Polyglutamine aggregation in Huntington's disease and spinocerebellar ataxia type 3: similar mechanisms in aggregate formation.

AIMS: Polyglutamine (polyQ) diseases are characterized by the expansion of a polymorphic glutamine sequence in disease-specific proteins and exhibit aggregation of these proteins. This is combated by the cellular protein quality control (PQC) system, consisting of chaperone-mediated refolding as well as proteasomal and lysosomal degradation pathways. Our recent study in the polyQ disease spinocerebellar ataxia type 3 (SCA3) suggested a distinct pattern of protein aggregation and PQC dysregulation. METHODS: To corroborate these findings we have investigated immunohistochemically stained 5 µm sections from different brain areas of Huntington's disease (HD) and SCA3 patients. RESULTS: Irrespective of disease and brain region, we observed peri- and intranuclear polyQ protein aggregates. A subset of neurones with intranuclear inclusions bodies exhibited signs of proteasomal dysfunction, up-regulation of HSPA1A and re-distribution of DNAJB1. The extent of the observed effects varied depending on brain area and disease protein. CONCLUSIONS: Our results suggest a common sequence, in which formation of cytoplasmic and nuclear inclusions precede proteasomal impairment and induction of the cellular stress response. Clearly, impairment of the PQC is not the primary cause for inclusion formation, but rather a consequence that might contribute to neuronal dysfunction and death. Notably, the inclusion pathology is not directly correlated to the severity of the degeneration in different areas, implying that different populations of neurones respond to polyQ aggregation with varying efficacy and that protein aggregation outside the neuronal perikaryon (e.g. axonal aggregates) or other effects of polyQ aggregation, which are more difficult to visualize, may contribute to neurodegeneration.

Involvement of the cholinergic basal forebrain nuclei in spinocerebellar ataxia type 2 (SCA2).

AIMS: Spinocerebellar ataxia type 2 (SCA2) belongs to the CAG repeat or polyglutamine diseases. Along with a large variety of motor, behavioural and neuropsychological symptoms the clinical picture of patients suffering from this autosomal dominantly inherited ataxia may also include deficits of attention, impairments of memory, as well as frontal-executive and visuospatial dysfunctions. As the possible morphological correlates of these cognitive SCA2 deficits are unclear we examined the cholinergic basal forebrain nuclei, which are believed to be crucial for several aspects of normal cognition and may contribute to impairments of cognitive functions under pathological conditions. METHODS: We studied pigment-Nissl-stained thick tissue sections through the cholinergic basal forebrain nuclei (that is, medial septal nucleus, nuclei of the diagonal band of Broca, basal nucleus of Meynert) of four clinically diagnosed and genetically confirmed SCA2 patients and of 13 control individuals according to the pathoanatomical approach. The pathoanatomical results were confirmed by additional quantitative investigations of these nuclei in the SCA2 patients and four age- and gender-matched controls. RESULTS: Our study revealed a severe and consistent neuronal loss in all of the cholinergic basal forebrain nuclei (medial septal nucleus: 72%; vertical nucleus of the diagonal band of Broca: 74%; horizontal limb of the diagonal band of Broca: 72%; basal nucleus of Meynert: 86%) of the SCA2 patients studied. Damage to the basal forebrain nuclei was associated with everyday relevant cognitive deficits only in our SCA2 patient with an additional Braak and Braak stage V Alzheimer's disease (AD)-related tau pathology. CONCLUSIONS: The findings of the present study: (1) indicate that the mutation and pathological process underlying SCA2 play a causative role for this severe degeneration of the cholinergic basal forebrain nuclei and (2) may suggest that degeneration of the cholinergic basal forebrain nuclei per se is not sufficient to cause profound and global dementia detrimental to everyday practice and activities of daily living.

The HSPB8-BAG3 chaperone complex is upregulated in astrocytes in the human brain affected by protein aggregation diseases.

