Frequency and Pathophysiology of Apathy in Huntington Disease: A Systematic Review and Meta-Analysis.

OBJECTIVE: Apathy is a common behavioral symptom of Huntington disease (HD). This systematic review describes current evidence on the pathophysiology, assessment, and frequency of apathy in HD. METHODS: This systematic review was conducted in accordance with PRISMA guidelines. Using a comprehensive search strategy, the investigators searched the MEDLINE, Embase, and PsycINFO databases. All studies that evaluated apathy in HD patients with a valid scale and reported apathy frequency or scores were included. Apathy scores were analyzed by mean or standardized mean differences in accordance with Cochrane guidelines. RESULTS: A total of 1,085 records were screened and 80 studies were ultimately included. The Problem Behaviors Assessment-Short was the most frequently used apathy assessment tool. Apathy frequency generally ranged from 10%-33% in premanifest HD to 24%-76% in manifest HD. A meta-analysis of 5,311 records of patients with premanifest HD showed significantly higher apathy scores, with a standardized mean difference of 0.41 (CI=0.29-0.52; p<0.001). A comparison of 1,247 patients showed significantly higher apathy scores in manifest than premanifest HD, with a mean difference of 1.87 (CI=1.48-2.26; p<0.001). There was evidence of involvement of various cortical and subcortical brain regions in HD patients with apathy. CONCLUSIONS: Apathy was more frequent among individuals with premanifest HD compared with those in a control group and among individuals with manifest HD compared with those with premanifest HD. Considering the complexity and unique pattern of development in neurodegenerative disease, further studies are required to explore the pathophysiology of apathy in HD.

Chorea.

PURPOSE OF REVIEW: This article provides an overview of the diagnostic and therapeutic approach to a patient with chorea. The phenomenology of chorea is described in addition to other common hyperkinetic movements that may be mistaken for or coexist with chorea. Chorea can be acquired or hereditary. Key historical and clinical features that can aid in determining the etiology are reviewed, and pharmacologic and nonpharmacologic treatment strategies are discussed. RECENT FINDINGS: Clinical investigations are under way to target transcription and translation of the mutant huntingtin protein as a potential disease-modifying strategy in Huntington disease (HD). Additional heritable factors have been revealed through genome-wide association studies. Symptom-focused treatments for HD are are being studied, including a third vesicular monoamine transporter-2 (VMAT2) inhibitor for chorea attenuation and drugs to target irritability and cognitive impairment. Increased availability of genetic testing has led to increased awareness of HD mimics (eg, C9orf72 and IgLON5). SUMMARY: Chorea is a relatively common hyperkinetic disorder with a broad differential. The first step in the approach to a patient with chorea is accurately defining the phenomenology. Once it has been determined that the patient has chorea, the investigation into determining an etiology can begin. Factors such as age of onset, time course, family history, unique clinical features, and imaging and laboratory findings can guide the diagnosis. Treatments for most causes of chorea are purely symptomatic, although it is important to recognize causes that are reversible or have disease-modifying interventions.

Cerebral blood flow is associated with markers of neurodegeneration in Huntington's disease.

INTRODUCTION: The ultimate cause of neuronal death in Huntington's disease (HD) is still uncertain. Apart from impairment in systems handling abnormal proteins, other mechanisms might contribute to neurodegeneration and progression of HD. Decreased cerebral blood flow (CBF) has been described in other neurodegenerative disorders and may play a role in HD. OBJECTIVES: To investigate CBF changes in HD gene carriers. METHODS: A group of 39 HD gene carriers (18 premanifest and 21 manifest HD) and 16 controls underwent a comprehensive clinical evaluation and a brain magnetic resonance imaging protocol that included pseudo-continuous arterial spin labeling to quantify CBF. Regions of interest (ROI) analyses were performed to compare CBF in controls vs premanifest HD vs manifest HD. Correlation analyses were performed to ascertain the relationship between CBF and clinical and biomarkers data. RESULTS: We found a decrease in CBF in bilateral caudate and putamen of patients with manifest HD in comparison with controls. CBF of premanifest HD carriers in the same ROIs was midway between controls and the HD patients, with differences not reaching statistical significance. Lower CBF in caudate and putamen was associated with worse motor symptoms, functionality, and cognitive performance. CBF was also associated with markers of neurodegeneration: higher CBF in caudate and putamen significantly correlated to higher volumes in the same ROI and to lower levels of neurofilament light chain. CONCLUSION: As CBF changes in caudate and putamen nuclei were associated with markers of neurodegeneration and with clinical outcomes, decreased CBF and oxygen supply could emerge as a relevant mechanism contributing to degeneration in HD.

HAP40 is a conserved central regulator of Huntingtin and a potential modulator of Huntington's disease pathogenesis.

