An autosomal dominant cerebellar ataxia linked to chromosome 16q22.1 is associated with a single-nucleotide substitution in the 5' untranslated region of the gene encoding a protein with spectrin repeat and Rho guanine-nucleotide exchange-factor domains

Spinocerebellar ataxia type 31 is associated with "inserted" penta-nucleotide repeats containing (TGGAA)n

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.

Spinocerebellar ataxia type 23: a genetic update

The spinocerebellar ataxia type 23 locus was identified in 2004 based on linkage analysis in a large, two-generation Dutch family. The age of onset ranged 43-56 years and the phenotype was characterized by a slowly progressive, isolated ataxia. Neuropathological examination revealed neuronal loss in the Purkinje cell layer, dentate nuclei, and inferior olives. Ubiquitin-positive intranuclear inclusions were found in nigral neurons, but were considered to be Marinesco bodies. The disease locus on chromosome 20p13-12.3 was found to span a region of approximately 6 Mb of genomic DNA, containing 97 known or predicted genes. To date, no other families have been described that also map to this SCA locus. Direct sequencing of the coding regions of 21 prioritized candidate genes did not reveal any disease-causing mutation. Apparently, the SCA23 gene is a disease gene with a different function than the genes that have been associated with other known SCA types. Work to elucidate the chromosomal organization of the SCA23 locus will eventually discover the responsible disease gene.

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.

Spinocerebellar ataxia type 28: a novel autosomal dominant cerebellar ataxia characterized by slow progression and ophthalmoparesis

We have recently mapped the spinocerebellar ataxia type 28 (SCA28) locus on chromosome 18p11.22 in a four-generation Italian family. The clinical phenotype in affected individuals of this family was characterized by juvenile onset, slowly progressive gait and limb ataxia, dysarthria, hyperreflexia at lower limbs, nystagmus, and ophthalmoparesis. The mean age at onset was 19.5 years, and no evidence of anticipation between generations was observed. The disease locus on chromosome 18p11.22-q11.2 was found to span a region of 7.9 Mb of genomic DNA. Direct sequencing of candidate genes within the critical interval led to the identification of a heterozygous point mutation in one of them. The mutation was located in a highly conserved domain with proposed functional properties in the protein product of the SCA28 gene, and segregated with the disease phenotype in all affected members of this family. Thereafter we have screened 105 patients with autosomal dominant spinocerebellar ataxia who had resulted negative for mutations in known SCA genes. Genetic screening allowed the identification in a second Italian family of a distinct missense mutation located in the very same functional domain of the protein. The affected members of this second family exhibited a neurological phenotype similar to that of the original family. Both mutations, not found in more than 500 chromosomes, are associated with amino acid changes (Glu-->Lys and Ser-->Leu, respectively) in evolutionarily conserved residues of the alleged SCA28 gene. Our data point to a putative pathogenic role of these mutations, and indicate SCA28 as the sixth recognized SCA genotype caused by point mutations.

Sporadic ataxias in Japan--a population-based epidemiological study

Sporadic spinocerebellar ataxias (SCAs) comprise heterogeneous diseases with poorly understood epidemiologies and etiologies. A population-based epidemiological analysis of sporadic ataxias in the Japanese population was described. The prevalence rate of SCAs in the Japanese population is estimated to be 18.5/100,000. Sporadic SCAs account for 67.2% of total SCAs including hereditary SCAs, with olivopontocerebellar atrophy (OPCA) being the most common form sporadic ataxia (64.7%). The natural history analysis conducted on the basis of International Cooperative Ataxia Rating Scale (ICARS) showed that only 33% of patients with OPCA were able to walk at least with one stick 4-5 years after the onset of OPCA, which is much less than that of patients with cortical cerebellar atrophy (CCA). Similarly, 43% of patients with OPCA were able to stand alone 4-5 years after the onset, while 76% of patients with CCA were able to stand alone at the same disease duration. A population-based epidemiological analysis should provide essential information on the natural history of SCAs.

