Rhesus Factor Blood Genes - RHD, RHCE, RHAG
This is a Genomics blog post about information about the Rh factor blood genes that include RHD, RHCE, and RHAG
Definitions/Descriptions of the genes are from Mayaan Lab's ARCHS4
Information about the genes' locations (including IGV screenshots), molecular functions, pathways, superpathways, and biological process is from GeneCards.
Information about the genes' expressions is from Human Protein Atlas.
RHD - 277 Publications including 16 Review Publications
RHCE - 140 Publications including 11 Review Publications
RHAG - 80 Publications including 5 Review Publications
external literature databases
PubMed, Google Scholar, NCBI Bookshelf, Europe PMC, BioRxiv, Medrxiv
RHD
chr1:25,272,393-25,330,445 (58,053 bp) Plus strand
Description:
The RHD gene encodes the RhD protein, which is a major component of the Rh blood group system expressed on the erythrocyte membrane. Its immunogenicity underlies critical clinical challenges in transfusion medicine and obstetrics, where differences in D antigen density and structure (including weak, partial, and DEL phenotypes) can lead to alloimmunization, hemolytic disease of the fetus and newborn, and even impact autoimmune responses as observed in conditions such as chronic lymphocytic leukemia. Advances in non‐invasive prenatal testing that detect fetal RHD sequences in maternal plasma—as well as improved molecular screening for aberrant alleles—have markedly increased the safety of managing RhD‐negative patients, while studies of maternal–fetal genotype incompatibility further implicate this locus in complex disease risk. (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23).
At the molecular level, the RhD protein is characterized by multiple transmembrane domains and extracellular loops that collectively form several overlapping epitope clusters. Detailed mutagenesis studies have pinpointed critical amino acid determinants necessary for D antigen expression, while homology models based on ammonium transporter templates have suggested that RhD may function as part of a membrane channel. Proper surface expression is contingent upon its association with the ancillary Rh-associated glycoprotein (RhAG), and alternative splicing—as seen in D(el) individuals—contributes to the spectrum of expressed variants. Evolutionary and phylogenetic analyses further highlight distinct allele clusters and categorize clinically significant variants such as D category VI, underscoring the complex structure–function relationships within the RHD gene. (24, 25, 26, 27, 28, 29, 30, 31, 32, 33).
Complementing these insights, advanced molecular techniques—including multiplex PCR, next-generation sequencing, and refined hybrid detection assays—have enabled high-resolution mapping of the extensive genetic diversity at the RHD locus across varied populations. Such population-based studies have revealed geographically and ethnically distinct patterns of RHD allele distribution, unmasking novel hybrid, partial, and weak D variants that correlate with variable antigen expression. These efforts have improved our understanding of genotype–phenotype relationships and enhanced transfusion strategies by informing risk prediction for alloimmunization and guiding the development of more reliable serologic and molecular diagnostic platforms. (34, 35, 36, 37, 38, 39, 40, 41, 42, 43).
Molecular functions
Protein binding - Binding to a protein.
Ammonium channel activity - Enables the energy-independent facilitated diffusion of ammonium through a transmembrane aqueous pore or channel.
Pathways
Rhesus blood group biosynthesis - The Rhesus (Rh) blood group system (including the Rh factor) is the second most important blood group system after the ABO blood group system. The Rh blood type was first discovered in 1937 by Karl Landsteiner and Alexander S. Wiener who named it after the rhesus macaque whose RBCs were used to generate the rabbit immune serum that first detected the human blood group system. Subsequent studies by them and Philip Levine and Rufus Stetson identified the antigen that induced this immunization as the "Rh factor" and also its association with hemolytic disease of the newborn (Levine & Stetson 1984, Landsteiner & Wiener 1941). Of the 50 defined Rh blood group antigens, five (D, C/c and E/e) are the major types expressed by the RHD and RHCE genes in the RH gene complex. Rh antigens are expressed on red cell (RBC) membranes in association with other membrane proteins and this whole complex interacts with the spectrin-based skeleton and contributes to the maintenance of the mechanical properties of the RBC membrane (Van Kim et al. 2006).
