The Role of MIR9-2 in Shared Susceptibility of Psychiatric Disorders during Childhood: A Population-Based Birth Cohort Study

Background: It has been suggested that microRNAs (miRNAs; short non-protein-coding RNA molecules that mediate post-transcriptional regulation), including mir-9 and mir-34 families, are important for brain development. Current data suggest that mir-9 and mir-34 may have shared effects across psychiatric disorders. This study aims to explore the role of genetic polymorphisms in the MIR9-2 (rs4916723) and MIR34B/C (rs4938723) genes on the susceptibility of psychiatric disorders in children from the 2004 Pelotas Birth Cohort. Methods: Psychiatric disorders were assessed in 3585 individuals using Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), criteria through the application of standard semi-structured interviews (using the Development and Well-Being Assessment, DAWBA) at the six-years-of-age follow-up. The outcome was defined as the presence of any mental disorder. We also considered two broad groups of internalizing and externalizing disorders to further investigate the role of these variants in mental health. Results: We observed an association between rs4916723 (MIR9-2) and the presence of any psychiatric disorder (odds ratios (OR) = 0.820; 95% CI = 0.7130–0.944; p = 0.006) and a suggestive effect on internalizing disorders (OR = 0.830; 95% CI = 0.698–0.987; p = 0.035). rs4938723 (MIR34B/C) was not associated with any evaluated outcome. Conclusion: The study suggests that MIR9-2 may have an important role on a broad susceptibility for psychiatric disorders and may be important mainly for internalization problems.