“We’ve known for a long time that one particular variant is associated with risk for Alzheimer’s, but we want to know what in the brain is being changed by that variant and when the effect emerges,” she says. “So, there were studies looking at typical adults looking at this particular variant, which did show effects on brain volume, and we, of course, looked in the neonate and saw similar changes. That suggests a very early effect.”
The medial temporal lobe is heavily involved in the human memory process. The study suggests that those individuals with smaller medial temporal lobe sections create a vulnerability to losing brain volume—and that, in term, causes active Alzheimer’s symptoms to develop earlier.
Still, Knickmeyer says not everyone with the genetic variant is guaranteed to develop Alzheimer’s.
“For instance, let’s say we take two people, both carrying the risk variant, both perhaps with smaller medial temporal lobes,” she says. “One of them may have other factors that cause them to preserve what they already have, whereas the other might have genetic or environmental factors that cause them to lose faster than the general population. Those two people will have very different outcomes.”
And Knickmeyer adds that while this study alone won’t be enough to establish early Alzheimer’s detection, it might be one more step in the process.
“Any single common genetic variant isn’t going to be a good predictor,” she says. “But if we can get predictions from a much wider set of variants in combination with actual information about people’s brain development trajectories—that, I think, does hold promise for early identification and intervention.”