Arab-Indian Research Articles

Profiling of 35 Cases of Hb S/Hb E (HBB: c.20A>T/HBB: c.79G>a), Disease and Association with α-Thalassemia and β-Globin Gene Cluster Haplotypes from Odisha, India

Hb S/Hb E (HBB: c.20A>T/HBB: c.79G>A) is an uncommon variant of sickle cell disease resulting from coinheritance of Hb S and Hb E. Clinico-hematological and biochemical parameters of 35 cases of Hb S/Hb E disease were studied and compared with 70 matched cases of homozygous sickle cell disease (Hb SS) and Hb S/β-thalassemia (β-thal) with IVS-I-5 (G>C) (HBB: c.92+5G>C). The influence of α-thal and that of of β-globin gene cluster haplotypes among Hb S/Hb E disease was also studied. Statistical analysis was done using GraphPad InStat version 3.06. Of the 35 cases, 20 (57.14%) had a moderate clinical presentation. Mean lactate dehydrogenase (LDH) level, vaso-occlusive crises (VOCs) per year, and annual blood transfusion requirements were significantly lower in Hb S/Hb E cases than in the other two groups. The hemoglobin (Hb) and packed cell volume (PCV) levels were significantly high in Hb S/Hb E cases with α-thal and these cases were associated with microcytic-hypochromic anemia. α-Thalassemia did not influence clinical presentation in Hb S/Hb E cases. The β-globin gene cluster haplotypes of 70 alleles of Hb S/Hb E revealed an association of five typical haplotypes [Arab-Indian (A-I), Benin, Bantu, Cameroon and Senegal] in 95.71% cases. Hb S/Hb E disease exhibit asymptomatic to moderate phenotypic expression. However, further in-depth studies on Hb S/Hb E will help in reducing the disease burden especially in high-risk countries like India.

HBB gene cluster haplotype diversity in sickle cell anemia patients of Chhattisgarh, India

Sickle cell anemia (SCA) is one of the hereditary hemoglobin disorders in Indian populations. An exceptionally high prevalence of SCA is observed in the populations of Chhattisgarh. Restriction fragment length polymorphism (RFLP) haplotypes of the beta globin (HBB) gene cluster are important as population data, anthropological purpose for tracing migration of SCA allele and predicting the severity of SCA disease. The purpose of this study was to elucidate the HBB haplotypes and their correlation with clinical and hematological profile of SCA patients of Chhattisgarh population. The HBB gene cluster haplotypes were determined in 190 SCA patients by the polymerase chain reaction-restriction fragment length polymorphism method. Medical records of patients were reviewed to obtain pertinent clinical features, hemoglobin fractions, and other biochemical variables. Among the analyzed patients, 74% had Arab-Indian (AI) haplotype, followed by 21% atypical haplotypes. Senegal, Benin, and Cameroon types of HBB haplotypes represented 3%, 1%, and 1% of the patients, respectively. Comparison of various biochemical and hematological variables and clinical complications among various haplotypes did not reveal significant differences. The high frequency of atypical haplotypes observed may have been generated by single and double crossing-over between AI haplotype and normal HBB haplotype. Considering the Indian population???s genetic structure and diversity, the results of our study should be considered as introductory, and our study can serve as a possible tool for additional studies of SCA in India.

Sickle cell disease in Sri Lanka: clinical and molecular basis and the unanswered questions about disease severity

BackgroundThough case reports and limited case series of Sickle cell disease in Sri Lanka have been reported previously, no attempt has been made hitherto to undertake a comprehensive genotypic-phenotypic analysis of this “rare” group of patients.ResultsAll accessible Sickle cell disease patients, totaling 60, including, 51 Sickle β-thalassaemia and 9 homozygous sickle patients were enrolled from seven thalassaemia treatment centres between December 2016–March 2019. The majority of patients were of Sinhalese ethnicity (n = 52, 86.67%). Geographically, two prominent clusters were identified and the distribution of Sickle haemoglobin in the island contrasted markedly with the other haemoglobinopathies. 3/ 9 homozygous sickle patients and 3/ 51 Sickle β-thalassaemia patients were receiving regular transfusion. Joint pain was the commonest clinical symptom among all sickle cell disease patients (n = 39, 65.0%). Dactylitis was significantly more common in homozygous sickle patients compared with the Sickle β-thalassaemia groups (p 0.027). Two genetic backgrounds sickle mutation were identified namely, Arab Indian and Benin. Among the regulators of Foetal hemoglobin in Sickle patients of the present study rs1427407 G > T seemed to be the most prominent modifier, with a significant association with Foetal haemoglobin levels (p 0.04).ConclusionsOverall, the clinical course of the Asian version of Sickle cell disease in Sri Lanka appears to be milder than that described in India.

