Spinocerebellar Ataxia Type 31 Is Associated with “Inserted” Penta-Nucleotide Repeats Containing (TGGAA)n

Department of Neurology and Neurological Science, Graduate School, Tokyo Medical and Dental University, Yushima 1-5-45, Bunkyo-ku, Tokyo 113-8519, Japan.
The American Journal of Human Genetics (Impact Factor: 10.93). 10/2009; 85(5):544-57. DOI: 10.1016/j.ajhg.2009.09.019
Source: PubMed


Spinocerebellar ataxia type 31 (SCA31) is an adult-onset autosomal-dominant neurodegenerative disorder showing progressive cerebellar ataxia mainly affecting Purkinje cells. The SCA31 critical region was tracked down to a 900 kb interval in chromosome 16q22.1, where the disease shows a strong founder effect. By performing comprehensive Southern blot analysis and BAC- and fosmid-based sequencing, we isolated two genetic changes segregating with SCA31. One was a single-nucleotide change in an intron of the thymidine kinase 2 gene (TK2). However, this did not appear to affect splicing or expression patterns. The other was an insertion, from 2.5-3.8 kb long, consisting of complex penta-nucleotide repeats including a long (TGGAA)n stretch. In controls, shorter (1.5-2.0 kb) insertions lacking (TGGAA)n were found only rarely. The SCA31 repeat insertion's length inversely correlated with patient age of onset, and an expansion was documented in a single family showing anticipation. The repeat insertion was located in introns of TK2 and BEAN (brain expressed, associated with Nedd4) expressed in the brain and formed RNA foci in the nuclei of patients' Purkinje cells. An electrophoretic mobility-shift assay showed that essential splicing factors, serine/arginine-rich splicing factors SFRS1 and SFRS9, bind to (UGGAA)n in vitro. Because (TGGAA)n is a characteristic sequence of paracentromeric heterochromatin, we speculate that the insertion might have originated from heterochromatin. SCA31 is important because it exemplifies human diseases associated with "inserted" microsatellite repeats that can expand through transmission. Our finding suggests that the ectopic microsatellite repeat, when transcribed, might cause a disease involving the essential splicing factors.

