HCN1 and heroin dependence: In the 5hmC differential genes, we identified the gene coding GRIN1, known to regulate μ-Opioid activity;38SOD2, previously described as associated with the risk of heroin dependence in an Iranian population (n = 1241);39 and HCN1, in which the protein is shown to be required for the activation of the μ opioid receptor40.