Alan L Whone

Parkinson's disease-associated mutant VPS35 causes mitochondrial dysfunction by recycling DLP1 complexes.

Mitochondrial dysfunction represents a critical step during the pathogenesis of Parkinsons disease (PD), and increasing evidence suggests abnormal mitochondrial dynamics and quality control as important underlying mechanisms. The VPS35 gene, which encodes a key component of the membrane protein–recycling retromer complex, is the third autosomal-dominant gene associated with PD. However, how VPS35 mutations lead to neurodegeneration remains unclear. Here we demonstrate that PD-associated VPS35 mutations caused mitochondrial fragmentation and cell death in cultured neurons in vitro, in mouse substantia nigra neurons in vivo and in human fibroblasts from an individual with PD who has the VPS35D620N mutation. VPS35-induced mitochondrial deficits and neuronal dysfunction could be prevented by inhibition of mitochondrial fission. VPS35 mutants showed increased interaction with dynamin-like protein (DLP) 1, which enhanced turnover of the mitochondrial DLP1 complexes via the mitochondria-derived vesicle–dependent trafficking of the complexes to lysosomes for degradation. Notably, oxidative stress increased the VPS35-DLP1 interaction, which we also found to be increased in the brains of sporadic PD cases. These results revealed a novel cellular mechanism for the involvement of VPS35 in mitochondrial fission, dysregulation of which is probably involved in the pathogenesis of familial, and possibly sporadic, PD.

Extrastriatal monoamine neuron function in Parkinson’s disease: An 18F-dopa PET study

The early motor manifestations of Parkinsons disease (PD) reflect degeneration of nigrostriatal dopamine neurons projecting to the caudal putamen. However, extrastriatal dopamine and other monoamine systems are also involved, particularly in later disease. We used (18)F-dopa PET in a cross-sectional study to characterize extrastriatal monoamine neuronal dysfunction in PD. 16 Controls and 41 patients underwent investigation. We found that (18)F-dopa uptake was decreased in cortical motor areas, particularly the motor cortex, even in early disease. Frontal association areas were also affected in later disease but limbic areas were spared except for hypothalamus. The substantia nigra, midbrain raphe and locus coeruleus showed normal or increased (18)F-dopa uptake until PD was advanced, indicating compensatory responses in intact monoamine neuron perikarya. The red nucleus, subthalamus, ventral thalamus and pineal gland were also eventually involved. These findings provide a further basis for understanding the complex pathophysiology of PD in vivo and complement pathological studies.

Retromer Binding to FAM21 and the WASH Complex Is Perturbed by the Parkinson Disease-Linked VPS35(D620N) Mutation

Summary Retromer is a protein assembly that plays a central role in orchestrating export of transmembrane-spanning cargo proteins from endosomes into retrieval pathways destined for the Golgi apparatus and the plasma membrane [1]. Recently, a specific mutation in the retromer component VPS35, VPS35(D620N), has linked retromer dysfunction to familial autosomal dominant and sporadic Parkinson disease [2, 3]. However, the effect of this mutation on retromer function remains poorly characterized. Here we established that in cells expressing VPS35(D620N) there is a perturbation in endosome-to-TGN transport but not endosome-to-plasma membrane recycling, which we confirm in patient cells harboring the VPS35(D620N) mutation. Through comparative stable isotope labeling by amino acids in cell culture (SILAC)-based analysis of wild-type VPS35 versus the VPS35(D620N) mutant interactomes, we establish that the major defect of the D620N mutation lies in the association to the actin-nucleating Wiskott-Aldrich syndrome and SCAR homolog (WASH) complex. Moreover, using isothermal calorimetry, we establish that the primary defect of the VPS35(D620N) mutant is a 2.2 ± 0.5-fold decrease in affinity for the WASH complex component FAM21. These data define the primary molecular defect in retromer assembly that arises from the VPS35(D620N) mutation and, by revealing functional effects on retromer-mediated endosome-to-TGN transport, provide new insight into retromer deregulation in Parkinson disease.

