Immunoglobulin A deficiency is the most common primary immunodeficiency.
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 ataxia-telangiectasia, and IgG subclass deficiencies, drugs (phenytoin, sulfasalazine), chromosomal abnormalities (esp chromosome 18), coeliac disease.
Sometimes seen in families as recessive trait, else dominant with variable penetrance.
- 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 (20-40%). But these antibodies also seen not uncommonly in normal population and do not help predict transfusion reactions, so testing controversial. 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.
Pathogenesis of IgA deficiency is presumably abnormalities in Ig class switching. T-cell function normal in most. Possibly part of CVID spectrum?
J Clin Pathol 2001;54:337-338 pmid 11328829