AIMS: HSPB8 is a small heat shock protein that forms a complex with the co-chaperone BAG3. Overexpression of the HSPB8-BAG3 complex in cells stimulates autophagy and facilitates the clearance of mutated aggregation-prone proteins, whose accumulation is a hallmark of many neurodegenerative disorders. HSPB8-BAG3 could thus play a protective role in protein aggregation diseases and might be specifically upregulated in response to aggregate-prone protein-mediated toxicity. Here we analysed HSPB8-BAG3 expression levels in post-mortem human brain tissue from patients suffering of the following protein conformation disorders: Alzheimer's disease, Parkinson's disease, Huntington's disease and spinocerebellar ataxia type 3 (SCA3). METHODS: Western blotting and immunohistochemistry techniques were used to analyse HSPB8 and BAG3 expression levels in fibroblasts from SCA3 patients and post-mortem brain tissues, respectively. RESULTS: In all diseases investigated, we observed a strong upregulation of HSPB8 and a moderate upregulation of BAG3 specifically in astrocytes in the cerebral areas affected by neuronal damage and degeneration. Intriguingly, no significant change in the HSPB8-BAG3 expression levels was observed within neurones, irrespective of their localization or of the presence of proteinaceous aggregates. CONCLUSIONS: We propose that the upregulation of HSPB8 and BAG3 may enhance the ability of astrocytes to clear aggregated proteins released from neurones and cellular debris, maintain the local tissue homeostasis and/or participate in the cytoskeletal remodelling that astrocytes undergo during astrogliosis.

Pathoanatomy of cerebellar degeneration in spinocerebellar ataxia type 2 (SCA2) and type 3 (SCA3).

The cerebellum is one of the well-known targets of the pathological processes underlying spinocerebellar ataxia type 2 (SCA2) and type 3 (SCA3). Despite its pivotal role for the clinical pictures of these polyglutamine ataxias, no pathoanatomical studies of serial tissue sections through the cerebellum have been performed in SCA2 and SCA3 so far. Detailed pathoanatomical data are an important prerequisite for the identification of the initial events of the underlying disease processes of SCA2 and SCA3 and the reconstruction of its spread through the brain. In the present study, we performed a pathoanatomical investigation of serial thick tissue sections through the cerebellum of clinically diagnosed and genetically confirmed SCA2 and SCA3 patients. This study demonstrates that the cerebellar Purkinje cell layer and all four deep cerebellar nuclei consistently undergo considerable neuronal loss in SCA2 and SCA3. These cerebellar findings contribute substantially to the pathogenesis of clinical symptoms (i.e., dysarthria, intention tremor, oculomotor dysfunctions) of SCA2 and SCA3 patients and may facilitate the identification of the initial pathological alterations of the pathological processes of SCA2 and SCA3 and reconstruction of its spread through the brain.

Cellular protein quality control and the evolution of aggregates in spinocerebellar ataxia type 3 (SCA3).

AIMS: A characteristic of polyglutamine diseases is the increased propensity of disease proteins to aggregate, which is thought to be a major contributing factor to the underlying neurodegeneration. Healthy cells contain mechanisms for handling protein damage, the protein quality control, which must be impaired or inefficient to permit proteotoxicity under pathological conditions. METHODS: We used a quantitative analysis of immunohistochemistry of the pons of eight patients with the polyglutamine disorder spinocerebellar ataxia type 3. We employed the anti-polyglutamine antibody 1C2, antibodies against p62 that is involved in delivering ubiquitinated protein aggregates to autophagosomes, antibodies against the chaperones HSPA1A and DNAJB1 and the proteasomal stress marker UBB⁺¹. RESULTS: The 1C2 antibody stained neuronal nuclear inclusions (NNIs), diffuse nuclear staining (DNS), granular cytoplasmic staining (GCS) and combinations, with reproducible distribution. P62 always co-localized with 1C2 in NNI. DNS and GCS co-stained with a lower frequency. UBB⁺¹ was present in a subset of neurones with NNI. A subset of UBB⁺¹-containing neurones displayed increased levels of HSPA1A, while DNAJB1 was sequestered into the NNI. CONCLUSION: Based on our results, we propose a model for the aggregation-associated pathology of spinocerebellar ataxia type 3: GCS and DNS aggregation likely represents early stages of pathology, which progresses towards formation of p62-positive NNI. A fraction of NNI exhibits UBB⁺¹ staining, implying proteasomal overload at a later stage. Subsequently, the stress-inducible HSPA1A is elevated while DNAJB1 is recruited into NNIs. This indicates that the stress response is only induced late when all endogenous protein quality control systems have failed.

