Following on from the hypothesis of a role for the ApoE ε4 and ε2 alleles as risk and protective factors, respectively, for late-onset Alzheimer's disease (AD) came inevitable questions regarding other psychiatric conditions of late onset including depressive illness and schizophrenia. Is ApoE ε4 a risk factor in these diseases and do carriers have an earlier age of onset? Does ApoE ε2 have a protective role, with carriers of this allele having a later age of onset?