This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'In α–thalassemia – \nSelect and explain. \nA. Excess α–chain, B. No α–chain, C. Excess β–chain, D. No β–chain', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Alpha - thalassemia\n\nPeople who do not produce enough alpha globin chain have alpha - thalassemia.\nAlpha globin chain is made by four genes, each gene contributes to 25% of the a-globin chains.\nThe severity of a-thalassemia varies greatly depending on the number of α-globin genes affected -\n\nI)\xa0\xa0Silent carrier state\n\nSingle α-globin gene is deleted.\nThese individuals are completely asymptomatic.\n\nii) α-thalassemia trait\n\nTwo α-globin genes are deleted\nThese individuals are asymptomatic with some red cell abnormalities like β-thalassemia minor.\n\niii) HbH disease\n\n\nThree genes of the a-globin chain are deleted.\nWith only one gene, the synthesis of α-chain is markedly reduced and tetramers of excess β-globin called HbH, form.\nHbH has an extremely high affinity for oxygen and therefore is not useful for oxygen exchange, leading to tissue hypoxia disproportionate to the level of haemoglobin.\nPatients have moderate to severe anaemia that may require an occasional blood transfusion.\n\niv) Hydrops fetalis\n\nDeletion of all four α-globin genes.\nIn the fetus, excess γ-globin chains form tetramers, known as haemoglobin harts.\nHemolgobin bart has such a high affinity for oxygen that it delivers almost no oxygen to tissues.\nMost individuals die before or shortly after birth.\nIn utero blood transfusion have allowed the birth of children with hydrops fetalis who then require life long blood transfusions.', 'role': 'assistant'}]