Your brain has multiple independent systems for clearing the beta-amyloid that accumulates in Alzheimer's disease.
Seven of the most validated genetic regulators of beta-amyloid clearance, microglial function, and amyloid precursor protein trafficking.
The Biology
The APOE gene affects Alzheimer's risk primarily through its role in beta-amyloid binding and transport. But the brain's clearance systems are more complex than a single protein. Microglial cells. The brain's immune cells. Must sense, engulf, and degrade amyloid aggregates. Endocytic pathways must efficiently process and recycle cellular waste. Complement system proteins must opsonize amyloid for phagocytosis. Sorting receptors must direct amyloid precursor protein away from the amyloidogenic processing pathway.
What Varia Analyzes
Seven variants across these systems. TREM2 R47H (rs75932628), which governs microglial amyloid sensing and phagocytosis and carries Alzheimer's risk comparable to APOE4 heterozygosity when present; CLU/Clusterin (rs11136000), which mediates beta-amyloid solubilization; PICALM (rs3851179), a regulator of endocytic amyloid clearance with documented APOE4 interaction; BIN1 (rs7561528), associated with tau pathology; CR1 (rs6656401), a complement system receptor for amyloid clearance; ABCA7 (rs3764650), an ABC transporter involved in microglial lipid efflux; and SORL1 (rs641120), a neuronal sorting receptor that diverts amyloid precursor protein away from beta-amyloid production.
Why It Matters
These seven variants were identified in landmark genome-wide association studies of Alzheimer's disease across tens of thousands of participants. Their effects are additive. Carrying multiple risk variants across this domain compounds the baseline APOE4 picture. Equally important, carrying protective variants (the T allele at CLU, the G allele at PICALM) partially offsets risk from other loci. This domain is most powerful when read alongside Domain I.
Key sources
- Guerreiro R, et al. TREM2 variants in Alzheimer's disease. N Engl J Med. 2013.
- Harold D, et al. Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's disease. Nat Genet. 2009.
- Lambert JC, et al. Genome-wide association study identifies variants at CLU and CR1 associated with Alzheimer's disease. Nat Genet. 2009.
- Rogaeva E, et al. The neuronal sortilin-related receptor SORL1 is genetically associated with Alzheimer disease. Nat Genet. 2007.