The MNS Blood Group Antigens, Vr (MNS12) and Mt^a (MNS14), Each Arise from an Amino Acid Substitution on Glycophorin A

Abstract

Background and Objectives: The antigens, Vr (MNS12) and Mt^a (MNS14), are low–incidence antigens of the MNS blood group system. The Vr antigen has been found only on the red blood cells (RBCs) of persons of Dutch ancestry whereas the Mt^a antigen has been found on the RBCs of persons from a wide geographic distribution. The objective of this study was to determine the molecular basis of Vr and Mt^a. Materials and Methods: Following RT–PCR amplification of total RNA isolated from one Vr+ person (G488) and one Mt(a+) person (GH), the genes encoding glycophorin A (GYPA) and glycophorin B (GYPB) were cloned and sequenced. To confirm the point mutation observed in the cDNA from G488 (Vr+), GYPA exon 3 was cloned and sequenced from the genomic DNA of G488 and a second unrelated Vr+ person (MU). A restriction fragment length polymorphism (RFLP) assay was used to analyze genomic DNA from 11 Mt(a+) persons (10 unrelated) following PCR amplification of GYPA exon 3. Results: The coding sequence of GYPB was normal in both G488 (Vr+) and GH (Mt(a+)). Sequencing data from GYPA clones derived from G488 showed to full length GYPA sequences: A normal GYPA M allele and a GYPA M allele with a point mutation 197C→A. Sequencing of GYPA exon 3 from G488 and MU confirmed the point mutation. Sequencing data drom GYPA clones derived from GH showed two full length GYPA sequences: a normal GYPA M allele and a GYPA N allele with a point mutation 230C→T. RFLP analysis based on the point mutation showed that DNA from 11 Mt(a+) samples were heterozygous for the point mutation. Conclusion: The Vr antigen arises from a point mutation 197C→A on GYPA which is predicted to change serine at position 47 to tyrosine. This change introduces a new α–chymotrypsin cleavage site. The Mt^a antigen arises from a point mutation 230C→T which is predicted to change threonine at position 58 to isoleucine.

First Example of Hemolytic Disease of the Newborn Caused by Anti-Or and Confirmation of the Molecular Basis of Or

“…Genomic DNA was isolated from whole blood from the baby’s father and cloned and sequenced as described [7]. …”

MN typing discrepancies based on GYPA‐B‐A hybrid

“…Besides the M and N determinants of GPA and S and s phenotypes of GPB, a total of 46 distinct antigens were described so far, most of them with low incidence [3]. Variant MNS phenotypes are a consequence of single amino acid substitutions, gene deletion and gene conversions between parts of GYPA and GYPB or GYPA and GYPE [3,4,[7][8][9][10]. GP hybrids may be detected by altered expression of M, N, S or s antigens, the absence of a high-prevalence antigen or the occurrence of a lowprevalence determinant.…”