Given the known influences of mood stabilizers on miR-34a levels and its potential role in neuronal maturation and plasticity, we decided to investigate the link between miR-34a and BD. Interestingly, two recent studies43, 44, as well as unpublished data (S.J.H, manuscript in preparation), reported decreased expression of the two putative miR-34a targets ANK3 and CACNA1C in cerebellum of BD individuals. Based on these findings and emerging literature linking the cerebellum with BD43–52, we hypothesized that miR-34a could be dysregulated in the cerebellum of BD patients. To test this hypothesis, we measured miR-34a expression in postmortem human brain samples from cerebellum. We observed a significant increase in miR-34a levels in the cerebellum of BD patients (N = 29) relative to healthy controls (N = 34) (Figure 1A), whereas no differences were seen in prefrontal cortex (PFC) or anterior cingulate cortex (Figure S1A and S1B). In contrast to this BD and brain region-specific difference in miR-34a expression, based on the recent identification by GWAS of a new susceptibility locus within the first intron of ODZ4 where miR-708 is encoded16, which is predicted
