APOE gene ε2/ε3/ε4 polymorphism has been associated with a number of neurodegenerative diseases such as Alzheimer's and Parkinson's diseases [8,9], raising the possibility that this polymorphism might predispose to neurodegeneration of the retinal ganglion cells and the optic nerve axons in glaucoma. Here, APOE is linked to Parkinson disease.