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3 HAEM > HAEMOGLOBINOPATHIES > Flashcards

HAEMOGLOBINOPATHIES Flashcards

1
Q

what is the structure of HbA

A

2 alpha globin like chains
2 beta globin like chains
one haem

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2
Q

what is the structure of HbA2

A

2 alpha globin

2 delta globin

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3
Q

what its he structure of HbF

A

2 alpha globin

2 gamma globin

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4
Q

which type of Hb is present in the greatest quantities

A

HbA

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5
Q

how many alpha globin producing genes are there present in each cell

A

4

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6
Q

on which chromosome are the alpha globin genes located

A

chromosome 16

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7
Q

how many beta globin producing genes are there in each cell

A

2

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8
Q

on which chromosome are the beta globin genes located

A

chromosome 11

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9
Q

how are the different genes for Hb production arranged on the chromosome

A

they are arranged in order of expression

eg embryonic Hb, then fetal, then adult

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10
Q

what are the two main groups of haemoglobinopathies

A

thalassaemias

structural Hb variants

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11
Q

how do thalassaemias affect Hb production

A

decreased rate of normal globin chain synthesis

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12
Q

how do structural Hb variants affect Hb production

A

normal production of structurally abnormal globin chains

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13
Q

what type of anaemia does Thalassaemia cause

A

microcytic hypochromic anaemia due to inadequate Hb production

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14
Q

what are the complications of unbalanced accumulation of globin chains in Thalassaemia

A

ineffective erythropoiesis and haemolysis

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15
Q

where are thalassaemias most commonly found geographically

A

Mediterranean coast, Southern Asia, North African coast, subsaharan Africa

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16
Q

which types of Hb are affected by alpha thal

A

HbA
HbA2
HbF

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17
Q

what is the normal genotype of individuals unaffected by alpha thatl

A

(aa/aa)

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18
Q

how do mutations affect the genotype of patients with alpha thal

A

a+ (-a) (deletion of one alpha gene)

a0 (–) (deletion of both alpha genes)

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19
Q

what are the potential genotypes in alpha thal trait

A

one or two genes missing (out of four)
a+/a (-a/aa)
a0/a (–/aa)
a+/a+ (-a/-a)

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20
Q

what is HbH disease (and genotype)

A

only one alpha gene is left

a0/a+ (–/-a)

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21
Q

what is Hb Parts hydrops fetalis (and genotype)

A

no functional alpha genes

a0/a0 (–/–)

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22
Q

what is the presentation of alpha tha trait

A

normal asymptomatic

microcytic, hypo chromic red cells with mild anaemia

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23
Q

how can you distinguish alpha thal trait from iron deficiency anaemia

A

ferritin will be normal

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24
Q

how does HbH disease present

A

anaemia with very low MCV and MCH

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25
Q

what are HbH molecules and why are they formed

A

tetramers of excess beta chains which are unable to carry oxygen
produced in severe alpha that due to lack of alpha chains

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26
Q

what are clinical features of HbH disease

A

moderate anaemia to transfusion dependent
splenomegaly due to extramdeullary haematopoiesis
jaundice

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27
Q

in which populations is HbH disease most prevalent

A

SE asia
Middle East
mediterranean

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28
Q

what is the management of severe HbH disease

A

splenectomy +/- transfusion

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29
Q

what is the severest form of alpha thal

A

Hb barts hydrops fetalis

30
Q

which types of Hb make up the majority of Hb at birth in hydrops fetalis

A

Hb barts (gamma tetramer) and HbH (beta tetramer)

31
Q

why is there increased production of Hb parts and HbH in hydrops fetalis

A

there are no alpha genes inherited from either parent so alpha globin can’t be made

32
Q

clinical features of hydrops fetalis

A 
severe anaemia 
cardiac failure 
growth retardation 
severe hepatosplenomegaly 
skeletal and cardiovascular abnormalities
33
Q

which types of Hb are affected in beta thal

A

HbA (a2b2)

34
Q

what is the genotype of beta thal trait

A

B+/B or B0/B

35
Q

what are the clinical features of beta thal trait

A

asymptomatic
no/mild anaemia
low MCV/MCH
raised HbA2

36
Q

what is the genotype of beta thal intermedia

A

B+/B+ or B0/B+

37
Q

what are the clinical features of beta thal intermedia

A

moderate severity anaemia

38
Q

what is the genotype of beta thal major

A

B0/B0

39
Q

at what age does beta thal major present and why

A

presents at 6-24 months

HbF (a2g2) levels fall and the circulation begins to depend on HbA (a2b2) which can’t be produced

