Association between repeat sizes and clinical and pathological characteristics in carriers of C9ORF72 repeat expansions (Xpansize-72): a cross-sectional cohort study
TL;DR: The findings indicate that expansion size does affect disease severity, which--if replicated in other cohorts--could be relevant for genetic counselling.
Abstract: Summary Background Hexanucleotide repeat expansions in chromosome 9 open reading frame 72 ( C9ORF72 ) are the most common known genetic cause of frontotemporal dementia (FTD) and motor neuron disease (MND). We assessed whether expansion size is associated with disease severity or phenotype. Methods We did a cross-sectional Southern blot characterisation study (Xpansize-72) in a cohort of individuals with FTD, MND, both these diseases, or no clinical phenotype. All participants had GGGGCC repeat expansions in C9ORF72 , and high quality DNA was available from one or more of the frontal cortex, cerebellum, or blood. We used Southern blotting techniques and densitometry to estimate the repeat size of the most abundant expansion species. We compared repeat sizes between different tissues using Wilcoxon rank sum and Wilcoxon signed rank tests, and between disease subgroups using Kruskal-Wallis rank sum tests. We assessed the association of repeat size with age at onset and age at collection using a Spearman's test of correlation, and assessed the association between repeat size and survival after disease onset using Cox proportional hazards regression models. Findings We included 84 individuals with C9ORF72 expansions: 35 had FTD, 16 had FTD and MND, 30 had MND, and three had no clinical phenotype. We focused our analysis on three major tissue subgroups: frontal cortex (available from 41 patients [21 with FTD, 11 with FTD and MND, and nine with MND]), cerebellum (40 patients [20 with FTD, 12 with FTD and MND, and eight with MND]), and blood (47 patients [15 with FTD, nine with FTD and MND, and 23 with MND] and three carriers who had no clinical phenotype). Repeat lengths in the cerebellum were smaller (median 12·3 kb [about 1667 repeat units], IQR 11·1–14·3) than those in the frontal cortex (33·8 kb [about 5250 repeat units], 23·5–44·9; p r =0·63; p=0·003) and age at sample collection ( r =0·58; p=0·006); we did not detect such a correlation in samples from the cerebellum or blood. When assessing cerebellum samples from the overall cohort, survival after disease onset was 4·8 years (IQR 3·0–7·4) in the group with expansions greater than 1467 repeat units (the 25th percentile of repeat lengths) versus 7·4 years (6·3–10·9) in the group with smaller expansions (HR 3·27, 95% CI 1·34–7·95; p=0·009). Interpretation We detected substantial variation in repeat sizes between samples from the cerebellum, frontal cortex, and blood, and longer repeat sizes in the cerebellum seem to be associated with a survival disadvantage. Our findings indicate that expansion size does affect disease severity, which—if replicated in other cohorts—could be relevant for genetic counselling. Funding The ALS Therapy Alliance, the National Institute of Neurological Disorders and Stroke, the National Institute on Aging, the Arizona Department of Health Services, the Arizona Biomedical Research Commission, and the Michael J Fox Foundation for Parkinson's Research.
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TL;DR: Extraordinary progress in understanding the biology of ALS provides new reasons for optimism that meaningful therapies will be identified, and emerging themes include dysfunction in RNA metabolism and protein homeostasis, with specific defects in nucleocytoplasmic trafficking.
Abstract: Amyotrophic lateral sclerosis (ALS) is a progressive and uniformly fatal neurodegenerative disease. A plethora of genetic factors have been identified that drive the degeneration of motor neurons in ALS, increase susceptibility to the disease or influence the rate of its progression. Emerging themes include dysfunction in RNA metabolism and protein homeostasis, with specific defects in nucleocytoplasmic trafficking, the induction of stress at the endoplasmic reticulum and impaired dynamics of ribonucleoprotein bodies such as RNA granules that assemble through liquid-liquid phase separation. Extraordinary progress in understanding the biology of ALS provides new reasons for optimism that meaningful therapies will be identified.
