These candidate genes included: (a) genes implicated in neurodegeneration such as AD and Parkinson's disease (PD); (b) AD‐related genes such as APP and APOE and interacting pathways; (c) genes implicated in cognitive function such as memory formation mechanism and neuronal receptors; and (d) genes implicated in lipid metabolism such as cholesterol synthesis, transport, and metabolism, e.g. APOE and CETP. Here, APOE is linked to Parkinson disease.