The more we understand about Alzheimer’s disease, the faster we can work for better treatment and ultimately for treatment, which makes the discovery of four different subtypes of brain disease important.
Using machine learning algorithms trained to scan the brains of 1,143 people with healthy brains or brains affected by Alzheimer’s disease, the researchers identified four different ways in which tau proteins become entangled among neurons.
Misshapen tau proteins are closely linked to the development and progression of Alzheimer’s disease, but the pattern of tau entanglement in the brain was thought to be more or less the same for everyone with the disease.
“We have identified four clear patterns of tau pathology that have become clear over time,”
“The prevalence of subgroups varies between 18 and 30 percent, which means that all of these variants of Alzheimer’s disease are actually quite common and no one dominates, as we thought before.”
The first variant, found in 33 percent of cases, sees that the tau spreads mainly in the temporal lobe and affects the patient’s memory. The second, found in 18 percent of cases, spreads to other parts of the cerebral cortex – memory problems are less common, but difficulties in planning and performing actions are more common.
The third option, found in 30 percent of all cases, is when the tau spreads to the visual cortex (used to process vision) – patients have trouble orienting, estimating distance, and identifying shapes. The fourth and final variant, observed in 19 percent of cases, spreads asymmetrically in the left hemisphere of the brain and affects the processing of the tongue.
The findings were made possible by detailed 3D scans with positron emission tomography (PET). Subsequent analysis over two years confirmed the presence of these four different models in people with Alzheimer’s disease and may help explain why different people show different symptoms as the disease progresses.
“This suggests that Alzheimer’s disease is an even more heterogeneous disease than previously thought,” said neuroscientist Jacob Vogel of McGill University in Canada.
“We now have reason to re-evaluate the concept of typical Alzheimer’s disease and, in the long run, the methods we use to assess disease progression.”
Alzheimer’s is already the leading form of dementia worldwide, and the number of people affected continues to rise sharply as the population ages. We know that it causes permanent loss of neurons, but it is not yet clear exactly why this happens – and there is still no cure.
However, progress is being made. Previous studies have also looked at the division of Alzheimer’s disease into subtypes to give us a better understanding of the disease, while we also learn more about neurons vulnerable to Alzheimer’s disease and how its effects can be reversed.
The next step is to extend the analysis over a longer period of time – up to 10 years, the researchers suggest. Knowing which subtype is present in a patient can, for example, give him a better idea of what symptoms to expect and when, as well as open up opportunities for new treatments.
“This knowledge is important for physicians who evaluate patients with Alzheimer’s disease, and also makes us think about whether the four subtypes may respond differently to different treatments,” says Hanson.
The study was published in Natural medicine.