SLC2A9 and Parkinson disease: MR was used by Simon et al. (2014) to investigate whether genetic variants that can predict serum urate levels can predict the rate of progression in patients with early PD, on the basis that higher serum urate levels lower the risk of developing pD. In this study, the authors used SLC2A9 gene as an IV, which explains most of the genetically specified variability in serum urate levels but does not have any known direct associations with the central nervous system.