A 18-month-old boy from rural Maharashtra presents with his mother to the pediatric clinic with a 3-month history of progressive irritability, poor weight gain, and delayed motor milestones. On examination, he is noted to have bowing of legs, frontal bossing, and delayed fontanelle closure. Biochemistry shows serum calcium 7.2 mg/dL (normal 8.5–10.5), phosphate 3.8 mg/dL (normal 2.5–4.5), and alkaline phosphatase 180 IU/L (normal 30–120). X-ray of the wrist shows loss of sharp metaphyseal margins and widening of the growth plate. What is the most likely diagnosis?