The RHD gene produces the D antigen, the most immunogenic Rh antigen. The term "Rh factor" refers only to the D antigen; Rh positive (Rh+) individuals have the D antigen on their RBC membranes whereas Rh negative (Rh-) individuals don't. Humans are not born with antibodies towards the D antigen in their blood, they have to be exposed to it (through blood transfusion or placental exposure during pregnancy) at some point in their lives before antibodies are made against it. Once exposed, however, Rh+ individuals remain sensitive for the rest of their lives. Importantly, if individuals are Rh+ and are exposed to Rh- blood, no immune response is mounted. Anti-D antibodies are only seen if an individual is lacking the D antigen (Rh-) and is exposed to Rh+ blood. The RHCE gene produces polypeptides with C/c and E/e antigens.
These polypeptides are the core components of their respective antigens but by themselves are devoid of the immunoreactivity which defines the Rh antigens. The remaining antigens are produced by partial deletion, recombination, mutation, or polymorphisms of one or both RHD and RHCE genes (Cartron 1999). Together, these antigens form the most complex and polymorphic blood group system based on the multitude of phenotypes that can be expressed on the RBC surface. The Fisher-Race system, the nomenclature used most commonly, uses the CDE system to depict the notation of Rh genotypes (Race 1948). The most common group of 3 genes inherited is CDe with ce (D negative) being the second most common. Rh genotyping is used in blood transfusion, paternity testing and to determine the risk of hemolytic disease of the newborn.
SuperPathways
Glycosaminoglycan metabolism and degradation - Groups pathways involved in the metabolism and breakdown of glycosaminoglycans, including hyaluronan and proteoglycan-associated GAGs. Includes sulfation processes via PAPS and lysosomal degradation pathways. Associated with mucopolysaccharidoses due to enzyme deficiencies in GAG catabolism.
Blood group systems biosynthesis - Groups pathways involved in the biosynthesis of blood group antigens, including ABO, Lewis, and Rhesus systems. Enriched for oligosaccharide and peptide biosynthetic processes. Antigens are expressed on red blood cells or secreted and can be absorbed onto cell surfaces.
Biological Processes
Ammonium transmembrane transport - The process in which ammonium is transported across a membrane. Ammonium is the cation NH4+.
Expression
Medium Protein Expression in Blood Marrow
Medium RNA Expression in Blood Marrow
https://www.proteinatlas.org/ENSG00000187010-RHD/
RHCE
chr1:25,362,249-25,430,203 (67,955 bp) Minus strand
Description:
RHCE codes for one of the principal Rhesus proteins expressed on red blood cell (RBC) membranes and is best known for its immunohematologic relevance. Although recognized primarily as an antigenic determinant in transfusion medicine and hemolytic disease of the newborn, its intrinsic physiological role remains less clear. Comparative and phylogenetic studies indicate that RHCE, along with its closely related partner RHD, diverged in key extracellular regions (notably around exon 7) where strong selective pressures have maintained amino acid differences that determine antigenic specificity rather than classic transporter function. (1, 2).
Structural modeling of Rh proteins, based on homology with bacterial ammonium transporters, initially suggested that RH proteins might function as channels mediating solute exchange. However, experimental investigations using heterologous expression systems indicate that while other members of this superfamily (such as Rh-associated glycoprotein, RhBG, and RhCG) facilitate electroneutral ammonium transport coupled with H⁺ exchange, the erythrocyte-specific RHCE (and RH D) proteins do not appear to directly mediate ammonia transport. This has led to the proposition that RHCE may be evolving a novel function in the red cell membrane distinct from that of its ancestral transporter activity. (3, 4).
Further insights have emerged from three‐dimensional modeling studies that predict a transmembrane channel–like structure for RH proteins, including RHCE, wherein specific amino acid substitutions could modulate channel properties. In addition, population-based and metabolic studies reveal an association between erythrocyte levels of 2,3‐bisphosphoglycerate (BPG)—a key regulator of oxygen off-loading—and expression levels of RHCE. This raises the possibility that as part of the Rh complex, RHCE might contribute indirectly to intracellular pH regulation and metabolic reprogramming in response to hypoxic stress, thereby linking antigenic variation with subtle roles in RBC physiology. (5, 6).
