Clinicopathology of spinocerebellar degeneration: its correlation to the unstable CAG repeat of the affected gene

The neostriatum in polyglutamine diseases: preferential decreases in large neurons in dentatorubral-pallidoluysian atrophy and Machado-Joseph disease and in small neurons in Huntington disease

The presence of polyglutamine-immunoreactive deposits in neurons of the neostriatum has been reported in dentatorubral-pallidoluysian atrophy (DRPLA), Machado-Joseph disease (MJD), and Huntington disease (HD). However, among these diseases, precise quantitative investigations on neurons have been performed only for HD. Changes in the number of neurons and the immunohistological features of polyglutamine deposits in the caudate head and putamen were examined in six patients with DRPLA, three with MJD, and four with HD. In the neostriatum in DRPLA, the numbers of large and small neurons were reduced to 33-38% and 48-68% relative to controls, respectively, whereas the corresponding figures in MJD were 19-26% and 65-76%, respectively, and those in HD were 34-35% and 12-16%, respectively. In DRPLA, 2-55% of neurons remaining in the neostriatum showed diffuse nuclear accumulation of polyglutamine, in contrast to 3-20% in MJD and a few percent in HD. These findings indicate that, in the neostriatum, a decrease in the number of small neurons is predominant in HD, whereas a decrease in the number of large neurons is predominant in DRPLA and MJD. Thus, it is suggested that disease processs differ among polyglutamine diseases.

Reconstructing the History of Machado-Joseph Disease

Machado-Joseph disease (MJD), or spinocerebellar ataxia type 3, was originally described in members of the families of Machado, Thomas, and Joseph from São Miguel Island, Azores, Portugal, in 1972. The purpose of this article is to present previous descriptions of hereditary ataxia resembling the heterogeneous phenotypic intra-familiar presentation of MJD. We suggest that the condition would best be called dominant spino-pontine atrophy.

In Human and Mouse Spino-Cerebellar Tissue, Ataxin-2 Expansion Affects Ceramide-Sphingomyelin Metabolism

Ataxin-2 (human gene symbol ATXN2) acts during stress responses, modulating mRNA translation and nutrient metabolism. Ataxin-2 knockout mice exhibit progressive obesity, dyslipidemia, and insulin resistance. Conversely, the progressive ATXN2 gain of function due to the fact of polyglutamine (polyQ) expansions leads to a dominantly inherited neurodegenerative process named spinocerebellar ataxia type 2 (SCA2) with early adipose tissue loss and late muscle atrophy. We tried to understand lipid dysregulation in a SCA2 patient brain and in an authentic mouse model. Thin layer chromatography of a patient cerebellum was compared to the lipid metabolome of Atxn2-CAG100-Knockin (KIN) mouse spinocerebellar tissue. The human pathology caused deficits of sulfatide, galactosylceramide, cholesterol, C22/24-sphingomyelin, and gangliosides GM1a/GD1b despite quite normal levels of C18-sphingomyelin. Cerebellum and spinal cord from the KIN mouse showed a consistent decrease of various ceramides with a significant elevation of sphingosine in the more severely affected spinal cord. Deficiency of C24/26-sphingomyelins contrasted with excess C18/20-sphingomyelin. Spinocerebellar expression profiling revealed consistent reductions of CERS protein isoforms, Sptlc2 and Smpd3, but upregulation of Cers2 mRNA, as prominent anomalies in the ceramide-sphingosine metabolism. Reduction of Asah2 mRNA correlated to deficient S1P levels. In addition, downregulations for the elongase Elovl1, Elovl4, Elovl5 mRNAs and ELOVL4 protein explain the deficit of very long-chain sphingomyelin. Reduced ASMase protein levels correlated to the accumulation of long-chain sphingomyelin. Overall, a deficit of myelin lipids was prominent in SCA2 nervous tissue at prefinal stage and not compensated by transcriptional adaptation of several metabolic enzymes. Myelination is controlled by mTORC1 signals; thus, our human and murine observations are in agreement with the known role of ATXN2 yeast, nematode, and mouse orthologs as mTORC1 inhibitors and autophagy promoters.