Prevalence and Diversity of Haplotypes of Sickle Cell Disease in the Eastern Province of Saudi Arabia

Hb F modulates sickle cell disease. Five major haplotypes of the β-globin gene cluster are associated with sickle cell disease. In the Eastern Province of Saudi Arabia, the Arab-Indian (AI) is most common. Single nucleotide polymorphism (SNP) genotyping (rs3834466, rs28440105, rs10128556, and rs968857) was carried out by nuclease allelic discrimination assay with target-specific forward and reverse primers, TaqMan probes, labeled with VIC and FAM. In 778 patients with sickle cell disease from the Eastern Province, a haplotype was assigned to 90.9% of all samples; 9.1% were classified as compound heterozygotes for the AI and an atypical haplotype. The distribution of haplotypes for 746 Hb S (HBB: c.20A > T) homozygotes was: 614 AI/AI, nine SEN/SEN (Senegal), 42 SEN/AI, nine CAM/CAM (Cameroon), one CAR (Central African Republic)/BEN (Benin), 71 AI/atypical. In Hb S/β-thalassemia (Hb S/β-thal), the distribution of Hb S haplotypes was: 22 AI/AI, one CAM/CAM, four AI/SEN, five AI/atypical. Mean Hb F in the haplotypes was: AI/AI 16.6 ± 7.5%, CAM/CAM 8.0 ± 4.1%, SEN/SEN 11.0 ± 5.1%, SEN/AI 15.1 ± 4.6%, AI/atypical 16.2 ± 6.5%. The presence of the SEN and CAM haplotypes was unexpected due to the apparent homogeneity of the population of the Eastern Province. We have successfully classified sickle cell disease haplotypes using the relatively inexpensive TaqMan assay for the first time. In addition, we have previously shown that children with AI haplotype have Hb F of 30.0% and mild disease, while in our cohort of adult AI patients, which might be the largest yet reported, Hb F was about 16.6%.

Sickle ß-globin haplotypes among patients with sickle cell anemia in Basra, Iraq: A cross-sectional study

BACKGROUND: Sickle cell disease is a monogenic disease with heterogeneous clinical course. Many genetic factors such as inheritance of α-thalassemia trait and fetal hemoglobin (Hb) level, related to the presence of specific haplotypes, are among the factors that modify disease severity. OBJECTIVES: To identify βS haplotypes of children with sickle cell anemia (SCA) in Basra and assess the association of clinical variables and hematological parameters with different βS haplotypes. PATIENTS AND METHODS: This analytical cross-sectional study included 62 patients with SCA registered at Basra Center of Hereditary Blood Disease. In addition to clinical data, blood samples were obtained for complete blood count, lactate dehydrogenase and polymerase chain reaction, and Sanger sequencing analysis of HBB gene. Statistical analysis was done using SPSS program version (23) software. RESULTS: The mean age of studied patients was 7.15 ± 3.81 years, with a male to female ratio of 1:1.7. The most common haplotype was the Arab Indian (AI) in 34 (54.8%) patients, followed by Benin and Senegal haplotypes in 12 (19.4%) patients for each, and an atypical haplotype in 4 (6.5%) patients. No significant differences were found in the mean age of diagnosis, the frequency of vaso-occlusive crises, blood transfusions and hospitalizations among patients with different βS haplotypes, P >0.05. However, patients with AI haplotype have significantly higher Hb, red blood cell count, hematocrit and fetal Hb compared to other haplotypes, P CONCLUSIONS: The AI is the most common haplotype among SCA patients from Basra and it was associated with significantly higher Hb, hematocrit, and fetal Hb levels.

