Differential diagnosis of chorea (guidelines of the German Neurological Society)

INTRODUCTION

Choreiform movement disorders are characterized by involuntary, rapid, irregular, and unpredictable movements of the limbs, face, neck, and trunk. These movements often initially go unnoticed by the affected individuals and may blend together with seemingly intended, random motions. Choreiform movements can occur both at rest and during voluntary movements. They typically increase in intensity with stress and physical activity and essentially cease during deep sleep stages. In particularly in advanced stages of Huntington disease (HD), choreiform hyperkinesia occurs alongside with dystonic postures of the limbs or trunk before they typically decrease in intensity. The differential diagnosis of HD can be complex. Here, the authors aim to provide guidance for the diagnostic process. This guidance was prepared for the German Neurological Society (DGN) for German-speaking countries.

RECOMMENDATIONS

Hereditary (inherited) and non-hereditary (non-inherited) forms of chorea can be distinguished. Therefore, the family history is crucial. However, even in conditions with autosomal-dominant transmission such as HD, unremarkable family histories do not necessarily rule out a hereditary form (e.g., in cases of early deceased or unknown parents, uncertainties in familial relationships, as well as in offspring of parents with CAG repeats in the expandable range (27-35 CAG repeats) which may display expansions into the pathogenic range).

CONCLUSIONS

The differential diagnosis of chorea can be challenging. This guidance prepared for the German Neurological Society (DGN) reflects the state of the art as of 2023.

Symptomatic treatment options for Huntington's disease (guidelines of the German Neurological Society)

INTRODUCTION

Ameliorating symptoms and signs of Huntington's disease (HD) is essential to care but can be challenging and hard to achieve. The pharmacological treatment of motor signs (e.g. chorea) may favorably or unfavorably impact other facets of the disease phenotype (such as mood and cognition). Similarly, pharmacotherapy for behavioral issues may modify the motor phenotype. Sometimes synergistic effects can be achieved. In patients undergoing pragmatic polypharmacological therapy, emerging complaints may stem from the employed medications' side effects, a possibility that needs to be considered. It is recommended to clearly and precisely delineate the targeted signs and symptoms (e.g., chorea, myoclonus, bradykinesia, Parkinsonism, or dystonia). Evidence from randomized controlled trials (RCTs) is limited. Therefore, the guidelines prepared for the German Neurological Society (DGN) for German-speaking countries intentionally extend beyond evidence from RCTs and aim to synthesize evidence from RCTs and recommendations of experienced clinicians.

RECOMMENDATIONS

First-line treatment for chorea is critically discussed, and a preference in prescription practice for using tiapride instead of tetrabenazine is noted. In severe chorea, combining two antidopaminergic drugs with a postsynaptic (e.g., tiapride) and presynaptic mode of action (e.g., tetrabenazine) is discussed as a potentially helpful strategy. Sedative side effects of both classes of compounds can be used to improve sleep if the highest dosage of the day is given at night. Risperidone, in some cases, may ameliorate irritability but also chorea and sleep disorders. Olanzapine can be helpful in the treatment of weight loss and chorea, and quetiapine as a mood stabilizer with an antidepressant effect.

CONCLUSIONS

Since most HD patients simultaneously suffer from distinct motor signs and distinct psychiatric/behavioral symptoms, treatment should be individually adapted.

Generation of two human iPSC lines from dermal fibroblasts of adult- and juvenile-onset Huntington's disease patients and two healthy donors

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a mutation in the HTT gene. To generate human-induced pluripotent stem cells (hiPSCs), we used dermal fibroblasts from 1 healthy adult control (K-Pic2), 1 HD manifest patient (M-T2), 1 healthy juvenile control (jK-N1), and 1 juvenile HD patient (jHD-V1). HD stage of patients was assessed by neurological tests and donors were without comorbidities and were non-smokers. Characterization showed that the obtained hiPSCs have the same number of CAG repeats as the parental fibroblast lines, express pluripotency markers and have the ability to differentiate into all 3 germ layers.

