How rare is hereditary angioedema?
A HAE affects one in 50,000 individuals of any race; it is inherited in an autosomal dominant manner and discovery of undiagnosed relatives is common.
Although there are no carriers, the frequency and severity of symptoms varies; affected individuals may have few, or no symptoms. Around 10 per cent of GP practices in the UK have HAE cases.
HAE results from a partial deficiency of C1 inhibitor, which regulates the classical complement and kallikrein-bradykinin pathways. At times of stress, uncontrolled bradykinin and complement activation causes oedema.
Attacks affect any part of the body – cutaneous swellings, abdominal pain and angioedema are the most common.
Facial or laryngeal angioedema may be mistaken for anaphylaxis, although symptoms build up over hours or days. The angioedema does not respond to epinephrine, steroids or antihistamines – as a result, there is a 30 per cent mortality in undiagnosed HAE sufferers through asphyxiation. C1 inhibitor concentrate is the treatment of choice, although fresh frozen plasma may be used.
Bowel oedema gives rise to abdominal pain and bloating, sometimes with diarrhoea or vomiting. Many patients are told they have allergies or IBS. Severe attacks may be mistaken for surgical emergencies.
HAE should be excluded in all patients with recurrent abdominal pain, angioedema without urticaria or unexplained cutaneous swellings, especially if members of the family have similar symptoms. In HAE, complement C4 is reduced, even between attacks, with a normal C3. The diagnosis can be confirmed by checking C1.
Attacks may be prevented by regular tranexamic acid or danazol. Patients should be referred to a specialist.
Dr Hilary Longhurst is a
consultant immunologist at
St Bartholomew's Hospital, London