Assessment of Perivascular Space Morphometry Across the White Matter in Huntington's Disease Using MRI

Background

Perivascular spaces (PVS) are fluid-filled cavities surrounding small cerebral blood vessels. There are limited reports of enlarged PVS across the grey matter in manifest Huntington's disease (HD). Little is known about how PVS morphometry in the white matter may contribute to HD. Enlarged PVS have the potential to both contribute to HD pathology and affect the distribution and success of intraparenchymal and intrathecally administered huntingtin-lowering therapies.

Objective

To investigate PVS morphometry in the global white matter across the spectrum of HD. Relationships between PVS morphometry and disease burden and severity measures were examined.

Methods

White matter PVS were segmented on 3T T2 W MRI brain scans of 33 healthy controls, 30 premanifest HD (pre-HD), and 32 early manifest HD (early-HD) participants from the Vancouver site of the TRACK-HD study. PVS count and total PVS volume were measured.

Results

PVS total count slightly increased in pre-HD (p = 0.004), and early-HD groups (p = 0.005), compared to healthy controls. PVS volume, as a percentage of white matter volume, increased subtly in pre-HD compared to healthy controls (p = 0.044), but not in early-HD. No associations between PVS measures and HD disease burden or severity were found.

Conclusions

This study reveals relatively preserved PVS morphometry across the global white matter of pre-HD and early-HD. Subtle morphometric abnormalities are implied but require confirmation in a larger cohort. However, in conjunction with previous publications, further investigation of PVS in HD and its potential impact on future treatments, with a focus on subcortical grey matter, is warranted.

Freesurfer Software Update Significantly Impacts Striatal Volumes in the Huntington's Disease Young Adult Study and Will Influence HD-ISS Staging

Background

The Huntington's Disease Integrated Staging System (HD-ISS) defined disease onset using volumetric cut-offs for caudate and putamen derived from FreeSurfer 6 (FS6). The impact of the latest software update (FS7) on volumes remains unknown. The Huntington's Disease Young Adult Study (HD-YAS) is appropriately positioned to explore differences in FS bias when detecting early atrophy.

Objective

Explore the relationships and differences between raw caudate and putamen volumes, calculated total intracranial volumes (cTICV), and adjusted caudate and putamen volumes, derived from FS6 and FS7, in HD-YAS.

Methods

Images from 123 participants were segmented and quality controlled. Relationships and differences between volumes were explored using intraclass correlation (ICC) and Bland-Altman analysis.

Results

Across the whole cohort, ICC for raw caudate and putamen was 0.99, cTICV 0.93, adjusted caudate 0.87, and adjusted putamen 0.86 (all p < 0.0005). Compared to FS6, FS7 calculated: i) larger raw caudate (+0.8%, p < 0.00005) and putamen (+1.9%, p < 0.00005), with greater difference for larger volumes; and ii) smaller cTICV (-5.1%, p < 0.00005), with greater difference for smaller volumes. The systematic and proportional difference in cTICV was greater than raw volumes. When raw volumes were adjusted for cTICV, these effects compounded (adjusted caudate +7.0%, p < 0.00005; adjusted putamen +8.2%, p < 0.00005), with greater difference for larger volumes.

Conclusions

As new software is released, it is critical that biases are explored since differences have the potential to significantly alter the findings of HD trials. Until conversion factors are defined, the HD-ISS must be applied using FS6. This should be incorporated into the HD-ISS online calculator.

Progressive alterations in white matter microstructure across the timecourse of Huntington's disease

BACKGROUND

Whole-brain longitudinal diffusion studies are crucial to examine changes in structural connectivity in neurodegeneration. Here, we investigated the longitudinal alterations in white matter (WM) microstructure across the timecourse of Huntington's disease (HD).

METHODS

We examined changes in WM microstructure from premanifest to early manifest disease, using data from two cohorts with different disease burden. The TrackOn-HD study included 67 controls, 67 premanifest, and 10 early manifest HD (baseline and 24-month data); the PADDINGTON study included 33 controls and 49 early manifest HD (baseline and 15-month data). Longitudinal changes in fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity, and radial diffusivity from baseline to last study visit were investigated for each cohort using tract-based spatial statistics. An optimized pipeline was employed to generate participant-specific templates to which diffusion tensor imaging maps were registered and change maps were calculated. We examined longitudinal differences between HD expansion-carriers and controls, and correlations with clinical scores, including the composite UHDRS (cUHDRS).

