Autonomic dysfunction in presymptomatic and early symptomatic Huntington's disease

Cardiac autonomic involvement in Huntington's disease

INTRODUCTION

Huntington's disease (HD) is known as a neurodegenerative disease with movement disorder and cognitive impairment; autonomic involvement is also becoming common in some recent studies. The aim of this study is to demonstrate the presence of cardiac autonomic involvement in HD patients.

METHOD

Time and frequency domain parameters obtained from the 24-h Holter ECG(hECG) were compared between 20 HD patients and 20 healthy control subjects.

RESULTS

Fourteen HD patients had tachycardia, bradycardia, and extra beats. Interval between two heartbeats, normal-to-normal (NN), standard deviation of all normal-to-normal (SDNN), square root of the mean of the sum of the squares of the differences between consecutive N-N intervals in ms (rMSSD), and the ratio of the number of consecutive pairs of N-N intervals that differ by more than 50 ms to the total number of N-N intervals (pNN50) were all significantly higher in the patient group than in the control group during 24-h hECG monitoring. However, hECG monitoring showed that the patient group had significantly higher values of the frequency-domain metrics high frequency (HF) than the control group did (P = 0.003). Very low frequency (VLF) was lower in the patient group (P = 0.009). There was no difference in low frequency (LF) in both groups. In comparison to the control group, LF/HF was much reduced in the patient group (P = 0.001).

CONCLUSION

Cardiac disfunction increases, and autonomic functions change in HD, but more comprehensive studies are needed to distinguish sympathetic and parasympathetic involvement.

The phase coherence of the neurovascular unit is reduced in Huntington's disease

Huntington's disease is a neurodegenerative disorder in which neuronal death leads to chorea and cognitive decline. Individuals with ≥40 cytosine-adenine-guanine repeats on the interesting transcript 15 gene develop Huntington's disease due to a mutated huntingtin protein. While the associated structural and molecular changes are well characterized, the alterations in neurovascular function that lead to the symptoms are not yet fully understood. Recently, the neurovascular unit has gained attention as a key player in neurodegenerative diseases. The mutant huntingtin protein is known to be present in the major parts of the neurovascular unit in individuals with Huntington's disease. However, a non-invasive assessment of neurovascular unit function in Huntington's disease has not yet been performed. Here, we investigate neurovascular interactions in presymptomatic (N = 13) and symptomatic (N = 15) Huntington's disease participants compared to healthy controls (N = 36). To assess the dynamics of oxygen transport to the brain, functional near-infrared spectroscopy, ECG and respiration effort were recorded. Simultaneously, neuronal activity was assessed using EEG. The resultant time series were analysed using methods for discerning time-resolved multiscale dynamics, such as wavelet transform power and wavelet phase coherence. Neurovascular phase coherence in the interval around 0.1 Hz is significantly reduced in both Huntington's disease groups. The presymptomatic Huntington's disease group has a lower power of oxygenation oscillations compared to controls. The spatial coherence of the oxygenation oscillations is lower in the symptomatic Huntington's disease group compared to the controls. The EEG phase coherence, especially in the α band, is reduced in both Huntington's disease groups and, to a significantly greater extent, in the symptomatic group. Our results show a reduced efficiency of the neurovascular unit in Huntington's disease both in the presymptomatic and symptomatic stages of the disease. The vasculature is already significantly impaired in the presymptomatic stage of the disease, resulting in reduced cerebral blood flow control. The results indicate vascular remodelling, which is most likely a compensatory mechanism. In contrast, the declines in α and γ coherence indicate a gradual deterioration of neuronal activity. The results raise the question of whether functional changes in the vasculature precede the functional changes in neuronal activity, which requires further investigation. The observation of altered dynamics paves the way for a simple method to monitor the progression of Huntington's disease non-invasively and evaluate the efficacy of treatments.

Systemic Symptoms in Huntington's Disease: A Comprehensive Review

BACKGROUND

Although Huntington's disease (HD) is usually thought of as a triad of motor, cognitive, and psychiatric symptoms, there is growing appreciation of HD as a systemic illness affecting the entire body.

OBJECTIVES

This review aims to draw attention to these systemic non-motor symptoms in HD.

METHODS

We identified relevant studies published in English by searching MEDLINE (from 1966 to September 2023), using the following subject headings: Huntington disease, autonomic, systemic, cardiovascular, respiratory, gastrointestinal, urinary, sexual and cutaneous, and additional specific symptoms.

RESULTS

Data from 123 articles were critically reviewed with focus on systemic features associated with HD, such as cardiovascular, respiratory, gastrointestinal, urinary, sexual and sweating.

CONCLUSION

This systematic review draws attention to a variety of systemic and autonomic co-morbidities in patients with HD. Not all of them correlate with the severity of the primary HD symptoms or CAG repeats. More research is needed to better understand the pathophysiology and treatment of systemic and autonomic dysfunction in HD.

Characterizing Heart Rate Variability Response to Maximal Exercise Testing in People with Huntington's Disease

Background

Huntington's disease (HD) is an autosomal dominant, neurodegenerative disease that involves dysfunction in the autonomic nervous system (ANS). Heart rate variability (HRV) is a valid and noninvasive measure for ANS dysfunction, yet no study has characterized HRV response to exercise in people with HD.

Objective

Characterize HRV response to exercise in individuals with HD and explore its implications for exercise prescription and cardiac dysautonomia mechanisms.

Methods

19 participants with HD were recruited as part of a cohort of individuals enrolled in the Physical Activity and Exercise Outcomes in Huntington's Disease (PACE-HD) study at Teachers College, Columbia University (TC). 13 non-HD age- and gender-matched control participants were also recruited from TC. HRV was recorded with a Polar H10 heart rate (HR) monitor before, during, and after a ramp cycle-ergometer exercise test.

Results

Participants with HD showed reduced HR peak (p < 0.01) and HR reserve (p < 0.001) compared with controls. Participants with HD demonstrated reduced root mean square of successive differences between normal-to-normal intervals (RMSSD) and successive differences of normal-to-normal intervals (SDSD) at rest (p < 0.001). Participants with HD also showed differences for low frequency (LF) power (p < 0.01), high frequency (HF) normalized units (nu) (p < 0.05), LF (nu) (p < 0.001), and HF/LF ratio (p < 0.05) compared with controls.

