A Sturrock

Development of biomarkers for Huntington's disease

Huntingtons disease is an autosomal dominant, progressive neurodegenerative disorder, for which there is no disease-modifying treatment. By use of predictive genetic testing, it is possible to identify individuals who carry the gene defect before the onset of symptoms, providing a window of opportunity for intervention aimed at preventing or delaying disease onset. However, without robust and practical measures of disease progression (ie, biomarkers), the efficacy of therapeutic interventions in this premanifest Huntingtons disease population cannot be readily assessed. Current progress in the development of biomarkers might enable evaluation of disease progression in individuals at the premanifest stage of the disease; these biomarkers could be useful in defining endpoints in clinical trials in this population. Clinical, cognitive, neuroimaging, and biochemical biomarkers are being investigated for their potential in clinical use and their value in the development of future treatments for patients with Huntingtons disease.

Tapping linked to function and structure in premanifest and symptomatic Huntington disease

Objective: Motor signs are functionally disabling features of Huntington disease. Characteristic motor signs define disease manifestation. Their severity and onset are assessed by the Total Motor Score of the Unified Huntingtons Disease Rating Scale, a categorical scale limited by interrater variability and insensitivity in premanifest subjects. More objective, reliable, and precise measures are needed which permit clinical trials in premanifest populations. We hypothesized that motor deficits can be objectively quantified by force-transducer-based tapping and correlate with disease burden and brain atrophy. Methods: A total of 123 controls, 120 premanifest, and 123 early symptomatic gene carriers performed a speeded and a metronome tapping task in the multicenter study TRACK-HD. Total Motor Score, CAG repeat length, and MRIs were obtained. The premanifest group was subdivided into A and B, based on the proximity to estimated disease onset, the manifest group into stages 1 and 2, according to their Total Functional Capacity scores. Analyses were performed centrally and blinded. Results: Tapping variability distinguished between all groups and subgroups in both tasks and correlated with 1) disease burden, 2) clinical motor phenotype, 3) gray and white matter atrophy, and 4) cortical thinning. Speeded tapping was more sensitive to the detection of early changes. Conclusion: Tapping deficits are evident throughout manifest and premanifest stages. Deficits are more pronounced in later stages and correlate with clinical scores as well as regional brain atrophy, which implies a link between structure and function. The ability to track motor phenotype progression with force-transducer-based tapping measures will be tested prospectively in the TRACK-HD study.

The Clinical and Genetic Features of Huntington Disease

Huntington disease (HD) is a dominantly inherited neurodegenerative disorder that usually presents in adulthood with characteristic motor and cognitive features and with variable and diverse psychiatric disturbances. Following the discovery of the causative defect in the HTT gene in 1993, great advances in understanding the pathogenesis of HD have been made, yet no effective disease-modifying therapy has been identified. In this new era of HD research, we have seen the emergence of a number of large clinical trials, the systematic search for novel biomarkers and the recent initiation of the first pre-manifest HD clinical studies. In this review, we seek to provide an overview of the clinical and genetic features of HD together with a summary of clinical research at this time.

Magnetic resonance spectroscopy biomarkers in premanifest and early Huntington disease

Objectives: To evaluate in vivo brain metabolite differences in control subjects, individuals with premanifest Huntington disease (pre-HD), and individuals with early HD using 1H magnetic resonance spectroscopy (MRS) and to assess their relationship with motor performance. Methods: Eighty-five participants (30 controls, 25 pre-HD, and 30 early HD) were recruited as part of the TRACK-HD study. Eighty-four were scanned at 3 T with single-voxel spectroscopy in the left putamen. Disease burden score was >220 among pre-HD individuals. Subjects underwent TRACK-HD motor assessment including Unified Huntingtons Disease Rating Scale (UHDRS) motor scoring and a novel quantitative motor battery. Statistical analyses included linear regression and one-way analysis of variance. Results: Total N-acetylaspartate (tNAA), a neuronal integrity marker, was lower in early HD (∼15%) vs controls (p < 0.001). N-acetylaspartate (NAA), a constituent of tNAA, was lower in pre-HD (∼8%) and early HD (∼17%) vs controls (p < 0.05). The glial cell marker, myo-inositol (mI), was 50% higher in early HD vs pre-HD (p < 0.01). In early HD, mI correlated with UHDRS motor score (R2 = 0.23, p < 0.05). Across pre-HD and early HD, tNAA correlated with performance on a tongue pressure task (R2 = 0.30, p < 0.0001) and with disease burden score (R2 = 0.17, p < 0.005). Conclusions: We demonstrate lower putaminal tNAA in early HD compared to controls in a cross-section of subjects. A novel biomarker role for mI in early HD was also identified. These findings resolve disagreement in the literature about the role of MRS as an HD biomarker. We conclude that putaminal MRS measurements of NAA and mI are promising potential biomarkers of HD onset and progression.

