RELN and major depressive disorder: 2024). The ε4 allele increases risk for late‐life depression, worsens cognitive outcomes in BD (Bellivier et al. 1997, De Souza et al. 2010, Feng et al. 2015, Kerr et al. 2016), and contributes to SZ‐related brain abnormalities via disrupted cholesterol regulation and interactions with reelin (Digney et al. 2005, Gibbons 2011, Vila‐Rodriguez 2011).