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: