Summary 

Selective immunoglobulin A deficiency (sIgAD) is the most common of the primary antibody deficiencies, affecting up to 1 in 600 people. It is not usually associated with bacterial infections but may be associated with autoimmune or allergic diseases. The genetic causes of sIgAD are unclear. People affected have very low or absent levels of one type of antibody, called immunoglobulin A (IgA), but produce protective antibodies of the other types of immunoglobulin (IgG and IgM). This could be why many people with sIgAD may appear healthy. 

IgA works to protect body surfaces, such as the respiratory tract and gut that come into contact with outside organisms, so if someone has infections, these are the most common sites of infection. Such individuals may have a partial IgG deficiency despite apparently normal IgG levels in the blood, and so should be investigated in an immunology clinic. 

People with IgA deficiency may have allergies (e.g. allergic asthma) or an increased tendency to develop autoimmune conditions, where the immune system attacks itself, and this may result in conditions such as coeliac disease, which affects about 10 per cent of IgA-deficient patients. No specific treatment is required for sIgAD. Infections should be treated promptly with antibiotics. 

In general, individuals who have sIgAD fall into one of four different types and can present with different symptoms:

  • People who are asymptomatic. This covers the majority of people, in whom a lack of IgA in the blood would not have come to notice had they not had an immunoglobulin test for another reason. Such people are entirely healthy, probably throughout their lives, because compensatory mechanisms make up for the lack of IgA. They are referred to as being asymptomatic and do not require follow-up.
  • People who have infections and IgA deficiency. These are individuals in whom sIgAD is a marker of other, more subtle, irregularities of their immune system, but having sIgAD is unlikely to be the cause. If associated with an IgG subclass or specific antibody deficiency, individuals may experience recurrent infections, often affecting the sinuses or ears.
  • People affected by allergies.
  • People who have health complications associated with autoimmunity because their immune system makes antibodies against their own tissues and organs. An example of autoimmunity is coeliac disease, a condition particularly associated with sIgAD.

Very few cases progress to common variable immune deficiency (CVID), and IgA deficiency may be present in those who have CVID in the family.

Most people with sIgAD do not have any symptoms. Others may have frequent infections of the ears, sinuses, lungs and gut but IgA deficiency alone is not usually the cause.

These patients may have an additional partial IgG deficiency – known as an IgG subclass deficiency – resulting in failure to make some (but not all) protective antibodies; IgG subclasses and protective antibodies can be measured to assess this.

How is sIgAD diagnosed?

A clinical immunologist usually makes the diagnosis of sIgAD.

Making the diagnosis

To diagnose sIgAD the specialist immunologist may carry out blood tests to:

  • Measure the levels of the different immunoglobulins: IgA, IgG and IgG subclasses, and IgM
  • Test for the presence of antibodies to previous immunisations or infections.

If antibodies are not present in the blood, you will be immunised and blood taken three to four weeks later to see if you have responded to the vaccines

  • Count the numbers of T- and B-cells in the blood – these should be normal in sIgAD.

Clusters of cases can occur within families, so the doctor may want to ask you about your relatives’ health. This is referred to as taking a family history. The genetic causes of sIgAD remain unknown. There may be a variety of causes  and they may vary from individual to individual. 

Most people with sIgAD do not require treatment or regular immunology review. Infections should be treated promptly with antibiotics, especially sinusitis, chest infections or diarrhoea. In rare cases, longer courses of antibiotics may be needed to prevent infections from coming back.

As in people who have healthy immune systems, recurrent sinusitis in sIgAD patients can be made worse by poor drainage of the sinuses. Obtaining the advice of an ear, nose and throat (ENT) specialist is often helpful to prevent further infections. Steroid nasal sprays may help to control ENT symptoms.

People with sIgAD who also do not respond to vaccination might benefit from immunoglobulin replacement therapy. This is done on a trial basis for one year in order to assess the clinical benefit in the patient as there is no published data available to advise on this treatment otherwise.

Iron deficiency anaemia is common if there have been gastrointestinal complications. In these cases iron tablets, or a gluten-free diet if coeliac disease is diagnosed, may be helpful.

Immunisation

Most vaccines are safe to be administered to patients with sIgAD, provided that other tests of immune function are normal. The infant and childhood vaccination schedule can be followed as normal. Vaccinations required in adulthood can be discussed with your clinical immunology team.

Your clinical immunologist will be on the look out for complications and will work with other clinical specialists to offer you the most appropriate advice and treatments.

Autoimmunity

Some people affected by sIgAD may develop antibodies directed against their own body tissues. These are known as autoantibodies and they can cause symptoms. A typical disorder is coeliac disease, which affects the small intestine and is associated with sensitivity or intolerance to gluten found in wheat, barley and rye.

Further information on autoimmunity in primary immunodeficiency (PID) can be found here.

Allergy and anaphylactic shock

People with IgA deficiency may develop antibodies to IgA. This is only a problem if they are documented to have reacted to blood products containing IgA. No specific caution or testing is needed if a patient hasn’t been transfused before:

  • they should be treated as someone without IgA deficiency for a first transfusion
  • or if they have been transfused without problem.

More on allergy in primary immunodeficiency (PID) can be found here.

You can download our information booklet here.