ReviewHuman immunoglobulin constant heavy G chain (IGHG) (Fcγ) (GM) genes, defining innate variants of IgG molecules and B cells, have impact on disease and therapy

- Frequency and function of alternative IGHG GM Fc* genes of *3 *1 *2 (14q32.3).
- Alleles genotypes haplotypes diplotypes allelic IgG subclasses B cells identified.
- Homozygous IGHG alleles (haplotypes) express restricted IgG subclasses and B cell.
- IGHG respond differently to bacteria virus allergens active passive immunotherapy.
- IGHG associated with infections immunodeficiency allergy autoimmunity malignancy.

The distinguished alternative GM allotypes localized in immunoglobulin constant heavy G chain IGHG (Fcγ) (GM) genes on chromosome 14q32.3 define two unique variants of respectively IgG3, IgG1 and IgG2 subclasses, with different structures and functions. The IGHG allele (allotypes), expressed in homozygous or heterozygous forms, are assessed by new serological methods. Fixed combinations of γ3, γ1 and γ2 allotypes constitute the haplotypes, which are indirect markers of B cells. We highlight the role of homozygous IGHG genes with restricted qualities of IgG subclass molecules and B cells. These common Mendelian IGHG genes respond differently to allergens and infections, both bacterial and viral, and to active and passive immunotherapies. IGHG genes have an impact on diseases such as allergy, immunodeficiency, autoimmunity and malignancy. Association/linkage of different IGHG genes gives information about risk/protection, good or bad prognosis, for improvement of clinical care. The IGHG gene map of healthy Caucasians is registered.