Conclusions

We found reduced aerobic exercise capacity and sympathovagal dysautonomia both at rest and during post-exercise recovery in people with HD, suggesting modified exercise prescription may be required for people with HD. Further investigations focusing on cardiac dysautonomia and underlying mechanisms of sympathovagal dysautonomia in people with HD are warranted.

Implications from proteomic studies investigating circadian rhythm disorder-regulated neurodegenerative disease pathology

Neurodegenerative diseases (NDs) affect 15% of the world's population and are becoming an increasingly common cause of morbidity and mortality worldwide. Circadian rhythm disorders (CRDs) have been reported to be involved in the pathogenic regulation of various neurologic diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis and amyotrophic lateral sclerosis. Proteomic technology is helpful to explore treatment targets for CRDs in patients with NDs. Here, we review the key differentially expressed (DE) proteins identified in previous proteomic studies investigating NDs, CRDs and associated models and the related pathways identified by enrichment analysis. Furthermore, we summarize the advantages and disadvantages of the above studies and propose new proteomic technologies for the precise study of circadian disorder-mediated regulation of ND pathology. This review provides a theoretical and technical reference for the precise study of circadian disorder-mediated regulation of ND pathology.

Gut dysbiosis and homocysteine: a couple for boosting neurotoxicity in Huntington disease

Huntington's disease (HD), a neurodegenerative disorder caused by an expansion of the huntingtin triplet (Htt), is clinically characterized by cognitive and neuropsychiatric alterations. Although these alterations appear to be related to mutant Htt (mHtt)-induced neurotoxicity, several other factors are involved. The gut microbiota is a known modulator of brain-gut communication and when altered (dysbiosis), several complaints can be developed including gastrointestinal dysfunction which may have a negative impact on cognition, behavior, and other mental functions in HD through several mechanisms, including increased levels of lipopolysaccharide, proinflammatory cytokines and immune cell response, as well as alterations in Ca²⁺ signaling, resulting in both increased intestinal and blood-brain barrier (BBB) permeability. Recently, the presence of dysbiosis has been described in both transgenic mouse models and HD patients. A bidirectional influence between host brain tissues and the gut microbiota has been observed. On the one hand, the host diet influences the composition and function of microbiota; and on the other hand, microbiota products can affect BBB permeability, synaptogenesis, and the regulation of neurotransmitters and neurotrophic factors, which has a direct effect on host metabolism and brain function. This review summarizes the available evidence on the pathogenic synergism of dysbiosis and homocysteine, and their role in the transgression of BBB integrity and their potential neurotoxicity of HD.

Posterior reversible encephalopathy syndrome due to arterial hypertension may mark the onset of the symptomatic phase in Huntington's disease

Autonomic dysregulation of cardiovascular functions marks early Huntingtons disease (HD). Blood-brain barrier (BBB) is dysfunctional in HD. A 37-year-old female carrying 41 CAG triplets in the huntingtin gene acutely presented with a multifaceted syndrome attributable to posterior reversible encephalopathy syndrome (PRES). Syndrome was associated with arterial hypertension (AHT). The syndrome fully recovered both by imaging and clinical signs after normalization of arterial pressure during hospitalization. Immediately after hospital discharge, the patient developed a complex psychiatric syndrome and choreic movements that represented conversion to the symptomatic phase of HD. A one-year later follow up clearly showed the patient had developed the symptomatic stage of HD by presenting both psychiatric symptoms and choreic movements. Onset of AHT may represent an early premonitory signal of HD becoming manifested. Induction of PRES might be associated with BBB impairment in HD.

Autonomic changes in Huntington's disease correlate with altered central autonomic network connectivity

Autonomic dysfunction has been described in patients with Huntington's disease, but it is unclear if these changes in autonomic tone are related to the central autonomic network. We performed a pilot study to investigate the relationship between the integrity of the central autonomic network and peripheral manifestiations of autonomic dysfunction in premanifest Huntington's disease. We recruited male participants with pre-motor-manifest Huntington's disease and a comparison group consisting of healthy, male participants of approximately the same age. As this was a pilot study, only males were included to reduce confounding. Participants underwent a resting-state functional magnetic resonance imaging study to quantify functional connectivity within the central autonomic network, as well as a resting 3-lead ECG to measure heart rate variability with a particular focus on the parasympathetic time-domain measures of root mean square of successive differences between normal heartbeats. The pre-motor-manifest Huntington's disease participants had significantly decreased root mean square of successive differences between normal heartbeats values compared with the healthy comparison group. The pre-motor-manifest Huntington's disease group had significantly lower functional connectivity within the central autonomic network, which was positively correlated with root mean square of successive differences between normal heartbeats. Patients with pre-motor-manifest Huntington's disease have reduced functional connectivity within the central autonomic network, which is significantly associated with observed changes in autonomic function.

A method to quantify autonomic nervous system function in healthy, able-bodied individuals

BACKGROUND

The autonomic nervous system (ANS) maintains physiological homeostasis in various organ systems via parasympathetic and sympathetic branches. ANS function is altered in common diffuse and focal conditions and heralds the beginning of environmental and disease stresses. Reliable, sensitive, and quantitative biomarkers, first defined in healthy participants, could discriminate among clinically useful changes in ANS function. This framework combines controlled autonomic testing with feature extraction during physiological responses.

METHODS

Twenty-one individuals were assessed in two morning and two afternoon sessions over two weeks. Each session included five standard clinical tests probing autonomic function: squat test, cold pressor test, diving reflex test, deep breathing, and Valsalva maneuver. Noninvasive sensors captured continuous electrocardiography, blood pressure, breathing, electrodermal activity, and pupil diameter. Heart rate, heart rate variability, mean arterial pressure, electrodermal activity, and pupil diameter responses to the perturbations were extracted, and averages across participants were computed. A template matching algorithm calculated scaling and stretching features that optimally fit the average to an individual response. These features were grouped based on test and modality to derive sympathetic and parasympathetic indices for this healthy population.

RESULTS

A significant positive correlation (p = 0.000377) was found between sympathetic amplitude response and body mass index. Additionally, longer duration and larger amplitude sympathetic and longer duration parasympathetic responses occurred in afternoon testing sessions; larger amplitude parasympathetic responses occurred in morning sessions.

CONCLUSIONS

These results demonstrate the robustness and sensitivity of an algorithmic approach to extract multimodal responses from standard tests. This novel method of quantifying ANS function can be used for early diagnosis, measurement of disease progression, or treatment evaluation.

