Immunoglobulin G Subclass Deficiency
A condition characterised by deficient serum levels of one or more of the four IgG subclasses (IgG1–IgG4) despite normal or near-normal total IgG concentrations, associated with recurrent infections.
Full Definition
IgG subclass deficiency refers to selective reduction of IgG1, IgG2, IgG3, or IgG4 below age-matched reference ranges. IgG2 deficiency is the most clinically significant subclass deficiency in children, as IgG2 antibodies predominate in responses to polysaccharide antigens from encapsulated bacteria. IgG3 deficiency is more common in adults and often presents with recurrent respiratory tract infections. IgG1 deficiency, in isolation, is rare because IgG1 comprises the majority of total IgG. The clinical relevance of isolated IgG4 deficiency is debated. Editors must note that the subclass numerals are always presented as subscripts in formal publication (IgG₁) but superscripts are erroneous; standard editorial practice in non-LaTeX environments uses IgG1–IgG4 with Arabic numerals without subscript when formatting is unavailable.
Usage
Usage note: Render subclass numerals as IgG1, IgG2, IgG3, IgG4 (Arabic numeral, no hyphen). Do not use 'IgG-2' or 'Igg2'. Confirm whether total IgG level is stated alongside subclass data, as the clinical interpretation depends on this.
In Context
- "IgG2 subclass deficiency was identified in the five-year-old with recurrent invasive pneumococcal disease, despite a normal total serum IgG level." — Paediatric immunology case report
- "The author rendered the subclasses inconsistently as 'IgG-2' and 'IgG2'; the copy-editor standardised all instances to 'IgG2' throughout." — Journal copy-editing note