ABNORMAL HEMOGLOBIN

ABNORMAL HEMOGLOBIN

Abnormal types of hemoglobin or hemoglobin variants are the pathologic mutant forms of hemoglobin. These variants are produced because of structural changes in the polypeptide chains caused by mutation in the genes of the globin chains. Most of the mutations do not produce any serious problem. Occasionally, few mutations result in some disorders.

There are two categories of abnormal hemoglobin:

1. Hemoglobinopathies

2. Hemoglobin in thalassemia and related disorders.

1. Hemoglobinopathies

Hemoglobinopathy is a genetic disorder caused by abnormal polypeptide chains of hemoglobin.

Some of the hemoglobinopathies are:

i. Hemoglobin S: It is found in sickle cell anemia. In this, the α-chains are normal and β-chains are

abnormal.

ii. Hemoglobin C: The β-chains are abnormal. It is found in people with hemoglobin C disease, which

is characterized by mild hemolytic anemia and splenomegaly.

iii. Hemoglobin E: Here also the β-chains are abnormal.

It is present in people with hemoglobin E disease which is also characterized by mild hemolytic

anemia and splenomegaly.

iv. Hemoglobin M: It is the abnormal hemoglobin present in the form of methemoglobin. It occurs

due to mutation of genes of both in α and β chains, resulting in abnormal replacement of amino acids.

It is present in babies affected by hemoglobin M disease or blue baby syndrome. It is an inherited

disease, characterized by methemoglobinemia.

Hemoglobin in Thalassemia and Related Disorders

In thalassemia, different types of abnormal hemoglobins are present. The polypeptide chains are decreased, absent or abnormal. In α-thalassemia, the α-chains are decreased, absent or abnormal and in β-thalassemia, the β-chains are decreased, absent or abnormal. Some of the abnormal hemoglobins found in thalassemia are hemoglobin G, H, I, Bart’s, Kenya, Lepore and constant spring.

ABNORMAL HEMOGLOBIN DERIVATIVES

‘Hemoglobin derivatives’ refer to a blood test to detect and measure the percentage of abnormal hemoglobin derivatives. Hemoglobin is the only carrier for transport of oxygen, without which tissue death occurs within few minutes. When hemoglobin is altered, its oxygen carrying capacity is decreased resulting in lack of oxygen. So, it is important to know about the causes and the effects of

abnormal hemoglobin derivatives. Abnormal hemoglobin derivatives are formed by carbon monoxide (CO) poisoning or due to some drugs like nitrites, nitrates and sulphanamides.

Abnormal hemoglobin derivatives are:

1. Carboxyhemoglobin

2. Methemoglobin

3. Sulfhemoglobin.

Normal percentage of hemoglobin derivatives in total hemoglobin:

Carboxyhemoglobin : 3% to 5 %

Methemoglobin : less than 3%

Sulfhemoglobin : trace (undetectable).

Abnormally high levels of hemoglobin derivates in blood produce serious effects. These derivatives

prevent the transport of oxygen resulting in oxygen lack in tissues, which may be fatal.

CARBOXYHEMOGLOBIN

Carboxyhemoglobin or carbon monoxyhemoglobin is the abnormal hemoglobin derivative formed by the

combination of carbon monoxide with hemoglobin. Carbon monoxide is a colorless and odorless gas. Since hemoglobin has 200 times more affinity for carbon monoxide than oxygen, it hinders the transport of oxygen resulting in tissue hypoxia. Normally, 1% to 3% of hemoglobin is in the form of carboxyhemoglobin