Meta-analysis of 2040 sickle cell anemia patients: BCL11A and HBS1L-MYB are the major modifiers of HbF in African Americans

0.2% of African-Americans have sickle cell anemia while, with 8% to 10% have sickle cell trait. This chapter provides an overiew of the etiology, pathophysiology, and treatment of sickle cell anemia as they affect anesthetic management—before, during, and after surgery.

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Association of Sickle Cell Trait with Risk of Coronary Heart Disease in African Americans

Blood ◽

10.1182/blood.v128.22.11.11 ◽

2016 ◽

Vol 128 (22) ◽

pp. 11-11 ◽

Cited By ~ 2

Author(s):

Hyacinth I Hyacinth ◽

Carty L Cara ◽

Samantha R Seals ◽

Marguerite R. Irvin ◽

Rakhi P. Naik ◽

...

Keyword(s):

Risk Factors ◽

Coronary Heart Disease ◽

Heart Disease ◽

African Americans ◽

Sickle Cell ◽

Sickle Cell Trait ◽

Meta Analysis ◽

Significant Heterogeneity ◽

Crude Incidence Rate ◽

Crude Incidence

Abstract Background The incidence of and mortality from coronary heart disease (CHD) is significantly higher among African Americans (AAs) compared to Whites, even after adjusting for traditional CHD risk factors. Studies suggests that the unexplained excess risk might be the result of genetic modifiers associated with African ancestry conferring a higher risk of CHD. One such gene variant is the sickle cell mutation. The heterozygous state, or sickle cell trait (SCT), with a prevalence of 8 - 12% among AAs, was previously deemed clinically benign; however, recent evidence indicates that SCT is associated with increased risk of chronic kidney disease venous thromboembolism and sudden death following exertion. Individuals with SCT have higher circulating levels of C-reactive protein, fibrinogen, prothrombin fragment 1.2 and D-dimer. We hypothesized that AAs with SCT have a higher risk for myocardial infarction (MI) and coronary heart disease (CHD) than AAs who are homozygous for wild-type hemoglobin. Methods We obtained genotype and phenotype data from the Women's Health Initiative (WHI) REasonsfor Geographic and Racial Differences in Stroke (REGARDS), Multi-Ethnic Study of Atherosclerosis (MESA), Jackson Heart Study (JHS) and Atherosclerosis Risk In Communities (ARIC) cohorts. The outcomes were incident MI or CHD. Incident MI was defined as adjudicated non-fatal or fatal MI, while incident CHD was defined as 1) adjudicated non-fatal MI, 2) fatal MI, 3) documented coronary revascularization procedures or 4) non-MI CHD death. SCT status was determined by either direct genotyping or imputation for rs334 using the 1000Genome reference panel. Homozygous individuals and those with a prior history of CHD were excluded. Individuals with incident “micro