Systems biology and its application to the understanding of neurological diseases

Recent advances in molecular biology, neurobiology, genetics, and imaging have demonstrated important insights about the nature of neurological diseases. However, a comprehensive understanding of their pathogenesis is still lacking. Although reductionism has been successful in enumerating and characterizing the components of most living organisms, it has failed to generate knowledge on how these components interact in complex arrangements to allow and sustain two of the most fundamental properties of the organism as a whole: its fitness, also termed its robustness, and its capacity to evolve. Systems biology complements the classic reductionist approaches in the biomedical sciences by enabling integration of available molecular, physiological, and clinical information in the context of a quantitative framework typically used by engineers. Systems biology employs tools developed in physics and mathematics such as nonlinear dynamics, control theory, and modeling of dynamic systems. The main goal of a systems approach to biology is to solve questions related to the complexity of living systems such as the brain, which cannot be reconciled solely with the currently available tools of molecular biology and genomics. As an example of the utility of this systems biological approach, network-based analyses of genes involved in hereditary ataxias have demonstrated a set of pathways related to RNA splicing, a novel pathogenic mechanism for these diseases. Network-based analysis is also challenging the current nosology of neurological diseases. This new knowledge will contribute to the development of patient-specific therapeutic approaches, bringing the paradigm of personalized medicine one step closer to reality.

Emerging pathogenic pathways in the spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are diseases characterized by neurodegeneration of the spinocerebellum. To date, 28 autosomal dominant SCAs have been described and seventeen causative genes identified. These genes play a role in a broad range of cellular processes. Recent studies focused on the wild type and pathogenic functions of these genes implicate both gene expression and glutamate-dependent and calcium-dependent neuronal signaling as important pathways leading to cerebellar dysfunction. Understanding how these genes cause disease will allow a deeper understanding of the cerebellum in particular as well as neurodegenerative disease in general.

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.

An update on inherited ataxias

This article provides an overview of recent advances in the field of inherited ataxias. In the past few years, new causative mutations that broaden the diagnostic spectrum of ataxias have been described. In addition, important advances have unveiled the molecular pathology of these disorders, resulting in a classification based on the pathogenetic pathways rather than clinical or genetic features. As concepts of treatment principles emerge, debate continues as to whether such concepts might be applicable to more than one genetically defined disorder or whether each ataxia disorder requires its own unique therapeutic approach. New clinical assessment instruments have been developed that will facilitate future interventional trials. A recent phase 2 clinical trial suggested a positive effect of high-dose idebenone in Friedreich's ataxia, raising hopes that a treatment option will soon be available for this disorder.

Chromosome 16q22.1-linked autosomal dominant cerebellar ataxia: an autopsy case report with some new observations on cerebellar pathology

An autopsy case of chromosome 16q22.1-linked autosomal dominant cerebellar ataxia is reported. The patient was a 77-year-old man who died after a clinical course of about 19 years characterized by pure cerebellar ataxia. Main neuropathological findings included moderate loss of Purkinje cells, variegated degenerative features of the remaining Purkinje cells, finely fibrillary material surrounding the perikarya of Purkinje cells, and ubiquitin-immunoreactive small dots in the molecular layer and cerebellar white matter. Neuritic hyperplasia surrounding the perikarya of Purkinje cells was also a prominent finding. Golgi impregnation study demonstrated poor dendritic arborization of some Purkinje cells. It is our assumption that the pathological processes leading to Purkinje cell death in this disorder are not singular because the intracellular functions of the protein coded by the mutant gene are manifold, and the multiplicity of the pathological processes is reflected in diverse cytomorphological changes seen in degenerating Purkinje cells.

[Hereditary ataxias, spastic parapareses and neuropathies in Eastern Canada]

It has been demonstrated, for many inherited diseases, that historical events have shaped the various regional gene pools of Eastern Canada. In so doing, it has given rise to the increased prevalence of some rare diseases due, to founder effects. The following neurogenetic disorders were first identified in patients from Eastern Canada: AOA-2, Arsacs, HSN-2, Arca-1, HMSN/ACC and Arsal. The population of Eastern Canada, we are convinced, will still allow the identification of new rare forms of hereditary ataxias, spastic parapareses and neuropathies as well as contribute to the uncovering of their mutated genes. We have summarized our current knowledge of the various hereditary ataxias, spastic parapareses and neuropathies in Eastern Canada. The study of the more common and homogenous features of these diseases has been largely completed.

