They also detected a positive correlation between DRD2 and DAT density and hypothesized that the iron deficiency–induced reduction in DRD2 presynaptic receptors, which are involved in negative-feedback regulation of the dopamine system through increased DAT density and clearance of dopamine from the synapse (Dickinson et al. 1999; Meiergerd et al. 1993) and therefore may be responsible for the reduced DAT activity and density. This evidence concerns the gene DRD2 and nutritional disorder.