Binding of Mecp2, in association with the Sin3a co-repressor complex, to the hypermethylated promoter of the Oprm1 gene, encoding Mu-type opioid receptor (MOR), correlates with transcriptional repression of Oprm1 in the cerebellum (Hwang et al. 2009. Hwang et al. 2010). In the mouse model of the Mecp2 duplication syndrome, transcription of the Oprm1 gene in the amygdala and hippocampus is increased compared to wild type mice (Samaco et al. 2012).