Expansion of a novel CAG trinucleotide repeat in the 5' region of PPP2R2B is associated with SCA12

Human-specific transcriptional regulation of CNS development genes by FOXP2

The signaling pathways orchestrating both the evolution and development of language in the human brain remain unknown. To date, the transcription factor FOXP2 (forkhead box P2) is the only gene implicated in Mendelian forms of human speech and language dysfunction1,2,3. It has been proposed, that the amino acid composition in the human variant of FOXP2 has undergone accelerated evolution, and this change occurred around the time of language emergence in humans4,5. However, this remains controversial, and whether the acquisition of these amino acids in human FOXP2 has any functional consequence in human neurons remains untested. Here, we demonstrate that these two amino acids alter FOXP2 function by conferring differential transcriptional regulation in vitro. We extend these observations in vivo to human and chimpanzee brain, and use network analysis to identify novel relationships among the differentially expressed genes. These data provide experimental support for the functional relevance of changes in FOXP2 that occur on the human lineage, highlighting specific pathways with direct consequences for human brain development and disease. Since FOXP2 has an important role in speech and language in humans, the identified targets may have a critical function in the development and evolution of language circuitry in humans.

Oxidative stress promotes autophagic cell death in human neuroblastoma cells with ectopic transfer of mitochondrial PPP2R2B (Bbeta2)

Background

The multifunctional protein phosphatase 2A (PP2A) is a heterotrimeric serine/threonine protein phosphatase composed of a scaffolding, catalytic and regulatory subunits. By modifying various downstream signal transducers, the aberrant expression of the brain-targeted regulatory subunit PPP2R2B is associated with the onset of a panel of neuronal disorders. The alternatively splicing of PPP2R2B encodes two regulatory subunit isoforms that determine cellular distribution of the neuron-specific holoenzyme to mitochondria (Bβ2) and cytoplasm (Bβ1), respectively.

Results

Human neuroblastoma cells were transfected with PPP2R2B constructs encoding the complete sequences of Bβ2 and Bβ1, respectively. The colonies with antibiotic resistance were selected as stable cell lines. Both ectopic Bβ1 and Bβ2 clones exhibited characteristics of autophagy. To test how cells respond to reactive oxygen species generators, the cells were treated with either hydrogen peroxide or t-butyl hydroperoxide and Bβ2 clones induced cell death. Suppression of autophagy using either RNA interference of the essential autophagy gene or pharmacological inhibitor rescued cell death caused by oxidative stress.

Conclusions

Cells with ectopically expressed mitochondria-targeted regulatory subunit PPP2R2B of the holoenzyme PP2A were shown predisposed to autophagy and oxidative stress induced cell death that is related to apoptosis. The results promised a model for studying the mechanism and function of aberrant PPP2R2B expression in neuronal cells. The work provided a new target for understanding and prevention of neuropathogenesis.

Utilizing linkage disequilibrium information from Indian Genome Variation Database for mapping mutations: SCA12 case study

Stratification in heterogeneous populations poses an enormous challenge in linkage disequilibrium (LD) based identification of causal loci using surrogate markers. In this study, we demonstrate the enormous potential of endogamous Indian populations for mapping mutations in candidate genes using minimal SNPs, mainly due to larger regions of LD. We show this by a case study of the PPP2R2B gene (approximately 400 kb) that harbours a CAG repeat, expansion of which has been implicated in spinocerebellar ataxia type 12 (SCA12). Using LD information derived from Indian Genome Variation database (IGVdb) on populations which share similar ethnic and linguistic backgrounds as the SCA12 study population, we could map the causal loci using a minimal set of three SNPs, without the generation of additional basal data from the ethnically matched population. We could also demonstrate transferability of tagSNPs from a related HapMap population for mapping the mutation.

Pathogenic RNAs in microsatellite expansion disease

The expansion of unstable microsatellites is the cause of a number of inherited neuromuscular and neurological disorders. While these expanded repeats can be located in either the coding or non-coding regions of genes, toxic RNA transcripts have been primarily implicated in the pathogenesis of non-coding expansion diseases. In this review, we briefly summarize studies which support this RNA-mediated toxicity model for several neurologic disorders and highlight how pathogenic RNAs might negatively impact nervous system functions. However, it is important to note that the distinction between coding versus non-coding regions has become muddled by recent observations that the transcribed portion of the genome or transcriptome is considerably larger than previously appreciated. Thus, we also explore the possibility that a combination of protein and RNA gain-of-function events underlie some microsatellite expansion diseases.

Cognitive dysfunction in spinocerebellar ataxias

Spinocerebellar ataxias (SCAs) comprise a heterogeneous group of complex neurodegenerative diseases, characterized by the presence of progressive cerebellar ataxia, associated or otherwise with ophthalmoplegia, pyramidal signs, extrapyramidal features, pigmentary retinopathy, peripheral neuropathy, cognitive dysfunction and dementia.

OBJECTIVE

To verify the presence of cognitive dysfunction among the main types of SCA described in the literature.

METHODS

the review was conducted using the search system of the PUBMED and OMIM databases.

RESULTS

Cognitive dysfunction occurs in a considerable proportion of SCA, particularly in SCA 3, which is the most frequent form of SCA worldwide. Dementia has been described in several other types of SCA such as SCA 2, SCA 17 and DRPLA. Mental retardation is a specific clinical feature of SCA 13.

CONCLUSIONS

The role of the cerebellum in cognitive functions has been observed in different types of SCAs which can manifest varying degrees of cognitive dysfunction, dementia and mental retardation.

