Huntington's Disease Gene Carriers Research Articles

Relationship between CAG repeat length and brain volume in premanifest and early Huntington’s disease

Huntington's disease (HD) is caused by an expanded CAG repeat on the gene encoding for the protein huntingtin. There are conflicting findings about the extent to which repeat length predicts signs of the disease or severity of disease progression in adults. This study examined the relationship between CAG repeat length and brain volume in a large cohort of pre- and post-motor onset HD gene carriers, using voxel-based morphometry (VBM), an approach which allowed us to investigate the whole brain without defining a priori regions of interest. We also used VBM to examine group differences between 20 controls, 21 premanifest, and 40 early HD subjects. In the 61 mutation-positive subjects higher CAG repeat length was significantly associated with reduced volume of the body of the caudate nucleus bilaterally, left putamen, right insula, right parahippocampal gyrus, right anterior cingulate, and right occipital lobe, after correcting for age. The group contrasts showed significant reduction in grey matter volume in the early HD group relative to controls in widespread cortical as well as subcortical areas but there was no evidence of difference between controls and premanifest subjects. Overall we have demonstrated that increased CAG repeat length is associated with atrophy in extra-striatal as well as striatal regions, which has implications for the monitoring of disease-modifying therapies in the condition.

Poster 11: Motor Symptom–Related Metabolic Network in Huntington's Disease

Objective To describe a brain metabolic network selectively expressed in symptomatic Huntington's disease (HD) gene carriers. Background A metabolic network specifically associated with HD motor symptoms may be useful in assessing new therapies. We used PET imaging and network analysis to identify a spatial covariance pattern expressed in newly symptomatic HD patients. Design/Methods We utilized serial FDG PET to study 12 presymptomatic HD gene carriers at baseline, 18, and 44 months. Four subjects became symptomatic by 44 months. Additionally, two phenoconverters and two non-phenoconverters were scanned at 68 months. To identify a symptom-related pattern, we conducted network analysis to compare the phenoconverted and non-phenoconverted scans at 44 months. Scans from 12 age-matched healthy controls were included for comparison. Results We identified an HD symptom-related metabolic covariance pattern (HDSP), which separated symptomatic and preclinical gene carriers ( p p p Conclusion The HDSP network emerged as preclinical HD subjects neared clinical onset; its expression also increased as symptoms progressed. A unique feature of the HDSP is its high sensitivity for the motor symptoms of HD. The correlation of pattern activity with clinical ratings indicates that this network may be particularly useful in assessing the emergence of HD symptoms and their response to therapy.

Poster 19: Basal Ganglia Pathology in Preclinical and Early Symptomatic Huntington's Disease: Diffusion Tensor Imaging, Magnetic Resonance Spectroscopy, and Volumetric Measures—Which Imaging Modality Is More Sensitive?

Background Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder characterized by motor, psychiatric, and cognitive dysfunction. One of the main focuses of clinical research now is to define valid and reliable biomarkers of disease onset and progression that can be of use in future treatment trials. Various neuropathological and neuroimaging studies have indicated early involvement of various components of the basal ganglia. Aim In this study, we examined the sensitivity of three magnetic resonance techniques in detecting basal ganglia pathology. Diffusion tensor imaging (DTI) is an MRI technique that measures indices of passive water diffusion, which is believed to reflect the tissue fiber density, fiber architecture, and uniformity of nerve fiber direction. Proton MRS (1H-MRS) is a non-invasive technique that allows the detection of brain chemicals that contain hydrogen, such as N-Acetyl-aspartate (NAA), choline-containing compounds (CHO), creatine/phosphocreatine (CRE), glutamine, glutamate, myoinositol (mI), and lactate (LAC). Volumetric measures of caudate and putamen can be obtained from structural MRI scans. Method We examined 25 HD gene carriers (13 preclinical and 12 early symptomatic) and 20 matched gene negative controls. The three imaging modalities were performed on each subject using a GE Signa 1.5T scanner during one scan session. Six HD gene carriers and two control subjects were scanned twice, two years apart. Clinical measures were also collected. Results The H-MRS revealed increased choline/creatine and myoinositol/creatine ratios in the basal ganglia in the symptomatic group and decreased glutamate+glutamine/creatine ratios in the preclinical group. Preliminary DTI analyses suggest reduced anisotropy, measured as fractional anisotropy in the basal ganglia. More detailed DTI results and volumetric data will be presented at the meeting. The sensitivity, limitations of, and relationship between the three MRI imaging modalities in detecting basal ganglia pathology in HD will be discussed. The combination of all three techniques may provide a more powerful tool to predict aspects of the clinical presentation.

