Circadian Rhythm, Cognition, and Mood Disorders in Huntington’s Disease

Sleep and circadian rhythm dysfunctions in movement disorders beyond Parkinson's disease and atypical parkinsonisms

PURPOSE OF REVIEW

This review aimed to comprehensively outline sleep and circadian rhythm abnormalities in hyperkinetic movement disorders beyond Parkinson's disease and atypical parkinsonisms, including tremor, dystonia, choreiform movements, tics, and ataxia disorders.

RECENT FINDINGS

Insomnia, poor sleep quality, and excessive daytime sleepiness (EDS) are commonly reported in essential tremor, Wilson's disease, tics or Tourette's syndrome, and spinocerebellar ataxia (SCA). REM sleep behavior disorder (RBD) have been observed in Wilson's disease and SCA. A combination of REM and non-REM parasomnias, along with nocturnal stridor with the initiation of sleep and re-entering after awakening, are characterized by undifferentiated Non-REM and poorly structured N2 in anti-IgLON5 disease. Restless legs syndrome (RLS) has been reported commonly in SCAs. Sleep-related dyskinesia has been reported in ADCY5-related disease and GNAO1-related movement disorder.

SUMMARY

Sleep problems can manifest as a result of movement disorders, either through direct motor disturbances or secondary nonmotor symptoms. Medication effects must be considered, as certain medications for movement disorders can exacerbate or alleviate sleep disturbances. Distinguishing sleep problems in some diseases might involve pathognomonic symptoms and signs, aiding in the diagnosis of movement disorders.

The multidimensional sleep health of individuals with multiple sclerosis and Huntington's disease and healthy controls

STUDY OBJECTIVES

Sleep issues are common for people with neurodegenerative conditions, yet research has focused on specific aspects of sleep. While important, a more holistic approach to investigating sleep, termed "sleep health," considers sleep's positive and negative aspects. Current studies exploring sleep health have lacked a control group for reference. For the first time, this study investigated the sleep health of people living with multiple sclerosis and Huntington's disease (HD) and compared it with a community sample.

METHODS

111 people, including 43 with multiple sclerosis, 19 with HD, and 49 from a community sample, participated in this study. The data, including actigraphy, Pittsburgh Sleep Quality Index, and Epworth Sleepiness Scale, were collected as part of ongoing research studies. Seven sleep health domains were determined from the collected data, and a composite sleep health score was developed. Analysis of variance and independent t tests were performed to identify population and sex differences.

RESULTS

The HD group had higher sleep regularity and lower sleep rhythmicity than the multiple sclerosis and community sample groups. The HD group had significantly less sleep duration than the multiple sclerosis group. No significant differences between the groups were observed in the sleep health composite score. Males had significantly higher sleep regularity within the HD group but significantly lower sleepiness scores in the community sample.

CONCLUSIONS

These findings indicate that people with HD may experience greater variance in their wake times, therefore decreasing the consistency of being awake or asleep 24 hours apart. Understanding the mechanisms for this should be explored in people with HD.

CITATION

Turner M, Griffiths M, Laws M, Vial S, Bartlett D, Cruickshank T. The multidimensional sleep health of individuals with multiple sclerosis and Huntington's disease and healthy controls. J Clin Sleep Med. 2024;20(6):967-972.

Associations between Sleep Quality and Serum Levels of Neurofilament Light in Individuals with Premanifest Huntington Disease

Objectives  To evaluate the associations between sleep quality and serum levels of neurofilament light (NfL) protein in individuals with premanifest Huntington disease (HD). Materials and Methods  We recruited 28 individuals with premanifest HD from a pre-existing database (of the Huntington's Environmental Research Optimisation Scheme, HEROs). The participants filled out the Pittsburgh Sleep Quality Index (PSQI), a subjective measure of sleep quality, and blood was collected via routine venepuncture to measure peripheral NfL levels. Results  The PSQI scores (median: 5.0; interquartile range: 4.0-7.5) indicated poor sleep quality. General linear modelling revealed no significant ( p  = 0.242) association between PSQI scores and NfL levels. No significant differences were found between individuals with good and poor sleep quality for any demographic variable collected. Discussion  Contrary to studies on other neurological conditions, there was no association between sleep quality and NfL levels in individuals with premanifest HD. This was unexpected, given the influence of environmental factors (such as social network size) on neurodegeneration in individuals with premanifest HD.

