APOE and Alzheimer disease: Multiple variants associated with PD risk have also been identified as risk factors for AD, DLB, or FTD including variants in the following genes: Triggering receptor expressed on myeloid cells 2 (TREM2), Microtubule-associated protein tau (MAPT), C9orf72, Glucocerebrosidase (GBA), and Apolipoprotein E (APOE) (Parsian et al., 2002; Harms et al., 2013; Davis et al., 2015; Benitez et al., 2016).