TRIAL REGISTRATION

This study registered with Clinicaltrials.gov , identifier NCT04100486 . Registered September 24, 2019, https://www.clinicaltrials.gov/ct2/show/NCT04100486 .

Systemic manifestation and contribution of peripheral tissues to Huntington's disease pathogenesis

Huntington disease (HD) is an autosomal dominant neurodegenerative disease that is caused by expansion of cytosine/adenosine/guanine repeats in the huntingtin (HTT) gene, which leads to a toxic, aggregation-prone, mutant HTT-polyQ protein. Beyond the well-established mechanisms of HD progression in the central nervous system, growing evidence indicates that also peripheral tissues are affected in HD and that systemic signaling originating from peripheral tissues can influence the progression of HD in the brain. Herein, we review the systemic manifestation of HD in peripheral tissues, and the impact of systemic signaling on HD pathogenesis. Mutant HTT induces a body wasting syndrome (cachexia) primarily via its activity in skeletal muscle, bone, adipose tissue, and heart. Additional whole-organism effects induced by mutant HTT include decline in systemic metabolic homeostasis, which stems from derangement of pancreas, liver, gut, hypothalamic-pituitary-adrenal axis, and circadian functions. In addition to spreading via the bloodstream and a leaky blood brain barrier, HTT-polyQ may travel long distance via its uptake by neurons and its axonal transport from the peripheral to the central nervous system. Lastly, signaling factors that are produced and/or secreted in response to therapeutic interventions such as exercise or in response to mutant HTT activity in peripheral tissues may impact HD. In summary, these studies indicate that HD is a systemic disease that is influenced by intertissue signaling and by the action of pathogenic HTT in peripheral tissues. We propose that treatment strategies for HD should include the amelioration of HD symptoms in peripheral tissues. Moreover, harnessing signaling between peripheral tissues and the brain may provide a means for reducing HD progression in the central nervous system.

Autonomic dysregulation as an early pathologic feature of Huntington Disease

OBJECTIVE

Autonomic nervous system (ANS) dysfunction has been described in adults with motor-manifest Huntington's Disease (HD) or those who are near their predicted motor onset. It is unclear if ANS dysfunction is present years prior to the onset of motor symptoms of HD. To bridge this gap in knowledge, we compared crude markers of ANS function between children with the gene-expansion that causes HD (GE group) who were decades from their predicted motor onset and gene-non-expanded children (GNE group).

METHODS

We included participants from the Kids-HD study who were <18 years old. Linear mixed effects regression models were constructed that controlled for sex, age, and BMI, and included a random effect per participant and per family. We compared resting heart rate (rHR), core body temperature (CBT), systolic blood pressure (SBP), and diastolic blood pressure (DBP) between the GE (n = 84) and GNE (n = 238) groups. We then grouped participants from the GE group based on their predicted years to onset (YTO) and compared their vital signs to the GNE group.

RESULTS

The GE group had higher rHR (∆ = 3.83, p = 0.0064), SBP (∆ = 2.38, p = 0.032), and CBT (∆ = 0.16, t = 2.92, p = 0.007). The mean rHR and CBT became significantly elevated compared to the GNE group in participants who had 15-25 YTO and those who had <15 YTO. The mean SBP of participants who had 25-35 YTO was significantly elevated compared to the GNE group.

CONCLUSION

ANS dysfunction in HD seems to occur approximately 20 years prior to the predicted onset of motor symptoms of HD.

Cardiac electrical remodeling and neurodegenerative diseases association

Cardiac impairment contributes significantly to the mortality associated with several neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), primarily recognized as brain pathologies. These diseases may be caused by aggregation of a misfolded protein, most often, in the brain, although new evidence also reveals peripheral abnormalities. After characterization of the cardiac involvement in neurodegenerative diseases, several studies concentrated on elucidating the cause of the impaired cardiac function. However, most of the current knowledge is focused on the mechanical aspects of the heart rather than the electrical disturbances. The main objective of this review is to summarize the most recent advances in the elucidation of cardiac electrical remodeling in the neurodegenerative environment. We aimed to determine a crosstalk between the heart and the brain in three neurodegenerative conditions: AD, PD, and HD. We found that the most studies demonstrated important alterations in the electrocardiogram (ECG) of patients with neurodegeneration and in animal models of the conditions. We also showed that little is described when considering excitability disruptions in cardiomyocytes, for example, action potential impairments. It is a matter of contention whether central nervous system abnormalities or the peripheral ones increase the risk of heart diseases in patients with neurodegenerative conditions. To determine this notion, there is a need for new heart studies focusing specifically on the cardiac electrophysiology (e.g., ECG and cardiomyocyte excitability). This review could serve as an important guide in designing novel accurate approaches targeting the heart in neuronal conditions.

Role of defective calcium regulation in cardiorespiratory dysfunction in Huntington's disease

Huntington’s disease (HD) is a progressive, autosomal dominant neurodegenerative disorder affecting striatal neurons beginning in young adults with loss of muscle coordination and cognitive decline. Less appreciated is the fact that patients with HD also exhibit cardiac and respiratory dysfunction, including pulmonary insufficiency and cardiac arrhythmias. The underlying mechanism for these symptoms is poorly understood. In the present study we provide insight into the cause of cardiorespiratory dysfunction in HD and identify a potentially novel therapeutic target. We now show that intracellular calcium (Ca²⁺) leak via posttranslationally modified ryanodine receptor/intracellular calcium release (RyR) channels plays an important role in HD pathology. RyR channels were oxidized, PKA phosphorylated, and leaky in brain, heart, and diaphragm both in patients with HD and in a murine model of HD (Q175). HD mice (Q175) with endoplasmic reticulum Ca²⁺ leak exhibited cognitive dysfunction, decreased parasympathetic tone associated with cardiac arrhythmias, and reduced diaphragmatic contractile function resulting in impaired respiratory function. Defects in cognitive, motor, and respiratory functions were ameliorated by treatment with a novel Rycal small-molecule drug (S107) that fixes leaky RyR. Thus, leaky RyRs likely play a role in neuronal, cardiac, and diaphragmatic pathophysiology in HD, and RyRs are a potential novel therapeutic target.

This study explores the role of ryanodine receptor calcium channels in the brain, the heart, and the diaphragm and central versus peripheral pathophysiological mechanisms in Huntington’s disease.

