Opioid K receptor variant is associated with a delayed onset of dyskinesias in Parkinson’s disease

Risk factors for levodopa-induced dyskinesias (LIDs) in Parkinson’s disease (PD) include young age at onset, disease progression and individual dose of levodopa.1 Nevertheless, established risk factors do not fully explain the marked individual variability in the time elapsing between levodopa initiation and the onset of LIDs, and genetic predisposition is likely to play a critical role. To identify the genetic determinants modulating the time at onset of LIDs, we investigated 10 polymorphisms previously associated with LIDs in PD. Among these variants, we selected those additionally associated with addictive disorders, based on the recent hypothesis that pathophysiological mechanisms underlying LIDs share similarities with non-motor hyper-dopaminergic states, such as addictive disorders (including impulse control disorders).2 Clinical records of consecutive outpatients diagnosed with PD, attending our clinic from April 2009 to April 2011 and contributing to the ‘Parkinson Institute Biobank’, were retrospectively reviewed. We included only patients who were free of LIDs at baseline and who developed LIDs during the follow-up (to maximise the accuracy in recording the date of onset of LIDs and to overcome the limitation due to the retrospective study design). Patients were visited at least twice/year by the same neurologist. The onset of LIDs was defined as the first-ever report by the neurologist (off-state dystonia excluded).(e-1) We compared demographic and clinical variables with those of an independent cohort of 1002 PD patients followed during the same period, fulfilling similar inclusion/exclusion criteria but whose genetic data were not available (see online …