In research on FXS, it has been found that the silenced FMR1 gene region is enriched with various histone methylation marks associated with transcriptional silencing, such as H3K9me2, H3K27me3, H3K9me3, and H4K20me3 (Kumari and Usdin, 2010; Basalingappa, 2020). Here, FMR1 is linked to fragile X syndrome.