Spinocerebellar ataxia 17 (SCA17) and Huntington's disease-like 4 (HDL4)

Spinocerebellar ataxia 17 (SCA17) or Huntington's disease-like-4 is a neurodegenerative disease caused by the expansion above 44 units of a CAG/CAA repeat in the coding region of the TATA box binding protein (TBP) gene leading to an abnormal expansion of a polyglutamine stretch in the corresponding protein. Alleles with 43 and 44 repeats have been identified in sporadic cases and their pathogenicity remains uncertain. Furthermore, incomplete penetrance of pathological alleles with up to 49 repeats has been suggested. The imperfect nature of the repeat makes intergenerational instability extremely rare and de novo mutations are most likely the result of partial duplications. This is one of the rarer forms of autosomal dominant cerebellar ataxia but the associated phenotype is often severe, involving various systems (cerebral cortex, striatum, and cerebellum), with extremely variable age at onset (range: 3-75 years) and clinical presentation. This gene is thought to account for a small proportion of patients with a Huntington's disease-like phenotype and cerebellar signs. Parkinson's disease-like, Creutzfeldt-Jakob disease-like and Alzheimer disease-like phenotypes have also been described with small SCA17 expansions. The abnormal protein is expressed at the same level as its normal counterpart and forms neuronal intranuclear inclusions containing other proteins involved in protein folding or degradation. The increase in the size of the glutamine stretch enhances transcription in vitro, probably leading to transcription deregulation. Interestingly, the TBP protein mutated in SCA17 is recruited in the inclusions of other polyglutaminopathies, suggesting its involvement in the transcription down-regulation observed in these diseases.

PPP2R2B CAG repeat length in the Han Chinese in Taiwan: Association analyses in neurological and psychiatric disorders and potential functional implications

PPP2R2B, a protein widely expressed in neurons throughout the brain, regulates the protein phosphatase 2A (PP2A) activity for the microtubule-associated protein tau and other substrates. Altered PP2A activity has been implicated in spinocerebellar ataxia 12, Alzheimer's disease (AD), and other tauopathies. Through a case-control study and a reporter assay, we investigated the association of PPP2R2B CAG repeat polymorphism with Taiwanese AD, essential tremor (ET), Parkinson's disease (PD), and schizophrenia and clarified the functional implication of this polymorphism. The distribution of the alleles was not significantly different between patients and controls, with 68.6-76.1% alleles at lengths of 10, 13, and 16 triplets. No expanded alleles were detected in either group. However, the frequency of the individuals carrying the short 5-, 6-, and 7-triplet alleles was notably higher in patients with AD (5/180 [2.8%], Fisher's exact test, P = 0.003; including 2 homozygotes) and ET (4/132 [3.0%], Fisher's exact test, P < 0.001) than in the controls (1/625 [0.2%]). The PPP2R2B transcriptional activity was significantly lower in the luciferase reporter constructs containing the (CAG)(5-7) allele than in those containing the common 10-, 13-, and 16-triplet alleles in both neuroblastoma and embryonic kidney cells. Therefore, our preliminary results suggest that the PPP2R2B gene CAG repeat polymorphism may be functional and may, in part, play a role in conferring susceptibility to AD and ET in Taiwan.

Therapeutic prospects for spinocerebellar ataxia type 2 and 3

Spinocerebellar ataxia type 2 (SCA2) and type 3 (SCA3) are autosomal-dominant neurodegenerative disorders. SCA2 primarily affects cerebellar Purkinje neurons. SCA3 primarily affects dentate and pontine nuclei and substantia nigra. Both disorders belong to a class of polyglutamine (polyQ) expansion disorders. SCA2 is caused by a polyQ expansion in the amino-terminal region of a cytosolic protein ataxin-2 (Atxn2). SCA3 is caused by a polyQ expansion in the carboxy-terminal portion of a cytosolic protein ataxin-3 (Atxn3). Both disorders are found worldwide, but SCA2 is common among people of Cuban decent and SCA3 is common among people of Portuguese decent. No effective treatment exist for SCA2, SCA3 or any other polyQ-expansion disorder. Based on anecdotal evidence, a number of small scale clinical trials have been attempted previously for SCA2 and SCA3. These trials were underpowered and did not yield any promising results so far. A number of pathogenic mechanisms have been proposed to explain neuronal dysfunction and degeneration in SCA2 and SCA3. Knockdown of mutant Atxn2 and Atxn3 protein by RNAi or similar approach is most promising avenue of therapeutic development in the long term, but translation of this approach to clinic faces very serious technical challenges. Recent preclinical studies in SCA2 and SCA3 genetic mouse model suggested that abnormal neuronal calcium (Ca²⁺) signaling may play an important role in SCA2 and SCA3 pathology. These studies also suggested that dantrolene and other Ca²⁺ signaling inhibitors and stabilizers may have a therapeutic value for treatment of SCA2 and SCA3. Controlled clinical evaluation of dantrolene, memantine, riluzole, dihydropyridines, CoQ10, creatine or other Ca²⁺ blockers and stabilizers in SCA2 and SCA3 patients is necessary to test clinical importance of these ideas. The EUROSCA consortium provides a potential framework for such clinical evaluation.

Spinocerebellar ataxia type 12 was not found in Korean Parkinsonian patients

BACKGROUND

Parkinsonism (PD) is occasionally seen in several types of spinocerebellar ataxia (SCA). Mutations in SCA gene have been reported in the patients of parkinsonism without ataxia.

METHODS

We examined spinocerebellar ataxia type 12 mutation in 877 PD and 199 multiple system atrophy (MSA) patients.

RESULTS AND CONCLUSIONS

No patients showed abnormal SCA12 expansion. It suggests that PD and MSA are not associated with SCA12 and it is not necessary to screen SCA12 in PD and MSA patients.

