Sniffing Out Why Alzheimer’s Patients Lose Their Sense Of Smell

The loss of smell is indicative of early stage Alzheimer’s disease, and Korean researchers now understand how this happens.

AsianScientist (Oct. 3, 2017) – A team of researchers led by Professor Moon Cheil of the Department of Brain and Cognitive Sciences at the Daegu Gyeongbuk Institute of Science and Technology (DGIST) has identified the reason why patients with the early stage of Alzheimer’s disease (AD) fail to smell. Their findings are published in Cell Death & Disease.

AD is the most common degenerative brain disease, accounting for 60 to 80 percent of all dementia cases. The greatest known risk factor is aging—the majority of people with AD are 65 years of age and older. In Korea, the number of patients with degenerative brain disease is increasing at an unprecedented rate.

Currently, there is no underlying cure for dementia, but early detection of dementia may ameliorate or delay the onset of symptoms. Most drugs available on the market are focused on slowing the progression of dementia symptoms rather than the direct treatment of dementia. Therefore, the ability to diagnose dementia at an early stage will allow such drugs to be administered in a timely manner.

Recent studies have reported the association between AD onset and olfactory deterioration, meaning that individuals first start to lose their sense of smell. However, the specific mechanism by which this occurs remains unclear.

In this study, researchers studied not only the brain, but also the peripheral olfactory nervous system during the early stage of AD. They carried out a behavioral experiment using an animal model with AD and confirmed that olfactory dysfunction precedes brain cognitive dysfunction.

They then looked for the presence of beta-amyloid (Aβ) plaques in both the central and peripheral nervous system. The team detected direct expression of Aβ in the olfactory epithelium which contains olfactory nerve cells that are part of the peripheral nervous system. The researchers further demonstrated that Aβ has a fatal effect on olfactory nerve cells and directly induces the failure of olfactory function.

“We have identified the mechanism of Aβ expression in the initial stage of AD that is responsible for olfactory dysfunction, which was unknown until now. We will carry out follow-up studies that will help in the development of early detection methods for dementia, as well as treatments for AD,” said Moon.

The article can be found at: Yoo et al. (2017) Differential Spatial Expression of Peripheral Olfactory Neuron-derived BACE1 Induces Olfactory Impairment by Region-specific Accumulation of β-amyloid Oligomer.


Source: Daegu Gyeongbuk Institute of Science and Technology; Photo: Shutterstock.
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