MI”, only defined in REGARDS, were also excluded from the analysis. Analysis was performed separately in each cohort using a Cox proportional hazard models to estimate the hazard ratio (HR) for incident MI or CHD comparing SCT carriers to non-carriers. Models in each cohort were adjusted for age, sex, study site or region of residence, hypertension or systolic blood pressure, diabetes, serum LDL or HDL or total cholesterol, and population stratification (using principal components of global ancestry). The results from each cohorts were then meta-analyzed using a random effect model due to significant heterogeneity between studies (I2 = 39.1%, p = 0.02 for MI meta-analysis and I2 = 56%, p = 0.01 for CHD meta-analysis). Results A total of 20,053 African American men and women were included in the combined sample; 1503 with SCT (7.5% prevalence). Average ages in years at baseline were: 65.0±6.0 in WHI (N = 2248), 62.0 ± 9.2 in REGARDS (N = 10573); 62.2±10.2 in MESA (N = 1556); 50.0 ± 11.9 in JHS (N = 2133); and 54.0 ± 6.0 in ARIC (N = 3543). There were no statistically significant differences in the distribution of traditional cardiovascular risk factors by SCT status within cohorts, except that atrial fibrillation was more prevalent among REGARDS participants with SCT compared to those without SCT (9.9% vs. 7.8%, p = 0.03). The crude incidence rate of MI per 1000 person years in those with SCT compared to those without SCT was: 4.0 vs. 5.2 in WHI; 5.7 vs. 5.0 in REGARDS; 5.8 vs 4.3 in MESA, 2.0 vs 2.1 in JHS; and 4.1 vs 5.9 in ARIC. For CHD, the crude incidence rate was: 5.8 vs. 7.2 in WHI, 8.9 vs. 7.4 in REGARDS; 15.4 vs. 6.4 in MESA; 3.4 vs. 3.4 in JHS; and 10.5 vs. 9.5 in ARIC. The HR (95% CI) for MI was: 0.96 (0.49 - 1.89) in WHI; 1.27 (0.8 - 2.0) in REGARDS; 1.84 (0.74 - 4.60) in MESA; 1.24 (0.28 - 5.44) in JHS; and 0.68 (0.42 - 1.10) in ARIC. And that for CHD was: 1.05 (0.63 - 1.74) in WHI; 1.49 (1.01 - 2.18) in REGARDS; 2.82 (1.48 - 5.38) in MESA; 1.45 (0.50 - 4.19) in JHS; and 1.10 (0.80 - 1.50) in ARIC. Meta-analysis showed that, while SCT status was not significantly associated with incident MI (1.10 [0.73 - 1.64]), it was significantly associated with incident CHD (1.42 [1.02 - 1.98] Figures 1a and 1b). Conclusions This study showed a significant association between SCT and incident CHD, but not MI. Our conclusion is limited by the significant heterogeneity that existed between studies. Since SCT status was not associated with MI, but was associated with CHD, further work is needed to confirm these findings, determine which CHD component(s) explain the observed association and elucidate the possible mechanism(s) involved. Disclosures No relevant conflicts of interest to declare.