The spinocerebellar ataxia 12 gene product and protein phosphatase 2A regulatory subunit Bbeta2 antagonizes neuronal survival by promoting mitochondrial fission

The neurodegenerative disorder spinocerebellar ataxia 12 (SCA12) is caused by CAG repeat expansion in the non-coding region of the PPP2R2B gene. PPP2R2B encodes Bbeta1 and Bbeta2, alternatively spliced and neuron-specific regulatory subunits of the protein phosphatase 2A (PP2A) holoenzyme. We show here that in PC12 cells and hippocampal neurons, cell stressors induced a rapid translocation of PP2A/Bbeta2 to mitochondria to promote apoptosis. Conversely, silencing of PP2A/Bbeta2 protected hippocampal neurons against free radical-mediated, excitotoxic, and ischemic insults. Evidence is accumulating that the mitochondrial fission/fusion equilibrium is an important determinant of cell survival. Accordingly, we found that Bbeta2 expression induces mitochondrial fragmentation, whereas Bbeta2 silencing or inhibition resulted in mitochondrial elongation. Based on epistasis experiments involving Bcl2 and core components of the mitochondrial fission machinery (Fis1 and dynamin-related protein 1), mitochondrial fragmentation occurs upstream of apoptosis and is both necessary and sufficient for hippocampal neuron death. Our data provide the first example of a proapoptotic phosphatase that predisposes to neuronal death by promoting mitochondrial division and point to a possible imbalance of the mitochondrial morphogenetic equilibrium in the pathogenesis of SCA12.

Experience and outcome of 3 years of a European EQA scheme for genetic testing of the spinocerebellar ataxias

The European Molecular Genetics Quality Network (EMQN) has been organizing an external quality assessment (EQA) scheme for molecular genetic testing of trinucleotide repeat mutations in the spinocerebellar ataxias (SCAs) since 2004. DNA samples were validated by at least two independent labs and two different methods. Together with mock clinical case descriptions and requests for specific SCA gene analyses, these were sent to registered participants each year. Laboratories were asked to use their routine procedures and protocols. A panel of assessors reviewed the final returns, including genotype results and reports, to assess the quality of (1) genotyping and (2) interpretation and reporting. A description of methods and raw data were also requested and were very useful for the final analysis. Altogether, during 3 years, 239 reports were received from the laboratories. Overall genotype error rate ranged 1.1-5.2%, a significant cause of concern. Scores for interpretation and reporting also showed that there is still much room for progress, although performance has improved over this period of assessment. The consequences of suboptimal laboratory practices, genotyping errors and misdiagnosis and of incorrect or incomplete interpretation and reporting have wide implications for patient lives, as well as for health management and counselling of relatives. EQA schemes are an important part of quality assurance in molecular genetic laboratories, and their use should become a routine part of laboratory diagnostic practice. Current evidence shows also that it is important that laboratories participate on a yearly basis and that this becomes mandatory for reference laboratories.

The autosomal dominant cerebellar ataxias are hereditary neurodegenerative diseases

Az autoszomális domináns cerebellaris ataxiák örökletes neurodegeneratív betegségek. Az ataxiák még néhány évtizeddel ezelőtt is a legkevésbé megértett idegi rendellenességek közé tartoztak, de molekuláris hátterük tisztázása mára lehetőséget teremtett a pontos diagnózis megállapítására, és segítséget nyújtott számos olyan különös jelenség értelmezésében is, mint például a családon belül változatosan megjelenő fenotípus. A spinocerebellaris ataxiák patogenezisének megismerése esélyt kínálhat sikeres terápiák kifejlesztésére, a jelenlegi, pusztán tüneti kezelések helyett. A gyors egymásutánban felfedezett gének és génlocusok, valamint a kialakított ataxiaaltípusok azonban zavart is okozhatnak a betegség pontos meghatározásában. Célunk rövid betekintést nyújtani e neurodegeneratív kórképek genetikai hátterébe, és a fontosabb ataxiaaltípusok jellemzésével megkönnyíteni az egyértelmű diagnózis felállítását.

Trinucleotide repeat disorders

The discovery that expansion of unstable repeats can cause a variety of neurological disorders has changed the landscape of disease-oriented research for several forms of mental retardation, Huntington disease, inherited ataxias, and muscular dystrophy. The dynamic nature of these mutations provided an explanation for the variable phenotype expressivity within a family. Beyond diagnosis and genetic counseling, the benefits from studying these disorders have been noted in both neurobiology and cell biology. Examples include insight about the role of translational control in synaptic plasticity, the role of RNA processing in the integrity of muscle and neuronal function, the importance of Fe-S-containing enzymes for cellular energy, and the dramatic effects of altering protein conformations on neuronal function and survival. It is exciting that within a span of 15 years, pathogenesis studies of this class of disorders are beginning to reveal pathways that are potential therapeutic targets.

Spectrum and prevalence of autosomal dominant spinocerebellar ataxia in Hokkaido, the northern island of Japan: a study of 113 Japanese families

Autosomal dominant cerebellar ataxia (ADCA) is a genetically heterogeneous group of neurodegenerative disorders. To shed further light on the clinical and genetic spectrum of ADCA in Japan, we conducted a study to determine the frequency of a new variety of different subtypes of SCAs among ADCA patients. This current study was carried out from April 1999 to December 2006 on the basis of patients with symptoms and signs of ADCA disorders. PCR and/or direct sequencing were evaluated in a total of 113 families. Among them, 35 families were found to have the mutation associated with SCA6, 30 with SCA3, 11 with SCA1, five with SCA2, five with DRPLA, and one with SCA14. We also detected the heterozygous -16C --> T single nucleotide substitution within the puratrophin-1 gene responsible for 16q22.1-linked ADCA in ten families. In this study, unusual varieties of SCA, including 27, 13, 5, 7, 8, 12, 17, and 16 were not found. Of the 113 patients, 14% had as yet unidentified ADCA mutations. The present study validates the prevalence of genetically distinct ADCA subtypes based on ethnic origin and geographical variation, and shows that 16q-linked ADCA has strong hereditary effects in patients with ADCAs in Japan.

