1730. A nine month old boy of Sindhl parents presented to you with complaints of progressive lethargy, Irritability & pallor since 6 months of age. Examination revealed severe pallor. Investigation showed Hb-3.8 mg%; MCV-58fl; MCH-19.4 pg/ cell. Blood film shows osmotic fragility Is normal (target cells and normoblasts). X-ray skull shows expansion of erythroid marrow. Which of the following Is the most likely diagnosis