By Dr. Priyom Bose, Ph.D. Reviewed by Lauren Hardaker Sep 4 2025 New research reveals that immune cells attack brainstem nerve fibers linked to smell, making loss of smell the earliest detectable sign of Alzheimer’s disease, and a potential window for earlier diagnosis. Study: Early Locus Coeruleus noradrenergic axon loss drives olfactory dysfunction in Alzheimer’s disease . Image credit: Ground Picture/Shutterstock.com A recent study in Nature Communications examines how the early loss of the