Dynamic mutations as digital genetic modulators of brain development, function and dysfunction

A substantial portion of the human genome has been found to consist of simple sequence repeats, including microsatellites and minisatellites. Microsatellites, tandem repeats of 1-6 nucleotides, form the template for dynamic mutations, which involve heritable changes in the lengths of repeat sequences. In recent years, a large number of human disorders have been found to be caused by dynamic mutations, the most common of which are trinucleotide repeat expansion diseases. Dynamic mutations are common to numerous nervous system disorders, including Huntington's disease, various spinocerebellar ataxias, fragile X syndrome, fragile X tremor/ataxia syndrome, Friedreich ataxia and other neurodegenerative disorders. The involvement of dynamic mutations in brain disorders will be reviewed, with a focus on the large group caused by CAG/glutamine repeat expansions. We will also outline a proposed role of tandem repeat polymorphisms (TRPs), with unique 'digital' genetic distributions, in modulating brain development and normal function, so as to generate additional mutational diversity upon which natural selection may act.

Clinical and genetic epidemiological study of 16q22.1-linked autosomal dominant cerebellar ataxia in western Japan

OBJECTIVE

Autosomal dominant cerebellar ataxia (ADCA) is a heterogeneous neurodegenerative disorder. A single nucleotide substitution in the puratrophin-1 gene is associated with 16q22.1-linked ADCA showing pure cerebellar ataxia. We screened patients with spinocerebellar degeneration (SCD) to investigate the frequency and clinical features of 16q22.1-linked ADCA.

MATERIALS AND METHODS

We examined 91 SCD patients from a 1998 community-based prevalence study of Tottori Prefecture in western Japan. We also analyzed samples from 176 patients with SCD collected from a 1996 to 2006 laboratory-based study.

RESULTS

In the community-based study, the prevalence of spinocerebellar ataxia 6 (SCA6) and 16q22.1-linked ADCA was 2.4 and 1.12 per 100,000 individuals, respectively. In the laboratory-based study, the frequency of SCA6 and 16q22.1-linked ADCA was 28% and 17%, respectively. We found two cases of 16q22.1-linked ADCA among 26 SCD patients with no family history.

CONCLUSION

In this area in Japan, 16q22.1-linked ADCA was the second most common type of hereditary SCD.

Redefining the disease locus of 16q22.1-linked autosomal dominant cerebellar ataxia

The 16q22.1-linked autosomal dominant cerebellar ataxia (16q-ADCA; Online Mendelian Inheritance in Man [OMIN] #117210) is one of the most common ADCAs in Japan. Previously, we had reported that the patients share a common haplotype by founder effect and that a C-to-T substitution (-16C>T) in the puratrophin-1 gene was strongly associated with the disease. However, recently, an exceptional patient without the substitution was reported, indicating that a true pathogenic mutation might be present elsewhere. In this study, we clarified the disease locus more definitely by the haplotype analysis of families showing pure cerebellar ataxia. In addition to microsatellite markers, the single nucleotide polymorphisms (SNPs) that we identified on the disease chromosome were examined to confirm the borders of the disease locus. The analysis of 64 families with the -16C>T substitution in the puratrophin-1 gene revealed one family showing an ancestral recombination event between SNP04 and SNP05 on the disease chromosome. The analysis of 22 families without identifiable genetic mutations revealed another family carrying the common haplotype centromeric to the puratrophin-1 gene, but lacking the -16C>T substitution in this gene. We concluded that the disease locus of 16q-ADCA was definitely confined to a 900-kb genomic region between the SNP04 and the -16C>T substitution in the puratrophin-1 gene in 16q22.1.

Noncoding RNAs and RNA Editing in Brain Development, Functional Diversification, and Neurological Disease

The progressive maturation and functional plasticity of the nervous system in health and disease involve a dynamic interplay between the transcriptome and the environment. There is a growing awareness that the previously unexplored molecular and functional interface mediating these complex gene-environmental interactions, particularly in brain, may encompass a sophisticated RNA regulatory network involving the twin processes of RNA editing and multifaceted actions of numerous subclasses of non-protein-coding RNAs. The mature nervous system encompasses a wide range of cell types and interconnections. Long-term changes in the strength of synaptic connections are thought to underlie memory retrieval, formation, stabilization, and effector functions. The evolving nervous system involves numerous developmental transitions, such as neurulation, neural tube patterning, neural stem cell expansion and maintenance, lineage elaboration, differentiation, axonal path finding, and synaptogenesis. Although the molecular bases for these processes are largely unknown, RNA-based epigenetic mechanisms appear to be essential for orchestrating these precise and versatile biological phenomena and in defining the etiology of a spectrum of neurological diseases. The concerted modulation of RNA editing and the selective expression of non-protein-coding RNAs during seminal as well as continuous state transitions may comprise the plastic molecular code needed to couple the intrinsic malleability of neural network connections to evolving environmental influences to establish diverse forms of short- and long-term memory, context-specific behavioral responses, and sophisticated cognitive capacities.

Identification of the porcine homologous of human disease causing trinucleotide repeat sequences

Expansion in the repeat number of intragenic trinucleotide repeats (TNRs) is associated with a variety of inherited human neurodegenerative diseases. To study the composition of TNRs in a mammalian species representing an evolutionary intermediate between humans and rodents, we describe in this paper the identification of porcine noncoding and polyglutamine-encoding TNR regions and the comparison to the homologous TNRs from human, chimpanzee, dog, opossum, rat, and mouse. Several of the porcine TNR regions are highly polymorphic both within and between different breeds. The TNR regions are more conserved in terms of repeat length between humans and pigs than between humans and rodents suggesting that TNR lengths could be implicated in mammalian evolution. The TNRs in the FMR2, SCA6, SCA12, and Huntingtin genes are comparable in length to alleles naturally occurring in humans, and also in FMR1, a long uninterrupted CGG TNR was identified. Most strikingly, we identified a Huntingtin allele with 21 uninterrupted CAG repeats encoding a stretch of 24 polyglutamines. Examination of this particular Huntingtin TNR in 349 porcine offspring showed stable transmission. The presence in the porcine genome of TNRs within genes that, in humans, can undergo pathogenic expansions support the usage of the pig as an alternative animal model for studies of TNR evolution, stability, and functional properties.