Rivastigmine for gait stability in patients with Parkinson's disease (ReSPonD): a randomised, double-blind, placebo-controlled, phase 2 trial

BACKGROUND Falls are a frequent and serious complication of Parkinsons disease and are related partly to an underlying cholinergic deficit that contributes to gait and cognitive dysfunction in these patients. Gait dysfunction can lead to an increased variability of gait from one step to another, raising the likelihood of falls. In the ReSPonD trial we aimed to assess whether ameliorating this cholinergic deficit with the acetylcholinesterase inhibitor rivastigmine would reduce gait variability. METHODS We did this randomised, double-blind, placebo-controlled, phase 2 trial at the North Bristol NHS Trust Hospital, Bristol, UK, in patients with Parkinsons disease recruited from community and hospital settings in the UK. We included patients who had fallen at least once in the year before enrolment, were able to walk 18 m without an aid, had no previous exposure to an acetylcholinesterase inhibitor, and did not have dementia. Our clinical trials unit randomly assigned (1:1) patients to oral rivastigmine or placebo capsules (both taken twice a day) using a computer-generated randomisation sequence and web-based allocation. Rivastigmine was uptitrated from 3 mg per day to the target dose of 12 mg per day over 12 weeks. Both the trial team and patients were masked to treatment allocation. Masking was achieved with matched placebo capsules and a dummy uptitration schedule. The primary endpoint was difference in step time variability between the two groups at 32 weeks, adjusted for baseline age, cognition, step time variability, and number of falls in the previous year. We measured step time variability with a triaxial accelerometer during an 18 m walking task in three conditions: normal walking, simple dual task with phonemic verbal fluency (walking while naming words beginning with a single letter), and complex dual task switching with phonemic verbal fluency (walking while naming words, alternating between two letters of the alphabet). Analysis was by modified intention to treat; we excluded from the primary analysis patients who withdrew, died, or did not attend the 32 week assessment. This trial is registered with ISRCTN, number 19880883. FINDINGS Between Oct 4, 2012 and March 28, 2013, we enrolled 130 patients and randomly assigned 65 to the rivastigmine group and 65 to the placebo group. At week 32, compared with patients assigned to placebo (59 assessed), those assigned to rivastigmine (55 assessed) had improved step time variability for normal walking (ratio of geometric means 0.72, 95% CI 0.58-0.88; p=0.002) and the simple dual task (0.79; 0.62-0.99; p=0.045). Improvements in step time variability for the complex dual task did not differ between groups (0.81, 0.60-1.09; p=0.17). Gastrointestinal side-effects were more common in the rivastigmine group than in the placebo group (p<0.0001); 20 (31%) patients in the rivastigmine group versus three (5%) in the placebo group had nausea and 15 (17%) versus three (5%) had vomiting. INTERPRETATION Rivastigmine can improve gait stability and might reduce the frequency of falls. A phase 3 study is needed to confirm these findings and show cost-effectiveness of rivastigmine treatment. FUNDING Parkinsons UK.

SGCE mutations cause psychiatric disorders: clinical and genetic characterization

Myoclonus dystonia syndrome is a childhood onset hyperkinetic movement disorder characterized by predominant alcohol responsive upper body myoclonus and dystonia. A proportion of cases are due to mutations in the maternally imprinted SGCE gene. Previous studies have suggested that patients with SGCE mutations may have an increased rate of psychiatric disorders. We established a cohort of patients with myoclonus dystonia syndrome and SGCE mutations to determine the extent to which psychiatric disorders form part of the disease phenotype. In all, 89 patients with clinically suspected myoclonus dystonia syndrome were recruited from the UK and Ireland. SGCE was analysed using direct sequencing and for copy number variants. In those patients where no mutation was found TOR1A (GAG deletion), GCH1, THAP1 and NKX2-1 were also sequenced. SGCE mutation positive cases were systematically assessed using standardized psychiatric interviews and questionnaires and compared with a disability-matched control group of patients with alcohol responsive tremor. Nineteen (21%) probands had a SGCE mutation, five of which were novel. Recruitment of family members increased the affected SGCE mutation positive group to 27 of whom 21 (77%) had psychiatric symptoms. Obsessive-compulsive disorder was eight times more likely (P < 0.001) in mutation positive cases, compulsivity being the predominant feature (P < 0.001). Generalized anxiety disorder (P = 0.003) and alcohol dependence (P = 0.02) were five times more likely in mutation positive cases than tremor controls. SGCE mutations are associated with a specific psychiatric phenotype consisting of compulsivity, anxiety and alcoholism in addition to the characteristic motor phenotype. SGCE mutations are likely to have a pleiotropic effect in causing both motor and specific psychiatric symptoms.

