Beta Thalassemia
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.
Next: What is Mediterranean anemia? »
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