Julie H. Carter

Variable expression of Parkinson's disease: A base‐line analysis of the DAT ATOP cohort

The DATATOP database, which includes clinical information on 800 patients with early untreated Parkinsons disease (PD), is well suited to explore clinical heterogeneity in PD. Patients with early-onset PD (≤40 years, N = 33) reached the same level of disability as the late-onset PD (≥70 years, N = 85) group at a significantly slower rate (2.9 vs. 1.7 years). Early-onset PD patients functioned cognitively better than late-onset PD patients. Bradykinesia, and postural instability and gait difficulty (PIGD), were more common at onset in patients with a rapid rate of disease progression (“malignant PD”; duration of symptoms <1 year and Hoehnflahr stage of 2.5, N = 11) as compared with those with a relatively slow rate of progression (“benign PD”; duration of symptoms >4 years, N = 65). Comparisons of tremor-dominant PD (mean tremor score/ mean PIGD score ≤1.5, N = 441) with the PIGD-dominant type (mean tremor score/mean PIGD score ≥1.0, N = 233) provided support for the existence of clinical subtypes. The PIGD group reported significantly greater subjective intellectual, motor, and occupational impairment than the tremor group. Stage II patients had higher depression scores than stage I patients. Among the patients participating in the DATATOP, older age at onset with bradykinesia, or with the PIGD form of PD, is associated with more functional disability than when the symptoms are dominated by tremor or begin at a younger age.

Randomized, double-blind trial of glial cell line-derived neurotrophic factor (GDNF) in PD

Objective: To assess the safety, tolerability, and biological activity of glial cell line-derived neurotrophic factor (GDNF) administered by an implanted intracerebroventricular (ICV) catheter and access port in advanced PD. Background: GDNF is a peptide that promotes survival of dopamine neurons. It improved 6-OHDA- or MPTP-induced behavioral deficits in rodents and monkeys. Methods: A multicenter, randomized, double-blind, placebo-controlled, sequential cohort study compared the effects of monthly ICV administration of placebo and 25, 75, 150, 300, and 500 to 4,000 μg of GDNF in 50 subjects with PD for 8 months. An open-label study extended exposure up to an additional 20 months and maximum single doses of up to 4,000 μg in 16 subjects. Laboratory testing, adverse events (AE), and Unified Parkinson’s Disease Rating Scale (UPDRS) scoring were obtained at 1- to 4-week intervals throughout the studies. Results: Twelve subjects received placebo and seven or eight subjects were assigned to each of the other GDNF dose groups. “On” and “off” total and motor UPDRS scores were not improved by GDNF at any dose. Nausea, anorexia, and vomiting were common hours to several days after injections of GDNF. Weight loss occurred in the majority of subjects receiving 75 μg or larger doses of GDNF. Paresthesias, often described as electric shocks (Lhermitte sign), were common in GDNF-treated subjects, were not dose related, and resolved on discontinuation of GDNF. Asymptomatic hyponatremia occurred in over half of subjects receiving 75 μg or larger doses of GDNF; it was symptomatic in several subjects. The open-label extension study had similar AE and lack of therapeutic efficacy. Conclusions: GDNF administered by ICV injection is biologically active as evidenced by the spectrum of AE encountered in this study. GDNF did not improve parkinsonism, possibly because GDNF did not reach the target tissues—putamen and substantia nigra.

Effect of peripheral catechol‐O‐methyltransferase inhibition on the pharmacokinetics and pharmacodynamics of levodopa in parkinsonian patients

Article abstract –Catechol-O-methyltransferase (COMT) metabolizes a portion of administered levodopa and thus makes it unavailable for conversion to dopamine in the brain. In an open-label trial, we examined the effects of entacapone, a peripheral inhibitor of COMT, administered acutely or for 8 weeks, on the pharmacokinetics and pharmacodynamics of levodopa in 15 parkinsonian subjects with a fluctuating response to levodopa. Acutely and chronically administered entacapone similarly decreased the plasma elimination of orally and intravenously administered levodopa. Absorption of levodopa was minimally affected. During chronic entacapone treatment, daily levodopa dosages were reduced by 27% yet mean plasma levodopa concentrations were increased by 23%. Plasma 3-O-methyldopa concentrations were decreased by 60%. Entacapone increased the duration of action of single doses of levodopa by a mean of 56%. The percent of the day “on” after 8 weeks of entacapone treatment was 77%; it dropped to 44% upon withdrawal of entacapone. We conclude that inhibition of COMT by entacapone increases the plasma half-life of levodopa and augments the antiparkinsonian effects of single and repeated doses of levodopa.

