Thalassaemia Flashcards
What is thalassaemia?
A blood condition which causes alteration of haemoglobin structure.
Two types: alpha and beta
Where is alpha-thalassaemia more common?
Mediterranean countries Africa The Middle East India Central Asia
What is the inheritance of alpha-thalassaemia
Complex: 2 alpha-globin alleles are inherited from each parent. The amount of missing alleles and the combination of HBA1 and HBA2 genes affected will determine the precise risk of inheriting alpha-thalassaemia
What are the variations of alpha-thalassaemia?
1 gene defect - asymptomatic silent carrier
2 gene defects - alpha-thalassaemia minor (minor anaemia)
3 gene defects - haemoglobin H disease (severe anaemia)
4 gene defects - haemoglobin Bart’s Hydrops Fetalis (fatal)
What is HBA1?
A gene which provides instructions for the production of alpha-globin.
What is alpha-globin?
A subunit of haemoglobin.
What is Haemoglobin A?
A type of haemoglobin making up ~97% of all haemoglobin in the body.
Consists of two alpha-globins and two beta-globins
What is Haemoglobin A2?
A type of haemoglobin making up ~3% of all haemoglobin in the body.
Made up of two alpha-globins and two delta-globins
What is HBA2?
Gene which produces alpha-globins
What is the cytogenetic location of the mutation for alpha-thalassaemia?
16p13.3
What is beta-thalassaemia?
Blood disorder involving a point mutation in the HBB gene in chromosome
What is alpha-thalassaemia>
Blood disorder involving the deletion of the HBA1 and HBA2 genes in chromosome 16
What is the location of the point mutation for beta-thalassaemia?
11p15.4
Where is beta-thalassaemia more common?
Mediterranean countries North Africa The Middle East India Central Asia South-East Asia
What is the inheritance for beta-thalassaemia?
Autosomal recessive
What are the variations of beta-thalassaemia?
(HHB↓ = decreased beta-chain synthesis, HBBX = no beta-chain synthesis)
HBB + HBB = wild type; healthy
HBB↓ + HBBX = beta thalassaemia minor
HBB↓ + HBB↓ = beta thalassaemia intermedia
HBBX + HBBX = beta thalassaemia major
How is thalassaemia diagnosed? When does diagnosis usually occur?
Full blood test
- measures haemoglobin
- measures different kinds of blood cells
Haemoglobin test
- measures different kinds of haemoglobin present
Genetic screening
Diagnosis usually occurs in first 6 months of life. Can be fatal in early childhood without treatment.
What is the treatment for thalassaemia?
No cure.
Management involves regular blood transfusions
- boosts haemoglobin levels
- can lead to buildup in iron levels, side effects including diabetes, heart failure and liver disease
- iron chelates are used to reduce iron levels
- bind with iron and allow it to be removed by the kidneys
What is the effect of thalassaemia on the gene pool?
More mutations in red blood cell formation increase the severity of the disease
- mild thalassaemia = 1-2 mutations
- severe thalassaemia = 3-4 mutations
More mutations in the gene pool increases the mortality rate
Resistance to malaria increases allele frequency
