Defects of the immune system present from birth, leading to recurrent infection and failure of normal growth
- Present at birth
- Due to an abnormal gene
- Gender as a risk factor depends on the type
- Lifestyle is not a significant factor
In immunodeficiency, the immune system is defective and therefore unable to combat infections effectively. As a result, infections are more frequent and severe and may be life-threatening. A child’s growth may also be affected. In children, immunodeficiency is usually caused by an underlying illness (see Acquired immunodeficiency). In rare cases, the condition is inherited and is present at birth, in which case it is called congenital immunodeficiency.
What are the types?
Congenital immunodeficiencies are due to an abnormal gene. This gene is either linked to the X chromosome or inherited in an autosomal recessive manner (see Gene disorders). The type of immunodeficiency depends on which part of the immune system is affected.
The most common type of immunodeficiency is agammaglobulinaemia, a disorder that affects only boys. In this condition, severe bacterial infections, especially of the chest, frequently occur because antibody production is greatly reduced. Other, less serious, types of immunodeficiency may be caused by failure of the immune system to produce some specific types of antibody.
Chronic granulomatous disease is another type of congenital immunodeficiency. In this disease, the phagocytes, the white blood cells that are responsible for engulfing and killing bacteria and fungi, are unable to function properly. As a consequence, a child who has this disorder may have frequent bacterial and fungal infections, especially of the skin, lungs, and bones.
Severe combined immunodeficiency (SCID) is a disorder in which a child is unable to fight most forms of infection because both the antibodies and the white blood cells are deficient.
What might be done?
It is possible to screen for congenital immunodeficiency during pregnancy if the fetus is thought to be at risk (see Antenatal genetic tests). More often, congenital immunodeficiency is suspected when a child has persistent unusual infections or fails to grow normally. The doctor may then arrange for blood tests to measure the levels of antibodies and white blood cells and assess the function of the child’s immune system. Sometimes, it is possible to detect the abnormal gene by a blood test.
All infections in a child who has a congenital immunodeficiency should be treated as soon as possible. Antibiotics will be given if appropriate. If antibodies are deficient, they can be replaced intravenously every few weeks. In some severe types of congenital immunodeficiency, such as SCID, a stem cell transplant may be necessary, and this will be done if a suitable donor can be found. If the transplant is successful, the transplanted stem cells will start to produce normal white blood cells that can fight infection.
If treatment for congenital immunodeficiencies is started sufficiently early, many children affected with these disorders can lead a normal life and have an average life expectancy.
In the future, treatment of congenital immunodeficiency may include gene therapy. The aim of this new treatment is to correct the genetic defects that affect the function of the immune system.
Genetic tests may be offered to relatives of affected people. Genetic counselling is offered to couples who are found to have the abnormal gene or who have an affected child and plan to have more children.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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