MNSs

Question 1

MNSs

Inherited as _______alleles, meaning both inherited alleles are expressed in the individual’s red blood cells (RBCs).

Answer 1

co-dominant

Question 2

MNSs

Located on Chromosome___

Answer 2

4

Question 3

MNSs

The system consists of two genes:

• → Responsible for the M and N antigens.

• → Responsible for the S, s, and U antigens

Answer 3

GYPA (Glycophorin A)

GYPB (Glycophorin B)

Question 4

Key Antigens in the MNSs System

• (4) are the four main antigens.

•___ antigen is only expressed when S and/or s are present.

Answer 4

M, N, S, and s

U

Question 5

• Fully developed at birth (important for Hemolytic Disease of the Fetus and Newborn, HDFN).

• Located on RBCs and tissues but NOT in secretions.

Answer 5

MNSs

Question 6

• M & N differ in only two amino acids at positions ____ and____on the Glycophorin A (GPA) protein.

Answer 6

1 and 5

Question 7

S & s differ in one amino acid at position____ on the Glycophorin B (GPB) protein.

Answer 7

29

Question 8

____antigen is expressed only if S and/or s are present.

Answer 8

U

Question 9

• All MNSs antigens exhibit dosage, meaning their reactivity is stronger in______ individuals and weaker in_____ individuals.

Answer 9

homozygous

heterozygous

Question 10

• Homozygous individuals (M+N− or M−N+) →_______

• Heterozygous individuals (M+N+) →_______

Answer 10

Stronger reaction

Weaker reaction

Question 11

Antigens are destroyed by______, meaning that proteolytic enzymes like papain, ficin, trypsin, and bromelin will degrade the MNSs antigens, affecting serologic testing.

Answer 11

enzymes

Question 12

• U antigen is always present if_______ are inherited.

Answer 12

S and/or s

Question 13

• U-negative individuals are extremely rare (found only in ______ populations).

Answer 13

Black

Question 14

• Approximately____% of S−s− individuals lack the U antigen.

Answer 14

85%

Question 15

Antigen Frequency

U+
Black
White

Answer 15

High-incidence antigen (99%)
99.9%

Question 16

Phenotype Frequency
Black
White

S-s-U (Very Rare)

Answer 16

<1
Extremely rare

Question 17

are typically IgM, react at cold temperatures (below 37°C), and are usually clinically insignificant unless reacting at 37°C.

Answer 17

M and N antibodies

Question 18

are mostly IgG, react at 37°C, and can cause Hemolytic Transfusion Reactions (HTRs) and Hemolytic Disease of the Fetus and Newborn (HDFN).

Answer 18

S and s antibodies

Question 19

_____individuals can develop anti-U, which can cause severe and fatal transfusion reactions and HDFN.

Answer 19

U-negative

Question 20

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

Answer 20

GYPA (Glycophorin A) and
GYPB (Glycophorin B) genes

Question 21

Deletion of the GYPB gene, which codes for S, s, and U

Answer 21

U-phenotype

Question 22

Deletion of the GYPA gene, which codes for M and N

Answer 22

En (a-) phenotype

Question 23

Deletion of both GYPA and GYPB genes

Answer 23

M^k phenotype (Silent Gene/Null Gene)*

Question 24

• This occurs when the GYPB gene is deleted, meaning there is no production of S or s antigens.

Answer 24

U− Phenotype (S−S−U−)

Question 25

• This results from the deletion of the GYPA gene, which encodes M and N antigens.

Answer 25

En(a−) Phenotype

Question 26

reacts with multiple parts of the Glycophorin A protein.

Answer 26

Anti-Ena

Question 27

• This occurs when both GYPA and GYPB genes are deleted. • All MNSS antigens are absent.

Answer 27

M^k Phenotype (Silent Gene/Null Gene)*

Question 28

_____ is usually IgG (50-80%) but can be IgM.

Answer 28

Anti-M

Question 29

• 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.

Answer 29

Anti-M and Anti-N

Question 30

_____ is clinically insignificant because it cannot cross the placenta. _____can rarely cause mild hemolytic disease of the fetus and newborn (HDFN).

Answer 30

• IgM Anti-M • IgG Anti-M

Question 31

• Clinically significant because they are primarily IgG. • IgG antibodies can bind complement, leading to cell lysis. • Cause severe hemolytic transfusion reactions (HTR) and HDFN.

Answer 31

Anti-S, Anti-s, and Anti-U

Question 32

• 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.

Answer 32

Anti-S and Anti-s

Question 33

• U- individuals must be registered in rare donor registries. • Causes severe and fatal HTR and HDFN.

Answer 33

Anti U

Question 34

• Found in S−s− (U−) individuals. • Requires U− blood for transfusion. • Extremely rare and mostly found in the Black population (<1%).

Answer 34

Anti-U

Question 35

• Highly clinically significant. • Reacts strongly with S+ or s+ red cells.

Answer 35

Anti-U