Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Charles Patrick Davis, MD, PhD
Methemoglobinemia is a condition in which more than 1% of the hemoglobin in red blood cells takes the form of methemoglobin. Methemoglobulin is an abnormal form of hemoglobin (the molecule responsible for carrying oxygen in the blood cells) that is unable to bind to oxygen. A small amount of methemoglobin is normal (less than 1% of hemoglobin). Symptoms of anemia develop when this percentage increases over 10%, and levels of 70% are generally fatal.
Methemoglobin can be increased due to two main causes. Some cases of methemoglobinemia are genetic, meaning that an inborn metabolic error leads to an increased proportion of methemoglobin. Most cases of methemoglobinemia are, however, acquired rather than inborn. Exposure to certain oxidizing substances may lead to the conversion of hemoglobin to methemoglobin.
What is methemoglobinemia, beta-globin type?
Beta-globin type methemoglobinemia is an inherited blood disorder. It disrupts the function of hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. Methemoglobinemia is characterized by increased levels of an atypical form of hemoglobin that is unable to deliver oxygen efficiently.
In most individuals with beta-globin type methemoglobinemia, the only symptom is cyanosis, which is a bluish appearance of the skin, mucous membranes, or the area underneath the fingernails due to a lack of oxygen in the blood. Symptoms may appear as early as age 3 to 4 months. Methemoglobinemia symptoms do not improve when affected individuals are given additional oxygen, because oxygen cannot bind effectively to the abnormal hemoglobin.
How common is methemoglobinemia, beta-globin type?
The incidence of beta-globin type methemoglobinemia is unknown.
What genes are related to methemoglobinemia, beta-globin type?
Mutations in the HBB gene cause methemoglobinemia, beta-globin type.
Hemoglobin consists of four protein subunits and four iron-containing molecules called heme. Heme molecules are necessary for red blood cells to pick up oxygen in the lungs and release oxygen to other cells in the body. Hemoglobin typically has two protein subunits call alpha-globin and two protein subunits called beta-globin. The HBB gene provides instructions for making beta-globin. Mutations in specific regions of the HBB gene lead to an atypical version of beta-globin known as hemoglobin M. Hemoglobin M interacts abnormally with heme molecules, which impairs the uptake of oxygen by red blood cells. As a result, a reduced amount of oxygen is delivered to cells throughout the body.
Other types of methemoglobinemia can be caused by abnormal alpha-globin, a shortage of a particular enzyme called NADH-cytochrome b5 reductase, or unusual reactions to certain drugs or chemicals.
How do people inherit methemoglobinemia, beta-globin type?
This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.
What other names do people use for methemoglobinemia, beta-globin type?
- blue baby syndrome
- congenital methemoglobinemia
- hemoglobin M disease
Genetics Home Reference. "Methemoglobinemia, beta-globin type." U.S. National Library of Medicine. 20 Feb. 2012. <http://ghr.nlm.nih.gov/condition/methemoglobinemia-beta-globin-type>.