The causes of HAE-nl-C1-INH have been ascribed to underlying genetic mutations in the genes for factor XII,79 plasminogen,80 angiopoietin-1,81 kininogen 1,82 myoferlin,83 and heparan sulfate-glucosamine 3-O-sulfotransferase 6.84 In an additional subset of patients,85 the responsible mutation has not been defined. This evidence concerns the gene SERPING1 and hereditary angioedema.