This may result in increased or diminished levels of one or more IgG subclasses. The most conspicuous consequence of a deficiency in one of the IgG subclasses is a defect of humoral immunity, although this does not necessarily lead to clinical manifestations. Over the last decades a large number of reports have appeared on deficiencies of IgG and its subclasses. A deficiency of total IgG will generally result in serious infectious problems. A decreased level of individual subclasses will have less dramatic consequences,although important infections may occur.
Deficiencies can occur in single or multiple IgG subclasses.
Deficiencies of IgG subclasses can be subdivided in different groups. A complete deficiency of one or more subclasses, caused by deletions in chromosome 14 loci, is rare. Such a total lack of one or more IgG subclasses due to deletions of the immunoglobulin heavy chain constant region genes is occaaionally found in healthy individuals. Since a decreased level of one IgG subclass may be accompanied by increased levels of one or more of the other subclasses, the total IgG level may well be normal. Consequently, the determination of IgG subclass levels is important, even when the total IgG level is within or only slightly below the reference range of healthy individuals.