Loss of smell and Alzheimer’s disease

Research is trying to identify more and more diagnostic methods for detecting Alzheimer's disease. Indeed, the earlier it is treated, the more likely it is that its progression can be slowed. One symptom could make its identification possible in its early stages: loss of smell.

𝐀𝐥𝐳𝐡𝐞𝐢𝐦𝐞𝐫'𝐬 𝐝𝐢𝐬𝐞𝐚𝐬𝐞 is a neurodegenerative disorder caused by the abnormal accumulation of 𝐛𝐞𝐭𝐚-𝐚𝐦𝐲𝐥𝐨𝐢𝐝 𝐩𝐞𝐩𝐭𝐢𝐝𝐞 and modification of the 𝐭𝐚𝐮 𝐩𝐫𝐨𝐭𝐞𝐢𝐧. According to the World Health Organization, 55 million people worldwide are affected. There is currently 𝐧𝐨 𝐜𝐮𝐫𝐚𝐭𝐢𝐯𝐞 𝐭𝐫𝐞𝐚𝐭𝐦𝐞𝐧𝐭. A blood test that detects biomarkers in plasma has just been approved in the United States. However, certain prodromal symptoms could be indicators of the disease, as approximately 85% of Alzheimer's patients experience 𝐞𝐚𝐫𝐥𝐲 𝐚𝐧𝐨𝐬𝐦𝐢𝐚/𝐡𝐲𝐩𝐨𝐬𝐦𝐢𝐚 before cognitive decline.

A German study published in 𝑁𝑎𝑡𝑢𝑟𝑒 𝐶𝑜𝑚𝑚𝑢𝑛𝑖𝑐𝑎𝑡𝑖𝑜𝑛𝑠 has shown that in mice, a 𝐥𝐨𝐬𝐬 𝐨𝐟 𝐧𝐨𝐫𝐚𝐝𝐫𝐞𝐧𝐞𝐫𝐠𝐢𝐜 𝐧𝐞𝐮𝐫𝐨𝐧𝐬 originating in the locus coeruleus, located in the brainstem and connected to the 𝐨𝐥𝐟𝐚𝐜𝐭𝐨𝐫𝐲 𝐛𝐮𝐥𝐛, coincides with olfactory disorders in mice, before the appearance of amyloid plaques. This loss of neurons is thought to be caused by the destruction of the axons of these noradrenergic neurons 𝐛𝐲 𝐦𝐢𝐜𝐫𝐨𝐠𝐥𝐢𝐚. This neuronal loss has also been found post-mortem in the 𝐛𝐫𝐚𝐢𝐧𝐬 𝐨𝐟 𝐝𝐞𝐜𝐞𝐚𝐬𝐞𝐝 𝐩𝐚𝐭𝐢𝐞𝐧𝐭𝐬 who had Alzheimer's disease.

Although there are no curative drugs available yet, four molecules targeting the symptoms of the disease are 𝐚𝐯𝐚𝐢𝐥𝐚𝐛𝐥𝐞 𝐨𝐧 𝐭𝐡𝐞 𝐦𝐚𝐫𝐤𝐞𝐭 𝐢𝐧 𝐅𝐫𝐚𝐧𝐜𝐞 (anticholinesterases and antiglutamates). Two new drugs (𝐚𝐧𝐭𝐢-𝐚𝐦𝐲𝐥𝐨𝐢𝐝 𝐚𝐧𝐭𝐢𝐛𝐨𝐝𝐢𝐞𝐬) are expected to appear on the market soon.