Brain’s immune cells may explain why a fading sense of smell is an early signal for Alzheimer's disease even before cognitive impairments manifest, according to a study.

Researchers at DZNE and Ludwig-Maximilians-Universität München (LMU) in Germany revealed that the brain's immune response seems to fatally attack neuronal fibres crucial for the perception of odours.

These olfactory dysfunctions arise because immune cells of the brain called "microglia" remove connections between two brain regions, namely the olfactory bulb and the locus coeruleus, they noted in the paper published in the journal Nature Communications.