The relationship between CAG repeat length and clinical progression in Huntington's disease

The Role of NRF2 in Trinucleotide Repeat Expansion Disorders

Trinucleotide repeat expansion disorders, a diverse group of neurodegenerative diseases, are caused by abnormal expansions within specific genes. These expansions trigger a cascade of cellular damage, including protein aggregation and abnormal RNA binding. A key contributor to this damage is oxidative stress, an imbalance of reactive oxygen species that harms cellular components. This review explores the interplay between oxidative stress and the NRF2 pathway in these disorders. NRF2 acts as the master regulator of the cellular antioxidant response, orchestrating the expression of enzymes that combat oxidative stress. Trinucleotide repeat expansion disorders often exhibit impaired NRF2 signaling, resulting in inadequate responses to excessive ROS production. NRF2 activation has been shown to upregulate antioxidative gene expression, effectively alleviating oxidative stress damage. NRF2 activators, such as omaveloxolone, vatiquinone, curcumin, sulforaphane, dimethyl fumarate, and resveratrol, demonstrate neuroprotective effects by reducing oxidative stress in experimental cell and animal models of these diseases. However, translating these findings into successful clinical applications requires further research. In this article, we review the literature supporting the role of NRF2 in the pathogenesis of these diseases and the potential therapeutics of NRF2 activators.

Latest advances on new promising molecular-based therapeutic approaches for Huntington's disease

Huntington's disease (HD) is a devastating, autosomal-dominant inherited, neurodegenerative disorder characterized by progressive motor deficits, cognitive impairments, and neuropsychiatric symptoms. It is caused by excessive cytosine-adenine-guanine (CAG) trinucleotide repeats within the huntingtin gene (HTT). Presently, therapeutic interventions capable of altering the trajectory of HD are lacking, while medications for abnormal movement and psychiatric symptoms are limited. Numerous pre-clinical and clinical studies have been conducted and are currently underway to test the efficacy of therapeutic approaches targeting some of these mechanisms with varying degrees of success. In this review, we update the latest advances on new promising molecular-based therapeutic strategies for this disorder, including DNA-targeting techniques such as zinc-finger proteins, transcription activator-like effector nucleases, and CRISPR/Cas9; post-transcriptional huntingtin-lowering approaches such as RNAi, antisense oligonucleotides, and small-molecule splicing modulators; and novel methods to clear the mHTT protein, such as proteolysis-targeting chimeras. We mainly focus on the ongoing clinical trials and the latest pre-clinical studies to explore the progress of emerging potential HD therapeutics.

Neurogenetic motor disorders

Advances in the field of neurogenetics have practical applications in rapid diagnosis on blood and body fluids to extract DNA, obviating the need for invasive investigations. The ability to obtain a presymptomatic diagnosis through genetic screening and biomarkers can be a guide to life-saving disease-modifying therapy or enzyme replacement therapy to compensate for the deficient disease-causing enzyme. The benefits of a comprehensive neurogenetic evaluation extend to family members in whom identification of the causal gene defect ensures carrier detection and at-risk counseling for future generations. This chapter explores the many facets of the neurogenetic evaluation in adult and pediatric motor disorders as a primer for later chapters in this volume and a roadmap for the future applications of genetics in neurology.

Coenzyme Q10: Role in Less Common Age-Related Disorders

In this article we have reviewed the potential role of coenzyme Q10 (CoQ10) in the pathogenesis and treatment of a number of less common age-related disorders, for many of which effective therapies are not currently available. For most of these disorders, mitochondrial dysfunction, oxidative stress and inflammation have been implicated in the disease process, providing a rationale for the potential therapeutic use of CoQ10, because of its key roles in mitochondrial function, as an antioxidant, and as an anti-inflammatory agent. Disorders reviewed in the article include multi system atrophy, progressive supranuclear palsy, sporadic adult onset ataxia, and pulmonary fibrosis, together with late onset versions of Huntington’s disease, Alexander disease, lupus, anti-phospholipid syndrome, lysosomal storage disorders, fibromyalgia, Machado-Joseph disease, acyl-CoA dehydrogenase deficiency, and Leber’s optic neuropathy.

The progression rate of spinocerebellar ataxia type 3 varies with disease stage

BACKGROUND

In polyglutamine (polyQ) diseases, the identification of modifiers and the construction of prediction model for progression facilitate genetic counseling, clinical management and therapeutic interventions.

METHODS

Data were derived from the longest longitudinal study, with 642 examinations by International Cooperative Ataxia Rating Scale (ICARS) from 82 SCA3 participants. Using different time scales of disease duration, we performed multiple different linear, quadratic and piece-wise linear growth models to fit the relationship between ICARS scores and duration. Models comparison was employed to determine the best-fitting model according to goodness-of-fit tests, and the analysis of variance among nested models.

RESULTS

An acceleration was detected after 13 years of duration: ICARS scores progressed 2.445 (SE: 0.185) points/year before and 3.547 (SE: 0.312) points/year after this deadline. Piece-wise growth model fitted better to studied data than other two types of models. The length of expanded CAG repeat (CAGexp) in ATXN3 gene significantly influenced progression. Age at onset of gait ataxia (AOga), a proxy for aging process, was not an independent modifier but affected the correlation between CAGexp and progression. Additionally, gender had no significant effect on progression rate of ICARS. The piece-wise growth models were determined as the predictive models, and ICARS predictions from related models were available.

CONCLUSIONS

We first confirmed that ICARS progressed as a nonlinear pattern and varied according to different stages in SCA3. In addition to ATXN3 CAGexp, AOga or aging process regulated the progression by interacting with CAGexp.

A Machine-Learning Derived Huntington's Disease Progression Model: Insights for Clinical Trial Design

BACKGROUND

Applying machine-learning algorithms to large datasets such as those available in Huntington's disease offers the opportunity to discover hidden patterns, often not discernible to clinical observation.

OBJECTIVES

To develop and validate a model of Huntington's disease progression using probabilistic machine learning methods.

METHODS

Longitudinal data encompassing 2079 assessment measures from four observational studies (PREDICT-HD, REGISTRY, TRACK-HD, and Enroll-HD) were integrated and machine-learning methods (Bayesian latent-variable analysis and continuous-time hidden Markov models) were applied to develop a probabilistic model of disease progression. The model was validated using a separate Enroll-HD dataset and compared with existing clinical reference assessments (Unified Huntington's Disease Rating Scale [UHDRS] diagnostic confidence level, total functional capacity, and total motor scores) and CAG-age product.