RESULTS

HD expansion-carriers from TrackOn-HD, with lower disease burden, showed a significant longitudinal decline in FA in the left superior longitudinal fasciculus and an increase in MD across subcortical WM tracts compared to controls, while in manifest HD participants from PADDINGTON, there were significant widespread longitudinal increases in diffusivity compared to controls. Baseline scores in clinical scales including the cUHDRS predicted WM microstructural change in HD expansion-carriers.

CONCLUSION

The present study showed significant longitudinal changes in WM microstructure across the HD timecourse. Changes were evident in larger WM areas and across more metrics as the disease advanced, suggesting a progressive alteration of WM microstructure with disease evolution.

Validating Automated Segmentation Tools in the Assessment of Caudate Atrophy in Huntington's Disease

Background: Neuroimaging shows considerable promise in generating sensitive and objective outcome measures for therapeutic trials across a range of neurodegenerative conditions. For volumetric measures the current gold standard is manual delineation, which is unfeasible for samples sizes required for large clinical trials. Methods: Using a cohort of early Huntington's disease (HD) patients (n = 46) and controls (n = 35), we compared the performance of four automated segmentation tools (FIRST, FreeSurfer, STEPS, MALP-EM) with manual delineation for generating cross-sectional caudate volume, a region known to be vulnerable in HD. We then examined the effect of each of these baseline regions on the ability to detect change over 15 months using the established longitudinal Caudate Boundary Shift Integral (cBSI) method, an automated longitudinal pipeline requiring a baseline caudate region as an input. Results: All tools, except Freesurfer, generated significantly smaller caudate volumes than the manually derived regions. Jaccard indices showed poorer levels of overlap between each automated segmentation and manual delineation in the HD patients compared with controls. Nevertheless, each method was able to demonstrate significant group differences in volume (p < 0.001). STEPS performed best qualitatively as well as quantitively in the baseline analysis. Caudate atrophy measures generated by the cBSI using automated baseline regions were largely consistent with those derived from a manually segmented baseline, with STEPS providing the most robust cBSI values across both control and HD groups. Conclusions: Atrophy measures from the cBSI were relatively robust to differences in baseline segmentation technique, suggesting that fully automated pipelines could be used to generate outcome measures for clinical trials.

Cerebrospinal fluid flow dynamics in Huntington's disease evaluated by phase contrast MRI

Multiple targeted therapeutics for Huntington's disease are now in clinical trials, including intrathecally delivered compounds. Previous research suggests that CSF dynamics may be altered in Huntington's disease, which could be of paramount relevance to intrathecal drug delivery to the brain. To test this hypothesis, we conducted a prospective cross-sectional study comparing people with early stage Huntington's disease with age- and gender-matched healthy controls. CSF peak velocity, mean velocity and mean flow at the level of the cerebral aqueduct, and sub-arachnoid space in the upper and lower spine, were quantified using phase contrast MRI. We calculated Spearman's rank correlations, and tested inter-group differences with Wilcoxon rank-sum test. Ten people with early Huntington's disease, and 10 controls were included. None of the quantified measures was associated with potential modifiers of CSF dynamics (demographics, osmolality, and brain volumes), or by known modifiers of Huntington's disease (age and HTTCAG repeat length); and no significant differences were found between the two studied groups. While external validation is required, the attained results are sufficient to conclude tentatively that a clinically relevant alteration of CSF dynamics - that is, one that would justify dose-adjustments of intrathecal drugs - is unlikely to exist in Huntington's disease.

The impact of occipital lobe cortical thickness on cognitive task performance: An investigation in Huntington's Disease

BACKGROUND

The occipital lobe is an important visual processing region of the brain. Following consistent findings of early neural changes in the occipital lobe in Huntington's Disease (HD), we examined cortical thickness across four occipital regions in premanifest (preHD) and early HD groups compared with controls. Associations between cortical thickness in gene positive individuals and performance on six cognitive tasks, each with a visual component, were examined. In addition, the association between cortical thickness in gene positive participants and one non-visual motor task was also examined for comparison.