Dietary fasting and time-restricted eating in Huntington's disease: therapeutic potential and underlying mechanisms

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by aggregation of the mutant huntingtin (mHTT) protein, resulting from a CAG repeat expansion in the huntingtin gene HTT. HD is characterized by a variety of debilitating symptoms including involuntary movements, cognitive impairment, and psychiatric disturbances. Despite considerable efforts, effective disease-modifying treatments for HD remain elusive, necessitating exploration of novel therapeutic approaches, including lifestyle modifications that could delay symptom onset and disease progression. Recent studies suggest that time-restricted eating (TRE), a form of intermittent fasting involving daily caloric intake within a limited time window, may hold promise in the treatment of neurodegenerative diseases, including HD. TRE has been shown to improve mitochondrial function, upregulate autophagy, reduce oxidative stress, regulate the sleep-wake cycle, and enhance cognitive function. In this review, we explore the potential therapeutic role of TRE in HD, focusing on its underlying physiological mechanisms. We discuss how TRE might enhance the clearance of mHTT, recover striatal brain-derived neurotrophic factor levels, improve mitochondrial function and stress-response pathways, and synchronize circadian rhythm activity. Understanding these mechanisms is critical for the development of targeted lifestyle interventions to mitigate HD pathology and improve patient outcomes. While the potential benefits of TRE in HD animal models are encouraging, future comprehensive clinical trials will be necessary to evaluate its safety, feasibility, and efficacy in persons with HD.

The relationship between disease-specific psychosocial stressors and depressive symptoms in Huntington's disease

BACKGROUND

Huntington's disease (HD) is an inherited neurodegenerative disease involving motor abnormalities, cognitive decline, and psychological difficulties. Depression is among the most common psychological difficulties in HD. People with HD encounter numerous stressors related to their diagnosis and the impact of HD on their daily lives. Understanding the relationship between HD-specific psychosocial stressors and depression symptoms is critical for optimising treatment and developing a holistic, disease-specific model of depression in HD.

METHODS

Fifty-seven adults with the HD gene expansion (33 pre-symptomatic, 24 symptomatic) completed a self-report depression questionnaire and rated how much stress they experienced in relation to 20 psychosocial challenges commonly associated with HD. We examined associations between depression symptoms and each stressor individually, and after clustering using principal components analysis.

RESULTS

Depression symptoms were significantly associated with most of the psychosocial stressors assessed. Clustering with principal components analysis revealed that higher depression scores had significant independent associations with greater stress related to the future implications of HD (β = .44, p = .001) and sleep and psychological difficulties (β = .28, p = .005), but not with stress related to functional limitations (β = .11, p = .33) or interpersonal issues caused by HD (β = .15, p = .21).

CONCLUSIONS

Stressful experiences associated with HD constitute an important risk factor for depression in HD. Our findings support the use of more psychologically informed models of depression in HD and necessitate further research on tailored psychosocial interventions for HD patients with depression.

Neuropsychological functioning of patients with major depression or bipolar disorder comorbid to substance use disorders: A systematic review

Major depression disorder (MDD) and bipolar disorder (BD) are usual comorbidities in patients with substance use disorders (SUD), a condition known as dual disorder (DD). MDD, BD and SUD are associated with cognitive impairment, potentially leading to a greater functional impairment in the context of DD.

OBJECTIVES

To review the existing data on the cognitive impairment in DD patients with comorbid MDD or BD, considering the influence of the depressive symptomatology.

METHODS

Following the PRISMA protocol 19 studies were selected from the last 17 years, 13 of which focused on BD, five on MDD and one included both diagnoses.

RESULTS

Studies based in BD+SUD showed that the most affected cognitive domains were attention and executive functions, but not all of them found a greater impairment due to the comorbidity. While fewer studies were found for depression, MDD+SUD works point to a similar impairment cognitive pattern. Furthermore, depression improvement could be associated to better cognitive performance.

LIMITATIONS

More standardized research is needed regarding the influence of depression on cognitive performance of DD patients, especially on those with comorbid MDD. Factors such as main substance, abstinence, or MDD/BD-related variables should be considered. Unstudied factors, like gender or circadian rhythms, are proposed to improve knowledge in this area.

CONCLUSIONS

Current studies suggest that DD could potentiate cognitive impairment in BD, MDD and SUD. However, additional research is needed to improve the understanding of comorbidity to apply more individualized therapies in the treatment of these patients, considering the interference of their neurocognitive functioning.