Molecular Functions
Ammonium channel activity - Enables the energy-independent facilitated diffusion of ammonium through a transmembrane aqueous pore or channel.
Pathways
Rhesus blood group biosynthesis - Rhesus blood group biosynthesis - The Rhesus (Rh) blood group system (including the Rh factor) is the second most important blood group system after the ABO blood group system. The Rh blood type was first discovered in 1937 by Karl Landsteiner and Alexander S. Wiener who named it after the rhesus macaque whose RBCs were used to generate the rabbit immune serum that first detected the human blood group system. Subsequent studies by them and Philip Levine and Rufus Stetson identified the antigen that induced this immunization as the "Rh factor" and also its association with hemolytic disease of the newborn (Levine & Stetson 1984, Landsteiner & Wiener 1941). Of the 50 defined Rh blood group antigens, five (D, C/c and E/e) are the major types expressed by the RHD and RHCE genes in the RH gene complex. Rh antigens are expressed on red cell (RBC) membranes in association with other membrane proteins and this whole complex interacts with the spectrin-based skeleton and contributes to the maintenance of the mechanical properties of the RBC membrane (Van Kim et al. 2006).
The RHD gene produces the D antigen, the most immunogenic Rh antigen. The term "Rh factor" refers only to the D antigen; Rh positive (Rh+) individuals have the D antigen on their RBC membranes whereas Rh negative (Rh-) individuals don't. Humans are not born with antibodies towards the D antigen in their blood, they have to be exposed to it (through blood transfusion or placental exposure during pregnancy) at some point in their lives before antibodies are made against it. Once exposed, however, Rh+ individuals remain sensitive for the rest of their lives. Importantly, if individuals are Rh+ and are exposed to Rh- blood, no immune response is mounted. Anti-D antibodies are only seen if an individual is lacking the D antigen (Rh-) and is exposed to Rh+ blood. The RHCE gene produces polypeptides with C/c and E/e antigens.
These polypeptides are the core components of their respective antigens but by themselves are devoid of the immunoreactivity which defines the Rh antigens. The remaining antigens are produced by partial deletion, recombination, mutation, or polymorphisms of one or both RHD and RHCE genes (Cartron 1999). Together, these antigens form the most complex and polymorphic blood group system based on the multitude of phenotypes that can be expressed on the RBC surface. The Fisher-Race system, the nomenclature used most commonly, uses the CDE system to depict the notation of Rh genotypes (Race 1948). The most common group of 3 genes inherited is CDe with ce (D negative) being the second most common. Rh genotyping is used in blood transfusion, paternity testing and to determine the risk of hemolytic disease of the newborn.
Blood group systems biosynthesis - Blood group systems biosynthesis - The association between blood type and disease has been studied since the beginning of the 20th Century (Anstee 2010, Ewald & Sumner 2016). Landsteiner's discovery of blood groups in 1900 was based on agglutination patterns of red blood cells when blood types from different donors were mixed (Landsteiner 1931, Owen 2000, Tan & Graham 2013). His work is the basis of routine compatibility testing and transfusion practices today. The immune system of patients receiving blood transfusions will attack any donor red blood cells that contain antigens that differ from their self-antigens. Therefore, matching blood types is essential for safe blood transfusions. Landsteiner's classification of the ABO blood groups confirmed that antigens were inherited characteristics. In the 1940s, it was established that the specificity of blood group antigens was determined by their unique oligosaccharide structures. Since then, exponential advances in technology have resulted in the identification of over 300 blood group antigens, classified into more than 35 blood group systems by the International Society of Blood Transfusion (ISBT) (Storry et al. 2016).
