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Haematology > Haemoglobinopathies > Flashcards

Haemoglobinopathies Flashcards

1
Q

What are the functions of the globin chains in Hb?

A

keep haem soluble and protect from oxidation

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2
Q

Which chromosome are alpha globin chains found on?

A

16

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3
Q

How many alpha genes are there per chromosome?

A

2

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4
Q

Which chromosome are beta like genes found on?

A

11

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5
Q

How many beta genes per chromosome?

A

1

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6
Q

How are genes on the chromsomes coding for globin arrranged?

A

in order of expression (eg, from 5 to 3 fetal to adult)

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7
Q

By what age have adult levels of Hb been reached?

A

6-12 months of age

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8
Q

What are haemoglobinopathies?

A

hereditary conditions affecting globin chain synthesis

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9
Q

How are haemogloinopatheis generally inherited?

A

autosomal recessive

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10
Q

What are the 2 main groups of haemoglobinopathy?

A

thalassaemias; structual haemoglobin variants

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11
Q

What happens in thalassaemias?

A

decreased rate of globin chain synthesis restuling in impaired Hb production

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12
Q

What are the two groups of thalassaemia?

A

alpha and beta

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13
Q

What type of anaemia is seen with thalassamia?

A

microcytic hypochromic anaemia (inadequate Hb production)

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14
Q

Why is there haemolysis in thalassaemia?

A

unbalanced accumulation of globin chains is toxic resulting in ineffective erythropoiesis

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15
Q

What has allowed thalassaemia to flourish?

A

malaria

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16
Q

What is a+?

A

deletion of one alpha gene from chromsome 16

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17
Q

Waht is a0?

A

both alpha genes have been lost from chromsome 16

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18
Q

what types of Hb are affected in alpha thalassaemia?

A

all forms- HbA; HbA2 and HbF as all contain alpha chains

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19
Q

What is the alpha thal trait?

A

one or two genes missing out of 4

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20
Q

What is HbH disease?

A

only one alpha gene left (a0/a+)

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21
Q

What is Hb Barts hydrops fetalis?

A

no functional a genes

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22
Q

What is seen with alpha thal trait?

A

asymptomatic and no rx needed- mild anaemia

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23
Q

What is seen with HbH disease?

A

anaemia with very low MCV and MCH

24
Q

What is HbH?

A

excess beta chains forming a tetramer called HbH- cant carry oxygen

25
Q

What are the clinical features of HbH?

A

mod anaemia to transfusion dependent; splenomegaly; jaundice

26
Q

Where is HbH commonest globally?

A

SE Asia; middle east and mediterranean

27
Q

What is the majority of Hb seen at birth with Hb Barts hydrops fetalis syndrome?

A

Hb Barts (gamma tetramer) and HbH

28
Q

What are the clinical features of Hb Barts hydrops fetalis syndrome?

A

almost all die in utero- severe anaemia; cardiac failure; growth retardation; severe hepatosplenomegaly; SK and CVS abnormalities

29
Q

What is the difference between the mutations causing beta and alpha thalassaemias?

A

alpha is caused by deletions whereas beta are usually point mutations

30
Q

What type of Hb is affected in beta thalassaemia?

A

HbA

31
Q

What is seen with beta thalassaemia trait?

A

(b+/b or b0/b) asymptomatic- low MCV/MCH; raised HbA2

32
Q

What is beta thalassaemia intermedia?

A

b+/b+ or b0/b+

moderate requiring occasional tranfusion

33
Q

What is beta thalassaemia major?

A

b0/b0 - svere, lifelong transfusion dependency

34
Q

When does beta thalassaemia major present?

A

6-24 months

35
Q

What does extramedullary haematompoisis cause?

A

hepatosplenomegaly; thickening of skull; organ damage; cord compression

36
Q

Why is regular transfusion required in beta thal major?

A

suppress ineffective erythropoiesis and inhibit over-absoprtion of iron

37
Q

Waht is the main cause of mrotality with treated beta thal major?

A

iron overload from transufion

38
Q

What are the consequences of iron overload?

A

impaired grwoth and puberty; DM; OP; cardiomyopathy; arrhythmias; cirrhosis; hepatocellular cancer; increased risk of sepsis

39
Q

How is iron overload managed?

A

iron chelation- desferrioxamine

40
Q

what is the mutation in sickling disorders?

A

point mutation in the beta globin gene substituting glutamine to valine producing bS

41
Q

What is the problem with HbS?

A

polymerises if exposed to low oxygen for a prolonged period which distorts the red cell damaging the RBC membraen

42
Q

Waht is the sickle trait?

A

one normal, one abnormal beta geen

43
Q

Why is there few clinical features of sickle trait?

A

HbS level too low to polymerise but may in severe hypoxia eg high altitude or under anaesthesia

44
Q

What is the inheritance of sickle cell anaemia?

A

autosomal recessive

45
Q

What is a sickle crisis?

A

episode of tissue infarction due to vascular occlusion

46
Q

Why do patients with sickle cell anaemia have chronic haemolysis?

A

shortened RBC lifespan

47
Q

Why do patients with HbSS have hyposplenism?

A

repeated splenic infarcts

48
Q

What is sickle cell disease?

A

compound heterozygosity for HbS and another beta chain mutation

49
Q

What is HbSC disease?

A

milder but increased risk of thrombosis

50
Q

What are the precipitatns of sickle crisis?

A

hypoxia; dehydration; infection; cold exposure; stress/fatigue

51
Q

What is the treatment of sickle crisis?

A

opiate; hydration; rest; oxygen; abx if infection; red cell exchange transfusion if severe

52
Q

What are the longterm effects of sickle cell anaemia?

A

impaired grwoth; pulmonary hypertension; renal disease; avascular necrosis; leg ulcers; stroke

53
Q

What is the long term mx of sickle cell anaemia?

A

hyposplenism so need to reduce infection risk; folic acid supplementation; hydroxycarbamide

54
Q

what is the function of hydroxycarbamide?

A

reduce severity of disease by inducing HbF production

55
Q

How can you quantify haemoglobins present?

A

high performance liquid chromatography or gel electrophoresis

56
Q

What does raised HbA2 on HPLC suggest?

A

beta thal trait

57
Q

What is the problem with HPLC in alpha thal trait?

A

is normal so DNA testing needed

Haematology (29 decks)

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