However, more recent study on natural enkephalinase inhibitors suggests that sialorhin has no effect on DSS-induced colitis, and human opiorphin does not alleviate colitis induced by TNBS in mice (Sałaga et al., 2017; Sobocińska et al., 2020), the cause of which still remains unclear and needs further investigations. The gene discussed is OPRPN; the disease is colitis.