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

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.

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.

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.

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.

Transmission is autosomal recessive.