COL18A1 and hereditary angioedema: Since then, genetic variants in the genes coding for Coagulation Factor XII (FXII), plasminogen, angiopoetin 1, kininogen 1, myoferlin, and heparan sulfatase have been described in HAE-nC1-INH patients; however, a subset of patients remain who do not have variants identified, a condition designated as HAE-unknown (HAE-U) (4).