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ID: 139: PROGRESSIVE GLOMERULAR DAMAGE IN SICKLE CELL TRAIT AND SICKLE CELL ANEMIA MOUSE MODELS

Journal of Investigative Medicine ◽

10.1136/jim-2016-000120.95 ◽

2016 ◽

Vol 64 (4) ◽

pp. 957.2-958

Author(s):

SL Saraf ◽

JR Sysol ◽

JA Arruda ◽

RF Machado ◽

VR Gordeuk ◽

...

Keyword(s):

Gene Expression ◽

African Americans ◽

Kidney Disease ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Sickle Cell Trait ◽

Linear Trend ◽

Mesangial Expansion ◽

Urine Protein ◽

Increased Risk

The hemoglobin S mutation, a glutamic acid to valine substitution in the β-globin chain, results in hemoglobin polymerization under hypoxic conditions and leads to vaso-occlusion and hemolysis. Homozygous inheritance (Hb SS; sickle cell anemia) affects 1 in 500 African Americans and is consistently associated with an increased risk for kidney disease which may be due to cell-free hemoglobin toxicity, ischemic injury, or hyperfiltration-mediated damage to the kidney. Heterozygous inheritance (Hb AS; sickle cell trait) affects 1 in 8 African Americans and has also been associated with an increased risk for kidney disease, although not in all cohorts and the mechanisms are not well understood.We investigated whether inheritance of the Hb S mutation resulted in incremental kidney damage in Hb AS and Hb SS mice compared to Hb AA mice by histology, proteinuria, and candidate gene expression using transgenic sickle mice ≥6 months of age (Townes model, Jackson Laboratory). Values are presented as mean±standard error and analyses are adjusted for age.Using Masson trichrome stained sections of the kidney, progressive patterns of mesangial expansion were observed in age-matched Hb AS and Hb SS mice versus Hb AA mice by renal pathologists blinded to the hemoglobin genotype (figure 1). Hb AS mice had diffuse (>50% of the glomeruli per slide being involved) mesangial expansion while Hb SS mice had diffuse and global (>50% of the individual glomerulus being involved) mesangial expansion. Glomerular perimeters were measured using NanoZoomer Whole Slide Imaging in 26 randomly selected glomeruli from 2 age-matched mice per genotype. Using the upper quartile as the definition for an enlarged glomerulus, the proportion of enlarged glomeruli progressively increased from Hb AA (15%) to Hb AS (31%) to Hb SS mice (58%) (Cochran's test of linear trend, P=0.001) (figure 2). Progressively higher kidney weights were also observed from Hb AA (429±28 mg, n=8) to Hb AS (446±27 mg, n=18) to Hb SS (567±19 mg, n=5) mice (Test for linear trend, P=0.047). We then measured urine protein and urine creatinine concentrations using the Bio-Rad dye method and Jaffé reaction, respectively. Progressively higher urine protein-to-creatinine ratios were observed from Hb AA to Hb AS to Hb SS mice (figure 3) (Test for linear trend, P=0.09). Gene expression of candidate genes (TGFB1, IL6, MMP9, Klotho, HMOX1, and SHROOM3) was determined by rt-PCR from kidneys of age-matched, female Hb AA and Hb AS mice (n=5). Increased expression of Klotho (P=0.09) was observed in Hb AS mice (figure 4). Klotho is a β-glucoronidase that is highly expressed in the kidney and acts as a cofactor that increases the affinity of the FGF23 ligand for the FGF receptor.In conclusion, we observed progressive glomerular injury, determined by mesangial expansion, proportion of enlarged glomeruli, and urine protein concentrations in Hb AS and Hb SS mice compared to Hb AA mice. Klotho was upregulated in Hb AS mice and may play a role in the pathophysiology of kidney damage in Hb AS which will require further investigation.Abstract ID: 139 Figure 1

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Hematuria in Sickle Cell Anemia -Not Always Benign: Evidence for Excess Frequency of Sickle Cell Anemia in African Americans with Renal Cell Carcinoma

Acta Haematologica ◽

10.1159/000204199 ◽

1994 ◽

Vol 92 (3) ◽

pp. 119-122 ◽

Cited By ~ 11

Author(s):

Beverly W. Baron ◽

Rosemarie Mick ◽

Joseph M. Baron

Keyword(s):

Renal Cell Carcinoma ◽

African Americans ◽

Cell Carcinoma ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Renal Cell

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Long-Term Safety of Hydroxyurea in Sickle Cell Anemia and Other Benign Diseases: Systematic Review and Meta-Analysis

Blood ◽

10.1182/blood.v124.21.560.560 ◽

2014 ◽

Vol 124 (21) ◽

pp. 560-560 ◽

Cited By ~ 4

Author(s):

Ali H. Algiraigri ◽

Mansoor Radwi

Keyword(s):

