A deficiency in one or more IgG subclasses may be associated with a clinical immunodeficiency.
IgG subclasses:
(1) IgG1
(2) IgG2
(3) IgG3
(4) IgG4
Criteria for subclass deficiency:
(1) serum concentration of the subclass less than 2 SD below the age-adjusted mean
(2) present on multiple occasions
(3) testing performed in the absence of clinical infection
Deficiencies can occur in any combination of the 4 subclasses (16 possible combination) with isolated IgG1, isolated IgG3 and combined IgG1/IgG3 deficiencies the most common.
The total IgG concentration may be normal, and the condition can only be diagnosed if all of the subclasses are measured.
Features:
(1) delayed diagnosis (typically in middle age)
(2) recurrent and severe respiratory tract infections (pneumonia, bronchiectasis, etc)
(3) poor antibody response to polysaccharide vaccines
(4) variable chronic rhinosinusitis
(5) variable furunculosis
