Dentatorubral-pallidoluysian Atrophy Research Articles

A case of late adult-onset dentatorubral-pallidoluysian atrophy mimicking central pontine myelinolysis

We report the case of a 52-year-old man with late-onset dentatorubral-pallidoluysian atrophy (DRPLA). MRI findings of late-onset DRPLA usually showed the involvement of cerebral white matter lesions with high intensity on T2-weighted images (WI), in addition to brainstem, globus pallidus, and thalamus. But our patient did not present with abnormal manifestation of white matter lesions of the cerebrum. In addition, the appearance of pontine base was remarkably similar to central pontine myelinolysis (CPM). There is no reported case of DRPLA mimicking CPM in the literature, while there is one previous report of CPM with cerebellar ataxia without pyramidal tract involvement, and CPM may exhibit cerebellar ataxia. Although there is differentiation between CPM and DRPLA by the presence of the atrophy of brainstem and cerebellum, the characteristic MRI findings of pontine base may make it difficult to differentiate CPM with cerebellar ataxia from DRPLA with inconspicuous leukoencephalopathy. In such a situation, we should return to the clinical history and background of a patient, and, if necessary, DNA analysis should be performed for a definite diagnosis.

Frequencies of spinocerebellar ataxia subtypes in Thailand: window to the population history?

Spinocerebellar ataxias (SCAs) are a heterogeneous group of disorders with almost 30 subtypes. The prevalence and relative frequency of each subtype vary among different populations. In this article, we report the relative frequency of six SCA subtypes in the Thai population and attempt to explain the observed pattern when compared with other populations in this region. We searched for SCA type 1, SCA2, SCA3, SCA6, SCA7 and dentatorubral-pallidoluysian atrophy mutations using GeneScan analysis in 340 patients from 182 families, in which at least one person had a clinical diagnosis of SCA. We analyzed the relative frequencies of SCA subtypes on a family basis, and compared these with the data in the Chinese and Indian populations. SCA3 was found in 19.2% of the patients (Agresti-Coull 95% confidence interval: 14.1-25.6%), SCA1 in 11.5% (7.6-17.1%) and SCA2 in 10.4% (6.7-15.8%). SCA6 was found in three families, with a relative frequency of 1.6% (0.3-5.0%). Compared with the related populations, the Thai SCA3 frequency was less than that of the Chinese, whereas it was higher than that in most of the Indian studies. The reverse is true for the SCA1/SCA2 frequency. A similar study in Singapore, where there was a clear history of population admixture, also showed the frequencies between those of the Chinese and the Indian populations. Although SCA3 was the most common identifiable SCA subtype in Thailand, SCA1 and SCA2 were also relatively common. Our results also supported some degree of admixture with the Indians in the Thai population and justify further study in the area.

Reassessment of phenytoin for treatment of late stage progressive myoclonus epilepsy complicated with status epilepticus

In order to find an effective treatment option for status epilepticus in progressive myoclonus epilepsy (PME), we reviewed the clinical course of 9 patients with PME. Initially, epilepsy was successfully treated with antiepileptics. However, it gradually became refractory to medication, and status epilepticus emerged 3-19 years after the onset of epilepsy. In these patients, status epilepticus in PME was classified into (1) myoclonic status epilepticus (MSE), (2) myoclonic-generalized status epilepticus (MGSE), and (3) generalized status epilepticus (GSE). MSE was common in patients with neuronal ceroid lipofuscinosis, and GSE was common in those with dentatorubral-pallidoluysian atrophy. MGSE was characterized by the mixture of escalating myoclonus and generalized seizures, and was observed in patients with Gaucher disease or unspecified PME. All patients were often refractory to infusion of benzodiazepines and barbiturates but phenytoin was able to terminate status epilepticus in 7 patients. Oral phenytoin administration as preventive therapy was effective in 6 patients. Aggravation of myoclonus was not provoked by these treatments. We propose that phenytoin should be considered as a treatment choice for PME patients at late stages to prevent the detrimental effects of prolonged or repeated status epilepticus on the brain tissues.

