About GAGE / G Antigen:
G is an antigen that is found on red blood cells in the Rh blood group. It is exclusively found on those red blood cells that contain either the Rh D or C antigens, and is absent from red blood cells that are C and D negative.
The appearance of the G antigen, commonly known as GAGE, depends on the presence of an amino acid (serine) that is found on the surface of both the C and the D antigens. This means that a person will have the G antigen if they carry either one of the RHD, RHCe, or RHCE alleles.
The majority of the human population are G positive, as there are only a select few genotypes that would result in someone being G-negative - namely, rr, rr”, and r”r”. Of these G-negative genotypes, rr is the most common, found in 15% of the US Caucasian population.
G Antigen Function
Individuals may form an antibody to the G antigen, commonly known as anti G. This antibody is formed also exclusively by patients who are D-negative and G-negative with the genotype rr If a patient undergoes a blood transfusion, this antigen can cause hemolytic transfusion reactions. In pregnancy, it can result in hemolytic disease of the fetus or newborn. However, it is less likely to cause these problems than the anti-D or anti-G antibodies. A patient that is Rh-negative who has an anti-G antibody may safely undergo a transfusion with red blood cells, as long as these cells are both D- and C-negative.