Prevalence and Geographical
Distribution:
Thalassemia is considered
the most common genetic disorder worldwide, about 3℅ of the world population
(150 million people) carry β-thalassemia genes and in Southeast Asia 5-10% of
the population carries genes for α-thalassemia (Honig, 2004).
According to ethnic group,
α-thalassemia trait is most prevalent in south East Asia,
affects 2.7% of American black newborns and less common in the Mediterranean
region. β-thalassemia occurs in 5% in certain areas of Italy, Greece,
Sardinia, India and 8% in American blacks (Weatherall,
2001).
Classification
of Thalassemias:
I. β-Thalassemia:
1-
β-thalassemia
minor (thalassemia trait): heterozygous β- thalassemia is associated with no
clinical abnormalities and may be mistaken for iron deficiency anemia.
2- β-thalassemia
major: heterozygous β-thalassemia in which there is defective formation of β chain.
There are 2 types:
a-
β° thalassemia: complete absence
of β chain.
b-
β+ thalassemia: β chain synthesis
is reduced.
3- β-thalassemia
intermedia: about 10℅ of heterozygous-thalassemia
have a syndrome of intermediate hematological severity. Those patients usually
have onset of anemia after 2 years of age and they do not require regular blood
transfusion.
4- IV.
β-thalassemia anemia: Avery mild form of β-thalassemia, which is discovered
accidentally during routine investigations.
5- Other
β-thalassemia syndromes: Hb-s-β-thalassemia, Hb-C-β-thalassemia and
Hb-D-β-thalassemia (Sturt and David, 1998).
II. α-Thalassemia:
In this group of thalassemia syndromes
there is decrease in α –chain synthesis due to decreased number of α globin
structure genes (Honig 2000).
III. Hereditary
persistence of fetal HB (HPFH):
No β or δ-chain synthesis. It is a group
of rare conditions characterized by continued synthesis of high levels of HbF
in adult life (Bunn and Forget, 1986).
Age of Presentation:
Patients with severe
β-thalassemia are usually diagnosed between 6 months and 2 years of age when
the physiological anemia of the newborn fails to improve. Occasionally, the
disease is not recognized until the age of 3 to 5 years because the infant is
able to partially compensate for the marrow inability to produce hemoglobin A
by prolonged production of HbF. On presentation affected infants usually have
pallor, poor growth and development and abdominal enlargement (Modell,
1984).
Sex:
Both sexes are equally
affected.
Dr.Nada Fathy
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