APOA1 and Parkinson disease: Directly linked to GPR5B (Figure 3) appears PCOLCE2, a gene coding for a procollagen C-proteinase enhancer [54] and involved in the regulation of proapolipoprotein (apo) AI (apoAI) posttranslational processing [55]: apoAI binds β-amyloid peptide, a major protein in the brain associated with Alzheimer's and Parkinson's diseases, thus preventing Abeta-induced neurotoxicity [76].