Neuronal intranuclear inclusions in SCA2: a genetic, morphological and immunohistochemical study of two cases

Spinocerebellar ataxia 2 (SCA2) belongs to the family of autosomal dominant cerebellar ataxias (ADCA), a genetically heterogeneous group of neurodegenerative diseases. The SCA2 gene maps to chromosome 12q24 and the causative mutation involves the expansion of a CAG repeat within the coding region of the gene. Pathologically, SCA2 presents as olivo-ponto-cerebellar atrophy (OPCA). We present the cases of a 41-year-old man and a 54-year-old woman who died after a long illness characterized by severe cerebellar ataxia. Diagnosis of SCA2 was confirmed by genetic analysis. The brains were moderately to severely atrophic and atrophy was particularly obvious in the cerebellum and brainstem. Histological examination revealed extreme loss of pontine and olivary nuclei and Purkinje cells, with preservation of the dentate nuclei, and of the pigmented cells in the substantia nigra. The whole spinal cord was also severely affected, with shrinkage of the dorsal columns and reduction in the number of neurones in the motor pool and Clarke's nuclei. Immunohistochemistry with 1C2 antibody showed granular neuronal cytoplasmic deposits in all the areas examined and widespread intranuclear inclusions, which were particularly numerous in the residual pontine nuclei. Intranuclear inclusions were not considered a feature in SCA2. Our results support the view that intranuclear inclusions are an integral part of the pathology of this mutation.

Neuropathology of some hereditary conditions affecting central and peripheral nervous system

Neuropathology plays a crucial role in the phenotypic individualization of hereditary disorders affecting the central and peripheral nervous system even if molecular genetics represents the most essential step in describing the genotypes. The neuropathological description of phenotypes and genotypes can be used for refining clinical skills and understanding many clinical, neurophysiological and neuroradiological features. It contributes to the diagnosis of such disorders. The use of immunohistochemical techniques in combination with molecular genetics improves also our knowledge of their pathogenesis and might participate to the future development of therapeutic strategies. We discuss new features of spino-cerebellar ataxia (SCA) type 7 and of a recently identified SCA17 in order to illustrate the significance of the neuronal intranuclear inclusions (NIIs) described in various CAG/polyglutamine repeat expansion diseases. In the field of the peripheral neuropathies we present data on a newly described autosomal recessive Charcot-Marie-Tooth disease (CMT4F) with mutations in the periaxin gene. We document a dysjunction between myelin loops and axolemma with disappearance of the septate-like junctions or transverse bands. The significance of this dysjunction is not yet elucidated. We hope to show by these examples that the combination of classical and new neuropathological methods is useful in the study of hereditary disorders of the nervous system.

Spastic paraplegia, ataxia, mental retardation (SPAR): a novel genetic disorder

OBJECTIVE

To describe a kindred with a dominantly inherited neurologic disorder manifested either as uncomplicated spastic paraplegia or ataxia, spastic paraplegia, and mental retardation.

METHODS

Neurologic examinations and molecular genetic analysis (exclusion of known SCA and HSP genes and loci; and trinucleotide repeat expansion detection [RED]) were performed in six affected and four unaffected subjects in this family. MRI, electromyography (EMG), and nerve conduction studies were performed in three affected subjects.

RESULTS

The phenotype of this dominantly inherited syndrome varied in succeeding generations. Pure spastic paraplegia was present in the earliest generation; subsequent generations had ataxia and mental retardation. MRI showed marked atrophy of the spinal cord in all patients and cerebellar atrophy in those with ataxia. Laboratory analysis showed that the disorder was not caused by mutations in genes that cause SCA-1, SCA-2, SCA-3, SCA-6, SCA-7, SCA-8, and SCA-12; not linked to other known loci for autosomal dominant ataxia (SCA-4, SCA-5, SCA-10, SCA-11, SCA-13, SCA-14, and SCA-16); and not linked to known loci for autosomal dominant hereditary spastic paraplegia (HSP) (SPG-3, SPG-4, SPG-6, SPG-8, SPG-9, SPG-10, SPG-12, and SPG-13) or autosomal recessive HSP SPG-7. Analysis of intergenerational differences in age at onset of symptoms suggests genetic anticipation. Using RED, the authors did not detect expanded CAG, CCT, TGG, or CGT repeats that segregate with the disease.

CONCLUSIONS

The authors describe an unusual, dominantly inherited neurologic disorder in which the phenotype (pure spastic paraplegia or spastic ataxia with variable mental retardation) differed in subsequent generations. The molecular explanation for apparent genetic anticipation does not appear to involve trinucleotide repeat expansion.

