Angioedema is a swelling similar to hives, but the swelling is beneath the skin rather than on the surface. The swellings are called welts.Wikipedia
Hereditary angioedema types I and II are caused by a diverse group of primarily dominant mutations in the C1 inhibitor C1NH gene, officially known as the SERPING1 gene, while another type of hereditary angioedema, HAE type III, is caused by mutations in the coagulation factor XII F12 gene. In general, the different mutations give rise to angioedemas that are indistinguishable from each other.
Hereditary angioedema is estimated to affect 1 in 50,000 people. Type I is the most common, accounting for 85 percent of cases. Type II occurs in 15 percent of cases, and type III is very rare.GHR
In 2018, the FDA approved the use of the monoclonal antibody Takhzyro (Ianadelumab) as a prophylactic treatment for HAE types I and II in patients 12 or older.FDA