The structural involvement of the cingulate cortex in premanifest and early Huntington's disease†‡§

The impact of Huntingtons disease neuropathology on the structure of the cingulate is uncertain, with evidence of both cortical enlargement and atrophy in this structure in early clinical disease. We sought to determine differences in cingulate volume between premanifest Huntingtons disease and early Huntingtons disease groups compared with controls using detailed manual measurements. Thirty controls, 30 subjects with premanifest Huntingtons disease, and 30 subjects with early Huntingtons disease were selected from the Vancouver site of the TRACK‐HD study. Subjects underwent 3 Tesla magnetic resonance imaging and motor, cognitive, and neuropsychiatric assessment. The cingulate was manually delineated and subdivided into rostral, caudal, and posterior segments. Group differences in volume and associations with performance on 4 tasks thought to utilize cingulate function were examined, with adjustment for appropriate covariates. Cingulate volumes were, on average, 1.7 mL smaller in early Huntingtons disease (P = .001) and 0.9 mL smaller in premanifest Huntingtons disease (P = .1) compared with controls. Smaller volumes in subsections of the cingulate were associated with impaired recognition of negative emotions (P = .04), heightened depression (P = .009), and worse visual working memory performance (P = .01). There was no evidence of associations between volume and ability on a performance‐monitoring task. This study disputes previous findings of enlargement of the cingulate cortex in Huntingtons disease and instead suggests that the cingulate undergoes structural degeneration during early Huntingtons disease with directionally consistent, nonsignificant differences seen in premanifest Huntingtons disease. Cingulate atrophy may contribute to deficits in mood, emotional processing, and visual working memory in Huntingtons disease.

A longitudinal study of magnetic resonance spectroscopy Huntington's disease biomarkers

Putaminal metabolites examined using cross‐sectional magnetic resonance spectroscopy (MRS) can distinguish pre‐manifest and early Huntingtons Disease (HD) individuals from controls. An ideal biomarker, however, will demonstrate longitudinal change over short durations. The objective here was to evaluate longitudinal in vivo brain metabolite profiles in HD over 24 months. Eighty‐four participants (30 controls, 25 pre‐manifest HD, 29 early HD) recruited as part of TRACK‐HD were imaged at baseline, 12 months, and 24 months using 3T MRS of left putamen. Automated putaminal volume measurement was performed simultaneously. To quantify partial volume effects, spectroscopy was performed in a second, white matter voxel adjacent to putamen in six subjects. Subjects underwent TRACK‐HD motor assessment. Statistical analyses included linear regression and one‐way analysis of variance (ANOVA). At all time‐points N‐acetyl aspartate and total N‐acetyl aspartate (NAA), neuronal integrity markers, were lower in early HD than in controls. Total NAA was lower in pre‐manifest HD than in controls, whereas the gliosis marker myo‐inositol (MI) was robustly elevated in early HD. Metabolites were stable over 24 months with no longitudinal change. Total NAA was not markedly different in adjacent white matter than putamen, arguing against partial volume confounding effects in cross‐sectional group differences. Total NAA correlations with disease burden score suggest that this metabolite may be useful in identifying neurochemical responses to therapeutic agents. We demonstrate almost consistent group differences in putaminal metabolites in HD‐affected individuals compared with controls over 24 months. Future work establishing spectroscopy as an HD biomarker should include multi‐site assessments in large, pathologically diverse cohorts.

