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.

Distribution of ataxin-7 in normal human brain and retina

Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disease caused by the expansion of a CAG repeat encoding a polyglutamine tract in the protein ataxin-7. We developed antibodies directed against two different parts of the ataxin-7 protein and studied its distribution in brain and peripheral tissue from healthy subjects. Normal ataxin-7 was widely expressed in brain, retina and peripheral tissues, including striated muscle, testis and thyroid gland. In the brain, expression of ataxin-7 was not limited to areas in which neurones degenerate, and the level of expression was not related to the severity of neuronal loss. Immunoreactivity was low in some vulnerable populations of neurones, such as Purkinje cells. In neurones, ataxin-7 was found in the cell bodies and in processes. Nuclear labelling was also observed in some neurones, but was not related to the distribution of intranuclear inclusions observed in an SCA7 patient. In this patient, the proportion of neurones with nuclear labelling was higher, on average, in regions with neuronal loss. Double immunolabelling coupled with confocal microscopy showed that ataxin-7 colocalized with BiP, a marker of the endoplasmic reticulum, but not with markers of mitochondria or the trans-Golgi network.

Identification of genes that modify ataxin-1-induced neurodegeneration

A growing number of human neurodegenerative diseases result from the expansion of a glutamine repeat in the protein that causes the disease. Spinocerebellar ataxia type 1 (SCA1) is one such disease-caused by expansion of a polyglutamine tract in the protein ataxin-1. To elucidate the genetic pathways and molecular mechanisms underlying neuronal degeneration in this group of diseases, we have created a model system for SCA1 by expressing the full-length human SCA1 gene in Drosophila. Here we show that high levels of wild-type ataxin-1 can cause degenerative phenotypes similar to those caused by the expanded protein. We conducted genetic screens to identify genes that modify SCA1-induced neurodegeneration. Several modifiers highlight the role of protein folding and protein clearance in the development of SCA1. Furthermore, new mechanisms of polyglutamine pathogenesis were revealed by the discovery of modifiers that are involved in RNA processing, transcriptional regulation and cellular detoxification. These findings may be relevant to the treatment of polyglutamine diseases and, perhaps, to other neurodegenerative diseases, such as Alzheimer's and Parkinson's disease.

The spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are diseases characterized by the progressive degeneration and subsequent loss of neurons accompanied by reactive gliosis, degeneration of fibers from the deteriorating neurons, and clinical symptoms reflecting the locations of the lost neurons. The degenerative changes affect specific neuronal groups while others remain preserved, and these diseases can therefore be viewed as system degenerations. The SCAs result from either genetically transmitted diseases with dominant inheritance or unknown causes with sporadic occurrence. Most of these disorders affect the cerebellum and its pathways, resulting in progressive deterioration of cerebellar function manifested by increasing unsteadiness of gait, incoordination of limb movements with impairment of skilled movements such as handwriting, and a distinctive dysarthria. Other neuronal systems are affected in some of these disorders, notably the corticospinal pathway, basal ganglia, and autonomic nuclei of the brain stem and spinal cord.

Large expansion of the ATTCT pentanucleotide repeat in spinocerebellar ataxia type 10

Spinocerebellar ataxia type 10 (SCA10; MIM 603516; refs 1,2) is an autosomal dominant disorder characterized by cerebellar ataxia and seizures. The gene SCA10 maps to a 3.8-cM interval on human chromosome 22q13-qter (refs 1,2). Because several other SCA subtypes show trinucleotide repeat expansions, we examined microsatellites in this region. We found an expansion of a pentanucleotide (ATTCT) repeat in intron 9 of SCA10 in all patients in five Mexican SCA10 families. There was an inverse correlation between the expansion size, up to 22.5 kb larger than the normal allele, and the age of onset (r2=0.34, P=0.018). Analysis of 562 chromosomes from unaffected individuals of various ethnic origins (including 242 chromosomes from Mexican persons) showed a range of 10 to 22 ATTCT repeats with no evidence of expansions. Our data indicate that the new SCA10 intronic ATTCT pentanucleotide repeat in SCA10 patients is unstable and represents the largest microsatellite expansion found so far in the human genome.

Morphological Purkinje cell changes in spinocerebellar ataxia type 6

Spinocerebellar ataxia type 6 (SCA6) was recently identified as a form of autosomal dominant spinocerebellar ataxia associated with a small CAG repeat expansion of the gene encoding an alpha 1 A-voltage-dependent calcium channel gene subunit on chromosome 19p13. In this study 50-microm-thick sections of cerebellar tissue from one patient with SCA6 were subjected to free-floating immunohistochemical staining with calbindin-D and parvalbumin antibodies. Severe loss of Purkinje cells was found, particularly in the vermis, and various morphological changes in Purkinje cells and their dendritic arborizations were demonstrated. Many of the remaining Purkinje cells were found to have heterotopic, irregularly shaped nuclei, an unclear cytoplasmic membrane outline, and somatic sprouts. Increased numbers of spine-like protrusions from swelling dendritic arborizations were found in the molecular layer. The axonal arrangement was disordered, and many torpedos were found in the granular layer and white matters. These morphological changes are completely different from those observed in paraneoplastic cerebellar degeneration (PCD) and multiple system atrophy (MSA) and are considered to be related to the genetic abnormality that causes abnormal development of Purkinje cells.

