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Point mutation on chromosome 11
61%
132/218
X-linked defect in ALA synthase
17%
36/218
Inhibition of ALA dehydratase
9%
20/218
Blood loss
6%
12/218
Malnutrition
3%
6/218
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The most likely diagnosis in this case is ß-thalassemia, which is caused by a point mutation in a splice site of chromosome 11 leading to decreased ß-globin synthesis. ß-thalassemia minor is the result of a heterozygous defect on chromosome 11 resulting in decreased production of the hemoglobin ß chain. Patients are generally asymptomatic though they may report mild symptoms of anemia such as fatigue and pallor. It is most prevalent in Mediterranean populations as seen in this Turkish patient. Lab findings include microcytic anemia with a mean corpuscular volume of less than 65 µm^3. A low mean corpuscular hemoglobin concentration is seen due to decreased hemoglobin production. Furthermore, target cells can be seen on peripheral smear and this finding is indicative of a thalassemia. Figure A shows the classic target cells seen on peripheral blood smear in a patient with thalassemia. Incorrect Answers: Answer 2: An X-linked defect in the ALA synthase gene is associated with sideroblastic anemia. Although sideroblastic anemia is also a microcytic anemia, it would be associated with basophilic stippling of RBCs. Answer 3: Lead poisoning leads to ALA dehydratase inhibition and subsequent sideroblastic anemia. Lead poisoning is most common in young children. Symptoms include LEAD (lead lines on gingivae and metaphyses of long bones, encephalopathy, abdominal colic, and wrist and foot drop). Answer 4: While iron deficiency anemia is the most common cause of microcytic anemia, this patient has no evidence of blood loss. Furthermore, the target cells on her peripheral smear point towards thalassemia rather than blood loss. Answer 5: Malnutrition may lead to anemia due to a host of deficiencies. Deficiency of iron results in a microcytic anemia while deficiencies of folate and B12 result in macrocytic anemia. In this case, we do not have any reason to believe this patient has a nutritional deficiency. Bullet Summary: ß-thalassemia minor is the result of decreased ß-globin synthesis due to an inherited mutation on chromosome 11.
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