PLAB-0454

A 5-year-old child was found to have orchidomegaly and splenomegaly. Blood tests show a WBC = 1.7 X 104/L, Hb = 7.1 g/dl and platelets = 44 X 104g/dl. His parents mention that he suffers from fatigue while at presentation he looks pale and has a fever. What is the most likely diagnosis?