Researchers continue to investigate why the ApoE4 gene variant is associated with Alzheimer's disease: "A well-known genetic risk factor for Alzheimer's disease triggers a cascade of signaling that ultimately results in leaky blood vessels in the brain, allowing toxic substances to pour into brain tissue in large amounts, scientists report ... a gene called ApoE4 makes people more prone to developing Alzheimer's. People who carry two copies of the gene have roughly eight to 10 times the risk of getting Alzheimer's disease than people who do not. [Scientists] found that ApoE4 works through cyclophilin A, a well-known bad actor in the cardiovascular system, causing inflammation in atherosclerosis and other conditions. The team found that cyclophilin A opens the gates to the brain assault seen in Alzheimer's. ... In the presence of ApoE4, increased cyclophilin A causes a breakdown of the cells lining the blood vessels in Alzheimer's disease in the same way it does in cardiovascular disease or abdominal aneurysm ... In studies of mice, the team found that mice carrying the ApoE4 gene had five times as much cyclophilin A compared to other mice in cells known as pericytes, which are crucial to maintaining the integrity of the blood-brain barrier. Blood vessels died, blood did not flow as completely through the brain as it did in other mice, and harmful substances like thrombin, fibrin, and hemosiderin, entered the brain tissue. When the team blocked the action of cyclophilin A, either by knocking out its gene or by using the drug cyclosporine A to inhibit it, the damage in the mice was reversed. Blood flow resumed to normal, and unhealthy leakage of toxic substances from the blood vessels into the brain was slashed by 80 percent."