[The role and importance of the microRNAs in the diagnosis and development of diseases].

MicroRNAs are small non-coding ribonucleic acids of endogenous nature. They persist in various groups of eukaryotes and perform critical functions during the development and the cell homeostasis. They have from 19 to 25 nucleotides in length and regulate the translation of the target RNA messenger (mRNA). MicroRNAs can inhibit its translation, stabilizing it or inducing its degradation. They regulate the genetic expression and are involved in the control of cellular functions (the differentiation, the proliferation, the apoptosis and the metabolism). They are also involved in the response to stress, the angiogenesis, the oncogenesis and in cardiovascular functions. That is the reason why their abnormal expressions are associated to many pathological conditions. The aim of this review was to describe the importance of microRNAs, their biological origin and their role in various diseases, such as cancer, diabetes, obesity, and neurological disorders. The microRNAs are an attractive therapeutic target because it has been observed that just one of them can regulate several genes and it could influence all the signaling route; besides, they could inhibit themselves in vivo without adverse effects related to the usual therapeutic agents. Since they can be detected in serum, plasma, urine and saliva samples in a stable, reproducible and consistent form between individuals of the same species, we expect them to be useful as biomarkers for the clinical diagnosis and the monitoring of diseases.