miRNA and Other Non-Coding RNAs as Promising Diagnostic Markers

Since the discovery of non-coding RNAs (ncRNAs) a new area has emerged in the field of biomarkers. NcRNAs are RNA molecules of different sizes that are transcribed as independent genes or as part of protein coding genes and are not translated, therefore they do not produce proteins. They have been classified according to their size and function and include microRNAs (miRNAs), piwiRNAs (piRNAs), snoRNAs and long non-coding RNAs (lncRNAs). These non-coding RNAs are present in different cell compartments participating in multiple cell functions, but they have also been identified in biological fluids, also known as cell-free or circulating ncRNAs, where they can be detected in exosomes, bound on lipoproteins as well as free circulating molecules. The role of circulating ncRNAs is still under investigation but are believed to be paracrine or endocrine messengers to systematically deliver signals between cells and tissues. Detecting ncRNAs in biological fluids has opened a new field in Clinical Chemistry utilizing them as biomarkers of diseases or prognostic markers for different pathological conditions. Herein, the different types of ncRNAs and their potential in the field of diagnostics are outlined.