Pontine atrophy precedes cerebellar degeneration in spinocerebellar ataxia 7: MRI-based volumetric analysis

BACKGROUND AND OBJECTIVE

Spinocerebellar ataxia 7 (SCA7) is characterised by cerebellar ataxia and visual loss. The aim of the present study was to elucidate the magnetic resonance imaging (MRI) findings characteristic of patients with SCA7.

METHODS

Twenty patients with SCA (eight SCA3, three SCA6, and nine SCA7) and 20 control subjects underwent an MRI-based volumetric analysis.

RESULTS

The pontine volume in patients with SCA7 was decreased by a greater amount than in patients with other types of SCA (p<0.01), whereas the cerebellar volume was not different from that in other types of SCA (p>0.05). Pontine atrophy was a consistent finding in all patients with SCA7 regardless of the degree of cerebellar atrophy or the severity or duration of illness. In contrast, cerebellar atrophy was not found in those with a short duration of illness or mild ataxia, but became prominent as the severity and duration of illness progressed.

CONCLUSIONS

Our study suggests that neurodegeneration is ongoing during the life of individuals with SCA7, and that the primary pathology in these individuals involves the brainstem rather than the cerebellum. In addition, pontine atrophy is a prominent, consistent finding in SCA7, and may help in establishing the clinical diagnosis of SCA7.

Cognitive impairments in cerebellar degeneration: a comparison with Huntington's disease

To determine the specificity of cognitive impairments in patients with cerebellar degeneration (CD), the neuropsychological test performance of 31 CD patients was compared to that of 21 patients with Huntington's disease (HD) and 29 normal adults. The CD and HD groups did not differ in age, education, or duration of illness, and their overall severity on a quantified neurological examination was similar. Fifteen neuropsychological test variables were reduced to five underlying domains: motor, verbal, spatial, memory, and executive functioning. The CD patients had their greatest impairment in the executive domain and their least in the memory domain. In contrast, the HD patients had very substantial spatial deficits and significant memory impairment, in addition to executive dysfunction. The findings indicate that 1) the cognitive impairment in CD is not as severe as in HD, and 2) the pattern of deficits in CD, while consistent with a subcortical dementia, differs in important ways from that in HD. These differences may reflect the involvement of the cerebellar dentate nucleus and the striatal nuclei in separate "loops" or closed circuits, linking them with specific areas of cerebral neocortex.

Mutation in the catalytic domain of protein kinase C gamma and extension of the phenotype associated with spinocerebellar ataxia type 14

BACKGROUND

Autosomal dominant cerebellar ataxias comprise a clinically, neuropathologically, and genetically heterogeneous group of neurodegenerative disorders. The vast majority of cases are caused by trinucleotide or pentanucleotide repeat expansions in 9 different genes. Spinocerebellar ataxia type 14 (SCA14) is a relatively pure form of autosomal dominant cerebellar ataxia mapped to chromosome 19q and caused by missense mutations in the gene encoding protein kinase C gamma (PRKCG), which are all located in the regulatory domain.

OBJECTIVES

To identify new SCA14 families and to describe the associated phenotype.

METHODS

We describe a new SCA14 family of French ancestry with 14 patients and 4 probably affected individuals. Linkage to the SCA14 locus was evaluated according to standard procedures using 5 markers covering the SCA14 candidate interval. All 18 exons of the PRKCG gene and splice junctions were screened with direct sequencing in the index patient.

RESULTS

Linkage to the SCA14 locus was established with lod scores greater than 3 in the interval between DNA segments D19S571 and D19S926. Direct sequencing of the PRKCG gene revealed a T-to-C transition in exon 18 responsible for a novel missense mutation, F643L, which mapped to a highly conserved amino acid of the catalytic domain of protein kinase C gamma. The mutation showed complete segregation with the disease phenotype, was present in all affected and probably affected individuals, and was not observed on 410 control chromosomes from healthy white subjects. Age at onset, assessed in 14 affected individuals, was broader than in previous reports and ranged from childhood to age 60 years. All affected patients had slowly progressive cerebellar ataxia frequently associated with brisk reflexes. Cognitive impairment was also a striking feature in this family and has not been reported previously. Interestingly, there was no axial myoclonus as reported in a Japanese SCA14 family, but electrophysiological recordings in a single patient showed diffuse myoclonus in the arms and legs.

