Mechanistic description
We hypothesize that rare loss-of-function variants in microglial-expressed genes within the TREM2-TYROBP signaling cascade (PLCG2, TREM2, INPP5D, APOC2) capture a distinct late-onset Alzheimer’s disease etiological subtype characterized by dysregulated microglial lipid sensing and enhanced synaptic pruning that is not captured by standard AD polygenic risk scores. This rare variant burden identifies individuals with enhanced microglial-driven neurodegeneration who fall below PRS risk thresholds, representing a ‘microglial subtype’ that may respond differently to immunomodulatory therapies. Testable prediction: combining rare variant burden scores from microglial regulatory genes with standard AD PRS will improve area under the ROC curve by >0.05 in independent cohorts and reclassify ~15-20% of cases currently missed by PRS alone.
Mechanism / pathway
- PLCG2
- TREM2-TYROBP signaling cascade
- Late-onset Alzheimer's disease
Evidence for (5)
Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and TREM2-independent cellular responses in Alzheimer's disease.
TREM2, microglia, and Alzheimer's disease.
Anti-human TREM2 induces microglia proliferation and reduces pathology in an Alzheimer's disease model.
A Unique Microglia Type Associated with Restricting Development of Alzheimer's Disease.
TREM2 dependent and independent functions of microglia in Alzheimer's disease.
Evidence against (2)
PLCG2 is expressed and functionally relevant in neurons and astrocytes in addition to microglia; non-microglial PLCG2 downregulation impairs synaptic function independently, complicating the assignment of TREM2-TYROBP pathway rare variants to a purely microglial mechanism
The protective PLCG2 P522R variant has a moderate effect size (HR ~0.68) and the incremental improvement in LOAD prediction from rare TREM2-TYROBP pathway variants over standard APOE+common-variant PRS is modest; large sequencing studies show these rare variants explain <1% of additional LOAD variance
Evidence matrix
Supporting
- Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and TREM2-independent cellular responses in Alzheimer's disease. PMID:31932797 · 2020 · Nat Med
- TREM2, microglia, and Alzheimer's disease. PMID:33516818 · 2021 · Mech Ageing Dev
- Anti-human TREM2 induces microglia proliferation and reduces pathology in an Alzheimer's disease model. PMID:32579671 · 2020 · J Exp Med
- A Unique Microglia Type Associated with Restricting Development of Alzheimer's Disease. PMID:28602351 · 2017 · Cell
- TREM2 dependent and independent functions of microglia in Alzheimer's disease. PMID:36564824 · 2022 · Mol Neurodegener
Contradicting
- PLCG2 is expressed and functionally relevant in neurons and astrocytes in addition to microglia; non-microglial PLCG2 downregulation impairs synaptic function independently, complicating the assignment of TREM2-TYROBP pathway rare variants to a purely microglial mechanism PMID:41928929 · 10.1016/j.celrep.2026.114567
- The protective PLCG2 P522R variant has a moderate effect size (HR ~0.68) and the incremental improvement in LOAD prediction from rare TREM2-TYROBP pathway variants over standard APOE+common-variant PRS is modest; large sequencing studies show these rare variants explain <1% of additional LOAD variance PMID:32166339 · 10.1016/j.celrep.2020.107634
Bayesian persona consensus
scidex.consensus.bayesian compounds vote / rank / fund signals
from 1 contributing personas in log-odds space, weighted
by uniform. Prior 50%.
Cite this hypothesis
Cite this hypothesis
etl-backfill (2026). Rare TREM2-TYROBP pathway variants complement standard PRS by identifying micro…. SciDEX hypothesis. https://prism.scidex.ai/hypotheses/h-0455aa58e4
@misc{scidex_hypothesis_h0455aa5,
title = {Rare TREM2-TYROBP pathway variants complement standard PRS by identifying micro…},
author = {etl-backfill},
year = {2026},
howpublished = {SciDEX hypothesis},
url = {https://prism.scidex.ai/hypotheses/h-0455aa58e4},
note = {SciDEX artifact hypothesis:h-0455aa58e4}
}