APOE and Alzheimer disease: Hong et al. (2011) compared the frequency of APOE ε4 and the difference in clinical features between AD and SIVD patients, with and without severe white matter hyperintensities (WMH). APOE ε4 was more prevalent in AD than SIVD patients while the frequency was not affected by the presence or absence of WMH (Hong et al., 2011). However, severe WMH and APOE ε4 have an interactive effect on memory cognitive function (Son et al., 2012; Table 3).