Previously, we have shown that incubation of plasma of HAE patients in a non-activating plastic test tube at 37°C evolves PKa activity that is not initiated by FXII, but is augmented by it, and is due to autoactivation of the prekallikrein–HK complex in phosphate buffer (28) when C1-INH levels are inadequate. This evidence concerns the gene SERPING1 and hereditary angioedema.