Huntington’s disease (HD), a devastating neurodegenerative disorder caused by a CAG repeat expansion on the HTT gene located on chromosome 4, is associated with a characteristic pattern of progressive cognitive dysfunction known to involve early deficits in executive function. A modified Go/No-go successive discrimination task was designed to assess the type of online response control/executive function known to be disrupted in patients with HD. The present studies show that this simple discrimination assay revealed early and robust deficits in two mouse models of HD, the zQ175 KI mouse (deficits from 28 weeks of age) and the R6/2 mouse, carrying ~240 CAG repeats (deficits from 9 weeks of age). These deficits are not due to gross motor dysfunction in the test animals, but instead appear to measure some inability to inhibit responding in the HD mouse models, suggesting this assay may measure deficits in underlying attentional and/or behavioral inhibition processes. Accordingly, this assay may be well suited to evaluation of simple deficits in cognitive function in mouse HD models, providing a potential platform for preclinical screening.
Objective: To assess the effects of an intensive, multidisciplinary rehabilitation program for patients with early to mid-stage Huntington’s disease.
Design: A prospective intervention study.
Setting: Two Norwegian inpatient rehabilitation centers.
Subjects: 37 patients, with early- to midstage Huntington’s disease
Interventions: A one year rehabilitation program, consisting of three admissions of three weeks each, and a five-day evaluation stay approximately 3 months after the last rehabilitation admission. Focus was on physical exercise, social activities, and group/teaching sessions. There was also emphasis to implement of coordinated health care and social services for the patients.
Main outcome measures: standard measures for motor function, including gait and balance, cognitive function, including MMSE and UHDRS cognitive assessment, anxiety and depression, activities of daily living (ADL), health related quality of life and Body Mass Index (BMI).
Results: Significant improvements were observed in gait function, balance, in physical quality of life, anxiety and depression, as well as in BMI. ADL-function remained stable with no significant decline. Only one cognitive measure (SDMT) showed significant decline, while no decline was observed for the remaining cognitive measures.
Conclusion: A multidisciplinary intensive rehabilitation program in patients with early and mid stage HD is associated with improved balance, gait function, physical quality of life and with reduced depressive and anxiety symptoms. Longer follow-up is needed to assess if these positive effects are sustained. There should be emphasis to establishment of long term and coordinated health care services for the HD patient
The genome of the Bacterial Artificial Chromosome (BAC) transgenic mouse model of Huntington’s Disease (BAC HD) contains the 170 kb human HTT locus modified by the addition of exon 1 with 97 mixed CAA-CAG repeats. BAC HD mice present robust behavioral deficits in both the open field and the accelerating rotarod tests, two standard behavioral assays of motor function. BAC HD mice, however, also typically present significantly increased body weights relative to wildtype littermate controls (WT) which potentially confounds the interpretation of any motor deficits associated directly with the effects of mutant huntingtin. In order to evaluate this possible confound of body weight, we directly compared the performance of BAC HD and WT female mice under food restricted versus free feeding conditions in both the open field and rotarod tasks to test the hypothesis that some of the motor deficits observed in this HTT-transgenic mouse line results solely from increased body weight. Our results suggest that the rotarod deficit exhibited by BAC HD mice is modulated by both body weight and non-body weight factors resulting from overexpression of full length mutant Htt. When body weights of WT and BAC HD transgenic mice were normalized using restricted feeding, the deficits exhibited by BAC HD mice on the rotarod task were less marked, but were still significant. Since the rotarod deficit between WT and BAC HD mice is attenuated when body weight is normalized by food restriction, utilization of this task in BAC HD mice during pre-clinical evaluation must be powered accordingly and results carefully considered as therapeutic benefit can result from decreased overall body weight and or motoric improvement that may not be related to body mass. Furthermore, after controlling for body weight differences, the hypoactive phenotype displayed by ad libitum fed BAC HD mice in the open field assay was not observed in the BAC HD mice undergoing food restriction. These findings suggest that assessment of spontaneous locomotor activity, as measured in the open field test, may not be the appropriate behavioral endpoint to evaluate the BAC HD mouse during preclinical evaluation since it appears that the apparent hypoactive phenotype in this model is driven primarily by body weight differences.
