Journal of Huntington's Disease

Aberrant communication between striatum, the main information processing unit of the basal ganglia, and cerebral cortex plays a critical role in the emergence of Huntington’s disease (HD), a fatal monogenetic condition that typically strikes in the prime of life. Although both striatum and cortex undergo substantial cell loss over the course of HD, corticostriatal circuits become dysfunctional long before neurons die. Understanding the dysfunction is key to developing effective strategies for treating a progressively worsening triad of motor, cognitive, and psychiatric symptoms. Cortical output neurons drive striatal activity through the release of glutamate, an excitatory amino acid. Striatal outputs, in turn, release γ-amino butyric acid (GABA) and exert inhibitory control over downstream basal ganglia targets. Ample evidence from transgenic rodent models points to dysregulation of corticostriatal glutamate transmission along with corresponding changes in striatal GABA release as underlying factors in the HD behavioral phenotype. Another contributor is dysregulation of dopamine (DA), a modulator of both glutamate and GABA transmission. In fact, pharmacological manipulation of DA is the only currently available treatment for HD symptoms. Here, we review data from animal models and human patients to evaluate the role of DA in HD, including DA interactions with glutamate and GABA within the context of dysfunctional corticostriatal circuitry.

In this review, we outline the role of the cholinergic system in Huntington’s disease, and briefly describe the dysfunction of cholinergic transmission, cholinergic neurons, cholinergic receptors and cholinergic survival factors observed in post-mortem human brains and animal models of Huntington’s disease. We postulate how the dysfunctional cholinergic system can be targeted to develop novel therapies for Huntington’s disease, and discuss the beneficial effects of cholinergic therapies in pre-clinical and clinical studies.

The role of aggregate formation in the pathophysiology of Huntington’s disease (HD) remains uncertain. However, the temporal appearance of aggregates tends to correlate with the onset of symptoms and the numbers of neuropil aggregates correlate with the progression of clinical disease. Using highly sensitive immunohistochemical methods we have detected the appearance of diffuse aggregates during embryonic development in the R6/2 and YAC128 mouse models of HD. These are initially seen in developing axonal tracts and appear to spread throughout the cerebrum in the early neonate.

Background: Modulation of gene transcription by HDAC inhibitors has been shown repeatedly to be neuroprotective in cellular, invertebrate, and rodent models of Huntington’s disease (HD). It has been difficult to translate these treatments to the clinic, however, because existing compounds have limited potency or brain bioavailability.

Objective: In the present study, we assessed the therapeutic potential of LBH589, an orally bioavailable hydroxamic acid-derived nonselective HDAC inhibitor in mouse models of HD.

Method: The efficacy of LBH589 is tested in two HD mouse models using various biochemical, behavioral and neuropathological outcome measures.

Results: We show that LBH589 crosses the blood brain barrier; induces histone hyperacetylation and prevents striatal neuronal shrinkage in R6/2 HD mice. In full-length knock-in HD mice LBH589-treatment improves motor performance and reduces neuronal atrophy.

Conclusions: Our efficacious results of LBH589 in fragment and full-length mouse models of HD suggest that LBH589 is a promising candidate for clinical assessment in HD patients and provides confirmation that non-selective HDAC inhibitors can be viable clinical candidates.

Background: Huntington disease (HD) is a neurodegenerative disease caused by a CAG repeat expansion on chromosome 4. Pathology is associated with CAG repeat length. Prior studies examining people in the intermediate allele (IA) range found subtle differences in motor, cognitive, and behavioral domains compared to controls.

Objective: The purpose of this study was to examine baseline and longitudinal differences in motor, cognitive, behavioral, functional, and imaging outcomes between persons with CAG repeats in three ranges: normal (≤26), intermediate (27–35), and reduced penetrance (36–39).

Methods: We examined longitudinal data from 389 participants in three allele groups: 280 normal controls (NC), 21 intermediate allele [IA], and 88 reduced penetrance [RP]. We used linear mixed models to identify differences in baseline and longitudinal outcomes between groups. Three models were tested: 1) no baseline or longitudinal differences; 2) baseline differences but no longitudinal differences; and 3) baseline and longitudinal differences.

Results: Model 1 was the best fitting model for most outcome variables. Models 2 and 3 were best fitting for some of the variables. We found baseline and longitudinal trends of declining performance across increasing CAG repeat length groups, but no significant differences between the NC and IA groups.

Conclusion: We did not find evidence to support differences in the IA group compared to the NC group. These findings are limited by a small IA sample size.

Background: In Huntington’s disease (HD) the innate immune system is activated, as reflected by increased plasma levels of different cytokines.

Objective: To explore whether increased cytokine levels are associated with neuropsychiatric symptoms and cognitive dysfunction in HD mutation carriers.

Method: Plasma cytokine levels of TNF-alpha, interleukin (IL)-1ra, IL-1β, IL-5, IL-6, IL-8 and Il-10 were assessed in 124 HD mutation carriers at two time points 2 years apart (totalling 214 observations). Using multilevel regression analysis, cytokines were analysed in relation to neuropsychiatric symptoms and cognitive dysfunction. Depressed mood was assessed with the depression subscale of the Problem Behaviours Assessment (PBA), apathy with the Apathy Scale, and irritability with the Irritability Scale. Cognitive functioning was assessed using the Mini-Mental State Examination (MMSE) and a battery of executive cognitive functioning tests, aggregated into an executive cognitive functioning (ExCog) score.