Neuropsychological Deficits in Huntington's Disease Gene Carriers and Correlates of Early "Conversion"

Neuropsychological Deficits in Huntington's Disease Gene Carriers and Correlates of Early "Conversion"

Basal ganglia volume and clinical correlates in ‘preclinical’ Huntington’s disease

To establish differences in basal ganglia and thalamic volume between preclinical carriers and non-carriers of the Huntington's disease (HD) gene and to link the volume to motor, cognitive and behavioural characteristics in carriers. Sixteen HD gene carriers without overt clinical motor signs and 14 non-gene carriers underwent clinical evaluation and a MRI scan. Volumes of the caudate nucleus, putamen, gobus pallidus and thalamus were measured using T1-weighted MR images. Motor, cognitive and behavioural functioning was assessed using the Unified Huntington's Disease Rating Scale (UHDRS), cognitive testing and the Beck Depression Inventory (BDI-II). Volumes of the caudate nucleus, putamen and globus pallidus were significantly smaller in carriers than in non-carriers while no differences between groups were found on clinical evaluation. In gene carriers smaller globus pallidus volume was associated with more motor abnormalities. A smaller putamen volume correlated significantly with worse psychomotor function on the Symbol Digit Modalities Task and the Trail Making Test B. In line with previous research we demonstrated that basal ganglia abnormalities precede overt disease manifestation of HD. Besides we showed that smaller basal ganglia volumes are related to subtle motor abnormalities and worse psychomotor performance in gene carriers without clinical diagnosis. Motor and psychomotor measures may be suitable clinical markers in future neuroprotective trials when combined with volumetric imaging.

A novel pathogenic pathway of immune activation detectable before clinical onset in Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disorder characterized by both neurological and systemic abnormalities. We examined the peripheral immune system and found widespread evidence of innate immune activation detectable in plasma throughout the course of HD. Interleukin 6 levels were increased in HD gene carriers with a mean of 16 years before the predicted onset of clinical symptoms. To our knowledge, this is the earliest plasma abnormality identified in HD. Monocytes from HD subjects expressed mutant huntingtin and were pathologically hyperactive in response to stimulation, suggesting that the mutant protein triggers a cell-autonomous immune activation. A similar pattern was seen in macrophages and microglia from HD mouse models, and the cerebrospinal fluid and striatum of HD patients exhibited abnormal immune activation, suggesting that immune dysfunction plays a role in brain pathology. Collectively, our data suggest parallel central nervous system and peripheral pathogenic pathways of immune activation in HD.