RESULTS

Nine disease states were discovered based on 44 motor, cognitive, and functional measures, which correlated with reference assessments. The validation set included 3158 participants (mean age, 48.4 years) of whom 61.5% had manifest disease. Analysis of transition times showed that "early-disease" states 1 and 2, which occur before motor diagnosis, lasted ~16 years. Increasing numbers of participants had motor onset during "transition" states 3 to 5, which collectively lasted ~10 years, and the "late-disease" states 6 to 9 also lasted ~10 years. The annual probability of conversion from one of the nine identified disease states to the next ranged from 5% to 27%.

CONCLUSIONS

The natural history of Huntington's disease can be described by nine disease states of increasing severity. The ability to derive characteristics of disease states and probabilities for progression through these states will improve trial design and participant selection. © 2021 International Parkinson and Movement Disorder Society.

Deep brain stimulation in Huntington's disease: a literature review

BACKGROUND

Huntington's disease (HD) is a neurodegenerative disorder characterized by involuntary movements, cognitive decline, and behavioral changes. The complex constellation of clinical symptoms still makes the therapeutic management challenging. In the new era of functional neurosurgery, deep brain stimulation (DBS) may represent a promising therapeutic approach in selected HD patients.

METHODS

Articles describing the effect of DBS in patients affected by HD were selected from Medline and PubMed by the association of text words with MeSH terms as follows: "Deep brain stimulation," "DBS," and "HD," "Huntington's disease," and "Huntington." Details on repeat expansion, age at operation, target of operation, duration of follow-up, stimulation parameters, adverse events, and outcome measures were collected.

RESULTS

Twenty eligible studies, assessing 42 patients with HD, were identified. The effect of globus pallidus internus (GPi) DBS on Unified Huntington's Disease Rating Scale (UHDRS) total score revealed in 10 studies an improvement of total score from 5.4 to 34.5%, and in 4 studies, an increase of motor score from 3.8 to 97.8%. Bilateral GPi-DBS was reported to be effective in reducing Chorea subscore in all studies, with a mean percentage reduction from 21.4 to 73.6%.

CONCLUSIONS

HD patients with predominant choreic symptoms may be the best candidates for surgery, but the role of other clinical features and of disease progression should be elucidated. For this reason, there is a need for more reliable criteria that may guide the selection of HD patients suitable for DBS. Accordingly, further studies including functional outcomes as primary endpoints are needed.

New Avenues for the Treatment of Huntington's Disease

Huntington’s disease (HD) is a neurodegenerative disorder caused by a CAG expansion in the HD gene. The disease is characterized by neurodegeneration, particularly in the striatum and cortex. The first symptoms usually appear in mid-life and include cognitive deficits and motor disturbances that progress over time. Despite being a genetic disorder with a known cause, several mechanisms are thought to contribute to neurodegeneration in HD, and numerous pre-clinical and clinical studies have been conducted and are currently underway to test the efficacy of therapeutic approaches targeting some of these mechanisms with varying degrees of success. Although current clinical trials may lead to the identification or refinement of treatments that are likely to improve the quality of life of those living with HD, major efforts continue to be invested at the pre-clinical level, with numerous studies testing novel approaches that show promise as disease-modifying strategies. This review offers a detailed overview of the currently approved treatment options for HD and the clinical trials for this neurodegenerative disorder that are underway and concludes by discussing potential disease-modifying treatments that have shown promise in pre-clinical studies, including increasing neurotropic support, modulating autophagy, epigenetic and genetic manipulations, and the use of nanocarriers and stem cells.

Can a Micronutrient Mixture Delay the Onset and Progression of Symptoms of Single-Point Mutation Diseases?

Single-point mutation diseases in which substitution of one nucleotide with another in a gene occurs include familial Alzheimer's disease (fAD), familial Parkinson's disease (fPD), and familial Creutzfeldt-Jacob disease (fCJD) as well as Huntington's disease (HD), sickle cell anemia, and hemophilia. Inevitability of occurrence of these diseases is certain. However, the time of appearance of symptoms could be influenced by the diet, environment, and possibly other genetic factors. There are no effective approaches to delay the onset or progression of symptoms of these diseases. The fact that increased oxidative stress and inflammation significantly contribute to the initiation and progression of these point mutation diseases shows that antioxidants could be useful. The major objectives are (a) to present evidence that increased oxidative stress and chronic inflammation are associated with selected single-point mutation diseases, such as fAD, fPD, and fCJD, HD, sickle cell anemia, and hemophilia; (b) to describe limited studies on the role of individual antioxidants in experimental models of some of these diseases; and (c) to discuss a rationale for utilizing a comprehensive mixture of micronutrients, which may delay the development and progression of symptoms of above diseases by simultaneously reducing oxidative and inflammatory damages.Key teaching pointsSelected single-point mutation diseases and their pattern of inheritanceCharacteristics of each selected single-point mutation diseaseEvidence for increased oxidative stress and inflammation in each diseasePotential reasons for failure of single antioxidants in human studiesRationale for using a comprehensive mixture of micronutrients in delaying the onset and progression of single-point mutation diseases.

A case of Huntington's disease with two reduced penetrance alleles

We present a case of Huntington's Disease (HD) with two reduced penetrance alleles and show that age of onset and motor symptoms are comparable to heterozygous patients with the same number of CAG triplet repeats. We performed a review of the literature on clinical presentation of homozygous HD cases and highlight that, so far, evidence exists that HD is a truly dominant disorder. This has important implications for pathophysiology concepts of the disease.

Imaging and Clinical Data on Swallowing Function of Individuals with Huntington's Disease and Dysphagia

BACKGROUND

Dysphagia is common in Huntington's disease (HD) affecting all phases of swallowing. Correlations exist between non-instrumental measures of dysphagia and clinical features of HD, including age, disease duration and degree of motor impairment. Lack of instrumental data limits our ability to wholly characterize HD-related dysphagia and prognosticate swallowing changes over time.

OBJECTIVE

To retrospectively describe a relatively large database of videofluoroscopic studies (VFSSs) and determine the relationships between dysphagia and HD clinical parameters, including disease duration and burden of pathology score.

METHODS

Medical and swallowing data of 49 individuals with HD and dysphagia were examined. VFSS data were interpreted using the Bethlehem Assessment Scale and Penetration-Aspiration Scale. Data from clinical bedside examination and social information were collated to describe the impact of dysphagia in HD. Repeated VFSS data were available for seven individuals.

RESULTS

Swallowing was characterized by lingual dysfunction, reduced soft palate elevation, delayed pharyngeal swallow initiation, and inability to clear matter from the pharynx. Two-thirds of cases presented with compromised airway protection with both liquid and solid consistencies. Tachyphagia and difficulty self-feeding were common. Dysphagia correlated with disease severity and duration. Longitudinal analysis revealed a mixed pattern of progression with some individuals presenting with worsening dysphagia whilst others appeared to remain stable or improved in function.