Clinical and genetic study of autosomal recessive cerebellar ataxia type 1

OBJECTIVE

Define the phenotype and genotype of a cluster of families with a relatively pure cerebellar ataxia referred to as autosomal recessive cerebellar ataxia type 1 (ARCA-1).

METHODS

We ascertained 64 probands and affected members of 30 French-Canadian families all showing similar clinical features and originating from the same region of Quebec. After informed consent, we performed detailed clinical history, neurological examination, brain imaging, nerve conduction studies, and SYNE1 mutation detection of all available subjects.

RESULTS

Based on the cases examined, ARCA-1 is a cerebellar syndrome characterized by recessive transmission, middle-age onset (mean, 31.60; range, 17-46 years), slow progression and moderate disability, significant dysarthria, mild oculomotor abnormalities, occasional brisk reflexes in the lower extremities, normal nerve conduction studies, and diffuse cerebellar atrophy on imaging. We identified a total of seven mutations in our population, thereby providing evidence of genotypic heterogeneity. Patients with different mutations did not show significant phenotypic heterogeneity.

INTERPRETATION

We identified a cluster of French-Canadian families with a new recessive ataxia of relatively pure cerebellar type caused by mutations in SYNE1. The function of SYNE1 is thus critical in the maintenance of cerebellar structure in humans. We expect that this disease will be a common cause of middle-age-onset recessive ataxia worldwide.

GEFs in growth factor signaling

Evolutionary conserved members of the Ras superfamily of small GTP-binding proteins function as binary molecular switches to control diverse biological processes. In the context of cellular signaling, these include functions in exocytic and endocytic trafficking, as well as roles in signal relay downstream of various cell surface receptors. We previously reviewed roles played by the large family of GTPase, activating proteins in these processes. In this companion review, we highlight recent findings relating to the regulation of another major class of Ras superfamily regulatory proteins, the guanine nucleotide exchange factors.

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.

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.

Diagnosis and management of early- and late-onset cerebellar ataxia

Cerebellar ataxias represent a heterogeneous group of neurodegenerative disorders. Two main categories are distinguished: hereditary and sporadic ataxias. Sporadic ataxias may be symptomatic or idiopathic. The clinical classification of hereditary ataxias is nowadays being replaced by an expanding genotype-based classification. A large spectrum of degenerative and metabolic disorders may also present with ataxia early or late in the course of disease. We present a diagnostic algorithm for the adult patient presenting with subacute cerebellar ataxia, based on family history and straightforward clinical characteristics of the patient. Along with the algorithm, an overview of the autosomal dominant, autosomal recessive, X-linked, mitochondrial, symptomatic and idiopathic subtypes of cerebellar ataxia is presented. An appropriate diagnosis is of utmost importance to such considerations as prognosis, genetic counselling and possible therapeutic implications.

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.

Protein-protein interaction networks in the spinocerebellar ataxias

A large yeast two-hybrid study shows that some proteins mutated in different spinocerebellar ataxias have interacting protein partners in common.

A large yeast two-hybrid study investigating whether the proteins mutated in different forms of spinocerebellar ataxia have interacting protein partners in common suggests that some forms do share common pathways, and will provide a valuable resource for future work on these diseases.

Mutations in the KIAA0196 gene at the SPG8 locus cause hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a progressive upper-motor neurodegenerative disease. The eighth HSP locus, SPG8, is on chromosome 8p24.13. The three families previously linked to the SPG8 locus present with relatively severe, pure spastic paraplegia. We have identified three mutations in the KIAA0196 gene in six families that map to the SPG8 locus. One mutation, V626F, segregated in three large North American families with European ancestry and in one British family. An L619F mutation was found in a Brazilian family. The third mutation, N471D, was identified in a smaller family of European origin and lies in a spectrin domain. None of these mutations were identified in 500 control individuals. Both the L619 and V626 residues are strictly conserved across species and likely have a notable effect on the structure of the protein product strumpellin. Rescue studies with human mRNA injected in zebrafish treated with morpholino oligonucleotides to knock down the endogenous protein showed that mutations at these two residues impaired the normal function of the KIAA0196 gene. However, the function of the 1,159-aa strumpellin protein is relatively unknown. The identification and characterization of the KIAA0196 gene will enable further insight into the pathogenesis of HSP.