Hypothalamic involvement in Huntington's disease: an in vivo PET study

Recent studies have shown alterations in metabolism, sleep and circadian rhythms as well as in several neuropeptides derived from the hypothalamic-pituitary axis in Huntington's disease patients; however, the pathology underlying these abnormalities is not known. Our aim was to assess in vivo D(2) receptor's loss/dysfunction and increases in microglial activation in the hypothalamus of symptomatic Huntington's disease patients and premanifest Huntington's disease gene carriers using PET with (11)C-raclopride (RAC), a specific D(2) receptor ligand and (11)C-(R)-PK11195 (PK), a marker of microglial activation. We have studied 9 symptomatic Huntington's disease patients (age = 46.8 +/- 4.7 years; mean +/- SD) and 10 premanifest Huntington's disease gene carriers (age = 41.9 +/- 8.2 years; mean +/- SD). RAC and PK findings for these subjects were compared with those of a group of normal controls (RAC, n = 9; PK, n = 10). In the symptomatic Huntington's disease group, we found a significant decrease (P = 0.0012) in mean hypothalamic RAC binding potential (BP) and a significant increase in mean hypothalamic PK BP (P = 0.0008). Similarly, a significant decrease (P = 0.0143) in mean hypothalamic RAC BP and a significant increase in mean hypothalamic PK BP (P = 0.0057) were observed in the premanifest Huntington's disease group. Hypothalamic RAC and PK BP values correlated with each other in combined Huntington's disease groups (r = -0.6180, P = 0.0048) but not with striatal RAC and PK BP values. Our data demonstrate, for the first time, significant D(2) receptor loss and microglia activation in the hypothalamus of Huntington's disease. These pathological changes occur very early in the course of the disease and may partly explain the development of commonly reported symptoms in Huntington's disease including progressive weight loss, alterations in sexual behaviour and disturbances in the wake-sleep cycle.

Implicit and explicit aspects of sequence learning in pre-symptomatic Huntington's disease

Learning deficits may be part of the early symptoms of Huntington's disease (HD). Here we characterized implicit and explicit aspects of sequence learning in 11 pre-symptomatic HD gene carriers (pHD) and 11 normal controls. Subjects moved a cursor on a digitizing tablet and performed the following tasks: SEQ: learning to anticipate the appearance of a target sequence in two blocks; VSEQ: learning a sequence by attending to the display without moving for one block, and by moving to the sequence in a successive block (VSEQ test). Explicit learning was measured with declarative scores and number of anticipatory movements. Implicit learning was measured as a strategy change reflected in movement time. By the end of SEQ, pHD had a significantly lower number of correct anticipatory movements and lower declarative scores than controls, while in VSEQ and VSEQ test these indices improved. During all three tasks, movement time changed in controls, but not in pHD. These results suggest that both explicit and implicit aspects of sequence learning may be impaired before the onset of motor symptoms. However, when attentional demands decrease, explicit, but not implicit, learning may improve.

Functional imaging of cognitive processes in Huntington’s disease and its presymptomatic mutation carriers

Cognitive deficits are among the core symptoms of patients with Huntington's disease (HD). While impaired attention, visuospatial processing, and memory can be observed during early stages of the illness, HD patients exhibit deficits in executive function on tests requiring planning, problem solving, and cognitive flexibility with progression of the disease. Cognitive dysfunction is already present in individuals who carry the HD gene mutation but remain presymptomatic for motor and cognitive disturbances. This review provides an overview and a discussion of functional neuroimaging findings on cognitive dysfunction in patients with HD and presymptomatic HD gene mutation carriers. In HD patients, currently available evidence suggests a functional deficit of multiple cortical and subcortical regions extending beyond volumetric abnormalities. Early dysfunction of lateral prefrontal and cingulate regions has been shown in individuals with presymptomatic HD, while compensatory responses of posterior brain regions may occur closer to the onset of manifest clinical symptoms. While functional neuroimaging techniques may substantially contribute to defining neurodegenerative disease phenotypes and to identifying neural biomarkers in presymptomatic individuals, the extant data on cognitive function in HD patients and HD gene carriers however is sparse and has to be expanded through further studies.

Low plasma total cholesterol in patients with Huntington’s disease and first-degree relatives

