MNSs Flashcards
MNSs
Inherited as _______alleles, meaning both inherited alleles are expressed in the individual’s red blood cells (RBCs).
co-dominant
MNSs
Located on Chromosome___
4
MNSs
The system consists of two genes:
• → Responsible for the M and N antigens.
• → Responsible for the S, s, and U antigens
GYPA (Glycophorin A)
GYPB (Glycophorin B)
Key Antigens in the MNSs System
• (4) are the four main antigens.
•___ antigen is only expressed when S and/or s are present.
M, N, S, and s
U
• Fully developed at birth (important for Hemolytic Disease of the Fetus and Newborn, HDFN).
• Located on RBCs and tissues but NOT in secretions.
MNSs
• M & N differ in only two amino acids at positions ____ and____on the Glycophorin A (GPA) protein.
1 and 5
S & s differ in one amino acid at position____ on the Glycophorin B (GPB) protein.
29
____antigen is expressed only if S and/or s are present.
U
• All MNSs antigens exhibit dosage, meaning their reactivity is stronger in______ individuals and weaker in_____ individuals.
homozygous
heterozygous
• Homozygous individuals (M+N− or M−N+) →_______
• Heterozygous individuals (M+N+) →_______
Stronger reaction
Weaker reaction
Antigens are destroyed by______, meaning that proteolytic enzymes like papain, ficin, trypsin, and bromelin will degrade the MNSs antigens, affecting serologic testing.
enzymes
• U antigen is always present if_______ are inherited.
S and/or s
• U-negative individuals are extremely rare (found only in ______ populations).
Black
• Approximately____% of S−s− individuals lack the U antigen.
85%
Antigen Frequency
U+
Black
White
High-incidence antigen (99%)
99.9%
Phenotype Frequency
Black
White
S-s-U (Very Rare)
<1
Extremely rare
are typically IgM, react at cold temperatures (below 37°C), and are usually clinically insignificant unless reacting at 37°C.
M and N antibodies
are mostly IgG, react at 37°C, and can cause Hemolytic Transfusion Reactions (HTRs) and Hemolytic Disease of the Fetus and Newborn (HDFN).
S and s antibodies
_____individuals can develop anti-U, which can cause severe and fatal transfusion reactions and HDFN.
U-negative
Can a Person Have No Expression of MNSS Antigens?
Yes, a person can completely lack MNSS antigens due to certain null phenotypes, which result from deletions or mutations in the (2) genes
GYPA (Glycophorin A) and
GYPB (Glycophorin B) genes
Deletion of the GYPB gene, which codes for S, s, and U
U-phenotype
Deletion of the GYPA gene, which codes for M and N
En (a-) phenotype
Deletion of both GYPA and GYPB genes
M^k phenotype (Silent Gene/Null Gene)*
• This occurs when the GYPB gene is deleted, meaning there is no production of S or s antigens.
U− Phenotype (S−S−U−)
• This results from the deletion of the GYPA gene, which encodes M and N antigens.
En(a−) Phenotype
reacts with multiple parts of the Glycophorin A protein.
Anti-Ena
• This occurs when both GYPA and GYPB genes are deleted.
• All MNSS antigens are absent.
M^k Phenotype (Silent Gene/Null Gene)*
_____ is usually IgG (50-80%) but can be IgM.
Anti-M
• Naturally occurring antibodies (do not require prior sensitization).
• Found in individuals who lack M or N antigen.
• Can be either IgG or IgM.
• Do not bind complement, meaning they are usually not clinically significant.
Anti-M and Anti-N
_____ is clinically insignificant because it cannot cross the placenta.
_____can rarely cause mild hemolytic disease of the fetus and newborn (HDFN).
• IgM Anti-M
• IgG Anti-M
• Clinically significant because they are primarily IgG.
• IgG antibodies can bind complement, leading to cell lysis.
• Cause severe hemolytic transfusion reactions (HTR) and HDFN.
Anti-S, Anti-s, and Anti-U
• Usually IgG.
• Can cause HTR and HDFN.
• If optimal reactivity occurs at 10-22°C, AHG testing should be performed without incubating at 37°C.
Anti-S and Anti-s
• U- individuals must be registered in rare donor registries.
• Causes severe and fatal HTR and HDFN.
Anti U
• Found in S−s− (U−) individuals.
• Requires U− blood for transfusion.
• Extremely rare and mostly found in the Black population (<1%).
Anti-U
• Highly clinically significant.
• Reacts strongly with S+ or s+ red cells.
Anti-U