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.

Mutations in SYNE1 lead to a newly discovered form of autosomal recessive cerebellar ataxia

The past decade has seen great advances in unraveling the biological basis of hereditary ataxias. Molecular studies of spinocerebellar ataxias (SCA) have extended our understanding of dominant ataxias. Causative genes have been identified for a few autosomal recessive ataxias: Friedreich's ataxia, ataxia with vitamin E deficiency, ataxia telangiectasia, recessive spastic ataxia of Charlevoix-Saguenay and ataxia with oculomotor apraxia type 1 (refs. 6,7) and type 2 (ref. 8). Nonetheless, genes remain unidentified for most recessive ataxias. Additionally, pure cerebellar ataxias, which represent up to 20% of all ataxias, remain poorly studied with only two causative dominant genes being described: CACNA1A (ref. 9) and SPTBN2 (ref. 10). Here, we report a newly discovered form of recessive ataxia in a French-Canadian cohort and show that SYNE1 mutations are causative in all of our kindreds, making SYNE1 the first identified gene responsible for a recessively inherited pure cerebellar ataxia.

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.

Father-to-daughter transmission of Cornelia de Lange syndrome caused by a mutation in the 5' untranslated region of the NIPBL Gene

Cornelia de Lange syndrome (CdLS; also called Brachmann de Lange syndrome) is a developmental disorder characterized by typical facial dysmorphism, growth and mental retardation, microcephaly, and various malformations. Mutations in the NIPBL gene have been identified in approximately 40% of reported cases, suggesting either genetic heterogeneity or that some NIPBL mutations are not detected by current screening strategies. We screened a cohort of 21 patients with no previously identified NIPBL anomaly for mutations in the 5' untranslated region (5'UTR) and the proximal promoter of the NIPBL gene. We identified a heterozygous deletion-insertion mutation in exon 1, 321 nucleotides upstream of the translation initiation codon (c.-321_-320delCCinsA) in one affected girl and her mildly affected father. This mutation altered highly conserved nucleotides, was not found in 400 control alleles, arose de novo in the father, and cosegregated with the disease in the family. Using real-time quantitative PCR, we showed that NIPBL mRNA expression was lowered in patients' lymphocytes compared to control samples. Finally, we showed that, when subcloned into a luciferase reporter vector, the mutation leads to a significant reduction of reporter gene activity. Our results demonstrate that mutations in the 5' noncoding region of the NIPBL gene can be involved in the pathogenesis of CdLS. Mutations affecting this region of the gene might be associated with a milder phenotype.

A Japanese case of SCA14 with the Gly128Asp mutation

Spinocerebellar ataxia type 14 (SCA14) is a rare form of autosomal dominant cerebellar ataxias caused by mutations in the protein kinase Cgamma gene (PRKCG). We have identified a Japanese patient with SCA14 who carried the Gly128Asp mutation in PRKCG. She first noticed gait unsteadiness at around age 42, and then her gait ataxia worsened very slowly for more than 20 years. At age 62, she was still ambulatory, although cerebellar ataxia was clinically evident. She is the second patient identified with the G128D mutation. Both patients with this mutation showed pure cerebellar ataxia. With only two families with SCA14 found in Japan prior to this study, the clinical features and disease-causing mutations in PRKCG are heterogeneous in the same ethnic background.

Intron length and accelerated 3' gene evolution

Genetic evolution depends in part upon a balance between negative selection and environmentally driven mutation. To explore whether this balance is affected by gene structure, we have used phylogenetic data mining to compare gene compositions across a range of species. Here we show that genomes of higher species exhibit a greater frequency of 5' CpG islands and of CpG-->TpG/CpA transitions. This latter mutational pattern exhibits a 5'-to-3' trend in higher species, consistent with a length-dependent effect on methylation-dependent CpG suppression. Associated strand asymmetry (TpG>CpA) declines with gene length, implying attenuation of transcription-coupled repair 3' to introns. A sharp 3' rise in coding region single-nucleotide polymorphism frequency further supports a mechanistic role for intron length in promoting genetic variation by reducing repair and/or weakening negative selection. Consistent with this, the Ka/Ks ratio of 3' exons exceeds that of centrally located exons in intron-containing, but not in intronless, genes (p<0.0003). We conclude that the efficiency of transcription-coupled repair decreases with gene length, suggesting in turn that 3' gene evolution is accelerated both by introns and by gene methylation.

