Molecular basis of blood group expression.

Antigen diversity arises from changes at the gene level that range from single nucleotide polymorphisms (SNPs) to intra- and inter-genic exchanges, inversions, insertions, and deletions. Nucleotide changes often result in amino acid difference from the wild-type gene product and with those changes new blood group antigens arise. Alternatively, there is loss of expression altogether, which is deemed the 'null' phenotype. Near complete knowledge of the genetic changes underlying the expression of blood group antigens will lead to the reality that red cell genotyping as a test-of-record. The importance of molecular testing in immunohematology necessitates appropriate training and competency programs to ensure that the highly skilled staff has the appropriate knowledge background. This review summarizes the core mechanisms for gene expression and provides a compilation of the molecular basis for blood group expression.