Genome-wide association studies of cognitive and motor progression in Parkinson’s disease

Abstract:

Background: There are currently no treatments that stop or slow the progression of Parkinson's disease (PD). Case-control genome-wide association studies (GWASs) have identified variants associated with disease risk, but not progression. Objective: To identify genetic variants associated with PD progression in GWASs. Methods: We analysed three large, longitudinal cohorts: Tracking Parkinson's, Oxford Discovery, and the Parkinson's Progression Markers Initiative. We included clinical data for 3,364 patients with 12,144 observations (mean follow-up 4.2 years). We used a new method in PD, following a similar approach in Huntington's disease, where we combined multiple assessments using a principal components analysis to derive scores for composite, motor, and cognitive progression. These scores were analysed in linear regressions in GWASs. We also performed a targeted analysis of the 90 PD risk loci from the latest case-control meta-analysis. Results: There was no overlap between variants associated with PD risk, from case-control studies, and PD age at onset versus PD progression. The APOE ϵ4 tagging variant, rs429358, was significantly associated with the rate of composite and cognitive progression in PD. No single variants were associated with motor progression. However in gene-based analysis, variation across ATP8B2, a phospholipid transporter related to vesicle formation, was nominally associated with motor progression (p=5.3 x 10^-6). Conclusions: This new method in PD improves measurement of symptom progression. We provide strong evidence that the APOE ϵ4 allele drives progressive cognitive impairment in PD. We have also reported loci of interest which need to be tested in further studies.