Blood Group Antigen Gene Mutation Database

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MNS Blood Group System

Introduction

Antigens are glycophorins A and B (GPA and GPB), products of two tightly linked homologous genes GYPA and GYPB of the glycophorin gene family, each present in two different allelic forms. GPA bears the epitopes for the M,N blood groups and GPB, for S,s blood groups. The M and N allelic forms are about equally distributed in world populations. GPA and GPB are type I integral membrane proteins. GPA is the major sialoglycoproteins of the erythrocyte membrane present in about one million copies per cell; it contains ~ 50% carbohydrate,clustered in its extracellular domain in form of sialylated tri- and tetrasaccharide O- glycans and a single complex biantennary N-glycan.The level of GPB at the membrane surface is one tenth less; GPB has the same disposition and pattern of glycosylation but it lacks the N- linked unit. GPE, another member of the gene family, does not appear to be expressed under normal physiological conditions; however, it participates in gene rearrangments resulting in variant alleles. Both GPB and GBE differ from GPA in that they contain pseudoexons equivalent to exons III and exon IV (GPE only) that participate in recombination events. Also, regions 3' of exon 5 differ in sequence.

The genes

The three glycophorin genes show a high degree of sequence homology and probably arose by gene duplication. Each gene is ~30 kb and they reside in a ~350 kb gene cluster (5'-GYPA-GYPB-GYPE-3') on 4q28-q31. Their high degree of sequence homology and organization along the chromosome may be responsible for the relatively frequent occurrence of unequal homologous recombinations and gene conversions among the three genes. A number of the resulting glycophorin products show variant blood group phenotypes, whose molecular studies, in turn, led to the documentation of those gene rearrangements.

Function of proteins

The function of GPA and GPB is not yet clear. However the absence of GPA and/or GPB from erythrocytes, as documented in certain variant erythrocytes in homozygous states (M^k, En(a), S-s-) does not result in significant physiological abnormalities. Possibly, as membrane abundantly glycosylated glycoproteins they provide a glycan coat to the erythrocyte; they serve as receptors for complement, cytokines, bacteria, viruses, P. falciparum; they may participate in regulation of the integrity of the membrane by association with cytoskeleton proteins. A role in Band 3 function is suggested by the absence of GPA in erythrocyte membranes from mice in which band 3 gene (SLC4A1) was inactivated (Hassouns H. et al., Blood, 91:2146, 1998).

Tissue distribution

Erythroid tissues exclusively

Disease association

So far, none apparent. Individuals bearing variant forms of glycophorins, including those who do not express glycophorins at the erythocyte surface appear to be physiologically sound.

Historical aspects

Variants of the MNS system were the first in which the molecular basis for blood group polymorphism was demonstrated, both at protein and gene levels (Mg and Mc in 1981, PMID 6166001; 6940143 and GYPBdel in 1987, PMID 2823938).

About the alleles

The MNS system is nearly unique (except for the Rh system) in that gene rearrangements are a prevailing mechanism for the observed DNA variation resulting in variant alleles. Names of alleles are based on serological phenotypes and on the nature of gene rearrangement, whenever it occurs. Incidence in world populations of most rare alleles is less than 1%, except GPSta (Japan: 6%), GPMiIII (over 90% in certain regions of Taiwan), GPHenshaw or deletion of GPB (high in certain Black populations). A recent study details, by genotyping, the incidence of variant alleles encoding the Miltenberger and Sta phenotypes among the Taiwanese (Shihset al. ).

In the list of alleles, the genomic or cDNA changes are numbered according to recommendations of den Dunnen and Antonarakis (Human Mutation 2000, 15:7-12) so that "A" of the first codon is number 1. In the case of introns, the first nucleotide of each intron is number 1. Note that codon 20 is the first codon expressed in the mature protein and that GYPB pseudoexon III is not expressed except in some hybrids. Thus numbering of altered residues may be awkward; see explanation included under "details" in allele designated GYPAM (reference) id331. GenBank sequences L31860 for GYPA and J02982 for GYPB are used as reference sequences.

Compilation of GYPA/B/E alleles in BGMUT. (Excel; March 2011)

Other database IDs and links

Literature

New PubMed entries with the terms MNS and blood from the last 30 days.
NCBI Book Sections with the terms MNS and blood.

Other

Information is also available on the orthologs of MNS system genes.

Contributors

Olga O. Blumenfeld, Dept. of Biochemistry, Albert Einstein College of Medicine, New York, N.Y., 10461

Contributors for specific alleles are listed with the alleles.

Links