Alzheimer’s disease can have two phases

THURSDAY, Oct. 17, 2024 (HealthDay News) — Alzheimer’s disease can damage the brain in two distinct phases, a new study suggests.

An early phase that occurs slowly and silently appears to lay the groundwork for a second, more broadly destructive phase of Alzheimer’s disease, according to sophisticated brain scans.

“The results fundamentally alter scientists’ understanding of how Alzheimer’s disease harms the brain and will guide the development of new treatments for this devastating disease,” said Dr. Richard Hodes, director of the National Institute on Aging.

Previous studies have suggested that the damage caused by Alzheimer’s disease occurs in several stages, characterized by increasing levels of neuron death, inflammation and the accumulation of toxic proteins in the brain.

But these results indicate that there are only two phases of Alzheimer’s disease, with most of the traditional symptoms and brain damage occurring quickly during the second phase, the researchers said.

Brain scans of 84 people suggest that the first phase occurs before any memory problems arise.

During this phase, damage occurs to a type of brain cell called an inhibitory neuron, which can trigger the neural problems underlying Alzheimer’s, researchers said.

Inhibitory neurons send calming signals to other cells, the researchers said. The loss of these cells can strip the brain of a fundamental level of protection.

The first phase is also marked by a slow accumulation of toxic protein plaques, activation of the brain’s immune system, and damage to the insulation that protects neurons.

“One of the challenges in diagnosing and treating Alzheimer’s disease is that much of the damage to the brain happens well before symptoms occur,” Hodes said. “The ability to detect these changes early means that, for the first time, we can see what is happening to a person’s brain during the early periods of the disease,”

Once the scene is set, the second phase of Alzheimer’s disease ensues. People begin to develop obvious memory and cognitive problems, and the harmful features of Alzheimer’s disease quickly accumulate – among them beta-amyloid plaques and tau tangles.

Researchers learned this by using advanced genetic analysis tools to study cells in the middle temporal gyrus, a part of the brain that controls language, memory and vision. This region has been shown to be vulnerable to many of the changes caused by Alzheimer’s disease and has been thoroughly mapped in previous research, the researchers said.

By comparing healthy brains with those of Alzheimer’s patients, researchers have created a genetic and cellular timeline of what happens during the disease.

The new study was published October 14 in the journal Neuroscience of Nature.

More information

The US Centers for Disease Control and Prevention has more information about Alzheimer’s disease.

SOURCE: National Institute on Aging, press release, October 15, 2024