Metabolism of carbohydrates and carbohydrate derivatives - Starches and sugars are major constituents of the human diet and the catabolism of monosaccharides, notably glucose, derived from them is an essential part of human energy metabolism (Dashty 2013). Glucose can be catabolized to pyruvate (glycolysis) and pyruvate synthesized from diverse sources can be metabolized to form glucose (gluconeogenesis). Glucose can be polymerized to form glycogen under conditions of glucose excess (glycogen synthesis), and glycogen can be broken down to glucose in response to stress or starvation (glycogenolysis). Other monosaccharides prominent in the diet, fructose and galactose, can be converted to glucose. The disaccharide lactose, the major carbohydrate in breast milk, is synthesized in the lactating mammary gland. The pentose phosphate pathway allows the synthesis of diverse monosaccharides from glucose including the pentose ribose-5-phosphate and the regulatory molecule xylulose-5-phosphate, as well as the generation of reducing equivalents for biosynthetic processes. Glycosaminoglycan metabolism and xylulose-5-phosphate synthesis from glucuronate are also annotated as parts of carbohydrate metabolism.
SuperPathways
Glycosaminoglycan metabolism and degradation - Groups pathways involved in the metabolism and breakdown of glycosaminoglycans, including hyaluronan and proteoglycan-associated GAGs. Includes sulfation processes via PAPS and lysosomal degradation pathways. Associated with mucopolysaccharidoses due to enzyme deficiencies in GAG catabolism.
Blood group systems biosynthesis - Groups pathways involved in the biosynthesis of blood group antigens, including ABO, Lewis, and Rhesus systems. Enriched for oligosaccharide and peptide biosynthetic processes. Antigens are expressed on red blood cells or secreted and can be absorbed onto cell surfaces.
Biological Processes
Ammonium transmembrane transport - The process in which ammonium is transported across a membrane. Ammonium is the cation NH4+.
https://preview.genecards.org/card/RHCE
Expression
Medium Protein Expression in Bone Marrow
Medium RNA Expression in Bone Marrow
https://www.proteinatlas.org/ENSG00000188672-RHCE/
RHAG
chr6:49,605,175-49,636,839 (31,665 bp) Minus strand
Description:
RHAG is a member of the Rh‐protein family that functions as a gas channel in erythrocytes and in heterologous expression systems. Studies have demonstrated that RHAG mediates transmembrane transport of ammonia and ammonium, contributing to both NH₃ influx and NH₄⁺/H⁺ exchange, and has measurable permeability for CO₂ as well. In Xenopus oocytes and red cell membrane ghosts, enhanced surface pH changes and altered gas fluxes indicate that RHAG facilitates the movement of these gaseous and ionic species, thereby playing a major role in cellular gas exchange and acid–base balance. (1, 2, 3, 4, 5, 6, 7, 8, 9, 10).
At the mechanistic level, RHAG exhibits distinct transporter characteristics that are sensitive to the transmembrane pH gradient, indicating that ammonium uptake can occur in an electrogenic or electroneutral manner depending on the prevailing ionic conditions. Its molecular structure is consistent with forming a pore‐like assembly that allows passage of NH₃ and, to some extent, NH₄⁺ across the plasma membrane. Moreover, RHAG is integral to the assembly and proper surface expression of the Rh complex in red cells—a function that is critical for maintaining efficient gas exchange and membrane integrity. (11, 12, 13, 14, 15, 16).
Mutational analyses have underscored the physiological and clinical importance of RHAG’s transporter function. Several studies have reported that missense and nonsense mutations in the RHAG gene can lead to loss or alteration of gas channel activity, resulting in aberrant ammonium transport and even abnormal monovalent cation leakage. Such defects are mechanistically linked to the Rh_null, Rh_mod, and overhydrated hereditary stomatocytosis phenotypes, where improper assembly of the Rh complex and reduced gas permeability compromise red blood cell function. These findings highlight that normal RHAG activity is essential not only for gas exchange but also for preserving red cell membrane stability. (17, 18, 19, 20, 21, 22, 23).
Molecular Functions
Ankyrin binding - Binding to ankyrin, a 200 kDa cytoskeletal protein that attaches other cytoskeletal proteins to integral membrane proteins.
