A systematic review of the treatment studies in Huntington's disease since 1990

Effects of different interventions on bruxism: an overview of systematic reviews

OBJECTIVE

This study aimed to evaluate, qualify, and summarize evidence presented in systematic reviews (SR) on treatments for bruxism.

METHODS

The overview was conducted using the PICO strategy: children, adolescents, and adults with bruxism (P) were submitted to different treatments (I) compared to other treatments, placebo, or no treatment (C) in order to evaluate incidence, prevalence, and number of episodes of bruxism (O). The search was carried out in six databases and gray literature up to July 2023. Data were extracted, and the ROBS tool was used, followed by a descriptive synthesis of the results.

RESULTS

A total of 31 SR were included. Sixteen showed a positive effect on episodes of bruxism (BE), while two had negative, one had neutral, and nine had inconclusive effects. Using the risk of bias in systematic reviews tool (ROBIS), risk of bias varied from low (n = 23) to high (n = 5) among the SR. Pharmacological treatment, oral rehabilitation, and other therapeutic approaches presented inconclusive or negative effects on BE, while oral appliances showed controversial effects. Biofeedback, physical therapy, laser therapy, and botulinum toxin showed positive effects on the reduction of BE.

CONCLUSION

Biofeedback, physical therapy, laser therapy, and botulinum toxin showed positive effects on the reduction of BE; there is still a lack of studies to support the safe and long-term use of these therapies.

REGISTRATION NUMBER

PROSPERO CRD42021273905.

The improvement of motor symptoms in Huntington's disease during cariprazine treatment

BACKGROUND

Huntington's disease (HD) is a progressive neurodegenerative disease, characterised by motor disturbances and non-motor (i.e., psychiatric) symptoms. Motor symptoms are the hallmark features of HD and take many forms. Their emergence is related to alterations in striatal dopaminergic neurotransmission: dopamine levels increase in the early stages of the disease, while more advanced stages are characterised by reduced dopamine levels. Such a biphasic change potentially explains the alterations in motor symptoms: increased dopamine-production induces hyperkinetic movements early in the disease course, while depleted dopamine storage leads to hypokinetic symptoms in the advanced phase. Dopamine D2-D3 partial agonists could be a promising treatment option in HD, as they have the potential to either elevate or lower the surrounding dopamine levels if the levels are too low or too high, respectively, potentially offering symptom-relief across the illness-course. Therefore, the present study aimed at exploring the effects of cariprazine, a dopamine D2-D3 partial agonist with high affinity to D3 receptors, on motor symptoms associated with HD.

METHODS

This was a single-centre, retrospective study where sixteen patients received off-label cariprazine treatment for 12 weeks (1.5-3 mg/day). Motor symptoms were evaluated using the Motor Assessment of the Unified Huntington's Disease Rating Scale. Least Square (LS) Mean Changes from Baseline (BL) to Week 8 and Week 12 in the Total Motor Score (TMS) were analysed using the Mixed Model for Repeated Measures method. In addition, improvement from BL to Week 8 and 12 was calculated for all motor items.

RESULTS

Data of 16 patients were collected, but data of only 15 patients were analysed as one patient dropped out due to non-compliance. Significant changes were observed from BL to Week 8 (LS Mean Change: -9.4, p < 0.0001) and to Week 12 (LS Mean Change: -12.8, p < 0.0001) in the TMS. The improvement was captured in the majority of motor functions, excluding bradykinesia and gait. Mild akathisia was the most commonly reported side-effect, affecting 3 patients.

CONCLUSION

This is the first study investigating the effectiveness of a D2-D3 partial agonist, cariprazine, in the treatment of HD. The findings of this study revealed that cariprazine was effective in the treatment of a wide range of motor symptoms associated with HD.

Symptomatic treatment options for Huntington's disease (guidelines of the German Neurological Society)

INTRODUCTION

Ameliorating symptoms and signs of Huntington's disease (HD) is essential to care but can be challenging and hard to achieve. The pharmacological treatment of motor signs (e.g. chorea) may favorably or unfavorably impact other facets of the disease phenotype (such as mood and cognition). Similarly, pharmacotherapy for behavioral issues may modify the motor phenotype. Sometimes synergistic effects can be achieved. In patients undergoing pragmatic polypharmacological therapy, emerging complaints may stem from the employed medications' side effects, a possibility that needs to be considered. It is recommended to clearly and precisely delineate the targeted signs and symptoms (e.g., chorea, myoclonus, bradykinesia, Parkinsonism, or dystonia). Evidence from randomized controlled trials (RCTs) is limited. Therefore, the guidelines prepared for the German Neurological Society (DGN) for German-speaking countries intentionally extend beyond evidence from RCTs and aim to synthesize evidence from RCTs and recommendations of experienced clinicians.

RECOMMENDATIONS

First-line treatment for chorea is critically discussed, and a preference in prescription practice for using tiapride instead of tetrabenazine is noted. In severe chorea, combining two antidopaminergic drugs with a postsynaptic (e.g., tiapride) and presynaptic mode of action (e.g., tetrabenazine) is discussed as a potentially helpful strategy. Sedative side effects of both classes of compounds can be used to improve sleep if the highest dosage of the day is given at night. Risperidone, in some cases, may ameliorate irritability but also chorea and sleep disorders. Olanzapine can be helpful in the treatment of weight loss and chorea, and quetiapine as a mood stabilizer with an antidepressant effect.

CONCLUSIONS

Since most HD patients simultaneously suffer from distinct motor signs and distinct psychiatric/behavioral symptoms, treatment should be individually adapted.

Genetic risk for Huntington Disease and reproductive decision-making: A systematic review

Huntington Disease (HD) is an incurable autosomal dominant single gene neurodegenerative disorder. Typical onset is between 30 and 40 years and characterised by motor difficulties, cognitive impairment, and behavioural and personality changes. The availability of reproductive testing means that affected and at-risk individuals can make reproductive decisions with genetic risk in mind. We aimed to summarise the literature on reproductive decision-making in the context of HD risk in terms of outcomes and the subjective experiences of at-risk individuals. Five databases were searched. Findings were synthesised using Framework analysis to identify common factors across results of quantitative and qualitative studies. Twenty five studies met inclusion criteria. Framework analysis identified the following key areas: 'The relationship between reproductive intentions and HD genetic risk', 'Views on assistive options', 'Complexity and challenges in reproductive decision-making', 'Actual reproductive outcomes', and 'Other factors influencing reproductive decision-making'. Quality of included studies was mixed. Reproductive decision making in the context of HD risk was found to be a complex and emotionally challenging process. Further research is required into reproductive decision-making and outcomes among those not utilising assistive options, and in developing a model of reproductive decision-making in HD.