Analysis of (CAG)n expansion in ATXN1, ATXN2 and ATXN3 in Chinese patients with multiple system atrophy

Multiple system atrophy (MSA) is a complex and multifactorial neurodegenerative disease, and its pathogenesis remains uncertain. Patients with MSA or spinocerebellar ataxia (SCA) show overlapping clinical phenotypes. Previous studies have reported that intermediate or long CAG expansions in SCA genes have been associated with other neurodegenerative disease. In this study, we screened for the number of CAG repeats in ATXN1, 2 and 3 in 200 patients with MSA and 314 healthy controls to evaluate possible associations between (CAG)_n in these three polyQ-related genes and MSA. Our findings indicated that longer repeat lengths in ATXN2 were associated with increased risk for MSA in Chinese individuals. No relationship was observed between CAG repeat length in the three examined genes and age at onset (AO) of MSA.

The Multiple Faces of Spinocerebellar Ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is among the most common forms of autosomal dominant ataxias, accounting for 15% of the total families. Occurrence is higher in specific populations such as the Cuban and Southern Italian. The disease is caused by a CAG expansion in ATXN2 gene, leading to abnormal accumulation of the mutant protein, ataxin‐2, in intracellular inclusions. The clinical picture is mainly dominated by cerebellar ataxia, although a number of other neurological signs have been described, ranging from parkinsonism to motor neuron involvement, making the diagnosis frequently challenging for neurologists, particularly when information about the family history is not available. Although the functions of ataxin‐2 have not been completely elucidated, the protein is involved in mRNA processing and control of translation. Recently, it has also been shown that the size of the CAG repeat in normal alleles represents a risk factor for ALS, suggesting that ataxin‐2 plays a fundamental role in maintenance of neuronal homeostasis.

Different subregional metabolism patterns in patients with cerebellar ataxia by 18F-fluorodeoxyglucose positron emission tomography

We evaluated cerebellar subregional metabolic alterations in patients with cerebellar ataxia, a representative disease involving the spinocerebellum. We retrospectively analyzed ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) images in 44 patients with multiple system atrophy of the cerebellar type (MSA-C), 9 patients with spinocerebellar ataxia (SCA) type 2, and 14 patients with SCA type 6 and compared with 15 patients with crossed cerebellar diaschisis (CCD) and 89 normal controls. Cerebellar subregional metabolism was assessed using 13 cerebellar subregions (bilateral anterior lobes [ANT], superior/mid/inferior posterior lobes [SUPP/MIDP/INFP], dentate nucleus [DN], anterior vermis [ANTV], and superior/inferior posterior vermis [SUPV/INFV]) to determine FDG uptake ratios. MSA-C and SCA type 2 showed severely decreased metabolic ratios in all cerebellar subregions compared to normal controls (ANT, 0.58 ± 0.08 and 0.50 ± 0.06 vs. 0.82 ± 0.07, respectively, p < 0.001). SCA type 6 showed lower metabolic ratios in almost all cerebellar subregions (ANT, 0.57 ± 0.06, p < 0.001) except INFV. Anterior-posterior lobe ratio measurements revealed that SCA type 2 (Right, 0.81 ± 0.05 vs. 0.88 ± 0.04, p < 0.001; Left, 0.83 ± 0.05 vs. 0.88 ± 0.04, p = 0.003) and SCA type 6 (Right, 0.72 ± 0.05 vs. 0.88 ± 0.04, p < 0.001; Left, 0.72 ± 0.05 vs. 0.88 ± 0.04, p < 0.001) showed preferential hypometabolism in the anterior lobe compared to normal controls, which was not observed in CCD and MSA-C. Asymmetric indices were higher in CCD and MSA-C than in normal controls (p < 0.001), whereas such differences were not found in SCA types 2 and 6. In summary, quantitative analysis of cerebellar subregional metabolism ratios revealed preferential involvement of the anterior lobe, corresponding to the spinocerebellum, in patients with cerebellar ataxia, whereas patients with CCD and MSA-C exhibited more asymmetric hypometabolism in the posterior lobe.

