To date, the relationship between EPO levels and iron status with cognitive functioning has only been assessed in experimental models and relatively small sample size populations, often involving specific patient populations, e.g., having mood disorders (Beard et al., 1997; Milward et al., 1999; Weiskopf et al., 2006) questioning the role of endogenous EPO levels and iron status with cognitive functioning in the general population. The gene discussed is EPO; the disease is mood disorder.