For anyone who knows they have an APOE4 allele, there's a potential lipid transport issue in the BBB. But there are multiple transport mechanisms, and the one that passes phospholipids seems unaffected. So, get your fish oil in phospholipid form, or develop a taste for caviar as fish eggs are the best source of omega-3 in phospholipid form.

Also that allele does not absolutely mean that you'll get dementia; you just need to be more careful/protective of your brain (do all the things that keep you from getting insulin resistant, avoid anything that might cause traumatic brain injury, e.g. football).

My mom, and one of her brothers, had Alzheimer's; I was pretty sure I had at least one APOE4. Major reason I sent a tube of spit off to get a DNA report, in spite of my concern over privacy. Turns out I don't have it. Gonna miss the caviar - but not the extra expense of phospholipid omega-3s.