Biallelic RFC1 pentanucleotide repeat expansions in Greek patients with late‐onset ataxia

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS): from clinical diagnosis towards genetic testing

Medizinische Genetik ◽

10.1515/medgen-2021-2098 ◽

2021 ◽

Vol 33 (4) ◽

pp. 301-310

Author(s):

Andreas Thieme ◽

Christel Depienne ◽

Dagmar Timmann

Keyword(s):

Cerebellar Ataxia ◽

Chronic Cough ◽

Late Onset ◽

Neurological Diseases ◽

Brain Mri ◽

Genetic Research ◽

Sensory Nerve ◽

Repeat Expansions ◽

Factor C ◽

Pentanucleotide Repeat

Abstract The cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a late-onset and recessively inherited ataxia. For many years, CANVAS has been diagnosed based on the clinical phenotype. Only recently, a large biallelic pentanucleotide repeat expansion in the replication factor C subunit 1 (RFC1) gene has been identified as the underlying genetic cause for the large majority of CANVAS cases. Subsequently, other phenotypes such as ataxia with chronic cough, incomplete CANVAS and MSA-C-like phenotypes have been associated with biallelic RFC1 repeat expansions. Because of this heterogeneity it has been suggested to change the name of the disease to “RFC1 disease”. Chronic cough is characteristic and can precede neurological symptoms by years or decades. In the neurological examination signs of cerebellar, sensory, and vestibular ataxia are frequently observed. Nerve conduction studies usually show absent or markedly reduced sensory nerve action potentials. On brain MRI cerebellar degeneration and spinal cord alterations are common. In later disease stages more widespread neurodegeneration with additional involvement of the brainstem and basal ganglia is possible. As yet, the exact incidence of RFC1-associated neurological diseases remains uncertain although first studies suggest that RFC1-related ataxia is common. Moreover, the pathophysiological mechanisms caused by the large biallelic pentanucleotide repeat expansions in RFC1 remain elusive. Future molecular and genetic research as well as natural history studies are highly desirable to pave the way towards personalized treatment approaches.

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Natural History, Phenotypic Spectrum, and Discriminative Features of Multisystemic RFC1-disease

Neurology ◽

10.1212/wnl.0000000000011528 ◽

2021 ◽

pp. 10.1212/WNL.0000000000011528

Author(s):

Andreas Traschütz ◽

Andrea Cortese ◽

Selina Reich ◽

Natalia Dominik ◽

Jennifer Faber ◽

...

Keyword(s):

Natural History ◽

Late Onset ◽

Premature Death ◽

Cross Sectional ◽

Treatment Trials ◽

Disease Spectrum ◽

Phenotypic Spectrum ◽

Multisystemic Disease ◽

Repeat Expansions ◽

Cerebellar Type

Objective:To delineate the full phenotypic spectrum, discriminative features, piloting longitudinal progression data, and sample size calculations of RFC1-repeat expansions, recently identified as causing cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS).Methods:Multimodal RFC1 repeat screening (PCR, southern blot, whole-exome/genome (WES/WGS)-based approaches) combined with cross-sectional and longitudinal deep-phenotyping in (i) cross-European cohort A (70 families) with ≥2 features of CANVAS and/or ataxia-with-chronic-cough (ACC); and (ii) Turkish cohort B (105 families) with unselected late-onset ataxia.Results:Prevalence of RFC1-disease was 67% in cohort A, 14% in unselected cohort B, 68% in clinical CANVAS, and 100% in ACC. RFC1-disease was also identified in Western and Eastern Asians, and even by WES. Visual compensation, sensory symptoms, and cough were strong positive discriminative predictors (>90%) against RFC1-negative patients. The phenotype across 70 RFC1-positive patients was mostly multisystemic (69%), including dysautonomia (62%) and bradykinesia (28%) (=overlap with cerebellar-type multiple system atrophy [MSA-C]), postural instability (49%), slow vertical saccades (17%), and chorea and/or dystonia (11%). Ataxia progression was ∼1.3 SARA points/year (32 cross-sectional, 17 longitudinal assessments, follow-up ≤9 years [mean 3.1]), but also included early falls, variable non-linear phases of MSA-C-like progression (SARA 2.5-5.5/year), and premature death. Treatment trials require 330 (1-year-trial) and 132 (2-year-trial) patients in total to detect 50% reduced progression.Conclusions:RFC1-disease is frequent and occurs across continents, with CANVAS and ACC as highly diagnostic phenotypes, yet as variable, overlapping clusters along a continuous multisystemic disease spectrum, including MSA-C-overlap. Our natural history data help to inform future RFC1-treatment trials.Classification of Evidence:This study provides Class II evidence that RFC1-repeat expansions are associated with CANVAS and ACC.