SCA-LSVD: A repeat-oriented locus-specific variation database for genotype to phenotype correlations in spinocerebellar ataxias

Repeat expansion has been implicated in 10 out of 17 candidate genes identified for autosomal dominant cerebellar ataxias (ADCAs)-commonly referred as spinocerebellar ataxias (SCAs). Though genetically distinct, the SCAs share a large number of features that confound their clinical classification. In addition, there is a difference in the prevalence and phenotypic expression of ataxias between different ethnic groups. We have created a new SCA-locus-specific variation database (LSVD) that aims to catalog and integrate information on SCAs associated with trinucleotide repeat expansion (SCA1, SCA 2, SCA 3, SCA 6, SCA 7, SCA 8, SCA 12, SCA 17, Friedreich's ataxia [FRDA], and dentatorubral-pallidoluysian atrophy [DRPLA]) from all over the world. The database has been developed using the Leiden Open (source) Variation Database (LOVD) software (Leiden University Medical Center, Leiden, the Netherlands). The database houses detailed information on clinical features, such as age and symptom at onset, mode of inheritance, and genotype information, pertaining to the SCA patients from more than 400 families across India. All the compiled genotype data conforms to the HGVS Nomenclature guidelines. This would be a very useful starting point for understanding the molecular correlates of phenotypes in ataxia-a multilocus disease in which related molecular mechanisms converge to overlapping phenotypes.

Clinical and molecular findings in the first identified Italian family with dentatorubral-pallidoluysian atrophy.

Dentatorubral-pallidoluysian atrophy (DRPLA) is a rare autosomal dominant neurodegenerative disorder mostly observed in Japan, rarely reported in American and North European populations. The aim of this study is to characterize the clinical and molecular features of the first identified Italian DRPLA family. We describe a 33-year-old female presenting with ataxia, intellectual decline, epilepsy, and choreoathetosis with an adult age onset. Genomic DNA was isolated from peripheral blood lymphocytes of the patient and of her healthy family members following standard procedures. Molecular tests were performed including genetic analysis for SCA1, 2, and 3 (spinocerebellar ataxias), Huntington's disease (HD) and DRPLA, due to a possible overlapping in clinical presentation. Molecular analysis revealed in our patient the presence of a pathological CAG expansion within the DRPLA gene. We have also documented the presence of a smaller CAG expansion in her apparently healthy brother, excluding the possibility of a de novo mutation. We conclude that both siblings may have inherited the molecular lesion from their deceased father, the mother being normal at molecular evaluation. Our kindred and a previously reported family from the island of Malta suggest that hereditary DRPLA may also be present in the Mediterranean area.

Prevalence of Spinocerebellar Degenerations in the Hokuriku District in Japan

Background: The prevalence of disease subtypes of spinocerebellar degenerations (SCDs) varies between countries, and even between areas within a country. We report unprecedented epidemiologic data on SCDs in the Hokuriku district, which is located in the central, western part of Japan. Methods: Clinical and genetic data on SCD patients were obtained via questionnaires distributed to all the departments of neurology, psychiatry and internal medicine in the Hokuriku district (n = 418). Results: Among the SCD patients, autosomal dominant cerebellar ataxias (ADCAs) were noted in 40.4%, multiple system atrophy in 24.7%, cortical cerebellar atrophy in 13.3% and autosomal recessive cerebellar ataxia in 0.3%. Genetically confirmed ADCA patients included those with Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 (SCA3; 63.3%), SCA6 (20.0%), ADCA linked to chromosome 16q22.1 (10.0%), dentatorubral pallidoluysian atrophy (4.4%), SCA1 (1.1%) and SCA2 (1.1%). MJD/SCA3 was highly prevalent in the Toyama prefecture of the Hokuriku district, accounting for 90% of genetically confirmed ADCAs by birthplace; MJD/SCA3 patients were concentrated in the Gosei area, the western part of the Toyama prefecture, giving an estimated prevalence of 19.1 per 100,000 inhabitants. Conclusions: The Hokuriku district, especially the Gosei area of Toyama, had a surprisingly high relative frequency and prevalence of MJD/SCA3, which is comparable to that in the Azores, Portugal.

