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Flashcards in Hemoglobinopathies Deck (60):
1

Hemoglobin alpha cluster

We have four copies of alpha both of which are preceded by fetal zeta (5')

Chromosome 16

2

Hemoglobin beta cluster

epsilon
Ggamma
Agamma
delta
beta

3

How many copies of beta?

two total (one on each homolog 11)

4

Embryonic hemoglobin?

zeta2epsilon2
alpha2epsilon2
zeta2gamma2

5

fetal hemoglobin?

alpha2gamma2

6

adult hemoglobin?

95% alpha2beta2
3.5% alpha2delta2

7

Globin switching during development
alpha cluster?

5th week switch from zeta to alpha

8

Globin switching during development
beta cluster?

Switch from epsilon to gamma in-utero
Switch from gamma to beta at birth

9

Locus control region

10 kb upstream - Regulates globin transcription of beta cluster
Both timing and level

10

What happens if we delete LCR of beta cluster?

Hispanic epsilongammadeltabeta thalassemia --> have much lower expression of beta isoforms

11

Sickle Cell Disease

Single gene disease
Single point mutation at codon 6 in exon 1 of beta globin

12

Sickle cell disease
Amino acid substitution

Glutamine for valine

13

Hemaglobin C disease

Same codon affected as sickle cell disease but different mutation (effects first position of codon and sickle effects second)- results in glutamine to lysine transition

14

Sickle cell and hemoglobin C inheritance pattern?

Autosomal recessive

15

Clinical manifestiation of hemoglobin C?

decrease solubility of hemoglobin - tends to lyse red blood cells

16

Diagnosing sickle cell: DNA diagnosis

Mst II restriction enzyme normally cleaves 5'cctnagg-3' but the sickle cell mutation changes the a to t and thus it is not recognized by the restriction enzyme - leading to a single heavier band in sickle

17

How can we distinguish sickle cell from Hemoglobin C with DNA diagnosis?

Hemoglobin C mutation does not effect restriction site of MstII, so Mst II will still cleave the DNA and yield two bands

18

Weight of Hb bands?

1.15
0.20
1.35 if uncleaved

19

Can we diagnosis hemoglobin diseases with electrophoresis

Yes, because HbS (sickle) has been changed from a negative charge (glutamate) to valine - so we would expect that it would not travel as far to the anode

HbC the glutamate has beeen changed to lysine (a positive charge) so we would expect it to travel the least distance

In order of migration, from farthest to shortest distance traveled we would expect
HbA
HbS
HbC

20

Hemoglobin oxygenate form

The heme is planar when oxygen is bound - via Fe - which is also bound to His

21

Hemoglobin deoxygenated form

The heme is domed (nonplanar/tense) when O2 is not bound

22

Hemoglobin Kempsey

High oxygen affinity
Less O2 to tissues
Overproduction of blood cells leads to polycythemia

23

Hemoglobin Kansas

Low oxygen affinity
Lower O2 level in RBC
Cyanosis

24

Thalassemia are due to?

Globin level imbalance

25

Alpha thalassemias are usually caused by ____ where as beta thalassemias are usually caused by _____

Alpha are usually caused by deletions

Beta are usually caused by point mutations

26

Alpha thalassemia
alpha
beta
gamma

low or zero alpha
beta and gamma in excess and preicipitates

27

alpha thalassemia onset?

both fetal and postnatal

28

Alpha thalassemia usually caused by?

deletions in alpha globin genes

29

Beta thalassemia
alpha
beta

low or zero beta globin
alpha globin in excess and precipitates

30

Beta thalassemia onset?

Postnatal only

31

What usually causes beta thalassemia?

Point mutations in the beta globin gene

32

What less commonly causes beta thalassemias?

Deletions in the LCR or the Beta gene cluster

33

If you have alpha thalassemia what do you have too much of, relatively speaking?

You have a lot more beta in adults and beta tends to form homotetramers
You can also form gamma tetramers

34

If you have beta thalassemia, what do you have too much of, relatively speaking?

You have a lot more alpha, which form alpha tetramers

35

What happens when you have homotetramers in alpha or beta thalassemia?