Non-Invasive Neuromodulation Methods to Alleviate Symptoms of Huntington's Disease: A Systematic Review of the Literature

Huntington's disease (HD) is a progressive and debilitating neurodegenerative disease. There is growing evidence for non-invasive neuromodulation tools as therapeutic strategies in neurodegenerative diseases. This systematic review aims to investigate the effectiveness of noninvasive neuromodulation in HD-associated motor, cognitive, and behavioral symptoms. A comprehensive literature search was conducted in Ovid MEDLINE, Cochrane Central Register of Clinical Trials, Embase, and PsycINFO from inception to 13 July 2021. Case reports, case series, and clinical trials were included while screening/diagnostic tests involving non-invasive neuromodulation, review papers, experimental studies on animal models, other systematic reviews, and meta-analyses were excluded. We have identified 19 studies in the literature investigating the use of ECT, TMS, and tDCS in the treatment of HD. Quality assessments were performed using Joanna Briggs Institute's (JBI's) critical appraisal tools. Eighteen studies showed improvement of HD symptoms, but the results were very heterogeneous considering different intervention techniques and protocols, and domains of symptoms. The most noticeable improvement involved depression and psychosis after ECT protocols. The impact on cognitive and motor symptoms is more controversial. Further investigations are required to determine the therapeutic role of distinct neuromodulation techniques for HD-related symptoms.

HSF1 and Its Role in Huntington's Disease Pathology

PURPOSE OF REVIEW

Heat shock factor 1 (HSF1) is the master transcriptional regulator of the heat shock response (HSR) in mammalian cells and is a critical element in maintaining protein homeostasis. HSF1 functions at the center of many physiological processes like embryogenesis, metabolism, immune response, aging, cancer, and neurodegeneration. However, the mechanisms that allow HSF1 to control these different biological and pathophysiological processes are not fully understood. This review focuses on Huntington's disease (HD), a neurodegenerative disease characterized by severe protein aggregation of the huntingtin (HTT) protein. The aggregation of HTT, in turn, leads to a halt in the function of HSF1. Understanding the pathways that regulate HSF1 in different contexts like HD may hold the key to understanding the pathomechanisms underlying other proteinopathies. We provide the most current information on HSF1 structure, function, and regulation, emphasizing HD, and discussing its potential as a biological target for therapy.

DATA SOURCES

We performed PubMed search to find established and recent reports in HSF1, heat shock proteins (Hsp), HD, Hsp inhibitors, HSF1 activators, and HSF1 in aging, inflammation, cancer, brain development, mitochondria, synaptic plasticity, polyglutamine (polyQ) diseases, and HD.

STUDY SELECTIONS

Research and review articles that described the mechanisms of action of HSF1 were selected based on terms used in PubMed search.

RESULTS

HSF1 plays a crucial role in the progression of HD and other protein-misfolding related neurodegenerative diseases. Different animal models of HD, as well as postmortem brains of patients with HD, reveal a connection between the levels of HSF1 and HSF1 dysfunction to mutant HTT (mHTT)-induced toxicity and protein aggregation, dysregulation of the ubiquitin-proteasome system (UPS), oxidative stress, mitochondrial dysfunction, and disruption of the structural and functional integrity of synaptic connections, which eventually leads to neuronal loss. These features are shared with other neurodegenerative diseases (NDs). Currently, several inhibitors against negative regulators of HSF1, as well as HSF1 activators, are developed and hold promise to prevent neurodegeneration in HD and other NDs.

CONCLUSION

Understanding the role of HSF1 during protein aggregation and neurodegeneration in HD may help to develop therapeutic strategies that could be effective across different NDs.

The functions of IRE1α in neurodegenerative diseases: Beyond ER stress

Inositol-requiring enzyme 1 α (IRE1α) is a type I transmembrane protein that resides in the endoplasmic reticulum (ER). IRE1α, which is the primary sensor of ER stress, has been proven to maintain intracellular protein homeostasis by activating X-box binding protein 1 (XBP1). Further studies have revealed novel physiological functions of the IRE1α, such as its roles in mRNA and protein degradation, inflammation, immunity, cell proliferation and cell death. Therefore, the function of IRE1α is not limited to its role in ER stress; IRE1α is also important for regulating other processes related to cellular physiology. Furthermore, IRE1α plays a key role in neurodegenerative diseases that are caused by the phosphorylation of Tau protein, the accumulation of α-synuclein (α-syn) and the toxic effects of mutant Huntingtin (mHtt). Therefore, targeting IRE1α is a valuable approach for treating neurodegenerative diseases and regulating cell functions. This review discusses the role of IRE1α in different cellular processes, and emphasizes the importance of IRE1α in neurodegenerative diseases.

Modulation of Huntington's disease in Drosophila

Huntington's disease (HD) is a progressive neurodegenerative disorder which deteriorates the physical and mental abilities of the patients. It is an autosomal dominant disorder and is mainly caused by the expansion of a repeating CAG triplet. A number of animal models ranging from worms, fruit flies, mice and rats to pigs, sheep and monkeys are available which have been helpful in understanding various pathways involved during the progression of the disease. Drosophila is one of the most commonly used model organisms for biomedical science, due to low cost maintenance, short life span and easily implications of genetic tools. The present review provides brief description of HD and the studies carried out for HD to date taking Drosophila as a model.

Striatal network modeling in Huntington's Disease

Medium spiny neurons (MSNs) comprise over 90% of cells in the striatum. In vivo MSNs display coherent burst firing cell assembly activity patterns, even though isolated MSNs do not burst fire intrinsically. This activity is important for the learning and execution of action sequences and is characteristically dysregulated in Huntington's Disease (HD). However, how dysregulation is caused by the various neural pathologies affecting MSNs in HD is unknown. Previous modeling work using simple cell models has shown that cell assembly activity patterns can emerge as a result of MSN inhibitory network interactions. Here, by directly estimating MSN network model parameters from single unit spiking data, we show that a network composed of much more physiologically detailed MSNs provides an excellent quantitative fit to wild type (WT) mouse spiking data, but only when network parameters are appropriate for the striatum. We find the WT MSN network is situated in a regime close to a transition from stable to strongly fluctuating network dynamics. This regime facilitates the generation of low-dimensional slowly varying coherent activity patterns and confers high sensitivity to variations in cortical driving. By re-estimating the model on HD spiking data we discover network parameter modifications are consistent across three very different types of HD mutant mouse models (YAC128, Q175, R6/2). In striking agreement with the known pathophysiology we find feedforward excitatory drive is reduced in HD compared to WT mice, while recurrent inhibition also shows phenotype dependency. We show that these modifications shift the HD MSN network to a sub-optimal regime where higher dimensional incoherent rapidly fluctuating activity predominates. Our results provide insight into a diverse range of experimental findings in HD, including cognitive and motor symptoms, and may suggest new avenues for treatment.