Spatio-temporal origin of cerebellar neurons and glias revealed by in utero electroporation

Previously, several studies have demonstrated changes in the levels of small heat shock proteins (sHSP) in the transgenic mouse models of familial amyotrophic lateral sclerosis (fALS) linked to mutations in Cu/Zn superoxide dismutase. Here, we compared the expression of sHSPs in transgenic mouse models of fALS, Parkinson's disease (PD), dentato-rubral pallido-luysian atrophy (DRPLA) and Huntington's disease (HD); where the expression of mutant cDNA genes was under the transcriptional regulation of the mouse prion protein promoter. These models express G37R mutant Cu/Zn superoxide dismutase (SOD1G37R; fALS), A53T mutant α-synuclein (α-SynA53T; PD), full-length mutant atrophin-1-65Q, and htt-N171-82Q (huntingtin N-terminal fragment; HD). We found that the levels and solubilities of two sHSPs, Hsp25 and αB-crystallin, were differentially regulated in these mice. Levels of both Hsp25 and αB-crystallin were markedly increased in subgroups of glias at the affected regions of symptomatic SODG37R and α-SynA53T transgenic mice; abnormal deposits or cells intensely positive for αB-crystallin were observed in SODG37R mice. By contrast, neither sHSP was induced in spinal cords of htt-N171-82Q or atrophin-1-65Q mice, which do not develop astrocytosis or major motor neuron abnormalities. Interestingly, the levels of insoluble αB-crystallin in spinal cords gradually increased as a function of age in nontransgenic animals. In vitro, αB-crystallin was capable of suppressing the aggregation of α-SynA53T, as previously described for a truncated mutant SOD1. The transgenes in these mice are expressed highly in astrocytes and thus our results suggest a role for small heat shock proteins in protecting activated glial cells such as astrocytes in neurodegenerative diseases.

Nucleation of protein aggregation kinetics as a basis for genotype-phenotype correlations in polyglutamine diseases

Recent studies of inherited neurodegenerative disorders have suggested a linkage between the propensity toward aggregation of mutant protein and disease onset. This is particularly apparent for polyglutamine (polyQ) diseases caused by expansion of CAG-trinucleotide repeats. However, a quantitative framework for relating aggregation kinetics with molecular mechanisms of neurodegeneration initiation is lacking. Here, using the repeat-length-dependent age-of-onset in polyQ diseases, we derived a mathematical model based on nucleation of aggregation kinetics to describe genotype-phenotype correlations, and validated the model using both in vitro data and clinical data. Instead of describing polyQ aggregation kinetics with a derivative equation, our model divided age-of-onset (equivalent to the time required for aggregation) into two processes: nucleation lag time (a first-order exponential function of CAG-repeat length) and elongation time. With the exception of spinocerebellar ataxia (SCA) 3, the relation between CAG-repeat length and age-of-onset in all examined polyQ diseases, including Huntington's disease, dentatorubral-pallidoluysian atrophy and SCA1, -2, -6 and -7, could be well explained by three parameters derived from linear regression analysis based on the nucleated growth polymerization model. These parameters composed of probability of nucleation at an individual repeat, a protein concentration associated factor, and elongation time predict the overall features of neurodegeneration initiation, including constant risk for cell death, toxic polyQ species, main pathological subcellular site and the contribution of cellular factors. Our model also presents an alternative therapeutic strategy according to the distinct subcellular loci by the finding that nuclear localization of soluble mutant protein monomers itself has great impact on disease onset.

