Consequently, individuals carrying these mutations have undetectable levels of sTREM2 in their CSF and blood.21 Given that the selective expression of TREM2 in microglia within the CNS is linked to both AD and neurodegeneration, let us hypothesize that sTREM2 in CSF could serve as an indicator of microglial function and its response to Aβ and tau pathologies, as well as neurodegeneration. Here, TREM2 is linked to Alzheimer disease.