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.

Spinocerebellar ataxia type 1--modeling the pathogenesis of a polyglutamine neurodegenerative disorder in transgenic mice

Spinocerebellar ataxia type 1 (SCA1) is one of a group of dominantly inherited neurodegenerative diseases caused by a mutant expansion of a polyglutamine-repeated sequence within the affected gene. One of the major cell types affected by the gene (ataxin-1) mutation in SCA1 is the cerebellar Purkinje cell. Targeted expression of mutant ataxin-1 in Purkinje cells of transgenic mice produces an ataxic phenotype with pathological similarities to the human disease. Other transgenic experiments using altered forms of mutant ataxin-1 have shown that nuclear localization of the mutant protein is necessary for pathogenesis and that nuclear aggregates of ubiquitinated mutant protein, while a feature of SCA1 and other polyglutamine diseases, are not a requirement for pathogenesis in transgenic models of SCA1. Present and future generations of transgenic mouse models of SCA1 will be valuable tools to further address mechanisms of pathogenesis in polyglutamine-related disorders.

Relationship between ataxin-1 nuclear inclusions and Purkinje cell specific proteins in SCA-1 transgenic mice

Spinocerebellar ataxia-1 (SCA-1), like other polyglutamine diseases, is associated with aggregation of mutant protein ataxin-1 in the nuclei of susceptible neurons. The role of ataxin-1 aggregates in the pathogenesis of susceptible neurons, especially cerebellar Purkinje cells, is unknown. The present study was initiated to determine the temporal relationship between ataxin-1 aggregation and the sequence of specific biochemical changes in Purkinje cells in SCA-1 transgenic mice (TM). Earlier, we demonstrated that SCA-1 TM with no Purkinje cell loss and no alterations in home cage behavior show decreased expression of calcium-binding proteins calbindin-D28k (CaB) and parvalbumin (PV) in Purkinje cells. To determine if increased expression of mutant ataxin-1 in TM is also associated with earlier biochemical changes in Purkinje cells, both heterozygous and homozygous (B05 line of SCA-1) TM were used. The age of onset of ataxia in SCA-1 TM was at 12 weeks in heterozygotes and 6 weeks in homozygotes. In 6 week old heterozygous TM, Western blot analysis of growth associated protein 43 (GAP-43) and synaptophysin revealed no significant alterations as compared with the age-matched nontransgenic mice (nTM), whereas CaB was significantly reduced. beta-III-Tubulin was used as a specific Purkinje cell marker protein, immunohistochemical localization showed strong beta-III-tubulin immunoreactivity (IR) in Purkinje cells in 6 week old heterozygous TM, whereas CaB and PV IR were markedly reduced in the same neurons (double immunofluorescence staining). Most Purkinje cells from heterozygous (12 weeks old) and homozygous (6 weeks old) TM contained ataxin-1 nuclear inclusions (NIs). Cells with and without visible NIs revealed reduced PV and CaB IR; however, the changes were overtly more severe in cells with visible NIs. In contrast, the same cells were strongly immunoreactive to beta-III-tubulin. CaB, which is also present in the nucleus, colocalized with ataxin-1 and ubiquitin positive NIs. Further, RT-PCR analysis of CaB mRNA in the cerebellum in 6 week old heterozygous TM demonstrated a significant decrease in mRNA in comparison with the aged-matched nTM. These data suggest that there are selective alterations in the expression of CaB and PV in Purkinje cells which possibly occur earlier than ataxin-1 aggregation. Further, we speculate that ataxin-1 aggregates may not be toxic in general; however, they may deplete specific proteins essential for Purkinje cell viability in SCA-1 TM.

Abnormal activity of membrane phospholipid synthetic enzymes in the brain of patients with Friedreich's ataxia and spinocerebellar atrophy type-1

