APOE and Alzheimer disease: Several studies (Tohgi et al., 1997; Reiman et al., 1998; O'Dwyer et al., 2012; Saeed et al., 2021) reported that individuals with APOE4 have markedly smaller HV, along with increased risks of AD and other dementias, compared to those without APOE4. The APOE4 may also interact with exposure to air pollution, including TRAP, potentially modifying its effects on AD-related traits (Schikowski et al., 2015; Ma et al., 2023).