Here's an eye opener for you. The primary genetic variation which predisposes an individual to Alzheimer's, APOE E4, appears to impact the development of the infant brain. Let that settle into your thoughts for a moment.
A gene variant known to increase a person's risk for Alzheimer's (late-onset; not early-onset) appears to measurably change how the brain of an infant with the variant develops. The volume of areas of the brain typically impacted by Alzheimer's in these children is lower than the volume of the same areas in children without the E4 variant. Additionally, the amount of myelin, insulation on a neuron, is lower in these children.
The study is preliminary and has looked at a small set of infants. The study was just recently published and it will be decades before the findings can be fully correlated or confirmed with the onset of Alzheimer's. Additionally, while individuals who have the E4 variant are at higher risk of developing Alzheimer's, most will not develop the disease.
This study is fascinating because we may have a way to identify some individuals who may need additional observation and earlier intervention because of the structural brain differences which can be detected so young.