Autonomic Changes in Juvenile-Onset Huntington's Disease

Patients with adult-onset Huntington’s Disease (AOHD) have been found to have dysfunction of the autonomic nervous system that is thought to be secondary to neurodegeneration causing dysfunction of the brain–heart axis. However, this relationship has not been investigated in patients with juvenile-onset HD (JOHD). The aim of this study was to compare simple physiologic measures between patients with JOHD (n = 27 participants with 64 visits) and participants without the gene expansion that causes HD (GNE group; n = 259 participants with 395 visits). Using data from the Kids-JOHD study, we compared mean resting heart rate (rHR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) between the JOHD and GNE groups. We also divided the JOHD group into those with childhood-onset JOHD (motor diagnosis received before the age of 13, [n = 16]) and those with adolescent-onset JOHD (motor diagnosis received at or after the age of 13 [n = 11]). We used linear mixed-effects models to compare the group means while controlling for age, sex, and parental socioeconomic status and including a random effect per participant and family. For the primary analysis, we found that the JOHD group had significant increases in their rHR compared to the GNE group. Conversely, the JOHD group had significantly lower SBP compared to the GNE group. The JOHD group also had lower DBP compared to the GNE group, but the results did not reach significance. SBP and DBP decreased as disease duration of JOHD increased, but rHR did not continue to increase. Resting heart rate is more sensitive to changes in autonomic function as compared to SBP. Therefore, these results seem to indicate that early neurodegenerative changes of the central autonomic network likely lead to an increase in rHR while later progression of JOHD leads to changes in blood pressure. We hypothesize that these later changes in blood pressure are secondary to neurodegeneration in brainstem regions such as the medulla.

Heart rate variability and falls in Huntington's disease

PURPOSE

Persons with Huntington's disease (HD) have a high incidence of falls. Autonomic nervous system dysfunction has been reported even in early stages of this disease. To date, there has been no analysis of the relationship between heart rate variability (HRV) and falls in this patient population. The aim of the study reported here was to evaluate the relationship between HRV and falls in persons with HD.

METHODS

Huntington's disease patients enrolled in a prospective study on fear of falling and falls were assessed using short-term HRV analyses and blood pressure measures in both the resting and standing states. Time-frequency domains and nonlinear parameters were calculated. Data on falls, the risk of falling (RoF) and disease-specific scales were collected at baseline and at the end of the 6-month follow-up.

RESULTS

Of the 24 HD patients who were invited to participate in the study, 20 completed the baseline analysis and 18 completed the 6-month follow-up. At baseline, seven (35%) HD patients reported at least one fall (single fallers) and 13 (65%) reported ≥ 2 falls (recurrent fallers) in the previous 12 months. At baseline, recurrent fallers had lower RMSSD (root mean square of successive RR interval differences) in the resting state (RMSSD-resting), higher LF/HF (low/high frequency) ratio in both states and higher DFA-α1 parameter (detrended fluctuation analyses over the short term) in both states. This association was similar at the 6-month follow-up for recurrent fallers, who showed lower RMSSD-resting and higher LF/HF ratio in the standing state (LF/HF-standing) than single fallers. Significant correlations were found between the number of falls, RMSSD-resting and LF/HF-standing. No differences were found between recurrent and single fallers for any blood pressure measures.

CONCLUSIONS

The observed HRV pattern is consistent with a higher sympathetic prevalence associated with a higher RoF. Reduced parasympathetic HRV values in this patient population predict being a recurrent faller at 6 months of follow-up, independently of orthostatic phenomena.

Circadian dysfunction in the Q175 model of Huntington's disease: Network analysis

Disturbances in sleep/wake cycle are a common complaint of individuals with Huntington's disease (HD) and are displayed by HD mouse models. The underlying mechanisms, including the possible role of the circadian timing system, have been the topic of a number of recent studies. The (z)Q175 mouse is a knock-in model in which the human exon 1 sequence of the huntingtin gene is inserted into the mouse DNA with approximately 190 CAG repeats. Among the numerous models available, the heterozygous Q175 offers strong construct validity with a single copy of the mutation, genetic precision of the insertion and control of mutation copy number. In this review, we will summarize the evidence that this model exhibits disrupted diurnal and circadian rhythms in locomotor activity. We found overwhelming evidence for autonomic dysfunction including blunted daily rhythms in heart rate and core body temperature (CBT), reduced heart rate variability, and almost a complete failure of the sympathetic arm of the autonomic nervous system to function during the baroreceptor reflex. Mechanistically, the Q175 mouse model exhibits deficits in the neural output of the central circadian clock, the suprachiasmatic nucleus along with an enhancement of at least one type of potassium current in these neurons. Finally, we report a novel network analysis examining the phase coherence between activity, CBT, and cardiovascular measures. Such analyses found that even young Q175 mutants (heterozygous or homozygous) show coherence degradation, and suggests that loss of phase coherence is a variable that should be considered as a possible biomarker for HD.

Evidence of cardiac electrical remodeling in patients with Huntington disease

OBJECTIVE

Although Huntington's disease (HD) is a disease of the central nervous system, HD mortality surveys indicate heart disease as a major cause of death. Cardiac dysfunction in HD might be a primary consequence of peripherally expressed mutant huntingtin or secondary to either a general decline in health or the onset of neurological dysfunction. The aim of the study was to clarify the heart muscle involvement.

MATERIALS AND METHODS

We measured conventional and advanced resting ECG indices. Thirty-one subjects with a confirmed huntingtin gene mutation and 31 age- and gender-matched controls were included. The HD subjects were divided into four groups based on their Unified Huntington Disease Rating Scale (UHDRS) motor score.

RESULTS

We detected changes in advanced ECG variables connected with electrical ventricular remodeling (t test, p < 0.01). The increase in the unexplained part of both QT variability and the standard deviation of normal-to-normal QT intervals, presumably reflecting beat-to-beat changes in repolarization, was most pronounced. Further, both variables correlated with the product of the cytosine-adenine-guanine (CAG) triplets' repeat length and the subjects' age (CAP), the former R = 0.423 (p = 0.018) and the latter R = 0.499 (p = 0.004). There was no correlation between the CAP score and any of variables representing autonomic nervous system activity.

CONCLUSIONS

Both autonomic nervous system dysfunction and cardiac electrical remodeling are present in patients with HD. The changes in advanced ECG variables observed in the study evolve with HD progression. The increased values of QT unexplained variability may be a marker of temporal inhomogeneity in ventricular repolarization associated with malignant ventricular arrhythmias.