CONCLUSIONS

We have identified a new SCA14 family with the first mutation (F643L) located in the catalytic domain of the enzyme. The wide range of ages at onset, the presence of myoclonus in the limbs, and the presence of cognitive impairment extend the phenotype associated with this genetic entity.

Behavioral disorder, dementia, ataxia, and rigidity in a large family with TATA box-binding protein mutation

BACKGROUND

Spinocerebellar ataxia type 17 is an autosomal dominant cerebellar ataxia caused by a CAG repeat expansion in the TATA box-binding protein gene. Ataxia is typically the first sign whereas behavioral symptoms occur later.

OBJECTIVE

To characterize the unusual phenotypic expression of a large spinocerebellar ataxia type 17 kindred.

DESIGN

Clinical, neuropathological, and molecular genetic characterization of a 4-generation family with 16 affected patients.

RESULTS

Behavioral symptoms and frontal impairment dominated the early stages preceding ataxia, rigidity, and dystonic movements. Neuropathological examination showed cortical, subcortical, and cerebellar atrophy. Purkinje cell loss and gliosis, pseudohypertrophic degeneration of the inferior olive, marked neuronal loss and gliosis in the caudate nucleus, and in the medial thalamic nuclei were salient features together with neuronal intranuclear inclusions stained with anti-TATA box-binding protein and antipolyglutamine antibodies. The disease was caused by a stable 52 CAG repeat expansion of the TATA box-binding protein gene, although there was apparent variability in the age of onset.

CONCLUSION

The characteristics of this family broaden the clinical picture of spinocerebellar ataxia type 17: initial presenile dementia with behavioral symptoms should be added to ataxia, rigidity, and dystonic movements, which are more commonly encountered.

Coexistence of familial transthyretin amyloidosis ATTR Val30Met and spinocerebellar ataxia type 1 in a Japanese family--a follow-up autopsy report

Three brothers in a family with Val30Met transthyretin (TTR) amyloid polyneuropathy (FAP) in Iiyama, Japan were studied pathologically. In this family, affected members have been reported to show typical clinical features of FAP, and some have been documented to exhibit symptoms and signs of central nervous system (CNS) involvement consisting of cerebellar ataxia and pyramidal tract signs. After the original description, this family was regarded as a unique phenotype of this form of FAP; however, subsequent molecular genetic studies revealed that some patients and asymptomatic members in the family had Val30Met TTR and/or spinocerebellar ataxia type 1 (SCA1) gene mutations. In this study, pathological examination of two patients with both FAP and CNS symptoms showed (1) TTR-immunoreactive leptomeningeal and cerebrovascular amyloid deposition compatible with Val30Met TTR FAP, and (2) neuronal loss and gliosis mainly in the Purkinje cell layer, spinocerebellar system, olivo-ponto-cerebellar system, dentato-rubral system, gracile nuclei, cuneate nuclei, and various nuclei of cranial nerves, accompanied by anti-expanded polyglutamine tract antibody positive neuronal intranuclear inclusions, all of which were compatible with the pathological findings of SCA1. On the other hand, the remaining patient with FAP symptoms only showed the former pathological finding alone. The present study demonstrates, at the pathological level, that Val30Met TTR FAP and SCA1 coexist in the same family members, and that the CNS dysfunction seen in the patients in this family is ascribable to SCA1 pathology but not to CNS amyloidosis.

Mapping of the SCA23 locus involved in autosomal dominant cerebellar ataxia to chromosome region 20p13-12.3

We report upon a Dutch autosomal dominant cerebellar ataxia (ADCA) family, clinically characterized by a late-onset (>40 years), slowly progressive, isolated spinocerebellar ataxia (SCA). Neuropathological examination in one affected subject showed neuronal loss in the Purkinje cell layer, dentate nuclei and inferior olives, thinning of cerebellopontine tracts, demyelination of posterior and lateral columns in the spinal cord, as well as ubiquitin-positive intranuclear inclusions in nigral neurons that were considered to be Marinesco bodies. Data obtained from the genome-wide linkage analysis revealed a maximal lod score of 3.46 at = 0.00 for marker D20S199. This new SCA locus, on chromosome region 20p13-p12.3, was designated SCA23 after approval by the HUGO Nomenclature Committee. Currently, candidate genes are being screened for mutations within the SCA23 interval. In addition to the recently identified SCA14, SCA19 and FGF14 families, SCA23 is yet another novel SCA locus in the Dutch ADCA population, which further defines the genetic heterogeneity of ADCA families in the Netherlands.

