A brain imaging study of 162 healthy babies (2-25 months) has found that those who carried the ApoE4 gene (60 of the 162) tended to have increased brain growth in areas in the frontal lobe, and decreased growth in several areas in the middle and rear of the brain (precuneus, posterior/middle cingulate, lateral temporal, and medial occipitotemporal regions) — areas that tend to be affected in Alzheimer’s disease.
While this does not mean that those children are destined to develop Alzheimer’s, the findings do suggest brains of ApoE4 carriers tend to develop differently from those of non-carriers, and perhaps these early changes provide a “foothold” for the development of Alzheimer’s pathologies.
 . Brain differences in infants at differential genetic risk for late-onset alzheimer disease: A cross-sectional imaging study. JAMA Neurology [Internet]. 2014 ;71(1):11 - 22. Available from: http://dx.doi.org/10.1001/jamaneurol.2013.4544