Identification of a new family of spinocerebellar ataxia type 14 in the Japanese spinocerebellar ataxia population by the screening of PRKCG exon 4

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disorder characterized by cerebellar ataxia and intermittent axial myoclonus. Various mutations have been found in the PRKCG gene encoding protein kinase C gamma in SCA14 families. Most of those mutations have been found in exon 4 of the PRKCG gene. We performed polymerase chain reaction (PCR)-based screening to clarify the approximate morbidity rate of the disease in the Japanese SCA population. We screened exon 4 of the PRKCG gene in 882 SCA patients with undefined etiologies using denaturing high-performance liquid chromatography and subsequent direct sequencing. We found a novel C/T missense mutation with a Ser119-to-Phe substitution (S119F) in 2 patients and subsequently found that they belonged to the same family. This S119F mutation was not found in 259 control individuals. Further PCR-based analysis revealed an additional 5 members with the same mutation in this family. Cerebellar ataxia was manifested in 5 of those 7 members. The main symptom in 4 of the 5 affected members was pure cerebellar ataxia with late onset. They had no myoclonus, extrapyramidal signs, ophthalmoplegia, or intellectual disturbance, some of which were found in previously reported SCA families. One patient showed intractable epilepsy, severe walking disturbance, and trunk ataxia with early onset. The results of this study suggest that the frequency of SCA14 in the Japanese SCA population is very low.

Clinical and genetic characterizations of 16q-linked autosomal dominant spinocerebellar ataxia (AD-SCA) and frequency analysis of AD-SCA in the Japanese population

Autosomal dominant spinocerebellar ataxias (AD-SCAs) form a clinically and genetically heterogeneous group of neurodegenerative disorders. Recently, a single nucleotide substitution in the 5'-untranslated region of the puratrophin-1 gene was found to be associated with one type of AD-SCA linked to chromosome 16q (16q-SCA). To obtain further insight into the contribution of the C-to-T substitution in the puratrophin-1 gene to the clinical and genetic characteristics of patients with 16q-SCA, we analyzed 686 families with 719 individuals diagnosed with progressive ataxia. We found C-to-T substitution in the puratrophin-1 gene in 57 unrelated families with 65 affected individuals. The mean age at onset in the patients with 16q-SCA was 59.1 (range, 46-77). Ataxia is the most common initial symptom. The elderly patients over 65 occasionally showed other accompanying clinical features including abnormalities in tendon reflexes, involuntary movements, and reduced vibration sense. We also examined the frequency of the AD-SCA subtype, considering the effects of age at onset. In the 686 AD-SCA families, SCA6 and Machado-Joseph disease/SCA3 are frequent subtypes, followed by dentatorubral-pallidoluysian atrophy and 16q-SCA. 16q-SCA is not a rare subtype of Japanese AD-SCA, particularly in patients with ages at onset over 60.

TRDB--the Tandem Repeats Database

Tandem repeats in DNA have been under intensive study for many years, first, as a consequence of their usefulness as genomic markers and DNA fingerprints and more recently as their role in human disease and regulatory processes has become apparent. The Tandem Repeats Database (TRDB) is a public repository of information on tandem repeats in genomic DNA. It contains a variety of tools for repeat analysis, including the Tandem Repeats Finder program, query and filtering capabilities, repeat clustering, polymorphism prediction, PCR primer selection, data visualization and data download in a variety of formats. In addition, TRDB serves as a centralized research workbench. It provides user storage space and permits collaborators to privately share their data and analysis. TRDB is available at https://tandem.bu.edu/cgi-bin/trdb/trdb.exe.

Altered MAP kinase phosphorylation and impaired motor coordination in PTPRR deficient mice

The neuronal protein tyrosine phosphatases encoded by mouse gene Ptprr (PTPBR7, PTP-SL, PTPPBSgamma-42 and PTPPBSgamma-37) have been implicated in mitogen-activated protein (MAP) kinase deactivation on the basis of transfection experiments. To determine their physiological role in vivo, we generated mice that lack all PTPRR isoforms. Ptprr-/- mice were viable and fertile, and not different from wildtype littermates regarding general physiology or explorative behaviour. Highest PTPRR protein levels are in cerebellum Purkinje cells, but no overt effects of PTPRR deficiency on brain morphology, Purkinje cell number or dendritic branching were detected. However, MAP kinase phosphorylation levels were significantly altered in the PTPRR-deficient cerebellum and cerebrum homogenates. Most notably, increased phospho-ERK1/2 immunostaining density was observed in the basal portion and axon hillock of Ptprr-/- Purkinje cells. Concomitantly, Ptprr-/- mice displayed ataxia characterized by defects in fine motor coordination and balance skills. Collectively, these results establish the PTPRR proteins as physiological regulators of MAP kinase signalling cascades in neuronal tissue and demonstrate their involvement in cerebellum motor function.

