APOE and type 2 diabetes mellitus: While genes such as TCF7L2, TNF, APOE and BDNF-related genes can heighten T2DM and schizophrenia risk (Alkelai et al., 2012; Mizuki et al., 2020; Perry et al., 2022), other genes may have opposing impacts and lead to inconsistent and biased LDSR findings (Perry et al., 2022).