Brainstem neurodegeneration correlates with clinical dysfunction in SCA1 but not in SCA2. A quantitative volumetric, diffusion and proton spectroscopy MR study

Magnetic resonance (MR) techniques enable in vivo measurement of the atrophy of the brainstem and cerebellum in spinocerebellar ataxia type 1 (SCA1) and 2 (SCA2) patients, which is accompanied by a decrease in the concentration of N-acetyl aspartate (NAA) or of the NAA/creatine ratio in the pons and cerebellum. Mean diffusivity (D) is emerging as an additional sensitive and quantitative MR parameter to investigate brain diseases. In order to explore differences between the MR features of SCA1 and SCA2 and correlate the MR and clinical findings in the two conditions, we examined 16 SCA1 patients, 12 SCA2 patients and 20 healthy control subjects. The MR protocol included T1-weighted 3D gradient echo sequences, single-voxel proton spectroscopy of the right cerebellar hemisphere (dentate and peridentate region) and of the pons with a PRESS sequence and an external reference quantitation method, and (in nine patients with SCA1 and nine patients with SCA2) diffusion-weighted echo-planar images with reconstruction of the D maps. The patients were evaluated with the Inherited Ataxia Clinical Rating Scale (IACRS). Compared with control subjects, the SCA1 and SCA2 patients showed a decrease (P < 0.01) in the volume of the brainstem and cerebellum and in the concentration of NAA in the pons and cerebellar hemisphere, whereas D of the brainstem and cerebellum was increased. No significant difference was observed between the SCA1 and SCA2 patient groups. No correlation between cerebellar volume and dentate and peridentate NAA concentration was found in SCA1 or SCA2 patients. The volume of the brainstem, D of the brainstem and cerebellum and the concentration of NAA in the pons were correlated (P < 0.05) with the IACRS score in SCA1 but not in SCA2. This discrepancy is in line with the clinical observation that the clinical deficit has a later onset and faster progression in SCA1 and an earlier onset and slower progression in SCA2, and suggests that neurodegeneration of the brainstem is a comparatively more rapid process in SCA1. In conclusion, our study indicates that SCA1 and SCA2 substantially exhibit the same MR features. The correlation in SCA1 between clinical severity and quantitative volumetric, diffusion MRI and proton MR spectroscopy findings in the brainstem indicates that these measurements might be employed for longitudinal studies and hopefully as surrogate markers in future pharmacological trials of this condition.

RNAi suppresses polyglutamine-induced neurodegeneration in a model of spinocerebellar ataxia

The dominant polyglutamine expansion diseases, which include spinocerebellar ataxia type 1 (SCA1) and Huntington disease, are progressive, untreatable, neurodegenerative disorders. In inducible mouse models of SCA1 and Huntington disease, repression of mutant allele expression improves disease phenotypes. Thus, therapies designed to inhibit expression of the mutant gene would be beneficial. Here we evaluate the ability of RNA interference (RNAi) to inhibit polyglutamine-induced neurodegeneration caused by mutant ataxin-1 in a mouse model of SCA1. Upon intracerebellar injection, recombinant adeno-associated virus (AAV) vectors expressing short hairpin RNAs profoundly improved motor coordination, restored cerebellar morphology and resolved characteristic ataxin-1 inclusions in Purkinje cells of SCA1 mice. Our data demonstrate in vivo the potential use of RNAi as therapy for dominant neurodegenerative disease.

Spinocerebellar ataxia type 8: molecular genetic comparisons and haplotype analysis of 37 families with ataxia

