Carsten Saft

Mitochondrial impairment in patients and asymptomatic mutation carriers of Huntington's disease

Huntingtons disease (HD) is an autosomal dominantly inherited neurodegenerative disorder caused by a CAG repeat expansion in the IT‐15 gene; however, it remains unknown how the mutation leads to selective neurodegeneration. Several lines of evidence suggest impaired mitochondrial function as a component of the neurodegenerative process in HD. We assessed energy metabolism in the skeletal muscle of 15 HD patients and 12 asymptomatic mutation carriers in vivo using 31P magnetic resonance spectroscopy. Phosphocreatine recovery after exercise is a direct measure of ATP synthesis and was slowed significantly in HD patients and mutation carriers in comparison to age‐ and gender‐matched healthy controls. We found that oxidative function is impaired to a similar extent in manifest HD patients and asymptomatic mutation carriers. Our findings suggest that mitochondrial dysfunction is an early and persistent component of the pathophysiology of HD.

NR2A and NR2B receptor gene variations modify age at onset in Huntington disease

Abstract. N -Methyl- d -aspartate (NMDA) receptor-mediated excitotoxicity has been proposed to play a role in the pathogenesis of Huntington disease (HD), an autosomal dominantly inherited disorder associated with defined expansions in a stretch of perfect CAG repeats in the 5′ part of the IT15 gene. The number of CAG repeat units is highly predictive for the age at onset (AO) in HD. However, AO is only modestly correlated with repeat length when the HD expansion range is in the high 30s or low 40s. Therefore, we investigated whether the genes for the different subunits composing the multimeric complexes of NMDA receptors (GRIN glutamate receptor, ionotropic, N -methyl- d -aspartate) represent candidates for modulating the AO of HD. In the studied cohort of 167 HD patients, the repeat range from 41 to 45 CAG units accounted for 30.8% of the variance in AO; 12.3% additional variance could be attributed to GRIN2B genotype variation and 4.5% to GRIN2A genotype variation. We conclude that these two genes, coding for NR2B and NR2A subtypes mainly expressed in the striatum, may influence the variability in AO of HD. Neuroprotective strategies for HD patients and persons at risk should be reconsidered in the light of these findings.

Efficacy of Fumaric Acid Esters in the R6/2 and YAC128 Models of Huntington's Disease

Huntingtons disease (HD) is an autosomal dominantly inherited progressive neurodegenerative disease. The exact sequel of events finally resulting in neurodegeneration is only partially understood and there is no established protective treatment so far. Some lines of evidence speak for the contribution of oxidative stress to neuronal tissue damage. The fumaric acid ester dimethylfumarate (DMF) is a new disease modifying therapy currently in phase III studies for relapsing-remitting multiple sclerosis. DMF potentially exerts neuroprotective effects via induction of the transcription factor “nuclear factor E2-related factor 2” (Nrf2) and detoxification pathways. Thus, we investigated here the therapeutic efficacy of DMF in R6/2 and YAC128 HD transgenic mice which mimic many aspects of HD and are characterized by an enhanced generation of free radicals in neurons. Treatment with DMF significantly prevented weight loss in R6/2 mice between postnatal days 80–90. At the same time, DMF treatment led to an attenuated motor impairment as measured by the clasping score. Average survival in the DMF group was 100.5 days vs. 94.0 days in the placebo group. In the histological analysis on day 80, DMF treatment resulted in a significant preservation of morphologically intact neurons in the striatum as well as in the motor cortex. DMF treatment resulted in an increased Nrf2 immunoreactivity in neuronal subpopulations, but not in astrocytes. These beneficial effects were corroborated in YAC128 mice which, after one year of DMF treatment, also displayed reduced dyskinesia as well as a preservation of neurons. In conclusion, DMF may exert beneficial effects in mouse models of HD. Given its excellent side effect profile, further studies with DMF as new therapeutic approach in HD and other neurodegenerative diseases are warranted.

Pridopidine for the treatment of motor function in patients with Huntington's disease (MermaiHD): a phase 3, randomised, double-blind, placebo-controlled trial