Preoperative Transfusion in Pediatric Patient with Sickle Cell Disease

Background: Sickle cell disease (SCD) is associated with perioperative complications. Red cell transfusion has been recommended in the management of SCD undergoing elective procedure to minimize perioperative complications. The aim of this study was to retrospectively review our experience in the management of children patients with SCD with the Arab-Indian (AI) haplotype undergoing elective and emergency surgery, and to determine blood transfusion requirement and surgery-related perioperative complications. Patients and Methods: A total number of 173 SCD patients undergoing surgery at Qatif Central Hospital, Qatif, Eastern province, Saudi Arabia was conducted between February 2007 and June 2019. children less than 14 years and above one year were included (111 boys and 62 girls). Patients were divided into two groups: Group A did not receive transfusion and Group B had top-up transfusion. The medical records were reviewed to define the perioperative risks and the postoperative complications in relation to the type of transfusion modality selected. Two surgical procedures were analyzed: a low and medium risk group including laparoscopic cholecystectomy, laparoscopic splenectomy, tonsillectomy, adenotonsillectomy, herniotomy and dental procedure. Results: eighty-three (n:83) patients (Group A) did not received transfusions (Group B) while . There were 15 (17.2%) postoperative complications; seven (8.4%) occurred in group A patients who did not received transfusion and eight (8.8%) occurred in group B patients who received top-up transfusion. Sickle cell disease-related complications consisted of acute painful vaso-occlusive crises in three patients (3.5%). Six patients (3.9%) had acute chest syndrome, 4 (4.5%) had hepatic crises and one had subclinical pancreatitis. Only one (1.2%) patient in group B (top up) had a mild hemolytic transfusion reaction. Moreover, there was no significant difference in the complications between the transfusion and none transfusion subgroups. Conclusion: Surgery in SCD patients is safe without a preoperative blood transfusion. Moreover, there was no significant difference in the complications between the transfusion and none transfusion subgroups. To conclude, blood transfusion or exchange blood transfusion should be individualized based on genotype, haplotype and type of surgery. Disclosures No relevant conflicts of interest to declare.

Fetal hemoglobin in sickle cell anemia: The Arab-Indian haplotype and new therapeutic agents.

Fetal hemoglobin (HbF) has well-known tempering effects on the symptoms of sickle cell disease and its levels vary among patients with different haplotypes of the sickle hemoglobin gene. Compared with sickle cell anemia haplotypes found in patients of African descent, HbF levels in Saudi and Indian patients with the Arab-Indian (AI) haplotype exceed that in any other haplotype by nearly twofold. Genetic association studies have identified some loci associated with high HbF in the AI haplotype but these observations require functional confirmation. Saudi patients with the Benin haplotype have HbF levels almost twice as high as African patients with this haplotype but this difference is unexplained. Hydroxyurea is still the only FDA approved drug for HbF induction in sickle cell disease. While most patients treated with hydroxyurea have an increase in HbF and some clinical improvement, 10 to 20% of adults show little response to this agent. We review the genetic basis of HbF regulation focusing on sickle cell anemia in Saudi Arabia and discuss new drugs that can induce increased levels of HbF.

A candidate transacting modulator of fetal hemoglobin gene expression in the Arab-Indian haplotype of sickle cell anemia.

Fetal hemoglobin (HbF) levels are higher in the Arab-Indian (AI) β-globin gene haplotype of sickle cell anemia compared with African-origin haplotypes. To study genetic elements that effect HbF expression in the AI haplotype we completed whole genome sequencing in 14 Saudi AI haplotype sickle hemoglobin homozygotes-seven selected for low HbF (8.2% ± 1.3%) and seven selected for high HbF (23.5% ± 2.6%). An intronic single nucleotide polymorphism (SNP) in ANTXR1, an anthrax toxin receptor (chromosome 2p13), was associated with HbF. These results were replicated in two independent Saudi AI haplotype cohorts of 120 and 139 patients, but not in 76 Saudi Benin haplotype, 894 African origin haplotype and 44 AI haplotype patients of Indian origin, suggesting that this association is effective only in the Saudi AI haplotype background. ANTXR1 variants explained 10% of the HbF variability compared with 8% for BCL11A. These two genes had independent, additive effects on HbF and together explained about 15% of HbF variability in Saudi AI sickle cell anemia patients. ANTXR1 was expressed at mRNA and protein levels in erythroid progenitors derived from induced pluripotent stem cells (iPSCs) and CD34+ cells. As CD34+ cells matured and their HbF decreased ANTXR1 expression increased; as iPSCs differentiated and their HbF increased, ANTXR1 expression decreased. Along with elements in cis to the HbF genes, ANTXR1 contributes to the variation in HbF in Saudi AI haplotype sickle cell anemia and is the first gene in trans to HBB that is associated with HbF only in carriers of the Saudi AI haplotype. Am. J. Hematol. 91:1118-1122, 2016. © 2016 Wiley Periodicals, Inc.

