MedGen

MN antigens reside on GYPA, one of the most abundant red-cell glycoproteins. The M and N antigens are 2 autosomal codominant antigens encoded by the first 5 amino acids of GYPA and include 3 O-linked glycans as part of the epitope. M and N differ at amino acids 1 and 5, where M is ser-ser-thr-thr-gly, and N is leu-ser-thr-thr-glu. M is the ancestral GYPA allele and is common in all human populations and Old World apes. GYPA, glycophorin B (GYPB; 617923), and glycophorin E (GYPE; 138590) are closely linked on chromosome 4q31. The N terminus of GYPB is essentially identical to that of GYPA except that it always expresses the N antigen, denoted 'N' or N-prime. Antigens of the Ss blood group (111740) reside on GYPB, and recombination and gene conversion between GYPA, GYPB, and GYPE lead to hybrid glycophorin molecules and generation of low-incidence antigens. Thus, the MN and Ss blood groups are together referred to as the MNSs or MNS blood group system. The U antigen refers to a short extracellular sequence in GYPB located near the membrane. Recombination results in 3 glycophorin-null phenotypes: En(a-) cells lack GYPA due to recombination between GYPA and GYPB; GYPB-negative (S-s-U-) cells lack GYPB due to recombination in GYPB; and M(k) cells (M-N-S-s-U-) lack both GYPA and GYPB due to recombination between GYPA and GYPE. Individuals with glycophorin-null phenotypes have decreased sialic acid content and increased resistance to malarial infection (see 611162). GYPA and GYPB are not essential for red-cell development or survival, and GYPA- and GYPB-null phenotypes are not associated with anemia or altered red-cell function (review by Cooling, 2015). [from OMIM]

Ss blood group antigens reside on the red-cell glycoprotein GYPB. The S and s antigens result from a polymorphism at amino acid 29 of GYPB, where S has met29 and s has thr29. The U antigen refers to a short extracellular sequence in GYPB located near the membrane. GYPB, glycophorin A (GYPA; 617922), and glycophorin E (GYPE; 138590) are closely linked on chromosome 4q31. Antigens of the MN blood group (111300) reside on GYPA. The M and N antigens differ at amino acids 1 and 5 of GYPA, where M is ser-ser-thr-thr-gly, and N is leu-ser-thr-thr-glu. The N terminus of GYPB is essentially identical to that of GYPA except that it always expresses the N antigen, denoted 'N' or N-prime. Recombination and gene conversion between GYPA, GYPB, and GYPE lead to hybrid glycophorin molecules and generation of low-incidence antigens. Thus, the MN and Ss blood groups are together referred to as the MNSs blood group system (see 111300). Recombination results in 3 glycophorin-null phenotypes: En(a-) cells lack GYPA due to recombination between GYPA and GYPB; GYPB-negative (S-s-U-) cells lack GYPB due to recombination in GYPB; and M(k) cells (M-N-S-s-U-) lack both GYPA and GYPB due to recombination between GYPA and GYPE. Individuals with glycophorin-null phenotypes have decreased sialic acid content and increased resistance to malarial infection (see 611162). GYPA and GYPB are not essential for red-cell development or survival, and GYPA- and GYPB-null phenotypes are not associated with anemia or altered red-cell function (review by Cooling, 2015). [from OMIM]

Myelodysplastic syndrome (MDS) is a heterogeneous group of clonal hematologic stem cell disorders characterized by ineffective hematopoiesis resulting in low blood counts, most commonly anemia, and a risk of progression to acute myeloid leukemia (AML; 601626). Blood smears and bone marrow biopsies show dysplastic changes in myeloid cells, with abnormal proliferation and differentiation of 1 or more lineages (erythroid, myeloid, megakaryocytic). MDS can be subdivided into several categories based on morphologic characteristics, such as low-grade refractory anemia (RA) or high-grade refractory anemia with excess blasts (RAEB). Bone marrow biopsies of some patients show ringed sideroblasts (RARS), which reflects abnormal iron staining in mitochondria surrounding the nucleus of erythrocyte progenitors (summary by Delhommeau et al., 2009 and Papaemmanuil et al., 2011). [from OMIM]