Methemoglobinemia may be passed down through families (inherited or congenital). Or, it may be caused by exposure to certain drugs, chemicals, or foods (acquired).
There are two forms of inherited methemoglobinemia. The first form is passed on by both parents. The parents usually do not have the condition themselves, but they carry the gene that causes the condition. It occurs when there is a problem with an enzyme called cytochrome b5 reductase.
There are two types of this form of methemoglobinemia:
- Type 1 (also called erythrocyte reductase deficiency) occurs when red blood cells lack the enzyme.
- Type 2 (also called generalized reductase deficiency) occurs when the enzyme doesn't work anywhere in the body.
The second form of inherited methemoglobinemia is called hemoglobin M disease. It is caused by defects in the hemoglobin molecule itself. Only one parent needs to pass on the abnormal gene for the child to inherit the disease.
Acquired methemoglobinemia is more common than the inherited forms. It occurs in some people after they are exposed to certain chemicals and drugs, including:
- Anesthetics such as benzocaine
- Certain antibiotics (including dapsone and chloroquine)
- Nitrites (used as additives to prevent meat from spoiling)
The condition may also occur in infants who are very ill or who are fed too many vegetables containing nitrates (such as beets).