Mechanistic description
TREM2 loss-of-function variants impair microglial survival, clustering around amyloid plaques, and phagocytic clearance, creating a non-cell-autonomous amplification loop where dysfunctional microglia accelerate tau pathology. This hypothesis has the strongest human genetic support (R47H OR ~2-4 for AD risk) and active clinical validation through AL002c Phase II trials (TRAILBLAZER-ALZ2). The mechanism is druggable via agonism antibodies, with validated biomarker (sTREM2) for patient stratification. Key uncertainties include timing dependency—TREM2 agonism likely beneficial only in early-mid disease—and species differences in TREM2 signaling. The Skeptic’s revised 0.78 confidence captures the modest effect size and bidirectional complexity, while Domain Expert assigns 0.82 reflecting the clinical validation trajectory.
Evidence for (8)
TREM2 R47H and R62H variants confer AD risk in large GWAS; PMID 28165511
TREM2 deficiency impairs plaque-associated microglial clustering and survival; PMID 26741508
TREM2 limits neurodegeneration in mouse models; PMID 29196612
AL002c (TREM2 agonist) in Phase II trials with biomarker readouts
CSF sTREM2 validated as pharmacodynamic marker correlating with disease progression
TREM2 deficiency decreases microglial chemotaxis toward amyloid plaques via dysregulated Syk kinase pathway activation
TREM2 signaling is required for microglial survival in amyloid-rich brain environments
TREM2 signaling is required for microglial survival in amyloid-rich brain environments
Evidence against (3)
TREM2 R47H OR 2-4 represents risk amplification, not primary driver; effect size modest for monotherapy
Some studies show TREM2 deficiency protects against excitotoxicity—bidirectional effects context-dependent
AL002c early-phase trials showed limited CNS target engagement and biomarker effects