The MNS antigen system is a

human blood group system The term human blood group systems is defined by the International Society of Blood Transfusion (ISBT) as systems in the human species where cell-surface antigens—in particular, those on blood cells—are "controlled at a single gene locus or by ...

based upon two genes ( glycophorin A and glycophorin B) on

chromosome 4 Chromosome 4 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 4 spans more than 186 million base pairs (the building material of DNA) and represents between 6 and 6.5 percent of the t ...

. There are currently 50 antigens in the system, but the five most important are called M, N, S, s, and U. The system can be thought of as two separate groups: the M and N antigens are at one location on the ECM and S, s, and U are on a closely related location. The two groups are very closely located together on

and are inherited as a

haplotype A haplotype ( haploid genotype) is a group of alleles in an organism that are inherited together from a single parent. Many organisms contain genetic material ( DNA) which is inherited from two parents. Normally these organisms have their DNA or ...

The MN blood group

The MN blood group in humans is under the control of a pair of co-dominant

allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

s, L^M and L^N. Most people in the

Inuit Inuit (; iu, ᐃᓄᐃᑦ 'the people', singular: Inuk, , dual: Inuuk, ) are a group of culturally similar indigenous peoples inhabiting the Arctic and subarctic regions of Greenland, Labrador, Quebec, Nunavut, the Northwest Territories ...

population are M/M, while this genotype is rare among Aborigines. In fact, they tend to possess the opposite genotype (N/N). The MN blood group system is under the control of an

autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

locus found on chromosome 4, with two alleles designated L^M and L^N. The blood type is due to a

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

present on the surface of a red blood cell (RBC), which behaves as a native

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

Phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...

expression at this locus is

codominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The first ...

because an individual may exhibit either one or both antigenic substances. Frequencies of the two

alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

vary widely among human populations.Ralph H. Kathan and Anthony Adamany. 1967. Comparison of Human MM, NN, and MN Blood Group Antigens. The Journal of Biological Chemistry, 242, 1736-1722. M+ and N+ RBCs are common (75% of population) and M+N+ cells are the most common genotype (50% of population). These antigens were an early discovery and are some of the oldest blood antigens known after the ABO system. They were first described by

Karl Landsteiner Karl Landsteiner (; 14 June 1868 – 26 June 1943) was an Austrian-born American biologist, physician, and immunologist. He distinguished the main blood groups in 1900, having developed the modern system of classification of blood groups from ...

and Philip Levine in 1927. Anti-M and anti-N antibodies are usually

IgM Immunoglobulin M (IgM) is one of several isotypes of antibody (also known as immunoglobulin) that are produced by vertebrates. IgM is the largest antibody, and it is the first antibody to appear in the response to initial exposure to an antig ...

and are rarely associated with

transfusion reactions Blood transfusion is the process of transferring blood products into a person's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but mod ...

. Anti-N is sometimes seen in dialysis patients due to cross-reactions with the residual

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

from sterilizing the equipment. This is usually irrelevant for transfusion since this variant of the antibody does not react at body temperature.

The U and Ss groups: an overview

The S antigen is relatively common (~55% of the population) and the s antigen is very common (~89% of the population). Anti-S and anti-s can cause

hemolytic transfusion reaction An acute hemolytic transfusion reaction (AHTR), also called immediate hemolytic transfusion reaction, is a life-threatening reaction to receiving a blood transfusion. AHTRs occur within 24 hours of the transfusion and can be triggered by a few milli ...

s and

hemolytic disease of the newborn Hemolytic disease of the newborn, also known as hemolytic disease of the fetus and newborn, HDN, HDFN, or erythroblastosis foetalis, is an alloimmune condition that develops in a fetus at or around birth, when the IgG molecules (one of the five ...

.The U antigen is a high incidence antigen, occurring in more than 99.9% of the population. The U was originally short for "Universal", though this is not the case. U negative RBCs can be found in people of

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

n descent. This mutation in red cell surface structure also makes the RBCs S- and s-. Anti-U has been associated with both hemolytic transfusion reactions and hemolytic disease of the newborn.

Other MNS antigens

The other 41 identified antigens in the MNS group are low incidence, such as He (0.8% of the population) or high incidence, such as EN^a (>99.9% of the population).

MNS glycoproteins and genes

Antigens of the MNS system are located on one of two glycoproteins: glycophorin A (GPA, CD235A) and glycophorin B (GPB, CD235B).Roback JD et al. AABB Technical Manual, 16th Ed. Bethesda: AABB Press, 2008. Each glycoprotein crosses the membrane once and has an external N-terminal domain (varying in length from 44 amino acids for GPB to 72 amino acids in length for GPA) as well as a C-terminal cytosolic domain (GPB, 8 amino acids in length; GPA, 36 amino acids in length).

MNS antibodies

Serology interpretation of antibody panel for blood group antigens

* MNS antibodies display dosage (they react stronger against cells which are homozygous vs heterozygous for the antigen in question). * Anti-M and anti-N antibodies are naturally occurring, cold-reacting IgM-class antibodies.Mais DD. ASCP Quick Compendium of Clinical Pathology, 2nd Ed. Chicago: ASCP Press, 2009. * Anti-M and anti-N are generally clinically insignificant. * Anti-S, anti-s and anti-U antibodies are acquired following exposure (via pregnancy or past transfusion with blood products) and are warm-reacting IgG-class antibodies. * Anti-S, anti-s and anti-U are usually clinically significant.

References

* https://www.mun.ca/biology/scarr/MN_bloodgroup.html * Mark E. Brecher, Editor (2005), ''AABB Technical Manual'', 15th edition, Bethesda, MD: AABB, , p. 336-340 * Denise M. Harmening (1999), ''Modern Blood Banking and Transfusion Practices'', Philadelphia, PA: F.A. Davis Company, p. 164-169

External links

MNS system
at BGMUT Blood Group Antigen Gene Mutation Database,

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{{DEFAULTSORT:Mns Antigen System Blood antigen systems Transfusion medicine