###HUMAN: among patients diagnosed with hemochromatosis due to repeated red blood cell transfusions, how many of them were unmarried?, ###ASSISTANT: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id WHERE demographic.marital_status = "SINGLE" AND diagnoses.long_title = "Hemochromatosis due to repeated red blood cell transfusions"