Thalassemia is an inherited blood disease that causes anemia. People suffering from thalassemia have abnormal formation of hemoglobin, the oxygen carrying substance in the blood. Their red blood cells contain only a small amount of hemoglobin, and these cells live for a shorter time than normal red blood cells. The faulty red blood cells carry less oxygen than normal, so the oxygen supply to the tissues of the body is reduced. Hemoglobin for the red blood cells is normally made in the bone marrow.
Thalassemia is common in people who come from the Mediterranean regions, the Middle East, and Southeast, Asia. If both parents have this condition, their children will have the illness in its most severe from. If only one parent has thalassemia, the children’s condition will be mild. Thalassemia can restrict a child’s development, and in its most severe form it can cause death. More than 300,000 babies severely affected with the condition are born each year.
Patients are treated with regular blood transfusions to keep the level of ordinary hemoglobin high and to provide a good supply of oxygen to their body tissues. These transfusions eventually cause a buildup of iron in the body, and drugs must be taken to help the kidneys excrete more iron. Treatment may include antibiotics to counter infection, and sometimes the spleen is removed.
If a person with severe thalassemia is to survive, he or she will need transfusions of about 25 units of blood per year.
Physiology of thalassemia
Thalassemias are characterized by the absence or decrease in the synthesis of one of the two constituent globins subunits of a normal hemoglobin molecule. In ?-thalassemia, decreased synthesis of ?-globulin results in accelerated red cell destruction because of the formation of insoluble Hb inclusion in the mature erythrocyte. The more severe ?- thalassemia reflects the extreme insolubility of ?- globins, which is present in excess in the red cell because of decreased ?- globins synthesis. Studies of RNA metabolism in erythroid cells have suggested that many patients with ?-thalassemia have a defect in RNA processing. This defect affects efficient RNA splicing during protein globins synthesis.
Etiology of thalassemia
The thalassemia, syndromes are among the most common genetic diseases in southern China, with the highest prevalence in areas where malaria has been or remains endemic. In Southeast Asia, with a population of approximately 450 million people, the burdens of inherited globins gene disorders in many regions are of such magnitude that they represent a public health concern.
These syndromes are caused by an abnormality in the rate of synthesis of the globins chains. This is in contrast to the true hemoglobinopathies (e.g., Hb S and Hb C) that result from an inherited structural defect in one of the globin chains that produces hemoglobin with abnormal physical or functional characteristics.
Inheritance of thalassemia is autosomal; whether it is autosomal; dominant or recessive is questionable because heterozygotes are not always symptomatic. Globin structural genes are found on chromosomes 11 and 16.
The alpha chain and its embryonic counterpart, the zeta chain, are located on chromosome 16. Two genes on each homologous chromosome, four per diploid cell, specify the ?-globins sequence. Only one gene per chromosome, two per diploid cell, specifies most of the non- ? chain on chromosome. In terms of the genetic basis of ? and ?-thalassemia, this represents an important difference.
All thalassemia genes that have been studied to date have been found to contain mutations that directly alter gene structures and subsequently gene function. One of five processes is now believed to be responsible for the genetic defect in thalassemia. These processes are:
- A nonsense mutation leading to early termination of the globin chain synthesis.
- A mutation in one of the non-coding intervening sequences of the original globin Hjjjchacachain gene, which causes inefficient splicing to mRNA.
- A mutation in the promoter area that decreases the rate of gene expression.
- A mutation at the termination of the gene that leads to lengthening of the globin chain with additional amino acids; the mRNA becomes unstable and causes a reduction in globin synthesis.
- A total or partial depletion of a globin gene, probably as the result of unequal chromosomes crossing over.
Signs and symptoms of thalassemia
Possible signs and symptoms of thalassemia major (also known as Cooley’s anemia, Mediterranean disease, and erythroblastic anemia) include a healthy neonate at birth, but during the second 6 months of life developing severe anemia, bone abnormalities, failure to thrive, and life threatening complications.
The first sings are pallor, yellow skin and sclera in infant’s ages 3 to 6 month. Later signs and symptoms include Splenomegaly, with abdominal enlargement; frequent infections; bleeding tendencies (especially nosebleeds); and anorexia. Most children with thalassemia major have a small body, a large head (characteristic features), and possible mental retardation. Infants may have features similar to Down syndrome, because of thickened bone at the base of the nose from bone marrow hyperactivity.
Signs and symptoms of thalassemia inter-media include some degree of anemia, jaundice, and Splenomegaly, and possibly signs of hemosiderosis due to increased intestinal absorption of iron.
Thalassemia minor may cause mild anemia but usually produce no symptoms and is commonly overlooked; it should be differentiated from iron deficiency anemia.
Complications of thalassemia
Possible complications of thalassemia include pathologic fractures due to expansion of the marrow cavities with thinning of the long bones, cardiac arrhythmias, and heart failure.