What this means

APOE is a gene involved in transporting cholesterol in the brain and in clearing amyloid-beta. The ε4 variant is one of three common forms (ε2, ε3, ε4) and is the single most studied genetic risk factor for late-onset Alzheimer's disease. Carrying ε4 is a *risk factor*, not a diagnosis — many ε4 carriers never develop Alzheimer's, and many people with Alzheimer's carry no ε4 alleles at all.

APOE makes a protein that helps move cholesterol around the brain and helps clear away a sticky substance called amyloid-beta. The gene comes in three common versions — ε2, ε3, and ε4. ε4 is the single most studied genetic risk factor for late-onset Alzheimer's disease. Having ε4 is a *risk factor*, not a diagnosis. Many people with ε4 never develop Alzheimer's, and many people with Alzheimer's don't have ε4 at all.

Caveats

• Risk estimates vary substantially across populations and have been most studied in people of European ancestry.
• Lifestyle factors (cardiovascular health, sleep, education, exercise) modify risk meaningfully.
• This does not predict early-onset Alzheimer's, which has very different genetics.
• Disclosing APOE status can carry psychological cost. Genetic counselling is recommended before acting on the result.

Populations

• Studied across most major ancestry groups

References

• Corder et al. — Gene dose of apolipoprotein E type 4 allele and the risk of Alzheimer's disease in late onset families (Science, 1993)
• Farrer et al. — Effects of age, sex, and ethnicity on the association between APOE genotype and Alzheimer disease (JAMA, 1997)
• Bellenguez et al. — New insights into the genetic etiology of Alzheimer's disease (Nature Genetics, 2022)