MNS blood group
The MNS antigen system is a human blood group system based upon two genes (glycophorin A, GYPA, and glycophorin B, GYPB) on chromosome 4. There are currently 46 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 primarily encoded by the GYPA gene and the S, s, and U are based on the GYPB gene. The two genes are very close to each other on chromosome 4 and are usually inherited as a haplotype, and, additional hybrid antigens may be formed by recombination and gene conversion events between the two genes.Wikipedia
The GYPA gene has two allelic forms called MNS1 and MNS2, which produce the M antigen and N antigen, respectively. The alleles are almost identical; the MNS1 allele encodes a serine at residue 1 and a glycine at residue 5, while the MNS2 allele encodes a leucine at residue 1 and glutamate at residue 5. The SNPs defining these variations are rs7682260 and rs7687256.
The GYPB gene also has two allelic forms, called MNS3 and MNS4, which produce the S antigen and the s antigen, respectively. These alleles differ in just one amino acid; MNS3 allele encodes a methionine at residue 29, while MNS4 allele encodes a threonine at that position. The SNP at that position is rs7683365.