Electroclinical features of epilepsy in patients with juvenile type dentatorubral‐pallidoluysian atrophy

To clarify the electroclinical characteristics of epileptic seizures in patients with juvenile type dentatorubral-pallidoluysian atrophy (DRPLA). Seventeen patients with juvenile type DRPLA confirmed by genetic analysis were studied retrospectively. The clinical records of all 17 patients and the ictal video electroencephalography (EEG) recordings from 12 of the 17 patients were reviewed. Electroclinical studies in 12 patients identified 11 habitual seizures in 6 patients as partial seizures on ictal video EEG recordings. Clinical manifestations composed mainly of versions of the head and loss of consciousness. These partial seizures were persistently recorded throughout the clinical course. Brief generalized seizures (atypical absence and myoclonic seizure) were observed in 6 of 12 patients at the early stage. In contrast, generalized tonic-clonic seizures (GTCS) were recorded in four advanced stage patients who were almost bedridden. Semiological studies in 17 patients showed that the prevalence of partial seizures was significantly higher in patients with younger epilepsy onset (below 10 years of age; chi(2) test, p < 0.05) and that the age of epilepsy onset was significantly lower in patients with partial seizures than in those without partial seizures (Mann-Whitney U test, p = 0.02). However, the number of CAG repeats and age at clinical onset were not significantly different between two groups. Partial seizure is one of the common epileptic features in juvenile type DRPLA, especially in patients with younger epilepsy onset. Seizure types may be affected in an age-dependent manner and change evolutionally during progression of the clinical stage.

Severe neurological phenotypes of Q129 DRPLA transgenic mice serendipitously created by en masse expansion of CAG repeats in Q76 DRPLA mice

We herein provide a thorough description of new transgenic mouse models for dentatorubral–pallidoluysian atrophy (DRPLA) harboring a single copy of the full-length human mutant DRPLA gene with 76 and 129 CAG repeats. The Q129 mouse line was unexpectedly obtained by en masse expansion based on the somatic instability of 76 CAG repeats in vivo. The mRNA expression levels of both Q76 and Q129 transgenes were each 80% of that of the endogenous mouse gene, whereas only the Q129 mice exhibited devastating progressive neurological phenotypes similar to those of juvenile-onset DRPLA patients. Electrophysiological studies of the Q129 mice demonstrated age-dependent and region-specific presynaptic dysfunction in the globus pallidus and cerebellum. Progressive shrinkage of distal dendrites of Purkinje cells and decreased currents through α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and γ-aminobutyrate type A receptors in CA1 neurons were also observed. Neuropathological studies of the Q129 mice revealed progressive brain atrophy, but no obvious neuronal loss, associated with massive neuronal intranuclear accumulation (NIA) of mutant proteins with expanded polyglutamine stretches starting on postnatal day 4, whereas NIA in the Q76 mice appeared later with regional specificity to the vulnerable regions of DRPLA. Expression profile analyses demonstrated age-dependent down-regulation of genes, including those relevant to synaptic functions and CREB-dependent genes. These results suggest that neuronal dysfunction without neuronal death is the essential pathophysiologic process and that the age-dependent NIA is associated with nuclear dysfunction including transcriptional dysregulations. Thus, our Q129 mice should be highly valuable for investigating the mechanisms of disease pathogenesis and therapeutic interventions.

Mutations in NR2E3 can cause dominant or recessive retinal degenerations in the same family

NR2E3, a photoreceptor-specific nuclear receptor (PNR), represses cone-specific genes and activates several rod-specific genes. In humans, mutations in NR2E3 have been associated with the recessively-inherited enhanced short-wavelength sensitive S-cone syndrome (ESCS) and, recently, with autosomal dominant (ad) retinitis pigmentosa (RP) (adRP). In the present work, we describe two additional families affected by adRP that carry a heterozygous c.166G>A (p.G56R) mutation in the NR2E3 gene. Functional analysis determined the dominant negative activity of the p.G56R mutant protein as the molecular mechanism of adRP. Interestingly, in one pedigree, the most common causal variant for ESCS (p.R311Q) cosegregated with the adRP-linked p.G56R mutation, and the compound heterozygotes exhibited an ESCS-like phenotype, which in 1 of the 2 cases was strikingly "milder" than the patients carrying the p.G56R mutation alone. Impaired repression of cone-specific genes by the corepressors atrophin-1 (dentatorubral-pallidoluysian atrophy [DRPLA] gene product) and atrophin-2 (arginine-glutamic acid dipeptide repeat [RERE] protein) appeared to be a molecular mechanism mediating the beneficial effect of the p.R311Q mutation. Finally, the functional dominance of the p.R311Q variant to the p.G56R mutation is discussed.

