Mild and severe beta-thalassemia among homozygotes from Turkey: identification of the types by hybridization of amplified DNA with synthetic probes.

Through the procedure of gene amplification combined with hybridization to synthetic 19 base pair (bp) oligonucleotide probes, it has been possible to identify nine different mutations in the DNA of 47 subjects from Turkey and Northern Cyprus with a beta-thalassemia homozygosity. The IVS-I nucleotide (nt) 110 G----A and the IVS-I nt 6 T----C substitutions and the frameshift at codon 8 were most frequently observed. Direct correlations were made between these data and clinical observations; mild disease was associated with homozygosity for IVS-I nt 6 T----C, for frameshift at codon 8, for the C----G substitution at nt -87, and for IVS-I nt 5 G----T, and for a double heterozygosity for some of these conditions. Moderate disease, observed in some of the patients, could be explained by combinations of specific mutations. All mutations were associated with specific haplotypes, while in some the observed beta zero-thalassemia was of the mild type due to a considerable production of Hb F.