Spinocerebellar ataxia type 8: clinical features in a large family

OBJECTIVE

To compare the clinical and genetic features of the seven-generation family (MN-A) used to define the spinocerebellar ataxia 8 (SCA8) locus.

BACKGROUND

The authors recently described an untranslated CTG expansion that causes a novel form of SCA (SCA8) characterized by reduced penetrance and complex patterns of repeat instability.

METHODS

Clinical and molecular features of 82 members of the MN-A family were evaluated by neurologic examination, quantitative dexterity testing, and, in some individuals, MRI and sperm analyses.

RESULTS

SCA8 is a slowly progressive, predominantly cerebellar ataxia with marked cerebellar atrophy, affecting gait, swallowing, speech, and limb and eye movements. CTG tracts are longer in affected (mean = 116 CTG repeats) than in unaffected expansion carriers (mean = 90, p < 10-8). Quantitative dexterity testing did not detect even subtle signs of ataxia in unaffected expansion carriers. Surprisingly, all 21 affected MN-A family members inherited an expansion from their mothers. The maternal penetrance bias is consistent with maternal repeat expansions yielding alleles above the pathogenic threshold in the family (>107 CTG) and paternal contractions resulting in shorter alleles. Consistent with the reduced penetrance of paternal transmissions, CTG tracts in all or nearly all sperm (84 to 99) are significantly shorter than in the blood (116) of an affected man.

CONCLUSIONS

The biologic relationship between repeat length and ataxia indicates that the CTG repeat is directly involved in SCA8 pathogenesis. Diagnostic testing and genetic counseling are complicated by the reduced penetrance, which often makes the inheritance appear recessive or sporadic, and by interfamilial differences in the length of a stable (CTA)n tract preceding the CTG repeat.

The ins and outs of a polyglutamine neurodegenerative disease: spinocerebellar ataxia type 1 (SCA1)

Polyglutamine neurodegenerative disorders are characterized by the expansion of a glutamine tract within the mutant disease-causing protein. Expression of the mutant protein induces a progressive loss of neuronal function and the subsequent neurodegeneration of a set of neurons characteristic to each disease. Spinocerebellar ataxia type 1 (SCA1) is one polyglutamine disease where various experimental model systems, in particular transgenic mice, have been utilized to dissect the molecular and cellular events important for disease. This review summarizes these findings and places them in a context of potential future research directions.

Pontine atrophy in spinocerebellar ataxia type 6

To investigate the clinical range of spinocerebellar ataxia type 6 (SCA6), we screened CAG repeat expansion in the voltage-dependent alpha 1A calcium channel gene (CACNL1A4) in 71 ataxic patients in 60 families; 54 patients in 43 families with hereditary ataxia and 17 sporadic patients. Thirteen patients with SCA6 were detected to have elongated CAG in CACNL1A4. Of these, 7 patients had been diagnosed as having hereditary cerebellar cortical atrophy, and 6 patients had been found to have sporadic occurrence. One patient showed distinct pontine atrophy with prominent horizontal or oblique gaze nystagmus which is an unusual feature in sporadic olivopontocerebellar atrophy. For the efficient screening of SCA6, we would propose testing CAG repeat expansion in CACNL1A4, in patients with one of two markers: (1) horizontal or oblique gaze nystagmus without other eye movement disorders, (2) pure cerebellar atrophy, even if occurrence is sporadic. We should note that the pontine atrophy could also be caused by CAG repeat expansion in CACNL1A4.

Electrophysiological studies in spinocerebellar ataxia type 6: a statistical approach

In spinocerebellar ataxia type 6 (SCA6), the cerebellum is predominantly affected, but several electrophysiological studies have revealed subclinical disorders other than cerebellar lesions. We conducted statistical analyses by comparing SCA6 patients and age-matched normal controls to asses whether electrophysiological abnormalities are directly associated with SCA6 because late onset of SCA6 may involve senile changes. We performed brain stem auditory evoked potentials (BAEP), visual evoked potentials, somatosensory evoked potentials and nerve conduction studies in 10 SCA6 patients. The BAEP latencies of wave I was prolonged and compound muscle action potentials of peroneal nerve and sensory nerve action potentials of sural nerve reduced in SCA6 patients. Our results suggest an existence of peripheral impairment in the auditory pathway and axonal neuropathy in SCA6.