back to the list

Beta-Thalassemia - HBB

Clinical Features

In beta-thalassemia, synthesis of the hemoglobin beta chain is reduced or abolished. The compensatory production of gamma or delta chains results in elevated levels of HbF and HbA2, depending on the patients age and the subtype of beta-thalassemia. According to the severity of clinical symptoms, there are different types of beta-thalassemia.

Beta-thalassemia minima and minor:
No or mild symptoms, clinically not relevant anemia (Hb>10g/dl), maybe iron-refractive hypochromia and microcytosis.

Beta-thalassemia intermedia or maior:
Moderate to severe anemia with (hepato-) splenomegaly, hypersiderinemia and mostly a considerably elevated fraction of HbA2 and eventually HbF in Hb electrophoresis.

Genetic Information

The different degrees of severity of beta-thalassemia are caused by different mutations in the HBB gene (hemoglobin-beta locus) on chromosome 11p15.5 and by the number of mutated alleles. In the less severe forms one allel is mutated. These are therefore often regarded as "carrier forms" of the disease.
In the severe types of beta-thalassemia, genetic defects of varying severity are found on both alleles. Thus, the severe types are inherited in an autosomal recessive manner.
Sickle cell anemia is also caused by a mutation in the HBB gene (see below).

Prevalence

Each population has its own disease prevalence and its own spectrum of mutations. Knowledge on the ethnic origin of affected individuals is therefore highly relevant for genetic testing.

Diagnostic