Generation of three human iPSC lines from patients with Huntington's disease with different CAG lengths and human control iPSC line from a healthy donor

Huntington's disease (HD) is a progressive neurodegenerative disorder with autosomal-dominant heritability that affect the central nervous system and peripheral tissues. The human-induced pluripotent stem cells (hiPSC) lines were generated from dermal fibroblasts of patients without comorbidities, non-smokers, at the pre-manifest (IIMCBi004-A), early-manifest (IIMCBi005-A), and manifest (IIMCBi006-A) HD stage assessed by neurological tests, as well as from a healthy donor (IIMCBi003-A). Characterization showed that the obtained hiPSC lines contained different CAG repeats consistent with the number of CAG repeats in original fibroblasts. Moreover, hiPSCs expressed pluripotency markers and were able to differentiate into three-germ layers in vitro.

Effect of Body Weight on Age at Onset in Huntington Disease: A Mendelian Randomization Study

Objective

Weight loss is associated with clinical progression in Huntington disease (HD), but whether body weight causally affects disease onset or progression is unknown. Therefore, we aimed to assess whether genetically determined variations in body weight are causally related to age at onset in HD.

Methods

Using data from different recent genome-wide association studies, we performed a 2-sample mendelian randomization (MR) analysis to assess whether genetic markers of body mass index (BMI) are causally related to residual age at onset in HD, i.e., the difference between observed and expected age at onset based on mutation size. Our study had a statistical power of 90% to detect a causal effect of ≥3.8 months per BMI unit change at a type I error rate of 0.05.

Results

Inverse-variance weighted MR estimates showed that a higher genetically determined BMI was not causally related to residual age at onset in HD (β = -0.44 years per unit increase in BMI, confidence interval: -1.33 to 0.46, p = 0.34). All other complementary (nonparametric) MR regression methods yielded similar results.

Conclusions

Although maintaining a healthy and stable body weight remains important in patients with HD, promoting weight gain with the aim of delaying disease onset or slowing down disease progression should be discouraged. Our findings point toward the existence of underlying pathologic processes that dictate both the rate of clinical progression and weight loss in HD, which need further elucidation as targeting these pathways, rather than body weight per se, could be of therapeutic value.

[Gene-selective treatment approaches for Huntington's disease]

In Germany at least 8000 and probably up to ca. 14,000 people currently suffer from clinically manifest Huntington's disease (HD). In addition, an estimated 24,000 Germans carry the HD mutation in the huntingtin (HTT) gene and will develop HD during their lifetime. Although HD is a rare neurodegenerative disease, it is currently in the focus of general medical interest: clinical trials have begun that provide a rational basis for hope to slow down the so far relentless progression of the disease, ultimately resulting in patients becoming entirely dependent on nursing care. If treatment is started early enough it may be possible to mitigate the clinical manifestation of HD. These innovative therapeutic approaches aim at inhibiting the de novo production of mutant HTT gene products. A first clinical drug trial to demonstrate the efficacy (phase III) of intrathecal antisense oligonucleotides (ASO, active substance RG6042) was started in 2019. Additional clinical studies on alternative treatment approaches with allele-selective ASOs as well as gene therapeutic approaches using RNA molecules and zinc finger repressor complexes are imminent. This article gives an overview of the current gene-selective therapeutic approaches in HD under discussion.

Identification of symbol digit modality test score extremes in Huntington's disease

Studying individuals with extreme phenotypes could facilitate the understanding of disease modification by genetic or environmental factors. Our aim was to identify Huntington's disease (HD) patients with extreme symbol digit modality test (SDMT) scores. We first examined in HD the contribution of cognitive measures of the Unified Huntington's Disease Rating Scale (UHDRS) in predicting clinical endpoints. The language-independent SDMT was used to identify patients performing very well or very poorly relative to their CAG and age cohort. We used data from REGISTRY and COHORT observational study participants (5,603 HD participants with CAG repeats above 39 with 13,868 visits) and of 1,006 healthy volunteers (with 2,241 visits), included to identify natural aging and education effects on cognitive measures. Separate Cox proportional hazards models with CAG, age at study entry, education, sex, UHDRS total motor score and cognitive (SDMT, verbal fluency, Stroop tests) scores as covariates were used to predict clinical endpoints. Quantile regression for longitudinal language-independent SDMT data was used for boundary (2.5% and 97.5% quantiles) estimation and extreme score analyses stratified by age, education, and CAG repeat length. Ten percent of HD participants had an extreme SDMT phenotype for at least one visit. In contrast, only about 3% of participants were consistent SDMT extremes at two or more visits. The thresholds for the one-visit and two-visit extremes can be used to classify existing and new individuals. The identification of these phenotype extremes can be useful in the search for disease modifiers.