Sleep Disorders in Patients with Choreic Syndromes

PURPOSE OF REVIEW

Patients with different types of choreic syndromes, specially those with Huntington's (HD) and Wilson's (WD) diseases, report frequent sleep complaints. This review focuses on the main findings of studies addressing the sleep features in these diseases, and other less frequent causes of chorea associated with sleep disorders, including a new syndrome described in the last decade associated with IgLON5 antibodies.

RECENT FINDINGS

Patients with HD and WD showed a bad quality of sleep and high frequency of insomnia and excessive daytime somnolence. WD patients also showed high scores on a specific scale for rapid eye movement sleep behavior disorders. HD and WD share decreased sleep efficiency and increased REM sleep latencies, percentage of sleep stage N1, and wake after sleep onset (WASO) among their polysomnographic features. Patients with HD and WD showed a high prevalence of different sleep disorders. Patients with other causes of chorea, including neuroacanthocytosis, parasomnia with sleep breathing disorder associated with antibodies to IgLON5, Sydenham's chorea, and choreic syndromes associated to certain genetic mutations show sleep disorders as well.

The temporal dynamics of mood and their association with depressive symptoms in Huntington's disease

BACKGROUND

Huntington's disease (HD) is an inherited neurodegenerative disorder characterised by progressive motor abnormalities, cognitive decline, and neuropsychiatric disturbances. Depression is among the most common neuropsychiatric syndromes in HD. Research in neurologically healthy samples has shown that depression is associated with distinct patterns of short-term fluctuations in mood, which may exacerbate negative effects on psychological wellbeing. The short-term dynamics of mood and their relationship with depression have not yet been investigated in HD.

METHODS

Fifty-five adults with the HD CAG expansion (33 pre-manifest, 22 manifest) completed single timepoint measures of depression, demographic factors, and clinical disease outcomes on day 1, then rated their mood daily for 28 consecutive days. Average mood, mood variability, and mood inertia (auto-correlation) were calculated across the 28 days.

RESULTS

Depression severity on day 1 was significantly associated with average mood across the 28 days, but not with day-to-day mood variability or inertia. Additionally, female HD CAG expansion carriers experienced more day-to-day variability in mood compared to males.

LIMITATIONS

Our sample did not include HD CAG expansion carriers with severe depressive symptoms or advanced HD, which limits the generalisability of the findings. Additionally, findings may have been affected by antidepressant and antipsychotic medication use among many participants.

CONCLUSIONS

In HD, short-term patterns of change in mood appear to be relatively independent of depression severity. Moreover, in female CAG-expansion carriers particularly, mood variability may warrant further clinical attention. These findings should be replicated in larger and more diverse samples, with different timescales and measures for assessing mood.

Sleep Disorders and Circadian Disruption in Huntington's Disease

Sleep and circadian alterations are common in patients with Huntington's disease (HD). Understanding the pathophysiology of these alterations and their association with disease progression and morbidity can guide HD management. We provide a narrative review of the clinical and basic-science studies centered on sleep and circadian function on HD. Sleep/wake disturbances among HD patients share many similarities with other neurodegenerative diseases. Overall, HD patients and animal models of the disease present with sleep changes early in the clinical course of the disease, including difficulties with sleep initiation and maintenance leading to decreased sleep efficiency, and progressive deterioration of normal sleep architecture. Despite this, sleep alterations remain frequently under-reported by patients and under-recognized by health professionals. The degree of sleep and circadian alterations has not consistently shown to be CAG dose-dependent. Evidence based treatment recommendations are insufficient due to lack of well-designed intervention trials. Approaches aimed at improving circadian entrainment, such as including light therapy, and time-restricted feeding have demonstrated a potential to delay symptom progression in some basic HD investigations. Larger study cohorts, comprehensive assessment of sleep and circadian function, and reproducibility of findings are needed in future in order to better understand sleep and circadian function in HD and to develop effective treatments.

Sleep, Circadian Rhythms, and Cognitive Dysfunction in Huntington's Disease

BACKGROUND

In healthy people, sleep and circadian disruption are linked to cognitive deficits. People with Huntington's disease (HD), who have compromised brain function and sleep and circadian disturbances, may be even more susceptible to these cognitive effects.

OBJECTIVE

To conduct a comprehensive review and synthesis of the literature in HD on the associations of cognitive dysfunction with disturbed sleep and circadian rhythms.

METHODS

We searched MEDLINE via OVID, CINAHL Plus, EMBASE via OVID, and PubMed in May 2023. The first author then screened by title and abstract and conducted a full review of remaining articles.

