Epigenetic modifications of the FMR1 gene.

The fragile X syndrome (FXS), the most common cause of heritable intellectual disability, is caused by expansion of a CGG repeat located at the 5' UTR of the FMR1 gene and subsequent epigenetic modifications of its promoter. Epigenetic modifications include both methylation of the cytosines of the CpG island in the promoter region and of the expanded CGG triplet, and posttranslational histone changes. The combination of these changes, one structural (expansion) and one epigenetic (methylation and histone modifications), results in transcriptional silencing, even though the coding region of the FMR1 gene remains intact. Here we describe the molecular methods used to study both DNA methylation and histone epigenetic modifications, namely, bisulfite sequencing and quantification of immunoprecipitated DNA after Chromatin Immunoprecipitation (ChIP).