– You have one of six possible variations of the APOE gene, having inherited one variant—e2, e3, or e4—from each parent. Reporting in the journal Neuron, University of Hawaii researchers found that the brain development of children as young as preschool age with two copies of e4 or one of e4 and one of e2 seem most adversely affected—an intriguing find in light of previous research that has linked the e4 variant to Alzheimer's. Researchers scanned the brains of 1,187 healthy people between the ages of 3 and 20 and found, for instance, that the size of the hippocampus tends to be smaller in those with the e2/e4 combination. They also found some kids with e4 didn't perform as well on tests of memory, though they caught up with their peers by age 10, reports HealthDay News. And while brain researcher Rebecca Knickmeyer, who didn't participate in the study but wrote an accompanying editorial, says the variants aren't necessarily predictive and people shouldn't start testing their kids, the research suggests that Alzheimer's may in fact be a developmental disorder, not strictly an aging one, reports the Los Angeles Times. That raises the possibility that adjustments to "diet or cognitive training" early on could change someone's "trajectory," per Knickmeyer. Three in four people have at least one copy of e3, which seems to offer a protective effect. About 14% of people have an e4 variant, which has been linked with an elevated risk of Alzheimer's, but Knickmeyer points out that there are many Alzheimer's patients without e4, and many with e4 who never develop Alzheimer's. (Some research suggests that memories lost to Alzheimer's are actually retrievable.)