HFE and Parkinson disease: Separately, a group reported observations relating to serum iron and PD, using data from PD GWAS.23 Three genetic variants were used as instrumental variables (HFE rs1800562, HFE rs1799945, and TMPRSS6 rs855791) and were associated with serum iron levels (accounting for 1.7%, 0.9%, and 1.7% of iron total variance, respectively).