6 significantly different genes, including SERPINI1, PI3, glutamate-ammonia ligase, late cornified envelope 1C, lipocalin 2, and interleukin 18 (S4 Table), were found between PD and normal samples in the validation dataset, of which 2 down-regulated genes, PI3 and SERPINI1, were consistent in the two datasets. This evidence concerns the gene IL18 and Parkinson disease.