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Cerebellar ataxia, neuropathy, vestibular areflexia syndrome due to RFC1 repeat expansion

Brain ◽

10.1093/brain/awz418 ◽

2020 ◽

Vol 143 (2) ◽

pp. 480-490 ◽

Cited By ~ 22

Author(s):

Andrea Cortese ◽

Stefano Tozza ◽

Wai Yan Yau ◽

Salvatore Rossi ◽

Sarah J Beecroft ◽

...

Keyword(s):

Cerebellar Ataxia ◽

Late Onset ◽

Sensory Neuropathy ◽

Repeat Expansion ◽

Cerebellar Dysfunction ◽

Full Spectrum ◽

Ataxic Neuropathy ◽

Walking Aids ◽

Repeat Expansions ◽

Walking Difficulty

Abstract Ataxia, causing imbalance, dizziness and falls, is a leading cause of neurological disability. We have recently identified a biallelic intronic AAGGG repeat expansion in replication factor complex subunit 1 (RFC1) as the cause of cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) and a major cause of late onset ataxia. Here we describe the full spectrum of the disease phenotype in our first 100 genetically confirmed carriers of biallelic repeat expansions in RFC1 and identify the sensory neuropathy as a common feature in all cases to date. All patients were Caucasian and half were sporadic. Patients typically reported progressive unsteadiness starting in the sixth decade. A dry spasmodic cough was also frequently associated and often preceded by decades the onset of walking difficulty. Sensory symptoms, oscillopsia, dysautonomia and dysarthria were also variably associated. The disease seems to follow a pattern of spatial progression from the early involvement of sensory neurons, to the later appearance of vestibular and cerebellar dysfunction. Half of the patients needed walking aids after 10 years of disease duration and a quarter were wheelchair dependent after 15 years. Overall, two-thirds of cases had full CANVAS. Sensory neuropathy was the only manifestation in 15 patients. Sixteen patients additionally showed cerebellar involvement, and six showed vestibular involvement. The disease is very likely to be underdiagnosed. Repeat expansion in RFC1 should be considered in all cases of sensory ataxic neuropathy, particularly, but not only, if cerebellar dysfunction, vestibular involvement and cough coexist.

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CANVAS: a late onset ataxia due to biallelic intronic AAGGG expansions

Journal of Neurology ◽

10.1007/s00415-020-10183-0 ◽

2020 ◽

Author(s):

Natalia Dominik ◽

Valentina Galassi Deforie ◽

Andrea Cortese ◽

Henry Houlden

Keyword(s):

Late Onset ◽

Replication Factor C ◽

Common Cause ◽

Progressive Ataxia ◽

The World ◽

Recent Developments ◽

C Subunit ◽

Repeat Expansions ◽

Visual Problems ◽

Factor C

Abstract The ataxias are a group of disorders that manifest with balance, movement, speech and visual problems. They can arise due to dysfunction of the cerebellum, the vestibular system and/or the sensory neurons. Genetic defects are a common cause of chronic ataxia, particularly common are repeat expansions in this group of conditions. Co-occurrence of cerebellar ataxia with neuropathy and vestibular areflexia syndrome has been termed CANVAS. Although CANVAS is a rare syndrome, on discovery of biallelic expansions in the second intron of replication factor C subunit 1 (RFC1) gene, we and others have found the phenotype is broad and RFC1 expansions are a common cause of late-onset progressive ataxia. We aim to provide a review and update on recent developments in CANVAS and populations, where the disorder has been reported. We have also optimised a protocol for RFC1 expansion screening which is described herein and expanded phenotype after analysing late-onset ataxia patients from around the world.