Recent studies indicate altered cholesterol homeostasis in Huntington’s disease (HD) after it was found that cultured human and mice cells expressing mutant huntingtin show reduced mRNA of cholesterol biosynthetic enzymes. Plasma total cholesterol (TC) levels have been connected to degenerative disorders, but data for HD are lacking. We estimated plasma TC in three groups of HD related subjects: (a) patients with overt symptomatology, (b) subjects with expanded CAG repeat number in the Huntington gene before disease onset, and (c) siblings or descendants of HD patients, with normal CAG repeat number. Compared to TC levels of age-matched controls, all three groups had significantly lower plasma TC levels. The expected positive correlation of TC to age, present in the control group, was absent in the whole group or the three subgroups of the HD subjects. TC of the ApoE genotype subgroups showed small, non-significant differences. In the group of patients, TC levels were not related to severity of illness, duration of illness, and presence of depression or dementia in their symptomatology, while lower TC levels were found in patients with psychotic features. The results indicate altered cholesterol homeostasis in members of families with HD patients. Low TC levels have been connected to increased suicide risk in several studies, and high suicidal ideation has been reported in both HD gene carriers and non-carriers. Although low plasma TC levels do not necessarily imply alterations in brain cholesterol levels, a more detailed study of plasma lipids in HD patients and their first-degree relatives, as well as the search for genetic factors regarding cholesterol synthesis and disposition, are warranted.

Oxidative stress parameters in plasma of Huntington's disease patients, asymptomatic Huntington’s disease gene carriers and healthy subjects

Animal data and postmortem studies suggest a role of oxidative stress in the Huntington's disease (HD), but in vivo human studies have been scarce. To assess the presence of oxidative stress in HD patients and its occurrence relative to clinical symptoms. Oxidative stress markers were determined in plasma of HD patients (n = 19), asymptomatic HD gene carriers (with > 38 CAG repeats) (n = 11) and their respective sex and agematched healthy controls (n = 47 and n = 22) in a cross-sectional study. With adjustment for age and sex, HD patients had higher plasma lipid peroxidation (LP) levels (ratio 1.20, 95% CI 1.09 to 1.32, p < 0.001) and lower reduced glutathione (GSH) levels (ratio 0.72, CI 0.55 to 0.94, p = 0.011) than their age and sex-matched controls. Although considerably younger, HD gene carriers did not differ from HD patients regarding LP and GSH levels, and had higher plasma LP (ratio 1.16, CI 1.02 to 1.32, p = 0.016) and lower GSH than their matched controls (ratio 0.73, CI 0.5 to 1.05). They had higher LP (ratio 1.18, CI 1.02 to 1.34, p = 0.019) and lower GSH (ratio 0.75, CI 0.51 to 1.11) than the healthy subjects matched to HD patients. Oxidative stress is more pronounced in HD patients and asymptomatic HD gene carriers than in healthy subjects. Differences in plasma LP and GSH are in line with the brain findings in animal models of HD. Data suggest that oxidative stress occurs before the onset of the HD symptoms.

Psychopathology in Verified Huntington's Disease Gene Carriers

Psychopathology in Verified Huntington's Disease Gene Carriers

Striatal gray matter loss in Huntington's disease is leftward biased

In Huntington's disease (HD), the distribution of pathological changes throughout the brain is incompletely understood. Some studies have identified leftward-biased lateralization, whereas others did not. We performed magnetic resonance imaging and a voxel-based asymmetry analysis in 44 right-handed HD gene carriers (presymptomatic, n = 5; stage I, n = 28; stage II, n = 11) and 44 right-handed healthy controls. The group comparison revealed leftward-biased gray matter loss in the striatum. Further analyses showed no indication of asymmetry in presymptomatic HD patients but an increase in asymmetry in the course of the HD stages under examination. Our study demonstrates and discusses leftward-biased gray matter loss in HD.

Microglial activation in presymptomatic Huntington's disease gene carriers

Microglial activation may play a role in the pathogenesis of Huntington's disease (HD). Using 11C-(R)-PK11195 (PK) positron emission tomography (PET), we investigated microglial activation in HD presymptomatic gene carriers (PGCs), its relationship with striatal neuronal dysfunction measured with 11C-raclopride (RAC) PET, and the role of PK PET as a possible marker of subclinical disease progression in PGCs. Eleven HD PGCs underwent PK and RAC PET. Their results were compared with those of healthy controls. PK and RAC binding was measured using region-of-interest analysis. Regional increases in PK binding were also localized with voxel-based statistical parametric mapping. HD PGCs had lower striatal RAC binding than the controls but significantly higher striatal and cortical PK binding. Individual levels of higher striatal PK binding in PGCs correlated with lower striatal RAC binding and, after excluding one outlier, with a higher probability of developing HD in 5 years. The inverse association between striatal PK and RAC binding in PGCs continues into early to moderate stages of HD. This study demonstrated for the first time in vivo widespread microglial activation in preclinical HD which correlated with striatal neuronal dysfunction. These findings indicate that microglial activation is an early event in the pathogenic processes of HD and is associated with subclinical progression of disease. PK PET may be a useful marker of active subclinical disease and a means of investigating the efficacy of neuroprotection strategies in PGCs.

