C1 Esterase Inhibitor Deficiency
Also known as:
Hereditary Angioedema, C1 Inhibitor Deficiency
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
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
- hands, feet, limbs or face.
- genital areas, sometimes causing temporary difficulty passing
- 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
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
- genetic tests are possible to confirm a diagnosis, but they are
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
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
- 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
- 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
C1 inhibitor deficiency is an autosomal dominant genetic
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 a Family's freephone helpline
for advice, information and, where possible, links to other
families. Contact a Family's web-based linking service can be
accessed at community.cafamily.org.uk
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