CONCLUSIONS

Dysphagia in HD is exacerbated by difficulties with self-feeding and monitoring feeding rate. Burden of pathology relates to pharyngeal swallow initiation and penetration and aspiration of fluid. Dysphagia did not appear to worsen in a systematic way in a subset of participants.

Age is an important independent modifier of SCA3 phenotype severity

OBJECTIVE

This study aimed to investigate factors modulating spinocerebellar ataxia type 3 (SCA3) phenotype severity besides the expanded CAG repeats (ExpCAG) of ATXN3.

METHODS

Data regarding CAG trinucleotide repeats, age at onset (AO), duration, age, sex, transmitting parent, and scale scores of SCA3 patients were collected. Multiple linear regression analysis was performed to identify influential independent variables. Age, AO, ExpCAG, and duration were considered control variables to analyze the correlation between independent variables and scale scores.

RESULTS

Duration, age, and ExpCAG were screened as influential independent variables (P = 0.000). Age had the greatest impact on multiple linear regression models (P<5E-8). ExpCAG and SARA/ICARS/INAS/Barthel index were not correlated (P > 0.05); considering only age as the control, ExpCAG was slightly-to-moderately correlated with all aforementioned scores except INAS (P < 0.05). Age and all scores, except INAS, were positively correlated (P < 0.05); considering duration, AO, or ExpCAG as controls, their correlations did not change significantly. On controlling age, AO was negatively correlated with all scores (P < 0.05), except for the Barthel index (P > 0.05). Furthermore, the interaction model revealed that the interaction between age, duration, and ExpCAG was significantly associated with SCA3 disease severity (P < 0.05).

CONCLUSION

Age is a potentially important modifier of SCA3 phenotype severity, through the interaction between ExpCAG and aging factors.

CAG Repeat Size Influences the Progression Rate of Spinocerebellar Ataxia Type 3

OBJECTIVE

In spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD), the expanded cytosine adenine guanine (CAG) repeat in ATXN3 is the causal mutation, and its length is the main factor in determining the age at onset (AO) of clinical symptoms. However, the contribution of the expanded CAG repeat length to the rate of disease progression after onset has remained a matter of debate, even though an understanding of this factor is crucial for experimental data on disease modifiers and their translation to clinical trials and their design.

METHODS

Eighty-two Dutch patients with SCA3/MJD were evaluated annually for 15 years using the International Cooperative Ataxia Rating Scale (ICARS). Using linear growth curve models, ICARS progression rates were calculated and tested for their relation to the length of the CAG repeat expansion and to the residual age at onset (RAO): The difference between the observed AO and the AO predicted on the basis of the CAG repeat length.

RESULTS

On average, ICARS scores increased 2.57 points/year of disease. The length of the CAG repeat was positively correlated with a more rapid ICARS progression, explaining 30% of the differences between patients. Combining both the length of the CAG repeat and RAO as comodifiers explained up to 47% of the interpatient variation in ICARS progression.

INTERPRETATION

Our data imply that the length of the expanded CAG repeat in ATXN3 is a major determinant of clinical decline, which suggests that CAG-dependent molecular mechanisms similar to those responsible for disease onset also contribute to the rate of disease progression in SCA3/MJD. ANN NEUROL 2021;89:66-73.

Oxidative Stress in DNA Repeat Expansion Disorders: A Focus on NRF2 Signaling Involvement

DNA repeat expansion disorders are a group of neuromuscular and neurodegenerative diseases that arise from the inheritance of long tracts of nucleotide repetitions, located in the regulatory region, introns, or inside the coding sequence of a gene. Although loss of protein expression and/or the gain of function of its transcribed mRNA or translated product represent the major pathogenic effect of these pathologies, mitochondrial dysfunction and imbalance in redox homeostasis are reported as common features in these disorders, deeply affecting their severity and progression. In this review, we examine the role that the redox imbalance plays in the pathological mechanisms of DNA expansion disorders and the recent advances on antioxidant treatments, particularly focusing on the expression and the activity of the transcription factor NRF2, the main cellular regulator of the antioxidant response.

Baseline Variables Associated with Functional Decline in 2CARE, A Randomized Clinical Trial in Huntington's Disease

BACKGROUND

Despite the clearly recognized progressive functional decline of Huntington's disease (HD), detailed investigations of factors associated with the rate of functional progression are limited.

OBJECTIVE

Understanding factors associated with functional decline through examination of existing HD clinical databases may improve efforts to mitigate it.

METHODS

We analyzed data from 2CARE, a randomized clinical trial with up to 5 years of follow-up, to assess potential risk factors for more rapid functional decline in HD.

RESULTS

Variables associated with faster functional decline included worse motor performance, worse cognitive test scores, female sex, lower weight and body mass index, and a higher CAG repeat length, especially in younger people.

CONCLUSION

While our data are limited to the structured environment and homogeneity of a clinical trial, attention to several of the identified risk factors may be useful towards managing functional decline over time. The observation that women progress faster than men, while potentially confounded by an association between sex and weight, deserves further study.

Sleep in Huntington's disease: a systematic review and meta-analysis of polysomongraphic findings

STUDY OBJECTIVES

Disturbed overnight sleep is a prominent feature of advanced stage Huntington's disease (HD). Several polysomnography (PSG) studies have reported significant changes of sleep in HD patients, but the findings are not unequivocal. To date, no meta-analysis has investigated the PSG changes in HD patients. The present study meta-analyzed results from studies examining the PSG changes in HD patients compared with controls.

METHODS

A literature search performed in MEDLINE, EMBASE, All EBM databases, PsycINFO, and CINAHL databases identified seven studies involving 152 HD patients and 144 controls which were included in our meta-analysis.

RESULTS

Pooled results indicated decreased sleep efficiency, percentage of slow wave sleep and rapid eye movement sleep, and increased percentage of N1 sleep, wake time after sleep onset, and rapid eye movement sleep latency in HD patients compared with controls. We found high heterogeneity in the effect sizes and no indication of systematic publication biases across studies. Meta-regression analyses showed that some of the heterogeneity was explained by age, body mass index (BMI), CAG repeat length, and disease severity of HD patients.

CONCLUSIONS

Our study showed that polysomnographic abnormalities are present in HD. Our findings also underscore the need for a comprehensive PSG assessment of sleep changes in patients with HD. Furthermore, the effects of age, BMI and CAG repeat length on sleep changes should be carefully considered and closely monitored in the management of HD.