Sickle Cell ◽

Sickle Cell Anemia ◽

Observational Studies ◽

Heart Diseases ◽

Meta Analysis ◽

Renal Stones ◽

Benign Diseases ◽

Cyanotic Congenital Heart Diseases

Background Hydroxyurea (HU) is an oral chemotherapeutic agent that has been used for the treatment of sickle cell anemia (SCA) and many other conditions. Although the efficacy of HU has been established in SCA, there is ambiguity regarding the long-term adverse events of this treatment. As significant risk such as secondary malignancies or myelodysplastic syndrome (MDS) have been linked to this drug but occur in small numbers across the various indications, we planned to pool the results from HU studies used in many conditions (excluding malignant and premalignant diseases) to obtain much wanted risk estimates. Objectives To evaluate the long-term safety (carcinogenicity) of HU therapy in people with SCA or any benign diseases (excluding malignant and premalignant diseases) of any age. Search strategy We searched MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), ongoing trials registers, and major preceding conferences. Hand searches were also conducted using reference lists from primary studies. All searches were updated to May 25 2014. Selection criteria Randomized controlled trials (RCTs) and observational studies (sample size ≥ 20 and mean/median follow up ≥ 2 years) assessing the toxicity of HU for the treatment of patients with any benign diseases were included. Data collection and analysis Two authors acted as reviewers and independently completed the search process, selected the studies, assessed study quality, and extracted data from the included studies. Authors of included studies were contacted if further information was required. Since the majority of the included studies were single-arm design with no control groups, the effect size was estimated as a proportion (events over patient-years on HU) and reported as overall cancer risk (OCR) for the included studies. All data was analyzed using comprehensive meta-analysis (CMA), version 2.0. Main results A total of 37 studies (3 RCTs and 34 observational studies) involving 3278 patients were included. We identified four benign diseases where HU has been used ≥ 2 years and met the inclusion criteria. These include SCA (26 studies), β-thalassemia (9 studies), cyanotic congenital heart diseases (one study), and renal stones (one study). HU was not associated with increased risk of cancers in the treated group with OCR of 0.2% (95% CI, 0.0-0.3%). Further to that, 12 studies or extension studies with ≥ 5 year follow up on HU showed stable result of 0.2%. This weighted effect size represent cancer incidence rate of 2 per 1000 which is not higher than the most recent published cancer incidence rate for all African-American or Whites, US 2005-2009 period. Acknowledging the differences between the two rates and they are not meant to be direct comparison, a useful representation can be extracted from them. Overall, there were 7 cases of malignancy/MDS were identified post relatively long-term use (≥ 2years) of HU in 3278 patients. In the narrative review, we identified another 13 cases of malignancies post HU use in hemoglobinopathy as described by different case reports and studies that did not meet our inclusion criteria with majority have been leukemia. The majority of the included studies had several limitations, such as small sample size, lack of comparison group, under-reporting of data and methods, and the majority having been observational studies. Authors’ conclusion The use of HU in treating patients with hemoglobinopathies does not appear to be associated with increase risk of secondary malignancies nor MDS despite being used for relatively long-term courses. However, ongoing long-term studies as well as updated national and international registries and other types of large database are highly needed to further consolidate this finding. Disclosures Off Label Use: Hydroxyurea for management of β-Thalassemia, Cyanotic congenital heart diseases, Renal stones, or Children with sickle cell anemia..

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Polymorphisms Associated with the Arab-Indian Haplotype of Sickle Cell Anemia Are Candidate Fetal Hemoglobin Gene Modulators

Blood ◽

10.1182/blood.v126.23.3388.3388 ◽

2015 ◽

Vol 126 (23) ◽

pp. 3388-3388

Author(s):

Vinod Vathipadiekal ◽

Abdulrahman Alsultan ◽

John Farrell ◽

A.M Al-Rubaish ◽

Fahad Al-Muhanna ◽

...

Keyword(s):

African Americans ◽

Gene Cluster ◽

Allele Frequency ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Olfactory Receptor ◽