Attenuated presentation of ataxia-telangiectasia with familial cancer history

JO N 2857 ing, generalized choreo-athetoid movements, spasmodic torticollis, writing tremor and myoclonic jerks. Examination also revealed cerebellar ataxia. The IQ was liminal. Neuroleptics, DL-hydroxytryptophan, trihexyphenidyl, and piribedil provided little or no improvement. By the age of 42, the patient was confined to a wheelchair, mainly due to the midline cerebellar disturbances. There was also limb ataxia, dystonia of the legs, torticollis and rest tremor. An ocular apraxia was noted without telangiectasia. Cognitive impairment had appeared with executive, judgement, reasoning and fixation memory troubles. Since age 16 a slowly worsening, predominantly sensory axonal neuropathy was known, whereas cerebral imaging showed global cerebellar atrophy. Standard blood tests, copper balance, vitamin E assay were normal. There was no evidence of metabolic or mitochondrial disorders. Genetic analysis excluded Friedreich’s disease, most frequent spinocerebellar ataxias, dentatorubropallidoluysian atrophy and Huntington’s disease. Igs serum level was normal. There was a slight rise in the serum level of αfetoprotein (AFP) (25.1 μg/L, Clemence Simonin David Devos Isabelle Vuillaume Berengere de Martinville Bernard Sablonniere Alain Destee Dominique Stoppa-Lyonnet Luc Defebvre

Molecular Genetics and Biomarkers of Polyglutamine Diseases

Polyglutamine diseases are hereditary neurodegenerative disorders caused by an abnormal expansion of a trinucleotide CAG repeat, which encodes a polyglutamine tract. To date, nine polyglutamine diseases are known: Huntington's disease (HD), spinal and bulbar muscular atrophy (SBMA), dentatorubral-pallidoluysian atrophy (DRPLA) and six forms of spinocerebellar ataxia (SCA). The diseases are inherited in an autosomal dominant fashion except for SBMA, which shows an X-linked pattern of inheritance. Although the causative gene varies with each disorder, polyglutamine diseases share salient genetic features as well as molecular pathogenesis. CAG repeat size correlates well with the age of onset in each disease, shows both somatic and germline instability, and has a strong tendency to further expand in successive generations. Aggregation of the mutant protein followed by the disruption of cellular functions, such as transcription and axonal transport, has been implicated in the etiology of neurodegeneration in polyglutamine diseases. Although animal studies have provided promising therapeutic strategies for polyglutamine diseases, it remains difficult to translate these disease-modifying therapies to the clinic. To optimize "proof of concept", the process for testing candidate therapies in humans, it is of importance to identify biomarkers which can be used as surrogate endpoints in clinical trials for polyglutamine diseases.

Huntington disease‐like 2: the first patient with apparent European ancestry

Huntington disease-like 2 (HDL2) is a rare autosomal dominant disorder of the nervous system, apparently indistinguishable from Huntington disease (HD). HDL2 is caused by the expansion above 40 CTG/CAG repeats, in a variably spliced exon of the junctophilin-3 gene, on chromosome 16q24.3. All patients described so far have been of African ancestry. A clinical evaluation, including the Unified Huntington's Disease Rating Scale, and brain Magnetic resonance imaging were achieved in a 48-year-old Brazilian man of apparent European extraction, and presenting a picture very suggestive of HD. Gene mutation analysis (HD, HDL1, HDL2, dentatorubralpallidoluysian atrophy and spinocerebellar ataxia 17) was performed. After exclusion of the HD mutation and other HDL disorders, we identified an expansion of 47 CTG/CAG at the HDL2 locus. To clarify the origin of the mutation and estimate the patient's ancestry, we performed haplotype studies and used the insertion/deletion polymorphisms method. Despite the fact that this patient had an estimated likelihood of 97.4% of being of European ancestry, the haplotype containing the expanded allele has been found only in Africans. Thus, this is the first HDL2 case reported in a patient with an apparent European ancestry, although bearing an African HDL2 haplotype. This work stresses the importance of performing the diagnosis of HDL2 in HD-like patients of various ethnicities, and particularly in highly mixed populations.

