[Hereditary methemoglobinemias]

The different forms of hereditary methemoglobinemia are described. Dominant hereditary methemoglobinemia (hemoglobin M diseases) is due to punctual mutations on the alpha or beta globin chain leading to its permanent oxidation. Recessive hereditary methemoglobinemia is due to a deficit of the NADH-cytochrome b5 reductase, with two different clinical presentations according to whether the deficit is limited to blood cells (type I) or is generalized (type II); the latter is extremely severe and justifies a prenatal diagnosis. Finally, the only known case of recessive hereditary methemoglobinemia due to a deficit of b5 cytochrome is quoted.