Monitoring of Huntington’s Disease Based on Wireless Sensing Technology

Huntington’s disease (HD) is a rare genetic disorder that cannot be cured by current medical techniques. With the development of the disease, the life of patients will become more and more difficult. It is necessary to timely and effectively evaluate the development of the patient’s condition based on the patient’s clinical symptoms to help doctors to formulate a reasonable and effective treatment plan, alleviate the condition, and improve the quality of life, which reflects humane care. Currently, wearable devices or video surveillance are generally used to monitor the patients, and these schemes have some disadvantages. This paper presents a new method to monitor patients with HD using wireless sensing technology. Firstly, experimental data were collected by the self-developed microwave sensing platform (MSP), and then the data were preprocessed. Finally, support vector machine (SVM) and random forest (RF) algorithms were used to train the model. The MSP system continuously monitors patients in a non-contact way, which will not bring inconvenience to patients’ lives, and will not involve privacy issues. The experimental results show that the prediction accuracy of SVM can be as high as 98.0% and that of RF can be as high as 96.7%, which proves the feasibility of the technical scheme described in this paper.

A Systematic Review of Rehabilitation for Corticobulbar Symptoms in Adults with Huntington's Disease

Background:

Corticobulbar symptoms have been reported in all stages of Huntington’s disease (HD); aspiration pneumonia associated with swallowing impairment has been identified as the most common cause of death. Whilst recent research has described positive effects of corticobulbar rehabilitation in other neurodegenerative conditions, it is unclear if this is similarly effective in HD. Preliminary evidence in corticospinal rehabilitation has revealed physical therapy and exercise could be beneficial for individuals with HD.

Objective:

This systematic review will explore the literature relative to rehabilitation of corticobulbar symptoms in adults with HD.

Methods:

Two investigators independently searched relevant electronic databases for literature related to corticobulbar rehabilitation in HD, published in English until October 2019. Included studies were critically appraised using the Oxford Centre for Evidence-based Medicine Levels of Evidence, Cochrane Risk of Bias Tool and Scottish Intercollegiate Guidelines Network checklists. Study outcomes included measurements of function, quality of life or neuromuscular physiology.

Results:

Seventy-seven publications were screened with eight studies meeting the inclusion criteria – two randomised control trials and six intervention studies. Validated and objective outcome measures of corticobulbar symptoms were infrequently used. There was a high risk of bias identified in 7/8 studies. The data suggested positive clinical outcomes, no adverse effects and no deterioration observed across longitudinal studies.

Conclusions:

This systematic review documented a lack of high-quality evidence to support the use of rehabilitation to treat corticobulbar symptoms in HD. However, the suggestion of potential positive effects based on available, albeit limited, studies provides justification for further research in this area.

Perceptions of the impact of chorea on health-related quality of life in Huntington disease (HD): A qualitative analysis of individuals across the HD spectrum, family members, and clinicians

Chorea, a hallmark symptom of Huntington's disease (HD), is characterized by jerky involuntary movements affecting the whole body that can interfere with daily functioning and impact health-related quality of life (HRQOL). To characterize chorea's impact on everyday functioning and HRQOL and identify patterns of perception and experiences of chorea among patients, caregivers, and providers. Data from focus groups of individuals with manifest HD (n = 8 early-stage HD; n = 16 late-stage HD), individuals at-risk or prodromal HD (n = 16), family HD caregivers (n = 17), and HD clinicians (n = 25). Focus group recordings were transcribed verbatim and analysed via constant comparison to identify meaningful and salient themes of living with chorea. Global themes of chorea's impact identified included: watching for chorea, experiences of stigma, and constraints on independence and relationships. Themes distinct to specific respondent groups included: Vigilance (at risk, prodromal); adaptation to chorea (early-stage); loss of autonomy and social life (late-stage); monitoring engagement (family caregivers) and safety (clinical providers). Living with chorea significantly constrains daily functioning, interactions, and HRQOL across the HD disease spectrum. Addressing these impacts via appropriate management of chorea can potentially enhance functioning, HRQOL, and overall satisfaction for persons with HD and their families.

The efficacy and safety of riluzole for neurodegenerative movement disorders: a systematic review with meta-analysis

Neurodegenerative movement disorders mainly include Parkinson’s disease, atypical parkinsonisms, Huntington disease, and hereditary ataxia. Riluzole is the only drug approved by the US Food and Drug Administration for amyotrophic lateral sclerosis. The neuroprotective effects of riluzole have been observed in experimental models of neurodegenerative movement disorders. In this paper, we aimed to systematically analyze the efficacy and safety of riluzole for patients with neurodegenerative movement disorder. We searched the electronic databases such as PubMed, EMBASE, CINAHL, Cochrane Library and China National Knowledge Infrastructure until June 2017 for the eligible randomized controlled trials, as well as the unpublished and ongoing trials. For continuous data, we calculated standardized mean differences with 95% confidence intervals if studies did not use the same scales to measure outcomes. For dichotomous data, we calculated risk differences if a trial reported no adverse events or dropouts. We pooled the results using a random-effects model. We included nine studies with 1320 patients with neurodegenerative movement disorders, which compared riluzole with placebo. No significant difference was found in the number of participants with adverse events but with motor improvement in hereditary ataxia. There were only two studies focusing on neuroprotective effect. Riluzole is well-tolerated in the patients with neurodegenerative movement disorders. Riluzole seems to be promising for patients with hereditary ataxia in symptomatic effect, which needs to be further confirmed by well-designed studies in the future. Moreover, it makes sense to design long-term study focusing on neuroprotective effect of riluzole in disease-modifying.

Huntington disease

Huntington disease is a monogenic neurodegenerative disorder that displays an autosomal-dominant pattern of inheritance. It is characterized by motor, psychiatric, and cognitive symptoms that progress over 15-20 years. Since the identification of the causative genetic mutation in 1993 much has been discovered about the underlying pathogenic mechanisms, but as yet there are no disease-modifying therapies available. This chapter reviews the epidemiology, genetic basis, pathogenesis, presentation, and clinical management of Huntington disease. The principles of genetic testing are explained. We also describe recent developments in the ongoing search for therapeutics and for biomarkers to track disease progression.

Reduced striato-cortical and inhibitory transcallosal connectivity in the motor circuit of Huntington's disease patients

Huntington's disease (HD) is a neurodegenerative disorder which is primarily associated with striatal degeneration. However, the alterations in connectivity of this structure in HD have been underinvestigated. In this study, we analyzed the functional and structural connectivity of the left putamen, while participants performed a finger-tapping task. Using fMRI and DW-MRI, 30 HD gene expansion carriers (HDGEC) and 29 healthy participants were scanned. Psychophysiological interaction analysis and DTI-based tractography were employed to examine functional and structural connectivity, respectively. Manifest HDGEC exhibited a reduced functional connectivity of the left putamen with the left and the right primary sensorimotor areas (SM1). Based on this result, the inhibitory functional connectivity between the left SM1 and the right SM1 was explored, appearing to be also decreased. In addition, the tract connecting these areas (motor corpus callosum), and the tract connecting the left putamen with the left SM1 appeared disrupted in HDGEC compared to controls. Significant correlations were found between measures of functional and structural connectivity of the motor corpus callosum, showing a coupling of both types of alterations in this tract. The observed reduction of functional and structural connectivity was associated with worse motor scores, which highlights the clinical relevance of these results. Hum Brain Mapp 39:54-71, 2018. © 2017 Wiley Periodicals, Inc.

