SCN9A and hereditary sensory and autonomic neuropathy: Studies on CIP patients that were potentially Nav1.7 null mutants in the pre-genomic era had already provided evidence that the endogenous opioid system contributed substantially to the pain free state.[41] When analgesia is established by the deletion of SCN9A encoding Nav1.7 in mice, the vast majority of analgesia is naloxone reversible.