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A considerable number of deletions of variable size and position that involve the beta-globin gene complex on chromosome 11 are associated with the clinical entities of hereditary persistence of fetal hemoglobin (HPFH) and delta beta thalassemia. Specific deletions appear to be associated with consistent phenotypes and some are known to be recurrent. To facilitate the molecular diagnosis of uncharacterized patients with HPFH and delta beta thalassemia, oligonucleotide primers have been designed to enzymatically amplify deletion-specific products for nine known deletions, which include those responsible for HPFH-1, HPFH-2, HPFH-3, Spanish (delta beta)zero thalassemia, hemoglobin (Hb) Lepore, Sicilian (delta beta)zero thalassemia, Chinese G gamma(A gamma delta beta)zero thalassemia, Asian-Indian inversion-deletion G gamma(A gamma delta beta)zero thalassemia, and Turkish inversion-deletion (delta beta)zero thalassemia. Using this approach, we have successfully characterized the molecular basis for delta beta thalassemia in 23 individuals from 16 families of diverse ethnic origins. Thirteen individuals from this group were shown to be heterozygous for the 13.4- kb Sicilian deletion, two were heterozygous for the 100-kb Chinese G gamma(A gamma delta beta)zero deletion, four were heterozygous for the Turkish form of inversion-deletion delta beta thalassemia, and three were heterozygous for the Asian-Indian form of inversion-deletion G gamma(A gamma delta beta)zero thalassemia. One Vietnamese subject was heterozygous for a 12.6-kb deletion, which we have fully characterized at the molecular level. Sequence analysis of the breakpoint regions of the Chinese deletion and the Turkish rearrangement indicates that, in each case, the mutation is likely to have arisen from a single origin. This hypothesis is supported by the evident geographical clustering of the various deletions described here.