BACKGROUND Huntingtons disease is a progressive neurodegenerative disorder, characterised by motor, cognitive, and behavioural deficits. Pridopidine belongs to a new class of compounds known as dopaminergic stabilisers, and results from a small phase 2 study in patients with Huntingtons disease suggested that this drug might improve voluntary motor function. We aimed to assess further the effects of pridopidine in patients with Huntingtons disease. METHODS We undertook a 6 month, randomised, double-blind, placebo-controlled trial to assess the efficacy of pridopidine in the treatment of motor deficits in patients with Huntingtons disease. Our primary endpoint was change in the modified motor score (mMS; derived from the unified Huntingtons disease rating scale) at 26 weeks. We recruited patients with Huntingtons disease from 32 European centres; patients were aged 30 years or older and had an mMS of 10 points or greater at baseline. Patients were randomly assigned (1:1:1) to receive placebo, 45 mg per day pridopidine, or 90 mg per day pridopidine by use of centralised computer-generated codes. Patients and investigators were masked to treatment assignment. We also assessed the safety and tolerability profile of pridopidine. For our primary analysis, all patients were eligible for inclusion in our full analysis set, in which we used the last observation carried forward method for missing values. We used an analysis of covariance model and the Bonferroni method to adjust for multiple comparisons. We used a prespecified per-protocol population as our sensitivity analysis. The α level was 0·025 for our primary analysis and 0·05 overall. This trial is registered with ClinicalTrials.gov, number NCT00665223. FINDINGS At 26 weeks, in our full analysis set the difference in mean mMS was -0·99 points (97·5% CI -2·08 to 0·10, p=0·042) in patients who received 90 mg per day pridopidine (n=145) versus those who received placebo (n=144), and -0·36 points (-1·44 to 0·72, p=0·456) in those who received 45 mg per day pridopidine (n=148) versus those who received placebo. At the 90 mg per day dose, in our per-protocol population (n=114), the reduction in the mMS was of -1·29 points (-2·47 to -0·12; p=0·014) compared with placebo (n=120). We did not identify any changes in non-motor endpoints at either dose. Pridopidine was well tolerated and had an adverse event profile similar to that of placebo. INTERPRETATION This study did not provide evidence of efficacy as measured by the mMS, but a potential effect of pridopidine on the motor phenotype of Huntingtons disease merits further investigation. Pridopidine up to 90 mg per day was well tolerated in patients with Huntingtons disease. FUNDING NeuroSearch A/S.

PGC-1alpha as modifier of onset age in Huntington disease

Although there is a strong correlation between CAG repeat length and age at onset (AO) of motor symptoms, individual Huntington disease (HD) patients may differ dramatically in onset age and disease manifestations despite similar CAG repeat lengths. This has led to a search for genetic factors that influence AO. In order to identify such a genetic modifier, we analysed polymorphisms in the PGC-1alpha gene. Recent data indicate inhibition of PGC-1alpha function by mutant Htt supporting a link between transcriptional deregulation and mitochondrial dysfunction in HD. In > 400 HD patients, a polymorphism located within intron 2, a potential recombination hot spot, explains a small, but statistically significant, amount of the variability in AO. Our data suggest that PGC-1alpha has modifying effects on the pathogenic process in HD.

Severe ultrastructural mitochondrial changes in lymphoblasts homozygous for Huntington disease mutation

Mutated huntingtin is expressed in nervous and non nervous system included lymphoblasts. Eneregetic metabolism is impaired in Huntingtons disease (HD) and other neurodegenerative diseases. Human HD lymphoblasts have provided clear-cut data on mitochondnal disruption. Here we report morphological, morphometric and membrane potential differences in mitochondria from lymphoblasts obtained from patients homozygous and heterozygous for the CAG mutation, and controls. Homozygotes, who despite a similar age at onset show a more aggressive phenotype than heterozygotes, had giant mitochondria and a reduced membrane potential. We argue that early mitochondrial impairment at basal level may affect the severity of HD progression in patients.

Mechanisms mediating parallel action monitoring in fronto-striatal circuits.

Flexible response adaptation and the control of conflicting information play a pivotal role in daily life. Yet, little is known about the neuronal mechanisms mediating parallel control of these processes. We examined these mechanisms using a multi-methodological approach that integrated data from event-related potentials (ERPs) with structural MRI data and source localisation using sLORETA. Moreover, we calculated evoked wavelet oscillations. We applied this multi-methodological approach in healthy subjects and patients in a prodromal phase of a major basal ganglia disorder (i.e., Huntingtons disease), to directly focus on fronto-striatal networks. Behavioural data indicated, especially the parallel execution of conflict monitoring and flexible response adaptation was modulated across the examined cohorts. When both processes do not co-incide a high integrity of fronto-striatal loops seems to be dispensable. The neurophysiological data suggests that conflict monitoring (reflected by the N2 ERP) and working memory processes (reflected by the P3 ERP) differentially contribute to this pattern of results. Flexible response adaptation under the constraint of high conflict processing affected the N2 and P3 ERP, as well as their delta frequency band oscillations. Yet, modulatory effects were strongest for the N2 ERP and evoked wavelet oscillations in this time range. The N2 ERPs were localized in the anterior cingulate cortex (BA32, BA24). Modulations of the P3 ERP were localized in parietal areas (BA7). In addition, MRI-determined caudate head volume predicted modulations in conflict monitoring, but not working memory processes. The results show how parallel conflict monitoring and flexible adaptation of action is mediated via fronto-striatal networks. While both, response monitoring and working memory processes seem to play a role, especially response selection processes and ACC-basal ganglia networks seem to be the driving force in mediating parallel conflict monitoring and flexible adaptation of actions.

