The blood is made of various cells suspended in plasma. The red blood cells are our major focus here since they contain within them hemoglobin, a substance which helps in the transport of oxygen to the tissues.
This hemoglobin is composed of 2 parts: a heme and globin (2 pairs of protein chains).
There are 2 alpha and 2 beta globin chains – the pair, and there is a way in which the chains ought to be arranged.
An error occurs when a protein substitution occurs in any one of these chains – but particularly in the globin chains (amino acids are the building blocks of proteins which make up the globin chains – so if amino acid ‘x’ is the normal, an abnormality occurs when instead of ‘x’ at a particular location along the chain, you have ‘y’.)
Genotype AA: At position 6 of both globin chains, the amino acid is GLUTAMATE
Genotype AS: At position 6 of one globin chain is GLUTAMATE and at position 6 of the second globin chain, you have VALINE
Genotype SS: At position 6 of both globin chains, the amino acid is VALINE
Genotype AC: At position 6 of one globin chain is GLUTAMATE and at position 6 of the second globin chain, you have LYSINE
Hemoglobinopathy is a genetic disorder caused by abnormal polypeptide chains of hemoglobin.
Some of the hemoglobinopathies are:
- Hemoglobin S: It is found in sickle cell anemia. In this, the alpha chains are normal and beta chains are abnormal. The sickle-cell disease occurs when the sixth amino acid, glutamate, is replaced by valine to change its structure and function. Valine is hydrophobic, causing the hemoglobin to collapse on itself occasionally. When enough hemoglobin collapses on itself the red blood cells become sickle-shaped.
- Hemoglobin C: is an abnormal hemoglobin in which substitution of a glutamic acid residue with a lysine residue at the 6th position of the β-globin chain has occurred. It reduces the normal plasticity of host erythrocytes causing a hemoglobinopathy.
People with hemoglobin C (carriers) do not have Hemoglobin C disease or sickle cell disease and cannot develop these diseases later in life.
They can pass the trait to their offspring: Individuals who carry the hemoglobin C trait can have a child with Hemoglobin C disease or Hemoglobin SC disease. Hemoglobin C disease IS NOT a form of sickle cell disease. It is present at birth, though some cases may not be diagnosed until adulthood. People with hemoglobin C disease can expect to lead a normal life.
Amino acid chain normal Hb-Top row and HbE- Bottom row
- Hemoglobin S-C disease is a hemoglobinopathy (see Hemoglobinopathies) that causes symptoms similar to those of sickle cell disease, but milder.
Hb S-C disease is suspected in patients whose clinical features suggest sickle cell disease or whose RBCs demonstrate sickling. Stained blood smears show target cells and a rare sickle cell. Sickling is identified in a sickling preparation, and Hb electrophoresis establishes the diagnosis. Treatment can be similar to that of sickle cell disease but is determined by severity of symptoms.
- Hemoglobin AC: Hemoglobin C trait results when the gene for hemoglobin C is inherited from one parent and the gene for hemoglobin A from the other. This carrier state does not usually result in health problems, although there may be a slightly low MCV and target cells.
- Hemoglobin E: Here also the beta chains are abnormal. It is present in people with hemoglobin E disease which is also characterized by mild hemolytic anemia and splenomegaly.
- Hemoglobin M: It is the abnormal hemoglobin present in the form of methemoglobin. It occurs due to mutation of genes of both in alpha and beta 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.