MNS system

The MNS system is one of the important blood type systems . It is based on three genes for glycoproteins ( GYPA , GYPB and GYPE ), which are located close together on chromosome 4 (4q28-q31) and are thus inherited together, and are largely structurally similar ( paralogue ). A total of 46 different antigens are combined in this system, including the antigens M, N, S, s and U, with the antigens S and s being the most important in transfusion medicine.

The antigens M and N were discovered by Karl Landsteiner and Philip Levine as early as 1927. The antigen S was described in 1947, the other antigens s and U followed. The distinction between the precursor proteins in glycophorin A and B was introduced in 1987, glycophorin E was added in 1990. The antigens M and N can be described independently as an MN system , since they are only formed from glycophorin A. The antigens S and s (as well as U) are formed from glycophorin B. Glycophorin E does not appear to be expressed under normal physiological conditions. Most of the 41 less common sub-variants (besides the 5 common ones) are recombinations of the two glycophorins A and B, so that the subgroup to the MN system is combined with other subgroups to the MNS system.

Antibodies anti-S and anti-s formed against S and s can lead to severe intolerance, in addition to general haemolytic transfusion reactions also to haemolyticus neonatorum disease in pregnancy. The antigen U originally stood for "universal" as it was believed to be generally present, but U-negative carriers were later identified. In U-negative patients, S-negative and S-negative also appear, with consequent medical relevance. Natural IgM antibodies are formed against the antigens M and N , which are only relevant for transfusion in special situations and must then be taken into account.

frequency

The antigens M and N are found in about 75% of the population, the genotype MN is most common with 50%. However, there are populations in which the distribution differs considerably, most Eskimo have the genotype MM, while Aborigines mostly belong to the genotype NN.

Distribution of blood groups in the MN system

genotypically	phenotypically	Inuits	Aboriginal	Egypt	Germany	China	Nigeria
MM	M +	83.5%	0.2%	27.6%	29.7%	33.2%	30.1%
MN	M + N +	15.6%	30.4%	48.9%	50.7%	48.6%	49.5%
NN	N +	0.9%	67.2%	23.3%	19.6%	18.2%	20.4%

The antigen S with a frequency of about 55% and the antigen s with a frequency of about 89% are relatively common. The U antigen occurs particularly frequently with a general frequency of more than 99.9%, but is noticeably absent in some Africans. The other homologous antigens that were added to the MNS system are mutations that occur very rarely, for example Henshaw (He) with 0.8%, or very common variants of the common blood groups, for example EN ^a (weak glycoprotein A) with Frequency above 99.9% (causes resistance to Plasmodium falciparum ).

Individual evidence

1. ↑ ^{a b} ISBT Committee on Terminology for Red Cell Surface Antigens: Table of blood group antigens within systems. (No longer available online.) International Society for Blood Transfusion, archived from the original on August 18, 2011 ; accessed on January 16, 2010 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
2. ↑ PD Siebert, M. Fukuda: Molecular cloning of a human glycophorin B cDNA: nucleotide sequence and genomic relationship to glycophorin A. In: Proceedings of the National Academy of Sciences . Volume 84, Number 19, October 1987, pp. 6735-6739, PMID 3477806 , PMC 299158 (free full text).
3. ↑ A. Vignal, C. Rahuel et al. a .: A novel gene member of the human glycophorin A and B gene family. Molecular cloning and expression. In: European Journal of Biochemistry. Volume 191, Number 3, August 1990, pp. 619-625, PMID 2390989 .
4. ↑ Uniprot P02724 / GYPA precursor quote: "... GYPA is responsible for the MNS blood group system. The molecular basis of the GPA M / N bloodgroup antigen is a variation at positions 20 and 24. Ser-20 and Gly-24 correspond to M (shown); 'Leu-20' and 'Glu-24' correspond to N. "
5. ↑ Uniprot P06028 / GYPB precursor quote: "... GYPB is responsible for the MNS blood group system. The molecular basis of the S / s blood group antigen is a single variation in position 48; Thr-48 corresponds to s = MSN4 and Met-48 to S = MNS3. "
6. ↑ Olga O. Blumenfeld: MNS (MNS) Blood Group System. NCBI dbRBC, December 11, 2009, accessed January 17, 2010 . 
7. ↑ Steven M. Carr: MN Blood Group system in Humans. 2004, accessed January 2010 . 

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