Résumé
In the present study we report the sequence haplotypes associated with 22 β-globin gene mutations present in Turkey. Nine nucleotide polymorphisms and an (AT)xTy motif located at the 5' end of the β-globin gene form the sequence haplotypes that were investigated in 204 unrelated β-thalassemia and wild-type chromosomes from Turkey. Twelve sequence haplotypes were observed in the chromosomes analyzed and haplotypic heterogeneity was found in the wild-type β-globin genes. Samples from the Black Sea region demonstrated a remarkable level of haplotypic heterogeneity in contrast to the homogeneity present in Central Anatolian samples. Of the 22 β-globin mutations analyzed, 18 were related with single sequence haplotypes. This simple association led to the attempt to determine the origin of these mutations by comparing their frequencies in Turkey with those in other countries and/or the world distribution of the haplotypes carrying them. However, the presence of several exceptions for the "one haplotype/one mutation" rule showed that the β-globin gene cluster is far from static. Each of the IVS-I-110 (G→A), Cd 39 (C→T), IVS-I-6 (T→C), and -30 (T→A) β-globin mutations was associated with a minimum of two sequence haplotypes. This fact is best explained by the likelihood of strong recombination mechanisms taking place, rather than by assuming multiple origins for each of these alíeles. According to our results, malarial selection for the oldest β-thalassemia alíele in Anatolia (i. e., IVS-I-110 G→> A) may have occurred between 6500 and 2000 B. C. From that date on, most of the common -thalassemia mutations in Turkey were established, and by the 13th century A. D. most of them were brought to frequencies close to those observed at present.