The role for alterations in neuronal activity in the pathogenesis of polyglutamine repeat disorders

Polyglutamine diseases are a class of neurodegenerative diseases that share an expansion of a glutamine-encoding CAG tract in the respective disease genes as a central hallmark. In all of these diseases there is progressive degeneration in a select subset of neurons, and the mechanisms behind this degeneration remain unclear. Emerging evidence from animal models of disease has identified abnormalities in synaptic signaling and intrinsic excitability in affected neurons, which coincide with the onset of symptoms and precede apparent neuropathology. The appearance of these early changes suggests that altered neuronal activity might be an important component of network dysfunction and that these alterations in network physiology could contribute to symptoms of disease. Here we review abnormalities in neuronal function that have been identified in both animal models and patients, and highlight ways in which these changes in neuronal activity may contribute to disease symptoms. We then review the literature supporting an emerging role for abnormalities in neuronal activity as a driver of neurodegeneration. Finally, we identify common themes that emerge from studies of neuronal dysfunction in polyglutamine disease.

Pallidopyramidal disease: a misnomer?

The combination of recessive early-onset parkinsonism and pyramidal tract signs caused by pallidopyramidal degeneration is known as pallidopyramidal disease or syndrome (PPD/S). We investigated whether patients diagnosed as Davison's PPD/S showed any definite proof of pyramidal and pallidal involvement, without findings suggestive of other nosological entities. Since Davison's original description, 15 other PPD/S cases have been reported, yet all lack proof of pyramidal or pallidal degeneration. Because of the dopa-responsiveness in all patients subsequent to Davison's report, we argue that these patients probably suffered from early-onset nigral parkinsonism or dopa-responsive dsystonia, rather than pallidal parkinsonism; in such cases, the presumed pyramidal Babinski could be a pseudobabinski ("striatal toe"). Secondary pallidopyramidal syndromes do occur, for example, in multiple system atrophy or Wilson's disease, but in these patients additional findings indicate diseases other than Davison's PPD/S. We conclude that the existence of PPD/S as a distinct clinico-pathological nosological entity, as proposed by Davison, is doubtful. In cases reported as Davison's PPD/S, the description "pallidopyramidal" seems to be a misnomer.

Spinocerebellar ataxia 2 (SCA2)

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited, neurodegenerative disease. It can manifest either with a cerebellar syndrome or as Parkinson's syndrome, while later stages involve mainly brainstem, spinal cord and thalamus. This particular atrophy pattern resembles sporadic multi-system-atrophy (MSA) and results in some clinical features indicative of SCA2, such as early saccade slowing, early hyporeflexia, severe tremor of postural or action type, and early myoclonus. For treatment, levodopa is temporarily useful for rigidity/bradykinesia and for tremor, magnesium for muscle cramps, but neuroprotective therapy will depend on the elucidation of pathogenesis. The disease cause lies in the polyglutamine domain of the protein ataxin-2, which can expand in families over successive generations resulting in earlier onset age and faster progression. Genetic testing in SCA2 and other polyglutamine disorders like the well-studied Huntington's disease is now readily available for family planning. Although these disorders differ clinically and in the affected neuron populations, it is not understood how the different polyglutamine proteins mediate such tissue specificity. The neuronal intranuclear inclusion bodies described in other polyglutamine disorders are not frequent in SCA2. For the quite ubiquitously expressed ataxin-2, a subcellular localization at the Golgi, the endoplasmic reticulum and the plasma membrane, in interaction with proteins of mRNA translation and of endocytosis have been observed. As a first victim of SCA2 degeneration, cerebellar Purkinje neurons may be preferentially susceptible to alterations of these subcellular pathways, and therefore our review aims to portray the particular profile of the SCA2 disease process and correlate it to the specific features of ataxin-2.

