The AD‐risk variant TREM2R47H—one of the strongest risk factors for late‐onset AD, second only to the ε4 allele of ApoE (ApoE4)15, 16—is thought to impair ligand binding by altering TREM2's CDR2 structure,17 compromising microglial function.14, 17, 18, 19. Here, APOE is linked to Alzheimer disease.