The former group accounts for approximately 5% of the total number of AD patients, those who develop AD at an early age (24–65 years) and often carry genetic mutations associated with excessive production of Aβ, especially Aβ 1–42, such as the mutation in Aβ precursor protein (APP) and APP shearing enzyme presenilin-1/2 [68]. The gene discussed is PSEN1; the disease is Alzheimer disease.