PKa activity was measured in plasma samples from patients with HAE with decreased C1 inhibitor (C1INH) levels or activity who were not receiving prophylactic medications for HAE (HAE-C1INH; n = 25), from individuals with a presumptive diagnosis of HAE with normal C1INH (HAE-nC1INH; n = 3), and from age-matched controls without HAE (n = 57). The gene discussed is SERPING1; the disease is hereditary angioedema.