Alpha thalassemia occurs when some or all of the 4 genes that make hemoglobin (the alphagobin genes) are missing or damaged.

There are 4 types of alpha thalassemia:

1. Alpha Thalassemia silent carrier.
2. Alpha Thalassemia carrier.
3. Hemoglobin H disease.
4. Alpha thalassemia major.

Persons with thalassemia minor have (at most) mild anemia (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 are iron deficient for other reasons).

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 (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 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 a significant illness.

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 (HbF). HbF 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 due to the profound anemia), bouts of fever, diarrhea, and other intestinal problems.