APOE and Alzheimer disease: Several genes like apolipoprotein (APOE4), presenilin-2 (PSEN2), presenilin-1(PSEN1), amyloid-beta precursor protein (APP), microtubule-associated protein tau (MAPT), etc., are also associated with a higher or lower risk of sporadic early or late-onset of AD (Fig. 4) [93].