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A survey of genetic fetal-haemoglobin modifiers in Nigerian patients with sickle cell anaemia.

ABSTRACT: Genetic variants at three quantitative trait loci (QTL) for fetal haemoglobin (HbF), BCL11A, HBS1L-MYB and the ?-globin gene cluster, have attracted interest as potential targets of therapeutic strategies for HbF reactivation in sickle cell anaemia (SCA). We carried out the first systematic evaluation of critical single nucleotide polymorphisms at these disease modifier loci in Nigerian patients with SCA. Common variants for BCL11A and HBS1L-MYB were strongly associated with HbF levels. At both loci, secondary association signals were detected, illustrating the mapping resolution attainable in this population. For BCL11A, the two independent sites of association were represented by rs1427407 (primary site, p = 7.0 x 10(-10)) and rs6545816 (secondary site, conditioned on rs1427407: p = 0.02) and for HBS1L-MYB by rs9402686 (HMIP-2B, p = 1.23 x 10(-4)) and rs66650371 (HMIP-2A, p = 0.002). Haplotype analysis revealed similarities in the genetic architecture of BCL11A and HBS1L-MYB in Nigerian patients. Variants at both loci also alleviated anaemia. The variant allele for the ? globin gene promoter polymorphism XmnI-HBG2 was too infrequent in our patients to be evaluated in this relatively small study. Studying the large and diverse SCA patient populations in African countries such as Nigeria will be key for a clearer understanding of how these loci work and for the discovery of new disease modifier genes.

SUBMITTER: Adeyemo TA

PROVIDER: S-EPMC5991720 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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A survey of genetic fetal-haemoglobin modifiers in Nigerian patients with sickle cell anaemia.

Adeyemo Titilope A TA Ojewunmi Oyesola O OO Oyetunji Idat A IA Rooks Helen H Rees David C DC Akinsulie Adebola O AO Akanmu Alani S AS Thein Swee Lay SL Menzel Stephan S

PloS one 20180607 6

Genetic variants at three quantitative trait loci (QTL) for fetal haemoglobin (HbF), BCL11A, HBS1L-MYB and the β-globin gene cluster, have attracted interest as potential targets of therapeutic strategies for HbF reactivation in sickle cell anaemia (SCA). We carried out the first systematic evaluation of critical single nucleotide polymorphisms at these disease modifier loci in Nigerian patients with SCA. Common variants for BCL11A and HBS1L-MYB were strongly associated with HbF levels. At both ...[more]

PMID: 29879141

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Project description:BackgroundSickle cell anemia (SCA) is a clinically heterogeneous, monogenic disorder. Medical care has less-than-optimal impact on clinical outcomes in SCA in Africa due to several factors, including patient accessibility, poor access to resources, and non-availability of specific effective interventions for SCA.MethodsAgainst this background, we investigated 192 African participants who underwent whole exome sequencing. Participants included 105 SCA patients spanning variable clinical expression: a "long survivor" group (age over 40 years), a "stroke" group (at least one episode of overt stroke), and a "random" group (patients younger than 40 years without overt cerebrovascular disease). Fifty-eight ethnically matched homozygous hemoglobin A controls were also studied. Findings were validated in an independently recruited sample of 29 SCA patients. Statistical significance of the mutational burden of deleterious and loss-of-function variants per gene against a null model was estimated for each group, and gene-set association tests were conducted to test differences between groups.ResultsIn the "long survivor" group, deleterious/loss-of-function variants were enriched in genes including CLCN6 (a voltage-dependent chloride channel for which rare deleterious variants have been associated with lower blood pressure) and OGHDL (important in arginine metabolism, which is a therapeutic target in SCA). In the "stroke" group, significant genes implicated were associated with increased activity of the blood coagulation cascade and increased complement activation, for example, SERPINC1, which encodes antithrombin. Oxidative stress and glutamate biosynthesis pathways were enriched in "long survivors" group. Published transcriptomic evidence provides functional support for the role of the identified pathways.ConclusionsThis study provides new gene sets that contribute to variability in clinical expression of SCA. Identified genes and pathways suggest new avenues for other interventions.

Project description:Sickle cell anemia is caused by a single type of mutation, a homozygous A?T substitution in the ß globin gene. Clinical severity is diverse, partially due to additional, disease-modifying genetic factors. We are studying one such modifier locus, HMIP (HBS1L-MYB intergenic polymorphism, chromosome 6q23.3). Working with a genetically admixed patient population, we have encountered the necessity to generate haplotype signatures of genetic markers to label genomic fragments with distinct genealogical origin at this locus. With the goal to generate haplotype signatures from patients experimentally, we have investigated the suitability of an existing nanofluidic assay platform to perform phase alignment with single-nucleotide polymorphism alleles.Patient DNA samples were loaded onto Fluidigm Digital Arrays and individual DNA molecules were assayed with allele-specific probes for SNP markers. Here we present data showing the utility of the nanofluidic approach, yielding haplotype data identical to those obtained with a family-based method. We then determined haplotype composition in a group of patients with sickle cell disease, including in those where a mathematical inference approach gave ambiguous or misleading results. Experimental phasing of genotypes across 3.8 kb for rs9399137, rs9402685, and rs11759553 created unequivocal haplotype signatures for each of the patients. In 68 patients, we found 8 copies of a haplotype signature ('C-C-T'), which is known to be prevalent in Europeans but to be absent in West African populations. We have confirmed the identity of our phased allele pairs by single-molecule sequencing and have demonstrated, in principle, that three-allele phasing (using three colors) is a potential extension to this method.Phased haplotypes yield more information than the individual marker genotypes. Procedures such as the one described here would therefore benefit genetic mapping and functional studies as well as diagnostic procedures where the identity or parental origin of short genetic fragments is of importance.

Dataset Information

A survey of genetic fetal-haemoglobin modifiers in Nigerian patients with sickle cell anaemia.

Publications

A survey of genetic fetal-haemoglobin modifiers in Nigerian patients with sickle cell anaemia.

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