Ultrasensitive measurement of huntingtin protein in cerebrospinal fluid demonstrates increase with Huntington disease stage and decrease following brain huntingtin suppression

Quantitation of huntingtin protein in the brain is needed, both as a marker of Huntington disease (HD) progression and for use in clinical gene silencing trials. Measurement of huntingtin in cerebrospinal fluid could be a biomarker of brain huntingtin, but traditional protein quantitation methods have failed to detect huntingtin in cerebrospinal fluid. Using micro-bead based immunoprecipitation and flow cytometry (IP-FCM), we have developed a highly sensitive mutant huntingtin detection assay. The sensitivity of huntingtin IP-FCM enables accurate detection of mutant huntingtin protein in the cerebrospinal fluid of HD patients and model mice, demonstrating that mutant huntingtin levels in cerebrospinal fluid reflect brain levels, increasing with disease stage and decreasing following brain huntingtin suppression. This technique has potential applications as a research tool and as a clinical biomarker.

F14 Speeded tapping assesses progression of huntington's disease within one year—results from the track-HD study

Background Speeded (ST) and metronome (MT) tapping have been shown to be sensitive in distinguishing premanifest (preHD) and manifest (HD) stages of Huntingtons disease (HD) in the cross-sectional analysis of the TRACK-HD study, and to detect an early motor phenotype even more than 14 years before predicted disease manifestation. Aims To investigate whether ST and MT are able to track disease progression within a 12 month follow-up period. Methods Participants from the four TRACK-HD sites (ST/MT: controls: 120/122, preHD: 117/118, HD: 117/121) were instructed to perform two tapping tasks with their non-dominant index finger. In ST, they had to tap at maximal speed for 10s; in MT, they were instructed to continue a given tapping rate of 1.8 Hz for 10s. After one year, the assessments were repeated. The annual change in performance of gene-carriers was compared to controls and to each other. The variability of tapping intervals expressed as logarithmic standard deviations was calculated for the primary outcome measures (ie, inter-onset interval (IOI) & tap duration (TD) in ST, inter-onset intervals (ΔIOI) & mid-tap interval (ΔMTI) in MT). Results The annual change in IOI and TD for ST showed significant results for HD versus controls and HD versus preHD. ΔIOI and ΔMTI, both MT variables, failed to make this distinction. Conclusions ST is able to detect changes in manifest HD within only one year of follow-up and may thus be applicable as an outcome measure for disease modifying clinical trials in early manifest HD. Possible changes in preHD may require longer follow-up periods or larger cohorts. The hypothesis that force-transducer-based MT and ST tasks may track the progression of a premanifest motor phenotype will be tested in the TRACK-HD study.

H06 Cross sectional and longitudinal 3T magnetic resonance spectroscopy in a TRACK-HD cohort of individuals with premanifest and early Huntington's disease

Background A potential biomarker role for magnetic resonance spectroscopy (MRS) in Huntingtons disease (HD) is unclear due to conflicting reports in the literature. Aim To investigate MRS as an HD biomarker through cross sectional and longitudinal examinations in a TRACK-HD study cohort. Methods Cross sectional MRS of the left putamen (at 3T field strength) was performed in the University of British Columbia TRACK-HD study cohort. 84 individuals (30 controls (C), 25 pre-HD (P), 29 early HD (E)) were scanned at baseline. 78 individuals (29 (C), 26 (P) and 23 (E)) underwent repeat MRS examination at 1 year. Metabolites of interest were total N-acetyl aspartate (tNAA) and myo-inositol (MI); markers of neuronal health and gliosis. Results Baseline tNAA concentrations in early HD were lower than in controls (mean (SD) 8.6 (0.7) mM (C) vs 7.3 (1.2) mM (E); p<0.001). MI was higher in early HD compared with controls (6.0 (2.6) mM (E) vs 4.3 (1.4) mM (C); p<0.005). After 1 year, MI concentrations remained 40% higher in early HD (6.0 (2.7) mM (E) vs 4.2 (1.1) mM (C); p<0.01). tNAA was still lower in early HD (p<0.001) but also in pre-HD (p<0.05) than controls (7.4 (0.9) mM (E) vs 8.2 (0.8) mM (P) vs 8.7 (0.6) mM (C)). Neither tNAA nor MI exhibited longitudinal change in any group. A novel observation was that of 30% increases in spectral linewidth in early HD at both time points (p<0.01). Conclusions Our data support patterns of higher MI levels and lower tNAA in early HD. The pattern of lower tNAA may begin in premanifest HD. The lack of longitudinal metabolite change is not unusual over such a short duration of follow-up. We also identified for the first time, consistent increases in MRS spectral linewidth in early HD.