TH protein levels are 5.6-fold greater in the mouse striatum relative to frontal cortex (p < 10−11; one-way ANOVA; Supplementary Fig. 13), which may explain the capacity to detect a decrease in striatal, but not frontal, TH in mice lacking the enhancer at Igf2. These data collectively suggest that in schizophrenia and bipolar disorder, epigenetic disruption of enhancer activity at the IGF2 locus in neurons leads to abnormalities in subcortical dopaminergic signaling, which is centrally involved in the development of psychotic symptoms. The gene discussed is TH; the disease is bipolar disorder.