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

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 1non-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. DisclosuresNo relevant conflicts of interest to declare.

A Candidate Trans-Acting Modulator of Fetal Hemoglobin Gene Expression in the Arab-Indian Haplotype of Sickle Cell Anemia

In the Arab-Indian (AI) β-globin gene (HBB) haplotype of sickle cell anemia, fetal hemoglobin (HbF) levels are higher and the disease phenotype milder than in African HBB haplotypes. To study the genetic basis of HbF regulation in the AI haplotype, whole genome sequencing (WGS) was done in 14 unrelated Saudi AI haplotype HbS homozygotes; 7 selected for low HbF (7.9±1.9%) and 7 for high HbF (18.5±3.2%). WGS was also done in 3 Indians with the AI haplotype (HbF 26.0±4.5%), 3 African Americans with the Benin haplotype selected because of the uncommonly high HbF for this haplotype (19.8±0.4%) and 1 African American homozygote with the Senegal haplotype (HbF 16.0%). Association of SNPs with HbF was tested using simple linear regression with an additive genetic model, and the Sequence Kernel Association Test using sliding windows of 5 SNPs. We found 465 SNPs that were significantly associated with HbF in a single SNP analysis (p≤10-5). Following annotation using SNPper and ENCODE RegulomeDB, PLINK was employed to remove all SNPs in high linkage disequilibrium (r2>0.8) ending with 128 SNPs for follow-up analysis. These prioritized variants were further investigated using functional evaluation tools such as SCAN, Hembase, ErythronDB and the results of WGS were followed by genome-wide SNP analysis, imputation of genotypes to 1000genomes, and targeted direct genotyping in the following cohorts with sickle cell anemia: 110 AI haplotype cases (HbF 18.0±7.0%); 71 Saudi Benin haplotype cases (HbF 11.4±4.1%); 44 Indian AI haplotype homozygotes (HbF 23.0±4.8%); 894 African Americans with diverse HBB haplotypes (HbF 5.2±5.6%). All cases were examined when the HbF levels had stabilized. None of the patients were using hydroxyurea when HbF was measured. Based on WGS, 2 SNPs, rs4527238 and rs35685045 (D'=1) in intron 9 of ANTXR1 (anthrax toxin receptor 1, 2p13.1) remained associated with HbF after correction for multiple comparisons. This result was replicated in the cohort of 110 additional AI haplotype Saudi patients but not in cohorts with other HBB haplotypes. The alternative alleles of these 2 SNPs had nearly equal frequencies in Saudis with the Saudi AI haplotype and lower frequencies in Indians, Saudi Benin haplotype and African Americans with sickle cell anemia. The T allele of rs4527238 and the C allele of rs35685045 are associated with high HbF. ANTXR1 SNPs explained 10% of the HbF variability compared with 8% for BCL11A; these genes had independent, additive effects on HbF and explained about 15% of HbF variability. RNA sequencing and gene expression microarray analysis at 3 time points during the erythroid differentiation of CD34+ and iPSCs isolated from the same subjects showed that only the long splice variant of ANTXR1 was expressed. Expression increased over time in CD34+ erythroid cells and decreased over time in iPSC-derived erythroid progenitors in a pattern similar to BCL11A expression, with increasing expression as CD34+ cells matured and HbF expression fell and declining expression as iPSCs differentiated and HbF expression increased. Immunofluorescence co-staining for ANTXR1 and HbF during the erythroid differentiation of sickle iPSCs showed that reduced expression of ANTXR1 was paralleled by increased expression of HbF. By GTEx analysis, eQTLs at rs4527238 and rs35685045 showed a trend for increased expression according to genotype with rs4527238 T/T having the lowest level of expression and T/C and C/C genotypes, higher expression levels (p= 0.08) and for rs35685045, C/C the lowest expression levels and C/T and T/T higher expression levels (p= 0.07); rs4527238 and rs35685045 had no effect on the expression of BCL11A, a repressor of HbF expression located at 2p16 (p=0.8). STRING 9.1 predicted protein interactions of ANTXR1 directly with LRP6, HDAC2, BCLX and BRAC1 with the highest level of confidence (0.95) with LRP6. The HbF phenotype in AI haplotype sickle cell anemia is unique and ANTXR1 is the first trans-acting element associated with HbF whose effects appear to be limited to the Saudi AI haplotype. ANTXR1 might have dual effects on HbF, indirectly affecting hematopoiesis via interactions with LRP6 and Wnt signaling, and directly modulating HBG expression through its effects on HDAC2. A dual effect on HbF expression has been suggested for MYB. Whether targeting ANTXR1 is a therapeutic option will require further studies. DisclosuresNo relevant conflicts of interest to declare.

