Disruption of the MOR gene leads to a complete loss of the main biological actions of morphine, including analgesia, reward, withdrawal, respiratory depression, immunosuppression and constipation, demonstrating that both therapeutic and adverse effects of the prototypic opioid results from its interaction with MOR gene products [35,36,37,38,39,40,41,42]. Here, OPRM1 is linked to Respiratory insufficiency due to muscle weakness.