RESULTS

Eight studies investigating the influence of sleep and/or circadian rhythms on cognitive function in HD were found. In manifest HD, poorer sleep was associated with worse cognitive function. For behavioral 24-hour (circadian) rhythms, two studies indicated that later wake times correlated with poorer cognitive function. No reported studies in HD examined altered physiological 24-hour (circadian) rhythms and cognitive impairment.

CONCLUSION

Some associations exist between poor sleep and cognitive dysfunction in manifest HD, yet whether these associations are present before clinical diagnosis is unknown. Whether circadian disturbances relate to cognitive impairment in HD also remains undetermined. To inform sleep and circadian interventions aimed at improving cognitive symptoms in HD, future research should include a range of disease stages, control for external factors, and utilize robust cognitive batteries targeted to the aspects of cognitive function known to be adversely affected in HD.

Cross talk mechanism of disturbed sleep patterns in neurological and psychological disorders

The incidence and prevalence of sleep disorders continue to increase in the elderly populace, particularly those suffering from neurodegenerative and neuropsychiatric disorders. This not only affects the quality of life but also accelerates the progression of the disease. There are many reasons behind sleep disturbances in such patients, for instance, medication use, nocturia, obesity, environmental factors, nocturnal motor disturbances and depressive symptoms. This review focuses on the mechanism and effects of sleep dysfunction in neurodegenerative and neuropsychiatric disorders. Wherein we discuss disturbed circadian rhythm, signaling cascade and regulation of genes during sleep deprivation. Moreover, we explain the perturbation in brainwaves during disturbed sleep and the ocular perspective of neurodegenerative and neuropsychiatric manifestations in sleep disorders. Further, as the pharmacological approach is often futile and carries side effects, therefore, the non-pharmacological approach opens newer possibilities to treat these disorders and widens the landscape of treatment options for patients.

The Lived Experiences of Depression in Huntington's Disease: A Qualitative Study

BACKGROUND

Depression is a common neuropsychiatric syndrome in Huntington's disease (HD) and has debilitating consequences, including poorer sleep, exacerbation of cognitive and functional decline, and suicidality. To date, no published studies have documented the lived experience of depression in HD, despite clinical evidence that depression may be experienced differently in HD compared to the general population.

OBJECTIVE

The aim of this study was to investigate the lived experiences of depression in people with the CAG expansion for HD using qualitative methods.

METHODS

We conducted semi-structured interviews with HD CAG expansion carriers who had current or previous experiences of depression, until data saturation was achieved. This resulted in interviews from 17 HD CAG expansion carriers (11 premanifest, 6 manifest) which were analyzed using thematic analysis.

RESULTS

The four key themes that emerged related to the temporal characteristics of depression in HD, the qualitative changes associated with depression, psychosocial stressors perceived to contribute to depression, and the perception of depression as an endogenous feature of HD.

CONCLUSION

This study provides an enriched understanding of the unique characteristics of depression in HD, and the attributions that CAG expansion carriers make for their depression symptoms. The themes identified in this study can be used to guide more targeted assessment and treatment of depression in HD.

Circadian rhythms in neurodegenerative disorders

Endogenous biological clocks, orchestrated by the suprachiasmatic nucleus, time the circadian rhythms that synchronize physiological and behavioural functions in humans. The circadian system influences most physiological processes, including sleep, alertness and cognitive performance. Disruption of circadian homeostasis has deleterious effects on human health. Neurodegenerative disorders involve a wide range of symptoms, many of which exhibit diurnal variations in frequency and intensity. These disorders also disrupt circadian homeostasis, which in turn has negative effects on symptoms and quality of life. Emerging evidence points to a bidirectional relationship between circadian homeostasis and neurodegeneration, suggesting that circadian function might have an important role in the progression of neurodegenerative disorders. Therefore, the circadian system has become an attractive target for research and clinical care innovations. Studying circadian disruption in neurodegenerative disorders could expand our understanding of the pathophysiology of neurodegeneration and facilitate the development of novel, circadian-based interventions for these disabling disorders. In this Review, we discuss the alterations to the circadian system that occur in movement (Parkinson disease and Huntington disease) and cognitive (Alzheimer disease and frontotemporal dementia) neurodegenerative disorders and provide directions for future investigations in this field.

Sleep disturbances by disease type and stage in Huntington's disease

INTRODUCTION

Sleep disturbances are a common symptom in patients with Huntington's disease (HD). However, it is unclear when in the disease course of HD sleep disturbances become more frequent compared to the general population. This study investigated the frequency and odds of developing sleep disturbances between adults with HD or at-risk for HD and non-HD controls.

