Thalassemia occurs due to which mutations -a)  Missenseb)  Splicingc)  Transitiond)  Frame-shifte) Truncation
Thalassemia syndrome

Adult hemoglobin is a tetramer, composed of two α globin chains and two β globin chains.
Thalassemia is an inherited autosomal recessive disorder.
In thalassemia, the genetic defect results in reduced β synthesis of one of the globin chains of hemoglobin.
β-Thalassemia is caused by deficient synthesis of β-chain with normal β-chain synthesis.
α-thalassemia is caused by deficient synthesis of α-chain with normal β-chain synthesis.
Molecular defect in pathogensis of thalassemia.

A. β-Thalassemia

Most common type of genetic abnormality in β-thalassemia is point mutation i.e., nonsense.
Some may also occur due to deletion or insertion i.e., frame shift mutations.
Defect may occur at different steps of β-chain synthesis.

(i) Splicing mutations

Mutations leading to aberrant splicing are the most common cause of β-thalassemia.

(ii) Chain terminator mutations

This cause premature termination of mRNA translation.

(iii) Promoter region mutations

This results in transcription defect.

B. α-Thalassemia

The most common cause of reduced a-chain synthesis is deletion of α-globin genes.
Rarely nonsense mutation may also cause α-thalassemia.
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