Deregulated microRNA expression in biospecimens from patients diagnosed with schizophrenia and bipolar disorder as a disease biomarker

The biological markers for schizophrenia (SZ) and bipolar disorder (BD) would represent a precious tool in evaluating the risk for the development of these common neuropsychiatric diseases and, possibly, in the prevention of either disease episodes and/or treatment efficiency monitoring. Since both SZ and BD are diseases with a significant genetic component, the research over the last decades has focused on the genes with altered function in the central nervous system (CNS) of individuals suffering from these illnesses. Recently, however, small non-coding RNA molecules (microRNAs, miRNAs, miRs) were shown to regulate the expression of human CNS genes involved in cell processes and functions negatively affected in neuropsychiatric disorders, including synaptic development and maturation, learning and memory. Differentially expressed sets of miRNAs have been reported in the tissues of SZ and BD patients in comparison to controls suggesting the emergence of a novel class of potential biomarkers. Here we review the reports on the changes in miRNA expression in postmortem brain tissue and peripheral blood in SZ and BD. We also evaluate the potential of miRNA packaged in exosomes, signaling vesicles released by neurons and glia, to contribute to the disaggregation of the molecular machinery underlying mental disorders and provide clinically useful biomarkers.