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Haemoglobinopathies Flashcards

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1
Q

What is the most common monogenic disorder worldwide

A

haemoglobinopathies

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2
Q

what is the structure of Hb

A

tetramer - 4 globin chains
2 alpha 2 beta
1 haem attached to each globin chain

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3
Q

what is the function of globin in Hb

A

to keep haem soluble and protect it from oxidation

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4
Q

what are the main types of Hb and what are they made up of

A 
HbA = 2a and 2B
HbA2 = 2a and 2delta 
HbF = 2a and 2gamma
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5
Q

on which chromosome are alpha like genes found

A

16

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6
Q

how many alpha genes are found on each chromosome

A

2 per chromsome

4 per cell

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7
Q

on which chromosome are beta like genes found

A

11

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8
Q

how many beta genes are found on each chromosome

A

1 per chromosome

2 per cell

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9
Q

expression of globin gene changes throughout embryonic life and childhood, true or false

A

true

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10
Q

which type of globin is found in all types of Hb

A

alpha chain globins

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11
Q

levels of which globins increase during the foetal period

A

alpha and gamma

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12
Q

what happens to globin levels at birth

A

gamma levels decrease

beta levels increase

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13
Q

when are adult levels of Hb reached after birth

A

6-12 months old

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14
Q

define haemoglobinopathy

A

hereditary condition with impaired globin synthesis

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15
Q

how are haemoglobinopathies inherited usually

A

AR

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16
Q

how are haemoglobinopathies classified

A

reduced globin synthesis - thalassaemia

abnormal globin struture - sickled

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17
Q

define thalassaemia

A

reduced globin chain synthesis resulting in decreased Hb synthesis

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18
Q

what is the abnormality in alpha thalassaemia

A

defect in alpha chain - not enough alpha globulin

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19
Q

what is the abnormality in beta thalassaemia

A

defect in beta chain - not enough beta globulin

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20
Q

what are the consequences of thalassaemia

A

microcytic hypochromic anaemia
unbalanced accumulation of globin chains
haemolysis
ineffective erythropoeisis

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21
Q

what is ineffective erythropoeisis

A

precurosor cells die in bone marrow because they are that bad

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22
Q

what types of Hb does aloha thalassaemia affect

A

all kinds because all Hb types contain alpha chains

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23
Q

what is the genotype of an unaffected person in alpha thalassaemia

A

presence of all 4 normal alpha genes

aa/aa

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24
Q

what can alpha thalassaemia do to levels of alpha globin

A

reduced or absent levels

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25
how is alpha thalassaemia classified
according to number of affected alpha genes
26
describe alpha thalassaemia trait genotype
loss of 1 or 2 alpha genes
27
describe HbH disease genotype
only 1 alpha gene is left out of 4 | --/-a
28
describe Hb Barts Hydrops Fetalis genotype
no functional alpha genes at all | --/--
29
describe the features of alpha thalassaemia trait
asymptomatic carrier with no treatment required | microcytic hypochromic cells with mild anaemia
30
are ferritin levels high or low in alpha thalassaemia trait
normal - excludes iron deficiency
31
describe the feature of HbH disease
more severe form of alpha thalassaemia | anaemia with low MCV and MCH
32
what happens to excess beta chains in HbH disease
they form tetramers B4 called HbH
33
clinical features of HbH disease
jaundice splenomegaly may need transfusion
34
describe features of Hb Barts Hydrops Fetalis
most severe form of alpha thalassaemia | no alpha chains results in Hb Barts (gamma4) and HbH (B4)
35
clinical features of Hb Barts
``` profound anaemia incompatible with life cardiac failure growth retardation severe hepatosplenomegaly ```
36
what is the cause of beta thalassaemia
point mutation resulting in reduced or absent B globulin
37
which type of Hb is affected in beta thalassaemia
HbA as it is the only one containing beta chains
38
how is beta thalassaemia classified
according to clinical severity
39
what are the subtypes of beta thalassaemia
beta thalassaemia trait beta thalassaemia intermidia beta thalassaemi major
40
what is the genotype of beta thalassaemia trait
B+/B or Bo/B
41
what are the features of beta thalassaemia trait
asymptomatic no/mild anaemia low MCV/MCH raised HbA2
42
what is diagnostic of beta thalassaemia trait
raised HbA2 levels
43
what is the genotype of beta thalassaemia intermedia
B+/B+ or Bo/B+
44
what are the features of beta thalassaemia intermedia
moderate severity | requires occasional transfusion
45
what is the genotype of beta thalassaemia major
Bo/Bo
46
what are the feature of beta thalassaemia major
no beta chain synthesis cannot make HbA severe lifelong transfusion dependency
47
when does beta thalassaemia major present
6-24 months old | as HbF goes down and body tries to make HbA
48
consequences of beta thalassaemia major
``` extramedullary haemoatopoeisis hepatosplenomegaly skeletal defects organ damage spinal cord compression ```
49
what is extramedullary haemoatopoeisis
RBC production outwith the bone marrow ie in liver and spleen leading to hepatosplenomegaly
50
management of beta thalassaemia major
regular tranfusion programme maintain Hb at 95-105g/L bone marrow transplant curative
51
what is a complication of lifelong blood transfusions
iron overload
52
what are complications of iron overload
endocrine: DM and pancreas, osteoporosis, impairs growth cardiac: cardiomyopathy, arrhythmias liver: cirrhosis, HCC sepsis: bacteria love iron
53
management of iron overload in beta thalassaemia major needing lifelong transfusion
iron chelating drugs eg desferrioxamine
54
what is the cause of sickling disorders
point mutation in codon 6 of beta globin chain in chromosome 11 substitutes glutamine for valine which produces Bs
55
what is the structure of HbS
2 alpha and 2 Bs
56
why is HbS bad
HbS polymerises if exposed to low oxygen levels for a long time which distorts the shape of the RBC and membrane
57
what is the genotype of sickle cell trait
1 normal and 1 abnormal beta chain | B/Bs
58
features of sickle cell trait
asymptomatic carrier state | few clinical features as HbS levels are too low to polymerise
59
can cells sickle in sickle cell trait
may sickle in severe hypoxia eg high altitude or anaesthesia
60
what is seen on the blood film of sickle cell trait
HbA | HbS <50%
61
what is the genotype of sickle cell anaemia HbSS
Bs/Bs
62
what proportion of HbS is present in HbSS
>80%
63
why are sickle cells dangerous
disrupt microvasculature and cause vaso-occlusion resulting in tissue ischaemia and pain
64
why do you get hyposplenism in HbSS
due to multiple splenic infarcts
65
what is a sickle crisis
episodes of tissue infarction dur to vascular occlusion | severe pain depending on site affected
66
list precipitants of a sickle crisis
``` hypoxia dehydration stress cold infection or none ```
67
what is the acute management of a sickle crisis
``` opiate analgesia rehydration oxygen rest antibiotics if there are signs of infection ``` red cell exchange transfusion
68
what is involved in red cell exchange transfusion
venesection --> transfusion --> venesection --> transfusion ...
69
what is the long term management of HbSS
hyposplenism: prophylactic penicillin and vaccinations folic acid hydroxycarbamide regular transfusion in some cases to prevent stroke
70
what is the role of hydroxycarbamide
induces HbF production to reduce disease severity
71
what investigations are done to diagnose haemoglobinopathies
``` FBC iron studies blood film - microcytic hypochromic cells ethnicity Hb measures: HPLC and electrophoresis ```
72
what is HPLC
high performance liquid chromatography

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