The molecular basis of beta-thalassemia in Thailand: application to prenatal diagnosis.

To enable the prenatal diagnosis of beta-thalassemia by direct detection of the mutant beta-globin genes, we have determined the spectrum of mutations causing this disease in Thailand. The techniques employed included a combination of synthetic oligonucleotide probe hybridization, direct sequencing of genomic DNA enzymatically amplified by the polymerase chain reaction, and cloning and sequencing of the beta-globin genes. A total of 116 beta-thalassemia genes from 78 Hb E/beta-thalassemia patients and from 19 homozygous beta-thalassemia patients were analyzed, and the mutation was characterized in 112/116 (97%) of them. Eleven mutations were found, of which four (-CTTT in codon 41/42, AAG----TAG in codon 17, C----T in position 654 of the IVS-2 region, and A----G in position -28 upstream of the beta-globin gene) accounted for 83%; two previously undescribed mutations have been identified. The spectrum of beta-thalassemia mutations is similar to that reported among the Chinese. However, within the Thai population itself, patients with homozygous beta-thalassemia show a wider spread of mutations in comparison with the Hb E/beta-thalassemia group, in whom the frameshift 41/42 mutation predominates at a frequency of 62%. This difference in distribution may reflect the difference in ethnic origin of the two groups. Characterization of these mutations should aid the planning of a prenatal diagnosis program for beta-thalassemia in Thailand.