G gamma beta+ hereditary persistence of fetal hemoglobin: cosmid cloning and identification of a specific mutation 5' to the G gamma gene.

Abstract

Hereditary persistence of fetal hemoglobin (HPFH) is a benign condition in which the normal shutoff of fetal hemoglobin (Hb F) production fails to occur. In the G gamma beta+ type of HPFH, erythrocytes of adult heterozygotes contain approximately equal to 20% Hb F, which is almost exclusively of the G gamma-globin variety, without increased levels of gamma-globin chains from the nearby A gamma-globin gene. Unlike some forms of HPFH, no major deletions in the globin gene cluster have been found by genomic blotting in the G gamma beta+ variety. We report here a family with this condition, from which cosmid clones of the beta-globin gene cluster from the G gamma beta+ HPFH allele have been obtained. Sequencing around the fetal genes has identified a point mutation 202 base pairs 5' to the G gamma-globin gene that is present in genomic DNA of 3/3 unrelated individuals with G gamma beta+ HPFH but in none of more than 100 non-HPFH individuals. Although the mutation could represent a tightly linked polymorphism, its location in a region suggested by recent data to be important in tissue-specific control of gene expression suggests the possibility that the -202 mutation accounts for the phenotype. The sequence created resembles elements of other eukaryotic promoters known to be important for efficient transcription.

A gene conversion located 5' to the A gamma gene in linkage disequilibrium with the Bantu haplotype in sickle cell anemia.

“…The 0T and AT genes from chromosome A are 85% homologous over a 5-kb region (1.5 kb upstream of the gene, 1.6 kb constituting (12), and (b) it is thought that the gene conversion that occurred 1 million years ago in chromosome A has its 3' boundary in this repeat (1 1). The novel TG repeat we described in the chromosome studied has the sequence (TG)jo(CG)3(TG)9, a sequence different from all others previously described (1 1 (9,(12)(13)(14)(15), but suggests that the regulatory sequences (in the absence of such mutations) that normally determine the ratio of expression between these two genes will have to be found elsewhere.…”

High Levels of Human γ-Globin Gene Expression in Adult Mice Carrying a Transgene of Deletion-Type Hereditary Persistence of Fetal Hemoglobin

“…The following human DNA fragments shown in Fig. 1B ␥ genes (GenBank Humhbb coordinates: 32820 to 45698) was purified from a cosmid clone containing the ␤ S -globin cluster described previously (8) and subcloned into the BamHI site of cosmid vector pWE15, which contained a modified polylinker. To construct the LCR G ␥ A ␥HPFH-2 transgene, a 12-kb BglII-HindIII genomic DNA fragment from a phage clone (B-1) containing the normal DNA overlapping the 3Ј breakpoint of HPFH-1 and HPFH-2 (42) was subcloned downstream of the 13-kb BglII genomic fragment containing the ␥-globin genes to yield a 25-kb DNA fragment whose structure is virtually identical to the structure of HPFH-2 DNA.…”

Control of globin gene expression during development and erythroid differentiation

“…The first clue came from Francis Collins and colleagues who, in 1983, found that a T-to-C substitution in position 175 of the G γ promoter underlies the G γ HPFH mutation they studied [38]. The second clue came from the study of the so-called Greek A γ HPFH [39].…”