Thalassaemia Flashcards
Genetic disorder: thalassaemia
Failure to synthesize certain globin chains
Sickle cell anaemia
Structural variants of Haemoglobin (Hb)
List third disorder of haemoglobin synthesis
Failure to switch from fetal Hb to adult Hb
Chromosome 16
Two genes for alpha-globin
Chromosome 11
One gene each for beta-globin, gamma-globin and delta-globin
Variation of fetal Hb
HbF = alpha2 gamma 2
Variation of adult Hb
- HbA = alpha2 beta2
- HbA2 = alpha2 delta2
Beta-thalassaemia
Reduced production of beta-globin chains
beta-thalassaemia is usually caused by?
- Usually caused by single base mutation
Beta-thalassaemia inheritance
Autosomal recessive inheritance
Beta-thalassaemia mutation can result in?
Reduced beta-globin or absent beta-globin
Beta-thalassaemia major
Two knock-out genes
Heterozygote carrier for beta-thalassaemia trait
one knock-out gene and one normal gene
List two effects of beta-thalassaemia
- HbF increases - no beta globin to replace gamma globin
- Excess alpha globin precipitate - no beta globin to pair with
HbF increases in beta-thalassaemia
Leads to high oxygen affinity of RBC -> tissue hypoxia since oxygen can’t dissociate
Excess alpha globin precipitate
leads to destruction of RBC precursors and haemolysis -> anaemia
Beta thalassaemia major clinical signs
- Iron accumulation
- Hepatomegaly and splenomegaly
- Bone deformation
Beta thalassaemia major haematological phenotype
- Hypochromic microcytic anaemia
- Anisopoikilocytosis (abnormal shape and size)
- Target and tear-drop cells
- Absent HbA
- Present HbA2
- Rise in HbF
List the beta thalassaemia traits
- Asymptomatic carrier
- Normal Hb
- Hypochromic microcytosis
- Raised HbA2
Alpha-thalassaemia definition
Reduced production of alpha-globin chains
Alpha-thalassaemia is usually genetically caused by
Full gene deletions
‘Normal’ variation of alpha-thalassaemia
4 normal genes
alpha+ trait of alpha-thalassaemia
3 normal genes
Homozygous alpha+ trait of alpha-thalassaemia
1 normal gene, 1 deleted gene on each chromosome (2 gene deletions)
alpha0 trait of alpha-thalassaemia
2 normal genes on one chromosome, 2 deleted genes on other
HbH disease variation of alpha-thalassaemia
1 normal gene
Hydrops fetalis variation of alpha-thalassaemia
0 normal genes
Variation in alpha trait of alpha thalassaemia affects ________ but presents similarly
inheritance pattern
Alpha-thalassaemia results in excess?
Excess beta and gamma chains forming precipitants:
- HbH bodies = beta4
- Hb Barts = gamma4
HbH bodies precipitants form?
Beta4
Hb Barts precipitant forms?
Gamma4
Pathophysiology of alpha-thalassaemia
- Defect haemoglobin synthesis
- Peripheral haemolysis
- High oxygen affinity of HbH and Hb barts
Peripheral haemolysis causes?
HbH is unstable and shortens lifespan
High oxygen affinity of HbH and Hb barts does?
Does NOT give up oxygen to tissue
Alpha-thalassaemia is clinically
Clinically asymptomatic
Two gene deletions in alpha-thalassaemia
- Mild hypochromic microcytosis anaemia
- No raise in HbA2
- Possible Hb Barts and HbH bodies
One gene deletion in alpha-thalassaemia
- Normal Hb
- Very mild reduction in MCV
- Rarely Hb Barts
Hb H Disease (3 gene deletions) leads to?
- Anaemia
- HbH formation
- Splenomegaly
- Bone changes
Hb Barts Hydrops Fetalis can lead to?
- Death in utero
- Hb Barts formation
- Massive hepatosplenomegaly