Genetics of validated Parkinson's disease subtypes in the Oxford Discovery and Tracking Parkinson's cohorts

OBJECTIVES

To explore the genetics of four Parkinson's disease (PD) subtypes that have been previously described in two large cohorts of patients with recently diagnosed PD. These subtypes came from a data-driven cluster analysis of phenotypic variables.

METHODS

We looked at the frequency of genetic mutations in glucocerebrosidase (GBA) and leucine-rich repeat kinase 2 against our subtypes. Then we calculated Genetic Risk Scores (GRS) for PD, multiple system atrophy, progressive supranuclear palsy, Lewy body dementia, and Alzheimer's disease. These GRSs were regressed against the probability of belonging to a subtype in the two independent cohorts and we calculated q-values as an adjustment for multiple testing across four subtypes. We also carried out a Genome-Wide Association Study (GWAS) of belonging to a subtype.

RESULTS

A severe disease subtype had the highest rates of patients carrying GBA mutations while the mild disease subtype had the lowest rates (p=0.009). Using the GRS, we found a severe disease subtype had a reduced genetic risk of PD (p=0.004 and q=0.015). In our GWAS no individual variants met genome wide significance (<5×10e-8) although four variants require further follow-up, meeting a threshold of <1×10e-6.

CONCLUSIONS

We have found that four previously defined PD subtypes have different genetic determinants which will help to inform future studies looking at underlying disease mechanisms and pathogenesis in these different subtypes of disease.

Combining biomarkers for prognostic modelling of Parkinson's disease

BACKGROUND

Patients with Parkinson's disease (PD) have variable rates of progression. More accurate prediction of progression could improve selection for clinical trials. Although some variance in clinical progression can be predicted by age at onset and phenotype, we hypothesise that this can be further improved by blood biomarkers.

OBJECTIVE

To determine if blood biomarkers (serum neurofilament light (NfL) and genetic status (glucocerebrosidase, GBA and apolipoprotein E (APOE))) are useful in addition to clinical measures for prognostic modelling in PD.

METHODS

We evaluated the relationship between serum NfL and baseline and longitudinal clinical measures as well as patients' genetic (GBA and APOE) status. We classified patients as having a favourable or an unfavourable outcome based on a previously validated model, and explored how blood biomarkers compared with clinical variables in distinguishing prognostic phenotypes .

RESULTS

291 patients were assessed in this study. Baseline serum NfL was associated with baseline cognitive status. Nfl predicted a shorter time to dementia, postural instability and death (dementia-HR 2.64; postural instability-HR 1.32; mortality-HR 1.89) whereas APOEe4 status was associated with progression to dementia (dementia-HR 3.12, 95% CI 1.63 to 6.00). NfL levels and genetic variables predicted unfavourable progression to a similar extent as clinical predictors. The combination of clinical, NfL and genetic data produced a stronger prediction of unfavourable outcomes compared with age and gender (area under the curve: 0.74-age/gender vs 0.84-ALL p=0.0103).

CONCLUSIONS

Clinical trials of disease-modifying therapies might usefully stratify patients using clinical, genetic and NfL status at the time of recruitment.

Neuropathology of dementia in patients with Parkinson's disease: a systematic review of autopsy studies

BACKGROUND

Dementia is a common, debilitating feature of late Parkinson's disease (PD). PD dementia (PDD) is associated with α-synuclein propagation, but coexistent Alzheimer's disease (AD) pathology may coexist. Other pathologies (cerebrovascular, transactive response DNA-binding protein 43 (TDP-43)) may also influence cognition. We aimed to describe the neuropathology underlying dementia in PD.

METHODS

Systematic review of autopsy studies published in English involving PD cases with dementia. Comparison groups included PD without dementia, AD, dementia with Lewy bodies (DLB) and healthy controls.

RESULTS

44 reports involving 2002 cases, 57.2% with dementia, met inclusion criteria. While limbic and neocortical α-synuclein pathology had the strongest association with dementia, between a fifth and a third of all PD cases in the largest studies had comorbid AD. In PD cases with dementia, tau pathology was moderate or severe in around a third, and amyloid-β pathology was moderate or severe in over half. Amyloid-β was associated with a more rapid cognitive decline and earlier mortality, and in the striatum, distinguished PDD from DLB. Positive correlations between multiple measures of α-synuclein, tau and amyloid-β were found. Cerebrovascular and TDP-43 pathologies did not generally contribute to dementia in PD. TDP-43 and amyloid angiopathy correlated with coexistent Alzheimer pathology.

CONCLUSIONS

While significant α-synuclein pathology is the main substrate of dementia in PD, coexistent pathologies are common. In particular, tau and amyloid-β pathologies independently contribute to the development and pattern of cognitive decline in PD. Their presence should be assessed in future clinical trials where dementia is a key outcome measure.

TRIAL REGISTRATION NUMBER

CRD42018088691.

