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MethemoglobinemiaDefinition Methemoglobinemia is a condition in which the iron in the hemoglobin molecule (the red blood pigment) is defective, making it unable to carry oxygen effectively to the tissues. Causes, incidence, and risk factors Methemoglobinemia may be inherited (congenital) or acquired. There are 2 forms of inheritable methemoglobinemia, type 1 and type 2. Most hereditary cases are type 2, and result from a deficiency in the enzyme cytochrome b5 reductase. The other inheritable type, called hemoglobin M disease (type 1), is an autosomal dominant condition (you only need one affected parent to inherit it) characterized by an inability to convert methemoglobin back to hemoglobin. This usually causes few problems. Acquired methemoglobinemia exposure to certain chemicals, which cause an increase in the production of methemoglobin. These chemicals include nitrites (used as additives to prevent spoilage of meat), anesthetics such as benzocaine and xylocaine, certain antibiotics (including dapsone and chloroquine), and benzene. Acquired methemoglobinemia may be severe in certain cases, and require treatment. In most mild cases, no treatment is required, other than avoiding the offending medication or chemical. Symptoms
Signs and tests
Treatment Medications used to treat this disorder include:
Complications In acute exposure:
Calling your health care provider Call your health care provider if there is a family history of methemoglobinemia and you develop symptoms of this disorder. Call your health care provider or emergency services immediately if there is severe shortness of breath. Prevention Genetic counseling is recommended for prospective parents with a family history of methemoglobinemia. Illustrations
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