Previously, a collection of thirty studies (search strategy in Table S7) surfaced in the genetic of Parkinson disease in Sweden, with alterations in the following genes: GBA, SNCA, POLG, PLPP4, HFE, LRRK2, S100B, PARK16, SLC45A3, NUCKS1, RAB7L1, SLC41A1, PM20D1, NFE2L2, GRIN2A, HLA-DRA, MAPT, GPNMB, CCDC62/HIP1R, SYT11, GAK, STX1B, MCCC1/LAMP3, ACMSD, FGF20, COMT, C9ORF72, POLG, GSTM1, NAT2, GSTP1, PSEN2, CYP2E1, UCH-L1, ERβ, CALCA, BDNF, and PON1. This evidence concerns the gene COMT and Parkinson disease.