METHODS

Cortical thickness was determined using FreeSurfer on T1-weighted 3T MR datasets from controls (N=97), preHD (N=109) and HD (N=69) from the TRACK-HD study. Regression models were fitted to assess between-group differences in cortical thickness, and relationships between performance on the cognitive tasks, the motor task and occipital thickness were examined in a subset of gene-positive participants (N=141).

RESULTS

Thickness of the occipital cortex in preHD and early HD participants was reduced compared with controls. Regionally-specific associations between reduced cortical thickness and poorer performance were found for five of the six cognitive tasks, with the strongest associations in lateral occipital and lingual regions. No associations were found with the cuneus. The non-visual motor task was not associated with thickness of any region.

CONCLUSIONS

The heterogeneous pattern of associations found in the present study suggests that occipital thickness negatively impacts cognition, but only in regions that are linked to relatively advanced visual processing (e.g., lateral occipital, lingual regions), rather than in basic visual processing regions such as the cuneus. Our results show, for the first time, the functional implications of occipital atrophy highlighted in recent studies in HD.

Short-interval observational data to inform clinical trial design in Huntington's disease

OBJECTIVES

To evaluate candidate outcomes for disease-modifying trials in Huntington's disease (HD) over 6-month, 9-month and 15-month intervals, across multiple domains. To present guidelines on rapid efficacy readouts for disease-modifying trials.

METHODS

40 controls and 61 patients with HD, recruited from four EU sites, underwent 3 T MRI and standard clinical and cognitive assessments at baseline, 6 and 15 months. Neuroimaging analysis included global and regional change in macrostructure (atrophy and cortical thinning), and microstructure (diffusion metrics). The main outcome was longitudinal effect size (ES) for each outcome. Such ESs can be used to calculate sample-size requirements for clinical trials for hypothesised treatment efficacies.

RESULTS

Longitudinal changes in macrostructural neuroimaging measures such as caudate atrophy and ventricular expansion were significantly larger in HD than controls, giving rise to consistently large ES over the 6-month, 9-month and 15-month intervals. Analogous ESs for cortical metrics were smaller with wide CIs. Microstructural (diffusion) neuroimaging metrics ESs were also typically smaller over the shorter intervals, although caudate diffusivity metrics performed strongly over 9 and 15 months. Clinical and cognitive outcomes exhibited small longitudinal ESs, particularly over 6-month and 9-month intervals, with wide CIs, indicating a lack of precision.

CONCLUSIONS

To exploit the potential power of specific neuroimaging measures such as caudate atrophy in disease-modifying trials, we propose their use as (1) initial short-term readouts in early phase/proof-of-concept studies over 6 or 9 months, and (2) secondary end points in efficacy studies over longer periods such as 15 months.

Cerebellar abnormalities in Huntington's disease: a role in motor and psychiatric impairment?

The cerebellum has received limited attention in Huntington's disease (HD), despite signs of possible cerebellar dysfunction, including motor incoordination and impaired gait, which are currently attributed to basal ganglia atrophy and disrupted fronto-striatal circuits. This study is the first to investigate a potential contribution of macro- and microstructural cerebellar damage to clinical manifestations of HD. T1- and diffusion-weighted 3T magnetic resonance imaging (MRI) scans were obtained from 12 controls and 22 early-stage HD participants. Manual delineation and voxel-based morphometry were used to assess between-group differences in cerebellar volume, and diffusion metrics were compared between groups within the cerebellar gray and white matter. Associations between these imaging measures and clinical scores were examined within the HD group. Reduced paravermal volume was detected in HD compared with controls using voxel-based morphometry (P < 0.05), but no significant volumetric differences were found using manual delineation. Diffusion abnormalities were detected in both cerebellar gray matter and white matter. Smaller cerebellar volumes, although not significantly reduced, were significantly associated with impaired gait and psychiatric morbidity and of borderline significance with pronate/supinate-hand task performance. Abnormal cerebellar diffusion was associated with increased total motor score, impaired saccade initiation, tandem walking, and timed finger tapping. In conclusion, atrophy of the paravermis, possibly encompassing the cerebellar nuclei, and microstructural abnormalities within the cerebellum may contribute to HD neuropathology. Aberrant cerebellar diffusion and reduced cerebellar volume together associate with impaired motor function and increased psychiatric symptoms in stage I HD, potentially implicating the cerebellum more centrally in HD presentation than previously recognized.