Clinical Features of Huntington's Disease

Huntington's disease (HD) is the most common monogenic neurodegenerative disease and the commonest genetic dementia in the developed world. With autosomal dominant inheritance, typically mid-life onset, and unrelenting progressive motor, cognitive and psychiatric symptoms over 15-20 years, its impact on patients and their families is devastating. The causative genetic mutation is an expanded CAG trinucleotide repeat in the gene encoding the Huntingtin protein, which leads to a prolonged polyglutamine stretch at the N-terminus of the protein. Since the discovery of the gene over 20 years ago much progress has been made in HD research, and although there are currently no disease-modifying treatments available, there are a number of exciting potential therapeutic developments in the pipeline. In this chapter we discuss the epidemiology, genetics and pathogenesis of HD as well as the clinical presentation and management of HD, which is currently focused on symptomatic treatment. The principles of genetic testing for HD are also explained. Recent developments in therapeutics research, including gene silencing and targeted small molecule approaches are also discussed, as well as the search for HD biomarkers that will assist the validation of these potentially new treatments.

Differential electrophysiological and morphological alterations of thalamostriatal and corticostriatal projections in the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is a fatal genetic disorder characterized by cell death of medium-sized spiny neurons (MSNs) in the striatum, traditionally attributed to excessive glutamate inputs and/or receptor sensitivity. While changes in corticostriatal projections have typically been studied in mouse models of HD, morphological and functional alterations in thalamostriatal projections have received less attention. In this study, an adeno-associated virus expressing channelrhodopsin-2 under the calcium/calmodulin-dependent protein kinase IIα promoter was injected into the sensorimotor cortex or the thalamic centromedian-parafascicular nuclear complex in the R6/2 mouse model of HD, to permit selective activation of corticostriatal or thalamostriatal projections, respectively. In symptomatic R6/2 mice, peak amplitudes and areas of corticostriatal glutamate AMPA and NMDA receptor-mediated responses were reduced. In contrast, although peak amplitudes of AMPA and NMDA receptor-mediated thalamostriatal responses also were reduced, the areas remained unchanged due to an increase in response decay times. Blockade of glutamate reuptake further increased response areas and slowed rise and decay times of NMDA responses. These effects appeared more pronounced at thalamostriatal synapses of R6/2 mice, suggesting increased activation of extrasynaptic NMDA receptors. In addition, the probability of glutamate release was higher at thalamostriatal than corticostriatal synapses, particularly in R6/2 mice. Morphological studies indicated that the density of all excitatory synaptic contacts onto MSNs was reduced, which matches the basic electrophysiological findings of reduced amplitudes. There was a consistent reduction in the area of spines but little change in presynaptic terminal size, indicating that the postsynaptic spine may be more significantly affected than presynaptic terminals. These results highlight the significant and differential contribution of the thalamostriatal projection to glutamate excitotoxicity in HD.

The Association of VDAC with Cell Viability of PC12 Model of Huntington's Disease

It is becoming increasingly apparent that mitochondria dysfunction plays an important role in the pathogenesis of Huntington’s disease (HD), but the underlying mechanism is still elusive. Thus, there is a still need for further studies concerning the upstream events in the mitochondria dysfunction that could contribute to cell death observed in HD. Taking into account the fundamental role of the voltage-dependent anion-selective channel (VDAC) in mitochondria functioning, it is reasonable to consider the channel as a crucial element in HD etiology. Therefore, we applied inducible PC12 cell model of HD to determine the relationship between the effect of expression of wild type and mutant huntingtin (Htt and mHtt, respectively) on cell survival and mitochondria functioning in intact cells under conditions of undergoing cell divisions. Because after 48 h of Htt and mHtt expression differences in mitochondria functioning co-occurred with differences in the cell viability, we decided to estimate the effect of Htt and mHtt expression lasted for 48 h on VDAC functioning. Therefore, we isolated VDAC from the cells and tested the preparations by black lipid membrane system. We observed that the expression of mHtt, but not Htt, resulted in changes of the open state conductance and voltage-dependence when compared to control cells cultured in the absence of the expression. Importantly, for all the VDAC preparations, we observed a dominant quantitative content of VDAC1, and the quantitative relationships between VDAC isoforms were not changed by Htt and mHtt expression. Thus, Htt and mHtt-mediated functional changes of VDAC, being predominantly VDAC1, which occur shortly after these protein appearances in cells, may result in differences concerning mitochondria functioning and viability of cells expressing Htt and mHtt. The assumption is important for better understanding of cytotoxicity as well as cytoprotection mechanisms of potential clinical application.

Functional Differences Between Direct and Indirect Striatal Output Pathways in Huntington's Disease

There is morphological evidence for differential alterations in striatal medium-sized spiny neurons (MSNs) giving rise to the direct and indirect output pathways in Huntington's disease (HD). MSNs of the indirect pathway appear to be particularly vulnerable and markers for these neurons are lost early in postmortem brains and in genetic mouse models. In contrast, MSNs of the direct pathway appear to be relatively spared in the early stages. Because of the great morphological and electrophysiological similarities between MSNs of these pathways, until recently it was difficult to tease apart their functional alterations in HD models. The recent use of the enhanced green fluorescent protein gene as a reporter to identify dopamine D1 (direct pathway) and D2 (indirect pathway) receptor-expressing MSNs has made it possible to examine synaptic function in each pathway. The outcomes of such studies demonstrate significant time-dependent changes in the balance of excitatory and inhibitory inputs to both direct and indirect pathway MSNs in HD and emphasize early increases in both excitatory and inhibitory inputs to direct pathway MSNs. There also is a strong influence of alterations in dopamine modulation that possibly cause some of the changes in excitatory and inhibitory synaptic transmission in the HD models. These changes will markedly alter the output structures, the GPi and the SNr. In the future, the use of combined optogenetics with identified neurons in each pathway will help unravel the next set of questions about how the output nuclei are affected in HD.

