Mechanisms of reactivation of the FMR1 gene and analysis of pathways involved in the pathogenesis of fragile X syndrome: towards a drug-based therapy

The fragile X syndrome is the most common cause of inherited mental retardation. The population prevalence of affected males is approximately 1 in 4000, and that of carrier females, at risk of having affected children, 1 in 250 or more. The syndrome is caused by a mutation of the FMR1 gene localized on the X chromosome. The mutation consists in an amplification and methylation of a DNA sequence within the promoter of the gene. This change blocks the expression of the gene, preventing the production of the FMRP protein, in spite of the fact that the coding sequence of the gene is intact. One might say that the gene is not broken; it is just switched off. We showed previously that the mutant gene can be switched back on by treating in vitro cell lines from fragile X syndrome patients with drugs that can remove the methylation from the DNA and thus relieve the block of the promoter. We also showed that regulation of the FMR1 gene activity depends not only on DNA methylation but also on epigenetic (reversible) structural changes occurring on the histones, i.e. those proteins on which the DNA double helix is wound. With the present project we intend to study in more detail the mechanisms that regulate the expression of the FMR1 gene, by: a) investigating in induced pluripotent stem cells (similar to embryonic stem cells) the factors that during development trigger those epigenetic changes that block the activity of the FMR1 gene; b) analyzing the role of small RNA molecules known to regulate gene expression; c) analyzing the effect of new drugs potentially capable of restoring the activity of the FMR1 gene. Our ultimate goal is to transfer in vivo the results obtained in vitro, hoping that this may lead to the discovery of an effective cure of the syndrome. We have recently completed in vivo clinical trials whose encouraging results suggest that that ultimate goal is attainable.