During an exam, a 22-year-old female student fainted. She grew up in a family with many children, has a history of frequent acute respiratory infections. Objectively: the patient has pale skin and mucous membranes, split-end hair, brittle nails. Blood test results: RBC-2,7 × 1012/l, Hb- 75 g/l, color index - 0,7, WBC-3,2 × 109/l, platelets - 210 × 109/l, ESR - 30 mm/h. Blood serum iron is 6 mmol/l. What is the most likely diagnosis?