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Haematology > Thalassaemia > Flashcards

Thalassaemia Flashcards

1
Q

What are the different forms of haemoglobin?

A

HbA (two alpha chains, two beta)
HbA2 (two alpha and two delta0
HbF (two alpha and two gama)

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2
Q

In adults what type is the majority of haemoglobin

A

HbA (97 percent)
HbA2 (2.5 percent)
HbF (0.5 percent)

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3
Q

What chromosome are the genes for alpha like globins

A

16

two alpha chain genes per chromosome - 4 per cell

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4
Q

What chromosome is the beta like genes on

A

11

one beta gene per chromosome - 2 per cell

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5
Q

how does the expression of globin chains change during embryotic life and child hood

A

In the fetus and early life the globin types are usually alpha and gamma
gamma decreases and is taken over by beta so that adult haemoglobin is made up mostly of alpha and beta globin

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6
Q

What are haemoglobinopathies and what are the two main groups

A

Hereditaty conditions affecting globin chain synthesis

Two main types - thalassaemias and structural haemoglobin varients

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7
Q

What are thalassaemias

A

A hereditary disorder of globin chain synthesis resulting in decreases rate of globin chain production and subsequently impaired haemoglobin production.

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8
Q

What are structural haemoglobinopathies

A

Normal production of structurally abnormal haemoglobin eg HbS

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9
Q

What type of anaemia occurs in thalassaemias and why

A

Microcytic hypochromic anaemia due to inadequate Hb production

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10
Q

What are the two variants of thalassaemias

A

Alpha or beta - depending on whether the alpha or beta globin chain is affected

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11
Q

Why is thalassaemia more common ins certain parts of the world

A

selective pressure in malaria endemic areas has allowed these mutation to thrive as they provide some protection from malaria
Therefore more common in Africa and south asia

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12
Q

How are reduced and absent alpha globin chain synthesis denoted in alpha thalassaemia

A

reduced= alpha+

absent=alpha0

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13
Q

What is the pathophysiological mechanism behind alpha thalassemia

A

A deletion of one (alpha+) or both (alpha0) genes from chromosome 16

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14
Q

What is non-deletional alpha thalassaemia

A

A point mutations causes more profound alpha chain reduction - rare

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15
Q

What are the classification of alpha thalassaemia

A

Unaffected have 4 normal genes (aa/aa)

Silent alpha thal trait = one gene affected (-a/aa)
Alpha thal train= two affected genes (–/aa) or (-a,-a)
HbH disease= usually 3 genes affected (–/-a)
Hb Barts hydrops fetalis= no functional genes (–/–)

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16
Q

What is the clinical features of alpha thalassaemia trait

A

This is due to (–/aa) or (-a/-a)
Asymptomatic, no treatment required
Microcytic, hypochromic red cells with mild anaemia
Different from iron deficiency because the ferritin is normal and there is a raised red cell count)

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17
Q

What is HbH disease?

A

Severe form of alpha thalassaemia
Only one working alpha gene per cell
Alpha chain production is less than 30 percent of normal
Anaemia with low MCV and MCH

18
Q

Why is it called HbH disease

A

due to globin chain imbalance, excess beta chains form tetramers called HbH which cannot carry oxygen
HbH is present in variable amounts

19
Q

What are the clinical features of HbH disease?

A

Wide variation from almost asymptomatic to transfusion dependent
Slenomegaly due to extramedullary haematopoiesis
Jaundice due to haemolyisis, ineffective erythropoiesis
Growth retardation, gallstones and iron overload

20
Q

what is the inheritance of HbH disease

A

autosomal recessive -like inheritance

21
Q

where is HbH disease most common

A

SE Asia, middle east, mediterranean

22
Q

how is HbH disease managed

A

transfusion at times of intercurrent illness
if sever may be transfusion dependent
Splenectomy may reduce transfusion need in severe cases
folic acid supplementation

23
Q

Why is there a need to supplement folate in hbh disease

A

there is increases RBC turnover so increased demand

24
Q

What is the most severe form of alpha thalassaemia

A

Hb Barts Hydrops Fetalis Syndrome

no alpha genes inherited from parents –>minimal or no alpha chain production so HbA cannot be produced

25
Q

What is Hb Barts

A

Four gamma globin chains - present in barts hydrops fetalis

26
Q

What are the clinical features of barts

A

pallor
oedema
cardiac failure
growth retardation
severe hepatosplenomegaly
skeletal and cardiovascular abnormalities
most die in utero but some survive to term and die shortly after birth

27
Q

Why is it important to detect Barts

A

High risk of obstetric complications if undiagnosed

Screening is done in (-a) carriers in scotland

28
Q

What is seen on the blood film in alpha thalassaemia

A

target cells

anisopoikilocytosis

29
Q

What is beta thalassaemia

A

Disorder of beta chain synthesis - either reduced or absemt chain production
Only affects HbA as it is B chains only

30
Q

what is the usual cause of beta thalassaemia

A 
point mutations
(vs alpha which is usually deletions)
31
Q

What mode of inheritance is beta thalassaemia

A

Autosomal recessive

32
Q

How is beta thalassaemia classified

A

Based on clinical severity:

  • Beta thalassaemia treat (usually -B/BB or –/BB)
  • Beta thalassaemia intermedia (usually (-B/-B or –/-B)
  • Beta thalassaemia major
33
Q

What is raised HbA2 diagnostic of

A

Beta thalassaemia trait

34
Q

What are the laboratory featured of beta thalassaemia major?

A

Moderate to severe anaemia
Low MCV
Reticulocytosis
Anisopoikilocytosis and target cells on blood film
Mainly HbF and HbA2 present, small amounts of HbA

35
Q

What are the clinical features of beta thalassaemia

A 
Presents aged 6-24 mths
Failure to thrive
Pallor
Extramedullary haematopoiesis causing hepatosplenomegaly
Skeletal changes
Organ damage
36
Q

How is B thal major managed

A

transfusion dependent to maintain Hb just about normal (95-105)
bone marrow transplant

37
Q

What is the main problem in treated beta thal major

A

Iron overload - main cause of death

38
Q

What does regular transfusion do in b thal major

A

Suppress ineffective erythropoiesis

Inhibit gut over absoption of iron

39
Q

What are the consequences of iron overload

A

Endocrine dysfunction- diabetes, osteoporosis

Cardiac myopathies and arrhythmias

Liver cirrhosis –> hepatocellular carcinoma

40
Q

how is iron overload managed

A

Iron chelation - desferrioxamine

Haematology (21 decks)

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