Levels of DNAJB family members (HSP40) correlate with disease onset in patients with spinocerebellar ataxia type 3.

In polyglutamine disorders, the length of the expanded CAG repeat shows a strong inverse correlation with the age at disease onset, yet up to 50% of the variation in age of onset is determined by other additional factors. Here, we investigated whether variations in the expression of heat shock proteins (HSP) are related to differences in the age of onset in patients with spinocerebellar ataxia (SCA)3. Hereto, we analysed the protein expression levels of HSPA1A (HSP70), HSPA8 (HSC70), DNAJB (HSP40) and HSPB1 (HSP27) in fibroblasts from patients and healthy controls. HSPB1 levels were significantly upregulated in fibroblasts from patients with SCA3, but without relation to age of onset. Exclusively for expression of DNAJB family members, a correlation was found with the age of onset independent of the length of the CAG repeat expansion. This indicates that DNAJB members might be contributors to the variation in age of onset and underlines the possible use of DNAJB proteins as therapeutic targets.

The p62 antibody reveals various cytoplasmic protein aggregates in spinocerebellar ataxia type 6.

Neuronal protein aggregates are considered as pathological hallmarks of various human neurodegenerative diseases, including the so-called CAG-repeat disorders, such as spinocerebellar ataxia Type 6 (SCA6). Since the immunocytochemical findings of an initial post-mortem study using a specific antibody against the disease protein of SCA6 (i.e., pathologically altered alpha-1A subunit of the P/Q type voltage-dependent calcium channel, CACNA1A) have not been confirmed so far, the occurrence and central nervous system distribution of neuronal protein aggregates in SCA6 is still a matter of debate. Owing to the fact that the antibody against the pathologically altered CACNA1A is not commercially available, we decided to apply a recently generated p62 antibody on brain tissue from two clinically diagnosed and genetically confirmed SCA6 patients. Application of this p62 antibody revealed numerous cytoplasmic neuronal inclusions in the degenerated cerebellar dentate nucleus and inferior olive of both SCA6 patients studied, whereby a subset of these aggregates were also ubiquitin-immunopositive. In view of the known role of p62 in protein degradation as well as aggresome/sequestosome formation, the p62 aggregate formation observed in the present study suggests that SCA6 not only is associated with an impairment of the calcium channel function and an elongated polyglutamine stretch in CACNA1A, but also with a defective protein handling by the protein quality control system.

Neurophysiological evaluation in children with Friedreich's ataxia.

INTRODUCTION: In children with Friedreich's ataxia (FRDA children), clinical ataxia outcomes are hardly substantiated by underlying neurophysiological parameters. In young FRDA children, some reports (based upon International Cooperative Ataxia Rating Scale scores (ICARS)) mention transient neurological improvement upon idebenone treatment. However, these outcomes are obtained with adult instead of pediatric reference values. It is unknown whether age-related neurophysiological parameters can really substantiate neurologic improvement. AIM: In young FRDA children, we aimed to determine longitudinal neurophysiological parameters during idebenone treatment. METHODS: During a two-year study period, 6 genetically proven FRDA children with cardiomyopathy (6-18years) were longitudinally assessed for neurophysiological parameters [sensory evoked potentials (SEPs), F response, peripheral nerve conduction and dynamometry] in association with age-matched ICARS-scores. RESULTS: In all FRDA children, SEPs remained absent during the two-year study period. Peroneal nerve conduction velocity declined (from -1SD to -2SD; p<.05), whereas F responses remained essentially unaltered. Total muscle force and leg muscle force decreased (from -2 to -3SD and -2.5 to -3.5SD; both p<.05) and age-related ICARS-scores deteriorated (median increase +41%; p<.05). CONCLUSION: In FRDA children, age-related neurophysiological and ataxia parameters deteriorate during idebenone treatment. Although we cannot exclude some (subjective) disease stabilization, age-related neurophysiological parameters do not substantiate neurologic improvement.

