A plain-English glossary of APOE4 terms

Reading about APOE4 means wading through vocabulary borrowed from genetics, neurology, and cardiology all at once. Keep this page open as a cheat sheet. The definitions are deliberately plain, with links to the deeper dives where they exist.

The genetics words

APOE is the gene (and the protein it makes, apolipoprotein E) responsible for moving cholesterol and fats around the body and brain.

Allele is a version of a gene. APOE has three common alleles: ε2, ε3, and ε4 (often written 2, 3, 4).

Genotype is your specific pair of alleles, one from each parent, for example 3/4 or 4/4. See the genotypes explained.

Carrier is shorthand for someone with at least one ε4 allele.

Homozygous / heterozygous: having two copies of the same allele (e.g. ε4/ε4, “homozygous”) versus two different ones (e.g. ε3/ε4, “heterozygous”).

The brain words

Amyloid-beta (Aβ) is a protein fragment that clumps into plaques between neurons, one of the hallmarks of Alzheimer’s. APOE4 is linked to clearing it less efficiently.

Tau is a protein that, in disease, forms tangles inside neurons. The other classic Alzheimer’s hallmark.

Neuroinflammation is the brain’s immune response; when chronic, it may accelerate damage.

MCI (mild cognitive impairment) is measurable decline beyond normal aging that doesn’t yet derail daily life. More in MCI and early detection.

Biomarker is a measurable biological signal (in spinal fluid, on a PET scan, or increasingly in blood) that reflects disease processes.

The heart and metabolic words

LDL-C is the cholesterol carried in LDL (“bad cholesterol”), the familiar number on a standard panel.

ApoB is a protein on every artery-clogging particle, so it counts those particles directly. It’s often a better risk signal than LDL-C; see ApoB vs. LDL-C.

Insulin resistance is when cells stop responding well to insulin, the engine behind prediabetes and a factor in metabolic and brain health.

The treatment words

Anti-amyloid antibodies are drugs (like lecanemab and donanemab) that clear amyloid and modestly slow early Alzheimer’s. See the deep dive.

ARIA (amyloid-related imaging abnormalities) is brain swelling or small bleeds seen on MRI during anti-amyloid treatment. It’s more common in APOE4 carriers, especially ε4/ε4, which is why genotype now factors into treatment decisions.

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If a term you’ve hit isn’t here, it’s a fair bet it links back to one of the deep dives. If you spot something we should add, that’s exactly the kind of gap we want to close.