In methemoglobinemia, patients have higher metHb than the healthy population. It could be congenital, resulting from deficiency of enzymes which convert metHb back to Hb, or acquired as a result of various chemical agents. Two clinical types of recessive hereditary methemoglobinemia have been described. Type I is a benign form in which cyanosis is the sole clinical symptom. In type II, cyanosis is associated with severe progressive neurological disabilities, including mental retardation, microcephaly, and movement disorders [
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