Analysis of CYP2D6 genotype and response to tetrabenazine

Tetrabenazine is effective in the treatment of the chorea associated with Huntington disease and other hyperkinetic movement disorders. Following oral administration, tetrabenazine is hepatically transformed into 2 active metabolites that are CYP2D6 substrates. There are 4 CYP2D6 genotypes: poor metabolizers, intermediate metabolizers, extensive metabolizers, and ultrarapid metabolizers. CYP2D6 genotyping was performed on sequential subjects treated with tetrabenazine, but results were not known at the time of titration. Duration of titration to a stable dose, total daily dose, response rating scores, and adverse events were retrospectively collected and subsequently analyzed. Of 127 patients, the majority (n = 100) were categorized as extensive metabolizers, 14 as intermediate metabolizers, 11 as poor metabolizers, and 2 as ultrarapid metabolizers. Ultrarapid metabolizer patients needed a longer titration (8 vs 3.3, 4.4, and 3 weeks, respectively; P < .01) to achieve optimal benefit and required a higher average daily dose than the other patients, but this difference did not reach statistical significance. The treatment response was less robust in the intermediate metabolizer group when compared with the extensive metabolizer patients (P = .013), but there were no statistically significant differences between the various groups with regard to adverse effects. Our findings demonstrate that, aside from the need for a longer titration in the ultrarapid metabolizers, there are no distinguishing features of patients with various CYP2D6 genotypes, and therefore the current recommendation to systematically genotype all patients prescribed more than 50 mg/day of tetrabenazine should be reconsidered. © 2012 Movement Disorder Society     

Which dyskinesia scale best detects treatment response?

Numerous scales assess dyskinesia in Parkinson's disease (PD), variably focusing on anatomical distribution, phenomenology, time, severity, and disability. No study has compared these scales and their relative ability to detect change related to an established treatment. We conducted a randomized placebo‐controlled trial of amantadine, assessing dyskinesia at baseline and at 4 and 8 weeks using the following scales: Unified Dyskinesia Rating Scale (UDysRS), Lang‐Fahn Activities of Daily Living Dyskinesia Rating Scale (LF), 26‐Item Parkinson's Disease Dyskinesia scale (PDD‐26), patient diaries, modified Abnormal Involuntary Movements Scale (AIMS), Rush Dyskinesia Rating Scale (RDRS), dyskinesia items from the Movement Disorder Society–sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS‐UPDRS), and Clinical Global Impression (severity and change: CGI‐S, CGI‐C). Scale order was randomized at each visit, but raters were aware of each scale as it was administered. Sensitivity to treatment was assessed using effect size. Sixty‐one randomized dyskinetic PD subjects (31 amantadine, 30 placebo) completed the study. Four of the 8 scales (CGI‐C, LF, PDD‐26, and UDysRS) detected a significant treatment. The UDysRS Total Score showed the highest effect size (η² = 0.138) for detecting treatment‐related change, with all other scales having effect sizes < 0.1. No scale was resistant to placebo effects. This study resolves 2 major issues useful for future testing of new antidyskinesia treatments: among tested scales, the UDysRS, having both subjective and objective dyskinesia ratings, is superior for detecting treatment effects; and the magnitude of the UDysRS effect size from amantadine sets a clear standard for comparison for new agents. © 2012 Movement Disorder Society     

