Variations in genes glucosylceramidase (GBA), microtubule-associated protein tau (MAPT), leucine-rich repeat serine/threonine-protein kinase 2 (LRRK2), α-synuclein (SNCA) and apolipoprotein E (APOE) are believed to impact cognition in PD patients [6]. The gene discussed is APOE; the disease is Parkinson disease.