One of the most common antibody deficiencies, incidence 1 in 700 healthy Western blood donors, but much rarer in some ethnic groups. FH only in a quarter. Defined as a serum IgA concentration of < 0.06g/L in patients over 4 years of age, with normal levels of IgG and IgM, which is not secondary to other causes e.g. myeloma. IgA subclass (IgA1 and IgA2) deficiencies described.
IgA deficiency may be found in
- IgG subclass deficiencies (although subclass deficiencies do not seem to have any clinical associations)
- Drugs (phenytoin, sulfasalazine)
- Chromosomal abnormalities (esp. chromosome 18)
- Coeliac disease (IgA levels are typically tested as part of coeliac 'serology' as IgA deficiency may result in false negative anti-tissue transglutaminase titres).
In children under 4, see Transient hypogammaglobulinaemia of infancy.
Sometimes seen in families as recessive trait, else dominant with variable penetrance. Pathogenesis of IgA deficiency is presumably abnormalities in Ig class switching. T-cell function normal in most. Possibly part of CVID spectrum?
- Infection - most individuals with IgA deficiency are clinically asymptomatic. Otherwise, higher than usual frequency of respiratory (incl. sinus) infections, and GI infections esp. giardiasis. Recurrent infections more often seen when accompanying IgG subclass deficiency (so consider IVIG, although contains small amount IgA, so might produce antibodies).
- Associated conditions - Long term follow up has found higher rate of gut and lymphoid malignancies. Increased frequency of coeliac disease, autoimmune disorders and allergy/atopy.
- Blood transfusion - IgA deficient patients can develop anti-IgA antibodies to blood products. But these antibodies also seen not uncommonly in normal population and do not help predict transfusion reactions. Severe reactions are v rare (1 in >20,000 transfusions).
- Enhanced surveillance for transfusion reactions recommended, and pre-medication with hydrocortisone/chlorphenamine should be considered.
- If a patient has previously had a reaction, then plasma reduced products or IgA def donor products (best) recommended. However, danger of delaying transfusion must be weighed against potential risk.
- Transfusion labs should be informed of patients with the diagnosis.