Authors:

Williams-Gray, C.H., HAMPSHIRE, A., Robbins, T., OWEN, A.M. & Barker, R.A

Reference:

Year of publication:

2007

CBU number:

6486

Abstract:

Full title: Catechol O-methyltransferase Val158Met genotype influences frontoparietal activity during planning in patients with Parkinson's disease. Cognitive dysfunction commonly occurs even in the early stages of Parkinson's disease (PD). Impairment on frontostriatally-based executive tasks is particularly well described, but affects only a proportion of early PD patients. Our previous work suggests that a common functional polymorphism (val158met) within the catechol O-methyltransferase (COMT) gene underlies some of this executive heterogeneity. In particular, an increasing number of methionine alleles, resulting in lower enzyme activity, is associated with impaired performance on the Tower of London planning task. The main objective of this study was to investigate the underlying neural basis of this genotype-phenotype effect in PD using functional MRI. We scanned 31 patients with early PD who were homozygous for either val (n=16) or met (n=15) at the COMT val158met polymorphism during performance of an executive task comprising both Tower of London ('planning') and simple subtracting ('control') problems. A cross-group comparison between genetic subgroups revealed that response times for planning problems were significantly longer in met compared to val homozygotes, whereas response times for control problems did not differ. Furthermore, imaging data revealed a significant reduction in BOLD signal across the frontoparietal network involved in planning in met/met compared to val/val patients. Hence we have demonstrated that COMT genotype impacts on executive function in PD through directly influencing fronto-parietal activation. Furthermore, the directionality of the genotype-phenotype effect observed in this study, when interpreted in the context of the existing literature, adds weight to the hypothesis that the relationship between prefrontal function and dopamine levels follows as inverted U-shaped curve.