Familial AD is mainly associated with mutations in PSEN1, PSEN2, and APP genes which lead to an excessive production of Aβ, or total tau (t-tau) and p-tau proteins [40, 41]. Aβ positron emission tomography is commonly used in clinical practice to quantify and localise the accumulation of Aβ in the brains of patients with AD. The gene discussed is PSEN2; the disease is Alzheimer disease.