APOE and familial Alzheimer disease: In addition, we performed subgroup analysis on the family history and the status of APOE4 to compare the difference in AAO between the two groups respectively, which showed that the AAO of FAD patients was significantly younger than that of SAD (63.2 ± 11.4 and 64.9 ± 10.6, respectively, p = 0.005), while no significant between APOE4 carriers and non-carriers (p = 0.953) (Fig. 3e, f).