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Haematology > Haemoglobinopathy overview > Flashcards

Haemoglobinopathy overview Flashcards

1
Q

Describe the structure of Hb?

A

Tetramer, made up of 2 alpha globin like chains and 2 beta globin like chains
ONE hame group attached to EACH globin chain

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2
Q

Name the major forms haemoglobin and their structure?

-which form is present in adults greatest quantities?

A 
-HbA 
(2 alpha chains and 2 beta chains)
HbA2 
(2 alpha chains and 2 delta chains)
HbF (foetal) 
(2 alpha chains and 2 gamma chains)

-HbA

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3
Q

What chromosomes are involved in alpha and beta globulin chain production?

A

Alpha like genes on chromosome 16
2 alpha genes per chromosome (4 per cell)

Beta like genes are on chromosome 11
1 beta gene per chromsome (2 per cell)

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4
Q

What are haemoglobinopathies?

  • inheritance?
  • what are the 2 main groups?
A

hereditary conditions affecting globin chain synthesis

  • usually autosomal recessive
  • Thalassaemias and structural Hb variants
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5
Q

-What are structural Hb variants?

A

-normal production of structurally abnormal globin chain = variants Hb e.g. HbS

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6
Q

Thalassaemias

  • definition?
  • what type of anaemia does this cause?
  • what happens to the resulting RBCs?
  • where are thalassaemias most prevalent
A
  • hereditary disorders of globin chain synthesis resulting in impaired Hb production
  • inadequate Hb production = Microcytic, hypochromic anaemia
  • there is ineffective erythropoiesis and so haemolysis occurs
  • malaria endemic areas
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7
Q

Alpha thalassaemia

  • mutation affects what?
  • underlying mutation?
  • Hb affected?
  • classification? (3)
A
  • alpha globin chain synthesis i.e. giving reduced/absent alpha chain synthesis
  • deletion of 1 or both alpha genes from chromosome 16
  • HbA, HbA2, HbF all affected
-Alpha thalassaemia trait
(one or two genes missing)
HbH disease 
(only one alpha been left
Hb Barts Hydrops fetalis
(no functional genes)
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8
Q

Alpha thalassaemia trait

  • presentation?
  • lab results?
  • mistaken for what?
A
  • asymptomatic, no treatment needed
  • Microcytic, hypo chromic red cells with MILD anaemia
  • iron def
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9
Q

HbH disease

  • how many genes per cell?
  • lab results?
  • what is HbH?
  • what can be seen on blood film?
  • clinical features & why? (5)
A
  • one
  • anaemia + very low MCV and MCH
  • excess Beta chains form tetramers called HbH which cannot carry oxygen
  • HbH bodies

-Anaemia
Splenomegaly (extra medullary haematopoiesis)
Jaundice (haemolysis and ineffective erythropoiesis)
commonest in S.E. Asian/middle east/ Med patients

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10
Q

Hb Bart’s hydrops fetalis syndrome

  • no. genes in cell?
  • consequence?
  • clinical features? (6)
A

-none

-minimal or no alpha chain production i.e. HbA not made
Hb Barts and HbH are then the majority of Hb at birth

-severe anaemia 
cardiac failure, oedema
growth retardation 
severe hepatosplenomegaly 
skeletal and CV abnormalities 
Most die in utero
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11
Q

Beta thalassaemia

  • what is it?
  • what Hb is affected?
  • caused by what form of mutation?
  • classification & features? (3)
A
  • disorder of beta chain synthesis
  • only HbA
  • point mutations
-B thalassaemia trait
(asymptomatic, low MCV/MCH)
Beta thalassaeia intermedia 
(moderate severity requiring occasional transfusion)
Beta thalassaemia major 
(no Beta chains produced, severe)
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12
Q

Beta thalassaemia major

  • what is seen on lab tests?
  • blood film?
  • type of Hb mostly present?
  • clinical features? (6)
  • management?
  • main complication of ^?
  • other complications? (4)
A

-severe anaemia
reticulocytosis, very low MCV/MCH

  • microcytosis, hypochromia, anisopoikilocytosis and target cells
  • HbF
-present ages 6-24 moths 
failure to thrive 
pallor
haepatosplenomegaly
skeletal changes
organ damage

-regular transfusion programme to maintain Hua t 95-105g/l
this will suppress ineffective erythropoiesis and inhibit over absorption of iron
BM transplant before complications develop

-Iron overload

-viral infection- HIV, Hep B and C
alloantibodies- hard to cross match
transfusion reactions
increased risk of bacterial sepsis

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13
Q

What are the consequences of iron overload?

  • endocrine (3)?
  • cardiac (2)?
  • liver (2)?
  • management?
A

-impaired growth and pubertal development

-cardiomyopathy
arrhythmias

-cirrhosis
hepatocellular cancer

-can’t of venesection as already anaemic
use Iron chelating drugs e.g. Desferrioxamine
(these for an Fe/chelator complex and excess iron excreted in stool)

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14
Q

Diagnosis of thalassameia

  • exclude?
  • what is seen on blood film generally?
  • investigation?
A
  • iron def
  • hypochromia, target cells, anisopoikilocytosis

-high performance liquid chromatography
this quantifies presence of HbA, HbA2 and HbF
identifies abnormal Hb

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15
Q

Describe the pathophysiology of sickling disorders:

  • type of mutation and location?
  • consequences of mutation?
A

-point mutation in codon 6 of the Beta globin gene that substitutes Glutamine to valine

-alters structure of Hb to form HbS
HbS polymerises if exposed to low O2 levels ad this distorts the red cell damaging the membrane

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16
Q

Sickle trait

  • how many abnormal genes?
  • presentation?
  • blood film?
  • main Hb present?
A
  • one abnormal gene
  • asymptomatic carrier (may sickle in extreme hypoxia)
  • normal
  • Mainly HbA, HbS < 50%
17
Q

Sickle cell anaemia (HbSS)

  • no. of abnormal genes?
  • main Hb present?
  • presentation? (3)
  • precipitants of a crisis? (6)
  • treatment of painful crisis?
  • long term effects? (3)
  • long term treatment? (3)
A
  • 2 abnormal genes
  • HbS > 80%, no HbA
-Sickle crisis 
(episodes of tissue infarction due to vascular occlusion  
can occur anywhere, pain may be severe) 
Chronic haemolysis 
(shortened RBC life span 
Hyposplenism
(repeated splenic infarcts)

-hypoxia, dehydration, infection, cold, stress/fatigue

-opiate analgesia
hydration
rest
Oxygen 
antibiotics if infection 
severe= red cell exchange transfusion (venesection + transfusion)

-impaired growth
risk of sepsis
risk of organ damage
(pulmonary hypertension, renal disease, avascular necrosis, leg ulcers, stroke)

-hyposplenism requires prophylactic penicillin, vaccination against pneumococcus, meningococcus, haemophilus
folic acid supplements
hydroxycarbamide to induce HbF production

18
Q

name another type of sickling disease?

A

compound heterozygosity for HbS and another Beta chain mutation
e.g. HbS/Beta thal
HbSC

19
Q

screening for Haemoglobinopathies

-how is this done?

A

Antenatal screening to identify carrier parents now standard
family origin questionnaire and FBC
further testing of from high risk area or abnormal RBS indices

Haematology (24 decks)

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