TH and nervous system disorder: For the genes identified in the Parkinson disease pathway, TH, DRD2, SLC18A2/VMAT2, and SLC6A3/DAT are well-known in PD for their roles in dopamine homeostasis including synthesis, signal receiving, storage and release, and reuptake (Venda et al., 2010); three tubulin genes, TUBA4A, TUBB2A, and TUBB3, are involved in microtubule-mediated axon outgrowth and maintenance, and vesicle trafficking (Lasser et al., 2018; Sferra et al., 2020), and mutations of these genes have been identified to cause neurological disorders (Chakraborti et al., 2016).