A protein-protein interaction network for human inherited ataxias and disorders of Purkinje cell degeneration

Many human inherited neurodegenerative disorders are characterized by loss of balance due to cerebellar Purkinje cell (PC) degeneration. Although the disease-causing mutations have been identified for a number of these disorders, the normal functions of the proteins involved remain, in many cases, unknown. To gain insight into the function of proteins involved in PC degeneration, we developed an interaction network for 54 proteins involved in 23 inherited ataxias and expanded the network by incorporating literature-curated and evolutionarily conserved interactions. We identified 770 mostly novel protein-protein interactions using a stringent yeast two-hybrid screen; of 75 pairs tested, 83% of the interactions were verified in mammalian cells. Many ataxia-causing proteins share interacting partners, a subset of which have been found to modify neurodegeneration in animal models. This interactome thus provides a tool for understanding pathogenic mechanisms common for this class of neurodegenerative disorders and for identifying candidate genes for inherited ataxias.

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.

Genetics of type 2 diabetes

After several years of uncertain progress, the stage is now set for a transformation in understanding the genetic landscape of type 2 diabetes. Advances in genome informatics, genotyping technology, and statistical methodology, allied to availability of large-scale clinical material, are having a salutary effect on susceptibility gene discovery. The advent of genuinely genome-wide association scans and the prospects for combining genetics with high-throughput genomics are additional sources of optimism for the future.

Mutations of the puratrophin-1 (PLEKHG4) gene on chromosome 16q22.1 are not a common genetic cause of cerebellar ataxia in a European population

Autosomal dominant cerebellar ataxia (ADCA) is a genetically heterogeneous group of neurodegenerative disorders with overlapping clinical presentation. Recently, a single nucleotide substitution in the 5'-untranslated region (UTR) of the puratrophin-1 (PLEKHG4) gene on chromosome 16q22.1 has been shown to be associated with ADCA in 52 unrelated Japanese families. As this mutation has so far not been investigated in other populations, we have screened 537 European patients with a clinical diagnosis of cerebellar ataxia for this specific nucleotide substitution. The mutation was not identified in our cohort. In addition, we screened the complete 5'-UTR as well as the entire coding region of this gene in 120 patients for variations that might account for their clinical symptoms. Several new rare variations were found. For none of the variations could an obvious pathogenetic relevance be postulated at this point, albeit some findings should be followed up in additional populations and by functional assays. We conclude that mutations of the puratrophin-1 gene are not a common cause of hereditary ataxia in our Caucasian population.

SCA28, a novel form of autosomal dominant cerebellar ataxia on chromosome 18p11.22-q11.2

We describe a four-generation Italian family with a novel form of juvenile-onset, slowly progressive, autosomal dominant cerebellar ataxia. Eleven affected family members have been evaluated. The mean age at onset was 19.5 years with no evidence of anticipation. The first symptoms were invariably unbalanced standing and mild gait incoordination. Gaze-evoked nystagmus was prominent at onset, while patients with longer disease duration developed slow saccades, ophthalmoparesis and, often, ptosis. Deep tendon reflexes in lower limbs were increased in 80% of the cases. Genetic analysis excluded the presence of pathological repeat expansions in spinocerebellar ataxia (SCA) types 1-3, 6-8, 10, 12 and 17, and DRPLA genes. Linkage exclusion tests showed no evidence of association with other known SCA loci. A genome-wide screen analysis identified linkage with chromosome 18 markers. A maximum two-point limit of determination score of 4.20 was found for marker D18S53. Haplotype analysis refined a critical region of 7.9 Mb between markers D18S1418 and D18S1104. This new SCA locus on 18p11.22-q11.2 has been designated SCA28. Candidate genes within the critical interval are currently screened for mutations.