C1 Esterase Inhibitor Deficiency

Also known as: C1 Inhibitor Deficiency; Hereditary Angioedema; Hereditary Angioneurotic Oedema


C1 inhibitor deficiency results from a genetic change to the C1 inhibitor gene on chromosome 11. C1 inhibitor deficiency attacks can often be mistaken for anaphylaxis, but adrenaline, antihistamines and steroids (treatments given during anaphylaxis) are ineffective.


Medical text written September 2001 by Dr HJ Longhurst. Last updated December 2012 by Dr HJ Longhurst, Consultant Immunologist, Barts Health NHS Trust, London, UK.

What are the symptoms?

People with C1 inhibitor deficiency experience intermittent angioedema (swellings), which last several days if untreated affecting:

  • hands, feet, limbs or face.
  • genital areas, sometimes causing temporary difficulty passing urine.
  • internal organs, usually causing severe pain, sometimes with vomiting, diarrhoea or faintness. These swellings may be mistaken for conditions such as appendicitis.
  • throat swellings. These are rare but unlike other swellings can be life-threatening. They should be treated immediately.

Urticaria (itchy weals, hives or nettle rash) is not a feature of C1 inhibitor deficiency.

Symptoms usually occur infrequently until adolescence when swellings may become more common. Occasionally C1 inhibitor deficiency is asymptomatic (without symptoms).

What are the causes?

A genetic mutation of the C1 inhibitor gene causes reduced production of C1 Inhibitor. C1 inhibitor regulates fluid leakage from blood vessels and prevents excess oedema (fluid build up). Low levels of C1 inhibitor result in a tendency for oedema to occur.

How is it diagnosed?

C1 inhibitor deficiency is diagnosed when there are typical features of angioedema but without urticaria being present. A diagnosis may be made if:

  • a family member has C1 inhibitor deficiency in many cases
  • blood tests show low C4 complement and low C1 inhibitor protein or function
  • genetic tests are possible to confirm a diagnosis, but they are not routine.

 Other causes of angioedema (swellings) include allergies, medications (particularly ACE inhibitors such as lisinopril, often used for high blood pressure) or may be idiopathic (with no known cause).

How is it treated?


Given when attacks are frequent to reduce the number and severity of swellings: may include:

  • tranexamic acid or
  • regular injections of C1 inhibitor concentrate (‘Berinert’ or ‘Cinryze’).
  • danazol or stanozolol are effective, but not recommended for children before growth is complete.

Treatment of swellings may be by:

  • C1 inhibitor concentrate given intravenously (by injection into a vein)
  • treatment is most effective when given early in the course of the swelling, which may take several hours to resolve
  • specialist centres teach parents and older children how to administer C1 inhibitor at home
  • icatibant is an alternative subcutaneous (injection under the skin) treatment which is easy to administer. However it has not yet been tested for children.

With appropriate treatment, available in specialist centres, people with C1 inhibitor deficiency have normal life expectancy and enjoy good health.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
C1 inhibitor deficiency is an autosomal dominant genetic condition.

Prenatal diagnosis
Not routinely available. However, preimplantation genetic diagnosis to ensure an unaffected baby is sometimes possible, although NHS funding for this is variable.

Is there support?

There is no support group for C1 inhibitor deficiency syndrome in the UK. Families can use Contact’s freephone helpline for advice, information and, where possible, links to other families. You can also join our closed Facebook group

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