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Evidence of genetic interaction between the beta-globin complex and chromosome 8q in the expression of fetal hemoglobin.

ABSTRACT: During human development, the switch from fetal to adult hemoglobin (Hb) is not complete with the residual gamma-globin expression being restricted to a subset of erythrocytes termed "F cells" (FC). Statistical analyses have shown the FC trait to be influenced by a common sequence variant (C-->T) at position -158 upstream of the Ggamma-globin gene, termed the "XmnI-Ggamma polymorphism." The XmnI-Ggamma site is believed to be involved in the expression of the Ggamma-globin gene through interaction with transcription factors, and polymorphisms in the transcription factors could be influencing fetal Hb expression, conditional on the XmnI-Ggamma site. Using a two-locus model, in which the second locus was the known quantitative-trait locus (QTL) at the XmnI-Ggamma site, we showed suggestive linkage to chromosome 8q. A maximum single-point LOD score of 4.33 and a multipoint LOD score of 4.75 were found in a 15-20 cM region of chromosome 8q. A single-locus analysis failed to show linkage of FC to the region when the XmnI-Ggamma site was accounted for by removing its effects from the data or including it as a covariate. Results of the single-locus analysis were significant when the effects of the XmnI-Ggamma site were not accounted for in any way. The results of analysis in a large Indian kindred indicate that there is an interaction between the XmnI-Ggamma site and a QTL on chromosome 8q that is influencing the production of fetal Hb.

SUBMITTER: Garner CP

PROVIDER: S-EPMC384958 | biostudies-literature | 2002 Mar

REPOSITORIES: biostudies-literature

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Evidence of genetic interaction between the beta-globin complex and chromosome 8q in the expression of fetal hemoglobin.

Garner Chad P CP Tatu Thanusak T Best Steve S Creary Lisa L Thein Swee Lay SL

American journal of human genetics 20020130 3

During human development, the switch from fetal to adult hemoglobin (Hb) is not complete with the residual gamma-globin expression being restricted to a subset of erythrocytes termed "F cells" (FC). Statistical analyses have shown the FC trait to be influenced by a common sequence variant (C-->T) at position -158 upstream of the Ggamma-globin gene, termed the "XmnI-Ggamma polymorphism." The XmnI-Ggamma site is believed to be involved in the expression of the Ggamma-globin gene through interactio ...[more]

PMID: 11822023

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Project description:Fetal hemoglobin is a major genetic modifier of the phenotypic heterogeneity in patients with sickle cell disease and certain β-thalassemias. Normal levels of fetal hemoglobin postnatally are approximately 1% of total hemoglobin. Patients who have hereditary persistence of fetal hemoglobin, characterized by elevated synthesis of γ-globin in adulthood, show reduced disease pathophysiology. Hereditary persistence of fetal hemoglobin is caused by β-globin locus deletions (deletional hereditary persistence of fetal hemoglobin) or γ-globin gene promoter point mutations (non-deletional hereditary persistence of fetal hemoglobin). Current research has focused on elucidating the pathways involved in the maintenance/reactivation of γ-globin in adult life. To better understand these pathways, we generated new β-globin locus yeast artificial chromosome transgenic mice bearing the (A)γ-globin -175 T > C or -195 C > G hereditary persistence of fetal hemoglobin mutations to model naturally occurring hereditary persistence of fetal hemoglobin. Adult -175 and -195 mutant β-YAC mice displayed a hereditary persistence of fetal hemoglobin phenotype, as measured at the mRNA and protein levels. The molecular basis for these phenotypes was examined by chromatin immunoprecipitation of transcription factor/co-factor binding, including YY1, PAX1, TAL1, LMO2, and LDB1. In -175 HPFH versus wild-type samples, the occupancy of LMO2, TAL1 and LDB1 proteins was enriched in HPFH mice (5.8-fold, 5.2-fold and 2.7-fold, respectively), a result that concurs with a recent study in cell lines showing that these proteins form a complex with GATA-1 to mediate long-range interactions between the locus control region and the (A)γ-globin gene. Both hereditary persistence of fetal hemoglobin mutations result in a gain of (A)γ-globin activation, in contrast to other hereditary persistence of fetal hemoglobin mutations that result in a loss of repression. The mice provide additional tools to study γ-globin gene expression and may reveal new targets for selectively activating fetal hemoglobin.

Project description:Increase of the expression of ?-globin gene and high production of fetal hemoglobin (HbF) in ?-thalassemia patients is widely accepted as associated with a milder or even asymptomatic disease. The search for HbF-associated polymorphisms (such as the XmnI, BCL11A and MYB polymorphisms) has recently gained great attention, in order to stratify ?-thalassemia patients with respect to expectancy of the first transfusion, need for annual intake of blood, response to HbF inducers (the most studied of which is hydroxyurea).A?-globin gene sequencing was performed on genomic DNA isolated from a total of 75 ?-thalassemia patients, including 31 ?039/?039, 33 ?039/?+IVSI-110, 9 ?+IVSI-110/?+IVSI-110, one ?0IVSI-1/?+IVSI-6 and one ?039/?+IVSI-6.The results show that the rs368698783 polymorphism is present in ?-thalassemia patients in the 5'UTR sequence (+25) of the A?-globin gene, known to affect the LYAR (human homologue of mouse Ly-1 antibody reactive clone) binding site 5'-GGTTAT-3'. This A?(+25 G->A) polymorphism is associated with the G?-globin-XmnI polymorphism and both are linked with the ?039-globin gene, but not with the ?+IVSI-110-globin gene. In agreement with the expectation that this mutation alters the LYAR binding activity, we found that the A?(+25 G->A) and G?-globin-XmnI polymorphisms are associated with high HbF in erythroid precursor cells isolated from ?039/?039 thalassemia patients.As a potential explanation of our findings, we hypothesize that in ?-thalassemia the G?-globin-XmnI/A?-globin-(G->A) genotype is frequently under genetic linkage with ?0-thalassemia mutations, but not with the ?+-thalassemia mutation here studied (i.e. ?+IVSI-110) and that this genetic combination has been selected within the population of ?0-thalassemia patients, due to functional association with high HbF. Here we describe the characterization of the rs368698783 (+25 G->A) polymorphism of the A?-globin gene associated in ?039 thalassemia patients with high HbF in erythroid precursor cells.

Dataset Information

Evidence of genetic interaction between the beta-globin complex and chromosome 8q in the expression of fetal hemoglobin.

Publications

Evidence of genetic interaction between the beta-globin complex and chromosome 8q in the expression of fetal hemoglobin.

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