FDG-PET underscores the key role of the thalamus in frontotemporal lobar degeneration caused by C9ORF72 mutations

C9ORF72 mutations are the most common cause of familial frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). MRI studies have investigated structural changes in C9ORF72-associated FTLD (C9FTLD) and provided first insights about a prominent involvement of the thalamus and the cerebellum. Our multicenter, ¹⁸F-fluorodeoxyglucose positron-emission tomography study of 22 mutation carriers with FTLD, 22 matched non-carriers with FTLD, and 23 cognitively healthy controls provided valuable insights into functional changes in C9FTLD: compared to non-carriers, mutation carriers showed a significant reduction of glucose metabolism in both thalami, underscoring the key role of the thalamus in C9FTLD. Thalamic metabolism did not correlate with disease severity, duration of disease, or the presence of psychotic symptoms. Against our expectations we could not demonstrate a cerebellar hypometabolism in carriers or non-carriers. Future imaging and neuropathological studies in large patient cohorts are required to further elucidate the central role of the thalamus in C9FTLD.

Biological and clinical manifestations of juvenile Huntington's disease: a retrospective analysis

BACKGROUND

Huntington's disease is a rare, neurodegenerative disease caused by an expanded CAG repeat mutation in the huntingtin gene. Compared with adult-onset Huntington's disease, juvenile Huntington's disease (onset ≤20 years) is even rarer and has not been studied extensively. We aimed to further characterise juvenile Huntington's disease by examining the effect of CAG repeat size on disease presentation, progression, and survival.

METHODS

We did a retrospective analysis of patients with juvenile Huntington's disease aged 20 years or younger, according to the length of their CAG repeat and who had disabling psychiatric symptoms (with motor symptoms) or motor symptoms alone, and of patients with adult-onset Huntington's disease manifesting aged 30-60 years with 40 or more CAG repeats, from the REGISTRY and ENROLL-HD platforms and from two institutional databases (Lega Italiana Ricerca Huntington Foundation and the Instituto Neurociencias de Buenos Aires and the Sanatorio de la Trinidad Mitre). Patients with psychiatric but no motor symptoms were excluded. We compared symptoms at onset and longitudinally in patients with juvenile Huntington's disease with highly expanded (HE subgroup) or low expansion (LE subgroup) mutations, grouped by hierarchical clustering analysis. We also compared disease progression (longitudinal change in Unified Huntington's Disease Rating Scale-Total Motor Score) and survival of patients with juvenile and adult-onset Huntington's disease.

FINDINGS

We extracted medical records from 580 patients entered into the studies or databases between June 23, 2004, and March 31, 2018, of whom 36 patients met our definition of juvenile Huntington's disease and 197 for adult-onset Huntington's disease. According to caregiver reports, gait disturbance was more often a first presenting symptom in the HE subgroup (eight [80%] of 10 patients) than in the LE subgroup (seven [27%] of 26 patients; p=0·0071), whereas loss of hand dexterity was more common in the LE subgroup (11 [42%] of 26 patients) than in the HE subgroup (0 [0%] of 10 patients; p=0·0160). Compared with the LE subgroup, development delay (0 [0%] in the LE subgroup vs nine [90%] in the HE subgroup; p<0·0001), severe gait impairment (nine [35%] in the LE subgroup vs nine [90%] in the HE subgroup; p=0·0072), and seizures (three [11%] in the LE subgroup vs eight [80%] in the HE subgroup; p<0·0001) prevailed over time in the HE subgroup. Disease progression was more rapid in juvenile Huntington's disease (n=14) than in adult-onset Huntington's disease (n=52; generalised estimating equation model, p=0·0003). Of 121 deceased patients, median survival was shorter in the juvenile Huntington's disease (n=17) cohort than in adult-onset Huntington's disease (n=104) cohort (hazard ratio 2·18 [95% CI 1·08-4·40]; p=0·002).