On autosomal dominant cerebellar ataxia (ADCA) other than polyglutamine diseases, with special reference to chromosome 16q22.1-linked ADCA

Autosomal dominant cerebellar ataxia (ADCA) is a group of heterogeneous conditions. More than 20 genes or gene loci have been identified that are responsible for ADCA. Although expansions of the trinucleotide (CAG) repeat that encode polyglutamine are known to cause some forms of ADCA, growing knowledge about the genetic basis of ADCA indicates that many subtypes of ADCA are caused by mutations other than the CAG repeat/polyglutamine expansion. In this paper, we review ADCA caused by mutations other than polyglutamine expansions (i.e. "non-polyglutamine diseases"). We also describe the neuropathology of chromosome 16q22.1-linked ADCA, which appears to be the most common non-polyglutamine disease in Japan. What we find to be characteristic on the chromosome 16q22.1-linked ADCA brain is the presence of atrophic Purkinje cells surrounded by the formation of amorphous material, the latter composed of the Purkinje cell dendrites stemming from the cell bodies, the presynaptic terminals innervated by certain neurons, and the astroglial processes. Such neuropathological findings seem to be unique for this disease.

Altered levels of PP2A regulatory B/PR55 isoforms indicate role in neuronal differentiation

The ubiquitously expressed serine/threonine-specific protein phosphatase 2A (PP2A) is prominent in brain where it serves a wide range of functions under both physiological and pathological conditions. PP2A holoenzymes are composed of a catalytic subunit and a tightly complexed scaffolding subunit. This core enzyme associates with regulatory subunits of the B/PR55, B'/PR56/PR61, B''/PR72 and B'''/PR93/PR110 families. We previously determined distribution and expression levels of the four members of the B/PR55 family in brain, as dysregulation of this subunit family has been specifically implicated in neurodegenerative disorders including Alzheimer's disease. In the present study, we used cell lines widely used in neuroscience research to determine levels of the four PR55 isoforms by qRT-PCR under different experimental conditions. We show that PR55alpha mRNA levels are highest in both HEK293 cells and SH-SY5Y neuroblastoma cells whereas PR55beta levels are lowest. Stepwise neuronal differentiation of SH-SY5Y cells causes the selective upregulation of PR55beta, and to some extent PR55gamma and PR55delta, but not PR55alpha mRNAs. In agreement with the qRT-PCR analysis, neuronal differentiation does not alter PR55alpha protein levels, whereas interestingly, PR55beta and PR55gamma protein levels are reduced when compared to undifferentiated cells. Our data point at specific roles for distinct regulatory B/PR55 subunits of PP2A in neuron-like cells with PR55alpha being the major isoform.

RNA-MEDIATED NEUROMUSCULAR DISORDERS

Myotonic dystrophy type 1 (DM1) is caused by a CTG expansion mutation located in the 3' untranslated portion of the dystrophica myotonin protein kinase gene. The identification and characterization of RNA-binding proteins that interact with expanded CUG repeats and the discovery that a similar transcribed but untranslated CCTG expansion in an intron causes myotonic dystrophy type 2 (DM2) have uncovered a new type of mechanism in which microsatellite expansion mutations cause disease through an RNA gain-of-function mechanism. This review discusses RNA pathogenesis in DM1 and DM2 and evidence that similar mechanisms may play a role in a growing number of dominant noncoding expansion disorders, including fragile X tremor ataxia syndrome (FXTAS), spinocerebellar ataxia type 8 (SCA8), SCA10, SCA12, and Huntington's disease-like 2 (HDL2).

Non-coding RNAs in the nervous system

Increasing evidence suggests that the development and function of the nervous system is heavily dependent on RNA editing and the intricate spatiotemporal expression of a wide repertoire of non-coding RNAs, including micro RNAs, small nucleolar RNAs and longer non-coding RNAs. Non-coding RNAs may provide the key to understanding the multi-tiered links between neural development, nervous system function, and neurological diseases.

A novel trinucleotide repeat expansion at chromosome 3q26.2 identified by a CAG/CTG repeat expansion detection array

CAG/CTG repeat expansions cause at least 12 different neurological disorders, and additional disorders of this type probably exist. Using the repeat expansion detection (RED) assay, we identified an expanded CAG/CTG repeat in a 50-year-old woman with an autosomal dominant syndrome with prominent progressive sensory neuropathy. The expansion could not be accounted for by any of the CAG/CTG repeats known to undergo expansion. To identify the locus of the expansion, we created a PCR array to assess the repeat length of all repeats of eight or more CAG or CTG triplets in the human genome. The expansion was localized to a repeat contained in an intron of a Genscan-predicted gene, 185 nt downstream of a predicted exon that is conserved through mouse. The closest experimentally verified gene in the region (TNIK, encoding a serine/threonine kinase) occurs approximately 63 Kb downstream from the repeat. The length of the expansion in the proband is 98 triplets. This repeat is not expanded in the proband's cousin (the only other affected family member for whom DNA is currently available) and no expansions were detected in a set of 230 patients with movement disorders of unknown cause. An expanded allele containing 58 triplets was detected in a single control individual, and no other expansions were detected in a set of 255 controls. The normal repeat length ranges from 5 to 30 triplets, with 8 triplets the most common allele. Our results suggest that this new repeat expansion is probably not the direct cause of the phenotype in the proband. Whether the repeat contributes to the patient's phenotype, or is associated with another phenotype, remains to be determined.

16q-linked autosomal dominant cerebellar ataxia: a clinical and genetic study

The autosomal dominant cerebellar ataxias (ADCAs) comprise a genetically and clinically heterogenous group of neurodegenerative disorders. Very recently, a C-to-T single nucleotide substitution in the puratrophin-1 gene was found to be strongly associated with a form of ADCA linked to chromosome 16q22.1 (16q-linked ADCA; OMIM 600223). We found the C-to-T substitution in the puratrophin-1 gene in 20 patients with ataxia (16 heterozygotes and four homozygotes) and four asymptomatic carriers in 9 of 24 families with an unknown type of ADCA. We also found two cases with 16q-linked ADCA among 43 sporadic patients with late-onset cortical cerebellar atrophy (LCCA). The mean age at onset in the 22 patients was 61.8 years, and that of homozygous patients was lower than that of heterozygous ones in one family. Neurological examination revealed that the majority of our patients showed exaggerated deep tendon reflexes in addition to the cardinal symptom of cerebellar ataxia (100%), and 37.5% of them had sensorineural hearing impairment, whereas sensory axonal neuropathy was absent. The frequency of 16q-linked ADCA was about 1/10 of our series of 110 ADCA families, making it the third most frequent ADCA in Japan.