Common data elements for clinical research in Friedreich's ataxia

To reduce study start‐up time, increase data sharing, and assist investigators conducting clinical studies, the National Institute of Neurological Disorders and Stroke embarked on an initiative to create common data elements for neuroscience clinical research. The Common Data Element Team developed general common data elements, which are commonly collected in clinical studies regardless of therapeutic area, such as demographics. In the present project, we applied such approaches to data collection in Friedreich's ataxia (FRDA), a neurological disorder that involves multiple organ systems. To develop FRDA common data elements, FRDA experts formed a working group and subgroups to define elements in the following: ataxia and performance measures; biomarkers; cardiac and other clinical outcomes; and demographics, laboratory tests, and medical history. The basic development process included identification of international experts in FRDA clinical research, meeting by teleconference to develop a draft of standardized common data elements recommendations, vetting of recommendations across the subgroups, and dissemination of recommendations to the research community for public comment. The full recommendations were published online in September 2011 at http://www.commondataelements.ninds.nih.gov/FA.aspx . The subgroups′ recommendations are classified as core, supplemental, or exploratory. Template case report forms were created for many of the core tests. The present set of data elements should ideally lead to decreased initiation time for clinical research studies and greater ability to compare and analyze data across studies. Their incorporation into new, ongoing studies will be assessed in an ongoing fashion to define their utility in FRDA. © 2012 Movement Disorder Society     

Pathological gambling in Parkinson's disease: Subthalamic oscillations during economics decisions

Pathological gambling develops in up to 8% of patients with Parkinson's disease. Although the pathophysiology of gambling remains unclear, several findings argue for a dysfunction in the basal ganglia circuits. To clarify the role of the subthalamic nucleus in pathological gambling, we studied its activity during economics decisions. We analyzed local field potentials recorded from deep brain stimulation electrodes in the subthalamic nucleus while parkinsonian patients with (n = 8) and without (n = 9) pathological gambling engaged in an economics decision‐making task comprising conflictual trials (involving possible risk‐taking) and non conflictual trials. In all parkinsonian patients, subthalamic low frequencies (2–12 Hz) increased during economics decisions. Whereas, in patients without gambling, low‐frequency oscillations exhibited a similar pattern during conflictual and non conflictual stimuli, in those with gambling, low‐frequency activity increased significantly more during conflictual than during non conflictual stimuli. The specific low‐frequency oscillatory pattern recorded in patients with Parkinson's disease who gamble could reflect a subthalamic dysfunction that makes their decisional threshold highly sensitive to risky options. When parkinsonian patients process stimuli related to an economics task, low‐frequency subthalamic activity increases. This task‐related change suggests that the cognitive‐affective system that drives economics decisional processes includes the subthalamic nucleus. The specific subthalamic neuronal activity during conflictual decisions in patients with pathological gambling supports the idea that the subthalamic nucleus is involved in behavioral strategies and in the pathophysiology of gambling. © 2013 International Parkinson and Movement Disorder Society     

MPTP‐induced dopamine neuron degeneration and glia activation is potentiated in MDMA‐pretreated mice

Clinical observations report a greater propensity to develop Parkinson's disease (PD) in amphetamine users. 3,4‐Methylenedioxymethamphetamine (MDMA; “ecstasy”) is an amphetamine‐related drug that is largely consumed by adolescents and young adults, which may have neuroinflammatory and neurotoxic effects. Here, the objective was to evaluate in mice whether consumption of MDMA during adolescence might influence the neuroinflammatory and neurotoxic effects of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP), a toxin known to induce PD in humans. The activation of astroglia and microglia by glial fibrillary acidic protein (GFAP) and complement receptor type 3 (CD11b) immunohistochemistry and the degeneration of dopaminergic neurons by tyrosine hydroxylase (TH) immunohistochemistry were evaluated. MPTP (20 mg/kg × 4) was administered to mice treated from ages 8 weeks to 17 weeks with MDMA (10 mg/kg twice daily, two times a week). In mice that were chronically treated with MDMA, administration of MPTP induced a higher microglial and astroglial response in both the striatum and the substantia nigra pars compacta (SNc) compared with vehicle‐treated or vehicle + MPTP‐treated mice. Inflammatory changes were associated with a decrease in TH immunoreactivity in the SNc of MDMA‐treated mice and with a further decrease in the striatum and the SNc of MDMA + MPTP‐treated mice compared with vehicle‐treated, MDMA‐treated, and MPTP‐treated mice. The results demonstrate that chronic administration of MDMA during late adolescence in mice exacerbates the neurodegeneration and neuroinflammation caused by MPTP, suggesting that MDMA may constitute a risk factor for dopaminergic neuron degeneration. © 2013 International Parkinson and Movement Disorder Society