Corpus callosal atrophy in premanifest and early Huntington's disease

BACKGROUND

Volumetric MRI studies have highlighted the pronounced loss of white matter in premanifest and early Huntington's Disease (HD). The current study focussed on the corpus callosum (CC) since it provides interhemispheric connections to vulnerable cortical areas.

OBJECTIVES

To investigate cross-sectional and longitudinal group differences in CC volume and hypothesis-driven associations with three cognitive tasks.

METHODS

Baseline and 24-month 3T MRI were analysed from 106 premanifest (PreHD), (59 preHD-A ≥10.8 and 47 preHD-B <10.8 years from predicted onset), 84 early HD (53 Stage 1 (HD1) and 31 Stage 2 (HD2)) and 101 control subjects from the TRACK-HD study, using a semi-automated technique for CC delineation. Between-group differences in volume and 24-month atrophy rates, and correlations with cognitive performance were investigated using regression models, adjusting for potential confounders.

RESULTS

PreHD-B, HD1 and HD2 had statistically significantly smaller baseline CC volumes (p < 0.001) and all groups had elevated 24-month atrophy rates compared with controls (p < 0.001). Smaller baseline CC volume was associated with impaired performance in the Circle Tracing Indirect task in early HD (p < 0.05). Positive, non-statistically significant relationships with Stroop Word Reading were shown in both gene-positive groups. There was no evidence of an association with the Trail Making B task.

CONCLUSIONS

We found reduced CC volume and elevated 24-month atrophy rates, even in individuals far from disease onset. Structural degeneration of interhemispheric connections may contribute to cognitive deficits, such as performance in the Circle Tracing Indirect task in HD. Examination of different image acquisitions may provide more specific information about underlying CC degeneration.

Longitudinal neuroimaging biomarkers in Huntington's Disease

Identifying markers able to characterise the progression of Huntington's Disease (HD) is of great importance to the HD research community, as such markers may provide valuable outcome measures in future clinical trials. Neuroimaging measures are obvious candidates because of their clear relevance to the neuropathology of the disease. Many also show improved precision and sensitivity compared with standard functional scales. This review summarizes findings from the wealth of longitudinal imaging studies in the literature, focusing on the most widely available imaging modalities: structural MRI (volumetric and diffusion imaging), functional MRI and PET. We discuss the longitudinal sensitivity, reproducibility and feasibility of each imaging modality for use in clinical trials.

Impact of the control for corrupted diffusion tensor imaging data in comparisons at the group level: an application in Huntington disease

Background

Corrupted gradient directions (GD) in diffusion weighted images may seriously affect reliability of diffusion tensor imaging (DTI)-based comparisons at the group level. In the present study we employed a quality control (QC) algorithm to eliminate corrupted gradient directions from DTI data. We then assessed effects of this procedure on comparisons between Huntington disease (HD) subjects and controls at the group level.

Methods

Sixty-one HD patients in early stages and forty matched healthy controls were studied in a longitudinal design (baseline and two follow-ups at three time points over 15 months), in a multicenter setting with similar acquisition protocols on four different MR scanners at four European study sites. A QC algorithm was used to identify corrupted GD in DTI data sets. Differences in fractional anisotropy (FA) maps at the group level with and without elimination of corrupted GD were analyzed.

Results

The elimination of corrupted GD had an impact on individual FA maps as well as on cross-sectional group comparisons between HD subjects and controls. Following application of the QC algorithm, less small clusters of FA changes were observed, compared to the analysis without QC. However, the main pattern of regional reductions and increases in FA values with and without QC-based elimination of corrupted GD was unchanged.