Clinical spectrum of ataxia-telangiectasia in adulthood.

OBJECTIVE: To describe the phenotype of adult patients with variant and classic ataxia-telangiectasia (A-T), to raise the degree of clinical suspicion for the diagnosis variant A-T, and to assess a genotype-phenotype relationship for mutations in the ATM gene. METHODS: Retrospective analysis of the clinical characteristics and course of disease in 13 adult patients with variant A-T of 9 families and 6 unrelated adults with classic A-T and mutation analysis of the ATM gene and measurements of ATM protein expression and kinase activity. RESULTS: Patients with variant A-T were only correctly diagnosed in adulthood. They often presented with extrapyramidal symptoms in childhood, whereas cerebellar ataxia appeared later. Four patients with variant A-T developed a malignancy. Patients with classic and variant A-T had elevated serum alpha-fetoprotein levels and chromosome 7/14 rearrangements. The mildest variant A-T phenotype was associated with missense mutations in the ATM gene that resulted in expression of some residual ATM protein with kinase activity. Two splicing mutations, c.331 + 5G>A and c.496 + 5G>A, caused a more severe variant A-T phenotype. The splicing mutation c.331 + 5G>A resulted in less ATM protein and kinase activity than the missense mutations. CONCLUSIONS: Ataxia-telangiectasia (A-T) should be considered in patients with unexplained extrapyramidal symptoms. Early diagnosis is important given the increased risk of malignancies and the higher risk for side effects of subsequent cancer treatment. Measurement of serum alpha-fetoprotein and chromosomal instability precipitates the correct diagnosis. There is a clear genotype-phenotype relation for A-T, since the severity of the phenotype depends on the amount of residual kinase activity as determined by the genotype.

Spinocerebellar ataxia type 6 (SCA6): neurodegeneration goes beyond the known brain predilection sites.

AIMS: Spinocerebellar ataxia type 6 (SCA6) is a late onset autosomal dominantly inherited ataxic disorder, which belongs to the group of CAG repeat, or polyglutamine, diseases. Although, it has long been regarded as a 'pure' cerebellar disease, recent clinical studies have demonstrated disease signs challenging the view that neurodegeneration in SCA6 is confined to the well-known lesions in the cerebellum and inferior olive. METHODS: We performed a systematic pathoanatomical study throughout the brains of three clinically diagnosed and genetically confirmed SCA6 patients. RESULTS: This study confirmed that brain damage in SCA6 goes beyond the known brain predilection sites. In all of the SCA6 patients studied loss of cerebellar Purkinje cells and absence of morphologically intact layer V giant Betz pyramidal cells in the primary motor cortex, as well as widespread degeneration of brainstem nuclei was present. Additional damage to the deep cerebellar nuclei was observed in two of three SCA6 patients. CONCLUSIONS: In view of the known functional role of affected central nervous grey components it is likely that their degeneration at least in part is responsible for the occurrence of a variety of SCA6 disease symptoms.

The human premotor oculomotor brainstem system - can it help to understand oculomotor symptoms in Huntington's disease?

Recent progress in oculomotor research has enabled new insights into the functional neuroanatomy of the human premotor oculomotor brainstem network. In the present review, we provide an overview of its functional neuroanatomy and summarize the broad range of oculomotor dysfunctions that may occur in Huntington's disease (HD) patients. Although some of these oculomotor symptoms point to an involvement of the premotor oculomotor brainstem network in HD, no systematic analysis of this functional system has yet been performed in brains of HD patients. Therefore, its exact contribution to oculomotor symptoms in HD remains unclear. A possible strategy to clarify this issue is the use of unconventional 100-microm-thick serial tissue sections stained for Nissl substance and lipofuscin pigment (Nissl-pigment stain according to Braak). This technique makes it possible to identify the known nuclei of the premotor oculomotor brainstem network and to study their possible involvement in the neurodegenerative process. Studies applying this morphological approach and using the current knowledge regarding the functional neuroanatomy of this human premotor oculomotor brainstem network will help to elucidate the anatomical basis of the large spectrum of oculomotor dysfunctions that are observed in HD patients. This knowledge may aid clinicians in the diagnosis and monitoring of the disease.

