The extent of microglial heterogeneity in humans remains a central yet poorly explored question in light of the development of therapies targeting this cell type. Here, we investigate the population structure of live microglia purified from human cerebral cortex samples obtained at autopsy and during neurosurgical procedures. Using single cell RNA sequencing, we find that some subsets are enriched for disease-related genes and RNA signatures. We confirm the presence of four of these microglial subpopulations histologically and illustrate the utility of our data by characterizing further microglial cluster 7, enriched for genes depleted in the cortex of individuals with Alzheimer’s disease (AD). Histologically, these cluster 7 microglia are reduced in frequency in AD tissue, and we validate this observation in an independent set of single nucleus data. Thus, our live human microglia identify a range of subtypes, and we prioritize one of these as being altered in AD.

Objective:Examine the relationship between scalp EEG biomarkers of hyperexcitability in Alzheimer’s disease (AD) and determine how these electrical biomarkers relate to the clinical expression of seizures in AD.Methods:In this cross-sectional study, we performed 24-hour ambulatory scalp EEGs on 43 cognitively normal elderly healthy controls (HC), 41 early-stage AD participants with no history or risk factors for epilepsy (AD-NoEp), and 15 early-stage AD participants with late-onset epilepsy related to AD (AD-Ep). Two epileptologists, blinded to diagnosis, visually reviewed all EEGs and annotated all potential epileptiform abnormalities. A panel of 9 epileptologists, blinded to diagnosis, was then surveyed to generate a consensus interpretation of epileptiform abnormalities in each EEG.Results:Epileptiform abnormalities were seen in 53% of AD-Ep, 22% of AD-NoEp, and 4.7% of HC participants. Specific features of epileptiform discharges, including high frequency, robust morphology, right temporal location, and occurrence during wakefulness and REM, were associated with clinical seizures in AD. Multiple electrical biomarkers concordantly demonstrated a pattern of left temporal lobe hyperexcitability in early stages of AD, whereas clinical seizures in AD were often associated with bi-temporal hyperexcitability. Frequent small sharp spikes were specifically associated with epileptiform EEGs and thus identified as a potential biomarker of hyperexcitability in AD.Conclusion:Epileptiform abnormalities are common in AD, but not all equivalent. Specific features of epileptiform discharges are associated with clinical seizures in AD. Given the difficulty recognizing clinical seizures in AD, these EEG features could provide guidance on which AD patients are at high risk for clinical seizures.

No abstract