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    • "Evidence for a more widespread role for RNA in neurodegenerative diseases has been steadily accumulating. SCA31 and SCA36 are due to large expansions of de novo 5 bp TGGAA repeat and an existing 6 bp GGCCTG repeat, respectively – both located within introns of different genes (Sato et al., 2009; Kobayashi et al., 2011). An expanded GGGGCC repeat has recently been found to cause a substantial proportion of cases of ALS and frontotemporal lobar dementia (FTLD; DeJesus-Hernandez et al., 2011; Renton et al., 2011). "
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    ABSTRACT: Repeat sequences that are expanded in copy number are the basis for ~20 dominantly inherited neurodegenerative diseases, including Huntington’s Disease. Despite some of the responsible genes being identified as long as 20 years ago, the identity and nature of the disease-causing pathogenic pathway remains a gap in knowledge for these diseases. This understanding is essential for rational approaches to delay onset, slow progression or ultimately effect cure. We have previously hypothesized that an RNA-based pathogenic pathway has a causal role in the dominantly inherited unstable expanded repeat neurodegenerative diseases. In support of this hypothesis we, and others, have characterized rCAG.rCUG100 repeat double-strand RNA (dsRNA) as a previously unidentified agent capable of causing pathogenesis in a Drosophila model of neurodegenerative disease. Dicer, Toll and autophagy pathways have distinct roles in this Drosophila dsRNA pathology. Dicer-dependence is accompanied by cleavage of rCAG.rCUG100 repeat double-strand RNA down to r(CAG)7 21-mers. Among the ‘molecular hallmarks’ of this pathway that have been identified in Drosophila, some [i.e. r(CAG)7 and elevated TNF] correlate with observations in affected people (e.g. HD, ALS) or in related animal models [i.e. autophagy]. The Toll pathway is activated in the presence of repeat-containing double-stranded RNA and toxicity is also dependent on this pathway. How might the endogenously expressed dsRNA mediate Toll-dependent toxicity in neuronal cells? Endogenous RNAs are normally shielded from Toll pathway activation as part of the mechanism to distinguish ‘self’ from ‘non-self’ RNAs. This typically involves post-transcriptional modification of the RNA. Therefore, it is likely that rCAG.rCUG100 repeat double-strand RNA has a characteristic property that interferes with or evades this normal mechanism of shielding. We predict that repeat expansion leads to an alteration in RNA structure and/or form that perturbs RNA mod
    Frontiers in Molecular Neuroscience 09/2013; 6:25. DOI:10.3389/fnmol.2013.00025 · 4.08 Impact Factor
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    • "ADCA patients [99,100]. In 2009, Sato and colleagues discovered 2.5 to 3.8 kb insertions of penta-nucleotide repeats, (TGGAA)n, (TACAA)n, and (TAAAA)n, on chromosome 16q21-q22 using southern blot analysis and sequencing analysis in 160 affected individuals from 98 families [101]. Among these repeats, (TGGAA)n is thought to be pathogenic in Japanese subjects. "
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    ABSTRACT: Autosomal Dominant Cerebellar Ataxia (ADCA) Type III is a type of spinocerebellar ataxia (SCA) classically characterized by pure cerebellar ataxia and occasionally, by non-cerebellar signs such as pyramidal signs, ophthalmoplegia, and tremor. The onset of symptoms typically occurs in adulthood; however, a minority of patients develop clinical features in adolescence. The incidence of ADCA Type III is unknown. ADCA Type III consists of six subtypes, SCA5, SCA6, SCA11, SCA26, SCA30, and SCA31. The subtype SCA6 is the most common. These subtypes are associated with four causative genes and two loci. The severity of symptoms and age of onset can vary between each SCA subtype and even between families with the same subtype. SCA5 and SCA11 are caused by specific gene mutations such as missense, inframe deletions, and frameshift insertions or deletions. SCA6 is caused by trinucleotide CAG repeat expansions encoding large uninterrupted glutamine tracts. SCA31 is caused by repeat expansions that fall outside of the protein-coding region of the disease gene. Currently, there are no specific gene mutations associated with SCA26 or SCA30, though there is a confirmed locus for each subtype. This disease is mainly diagnosed via genetic testing; however, differential diagnoses include pure cerebellar ataxia and non-cerebellar features in addition to ataxia. Although not fatal, ADCA Type III may cause dysphagia and falls, which reduce the quality of life of the patients and may in turn shorten the lifespan. The therapy for ADCA Type III is supportive and includes occupational and speech modalities. There is no cure for ADCA Type III, but a number of recent studies have highlighted novel therapies, which bring hope for future curative treatments.
    Orphanet Journal of Rare Diseases 01/2013; 18(8):14. DOI:10.1186/1750-1172-8-14 · 3.36 Impact Factor
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    • "However, these functions are impaired upon the sequestration of hnRNP K by RNA foci. In SCA31, nuclear RNA foci may sequester serine/arginine-rich splicing factors 1 and 9 (Sato et al., 2009). Finally, nuclear RNA foci are observed in frontal cortex and spinal cord tissue of c9FTD/ALS cases (Dejesus-Hernandez et al., 2011), but whether RNA-binding proteins are sequestered by these RNA foci has yet to be reported. "
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    ABSTRACT: Cellular viability depends upon the well-orchestrated functions carried out by numerous protein-coding and non-coding RNAs, as well as RNA-binding proteins. During the last decade, it has become increasingly evident that abnormalities in RNA processing represent a common feature among many neurodegenerative diseases. In "RNAopathies", which include diseases caused by non-coding repeat expansions, RNAs exert toxicity via diverse mechanisms: RNA foci formation, bidirectional transcription, and the production of toxic RNAs and proteins by repeat associated non-ATG translation. The mechanisms of toxicity in "RNA-binding proteinopathies", diseases in which RNA-binding proteins like TDP-43 and FUS play a prominent role, have yet to be fully elucidated. Nonetheless, both loss of function of the RNA binding protein, and a toxic gain of function resulting from its aggregation, are thought to be involved in disease pathogenesis. As part of the special issue on RNA and Splicing Regulation in Neurodegeneration, this review intends to explore the diverse RNA-related mechanisms contributing to neurodegeneration, with a special emphasis on findings emerging from animal models.
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