This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutritional anemia, Subject name: Pediatrics
A nine-month-old boy of Sindhi parents presented to you with complaints of progressive lethargy, irritability and pallor since 6 months of age. Examination revealed severe pallor. Investigation showed Hb-3.8 g%; MCV- 58 fL, MCH-19.4 pg/cell. Osmotic fragility is normal; Blood film shows target cells and normoblasts. X-ray skull shows expansion of erythroid marrow. Which of the following is the most likely diagnosis: 
Select and explain. 
A. Iron deficiency anemia, B. Acute lymphoblastic anemia, C. Hemoglobin D disease, D. Hereditary spherocytosis
C: Hemoglobin D disease
Answer: C: Hemoglobin D disease 
Explanation: Discussing options one by one: a. Iron deficiency anemia: So severe anemia & expansion of erythroid marrow are usually not seen b. Acute lymphoid Leukemia: Low MCV, no obvious involvement of other cell lines, and expansion of erythroid marrow are incompatible with diagnosis of ALL c. Hemoglobin D disease: Low MCV and MCH with target cells suggest abnormality of haemoglobin like HbD disease d. Hereditary spherocytosis: Normal osmotic fragility goes against hereditary spherocytosis