OPuS-2 is a Phase 3 clinical study that investigated the efficacy and safety of avoralstat, a kallikrein inhibitor, on hereditary angioedema (HAE) caused by mutations in the SERP-ING1 gene that leads to a deficiency of the kallikrein inhibitor, C1 inhibitor (C1-INH) [41]. This evidence concerns the gene KLK4 and hereditary angioedema.