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.
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