Neuro-Cardio Mechanisms in Huntington's Disease and Other Neurodegenerative Disorders

Although Huntington's disease is generally considered to be a neurological disorder, there is mounting evidence that heart malfunction plays an important role in disease progression. This is perhaps not unexpected since both cardiovascular and nervous systems are strongly connected - both developmentally and subsequently in health and disease. This connection occurs through a system of central and peripheral neurons that control cardiovascular performance, while in return the cardiovascular system works as a sensor for the nervous system to react to physiological events. Hence, given their permanent interconnectivity, any pathological events occurring in one system might affect the second. In addition, some pathological signals from Huntington's disease might occur simultaneously in both the cardiovascular and nervous systems, since mutant huntingtin protein is expressed in both. Here we aim to review the source of HD-related cardiomyopathy in the light of recently published studies, and to identify similarities between HD-related cardiomyopathy and other neuro-cardio disorders.

Neurocardiovascular pathology in pre-manifest and early-stage Huntington's disease

BACKGROUND AND PURPOSE

Cardiovascular events are a major cause of early death in the Huntington's disease (HD) population. Dysautonomia as well as deterioration of circadian rhythms can be detected early in the disease progression and can have profound effects on cardiac health. The aim of the present study was to determine if patients with HD and pre-manifest mutation carriers present a higher risk of cardiovascular disease than non-mutation-carrying controls.

METHODS

This was a prospective, cross-sectional, multicentre study of 38 HD mutation carriers (23 pre-manifest and 15 early-stage patients) compared with 38 age- and gender-matched healthy controls. Clinical and epidemiological variables, including the main haematological vascular risk factors, were recorded. Ambulatory blood-pressure monitoring and carotid intima-media thickness (CIMT) measurement were performed to assess autonomic function and as target-organ damage markers.

RESULTS

Most (63.2%) patients with HD (86.7% and 47.8%, respectively, of the early-stage and pre-manifest patients) were non-dippers compared with 23.7% of controls (P = 0.001). CIMT values were in the 75^th percentile in 46.7% and 43.5%, respectively, of the early-stage and pre-manifest patients, whereas none of the controls presented pathological values (P = 0.001 and P = 0.006, respectively). Nocturnal non-dipping was significantly associated with CIMT values in patients (P = 0.002) but not in controls.

CONCLUSIONS

These results suggest that higher cardiovascular risks and target-organ damage are present even in pre-manifest patients. Although larger studies are needed to confirm these findings, clinicians should consider these results in the cardiovascular management of patients with HD.

Neurocardiovascular deficits in the Q175 mouse model of Huntington's disease

Cardiovascular dysautonomia as well as the deterioration of circadian rhythms are among the earliest detectable pathophysiological changes in individuals with Huntington's disease (HD). Preclinical research requires mouse models that recapitulate disease symptoms and the Q175 knock-in model offers a number of advantages but potential autonomic dysfunction has not been explored. In this study, we sought to test the dual hypotheses that cardiovascular dysautonomia can be detected early in disease progression in the Q175 model and that this dysfunction varies with the daily cycle. Using radiotelemetry implants, we observed a significant reduction in the diurnal and circadian activity rhythms in the Q175 mutants at the youngest ages. By middle age, the autonomically driven rhythms in core body temperature were highly compromised, and the Q175 mutants exhibited striking episodes of hypothermia that increased in frequency with mutant huntingtin gene dosage. In addition, Q175 mutants showed higher resting heart rate (HR) during sleep and greatly reduced correlation between activity and HR HR variability was reduced in the mutants in both time and frequency domains, providing more evidence of autonomic dysfunction. Measurement of the baroreceptor reflex revealed that the Q175 mutant could not appropriately increase HR in response to a pharmacologically induced decrease in blood pressure. Echocardiograms showed reduced ventricular mass and ejection fraction in mutant hearts. Finally, cardiac histopathology revealed localized points of fibrosis resembling those caused by myocardial infarction. Thus, the Q175 mouse model of HD exhibits cardiovascular dysautonomia similar to that seen in HD patients with prominent sympathetic dysfunction during the resting phase of the activity rhythm.

Motor phenotype is not associated with vascular dysfunction in symptomatic Huntington's disease transgenic R6/2 (160 CAG) mice

Whereas Huntington’s disease (HD) is unequivocally a neurological disorder, a critical mass of emerging studies highlights the occurrence of peripheral pathology like cardiovascular defects in both animal models and humans. The overt impairment in cardiac function is normally expected to be associated with peripheral vascular dysfunction, however whether this assumption is reasonable or not in HD is still unknown. In this study we functionally characterized the vascular system in R6/2 mouse model (line 160 CAG), which recapitulates several features of human pathology including cardiac disease. Vascular reactivity in different arterial districts was determined by wire myography in symptomatic R6/2 mice and age-matched wild type (WT) littermates. Disease stage was assessed by using well-validated behavioural tests like rotarod and horizontal ladder task. Surprisingly, no signs of vascular dysfunction were detectable in symptomatic mice and no link with motor phenotype was found.

Functional impairment of precerebral arteries in Huntington disease

BACKGROUND

Cardiovascular pathology of Huntington disease (HD) appears to be complex; while microvascular dysfunction seems to appear early, deaths from cardiomyopathy and stroke might occur in the late phase of HD.

METHODS

Our study evaluated global risk factors for coronary heart disease (CHD), structure and function of precerebral arteries in 41 HD subjects and 41 matched controls. HD subjects were divided into groups by the United Huntington disease rating scale (presymptomatic-PHD, early-EHD, midstage-MHD and late-LHD). CHD risk factors assessment and Doppler examination of precerebral arteries were performed, including measurements of the carotid artery intima-media thickness (IMT), and parameters indicating local carotid artery distensibility (stiffness index β, pulse wave velocity, pressure strain elasticity module and carotid artery compliance).

RESULTS

In the HD and controls we identified a comparable number of non-obstructive plaques (<50% lumen narrowing). No obstructive plaques (>50% lumen narrowing) were found. There was significantly increased IMT in MHD. In PHD and EHD the parameters of arterial stiffness were significantly higher and the carotid artery compliance was significantly lower.

CONCLUSIONS

Our results reveal functional vascular pathology in PHD, EHD, and MHD. Precerebral arteries dysfunction in HD therefore appears to be mostly functional and in agreement with recently described autonomic nervous system changes in HD.