Involvement of the auditory brainstem system in spinocerebellar ataxia type 2 (SCA2), type 3 (SCA3) and type 7 (SCA7).

AIMS: The spinocerebellar ataxia type 2 (SCA2), type 3 (SCA3) and type 7 (SCA7) are clinically characterized by progressive and severe ataxic symptoms, dysarthria, dysphagia, oculomotor impairments, pyramidal and extrapyramidal manifestations and sensory deficits. Although recent clinical studies reported additional disease signs suggesting involvement of the brainstem auditory system, this has never been studied in detail in SCA2, SCA3 or SCA7. METHODS: We performed a detailed pathoanatomical investigation of unconventionally thick tissue sections through the auditory brainstem nuclei (that is, nucleus of the inferior colliculus, nuclei of the lateral lemniscus, superior olive, cochlear nuclei) and auditory brainstem fibre tracts (that is, lateral lemniscus, trapezoid body, dorsal acoustic stria, cochlear portion of the vestibulocochlear nerve) of clinically diagnosed and genetically confirmed SCA2, SCA3 and SCA7 patients. RESULTS: Examination of unconventionally thick serial brainstem sections stained for lipofuscin pigment and Nissl material revealed a consistent and widespread involvement of the auditory brainstem nuclei in the SCA2, SCA3 and SCA7 patients studied. Serial brainstem tissue sections stained for myelin showed loss of myelinated fibres in two of the auditory brainstem fibre tracts (that is, lateral lemniscus, trapezoid body) in a subset of patients. CONCLUSIONS: The involvement of the auditory brainstem system offers plausible explanations for the auditory impairments detected in some of our and other SCA2, SCA3 and SCA7 patients upon bedside examination or neurophysiological investigation. However, further clinical studies are required to resolve the striking discrepancy between the consistent involvement of the brainstem auditory system observed in this study and the comparatively low frequency of reported auditory impairments in SCA2, SCA3 and SCA7 patients.

Spinocerebellar ataxia type 7 (SCA7): widespread brain damage in an adult-onset patient with progressive visual impairments in comparison with an adult-onset patient without visual impairments.

Spinocerebellar ataxia type 7 (SCA7) represents a rare and severe autosomal dominantly inherited ataxic disorder and is among the known CAG-repeat, or polyglutamine, diseases. In contrast to other currently known autosomal dominantly inherited ataxic disorders, SCA7 may manifest itself with different clinical courses. Because the degenerative changes evolving during these different clinical courses are not well known, many neurological disease symptoms still are unexplained. We performed an initial pathoanatomical study on unconventional thick tissue sections of the brain of a clinically diagnosed and genetically confirmed adult-onset SCA7 patient with progressive visual impairments. In this patient we observed loss of myelinated fibres in distinct central nervous fibre tracts, and widespread degeneration of the cerebellum, telencephalon, diencephalon and lower brainstem. These degenerative changes offer appropriate explanations for a variety of less-understood neurological symptoms in adult-onset SCA7 patients with visual impairments: gait, stance and limb ataxia, falls, dysarthria, dysphagia, pyramidal signs, Parkinsonian features, writing problems, impairments of saccades and smooth pursuits, altered pupillary functions, somatosensory deficits, auditory deficits and mental impairments.

Neuronal intranuclear inclusions, dysregulation of cytokine expression and cell death in spinocerebellar ataxia type 3.