We reported elsewhere that an untranslated CTG expansion causes the dominantly inherited neurodegenerative disorder spinocerebellar ataxia type 8 (SCA8). SCA8 shows a complex inheritance pattern with extremes of incomplete penetrance, in which often only one or two affected individuals are found in a given family. SCA8 expansions have also been found in control chromosomes, indicating that separate genetic or environmental factors increase disease penetrance among SCA8-expansion-carrying patients with ataxia. We describe the molecular genetic features and disease penetrance of 37 different families with SCA8 ataxia from the United States, Canada, Japan, and Mexico. Haplotype analysis using 17 STR markers spanning an approximately 1-Mb region was performed on the families with ataxia, on a group of expansion carriers in the general population, and on psychiatric patients, to clarify the genetic basis of the reduced penetrance and to investigate whether CTG expansions among different populations share a common ancestral background. Two major ancestrally related haplotypes (A and A') were found among white families with ataxia, normal controls, and patients with major psychosis, indicating a common ancestral origin of both pathogenic and nonpathogenic SCA8 expansions among whites. Two additional and distinct haplotypes were found among a group of Japanese families with ataxia (haplotype B) and a Mexican family with ataxia (haplotype C). Our finding that SCA8 expansions on three independently arising haplotypes are found among patients with ataxia and cosegregate with ataxia when multiple family members are affected further supports the direct role of the CTG expansion in disease pathogenesis.

Ataxin-10, the spinocerebellar ataxia type 10 neurodegenerative disorder protein, is essential for survival of cerebellar neurons

Spinocerebellar ataxia (SCA) type 10, an autosomal dominant disease characterized by cerebellar ataxia, is caused by a novel pentanucleotide (ATTCT) repeat expansion in the SCA10 gene. Although clinical features of the disease are well characterized, nothing is known so far about the affected SCA10 gene product, ataxin-10 (Atx-10). We have cloned the rat SCA10 gene and expressed the corresponding protein in HEK293 cells. Atx-10 has an apparent molecular mass of approximately 55 kDa and belongs to the family of armadillo repeat proteins. In solution, it tends to form homotrimeric complexes, which associate via a tip-to-tip contact with the concave sides of the molecules facing each other. Atx-10 immunostaining of mouse and human brain sections revealed a predominantly cytoplasmic and perinuclear localization with a clear restriction to olivocerebellar regions. Knock down of SCA10 in primary neuronal cells by small interfering RNAs resulted in an increased apoptosis of cerebellar neurons, arguing for a loss-of-function phenotype in SCA10 patients.

Quantitative Assessment of Cerebral Blood Flow in Genetically Confirmed Spinocerebellar Ataxia Type 6

BACKGROUND

Spinocerebellar ataxia type 6 (SCA6) is an autosomal dominant cerebellar ataxia caused by CAG trinucleotide expansion. The characteristics of regional cerebral blood flow (rCBF) in SCA6 patients have not been established, whereas it has been reported that decreased rCBF in the cerebrum seems to be a remote effect of cerebellar impairment in other cerebellar disorders.

OBJECTIVE

To clarify the characteristics of rCBF, including cerebro-cerebellar relationship, and its correlation with clinical manifestations in patients with genetically confirmed SCA6 using quantitative assessment of rCBF by brain single-photon emission computed tomography (SPECT).

DESIGN

Technetium Tc 99m ethyl cysteinate dimer SPECT study using a Patlak plot. Patients Hiroshima University Hospital, Hiroshima, Japan. Ten patients with SCA6 and 9 healthy controls. Main Outcome Measure The rCBF of the cerebellar vermis, cerebellar hemisphere, and frontal lobes.

RESULTS

In SCA6 patients, rCBF was decreased only in the cerebellar vermis and hemisphere compared with healthy controls, and this was inversely correlated with duration of illness. The rCBF in the frontal lobes was slightly correlated with duration of illness without statistical significance. The rCBF in the vermis was inversely correlated with severity of dysarthria, but there was no significant correlation with CAG repeated expansions.

CONCLUSIONS

Decrease in rCBF was found only in the cerebellum and was associated with duration of illness, dysarthria and ataxia, and cerebellar atrophy. No remote effect of cerebellar hypoperfusion was found in the SCA6 patients.

ADC mapping of neurodegeneration in the brainstem and cerebellum of patients with progressive ataxias