1,382 citations
TL;DR: In vitro and in vivo models to dissect repeat RNA and dipeptide repeat protein toxicity are developed, consistent with a dual toxicity mechanism, whereby both arginine-rich proteins and repeat RNA contribute to C9orf72-mediated neurodegeneration.
Abstract: An expanded GGGGCC repeat in C9orf72 is the most common genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis. A fundamental question is whether toxicity is driven by the repeat RNA itself and/or by dipeptide repeat proteins generated by repeat-associated, non-ATG translation. To address this question, we developed in vitro and in vivo models to dissect repeat RNA and dipeptide repeat protein toxicity. Expression of pure repeats, but not stop codon-interrupted "RNA-only" repeats in Drosophila caused adult-onset neurodegeneration. Thus, expanded repeats promoted neurodegeneration through dipeptide repeat proteins. Expression of individual dipeptide repeat proteins with a non-GGGGCC RNA sequence revealed that both poly-(glycine-arginine) and poly-(proline-arginine) proteins caused neurodegeneration. These findings are consistent with a dual toxicity mechanism, whereby both arginine-rich proteins and repeat RNA contribute to C9orf72-mediated neurodegeneration.
604 citations
TL;DR: In this paper, the authors examined whether antisense transcripts resulting from bidirectional transcription of the expanded GGGGCC repeat behave in a similar manner and showed that ectopic expression of (CCCCGG)66 in cultured cells results in foci formation.
Abstract: Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are devastating neurodegenerative disorders with clinical, genetic, and neuropathological overlap A hexanucleotide (GGGGCC) repeat expansion in a non-coding region of C9ORF72 is the major genetic cause of both diseases The mechanisms by which this repeat expansion causes “c9FTD/ALS” are not definitively known, but RNA-mediated toxicity is a likely culprit RNA transcripts of the expanded GGGGCC repeat form nuclear foci in c9FTD/ALS, and also undergo repeat-associated non-ATG (RAN) translation resulting in the production of three aggregation-prone proteins The goal of this study was to examine whether antisense transcripts resulting from bidirectional transcription of the expanded repeat behave in a similar manner We show that ectopic expression of (CCCCGG)66 in cultured cells results in foci formation Using novel polyclonal antibodies for the detection of possible (CCCCGG)exp RAN proteins [poly(PR), poly(GP) and poly(PA)], we validated that (CCCCGG)66 is also subject to RAN translation in transfected cells Of importance, foci composed of antisense transcripts are observed in the frontal cortex, spinal cord and cerebellum of c9FTD/ALS cases, and neuronal inclusions of poly(PR), poly(GP) and poly(PA) are present in various brain tissues in c9FTD/ALS, but not in other neurodegenerative diseases, including CAG repeat disorders Of note, RNA foci and poly(GP) inclusions infrequently co-occur in the same cell, suggesting these events represent two distinct ways in which the C9ORF72 repeat expansion may evoke neurotoxic effects These findings provide mechanistic insight into the pathogenesis of c9FTD/ALS, and have significant implications for therapeutic strategies
484 citations
TL;DR: The phenotypic variability of ALS is reviewed and how it is reflected in familial and sporadic ALS, in the degree of upper and lower motor neuron involvement, in motor and extramotor involvement, and in the spectrum of ALS and frontotemporal dementia.
Abstract: Amyotrophic lateral sclerosis (ALS) is a genotypically and phenotypically heterogeneous disease, as reflected in the variability in age and site of onset, extent of extramotor involvement, and survival. Cognitive involvement is also common, and corroborates the connection between ALS and frontotemporal lobar degeneration. In this article, Robberecht and Swinnen review phenotypic heterogeneity in ALS and discuss some of its implications for understanding ALS pathogenesis and development of therapeutic interventions. Classic textbook neurology teaches that amyotrophic lateral sclerosis (ALS) is a degenerative disease that selectively affects upper and lower motor neurons and is fatal 3–5 years after onset—a description which suggests that the clinical presentation of ALS is very homogenous. However, clinical and postmortem observations, as well as genetic studies, demonstrate that there is considerable variability in the phenotypic expression of ALS. Here, we review the phenotypic variability of ALS and how it is reflected in familial and sporadic ALS, in the degree of upper and lower motor neuron involvement, in motor and extramotor involvement, and in the spectrum of ALS and frontotemporal dementia. Furthermore, we discuss some unusual clinical characteristics regarding presentation, age at onset and disease progression. Finally, we address the importance of this variability for understanding the pathogenesis of ALS and for the development of therapeutic strategies.
