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NCBI Bookshelf. Dean L. The Hh blood group contains one antigen, the H antigen, which is found on virtually all RBCs and is the building block for the production of the antigens within the ABO blood group. There is no ill effect with being H deficient, but if a blood transfusion is ever needed, people with this blood type can receive blood only from other donors who are also H deficient.
A transfusion of "normal" group O blood can trigger a severe transfusion reaction. Because the H antigen is the precursor of the ABO blood group antigens, if it is not produced, the ABO blood group antigens are also not produced. This can be misleading in paternity cases, a fact that has been exploited in soap opera story lines! In the show "General Hospital", the father of Monica's child was in doubt.
However, Alan is the father! View in own window. In Bombay, India, an individual was discovered to have an interesting blood type that reacted to other blood types in a way that had not been seen before. The individual's RBCs appeared to lack all of the ABO blood group antigens plus an additional antigen that was previously unknown. In , a paper about the "new blood group character related to the ABO blood group" was published 2. This new blood group character is the H antigen and it is the building block for the antigens of the ABO blood group.
Named for the city in which it was first discovered, the "Bombay phenotype" describes individuals whose RBCs lack the H antigen. Because of the rarity of this blood type, this normally means using blood donations from a suitable relative. The biosynthesis of the H antigen and the A and B antigens involves a series of enzymes glycosyltransferases that transfer monosaccharides.
The resulting antigens are oligosaccharide chains, which are attached to lipids and proteins that are anchored in the RBC membrane. The H antigen is produced by a specific fucosyltransferase.
If a person has blood group O, the H antigen remains unmodified. Therefore, the H antigen is present in the highest amounts in blood type O and in the least amounts in blood type AB. The Se locus contains the FUT2 gene, which is expressed in secretory glands. They produce a soluble form of H antigen that is found in saliva and other bodily fluids.
The enzyme encoded by FUT2 is also involved in the synthesis of antigens of the Lewis blood group. The Bombay phenotype and para-Bombay phenotype are relatively rare. In India, where H deficiency was first discovered, the frequency of both phenotypes combined is 1 in 10, 1. H deficiency is slightly more common in Taiwan, affecting 1 of 8, people 1. A relatively large number of H-deficient individuals were found on Reunion Island, which is a small French Island km east of Madagascar in the Indian Ocean 3.
Both the classical Bombay phenotype and a new variant type of partial H deficiency was seen in the islanders 4. In Europe, 1 per million people are H deficient 1. The H antigen shares the same broad tissue distribution as the A and B antigens. Likewise, in individuals who are "secretors", a soluble form of the H antigen is found in saliva and all fluids except cerebrospinal fluid.
The function of the H antigen, apart from being an intermediate substrate in the synthesis of ABO blood group antigens, is not known although it may be involved in cell adhesion 5. People who lack the H antigen do not suffer any deleterious effects, and being H-deficient is only an issue if they were to need a blood transfusion because they would require H-deficient blood. If patients with anti-H in their circulation receive transfusions of blood that contains the H antigen e.
In theory, the maternal production of anti-H during pregnancy could cause hemolytic disease in a fetus who did not inherit the mother's Bombay phenotype. In practice, cases of HDN caused in this way have not been described, possibly because of the rarity of the Bombay phenotype.
Because they are highly homologous, they are likely to have been the result of a gene duplication of a common gene ancestor.
The H locus contains four exons that span more than 8 kb of genomic DNA. The mutation introduces a stop codon, resulting in a truncated enzyme that lacks 50 amino acids at the C-terminal end, rendering the enzyme inactive.
In Caucasians, the Bombay phenotype may be caused by a number of mutations 9, Likewise, a number of mutations have been reported to underlie the para-Bombay phenotype Turn recording back on. National Center for Biotechnology Information , U. Show details Dean L. Search term. Chapter 6 The Hh blood group. At a glance Antigens of the Hh blood group View in own window Number of antigens 1: the H antigen Antigen specificity Carbohydrate The specificity of the H antigen is determined by the sequence of oligosaccharides.
More specifically, the minimum requirement for H antigenicity is the terminal disaccharide fucose-galactose, where the fucose has an alpha- - linkage. Antigen-carrying molecules Glycoproteins and glycolipids of unknown function The H antigen is attached to oligosaccharide chains that project above the RBC surface. These chains are attached to proteins and lipids that lie in the RBC membrane. FUT1 encodes a fucosyltransferase that catalyzes the final step in the synthesis of the H antigen.
The FUT2 gene indirectly encodes a soluble form of the H antigen, which is found in bodily secretions. Frequency of the H antigen Present on Anti-H reactivity Capable of hemolysis Anti-H can activate the complement cascade which lyses RBCs while they are still in the circulation intravascular hemolysis. Background information History In Bombay, India, an individual was discovered to have an interesting blood type that reacted to other blood types in a way that had not been seen before.
Nomenclature Number of H antigens: 1. Basic biochemistry The biosynthesis of the H antigen and the A and B antigens involves a series of enzymes glycosyltransferases that transfer monosaccharides. Common H phenotypes The two common H phenotypes are "secretor" and "non-secretor".
Secretor common H antigen is expressed on RBCs. Non secretor common H antigen is present on RBCs. Bombay phenotype H antigen is not expressed on RBCs. Expression of the H antigen The H antigen shares the same broad tissue distribution as the A and B antigens. Function of the H antigen The function of the H antigen, apart from being an intermediate substrate in the synthesis of ABO blood group antigens, is not known although it may be involved in cell adhesion 5.
Clinical significance of H antibodies Transfusion reactions If patients with anti-H in their circulation receive transfusions of blood that contains the H antigen e. Hemolytic disease of the newborn In theory, the maternal production of anti-H during pregnancy could cause hemolytic disease in a fetus who did not inherit the mother's Bombay phenotype. References 1. Second ed. A "new" blood group character related to the ABO system. H-deficient blood groups Bombay of Reunion Island.
Am J Hum Genet. Point mutations and deletion responsible for the Bombay H null and the Reunion H weak blood groups. Vox Sang. A novel function for a glucose analog of blood group H antigen as a mediator of leukocyte-endothelial adhesion via intracellular adhesion molecule 1.
J Biol Chem. Molecular basis for H blood group deficiency in Bombay Oh and para-Bombay individuals. Wide variety of point mutations in the H gene of Bombay and para-Bombay individuals that inactivate H enzyme. Biochem Biophys Res Commun. Polymorphism of the h allele and the population frequency of sporadic nonfunctional alleles.
A new h allele detected in Europe has a missense mutationin alpha 1,2 -fucosyltransferase motif II. Heterogeneity of the human H blood group alpha 1,2 fucosyltransferase gene among para-Bombay individuals. Copyright Notice. Chapter 6, The Hh blood group. In this Page. At a glance Background information Basic biochemistry Clinical significance of H antibodies Molecular information References. NCBI Resources. Other Resources.
Antigen-carrying molecules. Glycoproteins and glycolipids of unknown function The H antigen is attached to oligosaccharide chains that project above the RBC surface. Frequency of the H antigen. Present on Frequency of the H phenotype.
Hh blood group
This blood phenotype was first discovered in Bombay, now known as Mumbai , in India , by Dr. Bhende in The first person found to have the Bombay phenotype had a blood type that reacted to other blood types in a way never seen before. The serum contained antibodies that attacked all red blood cells of normal ABO phenotypes. The red blood cells appeared to lack all of the ABO blood group antigens and to have an additional antigen that was previously unknown. Individuals with the rare Bombay phenotype hh do not express H antigen also called substance H , the antigen which is present in blood group O.