APOE ε4 allele (mechanism)

The APOE ε4 allele is a gene variant that makes the E4 form of apolipoprotein E. It differs from the common ε3 form by a single building block at position 112 (cysteine swapped for arginine). That small change alters how the protein handles fats, so it clears triglyceride-rich remnants and LDL from your blood less efficiently. In your brain, E4 causes more trouble. It hampers clearance of amyloid-β across the blood-brain barrier and by support cells, promotes tau pathology, and fans neuroinflammation, partly on its own, apart from amyloid. Its Alzheimer's risk is dose-dependent. One copy raises risk about 3 to 4 times, and two copies about 8 to 12 times, in European populations, with the exact numbers varying by ancestry. Despite all this, ε4 stays common, at roughly 14% of gene copies worldwide (from about 8 to 10% in East Asia to over 30% in some African populations). That likely reflects ancient trade-offs around immune function, fertility, and early-life thinking.

Last reviewed: June 22, 2026

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