Perturbation of huntingtin (HTT)'s physiological function is one postulated pathogenic factor in Huntington's disease (HD). However, little is known how HTT is regulated in vivo. In a proteomic study, we isolated a novel ~40kDa protein as a strong binding partner of Drosophila HTT and demonstrated it was the functional ortholog of HAP40, an HTT associated protein shown recently to modulate HTT's conformation but with unclear physiological and pathologic roles. We showed that in both flies and human cells, HAP40 maintained conserved physical and functional interactions with HTT. Additionally, loss of HAP40 resulted in similar phenotypes as HTT knockout. More strikingly, HAP40 strongly affected HTT's stability, as depletion of HAP40 significantly reduced the levels of endogenous HTT protein while HAP40 overexpression markedly extended its half-life. Conversely, in the absence of HTT, the majority of HAP40 protein were degraded, likely through the proteasome. Further, the affinity between HTT and HAP40 was not significantly affected by polyglutamine expansion in HTT, and contrary to an early report, there were no abnormal accumulations of endogenous HAP40 protein in HD cells from mouse HD models or human patients. Lastly, when tested in Drosophila models of HD, HAP40 partially modulated the neurodegeneration induced by full-length mutant HTT while showed no apparent effect on the toxicity of mutant HTT exon 1 fragment. Together, our study uncovers a conserved mechanism governing the stability and in vivo functions of HTT and demonstrates that HAP40 is a central and positive regulator of endogenous HTT. Further, our results support that mutant HTT is toxic regardless of the presence of its partner HAP40, and implicate HAP40 as a potential modulator of HD pathogenesis through its multiplex effect on HTT's function, stability and the potency of mutant HTT's toxicity.

Olfactory Dysfunction in Huntington's Disease.

Olfactory dysfunction is a common symptom in patients with neurodegenerative disorders, including Huntington's disease (HD). Understanding its pathophysiology is important in establishing a preventive and therapeutic plan. In this literature review, we cover the physiology of olfaction, its role in neurodegeneration, and its characteristics in patients with HD. In the general population, olfactory dysfunction is present in 3.8-5.8%and the prevalence increases significantly in those older than 80 years. For HD, data regarding prevalence rates are lacking and the scales used have been inconsistent or have been restructured due to concerns about cross-cultural understanding. Pathogenic huntingtin deposits have been found in the olfactory bulb of individuals with HD, although no studies have correlated this with the grade of olfactory impairment. Olfactory dysfunction is present in both premanifest and manifest patients with HD, showing a progressive decline over time with more severe deficits at advanced stages. No specific treatment for olfactory impairment in HD has been proposed; identifying and avoiding potential medications that cause olfactory dysfunction, as well as general safety recommendations remain the basis of the therapeutic strategy.

Sleep Dysfunction in Huntington's Disease: Perspectives from Patients.

BACKGROUND: Despite the abundance of clinical tools, sleep disorders are still not routinely evaluated in patients with Huntington's disease (HD). Sleep disturbances can exacerbate cognitive impairment and mood disorders and seriously affect the life of the patients and their families. OBJECTIVE: The current study was designed to investigate sleep quality and its association with clinical symptoms in HD. As an exploratory aim, we also evaluated sleep quality in caregivers of patients with HD. METHODS: Twenty-nine patients with HD and 22 caregivers completed a series of self-reported questionnaires about sleep quality and pattern, cognitive function, and depression and anxiety symptoms. Spearman correlation analyses were performed to ascertain the association between sleep quality and severity of self-perceived clinical symptoms. RESULTS: The primary sleep complaints reported by the patients were related to waking up in the middle of the night or early in the morning; and increased sleep latency. Seventeen of 29 HD patients (59%) and 12 of 22 caregivers (55%) were classified as "poor" sleepers. Worse sleep quality among HD patients was associated with greater severity of anxiety and depression symptoms. Importantly, a decline in sleep quality was associated with decreased self-perceived cognitive function for both HD patients and caregivers. CONCLUSION: Increasing awareness and improving our understanding of sleep dysfunction in HD is imperative for individuals with HD and indirectly, their caregivers. Regularly incorporating sleep assessments when evaluating HD patients should be considered to address this troublesome nonmotor symptom.

Irritability in Huntington's Disease.

Huntington's disease (HD) is a heritable and fatal neurodegenerative disease characterized by a triad of motor, cognitive and neuropsychiatric symptoms. A common and particularly detrimental neuropsychiatric alteration in HD gene carriers is irritability, which frequently manifests as abrupt and unpredictable outbursts of anger. This symptom increases the burden of HD in multiple ways, such as jeopardizing employment and straining familial or caregiver support. Although irritability in HD is diagnosed by the administration of standardized rating scales and clinical expertise, measurement of severity and progression is complicated by several factors. Currently, individuals with HD who present with irritability may be managed with a variety of psychotropic medications, primarily antidepressants and antipsychotics. While these therapies offer relief to individuals suffering from irritability in HD, they are often not sufficient. Here, we review irritability in the context of HD and emphasize the need for treatments that are better tailored to mitigate this troublesome symptom. An expeditious strategy in pursuit of this goal involves evaluating the efficacy of approved medications that are used to treat similar neuropsychiatric symptoms.

Promises and pitfalls of immune-based strategies for Huntington's disease.

Huntington's disease (HD) is an autosomal-dominant neurodegenerative disease characterized by the selective loss of neurons in the striatum and cortex, leading to progressive motor dysfunction, cognitive decline and behavioral symptoms. HD is caused by a trinucleotide (CAG) repeat expansion in the gene encoding for huntingtin. Several studies have suggested that inflammation is an important feature of HD and it is already observed in the early stages of the disease. Recently, new molecules presenting anti-inflammatory and/or immunomodulatory have been investigated for HD. The objective of this review is to discuss the data obtained so far on the immune-based therapeutic strategies for HD.