Impairments in source memory for olfactory and visual stimuli in preclinical and clinical stages of Huntington's disease

Individuals in preclinical and clinical stages of Huntington's disease (HD) demonstrate impairments in olfactory functioning. In addition, HD patients are impaired in source memory for verbal stimuli. A task combining both source and odor memory may be particularly sensitive to early changes in HD. The present study examined source and item memory for olfactory and visual stimuli in 10 individuals with HD, 10 asymptomatic HD gene carriers, 8 nongene carriers who had a parent with HD, and 20 normal controls. During the study phase, a male and a female experimenter (sources) presented odors and objects to the participant in an alternating sequence. To assess item memory, a stimulus from the study phase (target) and a novel stimulus (distractor) were presented, and the participant was asked to choose the target. To assess source memory, the experimenter presented a stimulus and asked whether the male or female experimenter had previously presented the stimulus. Results indicate that source memory for both visual and olfactory stimuli was impaired in HD patients compared to normal controls. In asymptomatic gene carriers, however, source memory for olfactory stimuli, but not visual stimuli, was more impaired than in nongene carriers and normal controls. Furthermore, gene carriers and HD patients showed a similar degree of impairment in source memory for olfactory stimuli. The only significant impairment found in item memory was for olfactory stimuli in HD patients. These results suggest that source memory for olfactory stimuli may be particularly sensitive to neuropathological changes in preclinical stages of HD.

Brain-Derived Neurotrophic Factor Restores Synaptic Plasticity in a Knock-In Mouse Model of Huntington's Disease

Asymptomatic Huntington's disease (HD) patients exhibit memory and cognition deficits that generally worsen with age. Similarly, long-term potentiation (LTP), a form of synaptic plasticity involved in memory encoding, is impaired in HD mouse models well before motor disturbances occur. The reasons why LTP deteriorates are unknown. Here we show that LTP is impaired in hippocampal slices from presymptomatic Hdh(Q92) and Hdh(Q111) knock-in mice, describe two factors contributing to this deficit, and establish that potentiation can be rescued with brain-derived neurotrophic factor (BDNF). Baseline physiological measures were unaffected by the HD mutation, but LTP induction and, to a greater degree, consolidation were both defective. The facilitation of burst responses that normally occurs during a theta stimulation train was reduced in HD knock-in mice, as was theta-induced actin polymerization in dendritic spines. The decrease in actin polymerization and deficits in LTP stabilization were reversed by BDNF, concentrations of which were substantially reduced in hippocampus of both Hdh(Q92) and Hdh(Q111) mice. These results suggest that the HD mutation discretely disrupts processes needed to both induce and stabilize LTP, with the latter effect likely arising from reduced BDNF expression. That BDNF rescues LTP in HD knock-in mice suggests the possibility of treating cognitive deficits in asymptomatic HD gene carriers by upregulating production of the neurotrophin.

Thalamic metabolism and symptom onset in preclinical Huntington's disease.

