In patients with laboratory findings suggestive of HAE-C1INH-Type1 (reduced antigenic C1INH and antigenic C4 levels as well as C1INH function) without family history and late age of onset (>30 years), diagnosis of acquired angioedema due to C1INH deficiency should be excluded; measurement of C1q (typically normal in HAE-C1INH-Type1 and reduced in approximately 75% of cases of acquired angioedema due to C1INH deficiency) may be helpful for differential diagnosis.1 The gene discussed is C4A; the disease is hereditary angioedema.