OPRM1 and neuropathic pain: Rodent models of neuropathic pain, in example, were associated to higher methylation of the promoters of the Oprm1 (encoding mu 76 opioid receptor, MOR) and Kcna2 (Potassium Voltage-Gated Channel Subfamily A Member 2) genes and, in agreement with the role of DNA methylation in repression of gene expression, their protein levels were decreased [60,61,62].