Association of Variants at BCL11A and HBS1L-MYB with Hemoglobin F and Hospitalization Rates among Sickle Cell Patients in Cameroon

Abstract

BackgroundGenetic variation at loci influencing adult levels of HbF have been shown to modify the clinical course of sickle cell disease (SCD). Data on this important aspect of SCD have not yet been reported from West Africa. We investigated the relationship between HbF levels and the relevant genetic loci in 610 patients with SCD (98% HbSS homozygotes) from Cameroon, and compared the results to a well-characterized African-American cohort.Methods and FindingsSocio-demographic and clinical features were collected and medical records reviewed. Only patients >5 years old, who had not received a blood transfusion or treatment with hydroxyurea were included. Hemoglobin electrophoresis and a full blood count were conducted upon arrival at the hospital. RFLP-PCR was used to describe the HBB gene haplotypes. SNaPshot PCR, Capillary electrophoresis and cycle sequencing were used for the genotyping of 10 selected SNPs. Genetic analysis was performed with PLINK software and statistical models in the statistical package R. Allele frequencies of relevant variants at BCL11A were similar to those detected in African Americans; although the relationships with Hb F were significant (p <.001), they explained substantially less of the variance in HbF than was observed among African Americans (∼ 2% vs 10%). SNPs in HBS1L-MYB region (HMIP) likewise had a significant impact on HbF, however, we did not find an association between HbF and the variations in HBB cluster and OR51B5/6 locus on chromosome 11p, due in part to the virtual absence of the Senegal and Indian Arab haplotypes. We also found evidence that selected SNPs in HBS1L-MYB region (HMIP) and BCL11A affect both other hematological indices and rates of hospitalization.ConclusionsThis study has confirmed the associations of SNPs in BCL11A and HBS1L-MYB and fetal haemoglobin in Cameroonian SCA patients; hematological indices and hospitalization rates were also associated with specific allelic variants.

Genetics of Sickle Cell-Associated Cardiovascular Disease: An Expert Review with Lessons Learned in Africa

“…Fetal hemoglobin (HbF) is another genetic factor that has been shown to decrease stroke risk in both Nigerian and African-American cohorts (Table 1) and ameliorate the clinical phenotype of SCD (Enosolease et al, 2005;Fatunde and Scott-Emuakpor, 1992;Platt et al, 1991;Yetunde and Anyaegbu, 2001). HbF levels vary between 1% and 30% in SCD patients, and three genetic loci describe *20% of this variation; BCL11A, HBS1L-MYB, and the HBB cluster (Lettre et al, 2008;Wonkam et al, 2014;Xu et al, 2010). There is a further association with b-globin gene haplotypes (Powars et al, 1990) with the Indian-Arab and Senegal haplotypes associated with milder severity in comparison with the Benin, Bantu, and Cameroon haplotypes, which are associated with lower HbF and more severe clinical manifestations (Diagne et al, 2000;Diop et al, 1999).…”

Burden, genotype and phenotype profiles of adult patients with sickle cell disease in Cape Town, South Africa

“…Using a reported method, [9] SNaPshot genotyping, capillary electrophoresis and direct cycle sequencing were used to assay five selected HbF-associated variants: rs8176703, rs372091, rs2334880, rs1427407 and rs7606173. In addition, 18 other variants were analysed using the iPLEX Gold Sequenom Mass Genotyping Array (Inqaba Biotec, SA): X12_123681790, X16_391593, rs10468869, rs10756993, rs113267280, rs11754265, rs141494605, rs148706947, rs183437571, rs192197462, rs570013781, rs59329875, rs62573842, rs6466533, rs6590706, rs67104793, rs7163278 and rs76901220.…”

“…Variants at three principal loci, BCL11A, HBS1L-MYB intergenic polymorphism and the β-globin haplotype, have been shown to account for 10 -20% of the variance of fetal haemoglobin (HbF) levels and to be associated with the amelioration of SCD symptoms. [8][9][10] Other variants in the BCL11A erythroid-specific enhancer (rs1427407 and rs7606173) have been shown to account for 8% and 6.2% of HbF variance, respectively, among SCD patient cohorts in the USA, [11,12] Tanzania [13] and Cameroon. [14] The co-inheritance of α-thalassaemia has also been associated with improved clinical manifestations of SCD.…”

“…The number of annual vasoocclusive crises was similar to that reported in Cameroon, as was the mean number of vaso-occlusive crises per year. [9] Major challenges faced by healthcare professionals at GSH were patient compliance with HU treatment, compliance with supportive medication such as folic acid and patient clinic attendance. There were several barriers to HU treatment, including the financial implications of taking time off work to attend the clinic and receive it (maximum one month's supply), and misconceptions about the treatment and its possible carcinogenic effects, as well as potential impotence in male patients.…”

“…[28] Published primers and methods [29] genotyping five restriction fragment length polymorphic regions in the β-globin gene cluster were used to analyse XmnI (5ʹGγ), HindIII (Gγ), HindIII (Aγ), HincII (3˙ʹΨβ) and HinfI (5ʹβ) to determine the β-globin haplotype background. [19] Single-nucleotide polymorphisms (SNPs)Using a reported method, [9] SNaPshot genotyping, capillary electrophoresis and direct cycle sequencing were used to assay five selected HbF-associated variants: rs8176703, rs372091, rs2334880, rs1427407 and rs7606173. In addition, 18 other variants were analysed using the iPLEX Gold Sequenom Mass Genotyping Array (Inqaba Biotec, SA): X12_123681790, X16_391593, rs10468869, rs10756993, rs113267280, rs11754265, rs141494605, rs148706947, rs183437571, rs192197462, rs570013781, rs59329875, rs62573842, rs6466533, rs6590706, rs67104793, rs7163278 and rs76901220.…”