Multiple clinical features of Huntington's disease correlate with mutant HTT gene CAG repeat lengths and neurodegeneration

Huntington's disease (HD) is a fatal neurodegenerative disease caused by mutant HTT gene expansions of CAG triplet repeat numbers that are inherited in an autosomal dominant manner. HD patients display multiple clinical features that are correlated with HTT CAG repeat numbers that include age of disease onset, motor dysfunction, cognitive deficits, compromised daily living capacity, and brain neurodegeneration. It is important to understand the significant relationships of the multiple HD clinical deficits correlated with the number of mutant HTT CAG expansions that are the genetic basis for HD disabilities. Therefore, this review highlights the significant correlations of the HD clinical features of age of onset, motor and cognitive disabilities, decline in living capabilities, weight loss, risk of death, and brain neurodegeneration with respect to their associations with CAG repeat lengths of the HTT gene. Quantitative HTT gene expression patterns analyzed in normal adult human brain regions demonstrated its distribution in areas known to undergo neurodegeneration in HD, as well as in other brain regions. Future investigation of the relationships of the spectrum of clinical HD features with mutant HTT molecular mechanisms will be important to gain understanding of how mutant CAG expansions of the HTT gene result in the devastating disabilities of HD patients.

Overlap between age-at-onset and disease-progression determinants in Huntington disease

OBJECTIVE

A fundamental but still unresolved issue regarding Huntington disease (HD) pathogenesis is whether the factors that determine age at onset are the same as those that govern disease progression. Because elucidation of this issue is crucial for the development as well as optimal timing of administration of novel disease-modifying therapies, we aimed to assess the extent of overlap between age-at-onset and disease-progression determinants in HD.

METHODS

Using observational data from Enroll-HD, the largest cohort of patients with HD worldwide, in this study we present, validate, and apply an intuitive method based on linear mixed-effect models to quantify the variability in the rate of disease progression in HD.

RESULTS

A total of 3,411 patients with HD met inclusion criteria. We found that (1) about two-thirds of the rate of functional, motor, and cognitive progression in HD is determined by the same factors that also determine age at onset, with CAG repeat-dependent mechanisms having by far the largest effect; (2) although expanded HTT CAG repeat size had a large influence on average body weight, the rate of weight loss was largely independent of factors that determine age at onset in HD; and (3) about one-third of the factors that determine the rate of functional, motor, and cognitive progression are different from those that govern age at onset and need further elucidation.

CONCLUSION

Our findings imply that targeting of CAG repeat-dependent mechanisms, for example through gene-silencing approaches, is likely to affect the rate of functional, motor, and cognitive impairment, but not weight loss, in manifest HD mutation carriers.

Rating Scales and Performance-based Measures for Assessment of Functional Ability in Huntington's Disease: Critique and Recommendations

Limitation of functional ability is a major feature of Huntington's disease (HD). The International Parkinson and Movement Disorder Society (MDS) commissioned the appraisal of the use and clinimetric properties of clinical measures of functional ability that have been applied in HD studies and trials to date, to make recommendations regarding their use based on standardized criteria. After a systematic literature search, we included a total of 29 clinical measures grouped into two categories: (1) performance-based measures (e.g., balance, walking, and reaching/grasping), and (2) rating scales. Three performance-based measures are rated as "recommended": the Tinetti Mobility Test for screening of fall risk and for severity assessment of mobility in patients with manifest HD (up to stage III); the Berg Balance Scale for severity of balance impairment; and the Six-Minute Walk Test for assessment of walking endurance (severity) in HD subjects with preserved ambulation. No rating scale targeting functional ability reached a "recommended" status either for screening or severity measurement. The main challenges identified in this review include applying widely accepted conceptual frameworks to the identified measures, the lack of validation of clinical measures to detect change over time, and absence of validated measures for upper limb function. Furthermore, measures of capacity or ability to perform activities of daily living had ceiling effects in people with early and pre-manifest HD. We recommend that the MDS prioritize the development of new scales that capture small, but meaningful changes in function over time for outcome assessment in clinical trials, particularly in earlier stages of HD.

What do we know about Late Onset Huntington's Disease?

Background: Although the typical age of onset for Huntington’s disease (HD) is in the fourth decade, between 4.4–11.5% of individuals with HD have a late onset (over 60 years of age). Diagnosis of Late onset HD (LoHD) can be missed, due to the perceived low likelihood of HD in the over 60-year-olds.

Objective: To review the epidemiology, genotype and phenotype of LoHD.

Methods: We systematically searched MEDLINE, EMBASE and Web of Science (inception-November 2016). Web of Science was then used to search for papers citing identified studies. Content experts were consulted for any additional studies. We included all studies reporting the clinical phenotype of LoHD for more than one participant.

Results: 20 studies were identified from a potential list of 1243. Among Caucasian HD cohorts, 4.4–11.5% of individuals have LoHD, and this proportion may be increasing. Proportion of LoHD without a positive family history ranges from 3–68%. 94.4% of reported cases of LoHD had CAG repeat lengths of ≤44. Motor manifestations are the commonest initial presentation, although 29.2% presented with non-motor manifestations as the first clinical feature in one case series. Individuals with LoHD may have slower progression of illness. Cognitive impairment rather than chorea may be the major source of disability in this group.

Conclusions: LoHD represents a substantial proportion of new diagnoses of HD and has some unique features. Further characterization of this population will aid clinicians in diagnosis.

Assessing Decline: Visualising Progression in Huntington's Disease using a Clinical Dashboard with Enroll-HD Data

BACKGROUND

In Huntington's disease (HD), it remains unclear how symptom severity and rate of symptomatic change relates to age and CAG repeat number (CAGn). It is often difficult for clinicians to assess whether an affected individual's symptoms are progressing at a similar rate to their affected peers, limiting their ability to intervene at the most appropriate time.

OBJECTIVE

To develop a clinical dashboard that compares an individual's total motor score (TMS), total functional capacity (TFC) and symbol digit modality test (SDMT) scores against a global cohort, controlling for age and CAGn. The dashboard could then be used by clinicians to identify individuals progressing at a disproportionate rate to his or her peers.

METHODS

Annualised longitudinal clinical assessment scores from the Enroll-HD dataset were used to generate decline trajectories of the global cohort, allowing cross-sectional (TMS n = 734; TFC n = 734; SDMT n = 694) and longitudinal (TMS n = 270; TFC n = 270; SDMT n = 247) comparison with individual clinical symptom rating scores, to assess decline relative to affected peers.

RESULTS

An electronic dashboard with a dynamic output display was created that rapidly compares clinical symptom rating scores of a specific individual against affected peers from a global cohort of comparable CAGn.

CONCLUSIONS

This study shows the potential for use of multi-centre trial data in allowing comparison of the individual to a larger group to facilitate improved decision-making for individual patients. Visualisation of these metrics via a clinical dashboard demonstrates how it may aid identification of those with disproportionate decline, offering potential for intervention at specific critical points in the disease course.

