The catechol-O-methyltransferase Val(158)Met polymorphism modulates fronto-cortical dopamine turnover in early Parkinson's disease: a PET study. - Wu K; O'Keeffe D; Politis M; O'Keeffe GC; Robbins TW; Bose SK; Brooks DJ; Piccini P; Barker RA; Wu, Kit; O'Keeffe, Deirdre; Politis, Marios; et al. (Brain: A Journal of Neurology, 2012)