Reduction of Purkinje cell pathology in SCA1 transgenic mice by p53 deletion

The expansion of a polyglutamine tract in the ataxin-1 protein beyond a critical threshold causes spinocerebellar ataxia type 1 (SCA1). To investigate the mechanism of neuronal degeneration in SCA1, we analyzed the phenotype of an SCA1 transgenic mouse model in the absence of p53, an important regulator of cell death. p53 deficiency did not affect the early features of SCA1 mice such as impaired motor coordination and ataxin-1 nuclear inclusion formation but caused a notable reduction in later pathological features, including Purkinje cell heterotopia, dendritic thinning, and molecular layer shrinkage. To determine if this protective effect was mediated by an anti-apoptotic property of p53 deficiency, we looked for apoptosis in SCA1 mice but failed to detect any evidence of it even in the presence of p53. We propose that p53 acts after the initial pathogenic events in SCA1 to promote the progression of neuronal degeneration in SCA1 mice, but this activity may be unrelated to apoptosis.

Spinocerebellar ataxia type 6 and episodic ataxia type 2 in a Korean family

Spinocerebellar ataxia type 6 (SCA6), episodic ataxia type 2 (EA2) and familial hemiplegic migraine (FHM) have been known as allelic disorders, which are caused by the alteration of the alpha1A voltage-dependent calcium channel subunit. Expansions of the CAG repeat in the CACNA1A gene on the short arm of the chromosome 19 induce SCA6, and point mutations in the same gene are responsible for EA2 and FHM. In recent studies, both SCA6 and EA2 have been concurrently found in families with 26 CAG repeats without previously reported point mutations either in coding sequences or in intron-exon junctions. We describe a Korean family with CAG26 repeats in the CACNA1A gene. Some of the affected family members had progressive ataxia typical of SCA6 whereas others had episodic vertigo responsive to acetazolamide typical of EA2. Our family support that SCA6 and EA2 are allelic disorders with a high phenotypic variability.

Association of ataxin-7 with the proteasome subunit S4 of the 19S regulatory complex

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder characterized by ataxia and selective neuronal cell loss caused by the expansion of a translated CAG repeat encoding a polyglutamine tract in ataxin-7, the SCA7 gene product. To gain insight into ataxin-7 function and to decipher the molecular mechanisms of neurodegeneration in SCA7, a two-hybrid assay was performed to identify ataxin-7 interacting proteins. Herein, we show that ataxin-7 interacts with the ATPase subunit S4 of the proteasomal 19S regulatory complex. The ataxin-7/S4 association is modulated by the length of the polyglutamine tract whereby S4 shows a stronger association with the wild-type allele of ataxin-7. We demonstrate that endogenous ataxin-7 localizes to discrete nuclear foci that also contain additional components of the proteasomal complex. Immunohistochemical analyses suggest alterations either of the distribution or the levels of S4 immunoreactivity in neurons that degenerate in SCA7 brains. Immunoblot analyses demonstrate reduced levels of S4 in SCA7 cerebella without evident alterations in the levels of other proteasome subunits. These results suggest a role for S4 and ubiquitin-mediated proteasomal proteolysis in the molecular pathogenesis of SCA7.

Motor performance and regional brain metabolism of spontaneous murine mutations with cerebellar atrophy

Three spontaneous mutations with cerebellar atrophy were evaluated for motor coordination and regional brain metabolism, as assessed by cytochrome oxidase (CO) activity. Despite similar neuropathological characteristics, the behavioral phenotype of Lurcher is less severe than that of staggerer, possibly caused by the slower onset of their neuronal degeneration. Although fewer cerebellar cells degenerate in hot-foot than in Lurcher, their motor deficits are more severe, indicating the presence of dysfunctional cells. CO activity in the deep cerebellar nuclei was increased in Lurcher and staggerer but unchanged in hot-foot, probably due to the severe loss of GABAergic input from Purkinje cells in the first two mutants but not the third. Altered CO activity in cerebellar-related pathways was linearly correlated with motor performance, indicating that the activity of this enzyme is associated not only with neuronal activity but also with motor performance.

