Genotype-phenotype relationship of the delta-thalassemia and Hb A(2) variants: observation of 52 genotypes

The increase of Hb A(2) (?2?2) beyond the upper limit [2.0-2.2/3.3-3.4% of the total hemoglobin (Hb)] is an invaluable tool in the hematological screening of ?-thalassemia (?-thal) carriers. Factors decreasing Hb A(2) percentages can hinder correct diagnosis. In order to analyze the genotype-phenotype relationship, we characterized ?-, ?- and ?-globin genotypes in 190 families where the probands had Hb A(2) values of <=2.0% or were ?-thal heterozygotes with normal Hb A(2) levels. Hb A(2) was measured with cation exchange high performance liquid chromatography (HPLC). Mutations were detected with allele-specific methods or DNA sequencing; two multiplex-ARMS (amplification refractory mutation system) assays were set up. The molecular basis underlying the decrease in Hb A(2) was extremely heterogeneous. Nineteen ?-globin alleles (Hb A(2)-S.N. Garganico was new) were detected; their interaction with ?- or ?-globin alleles (10 and eight, respectively) led us to observe 52 genotypes in 261 carriers. The type of ?-globin mutations, the relative genotypes, the interaction with ?(0)-thal traits, are the most important factors in decreasing the Hb A(2) percentage. These results are extremely useful in addressing the molecular diagnosis of hemoglobinopathies and thalassemias.