OBJECTIVE: We analyzed the expression of the inflammatory mediators IL-1beta, IL-1ra, IL-6 and the transcription factors IRF-1 and C/EBPdelta (previously identified in a transgenic model of spinocerebellar ataxia type 3 (SCA3) by gene expression profiling) in the central nervous system of SCA3 patients in relation to neuronal cell loss and ataxin-3-positive neuronal intranuclear inclusions (NI), to identify a putative upregulation of cytokines or microglia in SCA3 brains and to investigate whether enhanced cytokine expression was a generalized event mediating neuronal dysfunction in SCA3. MATERIALS AND METHODS: Light- and electronmicroscopic immunohistochemistry was performed on SCA3 tissues derived from five patients from unrelated families with genetically confirmed diagnosis, and six individuals without a history of neurological or inflammatory disease. RESULTS: NI were found almost exclusively in brain regions that also showed neuronal cell loss, i.e. in pons and dentate nucleus neurons, rarely in putamen and thalamus, but not in cerebral or cerebellar cortex. NI displayed an irregular surface and were mostly attached to the nucleoli. Quantitative analysis of NI in the pons revealed an inverse relation of NI and cell loss, i.e. patients with more severe neuronal cell loss had a smaller proportion of neurons with NI. Thus, formation of NI is not necessarily an indicator of cell death but could exert a protective effect. We found increased expression of IL-1beta, IL-1ra, IL-6 and C/EBPdelta only in pons and dentate nucleus neurons and both in neurons with and without NI, suggesting that NI are not a prerequisite for transcriptional changes. CONCLUSIONS: Our data suggest that the selectively affected neuronal populations in SCA3 undergo a complex alteration of gene expression independent from the formation of NI.

Degeneration of ingestion-related brainstem nuclei in spinocerebellar ataxia type 2, 3, 6 and 7.

Dysphagia, which can lead to nutritional deficiencies, weight loss and dehydration, represents a risk factor for aspiration pneumonia. Although clinical studies have reported the occurrence of dysphagia in patients with spinocerebellar ataxia type 2 (SCA2), type 3 (SCA3), type 6 (SCA6) and type 7 (SCA7), there are neither detailed clinical records concerning the kind of ingestive malfunctions which contribute to dysphagia nor systematic pathoanatomical studies of brainstem regions involved in the ingestive process. In the present study we performed a systematic post mortem study on thick serial tissue sections through the ingestion-related brainstem nuclei of 12 dysphagic patients who suffered from clinically diagnosed and genetically confirmed spinocerebellar ataxias assigned to the CAG-repeat or polyglutamine diseases (two SCA2, seven SCA3, one SCA6 and two SCA7 patients) and evaluated their medical records. Upon pathoanatomical examination in all of the SCA2, SCA3, SCA6 and SCA7 patients, a widespread neurodegeneration of the brainstem nuclei involved in the ingestive process was found. The clinical records revealed that all of the SCA patients were diagnosed with progressive dysphagia and showed dysfunctions detrimental to the preparatory phase of the ingestive process, as well as the lingual, pharyngeal and oesophageal phases of swallowing. The vast majority of the SCA patients suffered from aspiration pneumonia, which was the most frequent cause of death in our sample. The findings of the present study suggest (i) that dysphagia in SCA2, SCA3, SCA6 and SCA7 patients may be associated with widespread neurodegeneration of ingestion-related brainstem nuclei; (ii) that dysphagic SCA2, SCA3, SCA6 and SCA7 patients may suffer from dysfunctions detrimental to all phases of the ingestive process; and (iii) that rehabilitative swallow therapy which takes specific functional consequences of the underlying brainstem lesions into account might be helpful in preventing aspiration pneumonia, weight loss and dehydration in SCA2, SCA3, SCA6 and SCA7 patients.

Spinocerebellar ataxias types 2 and 3: degeneration of the pre-cerebellar nuclei isolates the three phylogenetically defined regions of the cerebellum.

