Hereditary Angioedema (HAE) is a rare hereditary disease that can cause attacks of swelling, and often pain, in specific parts of the body including the stomach, hands, feet, arms, legs, genitals, throat, and face. Depending on the severity of the disease, some people will have many attacks each month, while others will go months without an attack.

People with HAE are missing or have low levels of a protein called C1 esterase inhibitor (C1-INH); in some cases, the C1-INH levels are sufficient, but the protein does not function properly. The defect with C1-INH lies within a person's genetic code, which is why HAE runs in families.

Hereditary Angioedema is classified into three types based on what problem the genetic defect causes.

• Type I - Low levels of C1-INH in the body; this is the most common form of HAE and accounts for ~85% of people with HAE.
• Type II – Normal or elevated levels of C1-INH, but C1-INH is dysfunctional; this accounts for ~15% of people with HAE.
• HAE with Normal C1-INH (formerly known as HAE Type III) - Normal and functioning levels of C1-INH; this type of HAE is extremely rare and not well understood.