MicroRNAs are short, highly conserved, non-coding ribonucleic acids that play an important role in the complex network of gene regulation, especially in gene silencing. MicroRNAs regulate gene expression highly specifically at the post-transcriptional level. MicroRNAs have a size of 21 to 23 nucleotides, but there can be even a few hundred. In recent years, knowledge about microRNAs has steadily grown. The miR Base database has shown an increase of over 4000 sequences within few years and, each miRNA has the potential to target a large number of genes. Why the database of new miRNAs is rising, is not completely understood to date. Working with miRNAs is at the forefront of biomedical research. Since their discovery in 1993, significant knowledge about miRNAs has been gathered: their biogenesis has been elucidated, the components involved in RNA interference have been identified, and insight into the therapeutic importance of miRNAs has been gained - both as drugs and as targets for new therapies. Further intensive research will help identify the key molecular players in this miRNA-mediated signaling pathway and understand their function. Strategies are being developed to influence the activity of these proteins, in order to draw conclusions from these experiments about their respective functions. This will certainly help develop new therapeutic approaches for the treatment of human diseases that can be attributed to RNA interference dysfunctions. The exact biological functions of most microRNAs are still unknown. According to computer-based predictions, approximately 20-30% of genes in the human genome could be regulated by microRNAs. It is assumed that several thousand different microRNAs are encoded. Micro-RNA`s play an important role in pathogenesis of many different pediatric diseases, which will be analyzed in this review in detail.

Keywords: Micro RNA, Nucleotides, Translation, Genome, Child