Conclusion

An impact on the result patterns of the comparison of FA maps between HD subjects and controls was observed depending on whether QC-based elimination of corrupted GD was performed. QC-based elimination of corrupted GD in DTI scans reduces the risk of type I and type II errors in cross-sectional group comparison of FA maps contributing to an increase in reliability and stability of group comparisons.

The neuroanatomy of subthreshold depressive symptoms in Huntington's disease: a combined diffusion tensor imaging (DTI) and voxel-based morphometry (VBM) study

BACKGROUND

Depressive symptoms are prominent psychopathological features of Huntington's disease (HD), making a negative impact on social functioning and well-being.

METHOD

We compared the frequencies of a history of depression, previous suicide attempts and current subthreshold depression between 61 early-stage HD participants and 40 matched controls. The HD group was then split based on the overall HD group's median Hospital Anxiety and Depression Scale-depression score into a group of 30 non-depressed participants (mean 0.8, s.d. = 0.7) and a group of 31 participants with subthreshold depressive symptoms (mean 7.3, s.d. = 3.5) to explore the neuroanatomy underlying subthreshold depressive symptoms in HD using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI).

RESULTS

Frequencies of history of depression, previous suicide attempts or current subthreshold depressive symptoms were higher in HD than in controls. The severity of current depressive symptoms was also higher in HD, but not associated with the severity of HD motor signs or disease burden. Compared with the non-depressed HD group DTI revealed lower fractional anisotropy (FA) values in the frontal cortex, anterior cingulate cortex, insula and cerebellum of the HD group with subthreshold depressive symptoms. In contrast, VBM measures were similar in both HD groups. A history of depression, the severity of HD motor signs or disease burden did not correlate with FA values of these regions.

CONCLUSIONS

Current subthreshold depressive symptoms in early HD are associated with microstructural changes - without concomitant brain volume loss - in brain regions known to be involved in major depressive disorder, but not those typically associated with HD pathology.

Test-Retest Reliability of Diffusion Tensor Imaging in Huntington's Disease

Diffusion tensor imaging (DTI) has shown microstructural abnormalities in patients with Huntington's Disease (HD) and work is underway to characterise how these abnormalities change with disease progression. Using methods that will be applied in longitudinal research, we sought to establish the reliability of DTI in early HD patients and controls. Test-retest reliability, quantified using the intraclass correlation coefficient (ICC), was assessed using region-of-interest (ROI)-based white matter atlas and voxelwise approaches on repeat scan data from 22 participants (10 early HD, 12 controls). T1 data was used to generate further ROIs for analysis in a reduced sample of 18 participants. The results suggest that fractional anisotropy (FA) and other diffusivity metrics are generally highly reliable, with ICCs indicating considerably lower within-subject compared to between-subject variability in both HD patients and controls. Where ICC was low, particularly for the diffusivity measures in the caudate and putamen, this was partly influenced by outliers. The analysis suggests that the specific DTI methods used here are appropriate for cross-sectional research in HD, and give confidence that they can also be applied longitudinally, although this requires further investigation. An important caveat for DTI studies is that test-retest reliability may not be evenly distributed throughout the brain whereby highly anisotropic white matter regions tended to show lower relative within-subject variability than other white or grey matter regions.

Evaluation of multi-modal, multi-site neuroimaging measures in Huntington's disease: Baseline results from the PADDINGTON study

Background

Macro- and micro-structural neuroimaging measures provide valuable information on the pathophysiology of Huntington's disease (HD) and are proposed as biomarkers. Despite theoretical advantages of microstructural measures in terms of sensitivity to pathology, there is little evidence directly comparing the two.

Methods

40 controls and 61 early HD subjects underwent 3 T MRI (T1- and diffusion-weighted), as part of the PADDINGTON study. Macrostructural volumetrics were obtained for the whole brain, caudate, putamen, corpus callosum (CC) and ventricles. Microstructural diffusion metrics of fractional anisotropy (FA), mean-, radial- and axial-diffusivity (MD, RD, AD) were computed for white matter (WM), CC, caudate and putamen. Group differences were examined adjusting for age, gender and site. A formal comparison of effect sizes determined which modality and metrics provided a statistically significant advantage over others.

