The Role of Noncoding RNAs in Neurodevelopmental Disorders: The Case of Rett Syndrome.

Current technologies have demonstrated that only a small fraction of our genes encode for protein products. The vast majority of the human transcriptome corresponds to noncoding RNA (ncRNA) of different size, localization, and expression profile. Despite the fact that a biological function remains yet to be determined for most ncRNAs, growing evidence points to their crucial regulatory roles at all stages in gene expression regulation, including transcriptional and posttranscriptional control, so that proper cell homeostasis seems to depend largely on a variety of ncRNA-mediated regulatory networks. This is particularly relevant in the human brain, which displays the richest repertoire of ncRNA species, and where several different ncRNA molecules are known to be involved in crucial steps for brain development and maturation. Rett syndrome is a neurodevelopmental disorder characterized by loss of function mutations in the X-linked gene encoding for methyl-CpG-binding protein 2 (MeCP2). MECP2 deficiency impacts globally on gene expression programs, mainly through its role as a transcriptional repressor, and growing data also points to an important dysregulation of the noncoding transcriptome in the disease. Here, we review the current knowledge on ncRNA alterations in Rett and explore links with other pathologies that might indicate the potential use of particular noncoding transcripts as therapeutical targets, tools, or disease biomarkers.