How to Navigate the RHCE Table
The International Society of Blood Transfusion currently recognizes 38 human blood groups, with the Rh system being the most clinically significant after the ABO system. The Rh system is highly polymorphic, with many gene variants due to genetic modifications such as conversions, insertions and deletions. The RHCE and RHD genes encode the 55 antigens in the Rh system. The most common antigens coded by the RHCE gene include the C, E, c, e and f antigens.
The New York Blood Center’s Immunohematology and Genomics department, along with the National Center for Blood Group Genomics (NCBGG), maintains a table of RHCE alleles that they update regularly to aid industry professionals,researchers and transfusion practitioners.
Overview
The RHCE table documents the RHCE alleles that have been reported. It contains the following information for nearly 150 RHCE alleles:
● ISBT Allele name
● Nucleotide change(s)
● Exon(s) where changes occur
● Amino Acid change(s)
● How allele was originally reported, and other alleles it may be linked to
● Allele frequency and ethnicity in which allele is found
● rs number
● Information regarding antigen expression, alloimmunization, and clinical significance of antibodies, if known
● Links to reference(s) in which allele was described
● GenBank ID
The alleles are listed in order, according to official ISBT allele nomenclature, but commonly used, or “reported as” designations are also included. Users can also search the table for a specific term.
Applications
The purpose of the RHCE table is to catalog the diversity of the gene, and to maintain a current database of reported alleles along with associated clinical findings. Information contained within the table may assist researchers or practitioners studying the prevalence of certain alleles in selected populations, describing new alleles, designing new genotyping assays, or resolving complex patient cases.
The diversity of the Rh system and the large number of reported altered alleles are due to the homology and position of the RHCE and RHD genes on chromosome 1. Often, variant RHCE alleles are linked to variant RHD alleles. These may in turn affect antigen expression on red cells, and can inform transfusion recommendations. The RHCE table facilitates a greater understanding of the diversity of RHCE alleles and their clinical importance.
The proximity and homology of the RHD and RHCE genes contribute to the diversity of RH alleles. Many RH alleles are formed by the exchange of gene fragments between RHD and RHCE, resulting in RHD-RHCE-RHD and RHCE-RHD-RHCE alleles. Gene conversions and single-point mutations have also produced RH variant alleles, further increasing the challenges of developing new genotyping assays. Many of the variant alleles code antigens that are missing some epitopes, increasing the risk of alloimmunization in individuals with these alleles.
Summary
The RHCE table provides current data and resources on reported RHCE alleles, including information relevant to researchers and clinical data that may be used to guide patient blood transfusion treatment.
Click here to access NCBGG’s RHCE table. We also invite you to download “Financial implications of RHD genotyping of pregnant women with a serologic weak D phenotype” by Kacker et al. (2015) for more on the benefits and cost of RHD genotyping.