Clinical significance of IgG subclass deficiency

IgG is quantitively and functionally the major class of immunoglobulin found in serum and all extra-vascular fluids except mucosal secretions. Four structurally and functionally distinct subclasses (IgG 1 to 4) have been described in man. ' Deficiencies of individual subclasses of IgG were first described almost 20 years ago,2 but their exact prevalence and significance is not accurately known.3 They do appear, however, to be relatively common-possibly more common than IgA deficiency which occurs in 1:500 of the healthy population.4 As with IgA deficiency, asymptomatic individuals are found both in blood donors5 and among the relatives of patients with a variety of immunodeficiencies, in-cluding family members of patients with IgG sub