INTERPRETATION

Patients with HE juvenile Huntington's disease differ clinically from patients with LE juvenile Huntington's disease or adult-onset Huntington's disease, suggesting reclassification of this particularly aggressive form of Huntington's disease might be required.

FUNDING

Lega Italiana Ricerca Huntington Foundation and IRCCS Ospedale Casa Sollievo della Sofferenza.

Altered Ca(2+) signaling in skeletal muscle fibers of the R6/2 mouse, a model of Huntington's disease

Huntington's disease (HD) is caused by an expanded CAG trinucleotide repeat within the gene encoding the protein huntingtin. The resulting elongated glutamine (poly-Q) sequence of mutant huntingtin (mhtt) affects both central neurons and skeletal muscle. Recent reports suggest that ryanodine receptor-based Ca(2+) signaling, which is crucial for skeletal muscle excitation-contraction coupling (ECC), is changed by mhtt in HD neurons. Consequently, we searched for alterations of ECC in muscle fibers of the R6/2 mouse, a mouse model of HD. We performed fluorometric recordings of action potentials (APs) and cellular Ca(2+) transients on intact isolated toe muscle fibers (musculi interossei), and measured L-type Ca(2+) inward currents on internally dialyzed fibers under voltage-clamp conditions. Both APs and AP-triggered Ca(2+) transients showed slower kinetics in R6/2 fibers than in fibers from wild-type mice. Ca(2+) removal from the myoplasm and Ca(2+) release flux from the sarcoplasmic reticulum were characterized using a Ca(2+) binding and transport model, which indicated a significant reduction in slow Ca(2+) removal activity and Ca(2+) release flux both after APs and under voltage-clamp conditions. In addition, the voltage-clamp experiments showed a highly significant decrease in L-type Ca(2+) channel conductance. These results indicate profound changes of Ca(2+) turnover in skeletal muscle of R6/2 mice and suggest that these changes may be associated with muscle pathology in HD.

Fat-free mass and its predictors in Huntington's disease

The causes of weight loss in Huntington's disease (HD) are not entirely clear. The aim was to identify risk factors that are associated with a loss of metabolically active tissues, i.e. fat-free mass. A consecutive cohort of non-diabetic HD participants (manifest HD, n = 43; CAG: mean 43.6.0 ± 3.6; preHD, n = 10; CAG: mean 41.4 ± 1.4) and 36 healthy controls was recruited. Twenty-five HD participants were early-stage HD (UHDRS Total Functional Capacity [TFC] stages I and II), 12 mid-stage HD (TFC stage III), and 6 participants were in late-stage HD (TFC stages IV and V). Food intake, basic metabolic rate and glucose homeostasis were assessed. In addition, fat-free mass was determined using bioelectric impedance analysis, and leptin, insulin and ghrelin as key metabolic regulators. Sex ratio and age were similar in HD participants (71 % women; age 50.6 ± 10.9) and controls (66 % women; age 46.4 ± 14.5). Body mass index (BMI) was lower in HD participants than controls (median 24.1 vs. 25.9, p = 0.04). However, fat-free mass and basic metabolic rate were not statistically different between groups and showed no association with disease burden. In controls and HD participants, leptin was the most important predictor of fat-free mass. While BMI was lower in HD participants, fat-free mass was similar to controls with leptin as its most important predictor. Leptin levels and fat-free mass measurements using bioelectric impedance analysis may be good screening tools to identify HD patients at risk for weight loss.

Abnormal resting-state connectivity of motor and cognitive networks in early manifest Huntington's disease

BACKGROUND

Functional magnetic resonance imaging (fMRI) of multiple neural networks during the brain's 'resting state' could facilitate biomarker development in patients with Huntington's disease (HD) and may provide new insights into the relationship between neural dysfunction and clinical symptoms. To date, however, very few studies have examined the functional integrity of multiple resting state networks (RSNs) in manifest HD, and even less is known about whether concomitant brain atrophy affects neural activity in patients.

