APOE4 is a variant of the APOE gene that is associated with higher Alzheimer’s risk. Carrying one copy is linked to roughly a three-fold increase in lifetime risk, and carrying two copies raises it further, with most research estimating a 40 to 60 percent lifetime risk. However, many people with APOE4 never develop Alzheimer’s, and many people with Alzheimer’s don’t carry it. APOE4 influences risk and timing — it is not a diagnosis.