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APOE helps move fats and cholesterol around the body and the brain. It comes in three common versions. One of them, ε4, raises the risk of Alzheimer's disease substantially; another, ε2, appears to lower it. Raising risk is not the same as causing disease: plenty of ε4 carriers never develop Alzheimer's, and plenty of people with Alzheimer's do not carry it.
APOE, at 19q13.32, encodes apolipoprotein E, existing as ε2, ε3 and ε4 isoforms. ε4 is the strongest common genetic risk factor for late-onset Alzheimer's disease, with risk increasing by copy number; ε2 appears protective. The Christchurch variant (R136S) has been associated with striking protection in a carrier of a dominant Alzheimer's mutation. Editing is used to construct isogenic models; therapeutic editing faces both delivery barriers and the difficulty of intervening against a risk factor.
Sources
- National Institute on Aging
Alzheimer's disease genetics fact sheet ↗