Huntingtin protein: A new option for fixing the Huntington's disease countdown clock

Huntington's disease is a dreadful, incurable disorder. It springs from the autosomal dominant mutation in the first exon of the HTT gene, which encodes for the huntingtin protein (HTT) and results in progressive neurodegeneration. Thus far, all the attempted approaches to tackle the mutant HTT-induced toxicity causing this disease have failed. The mutant protein comes with the aberrantly expanded poly-glutamine tract. It is primarily to blame for the build-up of β-amyloid-like HTT aggregates, deleterious once broadened beyond the critical ∼35-37 repeats threshold. Recent experimental findings have provided valuable information on the molecular basis underlying this HTT-driven neurodegeneration. These findings indicate that the poly-glutamine siding regions and many post-translation modifications either abet or counter the poly-glutamine tract. This review provides an overall, up-to-date insight into HTT biophysics and structural biology, particularly discussing novel pharmacological options to specifically target the mutated protein and thus inhibit its functions and toxicity.

Sphingomyelin and GM1 Influence Huntingtin Binding to, Disruption of, and Aggregation on Lipid Membranes

Huntington disease (HD) is an inherited neurodegenerative disease caused by the expansion beyond a critical threshold of a polyglutamine (polyQ) tract near the N-terminus of the huntingtin (htt) protein. Expanded polyQ promotes the formation of a variety of oligomeric and fibrillar aggregates of htt that accumulate into the hallmark proteinaceous inclusion bodies associated with HD. htt is also highly associated with numerous cellular and subcellular membranes that contain a variety of lipids. As lipid homeostasis and metabolism abnormalities are observed in HD patients, we investigated how varying both the sphingomyelin (SM) and ganglioside (GM1) contents modifies the interactions between htt and lipid membranes. SM composition is altered in HD, and GM1 has been shown to have protective effects in animal models of HD. A combination of Langmuir trough monolayer techniques, vesicle permeability and binding assays, and in situ atomic force microscopy (AFM) were used to directly monitor the interaction of a model, synthetic htt peptide and a full-length htt-exon1 recombinant protein with model membranes comprised of total brain lipid extract (TBLE) and varying amounts of exogenously added SM or GM1. The addition of either SM or GM1 decreased htt insertion into the lipid monolayers. However, TBLE vesicles with an increased SM content were more susceptible to htt-induced permeabilization, whereas GM1 had no effect on permeablization. Pure TBLE bilayers and TBLE bilayers enriched with GM1 developed regions of roughened, granular morphologies upon exposure to htt-exon1, but plateau-like domains with a smoother appearance formed in bilayers enriched with SM. Oligomeric aggregates were observed on all bilayer systems regardless of induced morphology. Collectively, these observations suggest that the lipid composition and its subsequent effects on membrane material properties strongly influence htt binding and aggregation on lipid membranes.

Rating scales for cognition in Huntington's disease: Critique and recommendations

Cognitive impairment is one of the main features of Huntington's disease and is present across the disease spectrum. As part of the International Parkinson's Disease and Movement Disorder Society-sponsored project to review all clinical rating scales used in Huntington's disease, a systematic review of the literature was performed to identify cognitive scales used in Huntington's disease and make recommendations for their use. A total of 17 cognitive scales were identified and evaluated. None of the scales met criteria for a "recommended" status. For assessing severity of cognitive dysfunction, the Montreal Cognitive Assessment was "recommended with caveats." The UHDRS Cognitive Assessment, the UHDRS-For Advanced Patients cognitive section, the Alzheimer's Disease Assessment Scale-Cognitive Subscale, the Frontal Assessment Battery, the Mattis Dementia Rating Scale, the Mini-Mental State Examination, and the Repeatable Battery for the Assessment of Neuropsychological Status were "suggested" for evaluating severity of cognitive impairment. The MoCA was "suggested" as a screening tool for cognitive impairment. The major challenge in the assessment of cognition in Huntington's disease is the lack of a formal definition of dementia and/or mild cognitive impairment in this disease. The committee concluded that there is a need to further validate currently available cognitive scales in Huntington's disease, but that it is premature to recommend the development of new scales. Recently developed Huntington's disease-specific scales, such as the Huntington's Disease-Cognitive Assessment Battery, hold promise but require the completion of more comprehensive clinimetric development. © 2017 International Parkinson and Movement Disorder Society.

Two Ethnic Clusters with Huntington Disease in Israel: The Case of Mountain Jews and Karaites

BACKGROUND

Worldwide prevalence estimates of Huntington disease (HD) vary widely, with no reliable information regarding the Jewish population in Israel.

METHODS

This specialized tertiary single-center cross-sectional study assessed clinical, cognitive, and demographic characteristics of 84 HD patients who were treated at the Movement Disorder Unit of the Tel Aviv Medical Center, Israel.

RESULTS

Our cohort was composed of one-third Ashkenazi Jews, 27% Mountain Jews (Caucasus Jews), 18% Sephardi Jews, and 21% Karaites, with both Mountain Jews and Karaites over-represented compared to their relevant proportion in the population of the state of Israel, which is less than 1%. No between-group differences were detected regarding the number of CAG (cytosine-adenine-guanine) repeats, age at onset, disease duration, years from symptom onset to diagnosis, gender, years of education, Unified Huntington Disease Rating Scale scores, or the Montreal Cognitive Assessment scores.

CONCLUSION

We detected clustering of HD among the population treated at our Medical Center, which has the only specialized HD clinic in the country, with a high percentage of HD among 2 relatively small subpopulations of Jews: Mountain Jews and Karaites.

Huntington Disease: Linking Pathogenesis to the Development of Experimental Therapeutics

Huntington disease (HD) is an autosomal dominant neurodegenerative condition caused by a CAG trinucleotide expansion in the huntingtin gene. At present, the HD field is experiencing exciting times with the assessment for the first time in human subjects of interventions aimed at core disease mechanisms. Out of a portfolio of interventions that claim a potential disease-modifying effect in HD, the target huntingtin has more robust validation. In this review, we discuss the spectrum of huntingtin-lowering therapies that are currently being considered. We provide a critical appraisal of the validation of huntingtin as a drug target, describing the advantages, challenges, and limitations of the proposed therapeutic interventions. The development of these new therapies relies strongly on the knowledge of HD pathogenesis and the ability to translate this knowledge into validated pharmacodynamic biomarkers. Altogether, the goal is to support a rational drug development that is ethical and cost-effective. Among the pharmacodynamic biomarkers under development, the quantification of mutant huntingtin in the cerebral spinal fluid and PET imaging targeting huntingtin or phosphodiesterase 10A deserve special attention. Huntingtin-lowering therapeutics are eagerly awaited as the first interventions that may be able to change the course of HD in a meaningful way.

