Aged microglial phenotypes need a temporal axis

The comparison of Trem2 R47H mutation, Trem2 deficiency, and control states in aged AppNL-F mice can establish genotype-associated differences, but a single late-age contrast cannot show how those differences emerged. Repeated measurements at matched ages would distinguish an early, persistent phenotype from progressive divergence or a transient state tied to contemporaneous pathology. The word “mild” also needs an explicit reference: effect size relative to within-group variability, measurement repeatability, and the difference produced by complete Trem2 deficiency. Functional divergence may matter even when aggregate phenotypic distance is small, so individual features should be linked prospectively to later cognitive, synaptic, or pathological outcomes. The strongest evidence would be an early within-animal microglial change that predicts subsequent functional decline beyond baseline pathology and chronological age.