Several types of HAE are described; the most explored one is due to C1 inhibitor deficiency, known as type I. It is caused by SERPING 1 mutation, on the long arm of chromosome 11, leading to C1 inhibitor deficiency which subsequently results in low C1 inhibitor and C4 protein levels in blood serum [2]. The gene discussed is C4A; the disease is hereditary angioedema.