Risk factors for the onset and progression of Huntington disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by chorea, behavioural and psychiatric manifestations, and dementia, caused by a CAG triplet repeat expansion in the huntingtin gene. Systematic review of the literature was conducted to determine the risk factors for the onset and progression of HD. Multiple databases were searched, using terms specific to Huntington disease and to studies of aetiology, risk, prevention and genetics, limited to studies on human subjects published in English or French between 1950 and 2010. Two reviewers independently screened the abstracts and identified potentially relevant articles for full-text review using predetermined inclusion criteria. Three major categories of risk factors for onset of HD were identified: CAG repeat length in the huntingtin gene, CAG instability, and genetic modifiers. Of these, CAG repeat length in the huntingtin gene is the most important risk factor. For the progression of HD: genetic, demographic, past medical/clinical and environmental risk factors have been studied. Of these factors, genetic factors appear to play the most important role in the progression of HD. Among the potential risk factors, CAG repeat length in the mutant allele was found to be a relatively consistent and significant risk factor for the progression of HD, especially in motor, cognitive, and other neurological symptom deterioration. In addition, there were many consistent results in the literature indicating that a higher number of CAG repeats was associated with shorter survival, faster institutionalization, and earlier percutaneous endoscopic gastrostomy.

Is There an Association of Physical Activity with Brain Volume, Behavior, and Day-to-day Functioning? A Cross Sectional Design in Prodromal and Early Huntington Disease

BACKGROUND

Huntington disease (HD) is a genetic neurodegenerative disease leading to progressive motor, cognitive, and behavioral decline. Subtle changes in these domains are detectable up to 15 years before a definitive motor diagnosis is made. This period, called prodromal HD, provides an opportunity to examine lifestyle behaviors that may impact disease progression.

THEORETICAL FRAMEWORK

Physical activity relates to decreased rates of brain atrophy and improved cognitive and day-to-day functioning in Alzheimer disease and healthy aging populations. Previous research has yielded mixed results regarding the impact of physical activity on disease progression in HD and paid little attention to the prodromal phase.

METHODS

We conducted analyses of associations among current physical activity level, current and retrospective rate of change for hippocampus and striatum volume, and cognitive, motor, and day-to-day functioning variables. Participants were 48 gene-expanded cases with prodromal and early-diagnosed HD and 27 nongene-expanded control participants. Participants wore Fitbit Ultra activity monitors for three days and completed the self-reported International Physical Activity Questionnaire (IPAQ). Hippocampal and striatal white matter volumes were measured using magnetic resonance imaging. Cognitive tests included the Stroop Color and Word Test, and the Symbol Digit Modalities Test (SDMT). Motor function was assessed using the Unified Huntington's Disease Rating Scale total motor score (TMS). Day-to-day functioning was measured using the World Health Organization Disability Assessment Schedule (WHODAS) version 2.0.

RESULTS

Higher Fitbit activity scores were significantly related to better scores on the SDMT and WHODAS in case participants but not in controls. Fitbit activity scores tracked better with TMS scores in the group as a whole, though the association did not reach statistical significance in the case participants. Higher Fitbit activity scores related to less day-to-day functioning decline in retrospective slope analyses. Fitbit activity scores did not differ significantly between cases and controls.

CONCLUSIONS

This is the first known study examining the associations between activity level and imaging, motor, cognitive, and day-to-day functioning outcomes in prodromal and early HD. Preliminary results suggest physical activity positively correlates with improved cognitive and day-to-day functioning and possibly motor function in individuals in the prodromal and early phase of the condition.

Huntington Disease in Asia

Objective:

The objective was to review the major differences of Huntington disease (HD) in Asian population from those in the Caucasian population.

Data Sources:

Data cited in this review were obtained from PubMed database and China National Knowledge Infrastructure (CNKI) from 1994 to 2014. All the papers were written in English or Chinese languages, with the terms of Asia/Asian, HD, genotype, epidemiology, phenotype, and treatment used for the literature search.

Study Selection:

From the PubMed database, we included the articles and reviews which contained the HD patients’ data from Asian countries. From the CNKI, we excluded the papers which were not original research. Due to the language's restrictions, those data published in other languages were not included.

Results:

In total, 50 papers were cited in this review, authors of which were from the mainland of China, Japan, India, Thailand, Taiwan (China), Korea, and western countries.

Conclusions:

The lower epidemiology in Asians can be partly explained by the less cytosine-adenine-guanine repeats, different haplotypes, and CCG polymorphisms. For the physicians, atypical clinical profiles such as the initial symptom of ataxia, movement abnormalities of Parkinsonism, dystonia, or tics need to be paid more attention to and suggest gene testing if necessary. Moreover, some pathogenesis studies may help progress some new advanced treatments. The clinicians in Asian especially in China should promote the usage of genetic testing and put more effects in rehabilitation, palliative care, and offer comfort of patients and their families. The unified HD rating scale also needs to be popularized in Asia to assist in evaluating the progression of HD.

Huntington's Disease: Relationship Between Phenotype and Genotype

Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disease with the typical manifestations of involuntary movements, psychiatric and behavior disorders, and cognitive impairment. It is caused by the dynamic mutation in CAG triplet repeat number in exon 1 of huntingtin (HTT) gene. The symptoms of HD especially the age at onset are related to the genetic characteristics, both the CAG triplet repeat and the modified factors. Here, we reviewed the recent advancement on the genotype-phenotype relationship of HD, mainly focus on the characteristics of different expanded CAG repeat number, genetic modifiers, and CCG repeat number in the 3' end of CAG triplet repeat and their effects on the phenotype. We also reviewed the special forms of HD (juvenile HD, atypical onset HD, and homozygous HD) and their phenotype-genotype correlations. The review will aid clinicians to predict the onset age and disease course of HD, give the genetic counseling, and accelerate research into the HD mechanism.

