In this study we have not attempted to identify risk factors for AD and depression, but instead have chosen circulating IL 6, TNF α and 25-hydroxyvitamin D as our study parameters because of the accumulated evidence that elevated pro-inflammatory cytokines or decreased 25-hydroxyvitamin D in peripheral circulation are causally associated with and potential risk factors for AD and depression [21,26,29,31]. The gene discussed is TNF; the disease is major depressive disorder.