By Dr. Brian McDonough, Medical Editor

PHILADELPHIA (CBS) - Scientists are constantly searching for the cause of Alzheimer’s. Now, new research explains how a protein associated with Alzheimer’s disease risk can cause vascular defects in the brain.

The work describes how expression of the protein apoe4 leads to breakdown of brain tissue and altered blood flow, which in turn can lead to neurodegenerative changes in mice.

The apoe4 gene has been connected to defects in the blood supply. Now researchers say it appears to affect the blood brain barrier. This causes the barrier, which has a job of preventing toxic elements from entering brain tissue, to break down. This leads to damage in the brain and what researchers say are many of the affects.