Spinocerebellar ataxia type 2 in a Turkish family

Autosomal dominant spinocerebellar ataxias are neurodegenerative disorders that generally present in adulthood. Due to extreme expansion of the repeat size during spermatogenesis, they can also be observed in childhood. The diagnosis in childhood is very difficult in the absence of family history. Here we describe an 8-year-old girl with spinocerebellar ataxia type 2 who presented with progressive ataxia, cognitive deficits, and dysarthria. A detailed family history exhibited similarly affected cases on the paternal side. Molecular testing for spinocerebellar ataxia type 2 revealed abnormal "cytosineadenine-guanosine" expansion in all affected family members. The number of cytosine-adenine-guanosine repeats in the index case was 70. The mean size of expansion in the relatives of the patient was 42 (39-46). This finding explains the early onset of symptoms in the index case.

Differentiation of SCA2 from MSA-C using proton magnetic resonance spectroscopic imaging

PURPOSE

To assess and compare biochemical and volumetric features of the cerebellum in patients with spinocerebellar ataxia type 2 (SCA2) and patients with the cerebellar variant of multiple system atrophy (MSA-C).

MATERIALS AND METHODS

Nine genetically assigned SCA2 patients and six MSA-C patients who met the clinical criteria of MSA-C underwent a clinical and neuroradiological workup with respect to cerebellar features. The MR protocol consisted of a sagittal T1-weighted three-dimensional fast low-angle shot (3D FLASH) sequence and a transversal T2- and spin-density-weighted turbo spin-echo sequence. The proton magnetic resonance spectroscopic imaging ((1)H-MRSI) protocol consisted of two chemical shift imaging (CSI) sequences (echo time (TE) = 20 and 135 msec).

RESULTS

Both short- and long-TE MR spectroscopy (MRS) images showed significant decreases in values for N-acetylaspartate to creatine (NAA/Cr), and choline to creatine (Cho/Cr) ratios in MSA-C and SCA2 compared to normal controls, though there was no difference between the two patient groups. In contrast, distinct cerebellar lactate (Lac) peaks were detected in seven SCA2 patients, and small peaks were detected in two. However, we did not detect any definite Lac peak in MSA-C or control subjects.

CONCLUSION

MRSI revealed Lac pathology in SCA2 but not in MSA-C. Whether this indicates distinct pathogenetic mechanisms of cerebellar degeneration remains to be established.

Degeneration of the inferior olive in spinocerebellar ataxia 6 may depend on disease duration: report of two autopsy cases and statistical analysis of autopsy cases reported to date

This report concerns a clinicopathological study of two autopsied patients with spinocerebellar ataxia 6 (SCA6), and a statistical analysis between neuronal loss of the inferior olive and disease duration of 15 SCA6 autopsy cases reported to date, including the two cases reported in this study. Cases 1 and 2 came from independent Japanese families. Case 1 developed gait disturbance at age 35 years and died at age 78 years; she had a CAG-repeat expansion of the SCA6 gene (25/13). Case 2 presented with gait disturbance at age 68 years and died at age 78 years; he had an expanded CAG-repeat of the SCA6 gene (22/13). Neuropathological examination of both cases disclosed not only neuronal loss of the Purkinje cells and inferior olive, but also some unnoticed features, including cactus-like expansion of the dendrite of Purkinje cells and relative preservation of Golgi cells in the granular layer of the cerebellum. Exploratory statistical analysis between 11 SCA6 autopsy cases with neuronal loss in the inferior olive (average disease duration: 27 years) and four SCA6 autopsy cases without neuronal loss in the olive (average disease duration: 14.5 years) was investigated by Kaplan-Meier estimates of survival and log-rank test, retrospectively. Kaplan-Meier estimates of survival revealed an obvious difference between the two groups. Survival of 10 years after the disease onset was 90.9% in the former 11 SCA6 autopsy cases, but was 50% in the latter four SCA6 autopsy cases. Furthermore, a log-rank test on the two groups disclosed a significant difference (P=0.0450). We postulate that the neuronal loss of the inferior olive in SCA6 may depend on disease duration.