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Very Late-Onset Friedreich Ataxia Despite Large GAA Triplet Repeat Expansions

Archives of Neurology ◽

10.1001/archneur.57.2.246 ◽

2000 ◽

Vol 57 (2) ◽

pp. 246 ◽

Cited By ~ 29

Author(s):

Sanjay I. Bidichandani ◽

Carlos A. Garcia ◽

Pragna I. Patel ◽

Mazen M. Dimachkie

Keyword(s):

Late Onset ◽

Friedreich Ataxia ◽

Triplet Repeat ◽

Repeat Expansions

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Molecular Mechanisms in Pentanucleotide Repeat Diseases

Cells ◽

10.3390/cells11020205 ◽

2022 ◽

Vol 11 (2) ◽

pp. 205

Author(s):

Joana R. Loureiro ◽

Ana F. Castro ◽

Ana S. Figueiredo ◽

Isabel Silveira

Keyword(s):

Phase Separation ◽

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Spinocerebellar Ataxias ◽

Genes Encoding ◽

Dna Strands ◽

Repeat Expansions ◽

Toxic Rna ◽

Pentanucleotide Repeat

The number of neurodegenerative diseases resulting from repeat expansion has increased extraordinarily in recent years. In several of these pathologies, the repeat can be transcribed in RNA from both DNA strands producing, at least, one toxic RNA repeat that causes neurodegeneration by a complex mechanism. Recently, seven diseases have been found caused by a novel intronic pentanucleotide repeat in distinct genes encoding proteins highly expressed in the cerebellum. These disorders are clinically heterogeneous being characterized by impaired motor function, resulting from ataxia or epilepsy. The role that apparently normal proteins from these mutant genes play in these pathologies is not known. However, recent advances in previously known spinocerebellar ataxias originated by abnormal non-coding pentanucleotide repeats point to a gain of a toxic function by the pathogenic repeat-containing RNA that abnormally forms nuclear foci with RNA-binding proteins. In cells, RNA foci have been shown to be formed by phase separation. Moreover, the field of repeat expansions has lately achieved an extraordinary progress with the discovery that RNA repeats, polyglutamine, and polyalanine proteins are crucial for the formation of nuclear membraneless organelles by phase separation, which is perturbed when they are expanded. This review will cover the amazing advances on repeat diseases.

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Clinical spectrum of the pentanucleotide repeat expansion in the RFC1 gene in ataxia syndromes

Neurology ◽

10.1212/wnl.0000000000010744 ◽

2020 ◽

Vol 95 (21) ◽

pp. e2912-e2923

Author(s):

Maria Gisatulin ◽

Valerija Dobricic ◽

Christine Zühlke ◽

Yorck Hellenbroich ◽

Vera Tadic ◽

...

Keyword(s):

Cerebellar Ataxia ◽

Late Onset ◽

Intron Retention ◽

Repeat Expansion ◽

Healthy Controls ◽

Neighboring Gene ◽

Number Of Patients ◽

C Subunit ◽

Factor C ◽

Pentanucleotide Repeat

ObjectiveTo determine the clinical significance of an intronic biallelic pentanucleotide repeat expansion in the gene encoding replication factor C subunit 1 (RFC1) in patients with late-onset cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS), in patients with other ataxias, and in healthy controls by comprehensive genetic analyses.MethodsIn this case-control study, we included 457 individuals comprising 26 patients with complete or incomplete CANVAS, 70 patients with late-onset cerebellar ataxia, 208 healthy controls, and 153 individuals from 39 multigenerational families without ataxia to determine repeat stability. All 96 patients were screened for the repeat expansion by duplex PCR. To further characterize the repeat type and lengths, we used fragment length analysis, repeat-primed PCR, Sanger sequencing, and Southern blotting. Expression of RFC1 and the neighboring gene WDR19 were determined by quantitative PCR.ResultsMassive biallelic pentanucleotide expansions were found in 15/17 patients with complete CANVAS (88%), in 2/9 patients with incomplete CANVAS (22%), in 4/70 patients with unspecified, late-onset cerebellar ataxia (6%), but not in controls. In patients, the expansion comprised 800–1,000 mostly AAGGG repeats. Nonmassively expanded repeat numbers were in the range of 7–137 repeats and relatively stable during transmission. Expression of RFC1 and WDR19 were unchanged and RFC1 intron retention was not found.ConclusionsA biallelic pentanucleotide repeat expansion is a frequent cause of CANVAS and found in a considerable number of patients with an incomplete clinical presentation or other forms of cerebellar ataxia. The mechanism by which the repeat expansions are causing disease remains unclear and warrants further investigations.