40
Q

how does beta thal major present

A 
pallor 
failure to thrive 
hepatosplenomegaly 
skeletal changes 
organ damage
41
Q

what will Hb analysis show in beta thal major

A

mainly HbF

minimal HbA

42
Q

what are complications of extramedullary haemotopiesis in beta thal major

A

frontal bossing

cord compression

43
Q

how is beta thal major managed

A

regular transfusions to maintain Hb at 95-105 g/L

44
Q

what is the purpose of regular transfusions in beta thal major, beyond correcting the Hb concentration

A

suppresses ineffective erythropoiesis

inhibits over-absorption of iron

45
Q

what are consequences of iron overload

A 
impaired growth and pubertal development 
diabetes 
osteoporosis 
cardiomypoathy 
arrhythmias 
cirrhosis 
hepatocellular cancer
46
Q

how is iron overload managed in beta thal major

A

iron chelating drugs

47
Q

how is iron bound to chelators excreted

A

in urine or stool

48
Q

what are complications of transfusions in beta thal major

A

viral infection (HIV, Hep)
alloantibodies
transfusion reactions

49
Q

why is there an increased risk of sepsis in an iron overloaded patient

A

bacteria like iron

50
Q

what type of mutations leads to production of Bs in sickling disorders

A

point mutation in codon 6 of the beta globin genes that substitutes glutamine to valine

51
Q

how is the structure of Hb altered in sickling disorders

A

HbA (a2B2) becomes HbS (a2Bs2)

52
Q

how is HbS less effective than HbA

A

it polymerises if exposed to low oxygen levels for a prolonged period of time
this distorts the red cell and damages the membrane

53
Q

what is the genotype in sickle cell trait

A

one normal gene, one abnormal

B/Bs

54
Q

what are the clinical features of sickle cell trait (HbAS)

A

few features are HbS levels are too low to polymerise

may sickle in severe hypoxia eg high altitude, under anaesthesia

55
Q

what features are present on a blood film in a patient with HbAS (sickle cell trait)

A

normal blood film

56
Q

what is the genotype in sickle cell anaemia (HbSS)

A

two abnormal genes (Bs/Bs)

57
Q

what types of Hb are present in HbSS

A

> 80% HbS

no HbA

58
Q

clinical features of HbSS

A

episodes of tissue infarction due to vascular occlusion (sickle crisis)
chronic haemolysis
sequestration of sickled RBCs in liver and spleen
hyposlenism due to repeated infarcts

59
Q

where are common sites of sickle crisis

A

digits
bone marrow
lung spleen
CNS

60
Q

what is sickle cell disease cf sickle cell anaemia

A

presence of HbS mutation in the presence of another beta chain mutation
eg HbS/beta thal

61
Q

what are triggers for sickle crisis

A 
hypoxia 
dehydration 
infection 
cold exposure 
stress/fatigue
62
Q

how are painful sickle crises treated

A 
opiate analgesia 
hydration 
rest 
oxygen 
antibiotics if evidence of infection
red cell exchange transfusion in severe crisis (eg chest crisis or stroke)
63
Q

what is red cell exchange transfusion and how does it improve symptoms in HbSS

A

combination of venesection followed by transfusion

decreases concentration of HbS and improves tissue perfusion

64
Q

what are long term effects of sickle cell anaemia

A

impaired growth

risk of end organ damage

65
Q

what are examples of end organ damage in sickle cell anaemia

A 
pulmonary HTN
renal disease 
avascular necrosis 
leg ulcers 
stroke
66
Q

what complication does hyposplenism cause and how is it managed

A

increased risk of infection

  • prophylactic penicillin
  • vaccination against pneumococcus, meningococcus, haemophilia
67
Q

long term management of sickle cell anaemia

A

folic acid supplementation (increased RBC turnover)
hydroxycarbamide (induces HbF production)
regular transfusion to prevent stroke

68
Q

how to investigate Hbopathy

A

FBC (Hb, red cell indices)
blood film
ethnic origin
high performance liquid chromatography or gel electrophoresis to quantify Hb present

69
Q

presence of HbS is indicative of what type go Hbopathy

A

sickling disease

70
Q

raised HbA2 is diagnostic of…

A

beta thal trait

3 HAEM (20 decks)

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