Abnormality with special cells that wrap around blood vessels in the brain leads to neuron deterioration, possibly affecting the development of Alzheimer's disease, a study reveals. 'Gatekeeper cells' called pericytes surround blood vessels. They contract and dilate to control blood flow to active parts of the brain. Pericyte degeneration may be ground zero for neurodegenerative disorders like Alzheimer's disease, ALS and possibly others, researchers said.