Characterization of nondeletion alpha-thalassemia mutations in the Greek population.

alpha-Thalassemia is usually due to deletions within the alpha-globin gene cluster, leading to loss of function of one (-alpha) or both [-(alpha) or --] alpha-globin genes. Nondeletion mutations (denoted alpha alpha T or alpha T alpha) are less frequent and in Greece are not well defined. We report the analysis of 16 nondeletion alpha-thalassemia chromosomes using a polymerase chain reaction method to amplify specifically the alpha 2-globin gene, which was subsequently screened using ASO hybridization or restriction enzyme analysis for four mutations already characterized in other Mediterranean and Middle Eastern populations. Of the 16 nondeletion chromosomes, nine had the polyadenylation signal mutation (alpha PolyA alpha), two the IVSI 5' pentanucleotide deletion (alpha Hph alpha), two the Hb Icaria mutation (alpha Ic alpha), and one the initiation codon mutation (alpha Nco alpha). In two, the defects are still undefined. These findings show that nondeletion alpha-thalassemia in Greece is heterogeneous and that the most frequent mutation (accounting for > 50%) is the polyadenylation signal mutation, which to date was most commonly found in the Saudi Arabian population.