stable in vitro for several days. Using this approach, we directly compared the neurotoxicity of protofibrils and mature amyloid fibrils, and demonstrate that both species are inherently toxic to neurons in culture. Thus, calcium may be an important predisposing factor for Aβ aggregation and toxicity. The high extracellular concentration of calcium in the brain, together with impaired intraneuronal calcium regulation in the aging brain and AD, may play an important role in the onset of amyloid-related pathology.
doi:10.1074/jbc.M602061200
PMCID: PMC1595535  PMID: 16870617

Results 1-12 (12)