Multiple-source current steering in subthalamic nucleus deep brain stimulation for Parkinson's disease (the VANTAGE study): a non-randomised, prospective, multicentre, open-label study

BACKGROUND High-frequency deep brain stimulation (DBS) with a single electrical source is effective for motor symptom relief in patients with Parkinsons disease. We postulated that a multiple-source, constant-current device that permits well defined distribution of current would lead to motor improvement in patients with Parkinsons disease. METHODS We did a prospective, multicentre, non-randomised, open-label intervention study of an implantable DBS device (the VANTAGE study) at six specialist DBS centres at universities in six European countries. Patients were judged eligible if they were aged 21-75 years, had been diagnosed with bilateral idiopathic Parkinsons disease with motor symptoms for more than 5 years, had a Hoehn and Yahr score of 2 or greater, and had a Unified Parkinsons disease rating scale part III (UPDRS III) score in the medication-off state of more than 30, which improved by 33% or more after a levodopa challenge. Participants underwent bilateral implantation in the subthalamic nucleus of a multiple-source, constant-current, eight-contact, rechargeable DBS system, and were assessed 12, 26, and 52 weeks after implantation. The primary endpoint was the mean change in UPDRS III scores (assessed by site investigators who were aware of the treatment assignment) from baseline (medication-off state) to 26 weeks after first lead implantation (stimulation-on, medication-off state). This study is registered with ClinicalTrials.gov, number NCT01221948. FINDINGS Of 53 patients enrolled in the study, 40 received a bilateral implant in the subthalamic nucleus and their data contributed to the primary endpoint analysis. Improvement was noted in the UPDRS III motor score 6 months after first lead implantation (mean 13·5 [SD 6·8], 95% CI 11·3-15·7) compared with baseline (37·4 [8·9], 34·5-40·2), with a mean difference of 23·8 (SD 10·6; 95% CI 20·3-27·3; p<0·0001). One patient died of pneumonia 24 weeks after implantation, which was judged to be unrelated to the procedure. 125 adverse events were reported, the most frequent of which were dystonia, speech disorder, and apathy. 18 serious adverse events were recorded, three of which were attributed to the device or procedure (one case each of infection, migration, and respiratory depression). All serious adverse events resolved without residual effects and stimulation remained on during the study. INTERPRETATION The multiple-source, constant-current, eight-contact DBS system suppressed motor symptoms effectively in patients with Parkinsons disease, with an acceptable safety profile. Future trials are needed to investigate systematically the potential benefits of this system on postoperative outcome and its side-effects. FUNDING Boston Scientific.

Combined pedunculopontine-subthalamic stimulation in Parkinson disease

Objective: To assess the effect of deep brain stimulation (DBS) in the pedunculopontine nucleus (PPN) and caudal zona incerta (cZi)—both separately and in combination—on motor symptoms and regional cerebral blood flow (rCBF) in patients with Parkinson disease (PD). Methods: Four patients with bilateral cZi and PPN DBS electrodes were rated with the Unified Parkinsons Disease Rating Scale motor subscale (UPDRS-III) when taking and withdrawn from medication. A block of 16 [15O]-H2O PET resting measurements of rCBF were performed in 4 different states with patients withdrawn from medication: 1) no stimulation, 2) cZi stimulation alone, 3) PPN stimulation alone, 4) combined PPN/cZi stimulation. Results: When patients were medicated, combined PPN/cZi stimulation produced a statistically significant improvement in UPDRS-III score compared to cZi stimulation alone. In the “off” medication state, the clinical effect of combined stimulation was not significantly different from that induced by cZi stimulation alone. Concomitant PPN/cZi stimulation had a cumulative effect on levels of rCBF, effectively combining subcortical and cortical changes induced by stimulation of either target in isolation. Conclusions: These findings suggest that concomitant low frequency stimulation of PPN and cZi regions induces additive brain activation changes and provides improved control of PD symptoms when medicated. Classification of evidence: This study provides Class IV evidence that concomitant low frequency stimulation of PPN and cZI improves motor symptoms in patients with PD on dopamine replacement. It provides Class III evidence that concomitant low frequency stimulation of PPN and cZi induces additive rCBF changes in motor areas of brain.