The pre-cerebellar nuclei act as a gate for the entire neocortical, brainstem and spinal cord afferent input destined for the cerebellum. Since no pathoanatomical studies of these nuclei had yet been performed in spinocerebellar ataxia type 2 (SCA2) or type 3 (SCA3), we carried out a detailed postmortem study of the pre-cerebellar nuclei in six SCA2 and seven SCA3 patients in order to further characterize the extent of brainstem degeneration in these ataxic disorders. By means of unconventionally thick serial sections through the brainstem stained for lipofuscin pigment and Nissl material, we could show that all of the pre-cerebellar nuclei (red, pontine, arcuate, prepositus hypoglossal, superior vestibular, lateral vestibular, medial vestibular, interstitial vestibular, spinal vestibular, vermiform, lateral reticular, external cuneate, subventricular, paramedian reticular, intercalate, interfascicular hypoglossal, and conterminal nuclei, pontobulbar body, reticulotegmental nucleus of the pons, inferior olive, and nucleus of Roller) are among the targets of both of the degenerative processes underlying SCA2 and SCA3. These novel findings are in contrast to the current neuropathological literature, which assumes that only a subset of pre-cerebellar nuclei in SCA2 and SCA3 may undergo neurodegeneration. Widespread damage to the pre-cerebellar nuclei separates all three phylogenetically and functionally defined regions of the cerebellum, impairs their physiological functions and thus explains the occurrence of gait, stance, limb and truncal ataxia, dysarthria, truncal and postural instability with disequilibrium, impairments of the vestibulo-ocular reaction and optokinetic nystagmus, slowed and saccadic smooth pursuits, dysmetrical horizontal saccades, and gaze-evoked nystagmus during SCA2 and SCA3.

Spinocerebellar ataxia type 7 (SCA7): first report of a systematic neuropathological study of the brain of a patient with a very short expanded CAG-repeat.

Spinocerebellar ataxia type 7 (SCA7) represents a very rare and severe autosomal dominantly inherited cerebellar ataxia (ADCA). It belongs to the group of CAG-repeat or polyglutamine diseases with its underlying molecular genetical defect on chromosome 3p12-p21.1. Here, we performed a systematic study of the neuropathology on unconventional thick serial sections of the first available brain tissue of a genetically confirmed late-onset SCA7 patient with a very short CAG-repeat expansion. Along with myelin pallor of a variety of central nervous fiber tracts, we observed i) neurodegeneration in select areas of the cerebral cortex, and ii) widespread nerve cell loss in the cerebellum, thalamus, nuclei of the basal ganglia, and brainstem. In addition, upon immunocytochemical analysis using the anti-polyglutamine antibody 1C2, immunopositive neuronal intranuclear inclusions bodies (NI) were observed in all cerebellar regions, in all parts of the cerebral cortex, and in telencephalic and brainstem nuclei, irrespective of whether they underwent neurodegeneration. These novel findings provide explanations for a variety of clinical symptoms and paraclinical findings of both our and other SCA7 patients. Finally, our immunocytochemical analysis confirms previous studies which described the presence of NI in obviously degenerated brain and retinal regions as well as in apparently well-preserved brain regions and retina of SCA7 patients.

Damage to the reticulotegmental nucleus of the pons in spinocerebellar ataxia type 1, 2, and 3.

BACKGROUND: The reticulotegmental nucleus of the pons (RTTG) is among the precerebellar nuclei of the human brainstem. Although it represents an important component of the oculomotor circuits crucial for the accuracy of horizontal saccades and the generation of horizontal smooth pursuits, the RTTG has never been considered in CAG repeat or polyglutamine diseases. METHODS: Thick serial sections through the RTTG of 10 patients with spinocerebellar ataxias (SCAs) assigned to the CAG repeat or polyglutamine diseases (2 SCA-1 patients, 4 SCA-2 patients, and 4 SCA-3 patients) were stained for neuronal lipofuscin pigment and Nissl material. RESULTS: The unconventionally thick tissue sections revealed the hitherto overlooked involvement of the RTTG in the degenerative processes underlying SCA-1, SCA-2, and SCA-3, whereby in one of the SCA-1 patients, in two of the SCA-2 patients, and in all of the SCA-3 patients, the RTTG underwent a conspicuous loss of its nerve cells. CONCLUSIONS: Neurodegeneration may not only affect the cranial nerve nuclei (i.e., oculomotor and abducens nuclei) of SCA-1, SCA-2 and SCA-3 patients integrated into the circuits, subserving accuracy of horizontal saccades and the generation of horizontal smooth pursuits, but likewise involves the premotor networks of these circuits. This may explain why the SCA-1, SCA-2, and SCA-3 patients in this study with a heavily damaged reticulotegmental nucleus of the pons developed dysmetric horizontal saccades and impaired smooth pursuits during the course of the disease.

