Bile acids have also been implicated in PD through genetic association studies. In a meta-analysis of genome-wide association study (GWAS) data based on the genotypes of 2,525,705 SNPs in 4238 PD cases and 4239 non-PD controls, a total of 3 SNPs were found to be statistically associated with PD, including a non-synonymous missense variant in HSD3B7 (hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 7) (Song and Lee, 2013). Recessive mutations in HSD3B7, which catalyzes the second step in the classical pathway of bile acid synthesis, are associated with loss of bile acid synthetic capability and progressive liver disease (Cheng et al., 2003). In a GWAS of 48,844 SNPs residing in miRNA-binding site variants, 32 SNPs were associated with PD that were located in the 3′ untranslated regions of 13 genes including HSD3B7 (Ghanbari et al., 2016), providing further genetic evidence for a role of bile acids in PD.