A gene variant called APOE4 dramatically increases the risk of late-onset Alzheimer's disease, the most common form of dementia. Now, emerging research is revealing APOE4's true role in the condition, and a new study pinpoints a possible way to treat it.Historically, scientists studying Alzheimer's disease have focused on two proteins that accumulate in patients' brains: amyloid-beta and tau. However, there's a "third thing that people didn't pay attention to, until recently," said study co-author Li-Huei Tsai, a neuroscientist at MIT. That third thing is the accumulation of droplets of fat, or lipids, in the brain, she told Live Science.The APOE gene makes proteins responsible for transport...