Much evidence, derived from biochemical studies of both blood and autopsied brain, has suggested that phospholipid metabolism is abnormal in patients with Friedreich's ataxia (FA), a disorder characterized by severe neuronal loss in the spinal cord and lower brain stem with no, or only modest, damage in other brain regions. To establish the cause of our recent finding of reduced brain levels of phospholipids in FA, we assayed activities of 10 phospholipid-metabolizing enzymes in the autopsied cerebellar cortex of patients with the disorder and, for comparison, in a group of patients with spinocerebellar ataxia type 1 (SCA-1), a disease characterized, unlike FA, by marked neuronal loss in the cerebellar cortex. Enzyme activities were also measured in four brain areas which are relatively unaffected morphologically in both FA and SCA-1. We found that ethanolamine kinase activity was increased in multiple brain regions of patients with FA (increased 31%-137%) and, more modestly, in SCA-1 (increased 39%-60%), suggesting a nonspecific enhancement of phosphoethanolamine production in both disorders. In contrast, the activity of phosphoethanolamine cytidylyltransferase (PECT), the rate-limiting enzyme of phosphatidylethanolamine synthesis, was significantly and markedly decreased by 35%-78% in the cerebellar, frontal, and occipital cortices of patients with FA but was normal in SCA-1. Reduced PECT activity in FA may explain the lower brain levels of phosphatidylethanolamine in the disorder. Moreover, because decreased PECT activity in FA occurs in brain regions having no, or only modest, morphologic damage, this may represent a systemic change consequent to the frataxin gene defect. Our data also suggest that therapeutic intervention in FA designed to increase synthesis of membrane phospholipids may warrant further investigation.

Molecular and clinical analyses of spinocerebellar ataxia type 8 in Japan

OBJECTIVE

To clarify the molecular and clinical features of the newly identified spinocerebellar ataxia type 8 (SCA8).

METHODS

We analyzed the CTG repeat region of the SCA8 gene in a series of Japanese patients with cerebellar ataxia. We also investigated the frequency of the CTG repeat length in Japanese normal elderly subjects older than age 79. Morphometric measurements on the cerebral MRI were compared between patients with SCA8 and SCA6.

RESULTS

The number of the combined CTA/CTG repeats of six affected SCA8 alleles was 106.3+/-24.4 (mean +/- SD) ranging from 89 to 155 and that of normal elderly subjects was 24.3+/-4.4 (n = 104 alleles) ranging from 15 to 34. The mean age at onset of the SCA8 cases was 53.8+/-19.7 years, with a range from 20 to 73 years. One father and daughter from an SCA8 family showed remarkable paternal anticipation. The number increase from father to daughter was + 16 CTG repeats, with a 31-year acceleration of onset. The six identified SCA8 patients were clinically characterized by high frequencies of incoordination of trunk and limbs, ataxic dysarthria, impaired smooth pursuit, and horizontal nystagmus, and the MRI showed significant atrophy of the cerebellar vermis and hemispheres compared with that of normal controls. There was no significant difference between SCA8 and SCA6 on the morphometric MRI study.

CONCLUSIONS

The CTG repeat expansions in the SCA8 alleles were much greater than the range of repeats in normal elderly subjects. The SCA8 phenotype manifested by cerebellar symptoms and atrophy corresponded to features of the autosomal dominant cerebellar ataxia type III (ADCA III).

An interrupted 34-CAG repeat SCA-2 allele in patients with sporadic spinocerebellar ataxia

In spinocerebellar ataxia type 2 (SCA-2), a difference of three CAG repeats distinguishes normal alleles (14 to 31 repeats) from pathogenic alleles (34 to 57 repeats). All sequenced pathogenic alleles have a pure CAG repeat structure, whereas interrupted repeats have been seen exclusively in normal alleles. The authors present two patients with sporadic SCA with an interrupted 34-CAG repeat allele, (CAG)24(CAA)(CAG)9, who showed a phenotype compatible with SCA-2. The interrupted allele coding for a 34 pure polyglutamine tract may cause the SCA phenotype.

Clinical and molecular advances in autosomal dominant cerebellar ataxias: from genotype to phenotype and physiopathology

Major advances have been made in the understanding of autosomal dominant cerebellar ataxias since genetic markers came into use in the 1980s. The subsequent mapping of nine genes, six of which have been identified, involved in this clinically diverse group of disorders highlighted their great genetic heterogeneity. Evidence is now accumulating that, except for SCA8, the same molecular and physiopathological processes underlie these diseases and other neurodegenerative disorders sharing the same mutational basis, the expansion of a (CAG)n-polyglutamine coding sequence. The clinical overlap among the different genetic entities makes prediction of the molecular origin impossible in a single patient so that molecular characterisation is necessary. However, extended clinical and neuropathological comparisons have shown that each genetic entity has a characteristic constellation of signs and symptoms that are related to CAG repeat size and disease duration. The combined genetic and clinical information form the basis of a new classification that will aid better understanding of disease evolution, assure follow up and permit genetic counselling by the clinician.

Clinical and MRI findings in spinocerebellar ataxia type 5

Spinocerebellar ataxia type 5 (SCA5), one of the genetically heterogeneous autosomal dominant cerebellar ataxias, was assigned to chromosome 11 in a single family descending from the grandparents of President Abraham Lincoln. We report a second, apparently unrelated, SCA5 family of French origin. The overall clinical picture was a slowly progressive cerebellar syndrome beginning mostly in the third decade (27+/-10 years, range 14 to 40). MRI showed a marked global cerebellar atrophy similar to SCA6.

