The APOE genotypes explained: from 2/2 to 4/4
You inherit one APOE allele from each parent. Here’s what each of the six combinations, from protective 2/2 to higher-risk 4/4, actually means.
By the OutliveAPOE4 editorial team. How we research & source.
The APOE gene comes in three common versions: ε2, ε3, and ε4 (often written 2, 3, 4). You inherit one from each parent, so your genotype is a pair. Here’s how to read yours.
The three alleles
- ε2 is the least common, and is associated with lower Alzheimer’s risk.
- ε3 is the most common worldwide, and is treated as the neutral reference.
- ε4 is associated with higher risk of late-onset Alzheimer’s and, to a degree, cardiovascular disease.
The six genotypes
Ordered roughly from lower to higher Alzheimer’s risk relative to the common 3/3. These are population averages, not personal verdicts:
- 2/2: least common, and lowest average risk.
- 2/3: below-average risk.
- 2/4: a mixed inheritance, where the ε2 appears to partly offset the ε4. Risk is generally considered intermediate.
- 3/3: the reference genotype, with “average” risk. The most common result.
- 3/4: one ε4 copy, carrying meaningfully higher average risk than 3/3.
- 4/4: two ε4 copies, carrying the highest average risk and a tendency toward an earlier average age of onset.
A landmark 1997 meta-analysis established this dose-dependent pattern, where risk rises with the number of ε4 copies, and also showed the effect varies by age, sex, and ancestry. (See our deep dive on women and sex differences.)
Caveats worth keeping in mind
- Risk is not destiny. Many 4/4 carriers never develop Alzheimer’s, and not everyone with Alzheimer’s carries ε4.
- The numbers are averages drawn largely from specific study populations, and they don’t transfer perfectly to every individual.
- Ancestry matters. The strength of the ε4 association differs across populations, an active area of research.
What to do with your genotype
Whatever your pair, the action items come back to the same modifiable levers: cardiovascular health, exercise, diet, sleep, and metabolic health. If you carry one or two ε4 copies, those levers may matter more, not less.
Knowing your genotype is a starting point for a conversation with a clinician or genetic counselor, not a diagnosis. See how to get tested.
Sources & further reading
Related deep dives
- What is APOE4? A plain-language primer APOE4 is the most common genetic risk factor for late-onset Alzheimer’s. Here’s what the gene does, what carrying it means, and what it doesn’t mean.
- How to get tested for APOE4, and whether you should Consumer kits, clinical tests, and genetic counseling compared, plus the psychological and practical trade-offs of learning your APOE status.
- APOE4 myths vs. facts Carrier forums and headlines spread a lot of half-truths about APOE4. Here are the ones worth correcting, and what the evidence actually supports.