Huntington disease

Huntington disease is devastating to patients and their families - with autosomal dominant inheritance, onset typically in the prime of adult life, progressive course, and a combination of motor, cognitive and behavioural features. The disease is caused by an expanded CAG trinucleotide repeat (of variable length) in HTT, the gene that encodes the protein huntingtin. In mutation carriers, huntingtin is produced with abnormally long polyglutamine sequences that confer toxic gains of function and predispose the protein to fragmentation, resulting in neuronal dysfunction and death. In this Primer, we review the epidemiology of Huntington disease, noting that prevalence is higher than previously thought, geographically variable and increasing. We describe the relationship between CAG repeat length and clinical phenotype, as well as the concept of genetic modifiers of the disease. We discuss normal huntingtin protein function, evidence for differential toxicity of mutant huntingtin variants, theories of huntingtin aggregation and the many different mechanisms of Huntington disease pathogenesis. We describe the genetic and clinical diagnosis of the condition, its clinical assessment and the multidisciplinary management of symptoms, given the absence of effective disease-modifying therapies. We review past and present clinical trials and therapeutic strategies under investigation, including impending trials of targeted huntingtin-lowering drugs and the progress in development of biomarkers that will support the next generation of trials. For an illustrated summary of this Primer, visit: http://go.nature.com/hPMENh.

Clinical diagnosis and management in early Huntington's disease: a review

This review focuses on clinical diagnosis and both pharmacological and nonpharmacological therapeutic options in early stages of the autosomal dominant inherited neurodegenerative Huntington's disease (HD). The available literature has been reviewed for motor, cognitive, and psychiatric alterations, which are the three major symptom domains of this devastating progressive disease. From a clinical point of view, one has to be aware that the HD phenotype can vary highly across individuals and during the course of the disease. Also, symptoms in juvenile HD can differ substantially from those with adult-onset of HD. Although there is no cure of HD and management is limited, motor and psychiatric symptoms often respond to pharmacotherapy, and nonpharmacological approaches as well as supportive care are essential. International treatment recommendations based on study results, critical statements, and expert opinions have been included. This review is restricted to symptomatic and supportive approaches since all attempts to establish a cure for the disease or modifying therapies have failed so far.

Motor and behavioral phenotype in conditional mutants with targeted ablation of cortical D1 dopamine receptor-expressing cells

D1-dopamine receptors (Drd1a) are highly expressed in the deep layers of the cerebral cortex and the striatum. A number of human diseases such as Huntington disease and schizophrenia are known to have cortical pathology involving dopamine receptor expressing neurons. To illuminate their functional role, we exploited a Cre/Lox molecular paradigm to generate Emx-1(tox) MUT mice, a transgenic line in which cortical Drd1a-expressing pyramidal neurons were selectively ablated. Emx-1(tox) MUT mice displayed prominent forelimb dystonia, hyperkinesia, ataxia on rotarod testing, heightened anxiety-like behavior, and age-dependent abnormalities in a test of social interaction. The latter occurred in the context of normal working memory on testing in the Y-maze and for novel object recognition. Some motor and behavioral abnormalities in Emx-1(tox) MUT mice overlapped with those in CamKIIα(tox) MUT transgenic mice, a line in which both striatal and cortical Drd1a-expressing cells were ablated. Although Emx-1(tox) MUT mice had normal striatal anatomy, both Emx-1(tox) MUT and CamKIIα(tox) MUT mice displayed selective neuronal loss in cortical layers V and VI. This study shows that loss of cortical Drd1a-expressing cells is sufficient to produce deficits in multiple motor and behavioral domains, independent of striatal mechanisms. Primary cortical changes in the D1 dopamine receptor compartment are therefore likely to model a number of core clinical features in disorders such as Huntington disease and schizophrenia.

Clinical Aspects of Huntington's Disease

Huntington's disease (HD) is a devastating inherited neurodegenerative condition characterized by progressive motor, cognitive, and psychiatric symptoms. Symptoms progress over 15-20 years, and there are currently no disease-modifying therapies. The causative genetic mutation is an expanded CAG repeat in the HTT gene encoding the Huntingtin protein, and is inherited in an autosomal dominant manner. In this chapter we discuss the genetics, clinical presentation, and management of this condition, as well as new data from large-scale clinical research studies on the natural history of HD.

Fetal striatal grafting slows motor and cognitive decline of Huntington's disease

OBJECTIVE

To assess the clinical effect of caudate-putaminal transplantation of fetal striatal tissue in Huntington's disease (HD).

METHODS

We carried out a follow-up study on 10 HD transplanted patients and 16 HD not-transplanted patients. All patients were evaluated with the Unified HD Rating Scale (UHDRS) whose change in motor, cognitive, behavioural and functional capacity total scores were considered as outcome measures. Grafted patients also received morphological and molecular neuroimaging.

RESULTS

Patients were followed-up from disease onset for a total of 309.3 person-years (minimum 5.3, median 11.2 years, maximum 21.6 years). UHDRS scores have been available since 2004 (median time of 5.7 years since onset, minimum zero, maximum 17.2 years). Median post-transplantation follow-up was 4.3 years, minimum 2.8, maximum 5.1 years. Adjusted post-transplantation motor score deterioration rate was reduced compared to the pretransplantation period, and to that of not-transplanted patients by 0.9 unit/years (95% CI 0.2 to 1.6). Cognitive score deterioration was reduced of 2.7 unit/years (95% CI 0.1 to 5.3). For grafted patients the 2-year post-transplantation [(18)F]fluorodeoxyglucose positron emission tomography (PET) showed striatal/cortical metabolic increase compared to the presurgical evaluation; 4-year post-transplantation PET values were slightly decreased, but remained higher than preoperatively. [(123)I]iodobenzamide single photon emission CT demonstrated an increase in striatal D2-receptor density during postgrafting follow-up.

CONCLUSIONS

Grafted patients experienced a milder clinical course with less pronounced motor/cognitive decline and associated brain metabolism improvement. Life-time follow-up may ultimately clarify whether transplantation permanently modifies the natural course of the disease, allowing longer sojourn time at less severe clinical stage, and improvement of overall survival.

Proteostasis in striatal cells and selective neurodegeneration in Huntington's disease

Selective neuronal loss is a hallmark of neurodegenerative diseases, including Huntington’s disease (HD). Although mutant huntingtin, the protein responsible for HD, is expressed ubiquitously, a subpopulation of neurons in the striatum is the first to succumb. In this review, we examine evidence that protein quality control pathways, including the ubiquitin proteasome system, autophagy, and chaperones, are significantly altered in striatal neurons. These alterations may increase the susceptibility of striatal neurons to mutant huntingtin-mediated toxicity. This novel view of HD pathogenesis has profound therapeutic implications: protein homeostasis pathways in the striatum may be valuable targets for treating HD and other misfolded protein disorders.

