RESUMO
Polymerase chain reaction-based techniques were used to study the molecular defects of 480 unrelated beta-thalassemia heterozygotes in Taiwan. Analysis of artificially created restriction sites and gap-polymerase chain reaction were performed to detect four common mutations, i.e. IVS-II-654 (C-->T), codons 41/42 (-TCTT), codon 17 (A-->T), -28 (A-->G), and a deletional form of delta beta-thalassemia in the Chinese population. In cases with negative or ambiguous results with the aforementioned methods, direct DNA cycle sequencing using either S35-dATP or a fluorescent dye terminator, was carried out to determine the defects. A total of 14 different mutations have been found in this series. The IVS-II-654 mutation was the most common (39.6%), followed by the codons 41/42 mutation (37.9%). The four common genotypes accounted for 92.3% of defects. Two new mutations were detected: codon 31 (-C) and codons 40/41 (+T). Both defects resulted in a frameshift and a premature terminator, the former at codon 60, the latter at codon 43. Although we have studied our cases extensively, the molecular defects in seven alleles are still unknown.