Analysis of the apparent diffusion coefficient (ADC) maps derived from diffusion-weighted MR imaging is emerging as a reproducible, sensitive, and quantitative tool to evaluate brain damage in diseases of the white and gray matter. To explore the potentials of ADC maps analysis in degenerative ataxias, we examined 28 patients and 26 age-matched controls with T1, T2, and diffusion (b values 0-1000 along the three main body axes)-weighted MR images. Twenty-four patients had inherited genetically proven diseases including spinocerebellar ataxia type 1 (SCA1) (n = 9), spinocerebellar ataxia type 2 (SCA2) (n = 8), and Friedreich's ataxia (FA) (n = 7), whereas four patients had sporadic adult onset pure cerebellar ataxia (three idiopathic, one gluten intolerance). Area and linear measurements of the CNS structures contained in the posterior cranial fossa (PCF) preliminary enabled classification of the patients in the three morphological categories reflecting the gross pathology findings, namely olivopontocerebellar atrophy (OPCA) (n = 10: six SCA2 and four SCA1), spinal atrophy (SA) (n = 7: all FA), and cortical cerebellar atrophy (CCA) (n = 4: three idiopathic and one gluten intolerance). Seven patients with SCA1 (n = 5) or SCA2 (n = 2) had morphologic changes reminiscent of OPCA, but their values were still in the lower normal range and were classified as undefined. Mean diffusivity (D) maps of the entire brain were generated and D was measured with regions of interest (ROI) in the medulla, pons, middle cerebellar peduncles, and the peridentate white matter. Moreover, after exclusion of the skull with manual segmentation and of the CSF with application of a threshold value, histograms were obtained for D of the brainstem and cerebellum and for D of the cerebral hemispheres. As compared to controls, a (P < 0.001) increase of D was observed in the medulla, middle cerebellar peduncles, and peridentate white matter in OPCA and undefined patients groups who had also significantly increased values of the 25th and 50th percentiles in the brainstem and cerebellum D histogram. In CCA (P = 0.01), an increase of the 25th and 50th percentile of the D value was observed in the brainstem and cerebellum histograms. The SA group showed (P < 0.001) an increased D in the medulla only. A correlation between clinical severity as assessed with the Inherited Ataxias Clinical Rating Scale (IACRS) and the 50th percentile of the D value in the brainstem and cerebellum histogram (r = 0.69) was observed in patients with SCA1 or SCA2. Diffusion MR imaging reveals variable patterns of increase of D in the brainstem, cerebellum, and cerebral hemispheres in degenerative ataxias that match the known distribution of the neuropathological changes.

Somatic and germline instability of the ATTCT repeat in spinocerebellar ataxia type 10

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant disorder characterized by ataxia, seizures, and anticipation. It is caused by an expanded ATTCT pentanucleotide repeat in intron 9 of a novel gene, designated "SCA10." The ATTCT expansion in SCA10 represents a novel class of microsatellite repeat and is one of the largest found to cause human diseases. The expanded ATTCT repeat is unstably transmitted from generation to generation, and an inverse correlation has been observed between size of repeat and age at onset. In this multifamily study, we investigated the intergenerational instability, somatic and germline mosaicism, and age-dependent repeat-size changes of the expanded ATTCT repeat. Our results showed that (1) the expanded ATTCT repeats are highly unstable when paternally transmitted, whereas maternal transmission resulted in significantly smaller changes in repeat size; (2) blood leukocytes, lymphoblastoid cells, buccal cells, and sperm have a variable degree of mosaicism in ATTCT expansion; (3) the length of the expanded repeat was not observed to change in individuals over a 5-year period; and (4) clinically determined anticipation is sometimes associated with intergenerational contraction rather than expansion of the ATTCT repeat.

Prolonged central motor conduction time of lower limb muscle in spinocerebellar ataxia 6

We investigated the function of corticospinal tract in spinocerebellar ataxia 6 (SCA6) by measuring the central motor conduction time (CMCT). Motor evoked potentials (MEP) of tibialis anterior (TA) muscle were elicited by magnetic stimulation to motor cortex and spinal cord in 9 SCA6 patients and 10 normal height- and age-matched subjects. CMCT in lower limb of SCA6 patients (18.1+/-1.9 ms) was significantly prolonged than that of the normal subjects (15.0+/-1.0 ms) ((p < 0.001). The prolonged CMCT was well correlated with the duration of disease (p = 0.005), but MEP amplitudes and stimulation intensities were not significantly different. These results indicate that the corticospinal tract function is also impaired and correlate with the disease duration in SCA6.

