MNS antigen system

The MNS system is one of the most important blood group systems. It is based on three genes for glycoproteins ( GYPA, GYPB and GYPE ), which are close together on chromosome 4 ( 4q28 - q31 ) and are therefore inherited together, and largely structurally similar ( paralog ) are. 46 different antigens in this system are summarized, including the antigens M, N, S, and U, where the antigens S and S transfusion medicine are the most important.

The antigens M and N were discovered by Karl Landsteiner and Philip Levine in 1927. The antigen S was described in 1947, followed by the other antigens and U s. The differentiation of the precursor proteins glycophorin A and B was introduced in 1987, the glycophorin E was added 1990. The antigens M and N can thereby be described as independent MN- system since formed only from the glycophorin A. The antigens S and s ( and U) are formed from the glycophorin B. Glycophorin E seems to be not expressed under normal physiological conditions. For most of the 41 rarer sub-variants ( in addition to the frequent 5 ) are recombinations of the two glycophorins A and B, so that the sub-group for MN- system are combined with other sub- groups to the MNS system.

V S and s antibody produced anti -S and anti -s can lead to serious incompatibilities, apart from general hemolytic transfusion reactions and hemolytic disease of the newborn in the pregnancies. The antigen U originally stood for "universal " because it was considered to be generally available, but U -negative slides were later identified. In U- negative patients also appear S- negative and s- negative, with consequent medical relevance. Against the antigens M and N are natural IgM antibodies are formed, the transfusion relevant only in special situations and are then taken into account.

Frequency

The antigens M and N are found in about 75 % of the population, the genotype MN is represented by 50 % at most. However, there are populations in which the distribution is significantly different, then there is at most Eskimo before the MM genotype, whereas Aboriginal people mostly belong to the genotype NN.

The antigen S with a frequency of about 55%, and the antigen S with a frequency of about 89% are quite common. The antigen U is particularly frequently occurring with a general frequency beyond 99.9 %, with some Africans but often strikingly absent. The other homologous antigens that have been added to the MNS system, each very rarely occurring mutations, for example Henshaw ( He) with 0.8 %, or very frequent variants of the common blood groups, for example ENa (weak glycoprotein A) Frequency beyond 99.9 % ( causes resistance to Plasmodium falciparum ).