METHOD

Using MRI, we investigated brain structure and RSN function in patients with early HD (n = 20) and healthy controls (n = 20). For resting-state fMRI data a group-independent component analysis identified spatiotemporally distinct patterns of motor and prefrontal RSNs of interest. We used voxel-based morphometry to assess regional brain atrophy, and 'biological parametric mapping' analyses to investigate the impact of atrophy on neural activity.

RESULTS

Compared with controls, patients showed connectivity changes within distinct neural systems including lateral prefrontal, supplementary motor, thalamic, cingulate, temporal and parietal regions. In patients, supplementary motor area and cingulate cortex connectivity indices were associated with measures of motor function, whereas lateral prefrontal connectivity was associated with cognition.

CONCLUSIONS

This study provides evidence for aberrant connectivity of RSNs associated with motor function and cognition in early manifest HD when controlling for brain atrophy. This suggests clinically relevant changes of RSN activity in the presence of HD-associated cortical and subcortical structural abnormalities.

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.

Visual system integrity and cognition in early Huntington's disease

Posterior cortical volume changes and abnormal visuomotor performance are present in patients with Huntington's disease (HD). However, it is unclear whether posterior cortical volume loss contributes to abnormal neural activity, and whether activity changes predict cognitive dysfunction. Using magnetic resonance imaging (MRI), we investigated brain structure and visual network activity at rest in patients with early HD (n = 20) and healthy controls (n = 20). The symbol digit modalities test (SDMT) and subtests of the Visual Object and Space Perception Battery were completed offline. For functional MRI data, a group independent component analysis was used. Voxel-based morphometry was employed to assess regional brain atrophy, and 'biological parametric mapping' analyses were included to investigate the impact of atrophy on neural activity. Patients showed significantly worse visuomotor and visual object performance than controls. Structural analyses confirmed occipitotemporal atrophy. In patients and controls, two spatiotemporally distinct visual systems were identified. Patients showed decreased activity in the left fusiform cortex, and increased left cerebellar activity. These findings remained stable after correction for brain atrophy. Lower fusiform cortex activity was associated with lower SDMT performance and with higher disease burden scores. These associations were absent when cerebellar function was related to task performance and disease burden. The results of this study suggest that regionally specific functional abnormalities of the visual system can account for the worse visuomotor cognition in HD patients. However, occipital volume changes cannot sufficiently explain abnormal neural function in these patients.

CAG repeat expansion in Huntington disease determines age at onset in a fully dominant fashion

OBJECTIVE

Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs.

METHODS

We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression.

RESULTS

An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a well-behaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele.

CONCLUSIONS

Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors.

Fully automated atlas-based MR imaging volumetry in Huntington disease, compared with manual volumetry

BACKGROUND AND PURPOSE

The atrophy of the caudate is considered the hallmark of HD-associated neurodegeneration and has high potential as a biomarker in structural MR imaging. This study aimed at comparing automated and manual caudate volumetry.

MATERIALS AND METHODS

In this cross-sectional volumetric study in 40 patients with HD and 30 healthy controls, a fully automated caudate measurement by ABV was used for the first time in HD and was directly compared with manual delineation as the generally accepted criterion standard of volumetry.

RESULTS

It could be shown that both techniques were able to separate patients and controls to a similar degree. The differences between the 2 volumetric measurements ranged within the limits of agreement; the systematically lower values by manual volumetry were caused by the different assessment of the dorsal caudate tail, which is hard to delineate manually.

CONCLUSIONS

ABV may be used instead of manual volumetry to quantify caudate volume loss. Additionally, the ABV technique has the advantage of being much faster, is less laborious, and is free of a subjective region-of interest definition. ABV might serve as a tool in potential future clinical trials of disease-modifying treatments in HD.

Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): somatosensory abnormalities in 1236 patients with different neuropathic pain syndromes

Neuropathic pain is accompanied by both positive and negative sensory signs. To explore the spectrum of sensory abnormalities, 1236 patients with a clinical diagnosis of neuropathic pain were assessed by quantitative sensory testing (QST) following the protocol of DFNS (German Research Network on Neuropathic Pain), using both thermal and mechanical nociceptive as well as non-nociceptive stimuli. Data distributions showed a systematic shift to hyperalgesia for nociceptive, and to hypoesthesia for non-nociceptive parameters. Across all parameters, 92% of the patients presented at least one abnormality. Thermosensory or mechanical hypoesthesia (up to 41%) was more frequent than hypoalgesia (up to 18% for mechanical stimuli). Mechanical hyperalgesias occurred more often (blunt pressure: 36%, pinprick: 29%) than thermal hyperalgesias (cold: 19%, heat: 24%), dynamic mechanical allodynia (20%), paradoxical heat sensations (18%) or enhanced wind-up (13%). Hyperesthesia was less than 5%. Every single sensory abnormality occurred in each neurological syndrome, but with different frequencies: thermal and mechanical hyperalgesias were most frequent in complex regional pain syndrome and peripheral nerve injury, allodynia in postherpetic neuralgia. In postherpetic neuralgia and in central pain, subgroups showed either mechanical hyperalgesia or mechanical hypoalgesia. The most frequent combinations of gain and loss were mixed thermal/mechanical loss without hyperalgesia (central pain and polyneuropathy), mixed loss with mechanical hyperalgesia in peripheral neuropathies, mechanical hyperalgesia without any loss in trigeminal neuralgia. Thus, somatosensory profiles with different combinations of loss and gain are shared across the major neuropathic pain syndromes. The characterization of underlying mechanisms will be needed to make a mechanism-based classification feasible.

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 Huntington's 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.

Normal and mutant HTT interact to affect clinical severity and progression in Huntington disease

OBJECTIVE

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG repeat expansion in the HD gene (HTT). We aimed to assess whether interaction between CAG repeat sizes in the mutant and normal allele could affect disease severity and progression.

METHODS

Using linear regression and mixed-effects models, the influence of mutant and normal CAG repeat sizes interaction was assessed on 1) age at onset in 921 patients with HD, 2) clinical severity and progression in 512 of these patients with follow-up data available, and 3) basal ganglia volume on magnetic resonance images in 16 premanifest HD mutation carriers.

RESULTS

Normal and mutant CAG repeat sizes interacted to influence 1) age at onset (p = 0.001), 2) severity or progression of motor, cognitive, and functional, but not behavioral, symptoms in patients with HD (all p < 0.05), and 3) in premanifest subjects, basal ganglia volumes (p < 0.05). In subjects with mutant CAG expansions in the low range, increasing size of the normal repeat correlated with more severe symptoms and pathology, whereas for those subjects with expansions in the high range, increasing size of the normal repeat correlated with less severe symptoms and pathology.

CONCLUSIONS

Increasing CAG repeat size in normal HTT diminishes the association between mutant CAG repeat size and disease severity and progression in Huntington disease. The underlying mechanism may involve interaction of the polyglutamine domains of normal and mutant huntingtin (fragments) and needs further elucidation. These findings may have predictive value and are essential for the design and interpretation of future therapeutic trials.

Cortical dysfunction in patients with Huntington's disease during working memory performance

Previous functional neuroimaging studies on executive function suggested multiple functionally aberrant cortical regions in patients with Huntington's disease (HD). However, little is known about the neural mechanisms of working memory (WM) function in this patient population. The objective of this study was to investigate the functional neuroanatomy of WM in HD patients. We used event-related functional magnetic resonance imaging and a parametric verbal WM task to investigate cerebral function during WM performance in 16 healthy control subjects and 12 mild to moderate stage HD patients. We excluded incorrectly performed trials to control for potential accuracy-related activation confounds. Voxel-based morphometry (VBM) was used to control for confounding cortical and subcortical atrophy. We found that HD patients were slower and less accurate than healthy controls across all WM load levels. In addition, HD patients showed lower activation in the left dorso- and ventrolateral prefrontal cortex, the left inferior parietal cortex, the left putamen, and the right cerebellum at high WM load levels only. VBM revealed gray matter differences in the bilateral caudate nucleus and the thalamus, as well as in inferior parietal and right lateral prefrontal regions. However, volumetric abnormalities in the patient group did not affect the activation differences obtained during WM task performance. These findings demonstrate that WM-related functional abnormalities in HD patients involve distinct WM network nodes associated with cognitive control and subvocal rehearsal. Moreover, aberrant cortical function in HD patients may occur in brain regions, which are relatively well preserved in terms of brain atrophy.