Degeneration of the central vestibular system in spinocerebellar ataxia type 3 (SCA3) patients and its possible clinical significance.

Although the vestibular complex represents an important component of the neural circuits crucial for the maintenance of truncal and postural stability, and it is integrated into specialized oculomotor circuits, knowledge regarding the extent of the involvement of its nuclei and associated fibre tracts in cases with spinocerebellar ataxia type 3 (SCA3) is incomplete. Accordingly, we performed a pathoanatomical analysis of the vestibular complex and its associated fibre tracts in four clinically diagnosed and genetically confirmed SCA3 patients with the aim of providing more exact information as to the involvement of the vestibular system in this disorder. By means of unconventionally thick serial sections through the vestibular nuclei stained for lipofuscin pigment and Nissl material, we could show that all five nuclei of this complex (interstitial, lateral, medial, spinal, and superior vestibular nuclei) are subject to neurodegenerative processes in SCA3, whereby examination of thick serial sections stained for myelin revealed that all associated fibre tracts (ascending tract of Deiters, juxtarestiform body, lateral and medial vestibulospinal tracts, medial longitudinal fascicle, vestibular portion of the eighth cranial nerve) underwent atrophy and demyelinization in all four of the patients studied. The reported lesions can help to explain the truncal and postural instability as well as the impaired optokinetic nystagmus, vestibulo-ocular reaction, and horizontal gaze-holding present in SCA3 cases.

Thalamic involvement in a spinocerebellar ataxia type 2 (SCA2) and a spinocerebellar ataxia type 3 (SCA3) patient, and its clinical relevance.

In spite of the considerable progress in clinical and molecular research, knowledge regarding brain damage in spinocerebellar ataxia type 2 (SCA2) and type 3 (SCA3) still is limited and the extent to which the thalamus is involved in both diseases is uncertain. Accordingly, we performed a pathoanatomical analysis on serial thick sections stained for lipofuscin granules and Nissl substance through the thalami of two genetically confirmed cases: one an SCA2 patient, the other an SCA3 patient. During this systematic study, we detected severe destruction of the reticular (RT), fasciculosus (FA), ventral anterior (VA), ventral lateral (VL), ventral posterior lateral (VPL), ventral posterior medial (VPM), cucullar (CU) and mediodorsal thalamic nuclei (MD), the lateral geniculate body (LGB) and inferior nucleus of the pulvinar (PU i) in the SCA2 case, and a severe neuronal loss in the RT, FA, VA and PU i of the SCA3 case. In the SCA2 patient, additional obvious neuronal loss was observed in all nuclei of the anterior and rostral intra laminar groups, in the lateral posterior nucleus (LP), the lateral (PU l) and the medial subnuclei of the pulvinar (PU m), whereas in the SCA3 patient only two of the nuclei that belong to the anterior thalamic group, the VL, VPL, VPM, LP, LGB, PU l and PU m, displayed marked neurodegeneration. These novel findings indicate that thalamic involvement in SCA2 and SCA3 patients has been underestimated in the past. In view of what is known about the functions of the affected thalamic nuclei, the present findings provide an appropriate pathoanatomical explanation for some of the disease-related symptoms seen in both of our and other SCA2 and SCA3 patients: gait, stance, truncal and limb ataxia, dysarthria or anarthria, falls, dysdiadochokinesia and bradykinesia, problems with writing, somatosensory deficits, saccadic dysfunctions, executive dysfunctions and abnormalities of visual evoked potentials.