Methemoglobinemia

Definition:

An inherited condition that causes the iron in hemoglobin (the red blood pigment) to be unable to carry oxygen.

Causes, incidence, and risk factors:

There are two forms of methemoglobinemia, both inheritable. The autosomal recessive condition results from an absence of an enzyme that normally converts methemoglobin back to normal hemoglobin thereby leading to an increase in methemoglobin and a decrease in the ability of blood to carry oxygen. This results in a bluish color to the skin (cyanosis).

The second type, called hemoglobin M disease, is an autosomal dominant trait characterized by the production of an abnormal methemoglobin, and is usually milder in its degree of cyanosis. Exposure to environmental chemicals causes an increase in production of methemoglobin in affected people. These chemicals are more commonly aniline dyes (in brightly colored cloths), nitrobenzene, and nitrites (used commonly to prevent spoilage of meat).