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Absence of the hemoglobin alpha-chain
8%
22/286
Absence of the hemoglobin beta-chain
56%
159/286
Presence of the fetal hemoglobin
4%
12/286
Mutation resulting in increased iron absorption
25%
71/286
Mutations resulting in copper accumulation
6%
16/286
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The patient in the question stem suffers from beta-thalassemia major in which the beta-chain is completely absent. Beta-thalassemia major manifests when patients are homozygous for the disease, which causes a significant deficiency in Hb A and beta chain production, resulting in severe hemolysis and ineffective erythropoiesis. Babies with this disorder appear normal at birth because of the prevalence of fetal hemoglobin (two alpha chains and two gamma chains); however, as fetal hemoglobin disappears, symptoms become more prevalent. As a result of frequent hemolysis, frequent transfusions, or a combination of the two, iron levels increase and deposition begins in multiple organ systems. This patient is presenting with urinary frequency and hyperglycemia consistent with diabetes, which results from iron overload and damage to pancreatic beta-cells. Beta-thalassemia is more common among individuals of Mediterranean descent. Incorrect Answers: Answer 1: Absence of the hemoglobin alpha-chain characterizes the most severe form of alpha-thalassemia. Answer 3: All humans are born with fetal hemoglobin. The presence of fetal hemoglobin is not specifically characteristic of any disorder. In fact, the presence of fetal hemoglobin persists in many of these patients longer than in individuals without thalassemia and provides some survival advantage. Answer 4: The mutation described would be responsible for hemochromatosis, which is secondary to an intrinsic defect in the body's ability to control iron absorption. Answer 5: An aberration in copper absorption is responsible for Wilson disease, not beta-thalassemia.
3.8
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