Protein binding - Binding to a protein.
Ammonium channel activity - Enables the energy-independent facilitated diffusion of ammonium through a transmembrane aqueous pore or channel.
Carbon dioxide transmembrane transporter activity - Enables the transfer of carbon dioxide (CO2) from one side of a membrane to the other.
Leak channel activity - Enables the transport of a solute across a membrane via a narrow pore channel that is open even in an unstimulated or 'resting' state.
Methylammonium transmembrane transporter activity - Enables directed movement of methylammonium, CH3NH2, from one side of a membrane to the other.
Pathways
Rhesus glycoproteins mediate ammonium transport - The Rhesus (Rh) glycoproteins were originally described in human blood cells as potent immunogens. There are three Rh glycoproteins in humans; an erythroid-specific Rh-associated glycoprotein (RhAG) and two non-erythroid Rh glycoproteins, RhBG and RhCG. These proteins are related to ammonium (NH4+) transporters of yeast and bacteria (methylammonium and ammonium permease and ammonium transporter, MEP/Amt) (Nakhoul NL and Hamm LL, 2004; Planelles G, 2007).
Erythrocytes take up oxygen and release carbon dioxide - Erythrocytes circulating through the capillaries of the lung must exchange carbon dioxide (CO2) for oxygen (O2) during their short (0.5-1 sec.) transit time in pulmonary tissue (Reviewed in Jensen 2004, Esbaugh and Tufts 2006, Boron 2010). CO2 bound as carbamate to the N-terminus of hemoglobin and protons (H+) bound to histidine residues in hemoglobin are released as hemoglobin (HbA) binds O2. Bicarbonate (HCO3-) present in plasma is taken up by erythrocytes via the band3 anion exchanger (AE1, SLC4A1) and combined with H+ by carbonic anhydrases I and II (CA1/CA2) to yield water and CO2 (Reviewed by Esbaugh and Tufts 2006). CO2 is passively transported out of the erythrocyte by AQP1 and RhAG. HCO3- in plasma is also directly dehydrated by extracellular carbonic anhydrase IV (CA4) present on endothelial cells lining the capillaries in the lung.
Erythrocytes take up carbon dioxide and release oxygen - Carbon dioxide (CO2) in plasma is hydrated to yield protons (H+) and bicarbonate (HCO3-) by carbonic anhydrase IV (CA4) located on the apical plasma membranes of endothelial cells. Plasma CO2 is also taken up by erythrocytes via AQP1 and RhAG. Within erythrocytes CA1 and, predominantly, CA2 hydrate CO2 to HCO3- and protons (reviewed in Geers & Gros 2000, Jensen 2004, Boron 2010). The HCO3- is transferred out of the erythrocyte by the band 3 anion exchange protein (AE1, SLC4A1) which cotransports a chloride ion (Cl-) into the erythrocyte.
Also within the erythrocyte, CO2 combines with the N-terminal alpha amino groups of HbA to form carbamates while protons bind histidine residues in HbA. The net result is the Bohr effect, a conformational change in HbA that reduces its affinity for O2 and hence assists the delivery of O2 to tissues.
O2/CO2 exchange in erythrocytes - In capillaries of the lungs Erythrocytes take up oxygen and release carbon dioxide. In other tissues of the body the reverse reaction occurs: Erythrocytes take up carbon dioxide and release oxygen (reviewed in Nikinmaa 1997, Jensen 2004).
In the lungs, carbon dioxide (CO2) bound as carbamate to the N-terminus of hemoglobin (HbA) and protons bound to histidine residues in HbA are released as HbA binds oxygen (O2). Bicarbonate (HCO3-) present in plasma is taken up by erythrocytes via the band3 anion exchanger (AE1, SLC4A1) and combined with protons by carbonic anhydrases I and II (CA1, CA2) to yield water and CO2 (reviewed by Esbaugh & Tufts 2006, De Rosa et al. 2007). The CO2 is passively transported out of the erythrocyte by AQP1 and RhAG. HCO3- in plasma is also directly dehydrated by extracellular carbonic anhydrase IV (CA4) present on endothelial cells lining the capillaries in the lung.