A -16C>T substitution in the 5' UTR of the puratrophin-1 gene is prevalent in autosomal dominant cerebellar ataxia in Nagano

The molecular bases of autosomal dominant cerebellar ataxia (ADCA) have been increasingly elucidated, but 17-50% of ADCA families still remain genetically undefined in Japan. In this study we investigated 67 genetically undefined ADCA families from the Nagano prefecture, and found that 63 patients from 51 families possessed the -16C>T change in the puratrophin-1 gene, which was recently found to be pathogenic for 16q22-linked ADCA. Most patients shared a common haplotype around the puratrophin-1 gene. All patients with the -16C>T change had pure cerebellar ataxia with middle-aged or later onset. Only one patient in a large, -16C>T positive family did not have this change, but still shared a narrowed haplotype with, and was clinically indistinguishable from, the other affected family members. In Nagano, 16q22-linked ADCA appears to be much more prevalent than either SCA6 or dentatorubral-pallidoluysian atrophy (DRPLA), and may explain the high frequency of spinocerebellar ataxia.

Altered phosphorylation of cytoskeletal proteins in mutant protein phosphatase 2A transgenic mice

Protein phosphatase 2A (PP2A) is a family of heterotrimeric enzymes with diverse functions under physiologic and pathologic conditions such as Alzheimer's disease. All PP2A holoenzymes have in common a catalytic subunit C and a structural scaffolding subunit A. These core subunits assemble with various regulatory B subunits to form heterotrimers with distinct functions in the cell. Substrate specificity of PP2A in vitro is determined by regulatory subunits with leucine 309 of the catalytic subunit C playing a crucial role in the recruitment of regulatory subunits into the complex. Here we expressed a mutant form of Calpha, L309A, in brain and Harderian (lacrimal) gland of transgenic mice. We found an altered recruitment of regulatory subunits into the complex, demonstrating a role for the carboxyterminal leucine of Calpha in regulating holoenzyme assembly in vivo. This was associated with an increased phosphorylation of tau in brain and an impaired dephosphorylation of vimentin demonstrating that both cytoskeletal proteins are in vivo substrates of distinct PP2A holoenzyme complexes.

Chemical modifiers of unstable expanded simple sequence repeats: what goes up, could come down

A mounting number of inherited human disorders, including Huntington disease, myotonic dystrophy, fragile X syndrome, Friedreich ataxia and several spinocerebellar ataxias, have been associated with the expansion of unstable simple sequence DNA repeats. Despite a similar genetic basis, pathogenesis in these disorders is mediated by a variety of both loss and gain of function pathways. Thus, therapies targeted at downstream pathology are likely to be disease specific. Characteristically, disease-associated expanded alleles in these disorders are highly unstable in the germline and somatic cells, with a tendency towards further expansion. Whereas germline expansion accounts for the phenomenon of anticipation, tissue-specific, age-dependent somatic expansion may contribute towards the tissue-specificity and progressive nature of the symptoms. Thus, somatic expansion presents as a novel therapeutic target in these disorders. Suppression of somatic expansion should be therapeutically beneficial, whilst reductions in repeat length could be curative. It is well established that both cis- and trans-acting genetic modifiers play key roles in the control of repeat dynamics. Importantly, recent data have revealed that expanded CAG.CTG repeats are also sensitive to a variety of trans-acting chemical modifiers. These data provide an exciting proof of principle that drug induced suppression of somatic expansion might indeed be feasible. Moreover, as our understanding of the mechanism of expansion is refined more rational approaches to chemical intervention in the expansion pathway can be envisioned. For instance, the demonstration that expansion of CAG.CTG repeats is dependent on the Msh2, Msh3 and Pms2 genes, highlights components of the DNA mismatch repair pathway as therapeutic targets. In addition to potential therapeutic applications, the response of expanded simple repeats to genotoxic assault suggests such sequences could also have utility as bio-monitors of environmentally induced genetic damage in the soma.

Adult onset spinocerebellar ataxia in a Canadian movement disorders clinic

BACKGROUND

The spinocerebellar ataxias (SCAs) are a genetically and clinically heterogeneous group of neurodegenerative disorders. Relative frequencies vary within different ethnic groups and geographical locations.

OBJECTIVES

1) To determine the frequencies of hereditary and sporadic adult onset SCAs in the Movement Disorders population; 2) to assess if the fragile X mental retardation gene 1 (FMR1) premutation is found in this population.

METHODS

A retrospective chart review of individuals with a diagnosis of adult onset SCA was carried out. Testing for SCA types 1, 2, 3, 6, 7, and 8, Dentatorubral-pallidoluysian atrophy (DRPLA), Friedreich ataxia and the FMR1 expansion was performed.

RESULTS

A total of 69 patients in 60 families were identified. Twenty-one (35%) of the families displayed autosomal dominant and two (3.3%) showed autosomal recessive (AR) pattern of inheritance. A positive but undefined family history was noted in nine (15%). The disorder appeared sporadic in 26 patients (43.3%). In the AD families, the most common mutation was SCA3 (23.8%) followed by SCA2 (14.3%) and SCA6 (14.3%). The SCA1 and SCA8 were each identified in 4.8%. FA was found in a pseudodominant pedigree, and one autosomal recessive pedigree. One sporadic patient had a positive test (SCA3).Dentatorubral-pallidoluysian atrophy and FMR1 testing was negative.