Similarities between spinocerebellar ataxia type 7 (SCA7) cell models and human brain: proteins recruited in inclusions and activation of caspase-3

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant polyglutamine disorder presenting with progressive cerebellar ataxia and blindness. The molecular mechanisms underlying the selective neuronal death typical of SCA7 are unknown. We have established SCA7 cell culture models in HEK293 and SH-SY5Y cells, in order to analyse the effects of overexpression of the mutant ataxin-7 protein. The cells readily formed anti-ataxin-7 positive, fibrillar inclusions and small, nuclear electron dense structures. We have compared the inclusions in cells expressing mutant ataxin-7 and in human SCA7 brain tissue. There were consistent signs of ongoing abnormal protein folding, including the recruitment of heat-shock proteins and proteasome subunits. Occasionally, sequestered transcription factors were found. Activated caspase-3 was recruited into the inclusions in both the cell models and human SCA7 brain and its expression was upregulated in cortical neurones, suggesting that it may play a role in the disease process. Finally, on the ultrastructural level, there were signs of autophagy and nuclear indentations, indicative of a major stress response in cells expressing mutant ataxin-7.

SCA8 repeat expansions in ataxia: a controversial association

The observation of large SCA8 alleles in healthy control subjects and nonataxic patients, together with a lack of segregation of the expanded repeat with ataxia in several families, has raised questions about the pathogenic role of the SCA8 expansion. The authors found allele sizes within the proposed pathogenic range in three patients with ataxia of unknown etiology, in two individuals from pedigrees with either SCA2 or Friedreich's ataxia, and in two patients with Alzheimer's disease. Sizing of SCA8 alleles should not be a routine diagnostic test until its etiologic role is clarified and the pathogenic threshold is determined.

Restless legs syndrome in spinocerebellar ataxia types 1, 2, and 3

To identify the prevalence and determinants of restless legs syndrome (RLS) in spinocerebellar ataxia (SCA) we studied 58 patients with a molecular diagnosis of SCA1, SCA2 and SCA3. Data on the symptoms of RLS were collected by a standardized questionnaire, and RLS was diagnosed when patients met the four minimal criteria of the syndrome as recently defined by an international study group. In addition, we studied the relationship between RLS and age, age at ataxia onset, CAG repeat length, and nerve conduction and evoked potentials data. RLS was significantly more frequent in SCA patients than in controls (28% vs. 10%). Age at RLS onset in SCA was 49.0 +/- 10.9 years. There were no significant differences in nerve conduction or evoked potentials between RLS and non-RLS SCA patients. The probability of developing RLS increased with age but not with CAG repeat length or higher age of ataxia onset. The data provide evidence that patients with SCA1, SCA2 and SCA3 are per se more susceptible to RLS than non-affected individuals. The probability of developing RLS is related principally to the period over which the CAG repeat mutation exerts its effect and not to CAG repeat length or age of ataxia onset.

Ophthalmological findings in patients with spinocerebellar ataxia type 1 are not correlated with neurological anticipation

BACKGROUND

Optic atrophy, attenuation of the oscillatory potentials (OPs) of the electroretinogram (ERG), and enlargement of corneal endothelial cells, have been reported in patients with spinocerebellar ataxia type 1 (SCA1). These patients have a trinucleotide repeat expansion in the SCA1 gene and show neurological anticipation. The purpose of this study was to determine whether the ophthalmological findings are correlated with the neurological disorders, and whether ophthalmological anticipation is present in patients with SCA1.

METHODS

The visual acuity, ERGs, and corneal endothelial cell density were examined in 14 patients whose DNA analysis revealed an expanded trinucleotide repeat in an allele of the SCA1 gene. The results of the tests were compared with the trinucleotide repeat number and the duration of the neuronal disease.

RESULTS

The neurological disorders in the patients showed anticipation. The negative correlation between the trinucleotide repeat number and the neurological disorder was statistically significant (P<0.0001). However, the correlations between trinucleotide repeat number and visual acuity, amplitude of OPs, and corneal endothelial cell density were not significant. Statistically significant correlations were found between the duration of the neuronal disease and the visual acuity, OPs, and corneal endothelial cell density (P<0.0001, P=0.0004, and P<0.0001, respectively). The ophthalmological disorders were prominent in patients who had neuronal disease for more than 10 years.

CONCLUSION

Unlike the neurological findings, the ophthalmological disorders in patients with SCA1 were not correlated with the trinucleotide repeat number of the SCA1 gene. The ophthalmological findings were most highly correlated with the duration of the neuronal disease.