Cholesterol Modifies Huntingtin Binding to, Disruption of, and Aggregation on Lipid Membranes

Huntington's disease (HD) is an inherited neurodegenerative disease caused by abnormally long CAG-repeats in the huntingtin gene that encode an expanded polyglutamine (polyQ) domain near the N-terminus of the huntingtin (htt) protein. Expanded polyQ domains are directly correlated to disease-related htt aggregation. Htt is found highly associated with a variety of cellular and subcellular membranes that are predominantly comprised of lipids. Since cholesterol homeostasis is altered in HD, we investigated how varying cholesterol content modifies the interactions between htt and lipid membranes. A combination of Langmuir trough monolayer techniques, vesicle permeability and binding assays, and in situ atomic force microscopy were used to directly monitor the interaction of a model, synthetic htt peptide and a full-length htt-exon1 recombinant protein with model membranes comprised of total brain lipid extract (TBLE) and varying amounts of exogenously added cholesterol. As the cholesterol content of the membrane increased, the extent of htt insertion decreased. Vesicles containing extra cholesterol were resistant to htt-induced permeabilization. Morphological and mechanical changes in the bilayer associated with exposure to htt were also drastically altered by the presence of cholesterol. Disrupted regions of pure TBLE bilayers were grainy in appearance and associated with a large number of globular aggregates. In contrast, morphological changes induced by htt in bilayers enriched in cholesterol were plateau-like with a smooth appearance. Collectively, these observations suggest that the presence and amount of cholesterol in lipid membranes play a critical role in htt binding and aggregation on lipid membranes.

Modelling the natural history of Huntington's disease progression

BACKGROUND

The lack of reliable biomarkers to track disease progression is a major problem in clinical research of chronic neurological disorders. Using Huntington's disease (HD) as an example, we describe a novel approach to model HD and show that the progression of a neurological disorder can be predicted for individual patients.

METHODS

Starting with an initial cohort of 343 patients with HD that we have followed since 1995, we used data from 68 patients that satisfied our filtering criteria to model disease progression, based on the Unified Huntington's Disease Rating Scale (UHDRS), a measure that is routinely used in HD clinics worldwide.

RESULTS

Our model was validated by: (A) extrapolating our equation to model the age of disease onset, (B) testing it on a second patient data set by loosening our filtering criteria, (C) cross-validating with a repeated random subsampling approach and (D) holdout validating with the latest clinical assessment data from the same cohort of patients. With UHDRS scores from the past four clinical visits (over a minimum span of 2 years), our model predicts disease progression of individual patients over the next 2 years with an accuracy of 89-91%. We have also provided evidence that patients with similar baseline clinical profiles can exhibit very different trajectories of disease progression.

CONCLUSIONS

This new model therefore has important implications for HD research, most obviously in the development of potential disease-modifying therapies. We believe that a similar approach can also be adapted to model disease progression in other chronic neurological disorders.

Linking genes to neurological clinical practice: the genomic basis for neurorehabilitation

Large-scale genomics projects such as the Human Genome Project and the International HapMap Project promise significant advances in the ability to diagnose and treat many conditions, including those with a neurological basis. A major focus of research has emerged in the neurological sciences to elucidate the molecular and genetic basis of various neurological diseases. Indeed, genetic factors are implicated in susceptibility for many neurological disorders, with family history studies providing strong evidence of familial risk for conditions such as stroke, Parkinson's, Alzheimer's, and Huntington's diseases. Heritability studies also suggest a strong genetic contribution to the risk for neurological diseases. Genome-wide association studies are also uncovering novel genetic variants associated with neurological disorders. Whole-genome and exome sequencing are likely to provide novel insights into the genetic basis of neurological disorders. Genetic factors are similarly associated with clinical phenotypes such as symptom severity and progression as well as response to treatment. Specifically, disease progression and functional restoration depend, in part, on the capacity for neural plasticity within residual neural tissues. Furthermore, such plasticity may be influenced in part by the presence of polymorphisms in several genes known to orchestrate neural plasticity including brain-derived neurotrophic factor (BDNF) and Apolipoprotein E. (APOE). It is important for neurorehabilitation therapist practicing in the "genomic era" to be aware of the potential influence of genetic factors during clinical encounters, as advances in molecular sciences are revealing information of critical relevance to the clinical rehabilitation management of individuals with neurological conditions. Video Abstract available (See Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A88) for more insights from the authors.

Potential trade-offs in treatment of premanifest Huntington's disease

The potential long-term consequences of treatments delaying manifestations of neurodegenerative diseases have not been explored. Using Huntington disease (HD) data and Markov chain Monte Carlo methods, we simulated the effects of therapies with equivalent effects on time to onset of HD and survival with HD. Our results suggest substantial potential trade-offs in effects of these therapies; significant delays in time to onset of HD were accompanied by significant prolongations of survival after onset of HD. Under a variety of assumptions, treatments delaying onset of HD result in some patients likely to have a greater increase in survival with manifest HD compared to delays in time to onset of HD. Our results suggest that future work in HD should be sensitive to the potential existence of such trade-offs and that understanding the preferences of HD patients and the broader HD community will be increasingly important. Future research, trial design, and treatment strategies in HD and other mid-life-onset neurodegenerative disorders should consider the possibility of trade-offs in long-term consequences of disease-modifying treatments.

Curvature enhances binding and aggregation of huntingtin at lipid membranes

Huntington disease (HD) is a genetic neurodegenerative disease caused by an expanded polyglutamine (polyQ) domain in the first exon of the huntingtin (Htt) protein, facilitating its aggregation. Htt interacts with a variety of membraneous structures within the cell, and the first 17 amino acids (Nt17) of Htt directly flanking the polyQ domain comprise an amphiphathic α-helix (AH) lipid-binding domain. AHs are also known to detect membrane curvature. To determine if Htt exon 1 preferentially binds curved membranes, in situ atomic force microscopy (AFM) studies were performed. Supported lipid bilayers are commonly used as model membranes for AFM studies of protein aggregation. However, these supported bilayers usually lack curvature. By forming a bilayer on top of silica nanobeads (50 ± 10 nm) deposited on a silicon substrate, model supported lipid bilayers with flat and curved regions were developed for AFM studies. The presence of the bilayer over the beads was validated by continual imaging of the formation of the bilayer, height measurements, and spatially resolved mechanical measurements of the resulting bilayer using scanning probe acceleration microscopy. Interpretation of this data was facilitated by numerical simulations of the entire imaging process. The curved supported bilayers associated with the beads were found to be more compliant than flat supported bilayers, consistent with the altered packing density of lipids caused by the induced curvature. This model bilayer system was exposed to a synthetic truncated Htt exon 1 peptide (Nt17Q35P10KK), and this peptide preferentially accumulated on curved membranes, consistent with the ability of AHs to sense membrane curvature.

The effects of flanking sequences in the interaction of polyglutamine peptides with a membrane bilayer

Huntington's disease (HD) is caused by the presence of an extended polyglutamine (polyQ) region at the N-terminus of the huntingtin (htt) protein. The presence of flanking sequences adjacent to the polyQ region has been reported to modulate the effects of potentially toxic protein-membrane interactions. In this study, we consider four peptide systems with various combinations of flanking sequences (KKQ35KK, KKQ35P11KK, N17Q35KK, N17Q35P11KK) and use atomistic molecular dynamics simulations to study the interactions with a DOPC lipid bilayer. We observe significant membrane thinning, disorderliness of lipid molecules, and compensation effects between the top and the bottom leaflets of the bilayer depending on the presence of particular flanking sequences. Overall, we find that the presence of the N-17 flanking sequence is crucial for membrane interactions. Polyproline decreases the interaction with the membrane in the absence of N-17, but enhances it when present along N-17.

