Many people think memory loss is the first sign of Alzheimer’s disease, but scientists have known for some time that this is not always true. One of the earliest changes can actually be a loss of smell.
People may notice they cannot smell food, flowers, or familiar scents as clearly as before. This can happen years before serious memory problems begin. Until now, scientists did not fully understand why this part of the brain is affected so early.
A new study has helped answer this question. The research was carried out by a team led by Professor Moon Cheil at the Daegu Gyeongbuk Institute of Science and Technology, working together with researchers from Maastricht University. The findings were published in the journal Alzheimer’s & Dementia.
To understand the importance of this work, it is helpful to know what happens in Alzheimer’s disease. This condition damages the brain slowly over time. It is caused in part by harmful proteins building up inside the brain.
Two of the most important proteins are amyloid beta and tau. These proteins form clumps and tangles that disrupt how brain cells communicate and eventually cause those cells to die.
Scientists already knew that these harmful proteins often appear early in areas of the brain linked to smell. These areas include the olfactory bulb, which receives smell signals, and the olfactory cortex, which helps the brain understand those smells.
However, what was not clear was how the brain’s immune system reacts in these areas during the early stages of the disease.
To investigate this, the researchers studied brain tissue from people who had died at different stages of cognitive health. Some had no signs of disease, some had mild memory problems, and others had Alzheimer’s disease. This allowed the team to track how changes developed over time.
The results showed that as Alzheimer’s disease progressed, harmful proteins increased sharply in both the olfactory bulb and the olfactory cortex. This confirmed that these areas are affected very early in the disease.
The most important discovery was how the brain’s immune cells responded differently in these two areas. The brain has special support cells, often called glial cells, that help protect and maintain brain health. Two main types of these cells are astrocytes and microglia.
In the olfactory cortex, astrocytes were more active. In the olfactory bulb, microglia played a larger role. This means that even though these two regions are closely connected, the brain reacts in different ways depending on the exact location.
The researchers compared this to firefighters using different methods depending on the type of building, even if the fire is part of the same event.
The study also found that a protein called apolipoprotein E builds up in the olfactory system in all patients, regardless of their genetic risk. This is important because one version of this protein, known as APOE ε4, is linked to a higher risk of Alzheimer’s.
However, this new finding suggests that the buildup may occur in many people, not just those with that genetic risk. This could make it useful as an early warning sign.
When reviewing these findings, it is clear that this study provides valuable new insight into how Alzheimer’s disease begins. It explains why problems with smell appear early and shows that different parts of the brain respond in unique ways. This could help scientists develop more targeted treatments in the future.
However, there are also limits to consider. The study used postmortem brain tissue, which means it shows what has already happened rather than how the disease develops in real time. More research in living patients will be needed to confirm how these findings can be used in diagnosis or treatment.
Even with these limitations, the study is an important step forward. It suggests that checking changes in smell and related brain areas could help detect Alzheimer’s disease earlier than before. Early detection is important because it may allow treatment to begin before serious damage occurs.
Overall, this research opens new possibilities for understanding and managing Alzheimer’s disease. It highlights the importance of paying attention to small changes, such as loss of smell, and shows how detailed brain studies can lead to better care in the future.
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Source: Daegu Gyeongbuk Institute of Science and Technology.