The neural basis for the transition from preclinical to symptomatic Huntington's disease (HD) is unknown. We used serial positron emission tomography (PET) imaging in preclinical HD gene carriers (p-HD) to assess the metabolic changes that occur during this period. Twelve p-HD subjects were followed longitudinally with [11C]-raclopride and [18F]-fluorodeoxyglucose PET imaging, with scans at baseline, 18 and 44 months. Progressive declines in striatal D2-receptor binding were correlated with concurrent changes in regional metabolism and in the activity of an HD-related metabolic network. We found that striatal D2 binding declined over time (P < 0.005). The activity of a reproducible HD-related metabolic covariance pattern increased between baseline and 18 months (P < 0.003) but declined at 44 months (P < 0.04). These network changes coincided with progressive declines in striatal and thalamic metabolic activity (P < 0.01). Striatal metabolism was abnormally low at all time points (P < 0.005). By contrast, thalamic metabolism was elevated at baseline (P < 0.01), but fell to subnormal levels in the p-HD subjects who developed symptoms. These findings were confirmed with an MRI-based atrophy correction for each individual PET scan. Increases in network expression and thalamic glucose metabolism may be compensatory for early neuronal losses in p-HD. Declines in these measures may herald the onset of symptoms in gene carriers.

Imaging microglial activation in Huntington's disease

Activated microglia have been proposed to play a major role in the pathogenesis of Huntington's Disease (HD). PK11195 is a ligand which binds selectively to peripheral benzodiazepine binding sites, a type of receptor selectively expressed by activated microglia in the central nervous system. Using 11C-(R)-PK11195 positron emission tomography (PET), we have recently shown in vivo evidence of increased microglial activation in both symptomatic and presymptomatic HD gene carriers and that the degree of microglial activation in the striatum correlates with the severity of striatal dopamine D2 receptor dysfunction measured with 11C-raclopride PET. Our findings indicate that microglial activation is an early process in the HD pathology, occurring before the onset of symptoms. The close spatial and temporal relationship between microglial activation and neuronal dysfunction lends further support to the pathogenic link between the two processes in HD. Further longitudinal studies are needed to fully elucidate this link.

Saccades in presymptomatic and early stages of Huntington disease

To evaluate quantitative measures of eye movements as possible biomarkers in prediagnostic and early stages of Huntington disease (HD). The study sample (n = 215) included individuals both at risk and recently diagnosed with HD. All participants completed a uniform clinical evaluation which included administration of the Unified Huntington's Disease Rating Scale (UHDRS) by a movement disorder neurologist and molecular testing to determine HD gene status. A high resolution, video-based eye tracking system was employed to quantify measures of eye movement (error rates, latencies, SD of latencies, velocities, and accuracies) during a computerized battery of saccadic and steady fixation tasks. Prediagnostic HD gene carriers and individuals with early HD demonstrated three types of significant abnormalities while performing memory guided and anti-saccade tasks: increased error rate, increased saccade latency, and increased variability of saccade latency. The eye movement abnormalities increased with advancing motor signs of HD. Abnormalities in eye movement measures are a sensitive biomarker in the prediagnostic and early stages of Huntington disease (HD). These measures may be more sensitive to prediagnostic changes in HD than the currently employed neurologic motor assessment.

At Risk for Huntington Disease

<h3>Objective</h3> To identify the emerging clinical precursors that indicate the early onset of Huntington disease (HD) in a reliable and gene-specific manner. This information is critical for the development of therapeutic trials aimed at postponing clinical onset in HD gene carriers. <h3>Methods</h3> Between July 1999 and January 2004, 1001 adults at 50-50 risk for HD agreed to provide longitudinal clinical data and a blood DNA sample under consent provisions that require their individual clinical and genetic information to never be revealed. <h3>Results</h3> The Prospective Huntington At Risk Observational Study (PHAROS) cohort is characterized by a 2:1 predominance of women to men, high educational attainment, and gainful employment. Despite the gender disparity, the demographic, hereditary, and clinical characteristics of the female and male participants were similar. Investigators, who are unaware of individual gene status, characterized the baseline cohort to be highly functional with minimal motor or cognitive impairment; 92.3% of participants were judged to have no or nonspecific motor abnormalities; 6.7%, to have possible or probable motor signs; and only 1.0%, to have unequivocal HD. <h3>Conclusion</h3> The baseline characteristics of the PHAROS cohort make it well suited to generate objective and prospective data about gene-specific clinical precursors that can be used as outcomes in controlled trials aimed at postponing the onset of HD.