Phenotyping with traditional behavioral assays constitutes a major bottleneck in the primary screening, characterization, and validation of genetic mouse models of disease, leading to downstream delays in drug discovery efforts. We present a novel and comprehensive one-stop approach to phenotyping, the PhenoCube™. This system simultaneously captures the cognitive performance, motor activity, and circadian patterns of group-housed mice by use of home-cage operant conditioning modules (IntelliCage) and custom-built computer vision software. We evaluated two different mouse models of Huntington’s Disease (HD), the R6/2 and the BACHD in the PhenoCube™ system. Our results demonstrated that this system can efficiently capture and track alterations in both cognitive performance and locomotor activity patterns associated with these disease models. This work extends our prior demonstration that PhenoCube™ can characterize circadian dysfunction in BACHD mice and shows that this system, with the experimental protocols used, is a sensitive and efficient tool for a first pass high-throughput screening of mouse disease models in general and mouse models of neurodegeneration in particular.
While there has been a guideline for laboratory/genetic diagnosis of Huntington Disease (HD) since 1998, no such statement exists for the diagnosis of clinical HD. Informally, the most frequently used criteria for diagnosis of clinical HD is ‘Motor 4’ within the Unified Huntington Disease Rating Scale ’99 (motor), made when the rater is highly confident that ‘motor abnormalities observed are unequivocal signs of HD’. Recent studies involving pre-manifest individuals illustrated the shortcomings of this motor-only diagnostic approach. For instance, PREDICT-HD found cognitive changes decades before the expected date of motor diagnosis. Using a number of case studies, we highlight some of the subtleties involved in diagnosing clinical HD, in the absence of unequivocal motor signs for HD. New, broader, criteria for the diagnosis of clinical HD would be helpful in many ways. However its formulation will need to flexible rather than prescriptive, and will require extensive consultation with clinicians and families with HD.
Metabolic dysfunction and mitochondrial involvement are recognised as part of the pathology in Huntington’s Disease (HD). Post-mortem examinations of the striatum from end-stage HD patients have shown a decrease in the in vitro activity of complexes II, III and IV of the electron transport system (ETS). In different models of HD, evidence of enzyme defects have been reported in complex II and complex IV using enzyme assays. However, such assays are highly variable and results have been inconsistent.
We investigated the integrated ETS function ex vivo using a sensitive high-resolution respirometric (HRR) method. The O2 flux in a whole-cell sample combined with the addition of mitochondrial substrates, uncouplers and inhibitors enabled us to accurately quantitate the function of individual mitochondrial complexes in intact mitochondria, while retaining mitochondrial regulation and compensatory mechanisms.
We used HRR to examine the mitochondrial function in striata from 12-week old R6/2 mice expressing exon 1 of human HTT with 130 CAG repeats. A significant reduction in complex II and complex IV flux control ratios was found in the R6/2 mouse striatum at 12 weeks of age compared to controls, confirming previous findings obtained with spectrophotometric enzyme assays.
This report represents a detailed description of experiments designed to replicate and extend the findings of a published study on the effects of treating the R6/2 Huntington’s disease (HD) mouse model with ~300 CAG repeats using the pimelic diphenylamide histone deacetylase (HDAC) inhibitor, HDACi 4b (Thomas et al., 2008). In addition to testing the R6/2 mice, similar experiments examined the effects of the drug on a second transgenic HD mouse model, the N171-82Q mice. As in the original study, the drug was delivered in the drinking water. In the present study we tested larger groups of mice than in the original study. The results indicated that we were unable to replicate the significant behavioral effects of oral HDACi 4b treatment in the R6/2 mice. There were however, non-significant trends for the treated R6/2 mice to be less affected on some of the measures and there were instances of phenotype progression being delayed in these treated mice. In contrast, we did replicate the protection from striatal atrophy in the R6/2 mice. We also did not observe any beneficial effects of HDACi 4b treatment in the N171-82Q mice. Although the behavioral procedures were replicated and an automated activity assessment was added, there were several unexpected complications in terms of solubility of the drug, CAG repeat length differences and gender differences in progression of the phenotype that could have affected outcomes. Clearly more studies will have to be performed using other methods of delivery as well as assessing effects in more slowly progressing HD models to better evaluate the effects of this HDAC inhibitor.
