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beta-Thalassemia is a hereditary disease caused by any of 90 different point mutations in the beta-globin gene. Specific populations generally carry a small number of mutations, the most common of which are those that are widely distributed regionally. The present study constitutes an extensive molecular characterization of this disease in a small, highly inbred ethnic group with a high incidence of beta-thalassemia--the Jews of Kurdistan. An unusual mutational diversity was observed. In 42 sibships 13 different mutations were identified, of which 3 are newly discovered: a C----A transversion at -88 to the cap site, a frameshift in codon 36/37, and an A----G transition in the polyadenylylation signal. Four of the mutations are unique to Kurdish Jews and have not been discovered in any other population. A fifth was found outside Kurdish Jews only in an Iranian from Khuzistan, a region bordering Kurdistan. Two-thirds of the mutant chromosomes carry the mutations unique to Kurdish Jews. We traced the origin of the mutations to specific geographic regions within Kurdistan. This information, supported by haplotype analysis, suggests that thalassemia in central Kurdistan (northern Iraq) has evolved primarily from multiple mutational events. In Turkish Kurdistan, the primary mechanism is genetic admixture with the local population. In Iranian Kurdistan, a founder effect appears to be partly responsible. We conclude that several evolutionary mechanisms contributed to the evolution of beta-thalassemia in this small ethnic isolate.

We recently described a "non-random" sequencing procedure for DNA inserts in bacteriophage M13 using Bal 3 nuclease and the dideoxy chain termination method (Poncz, M., Solowiejczyk, D., Ballantine, M., Schwartz, E., and Surrey, S. (1982) Proc. Natl. Acad. Sci. U. S. A., in press). Using this procedure, we have determined the nucleotide sequence of a cloned human beta-globin gene from a Kurdish Jew with beta +-thalassemia major. Comparison with the previously reported human beta-globin gene sequences (1-3) reveals a change in the "T-A-T-A" box. This region 5' to the capping site was previously demonstrated to be critical for the proper transcription in vitro of several different eukaryotic genes (4-7). This is the first report of a T-A-T-A box modification found in association with a spontaneously occurring human genetic disorder. In addition to this mutation, other base changes, an insertion, and a deletion in the cloned gene were found in the 5' and 3' flanking regions.