Abstract
A new reactive-centre P1 residue mutation (444Arg→Ser), has been identified in a dysfunctional C1 inhibitor protein, C1 inhibitor(Ba), contained in a type II hereditary angioedema plasma. This substitution is compatible with a point mutation of the 444Arg codon (CGC→AGC), and represents the first non-histidine, non-cysteine P1 residue mutant described for C1 inhibitor.