Based on studies in mice, MECP2 binds to the promoter of the OPRM1 gene, encoding Mu-type opioid receptor (Hwang et al. 2008, Hwang et al. 2010, Vucetic et al. 2011, Samaco et al. 2012). MECP2 binds to the OPRM1 promoter together with the SIN3A co-repressor complex, and MECP2 binding correlates with hypermethylation of the promoter region of OPRM1 (Hwang et al. 2009, Hwang et al. 2010).