APOE4 is a variant of the apolipoprotein E gene. It is the strongest known genetic risk factor for late-onset Alzheimer’s disease.

Carrying one copy triples lifetime risk; carrying two copies can increase it twelvefold. Carriers often develop reduced blood flow to memory regions of the brain years before symptoms appear.

A University of Missouri study tested four weeks of low-dose rapamycin in people aged 45 to 65. Only APOE4 carriers showed improved cerebral blood flow. The work appeared in the Journal of Cerebral Blood Flow & Metabolism.

Women showed the largest gains, important because women account for nearly two-thirds of Alzheimer’s cases.

Having APOE4 does not guarantee the disease. Scientists study it to find early prevention windows, since treating risk decades before symptoms may work better than treating the disease itself. Genetic testing can reveal APOE4 status, but doctors recommend counselling first. Researchers advise lifestyle steps like exercise, diet and blood pressure control.