Receptor Gene ◽

Fetal Hemoglobin ◽

Olfactory Receptor Gene ◽

Genome Wide

Abstract Fetal hemoglobin (HbF) inhibits HbS polymerization. Because of this, sufficient HbF in most sickle erythrocytes can lead to a milder disease phenotype. HbF levels differ amongst the β-globin gene (HBB) cluster haplotypes of sickle cell anemia. In the Arab-Indian (AI) haplotype, HbF was about 20% compared with 5-10% in the Bantu, Benin, and Senegal haplotypes. Functional elements linked to the HBB haplotype are likely to regulate the expression of HbF in addition to the effects of trans-acting modulators. To identify cis-acting SNPs in the HBB gene cluster that differentiate the AI haplotype from all others, including the Senegal haplotype-the Senegal haplotype shares some SNPs with the AI haplotype but its carriers have lower HbF-we studied patients with sickle cell anemia who were homozygous for HBB haplotypes by genome-wide SNP association analysis (GWAS; Table). First, we compared the results of GWAS of 42 Saudi AI haplotype homozygotes with GWAS in 71 Saudi Benin haplotype homozygotes. The only variants distinguishing these 2 populations with genome-wide significance (p-values between 9.6E-07 and 2.7E-45) were 223 SNPs in chromosome 11p15 from positions 3.5 to 6.5 mb. This region included the HBB gene cluster, its locus control region (LCR) and the upstream and downstream olfactory receptor gene clusters. The minor allele frequency of SNPs in MYB (chr 6q23), BCL11A (chr 2p16) and KLF1 (chr 19), trans-acting loci that affect expression of the HbF genes, were similar in these 2 cohorts. A novel candidate trans-acting locus was not found, however our power to detect such an association was low. We followed-up these observations by comparing allele frequencies in 303 African American cases homozygous for the haplotypes shown in the Table. Thirteen GWAS-significant SNPs, in addition to rs7482144 and rs10128556, were present in all AI haplotype cases but not in 83 Senegal haplotype chromosomes. The allele frequency of these SNPs was replicated in 62 independent AI haplotype cases. Rs2472530 is in the coding region of OR52A5; rs16912979, rs4910743 and rs4601817 are in the HBB gene cluster LCR; rs16912979 in DNase I hypersensitive site-4 altered motifs for POLR2A, GATA1, and GATA2 binding.The minor allele of rs10837771 causes a missense mutation in OR51B4 an upstream olfactory receptor gene. To see if any of these or other alleles might sometimes be associated with HbF in the Bantu and Benin haplotyes, we selected homozygotes and compound heterozygous for these haplotypes who had unexplained and uncharacteristically high HbF. Thirty-one African Americans, aged ≥5 yrs. who had a HbF of 21% were compared with 350 similar cases who had a mean HbF of 3%. Four additional SNPs on chromosome 11, from positions ranging from 5536415 to 5543705 in the UBQLNL/HBG2, region and present in 45-48% of AI haplotype and 3-13% of other haplotypes, were found at higher frequencies in the high HbF group compared with the low HbF group. These SNPs also altered transcription factor binding motifs. Loci marked by SNPs that distinguish the AI from the Senegal and other HBB haplotypes might contain functionally important polymorphisms and account in part for high HbF in AI haplotype sickle cell anemia, independent of, or in addition to, the effects associated with rs7482144 or rs10128556. They might also be rarely associated with high HbF found in other haplotypes. These observations provide a foundation for mechanistic studies focused on the role of these variants in the expression of their linked HbF genes.Table 1.non-codedallelegenomic locationSaudi AI(n=42)Saudi ben.ben(n=71)AA ben.ben(n=264)AA ban.ban(n=31)AA sen.sen(n=8)HbF (%)1711669rs10837771Gexon OR51B410.020.0200rs4601817GLCR10.020.0400rs4910743CLCR10.010.0100rs16912979CLCR00.960.920.111rs10488675Gintron HBE110.01000rs7482144*AHBG210001rs10128556#TIntron HBBP110001rs7935470COR51V110.020.0300rs10837582GOR51V1100.0200rs11036227TOR51V110000rs10734485COR51A1P00.990.9711rs10837461AOR52A110.01000rs2472522GOR52A110.01000rs2472530Gexon OR52A510.01000rs2499948TOR52A510.020.010.020Allele frequencies in haplotypes of sickle cell anemia. * Xmn1 5' HBG 2 restriction site. This SNP, not present on the SNP microarray, was genotyped independently; # LD with rs7482144; AA designates African Americans; ben-Benin; ban-Bantu; sen-Senegal. Disclosures No relevant conflicts of interest to declare.

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BCL11A enhancer Haplotypes Are Associated with the Distribution of HbF in Arab-Indian and African Haplotype Sickle Cell Anemia but Not the Different Population Levels of HbF

Blood ◽

10.1182/blood.v124.21.4066.4066 ◽

2014 ◽

Vol 124 (21) ◽

pp. 4066-4066

Author(s):

Paola Sebastiani ◽

John J. Farrell ◽

Shuai Wang ◽

Heather L Edward ◽

Heather M. Shappell ◽

...