Studying the pathophysiologic connection between cardiovascular and nervous systems using stem cells

The cardiovascular and nervous systems are deeply connected during development, health, and disease. Both systems affect and regulate the development of each other during embryogenesis and the early postnatal period. Specialized neural crest cells contribute to cardiac structures, and a number of growth factors released from the cardiac tissue (e.g., glial cell line-derived neurotrophic factor, neurturin, nerve growth factor, Neurotrophin-3) ensure proper maturation of the incoming parasympathetic and sympathetic neurons. Physiologically, the cardiovascular and nervous systems operate in harmony to adapt to various physical and emotional conditions to maintain homeostasis through sympathetic and parasympathetic nervous systems. Moreover, neurocardiac regulation involves a neuroaxis consisting of cortex, amygdala, and other subcortical structures, which have the ability to modify lower-level neurons in the hierarchy. Given the interconnectivity of cardiac and neural systems, when one undergoes pathological changes, the other is affected to a certain extent. In addition, there are specific neurocardiac diseases that affect both systems simultaneously, such as Huntington disease, Lewy body diseases, Friedreich ataxia, congenital heart diseases, Danon disease, and Timothy syndrome. Over the last decade, in vitro modeling of neurocardiac diseases using induced pluripotent stem cells (iPSCs) has provided an invaluable opportunity to elevate our knowledge about the brain-heart connection, since previously primary cardiomyocytes and neurons had been extremely difficult to maintain long-term in vitro. Ultimately, the ability of iPSC technology to model abnormal functional phenotypes of human neurocardiac disorders, combined with the ease of therapeutic screening using this approach, will transform patient care through personalized medicine in the future. © 2016 Wiley Periodicals, Inc.

Direct evidence of progressive cardiac dysfunction in a transgenic mouse model of Huntington's disease

HD is a progressive genetic neurological disorder, characterized by motor as well as cognitive impairments. The gene carrying the mutation causing Huntington's disease (HD) is not brain specific, and there is increasing evidence for peripheral, as well as brain pathology in this disorder. Here, we used in vivo and ex vivo techniques to assess the cardiac function of mice transgenic for the HD mutation. Using magnetic resonance imaging (MRI) of the beating heart, we show that abnormalities previously reported in end-stage mice are present by mid-stages of the disease. We also found abnormalities that have not been hitherto reported, including changes in cardiac efficiency and a mechanical distortion of the beating heart. Using the Langendorff preparation, we show reduced coronary blood flow, impaired myocardial contractility and reduced left ventricular developed pressure in HD mouse hearts. Together, our findings suggest that there is significant pathology of the HD mouse heart, even by mid stages of disease. Previous clinical research has demonstrated that the risk of cognitive symptoms increases markedly in patients with heart failure. R6/2 mice show significant progressive cognitive abnormalities, so we hypothesize that cardiac pathology in the R6/2 mouse may contribute, not only to their progressive decline and death, but also to their cognitive dysfunction. We suggest that closer attention should be paid to cardiovascular symptoms in HD patients.

Cardiac Dysfunction in the BACHD Mouse Model of Huntington's Disease

While Huntington's disease (HD) is classified as a neurological disorder, HD patients exhibit a high incidence of cardiovascular events leading to heart failure and death. In this study, we sought to better understand the cardiovascular phenotype of HD using the BACHD mouse model. The age-related decline in cardiovascular function was assessed by echocardiograms, electrocardiograms, histological and microarray analysis. We found that structural and functional differences between WT and BACHD hearts start at 3 months of age and continue throughout life. The aged BACHD mice develop cardiac fibrosis and ultimately apoptosis. The BACHD mice exhibited adaptive physiological changes to chronic isoproterenol treatment; however, the medication exacerbated fibrotic lesions in the heart. Gene expression analysis indicated a strong tilt toward apoptosis in the young mutant heart as well as changes in genes involved in cellular metabolism and proliferation. With age, the number of genes with altered expression increased with the large changes occurring in the cardiovascular disease, cellular metabolism, and cellular transport clusters. The BACHD model of HD exhibits a number of changes in cardiovascular function that start early in the disease progress and may provide an explanation for the higher cardiovascular risk in HD.

Three Huntington's Disease Specific Mutation-Carrying Human Embryonic Stem Cell Lines Have Stable Number of CAG Repeats upon In Vitro Differentiation into Cardiomyocytes

Huntington disease (HD; OMIM 143100), a progressive neurodegenerative disorder, is caused by an expanded trinucleotide CAG (polyQ) motif in the HTT gene. Cardiovascular symptoms, often present in early stage HD patients, are, in general, ascribed to dysautonomia. However, cardio-specific expression of polyQ peptides caused pathological response in murine models, suggesting the presence of a nervous system-independent heart phenotype in HD patients. A positive correlation between the CAG repeat size and severity of symptoms observed in HD patients has also been observed in in vitro HD cellular models. Here, we test the suitability of human embryonic stem cell (hESC) lines carrying HD-specific mutation as in vitro models for understanding molecular mechanisms of cardiac pathology seen in HD patients. We have differentiated three HD-hESC lines into cardiomyocytes and investigated CAG stability up to 60 days after starting differentiation. To assess CAG stability in other tissues, the lines were also subjected to in vivo differentiation into teratomas for 10 weeks. Neither directed differentiation into cardiomyocytes in vitro nor in vivo differentiation into teratomas, rich in immature neuronal tissue, led to an increase in the number of CAG repeats. Although the CAG stability might be cell line-dependent, induced pluripotent stem cells generated from patients with larger numbers of CAG repeats could have an advantage as a research tool for understanding cardiac symptoms of HD patients.

Right ventricular dysfunction in the R6/2 transgenic mouse model of Huntington's disease is unmasked by dobutamine

BACKGROUND

Increasingly, evidence from studies in both animal models and patients suggests that cardiovascular dysfunction is important in HD. Previous studies measuring function of the left ventricle (LV) in the R6/2 model have found a clear cardiac abnormality, albeit with preserved LV systolic function. It was hypothesized that an impairment of RV function might play a role in this condition via mechanisms of ventricular interdependence.

OBJECTIVE

To investigate RV function in the R6/2 mouse model of Huntington's disease (HD).

METHODS

Cardiac cine-magnetic resonance imaging (MRI) was used to determine functional parameters in R6/2 mice. In a first experiment, these parameters were derived longitudinally to determine deterioration of cardiac function with disease progression. A second experiment compared the response to a stress test (using dobutamine) of wildtype and early-symptomatic R6/2 mice.