In non-pulmonary tissues CO2 in plasma is hydrated to yield protons and HCO3- by CA4 located on the apical plasma membranes of endothelial cells. Plasma CO2 is also taken up by erythrocytes via AQP1 and RhAG. Within erythrocytes CA1 and, predominantly, CA2 hydrate CO2 to yield HCO3- and protons (reviewed in Geers & Gros 2000, Jensen 2004, Boron 2010). HCO3- is transferred out of the erythrocyte by the band 3 anion exchange protein (AE1, SLC4A1) which cotransports a chloride ion into the erythrocyte.
Also within the erythrocyte, CO2 combines with the N-terminal alpha amino groups of HbA to form carbamates while protons bind histidine residues in HbA. The net result is the Bohr effect, a conformational change in HbA that reduces its affinity for O2 and hence assists the delivery of O2 to tissues.
Miscellaneous transport and binding events - This section contains known transport and binding events that as of yet cannot be placed in exisiting pathways (Purves 2001, He et al. 2009, Rees et al. 2009).
SLC transporter disorders - The solute-carrier gene (SLC) superfamily encodes membrane-bound transporters comprising 55 gene families with at least 362 putatively functional protein-coding genes. The gene products include passive transporters, symporters and antiporters and are located in all cellular and organelle membranes. Curated here is a list of SLCs, where mutations within them can result in disease (Hediger et al. 2013).
Disorders of transmembrane transporters - Proteins with transporting functions can be roughly classified into 3 categories: ATP hydrolysis-coupled pumps, ion channels, and transporters. Pumps utilize the energy released by ATP hydrolysis to power the movement of substrates across the membrane against their electrochemical gradient. Channels in their open state can transfer substrates (ions or water) down their electrochemical gradient at an extremely high efficiency (up to 108 s-1). Transporters facilitate the movement of a specific substrate either against or with their concentration gradient at a lower speed (about 102 -104 s-1); as generally believed, conformational change of the transporter protein is involved in the transfer process. Diseases caused by defects in these transporter proteins are detailed in this section. Disorders associated with ABC transporters and SLC transporters are annotated here (Dean 2005).
SuperPathways
O2/CO2 Gas Exchange in Erythrocytes - Groups pathways involved in the exchange of oxygen and carbon dioxide in erythrocytes, including bicarbonate transport and carbamate formation with hemoglobin. Includes reversible binding of O2 and CO2 in lungs and tissues mediated by carbonic anhydrases and anion exchangers.
Ammonium and transmembrane transport events - Groups pathways involved in transmembrane transport, with a focus on ammonium transport mediated by Rhesus glycoproteins and related binding events not assigned to specific pathways.
SLC and ABC transporter disorders - Groups pathways involved in diseases caused by defects in transmembrane solute carriers (SLC) and ATP-binding cassette (ABC) transporters. Includes disorders associated with impaired substrate transport across cellular membranes due to mutations in transporter genes.
Biological Processes
Ammonium transmembrane transport - The process in which ammonium is transported across a membrane. Ammonium is the cation NH4+.
Erythrocyte development - The process whose specific outcome is the progression of an erythrocyte over time, from its formation to the mature structure.
Methylammonium transmembrane transport - The process in which methylammonium is transported across a membrane.
Intracellular monoatomic ion homeostasis - A homeostatic process involved in the maintenance of a steady state level of monoatomic ions within a cell. Monatomic ions (also called simple ions) are ions consisting of exactly one atom.
Multicellular organismal-level iron ion homeostasis - A chemical homeostatic process involved in the maintenance of a steady state level of iron within extracellular body fluids, such as blood, xylem or phloem, of a multicellular organism. This is distinct from maintenance of cellular homeostasis, which occurs within a cell.
https://preview.genecards.org/card/RHAG
Expression
High RNA Expression in Bone marrow
Medium Protein Expression in Testis
https://www.proteinatlas.org/ENSG00000112077-RHAG/
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