Metabotropic glutamate receptor 5 knockout promotes motor and biochemical alterations in a mouse model of Huntington's disease

Huntington's disease (HD) is an autosomal-dominant neurodegenerative disorder caused by a polyglutamine expansion in the amino-terminal region of the huntingtin protein, which promotes progressive neuronal cell loss, neurological symptoms and death. In the present study, we show that blockade of mGluR5 with MTEP promotes increased locomotor activity in both control (Hdh(Q20/Q20)) and mutant HD (Hdh(Q111/Q111)) mice. Although acute injection of MTEP increases locomotor activity in both control and mutant HD mice, locomotor activity is increased in only control mice, not mutant HD mice, following the genetic deletion of mGluR5. Interestingly, treatment of mGluR5 knockout mice with either D1 or D2 dopamine antagonists eliminates the increased locomotor activity of mGluR5 knockout mice. Amphetamine treatment increases locomotor activity in control mice, but not mGluR5 null mutant HD mice. However, the loss of mGluR5 expression improves rotarod performance and decreases the number of huntingtin intranuclear inclusions in mutant HD mice. These adaptations may be due to mutant huntingtin-dependent alterations in gene expression, as microarray studies have identified several genes that are altered in mutant, but not wild-type HD mice lacking mGluR5 expression. qPCR experiments confirm that the mRNA transcript levels of dynein heavy chain, dynactin 3 and dynein light chain-6 are altered following the genetic deletion of mGluR5 in mutant HD mice, as compared with wild-type mutant HD mice. Thus, our data suggest that mutant huntingtin protein and mGluR5 exhibit a functional interaction that may be important for HD-mediated alterations in locomotor behavior and the development of intranuclear inclusions.

Tracking motor impairments in the progression of Huntington's disease

The Unified Huntington's Disease Rating Scale is used to characterize motor impairments and establish motor diagnosis. Little is known about the timing of diagnostic confidence level categories and the trajectory of motor impairments during the prodromal phase. Goals of this study were to estimate the timing of categories, model the prodromal trajectory of motor impairments, estimate the rate of motor impairment change by category, and provide required sample size estimates for a test of efficacy in clinical trials. In total, 1010 gene-expanded participants from the Neurobiological Predictors of Huntington's Disease (PREDICT-HD) trial were analyzed. Accelerated failure time models were used to predict the timing of categories. Linear mixed effects regression was used to model the longitudinal motor trajectories. Age and length of gene expansion were incorporated into all models. The timing of categories varied significantly by gene expansion, with faster progression associated with greater expansion. For the median expansion, the third diagnostic confidence level category was estimated to have a first occurrence 1.5 years before diagnosis, and the second and first categories were estimated to occur 6.75 years and 19.75 years before diagnosis, respectively. Motor impairments displayed a nonlinear prodromal course. The motor impairment rate of change increased as the diagnostic confidence level increased, with added acceleration for higher progression scores. Motor items can detect changes in motor impairments before diagnosis. Given a sufficiently high progression score, there is evidence that the diagnostic confidence level can be used for prodromal staging. Implications for Huntington's disease research and the planning of clinical trials of efficacy are discussed.

Dopamine imbalance in Huntington's disease: a mechanism for the lack of behavioral flexibility

Dopamine (DA) plays an essential role in the control of coordinated movements. Alterations in DA balance in the striatum lead to pathological conditions such as Parkinson's and Huntington's diseases (HD). HD is a progressive, invariably fatal neurodegenerative disease caused by a genetic mutation producing an expansion of glutamine repeats and is characterized by abnormal dance-like movements (chorea). The principal pathology is the loss of striatal and cortical projection neurons. Changes in brain DA content and receptor number contribute to abnormal movements and cognitive deficits in HD. In particular, during the early hyperkinetic stage of HD, DA levels are increased whereas expression of DA receptors is reduced. In contrast, in the late akinetic stage, DA levels are significantly decreased and resemble those of a Parkinsonian state. Time-dependent changes in DA transmission parallel biphasic changes in glutamate synaptic transmission and may enhance alterations in glutamate receptor-mediated synaptic activity. In this review, we focus on neuronal electrophysiological mechanisms that may lead to some of the motor and cognitive symptoms of HD and how they relate to dysfunction in DA neurotransmission. Based on clinical and experimental findings, we propose that some of the behavioral alterations in HD, including reduced behavioral flexibility, may be caused by altered DA modulatory function. Thus, restoring DA balance alone or in conjunction with glutamate receptor antagonists could be a viable therapeutic approach.

Emotional face recognition deficits and medication effects in pre-manifest through stage-II Huntington's disease

Facial emotion recognition impairments have been reported in Huntington's disease (HD). However, the nature of the impairments across the spectrum of HD remains unclear. We report on emotion recognition data from 344 participants comprising premanifest HD (PreHD) and early HD patients, and controls. In a test of recognition of facial emotions, we examined responses to six basic emotional expressions and neutral expressions. In addition, and within the early HD sample, we tested for differences on emotion recognition performance between those 'on' vs. 'off' neuroleptic or selective serotonin reuptake inhibitor (SSRI) medications. The PreHD groups showed significant (p<0.05) impaired recognition, compared to controls, on fearful, angry and surprised faces; whereas the early HD groups were significantly impaired across all emotions including neutral expressions. In early HD, neuroleptic use was associated with worse facial emotion recognition, whereas SSRI use was associated with better facial emotion recognition. The findings suggest that emotion recognition impairments exist across the HD spectrum, but are relatively more widespread in manifest HD than in the premanifest period. Commonly prescribed medications to treat HD-related symptoms also appear to affect emotion recognition. These findings have important implications for interpersonal communication and medication usage in HD.

Recent advances in the management of choreas

The management of patients with chorea, in particular Huntington's disease, is a complex task requiring skills in a number of areas. This paper reviews new knowledge on this topic and places it in the context of established procedures. It is focused on Huntington's disease, since this is the disorder, for which most publications on management have been published in the past few years. Management starts with appropriate diagnosis and differential diagnosis, with the aim of finding disorders with chorea amenable to causative treatment. The place of genetic testing and the importance of genetic counselling is stressed, as well as the importance of precise observation in the course of the disorder to tailor appropriate therapies. Pharmacological treatment is based on poor evidence but to a large extent on expertise from centres devoted to the care of patients with Huntington's disease. It is focused mainly on motor and psychiatric aspects of the phenotype. Nonpharmacological treatment is important and is best offered in a multidisciplinary care setting.

Translational research in Huntington's disease: opening up for disease modifying treatment

Research on the molecular mechanisms involved in Huntington's disease, a monogenic disorder with a complex phenotype including motor, behaviour, and cognitive impairments, is advancing at a rapid path. Knowledge on several of the multimodal pathways has now lead to the establishment of rational strategies to prepare trials of several compounds in affected people. Furthermore, improved understanding of the phenotype and on ways of assessing it, as well as the process of developing biomarkers, allows setting the frame for such studies. In this brief review, the present status of some of these aspects is examined.