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.

Role of oxidative DNA damage in mitochondrial dysfunction and Huntington's disease pathogenesis

Huntington's disease (HD) is a neurodegenerative disorder with an autosomal dominant expression pattern and typically a late-onset appearance. HD is a movement disorder with a heterogeneous phenotype characterized by involuntary dance-like gait, bioenergetic deficits, motor impairment, and cognitive and psychiatric deficits. Compelling evidence suggests that increased oxidative stress and mitochondrial dysfunction may underlie HD pathogenesis. However, the exact mechanisms underlying mutant huntingtin-induced neurological toxicity remain unclear. The objective of this paper is to review recent literature regarding the role of oxidative DNA damage in mitochondrial dysfunction and HD pathogenesis.

The interaction of polyglutamine peptides with lipid membranes is regulated by flanking sequences associated with huntingtin

Huntington disease (HD) is caused by an expanded polyglutamine (poly(Q)) repeat near the N terminus of the huntingtin (htt) protein. Expanded poly(Q) facilitates formation of htt aggregates, eventually leading to deposition of cytoplasmic and intranuclear inclusion bodies containing htt. Flanking sequences directly adjacent to the poly(Q) domain, such as the first 17 amino acids on the N terminus (Nt17) and the polyproline (poly(P)) domain on the C-terminal side of the poly(Q) domain, heavily influence aggregation. Additionally, htt interacts with a variety of membraneous structures within the cell, and Nt17 is implicated in lipid binding. To investigate the interaction between htt exon1 and lipid membranes, a combination of in situ atomic force microscopy, Langmuir trough techniques, and vesicle permeability assays were used to directly monitor the interaction of a variety of synthetic poly(Q) peptides with different combinations of flanking sequences (KK-Q35-KK, KK-Q35-P10-KK, Nt17-Q35-KK, and Nt17-Q35-P10-KK) on model membranes and surfaces. Each peptide aggregated on mica, predominately forming extended, fibrillar aggregates. In contrast, poly(Q) peptides that lacked the Nt17 domain did not appreciably aggregate on or insert into lipid membranes. Nt17 facilitated the interaction of peptides with lipid surfaces, whereas the poly(P) region enhanced this interaction. The aggregation of Nt17-Q35-P10-KK on the lipid bilayer closely resembled that of a htt exon1 construct containing 35 repeat glutamines. Collectively, this data suggests that the Nt17 domain plays a critical role in htt binding and aggregation on lipid membranes, and this lipid/htt interaction can be further modulated by the presence of the poly(P) domain.

Irritability in Huntington's disease

Irritability is a frequent neuropsychiatric symptom in patients with Huntington's disease (HD). The Irritability Scale (IS) and the irritability factor of the Problem Behaviours Assessment (PBA) was used to assess irritability among 130 HD mutation carriers and 43 verified non-carriers. The IS was tested using receiver operating characteristic analysis against different cut-offs of the PBA irritability factor. A robust IS cut-off score of ≥14 points was found indicating that 45 (35%) of the 130 mutation carriers were irritable vs. 4 (9%) of the 43 non-carriers (P=0.001). The level of agreement between self-report and informant-report IS was of moderate strength (intraclass correlation=0.61). Using univariate and multivariate regression analyses, independent correlates of irritability were being married/living together (P=0.02), CAG repeat length (P=0.01), and use of benzodiazepines (P=0.008). Using the same model with the informant's irritability score, use of benzodiazepines was the only significant independent correlate of irritability (P=0.005). Irritability is a prominent symptom of HD and can be reliably assessed with the IS using a cut-off score ≥14 points. Although it is unclear whether benzodiazepine use causes irritability, or irritability leads to the prescription of benzodiazepines, clinical evaluation with respect to the use of benzodiazepines in HD warrants attention.

Identification of novel potentially toxic oligomers formed in vitro from mammalian-derived expanded huntingtin exon-1 protein

Huntington disease is a genetic neurodegenerative disorder that arises from an expanded polyglutamine region in the N terminus of the HD gene product, huntingtin. Protein inclusions comprised of N-terminal fragments of mutant huntingtin are a characteristic feature of disease, though are likely to play a protective role rather than a causative one in neurodegeneration. Soluble oligomeric assemblies of huntingtin formed early in the aggregation process are candidate toxic species in HD. In the present study, we established an in vitro system to generate recombinant huntingtin in mammalian cells. Using both denaturing and native gel analysis, we have identified novel oligomeric forms of mammalian-derived expanded huntingtin exon-1 N-terminal fragment. These species are transient and were not previously detected using bacterially expressed exon-1 protein. Importantly, these species are recognized by 3B5H10, an antibody that recognizes a two-stranded hairpin conformation of expanded polyglutamine believed to be associated with a toxic form of huntingtin. Interestingly, comparable oligomeric species were not observed for expanded huntingtin shortstop, a 117-amino acid fragment of huntingtin shown previously in mammalian cell lines and transgenic mice, and here in primary cortical neurons, to be non-toxic. Further, we demonstrate that expanded huntingtin shortstop has a reduced ability to form amyloid-like fibrils characteristic of the aggregation pathway for toxic expanded polyglutamine proteins. Taken together, these data provide a possible candidate toxic species in HD. In addition, these studies demonstrate the fundamental differences in early aggregation events between mutant huntingtin exon-1 and shortstop proteins that may underlie the differences in toxicity.

Predictors of survival in a Huntington's disease population from southern Italy

BACKGROUND

The primary aim of the present study was to determine the survival rates and identify predictors of disease duration in a cohort of Huntington's disease (HD) patients from Southern Italy.

METHODS

All medical records of HD patients followed between 1977 and 2008 at the Department of Neurological Sciences of Federico II University in Naples were retrospectively reviewed and 135 patients were enrolled in the analysis. At the time of data collection, 41 patients were deceased (19 males and 22 females) with a mean ± SD age at death of 56.6 ± 14.9 years (range 18-83).

RESULTS

The median survival time was 20 years (95% CI: 18.3-21.7). Cox regression analysis showed that the number of CAG in the expanded allele (HR 1.09 for 1 point triplet increase, p=0.002) and age of onset (HR 1.05 for 1 point year increase, p=0.002) were independent and significant predictors of lower survival rates.

CONCLUSIONS

We believe that these findings are important for a better understanding of the natural history of the disease and may be relevant in designing future therapeutic trials.