BCL11A enhancer haplotypes and fetal hemoglobin in sickle cell anemia.

Fetal hemoglobin (HbF) levels in sickle cell anemia patients vary. We genotyped polymorphisms in the erythroid-specific enhancer of BCL11A to see if they might account for the very high HbF associated with the Arab-Indian (AI) haplotype and Benin haplotype of sickle cell anemia. Six BCL112A enhancer SNPs and their haplotypes were studied in Saudi Arabs from the Eastern Province and Indian patients with AI haplotype (HbF ~20%), African Americans (HbF ~7%), and Saudi Arabs from the Southwestern Province (HbF ~12%). Four SNPs (rs1427407, rs6706648, rs6738440, and rs7606173) and their haplotypes were consistently associated with HbF levels. The distributions of haplotypes differ in the 3 cohorts but not their genetic effects: the haplotype TCAG was associated with the lowest HbF level and the haplotype GTAC was associated with the highest HbF level and differences in HbF levels between carriers of these haplotypes in all cohorts were approximately 6%. Common HbF BCL11A enhancer haplotypes in patients with African origin and AI sickle cell anemia have similar effects on HbF but they do not explain their differences in HbF.

Sickle cell disease in Saudi Arabia: the phenotype in adults with the Arab‐Indian haplotype is not benign

Sickle cell disease (SCD) in Saudi patients from the Eastern Province is associated with the Arab-Indian (AI) HBB (β-globin gene) haplotype. The phenotype of AI SCD in children was described as benign and was attributed to their high fetal haemoglobin (HbF). We conducted a hospital-based study to assess the pattern of SCD complications in adults. A total of 104 patients with average age of 27 years were enrolled. Ninety-six per cent of these patients reported history of painful crisis; 47% had at least one episode of acute chest syndrome, however, only 15% had two or more episodes; symptomatic osteonecrosis was reported in 18%; priapism in 17%; overt stroke in 6%; none had leg ulcers. The majority of patients had persistent splenomegaly and 66% had gallstones. Half of the patients co-inherited α-thalassaemia and about one-third had glucose-6-phosphate dehydrogenase deficiency. Higher HbF correlated with higher rate of splenic sequestration but not with other phenotypes. The phenotype of adult patients with AI SCD is not benign despite their relatively high HbF level. This is probably due to the continued decline in HbF level in adults and the heterocellular and variable distribution of HbF amongst F-cells.

UGT1A1 promoter polymorphism associated with serum bilirubin level in Saudi patients with sickle cell disease

BACKGROUND AND OBJECTIVESPolymorphism in (TA)n of the UGT1A1 promoter influences bilirubin level and risk of gallstones in patients with sickle cell disease (SCD) of African descent. Modifiers of bilirubin level and gallstones in Saudi patients with SCD are not known.DESIGN AND SETTINGSPatients with SCD presenting to participating institutions between July 2009 and July 2012 were enrolled in our study.METHODSA total of 223 SCD patients were enrolled. Laboratory workup at steady state included complete blood count, reticulocytes, serum bilirubin, lactate dehydrogenase (LDH), G6PD level, and hemoglobin (Hb) electrophoresis. The (TA)n UGT1A1 promoter polymorphism and presence of α-thalassemia were also determined.RESULTSTA6/6 in the UGT1A1 promoter was identified in 189 patients (84.7%), TA7/7 in 26 (11.7%), TA5/5 in 6 (2.7%), and TA5/6 in 2 (0.9%). Increased (TA)n of the UGT1A1 promoter (P<.0001), male gender (P=.02), higher LDH (P=.001), and lower Hb level (P=.009) were associated with higher bilirubin level, while the co-inheritance of α-thalassemia (P=.003) was linked with lower bilirubin level. UGT1A1 (TA)n (P<.0001) and Hb level (P=.005) remained significant on multivariate analysis. Gallstones were more frequent in patients with TA7/7 (72%) compared to patients with TA6/6 (57%) and TA5/5 or 5/6 (37%); however, this difference was not statistically significance (P=.18). Older age (P=.0001) and absence of α-thalassemia (P=.03) were associated with higher risk of gallstones.CONCLUSION(TA)n in the UGT1A1 promoter and intensity of hemolysis modify steady-state serum bilirubin level in SCD. Co-inheritance of α-thalassemia reduces the risk of gallstones in Saudi patients with SCD.