Neuronal intranuclear inclusions in spinocerebellar ataxia type 2: triple-labeling immunofluorescent study

Spinocerebellar ataxia type 2 (SCA2) is associated with an expansion of CAG/polyglutamine-repeat of a gene of unknown function. We performed an immunohistochemical study to identify the immunolocalization of the disease protein ataxin-2 in normal and SCA2 patients. Although normal and expanded ataxin-2 were ubiquitously localized to the cytoplasm of neurons, ubiquitinated intranuclear inclusions were observed selectively in 1-2% of neurons of affected brain regions except the cerebellum. Triple-labeling immunofluorescence revealed that ataxin-2, expanded polyglutamine and ubiquitin were colocalized to these neuronal intranuclear inclusions (NIs), indicating that SCA2 shares morphological characteristics common to other neurological disorders associated with an expansion of CAG/polyglutamine-repeat. Lack of NIs in the cerebellar lesion, however, suggests the discrepancy between formation of NIs and neuronal degeneration in SCA2.

Neuropathology of Joubert syndrome

Very little documentation of the neuropathologic changes in Joubert syndrome exists. This paper presents a detailed postmortem neuropathologic study of a clinically and radiographically well-documented case of Joubert syndrome. In addition to aplasia of the cerebellar vermis and fragmentation of the dentate nuclei, there was marked dysplasia of structures at the pontomesencephalic junction and caudal medulla. There was abnormal decussation of the superior cerebellar peduncles and an enlarged iter (rostral 4th ventricle) with elongated tegmental nuclei (including the locus coeruleus). Neurons of the basis pontis and reticular formation appeared reduced. Extensive malformations of the medulla included hypoplasia of the inferior olivary nuclei, solitary nuclei and tracts, and the nucleus and spinal tracts of trigeminal nerve (cranial nerve V). Even more striking was dysplasia of the caudal medulla at the cervicomedullary junction, which was characterized by the absence of a posterior median sulcus, neuronal swelling and axonal spheroids in the region of malformed nuclei gracilis and cuneatus, and absence of pyramidal decussation. This study suggests that, in addition to vermal agenesis, Joubert syndrome is characterized by malformation of multiple brainstem structures. The latter could explain certain clinical features of the syndrome, including episodic hyperpnea and oculomotor apraxia.

Spinocerebellar ataxia type 7 (SCA7) - correlations between phenotype and genotype in one large Belgian family

Spinocerebellar ataxia type 7 (SCA7), in which the degenerative process also affect the retina, belongs to the category of the autosomal dominant cerebellar ataxia type II (ADCA II). We have described the neuropathology of this condition [Martin JJ, Van Regemorter N, Krols L, Brucher JM, de Barsy T, Szliwowski H, et al. On an autosomal dominant form of retino-cerebellar degeneration: an autopsy study of five patients in one family. Acta Neuropathol (Berl) 1994;88:277-286] in a very large Belgian family (CA-1). We have observed anticipation in the age of onset with increasing severity of the symptoms in consecutive generations. The SCA7 gene was mapped to chromosome 3p12-13 [David G, Abbas N, Stevanin G, Dürr A, Yvert G, Cancel G, et al. Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion. Nat Genet 1997;17:65-70; Del-Favero J, Krols L, Michalik A, Theuns J, Löfgren A, Goossens D, et al. Molecular genetic analysis of autosomal dominant cerebellar ataxia with retinal degeneration (ADCA type II) caused by CAG triplet repeat expansion. Hum Mol Genet 1998;7:177-186], and the gene identified. SCA7 is a new gene of unknown function that contains an expansion of CAG repeats in SCA7 patients. During the procedure of positional cloning, we examined 26 patients belonging to the CA-1 family and realized, in some of them, an ophthalmologic examination and neuro-imaging of the brain. This allowed us to differentiate four groups: (1) asymptomatic young carriers with 38 to 43 CAG repeats; (2) mildly symptomatic, older patients with 38-41 CAG repeats; (3) patients with the full-blown picture of SCA7 and age of onset during adolescence, with 54-55 CAG repeats; (4) children with early onset and rapid fatal course of the disease who had over 55 CAG repeats. We were able to draw correlations between clinical phenotype, age at onset and CAG repeat number and to make predictions, to some extent, as to the clinical course of the disease in new patients.