Results

Macrostructural measures showed decreased regional and global volume in HD (p < 0.001); except the ventricles which were enlarged (p < 0.01). In HD, FA was increased in the deep grey-matter structures (p < 0.001), and decreased in the WM (CC, p = 0.035; WM, p = 0.053); diffusivity metrics (MD, RD, AD) were increased for all brain regions (p < 0.001). The largest effect sizes were for putamen volume, caudate volume and putamen diffusivity (AD, RD and MD); each was significantly larger than those for all other metrics (p < 0.05).

Conclusion

The highest performing macro- and micro-structural metrics had similar sensitivity to HD pathology quantified via effect sizes. Region-of-interest may be more important than imaging modality, with deep grey-matter regions outperforming the CC and global measures, for both volume and diffusivity. FA appears to be relatively insensitive to disease effects.

Clinical impairment in premanifest and early Huntington's disease is associated with regionally specific atrophy

TRACK-HD is a multicentre longitudinal observational study investigating the use of clinical assessments and 3-Tesla magnetic resonance imaging as potential biomarkers for future therapeutic trials in Huntington's disease (HD). The cross-sectional data from this large well-characterized dataset provide the opportunity to improve our knowledge of how the underlying neuropathology of HD may contribute to the clinical manifestations of the disease across the spectrum of premanifest (PreHD) and early HD. Two hundred and thirty nine gene-positive subjects (120 PreHD and 119 early HD) from the TRACK-HD study were included. Using voxel-based morphometry (VBM), grey and white matter volumes were correlated with performance in four domains: quantitative motor (tongue force, metronome tapping, and gait); oculomotor [anti-saccade error rate (ASE)]; cognition (negative emotion recognition, spot the change and the University of Pennsylvania smell identification test) and neuropsychiatric measures (apathy, affect and irritability). After adjusting for estimated disease severity, regionally specific associations between structural loss and task performance were found (familywise error corrected, P < 0.05); impairment in tongue force, metronome tapping and ASE were all associated with striatal loss. Additionally, tongue force deficits and ASE were associated with volume reduction in the occipital lobe. Impaired recognition of negative emotions was associated with volumetric reductions in the precuneus and cuneus. Our study reveals specific associations between atrophy and decline in a range of clinical modalities, demonstrating the utility of VBM correlation analysis for investigating these relationships in HD.

The progression of regional atrophy in premanifest and early Huntington's disease: a longitudinal voxel-based morphometry study

BACKGROUND

Unbiased longitudinal studies are needed to understand the distributed neurodegenerative changes of Huntington's disease (HD). They may also provide tools for assessing disease-modifying interventions. The authors investigated the progression of regional atrophy in premanifest and early HD compared with controls.

METHODS

Nine controls, 17 premanifest and 21 early HD subjects underwent volumetric MRI at baseline and 2 years. Premanifest subjects were on average 18.1 years before predicted motor onset. Non-linear registration was used to model within-subject change over the scanning interval, and statistical parametric mapping was used to examine group differences and associations with clinical variables.

RESULTS

In early HD, increased grey-matter (GM) atrophy rates were evident throughout the subcortical GM and over selective cortical regions compared with controls. This group also demonstrated strikingly widespread increases in white-matter (WM) atrophy rates. The authors observed no significant differences between premanifest HD and controls. Longer CAG was associated with higher atrophy rates over large WM areas including brainstem and internal capsule and over small GM regions including thalamus and occipital cortex. Worse baseline motor score was associated with regionally increased rates in the thalamus, internal capsule and occipital lobe. Sample-size calculations indicate that 19 and 24 early HD subjects per treatment arm would need to complete a 2-year trial in order to detect a 50% reduction in WM and GM atrophy rates respectively.

CONCLUSIONS

Degeneration of structural connectivity may play an important role in early HD symptoms. Assessment of WM and GM changes will be important in understanding the complexity of HD and its treatment.

Patterns of cortical thickness according to APOE genotype in Alzheimer's disease

BACKGROUND

Possession of one or more apolipoprotein E (APOE) epsilon4 alleles may influence the distribution of atrophy and clinical phenotype. We aimed to assess the influence of APOE genotype on cortical thickness and regional brain volumes in AD (Alzheimer's disease).