Focal dystonia as a presenting sign of spinocerebellar ataxia 17

We report on the clinical manifestation of spinocerebellar ataxia 17 (SCA17) in 3 members of a German family, in whom the pathological repeat expansion in the TATA-binding protein gene ranged from 53 to 55 repeats (normal: 29-42). The main clinical features were focal dystonia as presenting sign, followed by cerebellar ataxia, and, in the later course of one case, dementia and marked spasticity with signs of cerebellar and cerebral atrophy on brain computed tomography (CT) scan. In conclusion, SCA17 mutations should be considered in the differential diagnosis of focal dystonia.

Magnetic resonance imaging findings of Machado-Joseph disease: histopathologic correlation

PURPOSE

To determine the characteristic magnetic resonance imaging (MRI) findings of early- and late-stage Machado-Joseph disease (MJD) and to examine correlation with pathologic specimens.

PATIENTS AND METHODS

Four patients genetically diagnosed with MJD and a familial case of MJD were all examined using MRI. Machado-Joseph disease was pathologically confirmed in one of the four genetically diagnosed patients, and the findings were compared with the MRI results.

RESULTS

In all three patients who had MJD for less than 8 years, MRI confirmed mild cerebellar atrophy, particularly in the vermis, and atrophic changes in the superior cerebellar peduncle. Mild pontine atrophy was observed in these three patients. Atrophic changes in the pontine tegmentum were more prominent than those of the pontine base in these patients. Two of the three patients showed mild frontal atrophy. Of the five total patients, two had the disease for over 10 years and showed progressive atrophy of the brainstem and mild frontal atrophy. These two patients also showed pallidal atrophy. One autopsied case in which the disease duration was 17 years showed a typical pathologic picture of MJD. Macroscopic findings for this patient showed marked atrophy of the pons, mild cerebellar atrophy (particularly in the vermis), marked atrophy of the superior cerebellar peduncle, severe involvement of motor nuclei, and atrophy and discoloration of the pallidum and subthalamic nuclei.

CONCLUSION

In the early stages of MJD, mild pontine atrophy, particularly in the tegmentum, and mild cerebellar atrophy are typical MRI findings. Atrophic changes in the brainstem may be progressive. Pallidal atrophy may be observed in patients with long disease duration. These findings correlated with the pathologic findings.

Androgen receptor with elongated polyglutamine tract forms aggregates that alter axonal trafficking and mitochondrial distribution in motor neuronal processes

The CAG/polyglutamine (polyGln)-related diseases include nine different members that together form the most common class of inherited neurodegenerative disorders; neurodegeneration is linked to the same type of mutation, found in unrelated genes, consisting of an abnormal expansion of a polyGln tract normally present in the wild-type proteins. Nuclear, cytoplasmic, or neuropil aggregates are detectable in CAG/polyGln-related diseases, but their role is still debated. Alteration of the androgen receptor (AR), one of these proteins, has been linked to spinal and bulbar muscular atrophy, an X-linked recessive disease characterized by motoneuronal death. By using immortalized motoneuronal cells (the neuroblastoma-spinal cord cell line NSC34), we analyzed neuropil aggregate formation and toxicity: green fluorescent protein-tagged wild-type or mutated ARs were cotransfected into NSC34 cells with a blue fluorescent protein tagged to mitochondria. Altered mitochondrial distribution was observed in neuronal processes containing aggregates; occasionally, neuropil aggregates and mitochondrial concentration corresponded to axonal swelling. Neuropil aggregates also impaired the distribution of the motor protein kinesin. These data suggest that neuropil aggregates may physically alter neurite transport and thus deprive neuronal processes of factors or components that are important for axonal and dendritic functions. The soma may then be affected, leading to neuronal dysfunctions and possibly to cell death.

