Another DTI study comparing white matter in middle-aged APOE ε4 carriers and non-carriers (mean age, 47.6) significantly associated risk for AD with increased radial and mean diffusivity likewise in the corpus callosum and occipital pathways, among other regions (see Table 3 for full results) (Westlye et al., 2012). This evidence concerns the gene APOE and Alzheimer disease.