Weight loss in Huntington disease increases with higher CAG repeat number

OBJECTIVE

Huntington disease (HD) is a hereditary neurodegenerative disorder caused by an expanded number of CAG repeats in the huntingtin gene. A hallmark of HD is unintended weight loss, the cause of which is unknown. In order to elucidate the underlying mechanisms of weight loss in HD, we studied its relation to other disease characteristics including motor, cognitive, and behavioral disturbances and CAG repeat number.

METHODS

In 517 patients with early stage HD, we applied mixed-effects model analyses to correlate weight changes over 3 years to CAG repeat number and various components of the Unified Huntington's Disease Rating Scale (UHDRS). We also assessed the relation between CAG repeat number and body weight and caloric intake in the R6/2 mouse model of HD.

RESULTS

In patients with HD, mean body mass index decreased with -0.15 units per year (p < 0.001). However, no single UHDRS component, including motor, cognitive, and behavioral scores, was independently associated with the rate of weight loss. Patients with HD with a higher CAG repeat number had a faster rate of weight loss. Similarly, R6/2 mice with a larger CAG repeat length had a lower body weight, whereas caloric intake increased with larger CAG repeat length.

CONCLUSIONS

Weight loss in Huntington disease (HD) is directly linked to CAG repeat length and is likely to result from a hypermetabolic state. Other signs and symptoms of HD are unlikely to contribute to weight loss in early disease stages. Elucidation of the responsible mechanisms could lead to effective energy-based therapeutics.

[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.

Myopathy as a first symptom of Huntington's disease in a Marathon runner

A semi professional marathon runner at risk for Huntington's disease (HD) (43 CAG repeats) developed signs of a slowly progressive myopathy with exercise-induced muscle fatigue, pain, elevated creatine kinase level, and worsening of his running performance many years before first signs of chorea were detected. Muscle biopsy displayed a mild myopathy with mitochondrial pathology including a complex IV deficiency and analysis of the patient's fibroblast culture demonstrated deficits in mitochondrial function. Challenging skeletal muscle by excessive training might have disclosed myopathy in HD even years before the appearance of other neurological symptoms.

Radiosynthesis and evaluation of [11C]BTA-1 and [11C]3'-Me-BTA-1 as potential radiotracers for in vivo imaging of beta-amyloid plaques

AIM

To evaluate the in vitro and in vivo characteristics of [N-methyl-(11)C]2-(4'-(methylaminophenyl)-benzothiazole ([(11)C]BTA-1) as well as [N-methyl-(11)C]2-(3'-methyl-4'-(methylamino)phenyl)-benzothiazole ([(11)C]3'-Me-BTA-1) as diagnostic markers of amyloid-beta (Abeta) in Alzheimer's disease (AD).

MATERIAL, METHODS

Brain uptake and clearance was determined in wild-type mice. Binding affinities (K(i)) of [(11)C]BTA-1 and [(11)C]3'-Me-BTA-1 for aggregated Abeta(1-40) fibrils were assessed. Autoradiography was performed on brain sections of AD patients. To demonstrate binding specificity in vivo BTA-1 was injected i.p. in transgenic mice (Tg2576). Brain sections were analysed consecutively. Additionally, a [(11)C]BTA-1 PET study of an AD patient and a healthy control was performed.

