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: Pathology
Microcytosis is seen in - 
Select and explain. 
A. Thalassemia, B. Hb Lepore, C. Hb bart's, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Causes of microcytosis (MCV < 80fl)
• Iron deficiency anemia
• Thalassemia
• Sideroblastic anemia
• Anemia of chronic disease
In Hb Barts, all the four a chain genes are deleted resulting in formation of Barts Hb.
In Hb Lepore, there is nonhomologus fusion of b and d genes and forms an abnormal hemoglobin with total absence of normal b chain. It is one of the form of b thalassemia minor.