METHODS

Participants from the Enroll-HD study were split by both disease type and disease severity using CAG length, diagnostic confidence level, and total functional capacity score. Multivariate logistic regression was used to calculate odds ratios adjusted for age, sex, tobacco and alcohol use, depression and psychosis scores, and cognition to compare HD groups to non-HD controls. Cox proportional hazards models and Kaplan Meier curves were used to determine differences in probabilities of developing sleep disturbances and how sleep disturbances are related to age at motor onset.

RESULTS

There were significant differences between HD participants and non-HD controls in both the disease type and disease stage analyses (p < 0.001). The odds of a sleep disturbance increased with worsening disease stage and was highest in those with juvenile HD. The development of a sleep disorder in manifest HD participants was observed to be around the time of disease onset.

CONCLUSIONS

Sleep disturbances are more frequent in HD patients than those without HD. There are also differences based on disease type and stage. This is supplemented by the finding that the onset of sleep disturbances occurs near the time of motor onset of HD.

Sleep disturbance in movement disorders: insights, treatments and challenges

Sleep and circadian rhythm disturbances are central features of many movement disorders, exacerbating motor and non-motor symptoms and impairing quality of life. Understanding these disturbances to sleep is clinically important and may further our understanding of the underlying movement disorder. This review evaluates the current anatomical and neurochemical understanding of normal sleep and the recognised primary sleep disorders. In addition, we undertook a systematic review of the evidence for disruption to sleep across multiple movement disorders. Rapid eye movement sleep behaviour disorder has emerged as the most reliable prodromal biomarker for the alpha synucleinopathies, including Parkinson's disease and multiple system atrophy, often preceding motor symptom onset by several years. Abnormal sleep has also been described for many other movement disorders, but further evidence is needed to determine whether this is a primary or secondary phenotypic component of the underlying condition. Medication used in the treatment of motor symptoms also affects sleep and can aggravate or cause certain sleep disorders. Within the context of movement disorders, there is also some suggestion of a shared underlying mechanism for motor and sleep pathophysiology, with evidence implicating thalamic and brainstem structures and monoaminergic neurotransmission. This review highlights the need for an understanding of normal and abnormal sleep within the movement disorder clinic, an ability to screen for specific causes of poor sleep and to treat sleep disturbance to improve quality of life. Key sleep disorders also act as important biomarkers and have implications in diagnosis, prognosis and the development of future therapies.

Sleep in Patients With Neurologic Disease

PURPOSE OF REVIEW

This article provides a discussion of the current evidence and contemporary views on the relationship between sleep disorders and neurologic disease.

RECENT FINDINGS

Disrupted or disordered sleep can be associated with increased morbidity and mortality, the risk of cardiovascular events, increased seizure frequency, and altered immune responses. Studies have implicated disrupted sleep and circadian rhythm dysfunction with both amyloid-β (Aβ) deposition and tau deposition. A bidirectional relationship exists between disrupted sleep and the progression of Alzheimer disease pathology. Insomnia has been reported as a prodromal symptom in autoimmune encephalitis. Primary sleep disorders have now been increasingly recognized as a common comorbid condition in multiple sclerosis, making it imperative that neurologists feel comfortable differentiating multiple sclerosis fatigue from excessive daytime sleepiness caused by primary sleep disorders to optimally treat their patients.

SUMMARY

Sleep disorders are common across the population. By recognizing sleep disorders in patients with neurologic conditions, neurologists can provide comprehensive care and, in some cases, reduce neurologic disease burden.

Abnormal patterns of sleep and EEG power distribution during non-rapid eye movement sleep in the sheep model of Huntington's disease

