BIOLOGY 2F03 Chapter Notes - Chapter 3: Beta Thalassemia, Thalassemia, Hemoglobin E
20 May 2018
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3.6 – INTERACTIONS OF BETA THALASSAEMIA
1. Compound heterozygous states that are clinically significant
o When the other allele codes for a globin which is dangerous in high concs
o S, C, unstable alleles
o this is because you end up being totally unable to produce HbA
o he the other allele odes for a ariat thalassaei haeogloi
o E, Lepore
o When two different carriers reproduce, there is a 25% chance each of the offspring being normal,
either heterozygote or a compound heterozygote
2. Compund heterozygooisty with HbS
o is a type of SCD
o but much rarer than SCA and HbSHbC
o HbS/Hbthal+ is milder than HbS/Hb0 because you make more HbA; disrupts polymer formation
o both forms are milder anaemias than SCA because of higher levels of HbA2 and HbF
• Increased HbA2 = increased viscosity and less sickling
• osteonecrosis increased by 30% compared to SCD
3. Compund heterozygooisty with HbC
o Not a clinical problem
o blood film might show features of thalassaemia alongside HbC crystals and target cells
4. Compund heterozygooisty with HbE
o HbE only contributes 25% to the compound instead of 50%, hence this usually presents with
thalassaemic properties (microcytic anaemia and thalassaemic indices)
o often comparable to a thalassaemia minor or intermedia, but severity is not easily predictable
o since HbE is a thalassaemic Hb the net result is:
o very low globin chain and hence Hb synthesis = anaemia
o high alpha:beta ratio = precipitates = ineffective erythropoiesis
o compound heterozygopoisty accounts for a lot of beta-thalassaemia in SE asia
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