Fetal hemoglobin in sickle cell anemia: Genetic studies of the Arab-Indian haplotype

Sickle cell anemia is common in the Middle East and India where the HbS gene is sometimes associated with the Arab-Indian (AI) β-globin gene (HBB) cluster haplotype. In this haplotype of sickle cell anemia, fetal hemoglobin (HbF) levels are 3-4 fold higher than those found in patients with HbS haplotypes of African origin. Little is known about the genetic elements that modulate HbF in AI haplotype patients. We therefore studied Saudi HbS homozygotes with the AI haplotype (mean HbF 19.2±7.0%, range 3.6 to 39.6%) and employed targeted genotyping of polymorphic sites to explore cis- and trans- acting elements associated with high HbF expression. We also described sequences which appear to be unique to the AI haplotype for which future functional studies are needed to further define their role in HbF modulation. All cases, regardless of HbF concentration, were homozygous for AI haplotype-specific elements cis to HBB. SNPs in BCL11A and HBS1L-MYB that were associated with HbF in other populations explained only 8.8% of the variation in HbF. KLF1 polymorphisms associated previously with high HbF were not present in the 44 patients tested. More than 90% of the HbF variance in sickle cell patients with the AI haplotype remains unexplained by the genetic loci that we studied. The dispersion of HbF levels among AI haplotype patients suggests that other genetic elements modulate the effects of the known cis- and trans-acting regulators. These regulatory elements, which remain to be discovered, might be specific in the Saudi and some other populations where HbF levels are especially high.

A functional promoter polymorphism of the δ‐globin gene is a specific marker of the Arab‐Indian haplotype

A functional promoter polymorphism of the δ‐globin gene is a specific marker of the Arab‐Indian haplotype

3′ haplotypes of the β-globin gene in β s-chromosomes of Mexican individuals

The β-globin gene cluster has shown high polymorphic diversity organized in 5′ and 3′ haplotypes (Hps). β S-Chromosomes are in linkage disequilibrium with the 5′ Hps Bantu, Benin, Senegal, Cameroon, and Arab–Indian. In Mexican mestizos with African west coast origins, we observed the following 5′ Hps in β S-chromosomes: Bantu, 78.8%; Benin, 18.2%; and atypical Hp 9, 3.0%. With the purpose of establishing the 3′ Hps, we analyzed 35 polymorphic sites—6 by RFLP analysis and 29 by DNA sequencing—in 33 unrelated β S-chromosomes. The polymorphic sites were structured according to Harding et al. [R.M. Harding, S.M. Fullerton, R.C. Griffiths, J.B. Clegg, Archaic African and Asian lineages in the genetic ancestry of modern humans, Am. J. Hum. Genet. 60 (1997) 772–789] and Lapouméroulie et al. [C. Lapouméroulie, O. Dunda, R. Ducrocq, G. Trabuchet, M. Mony-Lobé, J.M. Bodo, P. Carnevale, D. Labie, J. Elion, R. Krishnamoorthy, A novel sickle cell mutation of yet another origin in Africa: the Cameroon type, Hum. Genet. 89 (1992) 333–337]. All Bantu β S-chromosomes showed the 12A1 3′ Hp with (AT) 6T 9 repeats (84.9%), a novel 3′ Hp. The Benin Hp was 2B2, with (AT) 8T 4 (12.1%), and the atypical Hp 9 4B1, (AT) 8T 5 (3.0%). Because of the high linkage disequilibrium observed for the Bantu and 12A1 Hps, we expect that, if there is a single origin of the Bantu β S mutation, all must show the 12A1 polymorphic DNA sequence in the 3′ Hp. A correlation between the 5′ and 3′ Hps could be observed with the other β S mutations. The atypical Hp 9 was also atypical at the 3′ Hp, with the same repeats as observed with the Cameroon β S mutation; however, it differed in one position from the typical Lapouméroulie Cameroon Hp, indicating that these β S-chromosomes arose by different genetic mechanisms or by a novel β S mutation. We stress the importance of the study of DNA polymorphisms at 3′ Hp to allow understanding of the genetic diversity of β S-chromosomes, as well as their implications in β S gene expression and the possible effects on the clinical phenotype.