Sleep disruption is a common invisible symptom of neurological dysfunction in Huntington's disease (HD) that takes an insidious toll on well-being of patients. Here we used electroencephalography (EEG) to examine sleep in 6 year old OVT73 transgenic sheep (Ovis aries) that we used as a presymptomatic model of HD. We hypothesized that despite the lack of overt symptoms of HD at this age, early alterations of the sleep-wake pattern and EEG powers may already be present. We recorded EEG from female transgenic and normal sheep (5/group) during two undisturbed 'baseline' nights with different lighting conditions. We then recorded continuously through a night of sleep disruption and the following 24 h (recovery day and night). On baseline nights, regardless of whether the lights were on or off, transgenic sheep spent more time awake than normal sheep particularly at the beginning of the night. Furthermore, there were significant differences between transgenic and normal sheep in both EEG power and its pattern of distribution during non-rapid eye movement (NREM) sleep. In particular, there was a significant decrease in delta (0.5-4 Hz) power across the night in transgenic compared to normal sheep, and the distributions of delta, theta and alpha oscillations that typically dominate the EEG in the first half of the night of normal sheep were skewed so they were predominant in the second, rather than the first half of the night in transgenic sheep. Interestingly, the effect of sleep disruption on normal sheep was also to skew the pattern of distribution of EEG powers so they looked more like that of transgenic sheep under baseline conditions. Thus it is possible that transgenic sheep exist in a state that resemble a chronic state of physiological sleep deprivation. During the sleep recovery period, normal sheep showed a significant 'rebound' increase in delta power with frontal dominance. A similar rebound was not seen in transgenic sheep, suggesting that their homeostatic response to sleep deprivation is abnormal. Although sleep abnormalities in early stage HD patients are subtle, with patients often unaware of their existence, they may contribute to impairment of neurological function that herald the onset of disease. A better understanding of the mechanisms underlying EEG abnormalities in early stage HD would give insight into how, and when, they progress into the sleep disorder. The transgenic sheep model is ideally positioned for studies of the earliest phase of disease when sleep abnormalities first emerge.

Can chronopharmacology improve the therapeutic management of neurological diseases?

The importance of circadian rhythm dysfunctions in the pathophysiology of neurological diseases has been highlighted recently. Chronopharmacology principles imply that tailoring the timing of treatments to the circadian rhythm of individual patients could optimize therapeutic management. According to these principles, chronopharmacology takes into account the individual differences in patients' clocks, the rhythmic changes in the organism sensitivity to therapeutic and side effects of drugs, and the predictable time variations of disease. This review examines the current literature on chronopharmacology of neurological diseases focusing its scope on epilepsy, Alzheimer and Parkinson diseases, and neuropathic pain, even if other neurological diseases could have been analyzed. While the results of the studies discussed in this review point to a potential therapeutic benefit of chronopharmacology in neurological diseases, the field is still in its infancy. Studies including a sufficiently large number of patients and measuring gold standard markers of the circadian rhythmicity are still needed to evaluate the beneficial effect of administration times over the 24-hour day but also of clock modulating drugs.

Circadian and Sleep Dysfunctions in Neurodegenerative Disorders-An Update

Disruptions of sleep and circadian rhythms are among the most debilitating symptoms in patients with neurodegenerative diseases. Their underlying pathophysiology is multilayered and multifactorial. Recent evidence suggests that sleep and circadian disturbances may influence the neurodegenerative processes as well as be their consequence. In this perspective, we provide an update of the current understanding of sleep and circadian dysregulation in Alzheimer's, Parkinson's, and Huntington's diseases.

Hypothalamic pathology in Huntington disease

Huntington's disease (HD), an autosomal dominant hereditary disorder associated with the accumulation of mutant huntingtin, is classically associated with cognitive decline and motor symptoms, notably chorea. However, growing evidence suggests that nonmotor symptoms are equally prevalent and debilitating. Some of these symptoms may be linked to hypothalamic pathology, demonstrated by findings in HD animal models and HD patients showing specific changes in hypothalamic neuropeptidergic populations and their associated functions. At least some of these alterations are likely due to local mutant huntingtin expression and toxicity, while others are likely caused by disturbed hypothalamic circuitry. Common problems include circadian rhythm disorders, including desynchronization of daily hormone excretion patterns, which could be targeted by novel therapeutic interventions, such as timed circadian interventions with light therapy or melatonin. However, translation of these findings from bench-to-bedside is hampered by differences in murine HD models and HD patients, including mutant huntingtin trinucleotide repeat length, which is highly heterogeneous across the various models. In this chapter, we summarize the current knowledge regarding hypothalamic alterations in HD patients and animal models, and the potential for these findings to be translated into clinical practice and management.

The Therapeutic Potential of Neuronal K-Cl Co-Transporter KCC2 in Huntington's Disease and Its Comorbidities

