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
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