To study the relative contribution of the H3K9 methylation to FMR1 gene silencing, we treated FXS cells with known inhibitors of H3K9 methylation (chaetocin, BIX01294 and UNC0638) and a global histone methylation inhibitor (DZNep) and analyzed the levels of FMR1 mRNA. This evidence concerns the gene FMR1 and fragile X syndrome.