Detection of large pathogenic expansions in FRDA1, SCA10, and SCA12 genes using a simple fluorescent repeat-primed PCR assay

At least 18 human genetic diseases are caused by expansion of short tandem repeats. Here we describe a successful application of a fluorescent PCR method for the detection of expanded repeats in FRDA1, SCA10, and SCA12 genes. Although this test cannot give a precise estimate of the size of the expansion, it is robust, reliable, and inexpensive, and can be used to screen large series of patients. It proved useful for confirming the presence of large expansions in the Friedreich ataxia gene following an ambiguous result of long-range PCR, as well as rapid pre-screening for large repeat expansions associated with Friedreich ataxia and SCA10 and the shorter repeat expansions associated with SCA12.

Disease progression despite early loss of polyglutamine protein expression in SCA7 mouse model

Nine neurodegenerative diseases including Huntington's disease (HD) and spinocerebellar ataxia type 7 (SCA7) are caused by an expansion of a polyglutamine (polyQ) stretch in the respective proteins. Aggregation of expanded polyQ-containing proteins into the nucleus is a hallmark of these diseases. Recent evidence indicates that transcriptional dysregulation may contribute to the molecular pathogenesis of these diseases. Using SCA7 and HD mouse models in which we recently described a retinal phenotype, we investigated whether altered gene expression underlies photoreceptor dysfunction. In both models, rhodopsin promoter activity was early and dramatically repressed, suggesting that downregulation of photoreceptor-specific genes plays a major role in polyQ-induced retinal dysfunction. Because the rhodopsin promoter drives mutant ataxin-7 expression in our SCA7 mice, we also assessed whether downregulation of mutant SCA7 transgene would reverse retinopathy progression and aggregate formation. Although residual expression of mutant ataxin-7 was found negligible from 9 weeks of age, SCA7 transgenic mice showed a progressive decline of photoreceptor activity leading to a complete loss of electroretinographic responses from 1 year of age. At this age, aggregates were cleared in only half of the photoreceptors, indicating that their formation is not fully reversible in this model. We demonstrate here that abolishing full-length mutant ataxin-7 expression did not reverse retinopathy progression in SCA7 mice, raising the possibility that some polyQ-induced pathological events might be irreversible.

A clinical and genetic study in a large cohort of patients with spinocerebellar ataxia type 6

In order to clarify the clinical and genetic features of SCA6, we retrospectively analyzed 140 patients. We observed an inverse correlation between the age of onset and the length of the expanded allele, and also between the age of onset and the sum of CAG repeats in the normal and the expanded alleles. The ages of onset of four homozygous patients correlated better with the sum of CAG repeats in both alleles rather than with the expanded allele calculated from heterozygous SCA6 subjects. Clinically, unsteadiness of gait was the main initial symptom, followed by vertigo and oscillopsia, and cerebellar signs were detected in nearly 100% of the patients. In contrast, extracerebellar signs were relatively mild and infrequent. The results of neuro-otological examination performed in 22 patients suggested the purely cerebellar abnormalities of ocular movements in nature. There was a close relationship between downbeat positioning nystagmus (DPN) and positioning vertigo, which became more common in the later stage. We conclude that total number of CAG repeat-units in both alleles is a good parameter for assessment of age of onset in SCA6 including homozygous patients. In addition, clinical and neuro-otological examinations suggested that SCA6 is a disease with predominantly cerebellar dysfunction.

Spinocerebellar ataxia with sensory neuropathy (SCA25) maps to chromosome 2p

Autosomal dominant cerebellar ataxias constitute one of the most clinically, neuropathologically, and genetically heterogeneous groups of neurodegenerative disorders. Approximately 50 to 80% of the families carry mutations in genes known to be implicated in spinocerebellar ataxias (SCAs). Numerous loci (SCAn) also have been mapped, often in single families, but the responsible genes have not yet been identified. This suggests further genetic heterogeneity. We have ascertained 18 subjects from a large French family in which cerebellar ataxia and prominent sensory neuropathy segregated as a dominant trait. Intrafamilial variability was high regarding age at onset (17 months to 39 years), severity, and the clinical picture that ranged from pure sensory neuropathy with little cerebellar involvement to a Friedreich's ataxia-like phenotype. After excluding known genes/loci responsible for SCA and hereditary sensory neuropathies, we detected linkage with chromosome 2p markers in a genomewide screen. We designated this new locus SCA25 after testing of 16 additional markers. Maximum two-point logarithm of odds scores of 3.15 and 3.10 were obtained at D2S2378 and D2S2734, respectively. Haplotype analysis defined a critical 12.6cM region of 15Mb between D2S2174 and D2S2736. No linkage to this locus was found in four other families. This interval contains several genes that could be responsible for the disease. One of these genes, CRIPT, encodes a postsynaptic protein, but no mutations were found by direct sequencing, excluding its responsibility in the disease. CAG repeat expansions often are involved in SCA pathogenesis, but no pathological expansions were found at the protein or at the DNA level using the 1C2 antibody and the repeat expansion detection method, respectively. The gene responsible for SCA25 remains to be identified.