RESULTS

There was progressive deterioration of RV systolic function with age in R6/2 mice. Furthermore, beta-adrenergic stimulation with dobutamine revealed RV dysfunction in R6/2 mice before any overt symptoms of the disease were apparent.

CONCLUSIONS

This work adds to accumulating evidence of cardiovascular dysfunction in R6/2 mice, describing for the first time the involvement of the right ventricle. Cardiovascular dysfunction should be considered, both when treatment strategies are being designed, and when searching for biomarkers for HD.

Dysfunction of the CNS-heart axis in mouse models of Huntington's disease

Cardiac remodelling and contractile dysfunction occur during both acute and chronic disease processes including the accumulation of insoluble aggregates of misfolded amyloid proteins that are typical features of Alzheimer's, Parkinson's and Huntington's disease (HD). While HD has been described mainly as a neurological disease, multiple epidemiological studies have shown that HD patients exhibit a high incidence of cardiovascular events leading to heart failure, and that this is the second highest cause of death. Given that huntingtin is ubiquitously expressed, cardiomyocytes may be at risk of an HD-related dysfunction. In mice, the forced expression of an expanded polyQ repeat under the control of a cardiac specific promoter led to severe heart failure followed by reduced lifespan. However the mechanism leading to cardiac dysfunction in the clinical and pre-clinical HD settings remains unknown. To unravel this mechanism, we employed the R6/2 transgenic and HdhQ150 knock-in mouse models of HD. We found that pre-symptomatic animals developed connexin-43 relocation and a significant deregulation of hypertrophic markers and Bdnf transcripts. In the symptomatic animals, pronounced functional changes were visualised by cardiac MRI revealing a contractile dysfunction, which might be a part of dilatated cardiomyopathy (DCM). This was accompanied by the re-expression of foetal genes, apoptotic cardiomyocyte loss and a moderate degree of interstitial fibrosis. To our surprise, we could identify neither mutant HTT aggregates in cardiac tissue nor a HD-specific transcriptional dysregulation, even at the end stage of disease. We postulate that the HD-related cardiomyopathy is caused by altered central autonomic pathways although the pathogenic effects of mutant HTT acting intrinsically in the heart may also be a contributing factor.

Huntington's disease (HD) is a neurodegenerative disorder for which the mutation results in an extra-long tract of glutamines that causes the huntingtin protein to aggregate. It is characterized by neurological symptoms and brain pathology that is associated with nuclear and cytoplasmic aggregates and with transcriptional dysregulation. Despite the fact that HD has been recognized principally as a neurological disease, there are multiple epidemiological studies showing that HD patients exhibit a high rate of cardiovascular events leading to heart failure. To unravel the cause of cardiac dysfunction in HD models, we employed a wide range of molecular and physiological methods using two well established genetic mouse models of this disease. We found that pre-symptomatic animals developed aberrant gap junction channel expression and a significant deregulation of hypertrophic markers that may predispose them to arrhythmia and an overall change in cardiac function. These changes were accompanied by the re-expression of foetal genes, apoptotic cardiomyocyte loss and a moderate degree of interstitial fibrosis in the symptomatic animals. Surprisingly, we could identify neither mutant HTT aggregates in cardiac tissue nor a HD-specific transcriptional dysregulation. Therefore, we conclude that the HD-related cardiomyopathy could be driven by altered central autonomic pathways.

A broad phenotypic screen identifies novel phenotypes driven by a single mutant allele in Huntington's disease CAG knock-in mice

Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by the expansion of a CAG trinucleotide repeat in the HTT gene encoding huntingtin. The disease has an insidious course, typically progressing over 10-15 years until death. Currently there is no effective disease-modifying therapy. To better understand the HD pathogenic process we have developed genetic HTT CAG knock-in mouse models that accurately recapitulate the HD mutation in man. Here, we describe results of a broad, standardized phenotypic screen in 10-46 week old heterozygous HdhQ111 knock-in mice, probing a wide range of physiological systems. The results of this screen revealed a number of behavioral abnormalities in HdhQ111/+ mice that include hypoactivity, decreased anxiety, motor learning and coordination deficits, and impaired olfactory discrimination. The screen also provided evidence supporting subtle cardiovascular, lung, and plasma metabolite alterations. Importantly, our results reveal that a single mutant HTT allele in the mouse is sufficient to elicit multiple phenotypic abnormalities, consistent with a dominant disease process in patients. These data provide a starting point for further investigation of several organ systems in HD, for the dissection of underlying pathogenic mechanisms and for the identification of reliable phenotypic endpoints for therapeutic testing.

Oral and dental health in Huntington's disease - an observational study

BACKGROUND

Only a few case reports and case series dealing with oral and dental health care are available in literature until now. The aim of the present pilot study was to determine the status of dental health in comparison to matched controls and to heighten the neurologists' and dentists' awareness of the oral aspects of the disease.

METHODS

42 Huntington's disease (HD) participants were scored according to the Unified Huntington's Disease Rating Scale. The dental status was assessed by using the well established score for decayed, missing, and filled teeth (DMFT) and the dental plaque score (Silness-Loe plaque index).

RESULTS

Compared to controls HD participants showed significantly more decayed teeth and more plaques in both plaque indices. A higher motor impairment and a lower functional status of the patients lead to a worsening in dental status.

CONCLUSION

Possible reasons for our findings are discussed. Apart from local oral complications general complications may also occur. Thus, as a consequence, we would encourage patients, caregivers, neurologists, and the dentists to ensure regular preventive dental examinations and dental treatments of individuals with Huntington's disease even in the premanifest stage of this disease.

Characteristics, pathophysiology and clinical management of weight loss in Huntington’s disease

SUMMARY Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG repeat expansion in the HTT gene. Clinically, the disease is characterized by motor impairment, cognitive deterioration and behavioral disturbances. Unintended weight loss is also a hallmark of the disease and frequently leads to general weakening and a decline in the quality of life of HD patients. Moreover, a higher BMI has been associated with a slower rate of disease progression. In this review, the authors first delineate the characteristics of weight loss in both HD patients and genetic models of the disease. Subsequently, they discuss the pathophysiological processes underlying weight loss in HD and highlight the implications for management and care of HD patients with, or at risk of, unintended weight loss.