SCA7 mouse models show selective stabilization of mutant ataxin-7 and similar cellular responses in different neuronal cell types

Accumulation of expanded polyglutamine proteins and selective pattern of neuronal loss are hallmarks of at least eight neurodegenerative disorders, including spinocerebellar ataxia type 7 (SCA7). We previously described SCA7 mice displaying neurodegeneration with progressive ataxin-7 accumulation in two cell types affected in the human pathology. We describe here a new transgenic model with a more widespread expression of mutant ataxin-7, including neuronal cell types unaffected in SCA7. In these mice a similar handling of mutant ataxin-7, including a cytoplasm to nucleus translocation and accumulation of N-terminal fragments, was observed in all neuronal populations studied. An extensive screen for chaperones, proteasomal subunits and transcription factors sequestered in nuclear inclusions (NIs) disclosed no pattern unique to neurons undergoing degeneration in SCA7. In particular, we found that the mouse TAF(II)30 subunit of the TFIID initiation complex is markedly accumulated in NIs, even though this protein does not contain a polyglutamine stretch. A striking discrepancy between mRNA and ataxin-7 levels in transgenic mice expressing the wild-type protein but not in those expressing the mutant one, indicates a selective stabilization of mutant ataxin-7, both in this model and the P7E/N model described previously. These mice therefore provide in vivo evidence that the polyglutamine expansion mutation can stabilize its target protein.

[Type 8 spinocerebellar ataxia. A report of a family]

INTRODUCTION

Over the past decade, from the genetic point of view, several of the entities included in the group of hereditary ataxias have been identified. We report a Spanish family with type 8 spinocerebellar ataxia (SCA8), one of the most recent hereditary ataxias to be described from the clinical and genetic points of view.

CLINICAL CASE

A 59 year old woman consulted us complaining of progressive dysarthria and unsteady gait. The only abnormal findings on neurological examination were those of cerebellar involvement. The patient s mother had a similar condition, characterized by difficulty in speaking which started when she was 62 years old and progressed to anarthria. Cranial magnetic resonance showed the presence of cerebellar atrophy with no signs of atrophy of the brainstem. On electromyographic studies there were no signs of neuropathy. Visual, auditory and sensory evoked potentials were normal. Genetic studies showed expansion of trinucleotide CTG (112 repetitions in the expanded allele and 28 repetitions in the normal allele) on the gene responsible for SCA8.

CONCLUSION

SCA8 should be included in the differential diagnosis of progressive cerebellar syndromes, especially when changes in speech predominate with regard to other cerebellar signs.

Clinical trial of acetazolamide in SCA6, with assessment using the Ataxia Rating Scale and body stabilometry

OBJECTIVE

To investigate the effect of acetazolamide on spinocerebellar ataxia type 6 (SCA6).

METHODS

Acetazolamide (250-500 mg/day) was administered orally for 88 weeks to 6 patients with SCA6, and its effect was quantitatively monitored using the Ataxia Rating Scale (ARS) and body sway analysis by stabilometry.

RESULTS

During administration of acetazolamide, the ARS score and the amplitude of body sway were significantly reduced compared with before administration. However, the response became weaker after 1 year of treatment.

CONCLUSION

Although this was an open trial, the results suggested that acetazolamide can temporarily reduce the severity of symptoms during the progression of SCA6.

Creatine-supplemented diet extends Purkinje cell survival in spinocerebellar ataxia type 1 transgenic mice but does not prevent the ataxic phenotype

It is not known why expression of a protein with an expanded polyglutamine region is pathogenic in spinocerebellar ataxia, Huntington's disease and several other neurodegenerative diseases. Dietary supplementation with creatine improves survival and motor performance and delays neuronal atrophy in the R6/2 transgenic mouse model of Huntington's disease. These effects may be due to improved energy and calcium homeostasis, enhanced presynaptic glutamate uptake, or protection of mitochondria from the mitochondrial permeability transition. We tested the effects of a 2% creatine-supplemented diet and treatment with taurine-conjugated ursodeoxycholic acid, a bile constituent that can inhibit the mitochondrial permeability transition, on ataxia and Purkinje cell survival in a transgenic model of spinocerebellar ataxia type 1. After 24 weeks, transgenic mice on the 2% creatine diet had cerebellar phosphocreatine levels that were 72.5% of wildtype controls, compared to 26.8% in transgenic mice fed a control diet. The creatine diet resulted in maintenance of Purkinje cell numbers in these transgenic mice at levels comparable to wildtype controls, while transgenic mice fed a control diet lost over 25% of their Purkinje cell population. Nevertheless, the ataxic phenotype was neither improved nor delayed. Repeated s.c. ursodeoxycholic acid injections markedly elevated ursodeoxycholic acid levels in the brain without adverse effects, but provided no improvement in phenotype or cell survival in spinocerebellar ataxia type 1 mice. These results demonstrate that preserving neurons from degeneration is insufficient to prevent a behavioral phenotype in this transgenic model of polyglutamine disease. In addition, we suggest that the means by which creatine mitigates against the neurodegenerative effects of an ataxin-1 protein containing an expanded polyglutamine region is through mechanisms other than stabilization of mitochondrial membranes.

