Delta-Beta-Thalassemia

Delta-beta-thalassemia is a form of beta-thalassemia (see this term) characterized by decreased or absent synthesis of the delta- and beta-globin chains with a compensatory increase in expression of fetal gamma-chain synthesis.

Epidemiology

Prevalence of this form is not known. The condition is found in many ethnic groups but is most common in Greece and Italy.

Clinical description

The heterozygous form of the condition is clinically asymptomatic with mild microcytosis and no elevation of HbA2 whereas the few homozygous patients have a mild clinical presentation. When inherited with heterozygous classical beta-thalassemia, patients usually have the thalassemia intermedia phenotype, but the thalassemia major phenotype has been described in some cases.

Etiology

Delta-beta-thalassemia is commonly caused by deletions of the entire delta and beta gene sequences with production of only gamma-globin and formation of HbF. Rarely, non-deletional forms have been reported.

Diagnostic methods

Diagnosis is based on hypochromic microcytic red cell indices with significant elevation of HbF, ranging from 5-15% in heterozygotes. HbF is heterogeneously distributed among the erythrocytes. The alpha/beta-globin synthesis ratio is >1.

Differential diagnosis

Hereditary persistence of fetal Hb and beta-thalassemia (see this term) is the main differential diagnosis. The distinction between these two conditions cannot always be made from routine hematologic analyses and alpha-beta-globin chain synthesis ratio and DNA analysis may be necessary.

Genetic counseling

Transmission is autosomal recessive.