All patients suspected to have HAE-1/2 (ie, recurrent angioedema in the absence of a known cause) should be assessed for blood levels of C4, C1-INH protein, and C1-INH function, and these tests, if abnormally low, should be repeated to confirm the diagnosis. The gene discussed is SERPING1; the disease is hereditary angioedema with C1Inh deficiency.