Heterozygosity for a mutation in the parkin gene leads to later onset Parkinson disease

Background: The vast majority of the parkin mutations previously identified have been found in individuals with juvenile or early onset PD. Previous screening of later onset PD cohorts has not identified substantial numbers of parkin mutations. Methods: Families with at least two siblings with PD were ascertained to identify genes contributing to PD susceptibility. Screening of the parkin gene, by both quantitative PCR and exon sequencing, was performed in those families with either early onset PD (age onset ≤50 years) or positive lod score with a marker in intron 7 of the parkin gene. Results: A total of 25 different mutations in the parkin gene were identified in 103 individuals from 47 families. Mutations were found in both parkin alleles in 41 of the individuals, whereas a single mutation in only one of the two parkin alleles was observed in 62 individuals. Thirty-five of the subjects (34%) with a parkin mutation had an age at onset of 60 years or above with 30 of these 35 (86%) having a detectable mutation on only one parkin allele. Few significant clinical differences were observed among the individuals with two, one, or no mutated copies of the parkin gene. Conclusion: Mutations in the parkin gene occur among individuals with PD with an older age at onset (≥60 years) who have a positive family history of the disease. In addition, the clinical findings of parkin-positive individuals are remarkably similar to those without mutations.

Dose-response relationship of levodopa with mood and anxiety in fluctuating Parkinson's disease: A double-blind, placebo-controlled study

We investigated the effect of levodopa on mood and anxiety in eight Parkinsons disease patients with motor fluctuations.Each patient received 0.0-, 0.5-, and 1.0-mg/kg/hr levodopa infusions in randomly assigned order under double-blind conditions on consecutive days. Mood elevation and anxiety reduction based on half-hourly patient rating and a corresponding increase in tapping speed occurred with active drug infusion but not placebo infusion. The effects were dose related. The higher-dose infusion rate produced more rapid onset, greater magnitude, and longer duration of response. We conclude that mood and anxiety fluctuations related to levodopa dosing are robust pharmacologic, and not placebo, effects. NEUROLOGY 1995;45: 1757-1760

Significant Linkage of Parkinson Disease to Chromosome 2q36-37

Parkinson disease (PD) is the second most common neurodegenerative disorder, surpassed in frequency only by Alzheimer disease. Elsewhere we have reported linkage to chromosome 2q in a sample of sibling pairs with PD. We have now expanded our sample to include 150 families meeting our strictest diagnostic definition of verified PD. To further delineate the chromosome 2q linkage, we have performed analyses using only those pedigrees with the strongest family history of PD. Linkage analyses in this subset of 65 pedigrees generated a LOD score of 5.1, which was obtained using an autosomal dominant model of disease transmission. This result strongly suggests that variation in a gene on chromosome 2q36-37 contributes to PD susceptibility.

Evolution of the response to levodopa during the first 4 years of therapy

The short‐duration response, long‐duration response, and dyskinetic response to levodopa change during long‐term levodopa therapy. How these responses evolve, and which changes contribute to the emergence of motor fluctuations, remain unclear. We studied 18 subjects with Parkinsons disease before they began levodopa therapy and after 6, 12, 24, and 48 months of long‐term levodopa therapy. The responses to 2‐hour levodopa infusions after overnight and after 3 days of levodopa withdrawal were studied from 6 months onward. The mean magnitude of the short‐duration response and the long‐duration response measured after overnight without antiparkinsonian medications did not change during the 4 years. However, after 3 days without levodopa, it was apparent that the short‐duration‐response magnitude was progressively increasing (p < 0.0001) and that the long‐duration response was decaying more rapidly (p = 0.0004). The short‐duration‐response magnitude at 4 years was inversely related to the long‐duration‐response magnitude (p = 0.022), suggesting that the long‐duration response was one determinant of the short‐duration‐response magnitude. Dyskinesia increased progressively in severity during the study (p = 0.013). The duration of the short‐duration response and dyskinesia did not change during the 4 years. Subject reports of motor fluctuations tended to be associated with a large short‐duration response (p = 0.054). We suggest that a larger long‐duration response, rather than a shortened one, is more important to the development of fluctuations. Improving the baseline or practical‐off motor function to reduce the magnitude of the short‐duration response may be a strategy to treat fluctuations.

Inosine to increase serum and cerebrospinal fluid urate in Parkinson disease: a randomized clinical trial.

