βthalassehia mutations in the portuguese; high frequencies of two alleles in restricted populations

We report the characterization of seven different βthalassemia mutations in 131 newly diagnosed Portuguese βthalassemia heterozygotes. Methodology included the detection of abnormal fragments by agar gel electrophoresis of PCR-amplified DNA fragments after digestion with specific restriction endonucleases, as well as hybridization with synthetic nucleotide probes and sequencing of amplified DNA. Four mutations, including the newly discovered TGG→TGA change at codon 15, occurred in excess of 10% and accounted for some 90% of the βthalassemia alleles in this population. The geographical distribution is uneven; the TGA→TGA mutation at codon 15 was primarily observed in the coastal region north of Lisbon, while the IVS-1-6 (T→C) mutation was confined to the central part of the country.