Results: Inverse associations were found in adjusted models between IL-6 and ExCog score (β= –0.114; p = 0.01) and between IL-1ra and ExCog score (β= –0.110; p = 0.02). No associations between cytokine levels and any of the other neuropsychiatric symptom scores remained statistically significant in adjusted models.

Conclusion: Higher plasma levels of IL-6 and IL-1ra are weakly associated with cognitive dysfunction in HD, but not with other neuropsychiatric symptoms.

Background: The number of people affected by Huntington’s disease (HD) is far greater than those with manifest HD because it also includes those at risk, both HD gene mutation carriers and family members not carrying the HD mutation. Many relevant needs of young adults from HD families may not be met at present. This includes advice on important life decisions e.g. family planning and having children, psychological support and treatment of medical conditions.

Objective: To survey the opinion of young adults from HD families about relevance and availability of information and support regarding several aspects of HD.

Methods: An online anonymous questionnaire translated into ten languages contained questions regarding the importance and availability of information and support about HD related topics, and attitudes towards research. Answers were captured in categories or on Likert scales.

Results: Information about HD related topics and the availability of peer and professional support are very important for young adults from HD families. In addition, with the exception of general information about HD, or predictive testing, the vast majority of respondents stated that they did not receive enough information on other important topics, for instance regarding legal advice and they did not feel supported enough by healthcare professionals. HD research was considered to be of high value, though most did not participate in HD research.

Conclusion: The results of this survey can help devise a strategy to address these unmet needs and also to facilitate research participation of more young adults from HD families.

Background: Suicidal ideation (SI) and attempts are increased in Huntington’s disease (HD), making risk factor assessment a priority.

Objective: To determine whether, hopelessness, irritability, aggression, anxiety, CAG expansion status, depression, and motor signs/symptoms were associated with Suicidal Ideation (SI) in those at risk for HD.

Methods: Behavioral and neurological data were collected from subjects in an observational study. Subject characteristics were calculated by CAG status and SI. Logistic regression models were adjusted for demographics. Separate logistic regressions were used to compare SI and non-SI subjects. A combined logistic regression model, including 4 pre-specified predictors, (hopelessness, irritability, aggression, anxiety) was used to assess the relationship of SI to these predictors.

Results: 801 subjects were assessed, 40 were classified as having SI, 6.3% of CAG mutation expansion carriers had SI, compared with 4.3% of non- CAG mutation expansion carriers (p = 0.2275). SI subjects had significantly increased depression (p < 0.0001), hopelessness (p < 0.0001), irritability (p < 0.0001), aggression (p = 0.0089), and anxiety (p < 0.0001), and an elevated motor score (p = 0.0098). Impulsivity, assessed in a subgroup of subjects, was also associated with SI (p = 0.0267). Hopelessness and anxiety remained significant in combined model (p < 0.001; p < 0.0198, respectively) even when motor score was included.

Conclusions: Behavioral symptoms were significantly higher in those reporting SI. Hopelessness and anxiety showed a particularly strong association with SI. Risk identification could assist in assessment of suicidality in this group.

Background: In preparation for a meeting with the U.S. Food and Drug Administration (FDA) on Patient-Focused Drug Development in Huntington’s disease, the Huntington’s Disease Society of America (HDSA) created and distributed two comprehensive surveys on the symptom experience and treatment approaches for Huntington’s disease.

Objective: The objective of these surveys was to identify the specific symptoms that most impact the daily lives of individuals with Huntington’s disease/Juvenile Huntington’s disease (HD/JHD) and their caregivers and to solicit input on the types of treatments desired by HD affected families. The data were shared with the FDA to offer background and insight in preparation for the patient-focused meeting, as well as to ensure representation by the community in a manner that would complement those who attended in person.

Methods: Two distinct surveys were created using SurveyMonkey to capture patient and caregiver perspectives on HD symptoms and current treatments. HDSA distributed the surveys to the HD community in August and September 2014 and collected responses through January 2015.

Results: More than 3,600 responses to the two surveys were received. The data showed that both caregivers and individuals with HD were severely impacted by the cognitive and behavioral symptoms of HD with HD patients reporting problems with executive functioning and cognitive decline as most impactful to them. However, 30 percent of caregivers reported that chorea was the most impactful symptom compared to 17 percent of people with HD. Across all the symptom categories, patients reported a lower occurrence of symptoms than were reported by their caregivers.

Conclusions: With only one drug approved for treatment of a symptom of Huntington’s disease and no disease modifying treatments available, there is a critical need for new medicines to treat the cognitive, psychiatric and motor symptoms associated with HD. While the surveys did not capture risk/benefit data, the data collected do provide new insights around the different perspectives of patients and caregivers. We believe that industry development of treatments would be well-informed by incorporating the patient community, which is more knowledgeable and engaged than given credit, in consideration of treatment regimens, risk-benefit and priorities for therapeutic development.