Haplotype analysis of the CAG and CCG repeats in 21 Brazilian families with Huntington's disease

We studied the allelic profile of CAG and CCG repeats in 61 Brazilian individuals in 21 independent families affected by Huntington's disease (HD). Thirteen individuals had two normal alleles for HD, two had one mutable normal allele and no HD phenotype, and forty-six patients carried at least one expanded CAG repeat allele. Forty-five of these individuals had one expanded allele and one individual had one mutable normal allele (27 CAG repeats) and one expanded allele (48 CAG repeats). Eleven of these forty-five subjects had a mutant allele with reduced penetrance, and thirty-four patients had a mutant allele with complete penetrance. Inter- and intragenerational investigations of CAG repeats were also performed. We found a negative correlation between the number of CAG repeats and the age of disease onset (r=-0.84; P<0.001) and no correlation between the number of CCG repeats and the age of disease onset (r=0.06). We found 40 different haplotypes and the analysis showed that (CCG)(10) was linked to a CAG normal allele in 19 haplotypes and to expanded alleles in two haplotypes. We found that (CCG)(7) was linked to expanded CAG repeats in 40 haplotypes (95.24%) and (CCG)(10) was linked to expanded CAG repeats in only two haplotypes (4.76%). Therefore, (CCG)(7) was the most common allele in HD chromosomes in this Brazilian sample. It was also observed that there was a significant association of (CCG)(7) with the expanded CAG alleles (χ(2)=6.97, P=0.0084). Worldwide, the most common CCG alleles have 7 or 10 repeats. In Western Europe, (CCG)(7) is the most frequent allele, similarly to our findings.

Lessons learned from the transgenic Huntington's disease rats

Huntington's disease (HD) is a fatal inherited disorder leading to selective neurodegeneration and neuropsychiatric symptoms. Currently, there is no treatment to slow down or to stop the disease. There is also no therapy to effectively reduce the symptoms. In the investigation of novel therapies, different animal models of Huntington's disease, varying from insects to nonhuman primates, have been created and used. Few years ago, the first transgenic rat model of HD, carrying a truncated huntingtin cDNA fragment with 51 CAG repeats under control of the native rat huntingtin promoter, was introduced. We have been using this animal model in our research and review here our experience with the behavioural, neurophysiological, and histopathological phenotype of the transgenic Huntington's disease rats with relevant literature.

Targeting mutant huntingtin for the development of disease-modifying therapy

Huntington's disease (HD) is a progressive and fatal neurodegenerative disease, and the most common inherited CAG repeat disorder. A polyglutamine expansion in the N-terminus of the huntingtin protein (HTT) leads to protein misfolding and downstream pathogenic processes culminating in widespread functional impairment and neurodegeneration in the striatum, cortex and other brain areas. To date, only symptomatic treatments are available that address motor, psychiatric and cognitive deficits. Here we review recent strategies for developing disease-modifying therapies designed to limit or abolish the pathogenic activities of the primary molecular target in HD, the mutant HTT protein itself.

In vivo Dopamine Efflux is Decreased in Striatum of both Fragment (R6/2) and Full-Length (YAC128) Transgenic Mouse Models of Huntington's Disease

Huntington's disease (HD) is characterized by numerous alterations within the corticostriatal circuitry. The striatum is innervated by a dense array of dopaminergic (DA) terminals and these DA synapses are critical to the proper execution of motor functions. As motor disturbances are prevalent in HD we examined DA neurotransmission in the striatum in transgenic (tg) murine models of HD. We used in vivo microdialysis to compare extracellular concentrations of striatal DA in both a fragment (R6/2) model, which displays a rapid and severe phenotype, and a full-length (YAC128) model that expresses a more progressive phenotype. Extracellular striatal DA concentrations were significantly reduced in R6/2 mice and decreased concomitantly with age-dependent increasing motor impairments on the rotarod task (7, 9, and 11 weeks). In a sample of 11-week-old R6/2 mice, we also measured tissue concentrations of striatal DA and found that total levels of DA were significantly depleted. However, the loss of total DA content (<50%) was insufficient to account for the full extent of DA depletion in the extracellular fluid (ECF; ∼75%). We also observed a significant reduction in extracellular DA concentrations in the striatum of 7-month-old YAC128 mice. In a separate set of experiments, we applied d-amphetamine (AMPH; 10 μm) locally into the striatum to stimulate the release of intracellular DA into the ECF. The AMPH-induced increase in extracellular DA levels was significantly blunted in 9-week-old R6/2 mice. There also was a decrease in AMPH-stimulated DA efflux in 7-month-old YAC128 mice in comparison to WT controls, although the effect was milder. In the same cohort of 7-month-old YAC128 mice we observed a significant reduction in the total locomotor activity in response to systemic AMPH (2 mg/kg). Our data demonstrate that extracellular DA release is attenuated in both a fragment and full-length tg mouse model of HD and support the concept of DA involvement in aspects of the syndrome.

An item response analysis of the motor and behavioral subscales of the unified Huntington's disease rating scale in huntington disease gene expansion carriers

Although the Unified Huntington's Disease Rating Scale (UHDRS) is widely used in the assessment of Huntington disease (HD), the ability of individual items to discriminate individual differences in motor or behavioral manifestations has not been extensively studied in HD gene expansion carriers without a motor-defined clinical diagnosis (ie, prodromal-HD or prHD). To elucidate the relationship between scores on individual motor and behavioral UHDRS items and total score for each subscale, a nonparametric item response analysis was performed on retrospective data from 2 multicenter longitudinal studies. Motor and behavioral assessments were supplied for 737 prHD individuals with data from 2114 visits (PREDICT-HD) and 686 HD individuals with data from 1482 visits (REGISTRY). Option characteristic curves were generated for UHDRS subscale items in relation to their subscale score. In prHD, overall severity of motor signs was low, and participants had scores of 2 or above on very few items. In HD, motor items that assessed ocular pursuit, saccade initiation, finger tapping, tandem walking, and to a lesser extent, saccade velocity, dysarthria, tongue protrusion, pronation/supination, Luria, bradykinesia, choreas, gait, and balance on the retropulsion test were found to discriminate individual differences across a broad range of motor severity. In prHD, depressed mood, anxiety, and irritable behavior demonstrated good discriminative properties. In HD, depressed mood demonstrated a good relationship with the overall behavioral score. These data suggest that at least some UHDRS items appear to have utility across a broad range of severity, although many items demonstrate problematic features.