Outcomes from stimulation of the caudal zona incerta and pedunculopontine nucleus in patients with Parkinson's disease

Introduction. Axial symptoms including postural instability, falls and failure of gait initiation are some of the most disabling motor symptoms of Parkinsons disease (PD). We performed bilateral deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) in combination with the caudal zona incerta (cZi) in order to determine their efficacy in alleviating these symptoms. Methods. Seven patients with predominant axial symptoms in both the ‘on’ and ‘off’ medication states underwent bilateral cZi and PPN DBS. Motor outcomes were assessed using the motor component of the Unified Parkinsons Disease Rating Scale (UPDRS 3) and a composite axial subscore was derived from items 27, 28, 29 and 30 (arising from chair, posture, gait and postural stability). Quality of life was measured using the PDQ39. Comparisons were made between scores obtained at baseline and those at a mean follow-up of 12 months. Results. In both the off and on medication states, a statistically significant improvement in the UPDRS part 3 score was achieved by stimulation of the PPN, cZi and both in combination. In the off medication state, our composite axial subscore of the UPDRS part 3 improved with stimulation of the PPN, cZi and both in combination. The composite axial subscore, in the ‘on’ medication state, however, only showed a statistically significant improvement when a combination of cZi and PPN stimulation was used. Conclusions. This study provides evidence that a combination of PPN and cZi stimulation can achieve a significant improvement in the hitherto untreatable ‘on’ medication axial symptoms of PD.

Bilateral caudal zona incerta nucleus stimulation for essential tremor: outcome and quality of life

Background Over the past few years, bilateral stimulation of the caudal or motor part of the zona incerta nucleus (cZI) has been performed by the authors in patients with essential tremor (ET). Outcomes including quality of life data in 15 patients with a follow-up period of up to 84 months (mean 31.7±28.6 months) are presented. Methods 15 consecutive ET patients underwent MRI guided bilateral cZI deep brain stimulation implantation. Patients were assessed by applying the Fahn–Tolosa–Marin Tremor Rating Scale and the Short Form Health Survey-36 (SF-36) to assess quality of life. Results The total tremor score improved by 73.8% (p<0.0001). The part A score (items 1–9) improved by 86.6% (p<0.0001). Postural tremor improved by 88.2% (p<0.0001) and action tremor by 82.2% (p<0.0001). The part B score, which evaluates the functional activities of the upper limbs, improved by 60.1% (p<0.0001). Part C score, which evaluates the activities of daily living, improved by 80.0% (p<0.0001). The SF-36 physical component score improved by 23.7% (p<0.0001) and the mental component score by 22.4% (p<0.0001). There was one wound infection and three patients developed stimulation related transient dysarthria. None developed any disequilibrium or tolerance to stimulation. Conclusion Bilateral cZI stimulation is safe and effective in suppressing the postural and action component of ET. It is associated with a low incidence of stimulation related complications and patients do not develop tolerance to stimulation with maintained clinical benefit over a follow-up period of up to 7 years.

Cognitive and motor effects of dopaminergic medication withdrawal in Parkinson's disease.

AIMS Recent evidence points towards dissociable effects of dopaminergic medication on motor function and cognitive function mediated by different fronto-striatal neural circuits. This study aimed to clarify the role of dopaminergic medication in spatial working memory, and reinforcement-based associative learning in relation to clinical changes in motor function in early Parkinsons disease (PD). METHOD We tested 14 patients with mild to moderate PD on and off dopaminergic medication, on a spatial delayed-response working memory task, and on spatial and non-spatial (visual) trial-and-error learning tasks based on reinforcement, carefully matched for motor requirements. In addition, we explored relationships between the effects of withdrawal on motor symptom expression and performance on the cognitive tasks. RESULTS Withdrawal from dopaminergic medication significantly exacerbated motor symptoms. This was related to spatial learning, but not visual learning, or delayed response accuracy. Moreover, medication withdrawal led to dissociable effects of response latency on the spatial learning and spatial delayed response tasks, with patients becoming faster after spatial learning, but relatively slower on the delayed response task. These changes in response latency were unrelated to motor symptom impairment. CONCLUSION Our findings suggest dissociable effects of dopamine medication withdrawal on cognitive processes putatively mediated by dorsal and ventral striatal regions.