What causes HAE

HAE affects between 1/25,000 to 1/50,000 of the population. Because it is so rare most doctors would not see a case in their entire career, and misdiagnosis is common. Patients can suffer for many years before they receive the correct diagnosis.

HAE patients have a defect in the gene that controls a blood protein called C1 Inhibitor (C1INH). C1INH is part of a complex cascade of reactions that control the release of fluids from capillaries into the surrounding tissues, thereby causing oedema (swelling).

Type I and Type II HAE are due to a known genetic mutation.

Type I
There are low levels of C1INH (in most cases).

Type II
The blood levels are normal but the C1INH has impaired function.

HAE with normal C1 Inhibitor
This is a very recently documented form: It mainly affects females and is exacerbated by high oestrogen levels, for example, oral contraceptives and pregnancy.

HAE with Normal C1 Inhibitor is not due to C1 INH deficiency; it is linked to elevated levels of bradykinin. The exact reasons it occurs are still being studied.

Acquired C1 Inhibitor deficiency (AAE)
Acquired C1 Inhibitor deficiency (AAE) is not inherited but is caused when the body produces an antibody to its own C1 inhibitor or uses too much C1 inhibitor.

AAE is often associated with an underlying condition of white blood cells, which is usually mild, but tests should be done to exclude more serious conditions such as lymphoma.

Common HAE triggers are:

  • Anxiety – bad and good
  • Stress
  • Minor trauma
  • Surgery
  • Other viral infections/colds/flu
  • Hormone changes
  • Puberty
  • Oestrogen containing contraceptives
  • Pregnancy
  • Hormone replacement therapy
  • ACE inhibitors
  • Dental procedures