Polyglutamine tract expansion of the androgen receptor in a motoneuronal model of spinal and bulbar muscular atrophy

Spinobulbar muscular atrophy (SBMA) is a late-onset disorder characterized by progressive muscle loss, degeneration of motoneurons in the spinal cord and brainstem, and partial androgen insensitivity. SBMA is directly correlated with the expansion of CAG repeats encoding a polyglutamine tract (polyQ) of extended length. The identification of polyQ expansion in SBMA led to the discovery of an entire class of neurodegenerative disorders. In fact, at least eight different diseases, including Huntington's disease, share a common molecular mechanism involving an expansion of a polyQ tract within different proteins. The elongated polyQ tract causes a toxic gain of function in the mutant protein and is associated with the formation of intracellular aggregates, whose pathogenetic role has not been fully established yet. Our observations in a motoneuron cell line (NSC34), indicate that the expression of the androgen receptor (AR) carrying the elongated polyQ tract (AR-Q48) has a toxic effect in aggregate-independent manner. In fact, in basal condition, AR-Q48 shows a cytoplasmic diffuse distribution, yet it reduces the viability of transfected NSC34. In contrast, testosterone treatment, while inducing aggregation of the mutant AR, also increases cell viability. Aggregates in NSC34 are localized mainly in the perinuclear region and occasionally in the neuropil, whereas no nuclear aggregate has ever been found. Further observations of the minor subset of cells showing neuropil aggregates, reveal an alteration of the neurite morphology, suggesting a different role of the two types of cytoplasmic aggregates.

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.

Molecular pathology of dentatorubral-pallidoluysian atrophy

Dentatorubral-pallidoluysian atrophy (DRPLA) is an autosomal dominant disorder characterized clinically by myoclonus, epilepsy, cerebellar ataxia, choreoathetosis and dementia. Cardinal pathological features of DRPLA are a combined degeneration of both the dentatorubral and the pallidoluysian systems. Although the early sporadic cases were reported by Western neuropathologists, a strong heritability and an age of onset-dependent variability of the clinical features were carefully deduced by Japanese clinicians. The disease is fairly common in Japan, but extremely rare in Caucasians. Since the gene was identified in 1994, DRPLA is known as one of the CAG repeat expansion diseases, in which the responsible gene is located on chromosome 12p and its product is called atrophin 1. DRPLA shows prominent 'anticipation', which is genetically clearly explained by a marked instability of the expanded CAG repeat length during spermatogenesis. Moreover, the instability of the CAG repeat length also seems to occur in the somatic cells, resulting in 'somatic mosaicism'. Possible mechanism(s) underlying the neuronal cell death in DRPLA are discussed in terms of molecular pathological points of view.

Multiple system atrophy

MSA is a complex disorder, with regard to its pathology and cause as well as its clinical diagnosis and treatment. Although a number of clinical treatments may improve quality of life for these patients, given the widespread pathology present, symptomatic treatment, particularly that involving neurotransmitter replacement, is likely to remain difficult. Truly effective treatment for these patients is likely to depend on an understanding of the underlying pathogenic mechanisms and methods to halt or reverse disease progression. A firm understanding of the classification of these disorders is the first step to understanding the relevant pathogenic mechanisms. The finding of intracytoplasmic glial inclusion bodies provides a compelling piece of evidence that SND, OPCA, and SDS do, in fact, belong to one nosologic entity. These inclusions do not seem to be present in familial cases of OPCA; thus, they may provide a means to improve diagnostic specificity as well as sensitivity. With the ability to define clearly the entity of MSA, an understanding of the pathophysiology can be developed along with other degenerative neurologic diseases, including Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, and Huntington's disease.