HAE-C1-INH is the most common type of HAE and its diagnosis is based mainly on clinical symptoms, a positive family history (although this may not be present in up to 15-20% of patients), and, finally, laboratory tests, with measurements of plasma levels of C4, C1-INH protein and C1-INH function being used to diagnose HAE-C1-INH with high accuracy (15). Here, C4A is linked to hereditary angioedema.