Intracellular chloride levels in the brain are regulated primarily through the opposing effects of two cation-chloride co-transporters (CCCs), namely K+-Cl- co-transporter-2 (KCC2) and Na+-K+-Cl- co-transporter-1 (NKCC1). These CCCs are differentially expressed throughout the course of development, thereby determining the excitatory-to-inhibitory γ-aminobutyric acid (GABA) switch. GABAergic excitation (depolarisation) is important in controlling the healthy development of the nervous system; as the brain matures, GABAergic inhibition (hyperpolarisation) prevails. This developmental switch in excitability is important, as uncontrolled regulation of neuronal excitability can have implications for health. Huntington's disease (HD) is an example of a genetic disorder whereby the expression levels of KCC2 are abnormal due to mutant protein interactions. Although HD is primarily considered a motor disease, many other clinical manifestations exist; these often present in advance of any movement abnormalities. Cognitive change, in addition to sleep disorders, is prevalent in the HD population; the effect of uncontrolled KCC2 function on cognition and sleep has also been explored. Several mechanisms by which KCC2 expression is reduced have been proposed recently, thereby suggesting extensive investigation of KCC2 as a possible therapeutic target for the development of pharmacological compounds that can effectively treat HD co-morbidities. Hence, this review summarizes the role of KCC2 in the healthy and HD brain, and highlights recent advances that attest to KCC2 as a strong research and therapeutic target candidate.

Circadian alterations in patients with neurodegenerative diseases: Neuropathological basis of underlying network mechanisms

Circadian organization of physiology and behavior is an important biological process that allows organisms to anticipate and prepare for daily changes and demands. Disruptions in this system precipitates a wide range of health issues. In patients with neurodegenerative diseases, alterations of circadian rhythms are among the most common and debilitating symptoms. Although a growing awareness of these symptoms has occurred during the last decade, their underlying neuropathophysiological circuitry remains poorly understood and consequently no effective therapeutic strategies are available to alleviate these health issues. Recent studies have examined the neuropathological status of the different neural components of the circuitry governing the generation of circadian rhythms in neurodegenerative diseases. In this review, we will dissect the potential contribution of dysfunctions in the different nodes of this circuitry to circadian alterations in patients with neurodegenerative diseases. A deeper understanding of these mechanisms will provide not only a better understanding of disease neuro-pathophysiology, but also hold the promise for developing effective and mechanisms-based therapies.

Increased plasma melatonin in presymptomatic Huntington disease sheep (Ovis aries): Compensatory neuroprotection in a neurodegenerative disease?

Melatonin is a pleiotrophic hormone, synthesised primarily by the pineal gland under the control of the suprachiasmatic nuclei (SCN). It not only provides a hormonal signal of darkness but also has neuroprotective properties. Huntington's disease (HD) is a progressive neurodegenerative disorder characterised by abnormal motor, cognitive and psychiatric symptoms. There is growing evidence, particularly from animal models, that circadian rhythms may also be disturbed in HD. We measured two circadian-regulated hormones, melatonin and cortisol, in plasma samples collected around-the-clock from normal and presymptomatic transgenic HD sheep (Ovis aries) at 5 and 7 years of age, to assess SCN-driven rhythms and the effect of genotype, sex and age. Melatonin-related precursors and metabolites (tryptophan, serotonin, kynurenine) were also measured by liquid chromatography (LC)-mass spectrometry (MS). At 5 years of age in both rams and ewes, plasma melatonin levels were significantly elevated in HD sheep. In ewes measured 2 years later, there was still a significant elevation of nocturnal melatonin. Furthermore, the daytime baseline levels of melatonin were significantly higher in HD sheep. Since increased melatonin could have global beneficial effects on brain function, we suggest that the increased melatonin measured in presymptomatic HD sheep is part of an autoprotective response to mutant huntingtin toxicity that may account, at least in part, for the late onset of disease that characterises HD.

Abnormal Photic Entrainment to Phase-Delaying Stimuli in the R6/2 Mouse Model of Huntington's Disease, despite Retinal Responsiveness to Light

The circadian clock located in the suprachiasmatic nucleus (SCN) in mammals entrains to ambient light via the retinal photoreceptors. This allows behavioral rhythms to change in synchrony with seasonal and daily changes in light period. Circadian rhythmicity is progressively disrupted in Huntington's disease (HD) and in HD mouse models such as the transgenic R6/2 line. Although retinal afferent inputs to the SCN are disrupted in R6/2 mice at late stages, they can respond to changes in light/dark cycles, as seen in jet lag and 23 h/d paradigms. To investigate photic entrainment and SCN function in R6/2 mice at different stages of disease, we first assessed the effect on locomotor activity of exposure to a 15 min light pulse given at different times of the day. We then placed the mice under five non-standard light conditions. These were light cycle regimes (T-cycles) of T21 (10.5 h light/dark), T22 (11 h light/dark), T26 (13 h light/dark), constant light, or constant dark. We found a progressive impairment in photic synchronization in R6/2 mice when the stimuli required the SCN to lengthen rhythms (phase-delaying light pulse, T26, or constant light), but normal synchronization to stimuli that required the SCN to shorten rhythms (phase-advancing light pulse and T22). Despite the behavioral abnormalities, we found that Per1 and c-fos gene expression remained photo-inducible in SCN of R6/2 mice. Both the endogenous drift of the R6/2 mouse SCN to shorter periods and its inability to adapt to phase-delaying changes will contribute to the HD circadian dysfunction.