Parkinson's disease: the effect of L-dopa therapy on urinary free catecholamines and metabolites

Background: L-dopa is an important antiparkinsonian drug. It is a precursor of dopamine and the other catecholamines. Potentially, administration of L-dopa could lead to increased urinary excretion of catecholamines and their metabolites to abnormal amounts. The current study aimed to determine these excretions in patients with Parkinson's disease (PD) receiving L-dopa compared with suitable controls. This is the first assessment of the effect of exogenous administration of L-dopa on urinary free metadrenalines.

Methods: Using one-way analysis of variance (ANOVA), urine catecholamines and metabolites, expressed as mmol per mole creatinine, were compared in: patients with PD who were receiving L-dopa; patients with PD but not receiving L-dopa; and patients without PD who were being investigated for the presence of phaechromocytoma but were found not to have the disease.

Results: Significantly higher values for urinary dopamine, homovanillic acid, free normetadrenaline and free metadrenaline were found in patients with PD receiving L-dopa compared with the other two control groups. In all the patients with PD, these four analytes were significantly correlated with daily dose of L-dopa.

Conclusion: L-dopa therapy can result in production of false positives for urinary excretion of dopamine, homovanillic acid, free normetadrenaline or free metadrenaline and thereby decrease the diagnostic value of these measurements in identifying phaeochromocytoma and related tumours.

Adherence to antiparkinson medication in a multicenter European study

Two small studies reported suboptimal therapy adherence in Parkinson's disease. We conducted a larger multicenter European study to assess medicine-taking behavior. Parkinson's disease patients taking dopaminergic therapy were enrolled in 8 centers in 5 countries, and disease severity and demographics recorded. Antiparkinson drug adherence was measured for 4 weeks using electronic monitoring bottles which record the date and time of cap opening (Aardex, Switzerland). One hundred twelve patients, mean age 65 years (standard deviation (SD) 10), with Parkinson's disease for 7.7 (SD 8.2) years completed the study. Total median adherence (doses taken/doses prescribed) was 97.7% (interquartile range [IQ] 90.6-100), days adherence (correct dose days) was 86.2% (IQ 61.1-96.2) and timing adherence (doses taken at correct time intervals) was 24.4% (IQ 5.3-56.5). Fourteen patients (12.5%) took less than 80% of prescribed doses, which was defined as suboptimal adherence. Patients with satisfactory adherence took a median of 8 mg/day (IQ 0-33) less than their prescribed dose of levodopa (P = NS), while suboptimal adherence patients took a median of 481 mg/day (IQ 205-670) less than their prescribed dose (P = 0.0006). The Parkinson motor score was significantly higher in patients with suboptimal adherence at 29 (IQ 20-40), versus those with satisfactory adherence at 19 (IQ 13-26), P = 0.005. Once daily drugs had significantly better adherence when compared with drugs prescribed more frequently (P < 0.0001). Suboptimal therapy adherence is associated with significant deviation from prescribed levodopa doses, despite greater Parkinson's motor severity. Optimizing oral medication intake has a potential role in maximizing the therapy response in Parkinson's disease.

Spheramine Titan/Schering

Spheramine, which is composed of microcarriers coated with dopamine-producing human retinal pigment epithelial cells, is being developed by Titan and Schering for the potential treatment of advanced Parkinson's disease. Phase II trials were ongoing in March 2005 and, at this time, were expected to be completed in the second half of 2006.

Trial of subtherapeutic pergolide in de novo Parkinson's disease

The effect of pergolide 25 mug twice daily on levodopa initiation was assessed in a randomized, placebo-controlled, parallel group, double-blind multicenter trial in 106 untreated early Parkinson's disease patients. The primary endpoint of mean time until levodopa was 520 days (95% confidence interval [CI], 422-618 days) for pergolide versus 434 days (95% CI, 358-609 days) for placebo. However, this increase of 86 days for pergolide was not statistically significant. The wash-in effect of pergolide was significant at 6 weeks (change in mean Unified Parkinson's Disease Rating Scale [UPDRS] 2 and 3 was -0.1 [95% CI, -1.4 to 1.3] for pergolide vs. 2.2 [95% CI, 1.1-3.3] for placebo). At termination, the change from baseline in mean UPDRS 2 and 3 score was 11.4 (95% CI, 8.8-14) for pergolide and 14.6 (95% CI, 12-17.2) for placebo (P=0.08). There was no significant change in UPDRS 2 and 3 for the 83 patients achieving the planned 4-week washout at termination (pergolide 1.2 [95% CI, -0.8 to 3.2] vs. placebo 0.0 [95% CI, -1.6 to 1.6]. Adverse events were infrequent and occurred equally for pergolide and placebo. The study shows no evidence of a neuroprotective effect but indicates a mild symptomatic benefit from pergolide at a dose normally considered subtherapeutic.

Switching from ergot to nonergot dopamine agonists in Parkinson's disease: A clinical series and five-drug dose conversion table

Of 99 patients on ergot-derived dopamine agonists informed about possible long-term side effects, switching to a nonergot was undertaken in 88 (89%). There were adverse events in 26%. After 11 months, 82% were on their switch agonist and 93% were on any agonist. Switching dopamine agonists is feasible in this population.