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Medical Definition of Hereditary methemoglobinaemic cyanosis
1. Methemoglobinaemia due to formation of any one of a group of abnormal a chain or b chain haemoglobins collectively known as haemoglobin M. Slate-gray cyanosis occurs in early infancy, without pulmonary or cardiac disease, and is resistant to ascorbic acid or methylene blue therapy; autosomal dominant inheritance, methemoglobinaemia due to deficiency of cytochrome b5 reductaseor methemoglobin reductase, the enzyme responsible for reduction of intraerythrocyte methemoglobin; cyanosis is improved by ascorbic acid or methylene blue; autosomal recessive inheritance, one case of methemoglobinaemia has been reported that apparently is due to a deficiency of cytochrome b5. Synonym: hereditary methemoglobinaemia, hereditary methemoglobinaemic cyanosis, primary methemoglobinaemia. (05 Mar 2000)