APOE and neurodegenerative disease: AD is a multifactorial neurodegenerative disease in which environmental risk factors (i.e., toxins, xenobiotics, ultraviolet radiation and pollutants) and genetic factors (including mutations of amyloid precursor protein (APP), presenilin genes (PSEN1 and 2) and allelic variation in apolipoprotein E (Apo E)) interact to enhance the incidence [15,16].