444 citations
University of California, San Diego1, Ludwig Institute for Cancer Research2, Mayo Clinic3, National University of Singapore4, Torrey Pines Institute for Molecular Studies5, Slovak Academy of Sciences6, Katholieke Universiteit Leuven7, National Institutes of Health8, Children's Hospital Oakland Research Institute9, German Center for Neurodegenerative Diseases10, King's College London11
TL;DR: Single-dose injection of antisense oligonucleotides (ASOs) that target repeat-containing RNAs but preserve levels of mRNAs encoding C9ORF72 produced sustained reductions in RNA foci and dipeptide-repeat proteins, and ameliorated behavioral deficits.
421 citations
Cites background from "Association between repeat sizes an..."
...At most, modest expansion was found within the CNS or peripheral tissues (Figures 2E, S3C, and S3D), in contrast to humans, for whom somatic heterogeneity and repeat instability have been reported, especially within the CNS (van Blitterswijk et al., 2013)....
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...While theminimal pathogenic repeat size inC9ORF72 patients is not established, somatic expansion can take the germlinetransmitted repeat to 3,000–5,000 repeats in the most affected brain regions (Gijselinck et al., 2015; van Blitterswijk et al., 2013)....
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References
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Book•
01 Mar 1973
TL;DR: An ideal text for an upper-level undergraduate or first-year graduate course, Nonparametric Statistical Methods, Second Edition is also an invaluable source for professionals who want to keep abreast of the latest developments within this dynamic branch of modern statistics.
Abstract: This Second Edition of Myles Hollander and Douglas A. Wolfe's successful Nonparametric Statistical Methods meets the needs of a new generation of users, with completely up-to-date coverage of this important statistical area. Like its predecessor, the revised edition, along with its companion ftp site, aims to equip readers with the conceptual and technical skills necessary to select and apply the appropriate procedures for a given situation. An extensive array of examples drawn from actual experiments illustrates clearly how to use nonparametric approaches to handle one- or two-sample location and dispersion problems, dichotomous data, and one-way and two-way layout problems. An ideal text for an upper-level undergraduate or first-year graduate course, Nonparametric Statistical Methods, Second Edition is also an invaluable source for professionals who want to keep abreast of the latest developments within this dynamic branch of modern statistics.
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TL;DR: A new reproducibility index is developed and studied that is simple to use and possesses desirable properties and the statistical properties of this estimate can be satisfactorily evaluated using an inverse hyperbolic tangent transformation.
Abstract: A new reproducibility index is developed and studied. This index is the correlation between the two readings that fall on the 45 degree line through the origin. It is simple to use and possesses desirable properties. The statistical properties of this estimate can be satisfactorily evaluated using an inverse hyperbolic tangent transformation. A Monte Carlo experiment with 5,000 runs was performed to confirm the estimate's validity. An application using actual data is given.
6,916 citations
TL;DR: It is found that repeat expansion in C9ORF72 is a major cause of both FTD and ALS, suggesting multiple disease mechanisms.
4,153 citations
01 Mar 1974
3,841 citations
National Institutes of Health1, Cardiff University2, VU University Amsterdam3, Erasmus University Rotterdam4, University of Manchester5, University College London6, University of Helsinki7, University of Oulu8, Georgetown University9, Johns Hopkins University10, Illumina11, University Hospital of Wales12, University of Eastern Finland13, University of Miami14, University of Turin15, University of Cagliari16, The Catholic University of America17, Microsoft18, University of Toronto19, University of Würzburg20, University of Washington21, Aneurin Bevan University Health Board22
TL;DR: The chromosome 9p21 amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) locus contains one of the last major unidentified autosomal-dominant genes underlying these common neurodegenerative diseases, and a large hexanucleotide repeat expansion in the first intron of C9ORF72 is shown.
3,784 citations