When news about a startling new insight into the cause of Alzheimer’s disease first emerged in 2005, it was highly speculative. But now the evidence for it has become very strong: Alzheimer’s is a form of diabetes, and the name being given to it is type 3.

In Alzheimer’s, proteins called beta amyloid plaques begin replacing normal brain cells, eventually leading to the classic symptoms of the disease, including disorientation, loss of memory and aspects of personality. How the plaques develop had been a mystery until the early 2000s, when Brown University neuropathologist Suzanne de la Monte began experimenting with blocking the path of insulin in lab rats’ brains.

When she did, the animals began exhibiting the symptoms of Alzheimer’s. She concluded that a lack of insulin could be a crucial factor in allowing the plaques to develop. In short, the onset of Alzheimer’s could be considered a form of diabetes, specific to the brain.