Therapeutic Use of Music, Dance, and Rhythmic Auditory Cueing for Patients with Huntington's Disease: A Systematic Review

Background:

Studies have assessed the therapeutic effect of music, dance, and rhythmic auditory cueing for patients with Huntington’s disease (HD). However, the synthesis of evidence in support of their positive impact on symptoms is lacking.

Objective:

We conducted a systematic literature review to evaluate the potential benefits of music, dance, and rhythm on the cognitive, psychiatric and motor function in patients with HD.

Methods:

Two- and three-keyword searches and a manual search identified medical literature published from 1999 through 2019. We considered literature that assessed outcomes of art-based rehabilitation programs or individual modalities for persons with early, middle, or advanced HD. Structured analysis was conducted using data entry tables with categories for patient health status, art methods, and outcomes.

Results:

Seven articles and six abstracts met eligibility criteria, of which nine evaluated art-based rehabilitation programs. Studies mainly assessed cognitive, psychiatric, and motor functions through music, dance, or rhythm modalities. Although results were conflicting, in summary improvements to motor function were dependent on disease severity and more responsive to art therapy programs than rhythm-motor synchronization. Benefits to global cognition that resulted from rhythmic training correlated with microstructural changes. Qualitative data verified a positive impact on language production, chorea, behavior, and quality of life.

Conclusions:

Our review has shown a potential benefit of music, dance, and rhythm for patients with HD, which is particularly important for a disease that has no cure. Art forms seemed to affect cognitive, psychiatric, motor, psychosocial, and neuroanatomical domains. However, evidence is preliminary, warranting further investigation to establish the foundation for this field.

Validity of irritability in Huntington's disease: A scoping review

PURPOSE

To scope the literature concerning irritability in Huntington's disease to determine whether or not irritability is a valid and meaningful construct within this population.

METHOD

A scoping literature review was conducted based on findings from a search of five databases (Academic Search Ultimate, PsycINFO, CINAHL, Scopus and Web of Science) in November 2018. From an initial return of 453 papers, 40 were found suitable for review.

RESULTS

Review of the 40 studies highlighted several aspects of irritability in people with HD which influence its validity as an independent construct in context of the disease. While various measures are used to assess irritability, a gold standard has yet to be identified and consequently irritability is assessed inconsistently across the literature. In addition, the results suggest that irritability may not reflect pathological disease processes in HD, but rather comprises a multidimensional construct which appears to be strongly associated with other psychological difficulties such as depression and anxiety.

CONCLUSIONS

The current concept of irritability in people with HD continues to lack a general consensus in the clinical literature, in terms of both operationalisation and assessment. Consequently, further research is warranted in order to determine the extent to which irritability is a valid construct within the context of HD, including its associated behavioural, cognitive and affective dimensions.

Sleep Disorders in Huntington's Disease

Huntington's chorea (Huntington's disease, HD) is a genetic disorder caused by autosomal dominant mutation, leading to progressive neurodegenerative changes in the central nervous system. Involuntary movements such as chorea occur typically in HD patients, accompanied by progressive cognitive and psychiatric disturbances. Other common symptoms of HD are circadian and sleep abnormalities, which are observed from the earliest stages of the disease or even before the occurrence of clinical symptoms. The most common sleep problems reported by HD patients include insomnia, difficulties in falling asleep, frequent nocturnal awakenings, and excessive daytime sleepiness. Also, specific changes in sleep architecture have been identified in HD. In this paper, we review studies on sleep and circadian rhythm disorders in HD. We outline findings concerning sleep patterns and disturbances of circadian rhythms in HD patients, as well as the role of psychiatric disorders and motor disorders in HD patients' sleep problems. We also discuss problems related to the different methods of diagnosing sleep disorders in HD. Furthermore, the adverse effects of medication used for the treatment of core HD symptoms as one of the sources of sleep disturbances in HD are emphasized. In conclusion, the diversity and complexity of the determinants of sleep and circadian rhythm disorders in HD are highlighted. Finally, the relevance of effective treatment to improve patients' functioning and quality of life as well as the potential relief of their cognitive and emotional symptoms is addressed.