Differential electrophysiological changes in striatal output neurons in Huntington's disease

There is considerable evidence that alterations in striatal medium-sized spiny neurons (MSSNs) giving rise to the direct (D1 receptor-expressing) and indirect (D2 receptor-expressing) pathways differentially contribute to the phenotype of Huntington's disease (HD). To determine how each subpopulation of MSSN is functionally affected, we examined spontaneous excitatory postsynaptic currents (sEPSCs) and dopamine (DA) modulation in two HD mouse models, the YAC128 and the BACHD (a bacterial-artificial chromosome). These mice also expressed enhanced green fluorescent protein (EGFP) under the control of the promoter for either DA D1 or D2 receptors to identify neurons. In early symptomatic YAC128 and BACHD mice, glutamate transmission was increased in both D1 and D2 MSSNs, but in different ways. D1 cells displayed increased sEPSC frequencies and decreased paired-pulse ratios (PPRs) while D2 cells displayed larger evoked glutamate currents but no change in sEPSC frequencies or PPRs. D1 receptor modulation of sEPSCs was absent in D1-YAC128 cells at the early symptomatic stage but was restored by treating the slices with tetrabenazine. In contrast, in fully symptomatic YAC128 mice, glutamate transmission was decreased specifically in D1 cells, and D1 receptor modulation was normal in D1-YAC128 cells. Behaviorally, early symptomatic mice showed increased stereotypies that were decreased by tetrabenazine treatment. Together, these studies support differential imbalances in glutamate and DA transmission in direct and indirect pathway MSSNs. Stereotypic behavior at an early stage could be explained by increased glutamate activity and DA tone in direct pathway neurons, whereas hypokinesia at later stages could result from reduced input onto these neurons.

Huntington's disease: from molecular pathogenesis to clinical treatment

Huntington's disease is a progressive, fatal, neurodegenerative disorder caused by an expanded CAG repeat in the huntingtin gene, which encodes an abnormally long polyglutamine repeat in the huntingtin protein. Huntington's disease has served as a model for the study of other more common neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. These disorders all share features including: delayed onset; selective neuronal vulnerability, despite widespread expression of disease-related proteins during the whole lifetime; abnormal protein processing and aggregation; and cellular toxic effects involving both cell autonomous and cell-cell interaction mechanisms. Pathogenic pathways of Huntington's disease are beginning to be unravelled, offering targets for treatments. Additionally, predictive genetic testing and findings of neuroimaging studies show that, as in some other neurodegenerative disorders, neurodegeneration in affected individuals begins many years before onset of diagnosable signs and symptoms of Huntington's disease, and it is accompanied by subtle cognitive, motor, and psychiatric changes (so-called prodromal disease). Thus, Huntington's disease is also emerging as a model for strategies to develop therapeutic interventions, not only to slow progression of manifest disease but also to delay, or ideally prevent, its onset.

Huntington's disease: clinical presentation and treatment

Huntington's disease (HD) is a devastating inherited neurodegenerative disease characterized primarily by progressive motor, cognitive, and psychiatric symptoms. It is caused by autosomal dominant inheritance of an expanded CAG repeat within the Huntington's gene on chromosome 4. In this chapter, we characterize the typical and variant motor phenotypes of the disease and then proceed to describe the cognitive and psychiatric profile. We then give an overview of a suggested multidisciplinary approach to the management of HD, emphasizing the fact that it is a disease which impacts on entire families rather than affecting individuals in isolation. We then describe the pharmacological and nonpharmacological options available for management of specific symptoms.

Vascular chorea in adults and children

Chorea may occur as part of the symptomatology of acute stroke; it occasionally also may be delayed or progressive. Patients with vascular-related chorea typically present with an acute or subacute onset of chorea of one side of the body (hemichorea), contralateral to the lesion. Cerebrovascular disease is the most common cause of sporadic chorea. Lesions are most frequently found in the thalamus and lentiform nucleus, and less often in subthalamic nucleus. The differential diagnosis of choreic syndromes relies not so much on differences in the phenomenology of the hyperkinesia but the age at onset, mode of onset, time course, family history, drug use, distribution of chorea in the body, and presence of accompanying neurological findings. Magnetic resonance imaging is preferred to demonstrate the presence of strategic small lesions in regions that are difficult to image with computed tomography, such as the globus pallidus, thalamus, and subthalamic nucleus. Although the prognosis of hemichorea can be benign, the long-term prognosis is not specifically determined by the hemichorea but by the long-term prognosis of stroke patients. Symptomatic treatment with antichoreic drugs may be necessary in the acute phase. Surgery is rarely indicated to treat vascular chorea.

Huntington's disease: a clinical review

Huntington disease (HD) is a rare neurodegenerative disorder of the central nervous system characterized by unwanted choreatic movements, behavioral and psychiatric disturbances and dementia. Prevalence in the Caucasian population is estimated at 1/10,000-1/20,000. Mean age at onset of symptoms is 30-50 years. In some cases symptoms start before the age of 20 years with behavior disturbances and learning difficulties at school (Juvenile Huntington's disease; JHD). The classic sign is chorea that gradually spreads to all muscles. All psychomotor processes become severely retarded. Patients experience psychiatric symptoms and cognitive decline. HD is an autosomal dominant inherited disease caused by an elongated CAG repeat (36 repeats or more) on the short arm of chromosome 4p16.3 in the Huntingtine gene. The longer the CAG repeat, the earlier the onset of disease. In cases of JHD the repeat often exceeds 55. Diagnosis is based on clinical symptoms and signs in an individual with a parent with proven HD, and is confirmed by DNA determination. Pre-manifest diagnosis should only be performed by multidisciplinary teams in healthy at-risk adult individuals who want to know whether they carry the mutation or not. Differential diagnoses include other causes of chorea including general internal disorders or iatrogenic disorders. Phenocopies (clinically diagnosed cases of HD without the genetic mutation) are observed. Prenatal diagnosis is possible by chorionic villus sampling or amniocentesis. Preimplantation diagnosis with in vitro fertilization is offered in several countries. There is no cure. Management should be multidisciplinary and is based on treating symptoms with a view to improving quality of life. Chorea is treated with dopamine receptor blocking or depleting agents. Medication and non-medical care for depression and aggressive behavior may be required. The progression of the disease leads to a complete dependency in daily life, which results in patients requiring full-time care, and finally death. The most common cause of death is pneumonia, followed by suicide.

Dopamine and glutamate in Huntington's disease: A balancing act

Huntington's disease (HD) is caused by a CAG repeat expansion in exon 1 of the HD gene resulting in a long polyglutamine tract in the N-terminus of the protein huntingtin. Patients carrying the mutation display chorea in early stages followed by akinesia and sometimes dystonia in late stages. Other major symptoms include depression, anxiety, irritability or aggressive behavior, and apathy. Although many neuronal systems are affected, dysfunction and subsequent neurodegeneration in the basal ganglia and cortex are the most apparent pathologies. In HD, the primary hypothesis has been that there is an initial overactivity of glutamate neurotransmission that produces excitotoxicity followed by a series of complex changes that are different in the striatum and in the cortex. This review will focus on evidence for alterations in dopamine (DA)-glutamate interactions in HD, concentrating on the striatum and cortex. The most recent evidence points to decreases in DA and glutamate neurotransmission as the HD phenotype develops. However, there is some evidence for increased DA and glutamate functions that could be responsible for some of the early HD phenotype. Significant evidence indicates that glutamate and dopamine neurotransmission is affected in HD, compromising the fine balance in which DA modulates glutamate-induced excitation in the basal ganglia and cortex. Restoring the balance between glutamate and dopamine could be helpful to treat HD symptoms.