A dedicated analysis of the APOC1 promoter variant that amplifies APOE4 pathology through two independent mechanisms.
Kept as its own domain because it works through a different mechanism from the TOMM40 variant in Domain II.
The Biology
APOE does not act in isolation. Its neighbors on chromosome 19 share regulatory regions with it and can influence how strongly the ε4 allele affects disease risk. The APOC1 protein normally limits receptor-mediated lipoprotein uptake by competing with APOE for binding to the LDL receptor. When the H2 haplotype raises APOC1 expression, that competition intensifies, worsening the lipid clearance deficit already seen with APOE4, while APOE4 expression in brain tissue also rises.
What Varia Analyzes
APOC1 (rs4420638), a proxy for the H2 promoter haplotype associated with higher APOC1 transcription. This analysis is kept separate from Domain II because APOC1 H2 works differently from TOMM40: it amplifies APOE4 pathology itself, through competitive LDL receptor inhibition that worsens lipoprotein clearance and through higher APOE4 expression in brain tissue.
Why It Matters
For people who carry APOE4, the APOC1 H2 result adds a second layer of context that a standard APOE test does not capture; two copies of APOE4 together with the H2 haplotype is the combination the catalog's sources describe as the strongest amplification. For people without APOE4, this result is typically neutral, and the analysis runs either way.
Key Sources
- Drigalenko E, et al. Interaction of the apolipoprotein E and CI loci in predisposing to late-onset Alzheimer's disease. Neurology. 1998.
- Petit-Turcotte C, et al. Apolipoprotein C-I expression in the brain in Alzheimer's disease. Neurobiol Dis. 2001.
- Jong MC, et al. Role of ApoCs in lipoprotein metabolism: functional differences between ApoC1, ApoC2, and ApoC3. Arterioscler Thromb Vasc Biol. 1999.