Three forms of HAE have been defined: (1) HAE due to C1-INH deficiency (type 1 HAE, HAE-1), characterized by low antigenic and functional C1-INH levels; (2) HAE due to C1-INH dysfunction (type 2 HAE, HAE-2), characterized by normal (or elevated) antigenic but low functional C1-INH levels; and (3) HAE with normal C1-INH antigenic and functional levels (HAE-3). Here, SERPING1 is linked to hyperinsulinemic hypoglycemia, familial, 4.