Based on studies in mice, association of MECP2 with the hypermethylated OPRM1 gene promoter, encoding Mu-type opioid receptor (MOR), correlates with transcriptional repression of OPRM1 in the cerebellum. MECP2-mediated transcriptional repression of OPRM1 may be relieved by interaction of MECP2 with SMARCA4 (BRG1), a component of the chromatin remodeling SWI/SNF complex (Hwang et al. 2009). MECP2-mediated repression of OPRM1 involves the SIN3A co-repressor complex (Hwang et al. 2010). In the mouse model of MECP2 duplication syndrome, OPRM1 transcription in the amygdala and hippocampus is increased compared to wild-type mice (Samaco et al. 2012).