Smell loss as an early sign of Alzheimer's — study in mice and humans

Researchers in Germany have found, in a study using mice and humans, that loss of the sense of smell can be one of the earliest signs of Alzheimer’s, before cognitive impairment. 

Prior observations indicated that the sense of smell is impaired in patients with Alzheimer’s disease, but it was not clear why or when this occurs in the disease progression. 

Using mice that mimic Azheimer’s symptoms, scientists at the German Center for Neurodegenerative Diseases and the Ludwig-Maximilians-Universität München found that microglia, a type of brain immune cell, attack nerve fibres involved in the perception of odours and impair the mice’s response to smell, in early stages of the disease.  

Analysis of brain samples from Alzheimer’s patients and positron emission tomography (PET) scans of both people with Alzheimer’s and mild cognitive impairment showed nerve damage and odour identification impairment, supporting the findings in mice.  

 “Our findings could pave the way for the early identification of patients at risk of developing Alzheimer’s, enabling them to undergo comprehensive testing to confirm the diagnosis before cognitive problems arise,” said Jochen Herms, co-author of the study published in Nature Communications.