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What are the thalassemias?

The thalassemias are a group of genetic (inherited) blood disorders that share in common one feature, the defective production of hemoglobin, the protein that enables red blood cells to carry oxygen (and carbon dioxide). There are many different disorders with defective hemoglobin synthesis and, hence, many types of thalassemia.

What is beta thalassemia?

The most familiar type of thalassemia is beta thalassemia. It involves decreased production of normal adult hemoglobin (Hb A), the predominant type of hemoglobin from soon after birth until death. (All hemoglobin consists of two parts: heme and globin). The globin part of Hb A has 4 protein sections called polypeptide chains. Two of these chains are identical and are designated the alpha chains. The other two chains are also identical to one another but differ from the alpha chains and are termed the beta chains. In persons with beta thalassemia, there is reduced or absent production of beta globin chains.

What is the difference between thalassemia minor and major?

There are two forms of beta thalassemia. They are thalassemia minor and thalassemia major (which is also called Cooley's anemia).

Thalassemia minor: The individual with thalassemia minor has only one copy of the beta thalassemia gene (together with one perfectly normal beta-chain gene). The person is said to be heterozygous for beta thalassemia.

Persons with thalassemia minor have (at most) mild anemia (with slight lowering of the hemoglobin level in the blood). This situation can very closely resemble that with mild iron-deficiency anemia. However, persons with thalassemia minor have a normal blood iron level (unless they have are iron deficient for other reasons). No treatment is necessary for thalassemia minor. In particular, iron is neither necessary nor advised.

Thalassemia major (Cooley's anemia): The child born with thalassemia major has two genes for beta thalassemia and no normal beta-chain gene. The child is homozygous for beta thalassemia. This causes a striking deficiency in beta chain production and in the production of Hb A. Thalassemia major is, therefore, a serious disease.

The clinical picture associated with thalassemia major was first described in 1925 by the American pediatrician Thomas Cooley. Hence, the name Cooley's anemia in his honor.

At birth the baby with thalassemia major seems entirely normal. This is because the predominant hemoglobin at birth is still fetal hemoglobin (Hb F). Hb F has two alpha chains (like Hb A) and two gamma chains (unlike Hb A). It has no beta chains so the baby is protected at birth from the effects of thalassemia major.

Anemia begins to develop within the first months after birth. It becomes progressively more and more severe. The infant fails to thrive (to grow normally) and often has problems feeding (due to easy fatigue from lack of oxygen, with the profound anemia), bouts of fever (due to infections to which the severe anemia predisposes the child) and diarrhea and other intestinal problems.