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At a glance

The thalassemias are a group of chronic microcytic hemolytic anemias, and the most common hematological genetic disorder affecting more than 200 million people worldwide. Clinical features include hepatosplenomegaly, bone deformations, and cardiac failure. Strict asepsis is needed. Heterous carriers (thalassemia trait) of the disease appear to be protected against Plasmodium falciparum.

Classification

  • α-Thalassemia (Alpha Thalassemia): It is due to impaired production of alpha chains from 1, 2, 3, or all 4 of the alpha globin genes, leading to a relative excess of beta globin chains. It is commonly found in Africa, the Middle East, India, Southeast Asia, southern China, and occasionally the Mediterranean region.

  • β-Thalassemia (Beta Thalassemia): Caused by mutations in the HBB gene on chromosome 11. It is inherited as autosomal recessive. The estimated global incidence is established as 1: 100,000. It is found in people of Mediterranean descent, such as Italians and Greeks, and is also found in the Arabian Peninsula, Iran, Africa, Southeast Asia and southern China.

  • Thalassemia Minor (Thalassemia Trait): The lack of beta protein is minimal and is not associated with problems in the normal functioning of the hemoglobin.

  • Thalassemia Intermedia: Clinically associated with moderate to severe anemia, causing significant health affected individual need blood transfusions to improve quality of life but not require to survive.

  • Cooley Anemia (β-Thalassemia Homozygote; Thalassemia Major): Most severe form caused by the complete absence of beta protein in the hemoglobin. Clinically characterized by life-threatening anemia requiring regular blood transfusions. Life expectancy reduces as a result of iron overload (from transfusions) and organ failure.

Incidence

Great geographic variability (β-thalassemia mainly in populations of Mediterranean origin: Greece, Turkey, North Africa, Middle East, Italy; α-thalassemia mainly in Southeast Asia and black population).

Genetic inheritance

Autosomal dominant except for major thalassemia, which is autosomal recessive.

Pathophysiology

The disease affects synthesis of either α (gene located at 16p13.33-16p13.11) or β chain (gene located at 11p15.5) of the hemoglobin.

Diagnosis

Hemoglobin synthesis normally provides a just balance between the three different major chains α, β, and γ. After birth, the following hemoglobin variants are normally present: hemoglobin A (α2β2), which is the most common combination with a normal amount over 95%, hemoglobin A2 (α2δ2) with a normal amount of 1.5 to 3.5% (the δ chain synthesis begins late in the third trimester) and hemoglobin F (α2γ2). Thalassemia modifies this status quantitatively and leads to abnormal combinations of tetramers such as β chain (hemoglobin H) and γ chain (hemoglobin Barts). Those allow quantifying of the severity of the thalassemia. Fetal hemoglobin, which disappears within a few months after birth by substitution with HbA, will also be higher. This is a quantitative deficit ...

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