CONCLUSION

A positive family history was present in 53.3% of our adult onset SCA patients. A specific genetic diagnosis could be given in 61.9% of dominant pedigrees with SCA3 being the most common mutation, followed by SCA2 and SCA6. The yield in sporadic cases was low. The fragile X premutation was not found to be responsible for SCA.

Frequency analysis and clinical characterization of different types of spinocerebellar ataxia in Serbian patients

The relative frequencies of different spinocerebellar ataxias (SCAs) vary widely among different ethnic groups, presumably due to a founder effect. We investigated the relative prevalence of SCA1-3, 6-8, 12, 17; dentate-rubro-pallidoluysian atrophy; and Friedreich's ataxia (FRDA) in Serbian patients with adult-onset (>20 years of age) hereditary and sporadic SCAs, and compared clinical features of patients with genetically confirmed SCAs. A total of 108 patients from 54 families (38 apparently dominant [ADCA] and 16 apparently recessive) with adult-onset hereditary ataxia and 75 apparently sporadic patients were assessed. Of 38 families with ADCA, 13 (34%) were positive for an expansion in an SCA1 and 5 families (13%) for an expansion in an SCA2 allele. In 20 families (53%), no expansions have been identified in any of the analyzed genes. Gaze palsy, spasticity, and hyperreflexia were significantly more common in SCA1, whereas slow saccades, hypotonia, hyporeflexia, and dystonia prevailed in SCA2 patients. Among the 16 families with an apparently recessive mode of ataxia inheritance, 4 (25%) were identified as having the FRDA mutation. Ataxia-causing mutations were identified in 8 (10.6%) of patients with apparently sporadic adult-onset ataxia.

Evidence of a common founder for SCA12 in the Indian population

Spinocerebellar ataxia type 12 (SCA12) is an autosomal dominant cerebellar ataxia associated with the expansion of an unstable CAG repeat in the 5' region of the PPP2R2B gene on chromosome 5q31-5q32. We found that it accounts for approximately 16% (20/124) of all the autosomal dominant ataxia cases diagnosed in AIIMS, a major tertiary referral centre in North India. The length of the expanded allele in this population ranges from 51-69 CAG triplets. Interestingly, all the affected families belong to an endogamous population, which originated in the state of Haryana, India. We identified four novel SNPs and a dinucleotide marker spanning approximately 137 kb downstream of CAG repeat in the PPP2R2B gene. Analysis of 20 Indian SCA12 families and ethnically matched normal unrelated individuals revealed one haplotype to be significantly associated with the affected alleles (P= 0.000), clearly indicating the presence of a common founder for SCA12 in the Indian population. This haplotype was not shared by the American pedigree with SCA12. Therefore, the SCA12 expansion appears to have originated at least twice.

Diseases of unstable repeat expansion: mechanisms and common principles

The list of developmental and degenerative diseases that are caused by expansion of unstable repeats continues to grow, and is now approaching 20 disorders. The pathogenic mechanisms that underlie these disorders involve either loss of protein function or gain of function at the protein or RNA level. Common themes have emerged within and between these different classes of disease; for example, among disorders that are caused by gain-of-function mechanisms, altered protein conformations are central to pathogenesis, leading to changes in protein activity or abundance. In all these diseases, the context of the expanded repeat and the abundance, subcellular localization and interactions of the proteins and RNAs that are affected have key roles in disease-specific phenotypes.

Expanded trinucleotide repeats in the TBP/SCA17 gene mapped to chromosome 6q27 are associated with schizophrenia

Schizophrenia has a complex and non-Mendelian mode of inheritance. Recently, trinucleotide repeat (TNR)-containing genes have been considered as the candidate genes predisposing to schizophrenia. The purpose of this study was to determine whether a genetic association could be observed between schizophrenia and the TNR polymorphisms within the KLHL1AS/SCA8, PPP2R2B/SCA12, and TBP/SCA17 genes. We studied 100 unrelated schizophrenia patients and 124 controls without evident neurodegenerative or psychiatric disorders. The overall allele frequency distributions of the KLHL1AS/SCA8 and PPP2R2B/SCA12 genes were not significantly different between the schizophrenic patients and the control subjects (P>0.05). The allele frequency distribution in the schizophrenic patients was significantly different from that in the controls at the TBP/SCA17 gene (P=0.0149), with an increased frequency of 36 repeats in the patients and two patients carrying 45 TNR expansions were identified. TBP/SCA17 is the TATA box binding protein gene mapped to chromosome 6q27. The study suggests that TNR expansions of the TBP/SCA17 gene may contribute to the genetic risk of schizophrenia in rare cases.

Gain-of-function screen identifies a role of the Sec61alpha translocon in Drosophila postmitotic neurotoxicity

To elucidate the intrinsic mechanisms of neurotoxicity induction, including those underlying neural cell death and neurodegeneration, we developed a gain-of-function screen for gene products causing neural cell loss. To identify novel genes with a cell-death-related function in neurons, we screened 4,964 Drosophila GS lines, in which one or two genes from much of the Drosophila genome can be overexpressed. Approximately 0.68% of the GS lines produced phenotypes involving a loss of postmitotic neurons. Of these, we identified and characterized the endd2 gene, which encodes the Drosophila ortholog of Sec61alpha (DSec61alpha), an endoplasmic reticulum protein with protein translocation activity. Ectopic expression of DSec61alpha caused neural cell death accompanied by the accumulation of ubiquitinated proteins, which was mediated by DSec61alpha's translocon activity. This supported our previous observation that the DSec61alpha translocon contributes to expanded polyglutamine-mediated neuronal toxicity, which is also associated with ubiquitinated protein accumulation. These data suggest that the translocon may be a novel component of neural cell death and degeneration pathways. Our approach can be used to identify potential neurotoxic factors within the whole genome, which will increase our understanding of the molecular mechanisms of various types of cell death, including those associated with human neurodegenerative diseases.