PRRG4 and Parkinson disease: Specifically, knockdown of Stmn2 upregulated nine PD GWAS genes (GPNMB, SREBF1, STAB1, LHFPL2, PRRG4, CTSB, FNDC3B, PPFIBP1, and COL5A2), and downregulated one PD GWAS gene (SYT4) at the mRNA level.