Further studies of the Rett syndrome mutants indicated that the MeCP2 protein can 1) bind tightly to biochemically defined 12-mer nucleosome arrays [199]; (2) bind to four-way junction DNA in a structure-specific methyl-CpG-independent manner [200]; (3) compact chromatin via its three AT-hook domain [204]; and (4) bind specifically to 5-hydroxymethylytosine, enriched in the target gene promoter [202]. The gene discussed is MECP2; the disease is Rett syndrome.