Polymorphisms in dopamine-associated genes and cognitive decline in Parkinson's disease

Abstract

Objectives: Cognitive decline is common in Parkinson's disease (PD), but the underlying mechanisms for this complication are incompletely understood. Genotypes affecting dopamine transmission may be of importance. This study investigates whether genotypes associated with reduced prefrontal dopaminergic tone and/or reduced dopamine D2-receptor availability (Catechol-O-methyltransferase [COMT] Val158Met genotype and DRD2 C957T genotype) affect the development of cognitive deficits in PD. Materials and methods: One hundred and 34 patients with idiopathic PD, participating in a regional, population-based study of incident parkinsonism, underwent genotyping. After extensive baseline investigations (including imaging and biomarker analyses), the patients were followed prospectively during 6-10 years with neuropsychological evaluations, covering six cognitive domains. Cognitive decline (defined as the incidence of either Parkinson's disease mild cognitive impairment [PD-MCI] or dementia [PDD], diagnosed according to published criteria and blinded to genotype) was studied as the primary outcome. Results: Both genotypes affected cognition, as shown by Cox proportional hazards models. While the COMT 158Val/Val genotype conferred an increased risk of mild cognitive impairment in patients with normal cognition at baseline (hazard ratio: 2.13, P =.023), the DRD2 957T/T genotype conferred an overall increased risk of PD dementia (hazard ratio: 3.22, P