Homotetramers do not carry oxygen well and tend to precipitate causing hemolysis

36

Three primary consequences of thalassemia (globin level imbalance)

Hemolysis
Microcytosis
Hypochromia

37

Microcytosis

Smaller RBCs because total protein is less

38

Hypochromia

poor oxygen binding gives rise to paler color of RBC

39

Alpha thalassemia Globin Level Phenotype
alpha alpha / apha apha -
alpha alpha / alpha ____
alpha alpha / ____ ____
alpha____/ alpha_____
alpha____ /____ ______
___________________

Globin level Symptoms
100% normal
75% silent
50% alpha thalassemia 1 trait
50% alpha thalassemia 2 trait
25% HbH
0% fetal death

alpha thalassemia trait - mild anemia
HbH4 (B4) severe anemia
gamma 4 - fetal death = hydrops fetalis - not sufficient to carry infant to term

40

When do alpha thalassemia start exerting effect?

early fetal development through adulthood, because...
alpha is turned on in fetal development (5wk) and stays on throughout life - so if you have less alpha expression you effect fetus and adult

41

Alpha-thalassemia - high risk groups

alpha-thal-1 allele (- -) Southeast Asia

alpha thal-2 allel (alpha -) Africa/Meditteranean/Asia

42

Dangers of alpha-thal-1

In alpha-thal-1 both copies of alpha are deleted on the same chromosome
Thus, if two carriers get together and have a baby - and their fetus happened to receive both (- -) alleles --> hydrops fetalis (- - / - -) (gamma4)

43

What would happen in an alpha-thal-1- allele (- -) and single deletion (alpha - ) came from a mating?
Which population is at increased risk?

HbH disease
(alpha - ) (- - ) (B4)

Southeast Asia

44

Even though both alpha thalassemia 1 and alpha thalassemia 2 have the same level of alpha expression (50%), why is alpha thalassemia 1 more worrisome?

Because the deletions are on the same chromosome

In alpha thalassemia 2, the deletions are on opposite chromosomes, so there is no worry that there could be hydrops fatalis

45

What is hemogoblin H?

When you have HbH (beta4)

46

When do beta thalassemia start to exert their effect?

after birth - because beta globin genes not turned on until after birth

47

How long does it take for beta thalassemias to show up

It takes a few months after birth because RBC turnover is 120 days, so you need around that much time to turnover the fetal gamma to beta

48

Thalassemia major

severe enough you need treatment

49

Thalassemia minor

mild symptoms or no symptoms

50

Beta-o heterozygote -->

50% beta
Beta thalassemia minor

51

Beta+ heterozgote -->

>50% because you mutated allele makes some
Beta thalassemia minor

52

Beta-o homozygote -->

Beta thalassemia major

53

Beta+ / Beta-o

Beta thalassemia major

54

Beta thalassemia causing mutations can result from

Basically anything that can go wrong has gone wrong

Transcription
splicing
cap site
rna cleavage
frameshift
nonsense
unstable
deletion

upstream
downstream
intron
exon

55

Complex beta thalassemias

Caused by larger chunk of genes deleted (beta cluster combo) or LCR

56

LCR deletion -->

Hispanic thalassemia

57

Hereditary persistance of fetal hemoglobin expression (HPFH)

Doesnt usually take out coding sequence in beta cluster but take out sequence further downstream that causes HPFH

58

HPFH: mechanism (2) and implication

1. large deletion downstream may bring downstream enahncer closer to gamma locus that will keep expression elevated after birth

2. point mutation in gamma promoter where suppressor would bind may prevent suppression

can manipulate to jack up expression gamma to help treat (sub) for beta thalassemia

59

Inhibition of gamma repression

BCL11A is required to repress gamma - we could potentially target BCL11A via miRNA inhibition gene silencing

60

Partial trisomy 13 and fetal hemoglobin

miRNA15a and 16-1 are on chromosome 13, people with partial trisomy 13 have fetal hemoglobin because these miRNA inhibit an inhibitor of gamma - leaving gamma active.