Haplotype analysis andAγ gene polymorphism associated with the Brazilian type of hereditary persistence of fetal hemoglobin

We have identified three unrelated individuals and three members of a family with the non-deletion form of Agamma-hereditary persistence of fetal hemoglobin (HPFH). Molecular analysis showed that each individual is a heterozygote for a previously described -195 Agamma (C-->G) mutation. The beta-globin gene cluster was studied using the polymerase chain reaction and related techniques. Haplotyping using nine restriction sites identified two closely related chromosomes with the -195Agamma mutation, differing only in a single site 3' to the beta-globin gene. Further analysis of beta-globin framework indicated that the HPFH allele segregates with haplotype V, according to Orkin's classification. The second haplotype probably originated by a point mutation or DNA rearrangement of a pre-existing -195Agamma chromosome. We also determined the sequences from -622 to +55 bp upstream to the Agamma gene and part of the Agamma IVS-2. We found four polymorphisms associated to the -195Agamma promoter region. All -195Agamma chromosomes had a G at positions -588 and +25 relative to the Agamma gene. One individual was also homozygous for polymorphisms at -398 (G-->A), and another at -369 (C-->G). Cloning and sequencing of the polymorphic patterns of the 3' region of Agamma IVS-2 showed that the mutated allele is linked to beta-globin chromosome B. Some correlations between chromosome characteristics and Agamma point mutations were also observed.