METHODS

We included 38 patients (9 epsilon4 non-carriers, 23 epsilon4 heterozygotes, 6 epsilon4 homozygotes) and 23 controls. Each subject had 2 magnetic resonance imaging (MRI) scans and a neuropsychological battery. Cortical thickness and isthmus cingulate volume were measured using FreeSurfer; the volumes of the hippocampus, whole brain, and lateral ventricles were calculated using manual and semi-automated volumetry.

RESULTS

Compared with controls, cortical thickness was significantly lower: in the bilateral temporal, posterior parietal and occipital regions in non-carriers, in the medial temporal and left parietal regions in heterozygotes, and in the medial temporal lobe in homozygotes. Comparisons between AD subgroups did not show significant differences. A trend for larger brain and isthmus cingulate volumes and smaller hippocampal and ventricular volumes with increasing epsilon4 dose were seen. These differences were supported by neuropsychological profiles.

CONCLUSION

These results suggest that APOE genotype may influence the topography of regional atrophy and cortical thinning in AD.

Onset and progression of pathologic atrophy in Huntington disease: a longitudinal MR imaging study

BACKGROUND AND PURPOSE

Longitudinal MR imaging measures provide an opportunity to track progression in HD before the emergence of clinical symptoms. This may prove useful in assessing disease-modifying treatments. We investigated how caudate and global volumes change as HD progresses from premanifest to early disease.

MATERIALS AND METHODS

Forty HD gene-positive individuals and 19 controls underwent serial volumetric MR imaging (baseline, 12 and 27 months; 2 or 3 scans per person). At baseline, 3 patients with HD were premanifest but developed overt motor features during the study, and 37 had early HD. All had dates of motor onset recorded. Caudates, lateral ventricles, and TIVs were measured using semiautomated procedures. Linear mixed models were used to investigate differences between HD and controls in relation to motor onset, controlling for TIV, sex, and age.

RESULTS

Extrapolating backwards in time, we found that differences in caudate and ventricular volumes between patients with HD and controls were evident 14 and 5 years, respectively, before motor onset (P < .05). At onset, caudate volume was 2.58 mL smaller than that in controls (P < .0001); ventricular volume was 9.27 mL larger (P < .0001). HD caudate atrophy rates were linear, showed low variability between subjects, and were approximately 10-fold higher than those in controls (P < .001). HD ventricular enlargement rates were variable between subjects, were approximately 4-fold higher than those in controls at onset (P < .001), and accelerated with disease duration (P = .02).

CONCLUSIONS

We provide evidence of acceleration of global atrophy in HD with disproportionate caudate involvement. Both caudate and global measures may be of use as early markers of HD pathology.

Whole-brain atrophy as a measure of progression in premanifest and early Huntington's disease

Therapeutic trials in Huntington's disease (HD) are challenging as clinical progression is slow and variable and reliable biomarkers are lacking. We used magnetic resonance imaging and the brain boundary shift integral to quantify whole-brain atrophy rates over 1 year in early and premanifest HD subjects, and controls. Early HD subjects had statistically significantly (P = 0.007) increased (threefold higher) rates of whole-brain atrophy compared with controls. Higher atrophy rates were associated with longer CAG repeat length. MRI-based measures of whole-brain atrophy may have potential as a measure of progression in HD.

Magnetic resonance imaging of Huntington's disease: preparing for clinical trials

The known genetic mutation causing Huntington's disease (HD) makes this disease an important model to study links between gene and brain function. An autosomal dominant family history and the availability of a sensitive and specific genetic test allow pre-clinical diagnosis many years before the onset of any typical clinical signs. This review summarizes recent magnetic resonance imaging (MRI)–based findings in HD with a focus on the requirements if imaging is to be used in treatment trials. Despite its monogenetic cause, HD presents with a range of clinical manifestations, not explained by variation in the number of CAG repeats in the affected population. Neuroimaging studies have revealed a complex pattern of structural and functional changes affecting widespread cortical and subcortical regions far beyond the confines of the striatal degeneration that characterizes this disorder. Besides striatal dysfunction, functional imaging studies have reported a variable pattern of increased and decreased activation in cortical regions in both pre-clinical and clinically manifest HD-gene mutation carriers. Beyond regional brain activation changes, evidence from functional and diffusion-weighted MRI further suggests disrupted connectivity between corticocortical and corticostriatal areas. However, substantial inconsistencies with respect to structural and functional changes have been reported in a number of studies. Possible explanations include methodological factors and differences in study samples. There may also be biological explanations but these are poorly characterized and understood at present. Additional insights into this phenotypic variability derived from study of mouse models are presented to explore this phenomenon.

