D. Langbehn

Evaluation of longitudinal 12 and 24 month cognitive outcomes in premanifest and early Huntington's disease

Background Deterioration of cognitive functioning is a debilitating symptom in many neurodegenerative diseases, such as Huntingtons disease (HD). To date, there are no effective treatments for the cognitive problems associated with HD. Cognitive assessment outcomes will have a central role in the efforts to develop treatments to delay onset or slow the progression of the disease. The TRACK-HD study was designed to build a rational basis for the selection of cognitive outcomes for HD clinical trials. Methods There were a total of 349 participants, including controls (n=116), premanifest HD (n=117) and early HD (n=116). A standardised cognitive assessment battery (including nine cognitive tests comprising 12 outcome measures) was administered at baseline, and at 12 and 24 months, and consisted of a combination of paper and pencil and computerised tasks selected to be sensitive to cortical-striatal damage or HD. Each cognitive outcome was analysed separately using a generalised least squares regression model. Results are expressed as effect sizes to permit comparisons between tasks. Results 10 of the 12 cognitive outcomes showed evidence of deterioration in the early HD group, relative to controls, over 24 months, with greatest sensitivity in Symbol Digit, Circle Tracing direct and indirect, and Stroop word reading. In contrast, there was very little evidence of deterioration in the premanifest HD group relative to controls. Conclusions The findings describe tests that are sensitive to longitudinal cognitive change in HD and elucidate important considerations for selecting cognitive outcomes for clinical trials of compounds aimed at ameliorating cognitive decline in HD.

Diffusion Tensor Imaging in Preclinical Huntington's Disease.

Diffusion tensor imaging was used to study brain related changes in white matter that may be associated with Huntington’s Disease progression. Thirty-one preclinical gene-mutation carriers were imaged cross-sectionally using diffusion tensor and anatomical brain imaging. Subjects were individuals who had a known gene mutation for HD but did not manifest motor diagnostic criteria for HD. Fractional anisotropy scalar maps showed a positive correlation with five year probability of diagnosis (based upon gene repeat length and current age) in the putamen and a negative correlation in the external capsule. This study shows that scalar maps generated from diffusion tensor imaging may be directly related to the earliest stages of disease progression within HD, even before a diagnosis is given. Findings suggest that DTI measures, therefore, may have the ability to act as a biomarker for disease progression in clinical trials of pre-manifest subjects.

Structural and functional brain network correlates of depressive symptoms in premanifest Huntington's disease

Depression is common in premanifest Huntingtons disease (preHD) and results in significant morbidity. We sought to examine how variations in structural and functional brain networks relate to depressive symptoms in premanifest HD and healthy controls. Brain networks were constructed using diffusion tractography (70 preHD and 81 controls) and resting state fMRI (92 preHD and 94 controls) data. A sub‐network associated with depression was identified in a data‐driven fashion and network‐based statistics was used to investigate which specific connections correlated with depression scores. A replication analysis was then performed using data from a separate study. Correlations between depressive symptoms with increased functional connectivity and decreased structural connectivity were seen for connections in the default mode network (DMN) and basal ganglia in preHD. This study reveals specific connections in the DMN and basal ganglia that are associated with depressive symptoms in preHD. Hum Brain Mapp 38:2819–2829, 2017.

Medication use in early-HD participants in track-HD: an investigation of its effects on clinical performance

Insufficient evidence exists to guide the long-term pharmacological management of Huntington’s disease (HD) although most current interventions rely on symptomatic management. The effect of many frontline treatments on potential endpoints for HD clinical trials remains unknown. Our objective was to investigate how therapies widely used to manage HD affect the symptom for which they are prescribed and other endpoints using data from TRACK-HD. We used longitudinal models to estimate effects of medication use on performance on tests of motor, cognitive and neuropsychiatric function using data from 123 TRACK-HD stage 1/2 participants across four study visits. Adjustment for confounding by prior medication use, prior clinical performance, concomitant use of other medications, and baseline variables (sex, disease group, age, CAG, study site, education) enabled a closer-to-causal interpretation of the associations. Adjusting for baseline variables only, medication use was typically associated with worse clinical performance, reflecting greater medication use in more advanced patients. After additional adjustment for longitudinal confounders such “inverse” associations were generally eliminated and in the expected directions: participants taking neuroleptics tended to have better motor performance, improved affect and poorer cognitive performance, and those taking SSRI/SNRIs had less apathy, less affect and better total behaviour scores. However, we uncovered few statistically significant associations. Limitations include sample size and unmeasured confounding. In conclusion, adjustment for confounding by prior measurements largely eliminated associations between medication use and poorer clinical performance from simple analyses. However, there was little convincing evidence of causal effects of medication on clinical performance and larger cohorts or trials are needed.

B17 Blood transcriptome replicates dysregulation found in human huntington’s disease brain and shares an immune signature with alzheimer’s disease

Background In Huntington’s disease (HD) mutant HTT is ubiquitously expressed and has systemic effects. Availability of brain tissue is limited and postmortem samples are from advanced disease. Blood, however, is readily available, can be studied longitudinally, and contains cells shown to be dysfunctional in HD. There is marked transcriptional dysregulation in HD brain. Differential expression has also been described in muscle and blood, though changes are inconsistent and poorly replicate CNS findings, questioning their biological relevance. Aims and methods We used RNA-Seq to analyse the transcriptome of whole blood in two separate cohorts comprising a total of 186 HD subjects and 49 controls. Results Though individual transcripts were not significantly differentially expressed in either cohort, gene set enrichment analysis applied to publicly-available pathway databases and HD and control brain co-expression modules showed a significant overlap in dysregulated pathways between the cohorts. In particular, immune pathways were upregulated in both cohorts. Notably, modules previously shown to be significantly dysregulated in HD caudate were also significantly dysregulated in the same direction in both blood cohorts, as well as an independent cortex expression dataset. In addition, we identified overlapping immune upregulation in HD and Alzheimer’s disease (AD), suggesting these two distinct neurodegenerative diseases share some common pathogenic mechanisms. Conclusions We have therefore shown that transcriptional dysregulation in key pathways in HD blood parallels changes found in brain. This overlaps with the transcriptional signature in AD, raising the potential for shared therapeutic approaches. Furthermore, analysing pathways may overcome the cellular and technical heterogeneity that prevent the blood transcriptome replicating changes in the brain transcriptome at a single-gene level.