Huntington's disease phenocopies are clinically and genetically heterogeneous

Huntington's disease (HD) classically presents with movement disorder, cognitive dysfunction and behavioral problems but is phenotypically variable. One percent of patients with HD-like symptoms lack the causative mutation and are considered HD phenocopies. Genetic diseases known to cause HD phenocopies include HD-like syndromes HDL1, HDL2, and HDL4 (SCA17). HD has phenotypic overlap with dentatorubral-pallidoluysian atrophy, the spinocerebellar ataxias and neuroferritinopathy. Identifying the genetic basis of HD phenocopies is important for diagnosis and may inform the search for HD genetic modifiers. We sought to identify neurogenetic diagnoses in the largest reported cohort of HD phenocopy patients. Two hundred eighty-five patients with syndromes consistent with HD, who were HD expansion-negative, were screened for mutations in PRNP, JPH3, TBP, DRPLA, SCA1, SCA2, SCA3, FTL and FRDA. Genetic diagnoses were made in 8 subjects: we identified 5 cases of HDL4, 1 of HDL1 and 1 of HDL2. One patient had Friedreich's ataxia. There were no cases of DRPLA, SCA1, SCA2, SCA3, or neuroferritinopathy. HD phenocopies are clinically and genetically diverse and a definitive genetic diagnosis is currently possible in only a minority of cases. When undertaken, it should be clinically directed and patients and clinicians should be prepared for the low probability of reaching a genetic diagnosis in this group of patients.

Huntington's disease phenocopy syndromes

Patients presenting with features of Huntington's disease but lacking the causative genetic expansion can be challenging diagnostically. The differential diagnosis of such Huntington's disease phenocopy syndromes has not recently been reviewed. Cohort studies have established the relative frequencies of known Huntington's disease phenocopy syndromes, whereas newly described ones have been characterized genetically, clinically, radiologically and pathologically. About 1% of suspected Huntington's disease cases emerge as phenocopy syndromes. Such syndromes are clinically important in their own right but may also shed light on the pathogenesis of Huntington's disease. Huntington's disease produces a range of clinical phenotypes, and the range of syndromes that may be responsible for Huntington's disease phenocopies is correspondingly wide. Cohort studies have established that, while the majority of phenocopy patients remain undiagnosed, in those patients where a genetic diagnosis is reached the commonest causes are SCA17, Huntington's disease-like syndrome 2 (HDL2), familial prion disease and Friedreich's ataxia. We review the features of the reported genetic causes of Huntington's disease phenocopy syndromes, including HDL1-3, SCA17, familial prion disease, spinocerebellar ataxias, dentatorubral-pallidoluysian atrophy, chorea-acanthocytosis and iron-accumulation disorders. We present an evidence-based framework for the genetic testing of Huntington's disease phenocopy cases.

Dentatorubral pallidoluysian atrophy in South Wales

Background:Dentatorubral pallidoluysian atrophy (DRPLA) is a rare, autosomal dominant, clinically heterogeneous neurodegenerative disorder characterised clinically by progressive dementia, ataxia, chorea, myoclonic epilepsy and psychiatric disturbance and pathologically by combined degeneration...