Circadian and sleep disorder in Huntington's disease

Huntington's disease is a progressive neurological disorder that starts insidiously with motor, cognitive or psychiatric disturbance, and progresses through a distressing range of symptoms to end with a devastating loss of function, both motor and executive. There is a growing awareness that, in addition to cognitive and psychiatric symptoms, there are other important non-motor symptoms in HD, including sleep and circadian abnormalities. It is not clear if sleep-wake changes are caused directly by HD gene-related pathology, or if they are simply a consequence of having a neurodegenerative disease. From a patient point of view, the answer is irrelevant, since sleep and circadian disturbances are deleterious to good daily living, even in neurologically normal people. The assumption should be that, at the very least, sleep and/or circadian disturbance in HD patients will contribute to their symptoms. At worst, they may contribute to the progressive decline in HD. Here I review the state of our understanding of sleep and circadian abnormalities in HD. I also outline a set of simple rules that can be followed to improve the chances of a good night's sleep, since preventing any 'preventable' symptoms is the a logical first step in treating disease. The long-term impact of sleep disruption in HD is unknown. There have been no large-scale systematic studies of in sleep in HD. Furthermore, there has never been a study of the efficacy of pharmaceuticals that are typically used to treat sleep deficits in HD patients. Thus treatment of sleep disturbance in HD is necessarily empirical. A better understanding of the relationship between sleep/circadian abnormalities and HD pathology is needed, if treatment of this aspect of HD is to be optimized.

Aberrant heart rate and brainstem brain-derived neurotrophic factor (BDNF) signaling in a mouse model of Huntington's disease

Huntington's disease (HD) is associated with profound autonomic dysfunction including dysregulation of cardiovascular control often preceding cognitive or motor symptoms. Brain-derived neurotrophic factor (BDNF) levels are decreased in the brains of HD patients and HD mouse models, and restoring BDNF levels prevents neuronal loss and extends survival in HD mice. We reasoned that heart rate changes in HD may be associated with altered BDNF signaling in cardiovascular control nuclei in the brainstem. Here we show that heart rate is elevated in HD (N171-82Q) mice at presymptomatic and early disease stages, and heart rate responses to restraint stress are attenuated. BDNF levels were significantly reduced in brainstem regions containing cardiovascular nuclei in HD mice and human HD patients. Central administration of BDNF restored the heart rate to control levels. Our findings establish a link between diminished BDNF expression in brainstem cardiovascular nuclei and abnormal heart rates in HD mice, and suggest a novel therapeutic target for correcting cardiovascular dysfunction in HD.

Baroreceptor reflex dysfunction in the BACHD mouse model of Huntington's disease

Huntington’s disease is a progressive, neurodegenerative disorder that presents with a triad of clinical symptoms, which include movement abnormalities, emotional disturbance and cognitive impairment. Recent studies reported dysfunction of the autonomic nervous system in Huntington’s disease patients, which may contribute to the increased incidence of cardiovascular events in this patient population that often leads to death. We measured the baroreceptor reflex, a process dependent on proper autonomic function, in the BACHD mouse model of Huntington’s disease. We found a blunted response of the baroreceptor reflex as well as significantly higher daytime blood pressure in BACHD mice compared to WT controls, which are both indications of autonomic dysfunction. BACHD mice had increased heart weight to tibia length ratios at 7 and 12 mo of age suggesting hypertrophic changes of the heart, which we speculate is a response to the increased blood pressure and aberrant baroreceptor reflex. Despite these structural changes, the hearts of BACHD mice continue to function normally as assessed by echocardiographic analysis. Studies of autonomic and cardiovascular function in BACHD mice may help elucidate the pathophysiology of Huntington’s disease and aid in the development of clinical strategies to offset the incidence of fatal cardiovascular events in the Huntington’s disease patient population.

Microcirculation response to local cooling in patients with Huntington's disease

Altered autonomic nervous system (ANS) functioning in early stages of Huntington's disease (HD) has been suggested, presumably due to distorted high-order autonomic control. ANS functioning in the early stages of HD was further investigated. Laser-Doppler (LD) flux in the skin of the fingertips, heart rate (HR), HR variability, systolic and diastolic blood pressure were measured during rest and during a 6 min cooling of one hand at 15°C. Data of 15 presymptomatic gene mutation carriers (PHD), 15 early symptomatic HD patients (EHD), and two groups of 15 age- and sex-matched controls were compared. The area under the low frequency (LF) and high frequency (HF) bands of the HR variability spectrum were calculated. An augmented reduction of cutaneous LD flux was found in response to the direct cooling in the PHD group (37.5 ± 8.5% of resting value) compared to the PHD controls (67.27 ± 8.4%) (p < 0.05). In addition, the PHD group had higher (LF/(LF + HF) index of primary sympathetic modulation of the HR at rest (53.6 ± 3.3) compared to the EHD patients (39.7 ± 4.2) (p < 0.05). In the EHD group, a significantly smaller change of HR during cooling (100.26 ± 1.2%) was found compared to the EHD controls (95.9 ± 1.0%) (p < 0.05). The results are in line with the hypothesis that ANS dysfunction occurs even in PHD subjects. Further, they support the hypothesis that dysfunction of the high-order autonomic centres are involved in HD.

Dysfunctions in circadian behavior and physiology in mouse models of Huntington's disease

Many patients with Huntington's disease (HD) exhibit disturbances in their daily cycle of sleep and wake as part of their symptoms. These patients have difficulty sleeping at night and staying awake during the day, which has a profound impact on the quality of life of the patients and their care-givers. In the present study, we examined diurnal and circadian rhythms of four models of HD including the BACHD, CAG 140 knock-in and R6/2 CAG 140 and R6/2 CAG 250 lines of mice. The BACHD and both R6/2 lines showed profound circadian phenotypes as measured by wheel-running activity. Focusing on the BACHD line for further analysis, the amplitude of the rhythms in the BACHD mice declined progressively with age. In addition, the circadian regulation of heart rate and body temperature in freely behaving BACHD mice were also disrupted. Furthermore, the distribution of sleep as well as the autonomic regulation of heart rate was disrupted in this HD model. To better understand the mechanistic underpinnings of the circadian disruption, we used electrophysiological tools to record from neurons within the central clock in the suprachiasmatic nucleus (SCN). The BACHD mice exhibit reduced rhythms in spontaneous electrical activity in SCN neurons. Interestingly, the expression of the clock gene PERIOD2 was not altered in the SCN of the BACHD line. Together, this data is consistent with the hypothesis that the HD mutations interfere with the expression of robust circadian rhythms in behavior and physiology. The data raise the possibility that the electrical activity within the central clock itself may be altered in this disease.