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standard risk factors

Symptoms and Signs

Clinical features of thalassemias are similar but vary in severity depending on the amount of normal hemoglobin present.

Alpha-thalassemia

Patients with a single alpha + allele (alpha/alpha;alpha/–) are clinically normal and are called silent carriers.

Heterozygotes with defects in 2 of the 4 genes such as two alpha + alleles (alpha/–;alpha/–) or one alpha 0 allele (alpha/alpha;–/–) tend to develop mild to moderate microcytic anemia but no symptoms. These patients have alpha-thalassemia trait.

Defects in 3 of the 4 genes caused by coinheritance of both alpha + and alpha 0 (alpha/–;–/–) severely impair alpha-chain production. This results in the formation of tetramers of excess beta-chains termed Hb H or, in infancy, gamma-chains termed Bart’s hemoglobin. Patients with Hb H disease often have symptomatic hemolytic anemia and splenomegaly.

Defects in all 4 genes via two alpha 0 alleles (–/–;–/–) is a lethal condition in utero (hydrops fetalis), because hemoglobin that lacks alpha chains does not transport oxygen.

Beta-thalassemia

In beta-thalassemia, clinical phenotypes are classified into 3 groups based on the degree to which beta globin production is impaired:

  • Minor (or trait)
  • Intermedia
  • Major

Beta-thalassemia minor (trait) occurs in heterozygotes (beta/beta + or beta/beta 0), who are usually asymptomatic with mild to moderate microcytic anemia. This phenotype may also occur in mild cases of beta +/beta +.