Choreiform movements in spinocerebellar ataxia type 1

We describe the unusual case of a 51-year-old woman with spinocerebellar ataxia type 1 (SCA1) who showed choreiform movements in addition to cerebellar ataxia. To date, extrapyramidal signs including involuntary movements have been rarely reported in SCA1. Surface electromyogram in our patient revealed grouped discharges whose duration was longer than that of chorea observed in HD, indicating that the involuntary movements represented choreoathetosis rather than pure chorea. These choreiform movements have not been seen in non-hereditary spinocerebellar ataxia. Therefore, if "sporadic" cases of cerebellar ataxia show such movements, the possibility of genetic origin of the ataxia is high and a surveillance of various forms of hereditary spinocerebellar ataxia including SCA1 is required.

Slowing of voluntary and involuntary saccades: an early sign in spinocerebellar ataxia type 7

We describe quantitative oculomotor findings in a patient with subclinical spinocerebellar ataxia type 7 (SCA7) and a borderline mutation of 38 CAG repeats and her daughter with SCA7 and 46 repeats. Both subjects demonstrated significant slowing of voluntary and involuntary saccades, but retinal examination was normal. Smooth pursuit and fixation suppression of VOR were mildly impaired. Slow saccades may be the earliest neurologic finding even in asymptomatic SCA7 patients with normal ocular fundi. The SCA7 mutation probably has an early impact on brainstem fast eye movement centers.

Meiotic instability of the CAG repeats in the SCA6/CACNA1A gene in two Japanese SCA6 families

Intergenerational stability of the CAG repeat number has been considered to be a specific molecular feature of SCA6 compared with other CAG repeat diseases. Nevertheless, we showed meiotic instability of the CAG repeats in the SCA6/CACNL1A gene in two Japanese SCA6 families, including de novo expansion. In one family, the CAG20 allele expanded to the CAG26 one during paternal transmission, and in the other family, the CAG19 allele expanded to the CAG20 one during maternal transmission. Although it is controversial as to whether the CAG20 allele is pathological or not, this is the first case of haplotype analysis-proven de novo expansion in SCA6, confirming the derivation of an expanded allele from one normal allele. We should carefully follow up the individuals carrying the CAG20 allele in our family who show normal neurological and radiological findings at present.

Case of spinocerebellar ataxia type 1 showing high intensity lesions in the frontal white matter on T2-weighted magnetic resonance images

We report a case of genetically confirmed spinocerebellar ataxia type 1 (SCA1) in which magnetic resonance imaging (MRI) demonstrated a high signal intensity on T2-weighted images in the white matter of the frontal lobes. The patient was a 60-year-old Japanese man who complained of gait instability and speech difficulties. He was diagnosed as having spinocerebellar ataxia at the age of 46. A CAG repeat number of the patient was 48/26. Brain MRI showed marked atrophy of the cerebellum and brain stem. The high-signal intensity lesions on T2-weighted MRI in the white matter of the frontal lobes were evident in the periventricular regions. Such MRI abnormalities have not been described in SCA1 previously.

[Hereditary ataxias in Cuba. Historical, epidemiological, clinical, electrophysiological and quantitative neurological features]

OBJECTIVE

This review has been designed to describe the main clinical, epidemiological, electrophysiological, molecular and quantitative neurological characteristics in SCA2.

DEVELOPMENT

The prevalence rate of patients with ataxia in Holguin province is 43 per 100,000 inhabitants. The prevalence of family members at risk of having this disorder is 159.33 per 100 thousand in this province. The main neurophysiological abnormality observed was reduction in the amplitudes of sensory potentials. These alterations are the expression of a predominantly axonal peripheral lesion with signs of myelin damage. Techniques of quantitative neurology were developed for evaluation of the main disorders of coordination such as asymmetry and adiadochokinesis. In Cuba 125 families have hereditary ataxia, 772 patients and 8 to 10,000 family members are at risk of developing this condition. Seventy percent of the patients with ataxia are concentrated in Holguin province. The most severely affected towns are Báguanos (a rate of 129.20 per 100,000 inhabitants), Holguin (71.85 per 100,000) and Cacocúm (69.83 per 100,000). These are the highest rates in the world.

CONCLUSIONS

The commonest molecular form in Cuba is the SCA2, observed in 120 families. Clinically it is characterized by a cerebellar syndrome associated with disorders of eye movements and osteotendinous reflexes.