Motor complications in patients form the German Competence Network on Parkinson's disease and the DRD3 Ser9Gly polymorphism

In addition to levodopa treatment and disease duration, genetic predisposition might contribute to the development of medication-related complications in Parkinson's disease (PD). As recent observations indicate the dopamine D₃ receptor (DRD3) to modulate both therapeutic action of levodopa and dyskinesia, we reappraised the impact of the DRD3 Ser9Gly polymorphism on development of motor complications in a large scale association study based on the gene bank of the German Competence Network on Parkinson's disease. Stepwise regression analysis revealed no effect of DRD3 Ser9Gly on chorea, dystonia, or motor fluctuations in PD, despite incorporating established clinical risk factors to avoid overlooking an effect of genotype. Duration of PD was confirmed as the most important clinical risk factor, followed by age of disease onset and female sex. Additional studies incorporating grading of motor complications, and combinations of risk genotypes, are warranted.