Plasma 24S-hydroxycholesterol and caudate MRI in pre-manifest and early Huntington's disease

Huntington's disease (HD) is a hereditary neurodegenerative disorder for which biological indicators of disease progression, or disease stage, would be especially important for therapeutic trials. 24S-hydroxycholesterol (24OHC) is a brain-generated cholesterol metabolite which has been associated with neurodegeneration, and alterations of cholesterol metabolism in murine HD models and patients' tissues have been recently identified. On these grounds, and with the aim of identifying putative biomarkers in HD, we studied cholesterol metabolism through the analysis in vivo of plasma 24OHC and cholesterol in two independent cohorts of controls and patients of Italian and British origin. We analysed a total of 62 controls, 96 HD symptomatic patients at different disease stages (stage 1-3), and 33 HD gene-positive pre-manifest subjects [pre-manifest HD (pre-HD)]. Cholesterol and 24OHC plasma levels were comparable in both the British and Italian subjects, and were not influenced by fasting or post-meal status. Cholesterol levels did not show differences between controls, pre-HD subjects and HD patients. In contrast, the plasma levels of 24OHC were significantly higher in controls than in HD patients at all disease stages (P < 0.001). Interestingly, in pre-HD subjects plasma 24OHC concentrations were similar to those of controls, and thus significantly greater than those of HD patients at any disease stage (P < 0.001). As expected, significant differences in caudate volumes between stage 1-2 HD patients and pre-HD subjects, and pre-HD subjects and controls were found. The pre-HD cohort of subjects was heterogeneous as to 24OHC levels, since subjects closer to predicted development of motor signs of disease had lower 24OHC levels than those far from onset. Our data indicate that the brain-generated cholesterol metabolite 24OHC measured in plasma was significantly depleted in HD patients at any disease stage, and it could discriminate pre-manifest subjects from patients with overt motor disease. However, 24OHC levels failed to mark further disease progression in patients with manifest HD. Overall, we demonstrate that 24OHC levels parallel the large decrease in caudate volumes observed in gene-positive subjects from pre-manifest to HD stage 1, thus reflecting a critical phase characterized by neuronal loss. We conclude that that 24OHC levels complement MRI morphometry as a valuable tool to follow neurodegenerative changes in the early stages of Huntington disease.

Defective emotion recognition in early HD is neuropsychologically and anatomically generic

Huntington's disease (HD) is an inherited neurodegenerative disorder that classically presents with motor, cognitive and psychiatric symptoms. However, other abnormalities also occur in this condition, notably deficient recognition of facial emotional expressions. Deficits in emotion recognition impact significantly on the lives of HD patients and their families and thus it is important to clarify the onset and pattern of impairment. This study investigated facial emotion recognition in a large cohort of early HD patients, and premanifest gene-carriers. We used voxel-based morphometry (VBM) to examine the neuroanatomical correlates of emotion recognition performance. Forty patients with early HD, 21 premanifest gene carriers and 20 controls were assessed using 24 faces from the Ekman Pictures of Facial Affect, and volumetric brain MRI. The HD group was significantly worse than controls at recognising, surprise, disgust, anger and fear, and worse than the premanifest group at recognising disgust and anger. When patient data were expressed as z-scores, recognition of anger was significantly worse than disgust in the early HD group. In the VBM analysis, these deficits were associated with common regional atrophy: impaired recognition of surprise, disgust, anger and fear were all associated with striatal volume loss. Fear was associated with additional atrophy of the right insula and left and right lateral orbitofrontal cortex. Even in early HD there is a wide-ranging impairment in recognition of negative emotions denoting 'threat'. Our findings implicate a generic fronto-subcortical network in the pathogenesis of these emotion recognition deficits.