IMPORTANCE Convergent biological, epidemiological, and clinical data identified urate elevation as a candidate strategy for slowing disability progression in Parkinson disease (PD). OBJECTIVE To determine the safety, tolerability, and urate-elevating capability of the urate precursor inosine in early PD and to assess its suitability and potential design features for a disease-modification trial. DESIGN, SETTING, AND PARTICIPANTS The Safety of Urate Elevation in PD (SURE-PD) study, a randomized, double-blind, placebo-controlled, dose-ranging trial of inosine, enrolled participants from 2009 to 2011 and followed them for up to 25 months at outpatient visits to 17 credentialed clinical study sites of the Parkinson Study Group across the United States. Seventy-five consenting adults (mean age, 62 years; 55% women) with early PD not yet requiring symptomatic treatment and a serum urate concentration less than 6 mg/dL (the approximate population median) were enrolled. INTERVENTIONS Participants were randomized to 1 of 3 treatment arms: placebo or inosine titrated to produce mild (6.1-7.0 mg/dL) or moderate (7.1-8.0 mg/dL) serum urate elevation using 500-mg capsules taken orally up to 2 capsules 3 times per day. They were followed for up to 24 months (median, 18 months) while receiving the study drug plus 1 washout month. MAIN OUTCOMES AND MEASURES The prespecified primary outcomes were absence of unacceptable serious adverse events (safety), continued treatment without adverse event requiring dose reduction (tolerability), and elevation of urate assessed serially in serum and once (at 3 months) in cerebrospinal fluid. RESULTS Serious adverse events (17), including infrequent cardiovascular events, occurred at the same or lower rates in the inosine groups relative to placebo. No participant developed gout and 3 receiving inosine developed symptomatic urolithiasis. Treatment was tolerated by 95% of participants at 6 months, and no participant withdrew because of an adverse event. Serum urate rose by 2.3 and 3.0 mg/dL in the 2 inosine groups (P < .001 for each) vs placebo, and cerebrospinal fluid urate level was greater in both inosine groups (P = .006 and <.001, respectively). Secondary analyses demonstrated nonfutility of inosine treatment for slowing disability. CONCLUSIONS AND RELEVANCE Inosine was generally safe, tolerable, and effective in raising serum and cerebrospinal fluid urate levels in early PD. The findings support advancing to more definitive development of inosine as a potential disease-modifying therapy for PD. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00833690.

ABT-431, a D1 receptor agonist prodrug, has efficacy in Parkinson's disease

Studies in animal models show a selective D1 receptor agonist with full functional efficacy compared with dopamine to have antiparkinsonian efficacy of similar magnitude to levodopa, without the same propensity for inducing dyskinesia. To date, no such agent has been tested in humans. ABT‐431 is the prodrug of A‐86929, a full, selective D1 receptor agonist. Subjects (n = 14) with levodopa‐responsive Parkinsons disease received five doses of ABT‐431 (5, 10, 20, 30, and 40 mg) and one of placebo after a 12‐hour levodopa holiday. Response was assessed by using the Unified Parkinsons Disease Rating Scale motor subsection. Dyskinesia was separately graded. ABT‐431 showed efficacy significantly superior to placebo at doses of 10 mg and more, and of similar magnitude to that seen with levodopa. Dyskinesia was reduced in several patients after receiving ABT‐431. There were no serious adverse events, the most common minor events being nausea and emesis, dizziness, and hypotension. Assuming that ABT‐431 is not transformed in humans into an unknown active D2 metabolite, and remains selective for D1 receptors, it is the first dopamine D1 receptor agonist to demonstrate a full antiparkinsonian effect in patients with Parkinsons disease. These preliminary findings also suggest that it may exhibit a reduced tendency to provoke dyskinesia. The emergence of a well‐tolerated D1 agonist should allow for the development of a better understanding of the relation between motor efficacy and dyskinesia in Parkinsons disease. Ann Neurol 1999;45:736–741

Interactions between deep brain stimulation and levodopa in Parkinson’s disease

Objective: To quantify the effects of deep brain stimulation (DBS) of globus pallidus interna (GPi) and subthalamic nucleus (STN) on motor fluctuations and dyskinesia in PD and to determine how the response to levodopa was modified by DBS. Background: Patients report that DBS reduces levodopa-induced motor fluctuations and dyskinesia throughout the day, but this has not been objectively measured. Further, the means by which DBS alters the response to levodopa to improve motor fluctuations is unknown. Methods: Twelve subjects, six with bilateral GPi electrodes and six with bilateral STN electrodes, were studied 12 to 33 months after surgery. To quantify motor fluctuations and dyskinesia, subjects were monitored hourly throughout 2 waking days with their usual oral medications, 1 day with DBS on and 1 day with DBS off, with subjects and nurse raters blinded to DBS status. To examine the effects of DBS on levodopa pharmacodynamics, the effects of a 2-hour levodopa infusion were examined, 1 day with DBS on and 1 day with DBS off, again under double-blind conditions. Time course of variations in parkinsonism was evaluated by tapping speed, arising and walking speed, tremor scores, and dyskinesia scores. Results: DBS raised the mean tapping speed and reduced the coefficient of variation during the waking day. This was achieved by increasing the lowest or trough tapping speed between doses of antiparkinson medications. Mean walking speed was modestly increased and mean tremor scores were reduced. DBS increased the drug-off tapping speed, but neither the peak response nor the duration of response to levodopa was affected by DBS. The study was not powered to detect differences between GPi and STN stimulation and the only difference that approached significance was that GPi reduced peak dyskinesia and STN tended to increase peak dyskinesia. Conclusion: DBS objectively reduces motor fluctuations. This is achieved by reduction of drug-off disability and not by alterations in levodopa pharmacodynamics. This finding suggests alleviation of interdose trough disability as an alternative strategy to prolonging the effects of each dose of levodopa as a means to reduce motor fluctuations.