Dominantly inherited ataxia and dysphonia with dentate calcification: spinocerebellar ataxia type 20

We describe a pedigree of Anglo-Celtic origin with a phenotypically unique form of dominantly inherited spinocerebellar ataxia (SCA) in 14 personally examined affected members. A remarkable observation is dentate nucleus calcification, producing a low signal on MRI sequences. Unusually for an SCA, dysarthria is typically the initial manifestation. Mild pyramidal signs and hypermetric saccades are noted in some. Its distinguishing clinical features, each present in a majority of affected persons, are palatal tremor, and a form of dysphonia resembling spasmodic dysphonia. Repeat expansion detection failed to identify either CAG/CTG or ATTCT/AGAAT repeat expansions segregating with the disease in this family. The testable SCA mutations have been excluded. On linkage analysis, the locus maps to chromosome 11, which rules out all the remaining mapped SCAs except for SCA5. While locus homogeneity with SCA5 is not formally excluded, we consider it rather unlikely on phenotypic grounds, and propose that this condition may represent an addition to the group of neurogenetic disorders subsumed under the rubric SCA. The International Nomenclature Committee has made a provisional assignment of 'SCA20', although firm designation will have to await a definite molecular distinction from SCA5.

Spinocerebellar ataxia type 8 in Scotland: genetic and clinical features in seven unrelated cases and a review of published reports

OBJECTIVES

To establish whether the DNA expansion linked to spinocerebellar ataxia type 8 (SCA 8) is associated with ataxia in Scotland; to clarify the range of associated clinical phenotypes; and to compare the findings with previous reports.

METHODS

DNA was screened from 1190 anonymised controls, 137 subjects who had tested negative for Huntington's disease, 176 with schizophrenia, and 173 with undiagnosed ataxia. Five unrelated ataxic patients with the SCA 8 expansion and a sixth identified subsequently had clinical and psychometric assessment; the clinical features were available in a seventh. A systematic search for other reports of SCA 8 was undertaken.

RESULTS

Over 98% of SCA 8 CTA/CTG repeat lengths fell between 14 and 40. Repeat lengths over 91 were observed in three healthy controls (0.12%), two patients with suspected Huntington's disease (0.73%), and six ataxic subjects (1.74%; p<0.0005 v healthy controls). Repeat lengths over 100 occurred in five ataxic subjects but in only one control. All seven symptomatic subjects with the SCA 8 expansion had a cerebellar syndrome; four had upper motor neurone signs; and 5/6 assessed had cognitive complaints. There was personality change in two and mood disturbance in three. In published reports, SCA 8 repeat lengths over 91 occurred in approximately 0.5% of the healthy population but were over-represented among ataxic patients (3.4%; p<0.0001). The predominant clinical phenotype was cerebellar, with pyramidal signs in 50%, and neuropsychiatric features in some cases.

CONCLUSIONS

SCA 8 expansion is a risk factor for a cerebellar syndrome, often associated with upper motor neurone and neuropsychiatric features. The expansion occurs unexpectedly often in the general population.

Spinocerebellar ataxia type 2 with glial cell cytoplasmic inclusions

Glial cell cytoplasmic inclusions were identified in a case of spinocerebellar ataxia type 2. These have not been reported before. The inclusions were found in low frequency in the dentate nucleus, cerebellar white matter, pontine transverse fibres, and the inferior olivary nucleus. They were of variable size and shape and expressed ubiquitin, thus resembling glial cytoplasmic inclusions in multiple system atrophy. However, their immunohistochemical profile was different as they did not show immunoreactivity for either tau protein or alpha-synuclein. There was no evidence of expanded polyglutamine tracts in these inclusions, which also failed to label with silver stains. As in many other neurodegenerative diseases, in spinocerebellar ataxia type 2 there may be pathogenic contributions of glial cells other than the common astrogliotic response to neuronal damage.