Abnormalities in brain cholesterol homeostasis have been reported in Huntington’s disease (HD), an adult-onset neurodegenerative disorder caused by an expansion in the number of CAG repeats in the huntingtin (HTT) gene. However, the results have been contradictory with respect to whether cholesterol levels increase or decrease in HD models. Biochemical and mass spectrometry methods show reduced levels of cholesterol precursors and cholesterol in HD cells and in the brains of several HD animal models. Abnormal brain cholesterol homeostasis was also inferred from studies in HD patients. In contrast, colorimetric and enzymatic methods indicate cholesterol accumulation in HD cells and tissues. Here we used several methods to investigate cholesterol levels in cultured cells in the presence or absence of mutant HTT protein.
Colorimetric and enzymatic methods with low sensitivity gave variable results, whereas results from a sensitive analytical method, gas chromatography-mass spectrometry, were more reliable. Sample preparation, high cell density and cell clonality also influenced the detection of intracellular cholesterol.
Detection of cholesterol in HD samples by colorimetric and enzymatic assays should be supplemented by detection using more sensitive analytical methods. Care must be taken to prepare the sample appropriately. By evaluating lathosterol levels using isotopic dilution mass spectrometry, we confirmed reduced cholesterol biosynthesis in knock-in cells expressing the polyQ mutation in a constitutive or inducible manner.
*Correspondence should be addressed to Elena Cattaneo: email@example.com
Juvenile Huntington’s disease (JHD) is usually defined as Huntington’s disease with an onset ≤ 20 years. The proportion of JHD cases reported in studies of Huntington’s disease (HD) varies. A review of the literature found 62 studies that reported the proportion of JHD cases amongst all HD cases. The proportion of JHD cases in these studies ranged from 1% to 15%, and in a meta-analysis the pooled proportion of JHD cases was 4.92% (95% confidence interval of 4.07% to 5.84%). Limiting the analysis to the 25 studies which used multiple methods of ascertainment resulted in a similar pooled proportion of 5.32%, (95% confidence interval 4.18% to 6.60%).
A small difference was observed when the meta-analysis was restricted to studies from countries defined by the World Bank as high income, that used multiple methods of ascertainment, and that were conducted since 1980 (4.81%, 95% confidence interval 3.31% to 6.58%, n=11). This contrasts with the pooled result from three post 1980 studies using multiple methods of ascertainment from South Africa and Venezuela, defined by the World Bank as upper middle income, where the estimated mean proportion was 9.95%, (95% confidence interval 6.37% to 14.22%).
These results, which are expected to be more robust than those from a single study alone, may be helpful in estimating the proportion of JHD cases in a given population.
Key Words: Juvenile Huntington’s disease, prevalence, epidemiology
Huntington’s disease (HD) is a late-onset progressive neurodegenerative disorder characterised by irrepressible motor dysfunction, cognitive decline and psychiatric disturbances for which there is no effective disease-modifying treatment. The proteolytic cleavage of huntingtin (HTT) to generate N-terminal fragments has been proposed to be a key aspect of HD pathogenesis. In particular, it has been shown that HTT can be cleaved at amino acid 586 by caspase-6 (CASP6) and that prevention of cleavage at this site is neuroprotective and can rescue HD-related phenotypes in YAC transgenic HD mouse models. To determine the role that CASP6 plays in HTT proteolysis, we evaluated the effects of the genetic ablation of Casp6 in the HdhQ150 knock-in mouse model of HD. Here we show that the loss of CASP6 had no effect on the proteolysis of HTT, and did not modify the pattern of N-terminal HTT fragments that are present in the brains of these animals. Furthermore, we show that CASP6 ablation does not influence the steady-state levels of soluble HTT in the brains of presymptomatic mice. Therefore, we conclude that CASP6 is not necessary for HTT proteolysis in the HdhQ150 mouse model of HD, and that targeting CASP6 as a therapeutic strategy should be approached with caution in the context of this complex disease.
* Corresponding author: Gillian P. Bates, Department of Medical and Molecular Genetics, King’s College London School of Medicine, 8th Floor Tower Wing, Guy’s Hospital, London, SE1 9RT, United Kingdom. Phone: +44 20 7188 3722; Fax: +44 20 7188 2585; Email: firstname.lastname@example.org