Keyword(s):

African Americans ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Transcription Initiation ◽

Conflicts Of Interest ◽

Globin Gene ◽

Initiation Site ◽

Skewed Distribution ◽

African Origin ◽

Hbf Level

Abstract Fetal hemoglobin (HbF) modulates the phenotype of sickle cell anemia. In the Middle East and India the HbS gene is often on an Arab-Indian HBB haplotype that is associated with high HbF levels. HbF is “normally” distributed in this population with a mean ~20%. In African HbS haplotypes, HbF levels are much lower (mean value ~6%) with a highly skewed distribution. BCL11A is an important modulator of γ-globin gene (HBG2 and HBG1) expression and BCL11A is regulated by erythroid specific enhancers in its 2nd intron. The enhancers consist of 3 DNase hypersensitive sites (HS) +62, +58 and +55 kb from the transcription initiation site of this gene. Polymorphisms (SNPs) in these enhancers are associated with HbF. The strongest association with HbF levels in African Americans with sickle cell anemia was with rs1427407 in HS +62 and to a lesser extent, rs7606173 in HS+55. Using the results of whole genome sequencing of 14 AI haplotype patients—half with HbF <10%, half with HbF >20%—6 SNPs in the BCL11A enhancer region, rs1427407, rs7599488, rs6706648, rs6738440, rs7565301, rs7606173 and 2 indels rs3028027 and rs142027584 (CCT, CCTCT and AAAAC respectively), were detected as possibly associated with HbF level. There were no novel polymorphisms detected. We genotyped the 6 SNPs and studied their associated haplotypes in 137 Saudi (HbF18.0±7.0%) and 44 Indian patients (HbF23.0±4.8%) with the Arab-Indian HBB haplotype; 50 African Americans with diverse African haplotypes, including 4 Senegal haplotype heterozygotes, (20 with HbF 17.2±4.6% and 30 with HbF 5.0±2.5%) and imputed genotypes for these SNPs in 847 African Americans with sickle cell anemia and diverse haplotypes (HbF 6.6±5.5%). Four SNPs (rs1427407, rs6706648, rs6738440, and rs7606173) in the HS sites showed consistent associations with HbF levels in all 4 cohorts. Haplotype analysis of these 4 SNPs showed that there were 4 common and 10 rare haplotypes. The most common, GCAG, was found in ~54% of Arab-Indian haplotype carriers (HbF, ~20%) and in ~33% of African origin haplotype carriers (HbF, ~5.5%). Two haplotypes, GTAC and GTGC, were carried by ~40% of African American patients and were associated with lower levels of HbF (3.6%-4%). These same haplotypes were carried by 18% of Arab-Indian haplotype carriers and their average HbF level was 17%. These differences were significant. Haplotype TCAG was present in 20% of Arab-Indian and 25% of African haplotype cases, and carriers had on average higher HbF levels (~22% in the Arab-Indian haplotype, ~8% in African Americans). The analysis shows that: BCL11A enhancer haplotypes are differentially distributed among patients with the HbS gene on Arab-Indian or African origin haplotypes; haplotype pairs TCAG/TCAG and GTAC/GTGC are associated with the highest and lowest HbF levels in all the studied groups; the population-specific prevalence of HbF BCL11A enhancer haplotypes are likely to explain the different distributions of HbF in African origin and Arab-Indian haplotypes but do not account for the differences in average population levels of HbF or the high HbF of the Arab-Indian haplotype. Novel SNPs in BCL11A do not explain the high HbF of the Arab-Indian haplotype. Other important loci must have a predominant role in the differential expression of HbF among HbS Arab-Indian haplotype carriers. Disclosures No relevant conflicts of interest to declare.

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