Beta-Thalassemia Minor


Hopefully this will help anyone else out there with this genetic disorder.

Thalassemia is an inherited blood disorder in which the body is unable to make adequate hemoglobin. This is due to an inborn error of metabolism that leads to absence or reduced synthesis of one or more types of globin polypeptide chains of the hemoglobin molecule.

¤ Geographical distribution

The thalassemias are wide-spread with about 5% of the world population affected by it. It is most prevalent around the Mediterranean Sea i.e. countries like Greece, Italy, Turkey and North African countries. It is also seen in Saudi Arabia, Iran, Afghanistan, Pakistan India and south East Asian countries like Thailand and Indonesia. The prevalence is highest in Italy, Greece and Cyprus.
In India, prevalence of Thalassemia is very high among certain communities like Punjabi, Sindhi, Gujarati, Bengali, Parsee, Lohana and certain tribes, i.e. northern, western and eastern parts, while it is much less in the south of India.

¤ Structure of normal hemoglobin

The hemoglobin molecule is made up of two parts - heme and globin. Heme is a porphyrin containing iron. Globin is made up of four polypeptide chains of two types - alpha and beta. Thus each globin molecule is made up of two alpha chains and two beta chains. This hemoglobin is called hemoglobin A because this forms the major part of hemoglobin found in adults. In adults there is another small fraction of hemoglobin called called Hb A2, the globin portion of which is made up of two alpha chains and two delta chains. Normally the concentration of HbA2 is less than 3.5% of the total hemoglobin. During fetal life, the major part of hemoglobin is Hb F, the globin of which is made up of two alpha chains and two gamma chains. The concentration of HbF falls after birth and in adults HbF is less than 2-3% of the total hemoglobin. The genetic control of gamma, alpha and beta chains is interrelated, so that after birth, the production of gamma chains slows down and beta chains increases correspondingly.

¤ Inheritence of Thalassemia

Like all body characteristics and functions, hemoglobin formation is also controlled by a pair of genes, one inherited from each parent. Normal persons have inherited normal genes from both the parents and thus form normal hemoglobin. Thalassemia carriers or traits have one normal and one abnormal gene. They are usually healthy because the normal gene masks the function of the abnormal gene. If a person inherits abnormal genes from both the parents, as occurs in thalassemia major, body cannot form enough hemoglobin and hence survival depends on regular transfusions.

¤ Types of thalassemia

In thalassemia there is impaired production of alpha or beta chains. If the production of alpha chains is impaired, the condition is called alpha thalassemia and if the production of beta chains is impaired the condition is called beta thalassemia. If the person is heterozygous i.e. has only one abnormal gene, the clinical picture is very mild - called respectively as alpha thalassemia minor or beta thalassemia minor depending upon whether alpha or beta chains are affected. When both the genes are defective i.e. homozygous state, then condition is celled thalassemia major as the patient has severe clinical manifestations.
A child might inherit a beta thalassemia trait from one parent and a trait of another abnormal hemoglobin from another parent like Hb S, Hb E, Hb D, etc. Such a patient is heterozygous for two different abnormal hemoglobins and the clinical picture is variable. All these conditions together are labeled as the thalassemia syndromes.

¤ Beta thalassemia minor or thalassemia trait

These patients are either asymptomatic or have mild anemia and rarely moderate degree of anemia. Clinical examination is normal except for mild anemia. Usually patients are given iron and vitamin supplements to which they do not respond. The peripheral blood smear shows microcytosis, hypochromia, anisocytosis, poikilocytosis and target cells. Serum iron studies are normal, except in those who have coexisting iron deficiency - a condition not uncommon in our country. Diagnosis is made by hemoglobin electrophoresis which shows increase in Hb A2 to more than 3.5%. HbF is usually normal but may be elevated in some cases.

¤ Treatment

The condition usually requires no treatment. Folic acid supplements may help to prevent relative folate deficiency which may occur as a result of increased cell turnover. Though red cells are hypochromic and microcytic, they do not need iron. Unfortunately, this fact is ignored by many and results in injudicious prescription of hematinics containing iron to all who look pale or have anemia. Not only is this therapy of no use but it could lead to iron overload and its complications. Thus use of iron supplements is contraindicated unless there is coexisting iron deficiency. Iron supplements are required in pregnant women with beta thalassemia minor, but serum iron should be carefully monitored.
These patients should be educated about thalassemia major if they do not have a child suffering from the disease in their family. They should be told about means of preventing the birth of a thalassemia major baby i.e. by sceening the spouse of the affected patient and by prenatal diagnosis.


From:
Shah A. Thalassemia Syndromes. Indian J Med Sci [serial online] 2004 [cited 2006 May 18];58:445-449.