microRNA signatures in prodromal REM sleep behavior disorder and early Parkinson's disease as noninvasive biomarkers.

The flow of gene expression or "The central dogma of molecular biology": DNA - RNA - protein, proposed by Watson & Crick sixty years ago, is a tightly controlled cell process. In the middle of this journey, the mRNA molecule is regulated by "RNA interference" (RNAi), a posttranscriptional gene silencing mechanism. A microRNA is an endogenous short double-stranded RNA that down-regulates hundreds of mRNAs by RNAi, maintaining healthy cell physiology. In contrast, aberrant expressions of microRNAs play a role in Parkinson's disease (PD) pathogenesis. The damage may start at an early period of brain degeneration, in the non-motor or "prodromal" stage, where autonomic, mood and sleep changes are often manifested. REM-sleep behavior disorder (RBD) is the prodromal manifestation with the highest odds for conversion into PD, thereby a valuable phenotype for disease prediction. The present review focuses on microRNAs' role in the pathogenesis of PD and RBD, summarizing the state-of-the-art of these RNA molecules as noninvasive biomarkers for non-motor prodromal (RBD) and early PD.