Oxidative stress in neurodegeneration in dentatorubral-pallidoluysian atrophy

Dentatorubral-pallidoluysian atrophy (DRPLA) is one of the CAG-repeat diseases, and is classified into juvenile and early adult types showing progressive myoclonus epilepsy (PME) in addition to late adult type. We immunohistochemically examined accumulation of oxidative products and expression of superoxide dismutase (SOD) in autopsy cases of DRPLA. Oxidative products to nucleosides, 8-hydroxy-2'-deoxyguanosine and 8-hydroxyguanosine, were accumulated in the lenticulate nucleus predominantly in DRPLA cases having PME. Neuronal accumulation of 4-hydroxy nonenal, a reactive lipid aldehyde, was found in the hippocampus, globus pallidus and cerebellar dentate nucleus in adult DRPLA cases and controls. Cytoplasmic immunoreactivity for Cu/ZnSOD was reduced in the external segment of globus pallidus, dentate nucleus and cerebellar cortex in DRPLA cases. Mitochondrial immunoreactivity for MnSOD was reduced in the lenticulate nucleus and cerebellum in DRPLA cases having PME. Some DRPLA cases showed reduced immunoreactivity for MnSOD in the cerebral cortex. Coexistence of reduced SOD expression and polyglutamine was observed in a few cases. It has been discussed in Huntington's disease that expanded polyglutamine can lead to oxidative neurodegeneration. It is likely that oxidative stress can be involved in DRPLA, although relationship with expanded polyglutamine remains to be elusive.

CAG repeat disorder models and human neuropathology: similarities and differences

CAG repeat diseases are hereditary neurodegenerative disorders caused by expansion of a polyglutamine tract in each respective disease protein. They include at least nine disorders, including Huntington's disease (HD), dentatorubral pallidoluysian atrophy (DRPLA), spinal and bulbar muscular atrophy (SBMA), and the spinocerebellar ataxias SCA1, SCA2, SCA3 (also known as Machado-Joseph disease), SCA6, SCA7, and SCA17. It is thought that a gain of toxic function resulting from the protein mutation plays important and common roles in the pathogenesis of these diseases. Recent studies have disclosed that, in addition to the presence of clinical phenotypes and conventional neuropathology in each disease, human brains affected by CAG repeat diseases share several polyglutamine-related changes in their neuronal nuclei and cytoplasm including the formation of intranuclear inclusions. Although these novel pathologic changes also show a distribution pattern characteristic to each disease, they are generally present beyond the lesion distribution of neuronal loss, suggesting that neurons are affected much more widely than has been recognized previously. Various mouse models of CAG repeat diseases have revealed that CAG repeat lengths, which are responsible for polyglutamine diseases in humans, are not sufficient for creating the conditions characteristic of each disease in mice. Although high expression of mutant proteins in mice results in the successful generation of polyglutamine-related changes in the brain, there are still some differences from human pathology in the lesion distribution or cell types that are affected. In addition, no model has yet successfully reproduced the specific neuronal loss observed in humans. Although there are no models that fully represent the neuropathologic changes present in humans, the data obtained have provided evidence that clinical onset is not clearly associated with neuronal cell death, but depends on intranuclear accumulation of mutant proteins in neurons.

The Huntington's disease-like syndromes: what to consider in patients with a negative Huntington's disease gene test

Huntington's disease (HD), which is caused by a triplet-repeat expansion in the IT15 gene (also known as huntingtin or HD), accounts for about 90% of cases of chorea of genetic etiology. In recent years, several other distinct genetic disorders have been identified that can present with a clinical picture indistinguishable from that of HD. These disorders are termed Huntington's disease-like (HDL) syndromes. So far, four such conditions have been recognized, namely disorders attributable to mutations in the prion protein gene (HDL1), the junctophilin 3 gene (HDL2), and the gene encoding the TATA box-binding protein (HDL4/SCA17), and a recessively inherited HD phenocopy in a single family (HDL3), the genetic basis of which is currently poorly understood. These disorders, however, account for only a small proportion of cases with the HD phenotype but a negative genetic test for HD, and the list of HDL genes and conditions is set to grow. In this article, we review the most important HD phenocopy disorders identified to date and discuss the clinical clues that guide further investigation. We will concentrate on the four so-called HDL syndromes mentioned above, as well as other genetic disorders such as dentatorubral-pallidoluysian atrophy, neuroferritinopathy, pantothenate-kinase-associated neurodegeneration and chorea-acanthocytosis.