Question

In α-thalassemia
(A) α-globin chain is produced in less number.
(B) Two closely linked genes HBA1 and HBA2 on chromosome 16 are affected.
(C) Incorrectly functioning globin chain is synthesized.
Correct statements is/are

• A. Only A.
• B. Only B.
• C. Only A and B.
• D. Only B and C.

Answer 1

Answer: (C)

Thalassemia is a recessive autosomal genetic defect, originated in the Mediterranean region by mutation, deletion or recessive autosomal transmission. Thalassemia are group of disorders caused by defects in the synthesis of globin polypeptide in RBC. In this case, the synthesis of one chain is in excess while the other is absent or reduced. As a result, free insoluble globin chains start accumulating inside the blood cells and form precipitates which damage the cell, causing cell lysis and resulting in anemia. There are two main types of thalassemia in which the synthesis of α or β globin is defective. It is common in the Mediterranean, Middle East, Indian subcontinent, and in South-east Africa.
Alpha (α) thalassemia: The α-thalassemia involves the genes HBA1 and HBA2, inherited in a Mendelian recessive fashion. There are four alleles on two gene loci. It is also connected to the detection of the 16p (short-arm) chromosome. α-Thalassemia results in decreased α-globin production and, therefore, fewer α-globin chains are produced, resulting in excess of β chains in adults and excess γ chains in newborns. The excess β chains form HbH of four β chains (an unstable tetramer) which have abnormal oxygen dissociation curves.
Beta (β) thalassemia: β-Thalassemia is due to mutations in the HBB gene on chromosome 11, also inherited in an autosomal recessive fashion. Mutations are characterized as (β⁰ or β thalassemia) if β chain is not produced; they are characterized as (β+ or β thalassemia intermedia) if they allow some β chain formation to occur. In either case, there is a relatively less number of β chains, but these do not form tetramers; they bind to the red blood cell membranes, producing membrane, and at high concentrations, they form toxic aggregates.
Delta thalassemia: Just like β-thalassemia, a mutation can occur which may affect the ability of this gene to produce delta chains. α and β chains are present in hemoglobin but about 3% of adult hemoglobin is made of alpha and delta chains. In sickle cell anemia, there is a synthesis of incorrectly functioning globin but in thalassemia, the number of globins synthesized are low.