Autonomic nervous system function in Huntington's disease

Objective: To investigate whether Huntingtons disease (HD) affects autonomic nervous system (ANS) functioning. Methods: Twenty patients with HD who had positive genetic test results underwent standardised ANS function tests including sympathetic skin responses (SSRs) of the hands and feet, measurements of heart rate variability (HRV), both during five minutes of resting and deep respiration, and an orthostatic blood pressure test. Patients were classified according to the motor subscale of the unified Huntingtons disease rating scale (UHDRS; mean (SD) score 26.4 (13.6)) and divided into two subgroups: UHDRS <25 points (early stages, E-HD) and UHDRS ≥25 points (mid stages, M-HD). Autonomic indices were compared with those obtained for a group of well matched healthy controls (n=60). Results: Overall, patients showed lower HRV indices than controls. Multivariate analysis with the independent factor of “group” (controls, E-HD, M-HD) showed a significant group effect on both the high frequency power (F=4.32, p=0.017) and the coefficient of variation (F=4.23, p=0.018), indicating a significant reduction in vagal modulation in the M-HD group. There was a shift in autonomic neurocardiac balance towards sympathetic predominance in the M-HD group compared with controls (F=2.89, p=0.062). Moreover, we found an inverse correlation between the severity of clinical HD symptoms (assessed by the UHDRS) and the modulation of cardiovagal activity (p=0.028). Vagal dysregulation was present in two patients; one of them also showed a pathological blood pressure test and a latency prolongation in the SSRs of the hands. Two other patients had pathologically reduced SSR amplitudes. Only patients of the M-HD group were affected. Conclusion: Autonomic dysfunction is present even in the middle stages of HD and affects both the sympathetic and parasympathetic branch of the ANS.

Response inhibition in Huntington's disease : A study using ERPs and sLORETA

Huntingtons disease (HD) is an autosomal dominant inherited neurodegenerative disorder, with neurodegeneration mainly affecting the striatum. We investigated executive functions related to response inhibition in (HD) and healthy controls by means of event-related potentials (ERP) in a simple Go/Nogo-task. In Nogo as opposed to Go trials two fronto-central ERP components are elicited: the Nogo-N2 and Nogo-P3. These components are supposed to depend on (medial) prefrontal regions, especially the anterior cingulate cortex (ACC). The results show that the Nogo-N2 did not differ between the groups, while the Nogo-P3 demonstrated a strong attenuation in the HD-group, which also showed more false alarms in the Nogo-condition. Using sLORETA it is shown that this attenuation was related to the medial frontal cortex, especially the ACC, and superior frontal cortex areas. Moreover, the attenuation was related to the underlying genetic disease load (CAG-index). The decline in inhibition is likely mediated via a dysfunction in the ACC, which is known to be dysfunctional in HD. Moreover, the results may be interpreted that the decline in response inhibition in HD is gene-associated. The differentially affected Nogo-components suggest that they rely on different neuronal circuits, even within the ACC. For HD this suggests that this structure is not entirely dysfunctional.

Stimulus-Response Compatibility in Huntington's Disease: A Cognitive-Neurophysiological Analysis

The basal ganglia are assumed to be of importance in action/response selection, but results regarding the importance are contradictive. We investigate these processes in relation to attentional processing using event-related potentials (ERPs) in Huntingtons disease (HD), an autosomal genetic disorder expressed by degeneration of the basal ganglia, using a flanker task. A symptomatic HD group, a presymptomatic HD group (pHD), and healthy controls were examined. In the behavioral data, we found a general response slowing in HD while the compatibility effect was the same for all groups. The ERP data show a decrease of the N1 on the flanker in HD and pHD; this suggests deficient attentional processes. The N1 on the target was unaffected, suggesting that the attentional system in HD is not entirely deficient. The early lateralized readiness potential (LRP), reflecting automatic response activation due to the flankers, was unchanged, whereas the late LRP, reflecting controlled response selection due to the target information, was delayed in HD. Thus levels of action-selection processes are differentially affected in HD with automatic processes seeming to be more robust against neurodegeneration. The N2, usually associated with conflict processing, was reduced in the HD but not in the pHD and the control groups. Because the N2 was related to the LRP and reaction times in all groups, the N2 may generally not be related to conflict but rather to controlled response selection, which is impaired in HD. Overall, the results suggest alterations in attentional control, conflict processing, and controlled response selection in HD but not in automatic response selection.