The cause of the progression of Alzheimer’s disease discovered

British and American researchers have just made a breakthrough that could potentially improve substantially the treatments against Alzheimer’s disease. A great hope for the 40 million people suffering from that disease worldwide.

This is a major advance in the understanding of Alzheimer's disease. In a study published in Sciences Advances, a team of researchers from the universities of Cambridge, University College London and Harvard describe the cause of the progression of Alzheimer's disease.

The scientific community knew that a protein called tau was involved in the disease. This one and another protein, beta-amyloid, accumulate, causing brain cells to die and the brain to shrink.

This causes, among other things, memory loss and an inability to perform everyday tasks. The disease is one of the major public health problems, affecting more than 40 million people worldwide.

However, although they are thought to be responsible for the cognitive decline associated with Alzheimer's disease, it was not known that they accumulate in different areas of the brain over decades. The study thus overturns the theory that clusters form in one place and trigger a chain reaction in other areas, a pattern seen in mice. Such a spread can occur, but it is not the main driver, according to the researchers.

A study made possible by analysis of human data

To reach such conclusions, the researchers used human data for the first time to quantify the speed of the molecular processes leading to this neurodegenerative disease. Such data could influence the way treatments are designed.

Georg Meisl, a chemist at the University of Cambridge and one of the lead authors of the paper, tells Agence France Presse:

"Two things made this work possible. First, the study of very detailed data from PET scans [a type of medical imaging test] and various data sets collected; and second, the mathematical models that have been developed over the last ten years," he says.

The researchers used 400 brain samples taken after the death of people with Alzheimer's and 100 PET scans from people living with the disease to track the aggregation of the tau protein.

A discovery full of hope

The researchers also found that it takes five years for the aggregates to double in number. This is an encouraging figure, according to Georg Meisl, because it shows that neurons are already capable of fighting aggregates.

"Perhaps if we can improve them a little, we can delay the onset of the serious disease considerably," says Georg Meisl.

Alzheimer's disease is classified according to Braak's stages, and scientists have found that it takes about 35 years to go from stage 3, where mild symptoms appear, to stage 6, the most advanced.

The clusters grow exponentially, which explains why the disease takes so long to develop and why people tend to get worse quickly, says Georg Meisl.

The team wants to apply the same methods to study traumatic brain injury and frontotemporal dementia, in which tau protein also plays a role. As far as Alzheimer’s disease concerned, scientists now will have to tackle another issue of the disease: neurofibrillary degenerations, which consist of serious lesions of neurons as well.