APOA1 and Parkinson disease: ApoA1, as the main component of HDL, is also necessary for cholesterol transportation in the brain, and the plasma level of apoA1 is lower in PD patients than that in normal individuals, indicating a possible role for apoA1 in the pathogenesis of PD (Swanson et al. 2015; Qiang et al. 2013; Wang et al. 2010).