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Investigation of the pathogenic RFC1 repeat expansion in a Canadian and a Brazilian ataxia cohort: identification of novel conformations

10.1101/593871 ◽

2019 ◽

Author(s):

Fulya Akçimen ◽

Jay P. Ross ◽

Cynthia V. Bourassa ◽

Calwing Liao ◽

Daniel Rochefort ◽

...

Keyword(s):

General Population ◽

Late Onset ◽

Genetic Diagnosis ◽

The Novel ◽

Adult Onset ◽

Dynamic Nature ◽

Common Cause ◽

Cohort Identification ◽

Repeat Expansions ◽

Type Sequence

AbstractA homozygous pentanucleotide expansion in the RFC1 gene has been shown to be a common cause of late-onset ataxia. In the general population a total of four different repeat conformations have been observed: a wild type sequence AAAAG (11 repeats), and longer expansions of AAAAG, AAAGG and AAGGG sequences. However, in ataxia cases only the AAGGG expansion has been shown to be pathogenic. In this study, we assessed the prevalence and nature of RFC1 repeat expansions in three adult-onset ataxia cohorts: Brazilian (n = 23) and Canadian (n = 26) cases that tested negative for other known ataxia mutations, as well as a cohort of randomly selected Canadian cases (n = 128) without regard to a genetic diagnosis. We identified the homozygous AAGGG pathogenic expansion in only one Brazilian family with two affected siblings, and in one Canadian case. The RFC1 expansion may therefore not be a common cause of adult-onset ataxia in these populations. Interestingly we observed two new repeat motifs, AAGAG and AGAGG, which indicates the dynamic nature of the pentanucleotide expansion sequence. To assess the frequency of these two new repeat conformations in the general population we screened 163 healthy individuals. These novel motifs were more frequent in patients versus controls. While we cannot be certain that the homozygous genotypes of the novel expanded conformations are pathogenic, their occurrence should nonetheless be taken into consideration in future studies.

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A polyalanine antibody for the diagnosis of oculopharyngeal muscular dystrophy and polyalanine-related diseases

MNI Open Research ◽

10.12688/mniopenres.12765.1 ◽

2017 ◽

Vol 1 ◽

pp. 1

Author(s):

Shawn J. Stochmanski ◽

François Blondeau ◽

Martine Girard ◽

Pascale Hince ◽

Daniel Rochefort ◽

...

Keyword(s):

Muscular Dystrophy ◽

Trinucleotide Repeat ◽

Late Onset ◽

Cag Repeat ◽

Spinocerebellar Ataxia Type ◽

Causative Mutation ◽

Oculopharyngeal Muscular Dystrophy ◽

Spinocerebellar Ataxia Type 3 ◽

Repeat Tract ◽

Repeat Expansions

Eighteen severe human diseases have so far been associated with trinucleotide repeat expansions coding for either polyalanine (encoded by a GCN repeat tract) or polyglutamine (encoded by a CAG repeat tract). Among them, oculopharyngeal muscular dystrophy (OPMD), spinocerebellar ataxia type-3 (SCA3), and Huntington’s disease (HD) are late-onset autosomal-dominant disorders characterized by the presence of intranuclear inclusions (INIs). We have previously identified the OPMD causative mutation as a small expansion (from 2 in normal to 7 in disease) of a GCG repeat tract in the PABPN1 gene. In addition, -1 ribosomal frameshifting has been reported to occur in expanded CAG repeat tracts in the ATXN3 (SCA3) and HTT (HD) genes, resulting in the translation of a hybrid CAG/GCA repeat tract and the production of a polyalanine-containing peptide. Previous studies on OPMD suggest that polyalanine-induced toxicity is very sensitive to the dosage and length of the alanine stretch. Here we report the characterization of a polyclonal antibody that selectively recognizes pathological expansions of polyalanine in PABPN1. Furthermore, our antibody also detects the presence of alanine proteins in INIs of SCA3 and HD patient samples.

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