RESULTS

In mice brain uptake and clearance of [(11)C]BTA-1 is compatible with the half life of (11)C (2 min: 12.7 % ID/g; 30 min: 4.6% ID/g). In contrast clearance rate of [(11)C]3'-Me-BTA-1 is too slow (2 min 4% ID/g; 30 min 12% ID/g) to achieve sufficient clearance of free and non specifically bound radioactivity. K(i) of [(11)C]BTA-1 is 11 nmol/l and that of [(11)C]3'-Me-BTA-1 27 nmol/l. Both radioligands label Abeta selectively and specifically in AD patients and transgenic mice in vitro. The in vivo stained brain sections show a labelling of Abeta plaques. The AD patient has a higher prefrontal, parietal and striatal [(11)C]BTA-1 accumulation than the healthy control. Metabolite analysis revealed approximately 75% intact [(11)C]BTA-1 after 30min in plasma.[(11)C]BTA-1 is favourable for in vivo imaging of Abeta due to its rapid brain entry, sufficient clearance and good binding affinity for Abeta.

CONCLUSION

The ability to label Abeta plaques in vivo in human subjects supports the suitability of [(11)C]BTA-1 as a plaque imaging agent.

Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): Standardized protocol and reference values

The nationwide multicenter trials of the German Research Network on Neuropathic Pain (DFNS) aim to characterize the somatosensory phenotype of patients with neuropathic pain. For this purpose, we have implemented a standardized quantitative sensory testing (QST) protocol giving a complete profile for one region within 30 min. To judge plus or minus signs in patients we have now established age- and gender-matched absolute and relative QST reference values from 180 healthy subjects, assessed bilaterally over face, hand and foot. We determined thermal detection and pain thresholds including a test for paradoxical heat sensations, mechanical detection thresholds to von Frey filaments and a 64 Hz tuning fork, mechanical pain thresholds to pinprick stimuli and blunt pressure, stimulus/response-functions for pinprick and dynamic mechanical allodynia, and pain summation (wind-up ratio). QST parameters were region specific and age dependent. Pain thresholds were significantly lower in women than men. Detection thresholds were generally independent of gender. Reference data were normalized to the specific group means and variances (region, age, gender) by calculating z-scores. Due to confidence limits close to the respective limits of the possible data range, heat hypoalgesia, cold hypoalgesia, and mechanical hyperesthesia can hardly be diagnosed. Nevertheless, these parameters can be used for group comparisons. Sensitivity is enhanced by side-to-side comparisons by a factor ranging from 1.1 to 2.5. Relative comparisons across body regions do not offer advantages over absolute reference values. Application of this standardized QST protocol in patients and human surrogate models will allow to infer underlying mechanisms from somatosensory phenotypes.

An isoform of ataxin-3 accumulates in the nucleus of neuronal cells in affected brain regions of SCA3 patients

Autosomal dominant spinocerebellar ataxias (SCA) form a group of clinically and genetically heterogeneous neurodegenerative disorders. The defect responsible for SCA3/Machado-Joseph disease (MJD) has been identified as an unstable and expanded (CAG)n trinucleotide repeat in the coding region of a novel gene of unknown function. The MJD1 gene product, ataxin-3, exists in several isoforms. We generated polyclonal antisera against an alternate carboxy terminus of ataxin-3. This isoform, ataxin-3c, is expressed as a protein of approximately 42 kDa in normal individuals but is significantly enlarged in affected patients confirming that the CAG repeat is part of the ataxin-3c isoform and is translated into a polyglutamine stretch, a feature common to all known CAG repeat disorders. Ataxin-3 like immunoreactivity was observed in all human brain regions and peripheral organs studied. In neuronal cells of control individuals, ataxin-3c was expressed cytoplasmatically and had a somatodendritic and axonal distribution. In SCA3 patients, however, C-terminal ataxin-3c antibodies as well as anti-ataxin-3 monoclonal antibodies (1 H9) and anti-ubiquitin antibodies detected intranuclear inclusions (NIs) in neuronal cells of affected brain regions. A monoclonal antibody, 2B6, directed against an internal part of the protein, barely detected these NIs implying proteolytic cleavage of ataxin-3 prior to its transport into the nucleus. These findings provide evidence that the alternate isoform of ataxin-3 is involved in the pathogenesis of SCA3/MJD. Intranuclear protein aggregates appear as a common feature of neurodegenerative polyglutamine disorders.