Haemoglobins are globular proteins found in red blood cells. They are able to bind molecular oxygen and transport oxygen through the lungs and other blood vessels in the body. Haemoglobin variants include;haemoglobin A, haemoglobin S, haemoglobin C, haemoglobin D, haemoglobin E and haemoglobin F (fetal haemoglobin).
Haemoglobinopathies are genetic disorders or abnormalities which result in abnormal structure of one of the globin chains of the haemoglobin molecule. Also ,low levels of synthesis of the normal polypeptide chains (i.e alpha and beta) and production of abnormal chains(i.e delta and epsilon ) result in haemoglobinopathy. These disorders result in thalassemias (alpha and beta), haemoglobin S (Hb S) disease ,haemoglobin C (Hb C) disease, haemoglobin D (Hb D ) disease, and haemoglobin E (Hb E) disease.
Alpha thalassemia results from genetic deletion and this occurs because the α-globin genes are duplicated. This results in unequal crossing over between adjacent α-alleles. Beta thalassemia results from mutations that produces frameshift in the β-globin coding sequence. Studies reveal that majority of β-thalassemias result from mutations affecting the biosynthesis of β-globin mRNA. Thalassemias are classified as major, minor, and intermediate respectively.
Haemoglobin A is the normal haemoglobin found in humans. Two subgroups exists viz; HbA1 and HbA2. The polypeptide chain composition of both HbA1 and HbA2 are α2β2 and α2δ2 respectively. This type of haemoglobin is found in normal shaped erythrocytes and do not possess pathological problem.
In haemoglobin S , there is a replacement of the amino acid glutamic acid with valine at the sixth position in the β-chain. In haemoglobin C, the replacement of the amino acid glutamine with lysine occurs at the sixth position of the β-globin chain. It is pertinent to note that HbC exhibits less haemolysis than HbS. Both HbS and HbC mutant haemoglobins are commonly found among certain black African population. Individuals with HbSC disorder will have an intermediate anaemia from that observed for HbSS. HbSS individuals suffer from sickle cell disease. It is characterized by sickle-shaped erythrocytes, formation of tactoid structure. Victims experience trauma and crises, and require blood transfusions.
HbAS individuals possess the sickling trait but do not suffer from sickle cell disease. However ,when two HbAS individuals marry, they are likely to produce an offspring with the HbSS genetic combination ( i.e a sickler )
Studies reveal that disease conditions associated with these disorders include splenomegaly, haemolytic anaemia, urobilinuria, jaundice and so on.
Management of these disorders include the use of blood transfusion coupled with desferoxamine, folic acid supplement, use of hypoxurea and bone marrow transplantation. HbAS individuals should be discouraged from marrying other HbAS individuals.
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