Mutations in presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP) are associated with early-onset AD, whereas familial PD has been linked to genetic variants in leucine-rich repeat kinase 2 (LRRK2) and synuclein alpha (SNCA) [3,6]. Here, APP is linked to Alzheimer disease.