βS Haplotypes Research Articles

Molecular Analysis of Xmn1-Polymorphic Site ´5 to Gγ of the β-Globin Gene Cluster in a Saudi Population of Jazan Region in Correlation with Hb F Expression.

The southern part of Saudi Arabia has an ethnically diverse population where sickle-cell anemia (sickle cell disease) is common, but little is known about its βs haplotypes. The goal of the current study is to ascertain the prevalence of the Hb S gene with analysis of Xmn1 ′5 to Gγ haplotype among the Saudi population in the Jazan area. Initially recorded findings of (1) Hb S gene and (2) hematological parameters with Hb F levels were collected from 5990 participants. Then, the second series of 70 different patients with established sickling disease and 30 healthy individuals as a control group was recruited, in which the genotype of Xmn1 ′5 to Gγ-SNP was performed by PCR-RFLP. In the first series, the prevalence of Hb types was AA at 86.8% (N = 5198), AS at 12.4% (N = 745), and SS at 0.8% (N = 47). Of the second series, three patients (4.3%) were (±) Xmn1 ′5 to Gγ and 67 (95.7%) were (−/−) in Xmn1 ′5 to Gγ. In the controls, the (±) Xmn1 ′5 to Gγ was observed in only one individual (3.3%), aged 30. These findings possibly represent a new Saudi haplotype, [±] Xmn1 ′5 to Gγ. Our results demonstrate that most patients with SCD in Jazan have [−/−] Xmn1 with higher levels of Hb F and positive Xmn1 ′5 to Gγ normally associated with a low level of Hb F.

Influence of UGT1A1 promoter polymorphism, α-thalassemia and βs haplotype in bilirubin levels and cholelithiasis in a large sickle cell anemia cohort.

Hyperbilirubinemia in patients with sickle cell anemia (SCA) as a result of enhanced erythrocyte destruction, lead to cholelithiasis development in a subset of patients. Evidence suggests that hyperbilirubinemia may be related to genetic variations, such as the UGT1A1 gene promoter polymorphism, which causes Gilbert syndrome (GS). Here, we aimed to determine the frequencies of UGT1A1 promoter alleles, alpha thalassemia, and βS haplotypes and analyze their association with cholelithiasis and bilirubin levels. The UGT1A1 alleles, -3.7 kb alpha thalassemia deletion and βS haplotypes were determined using DNA sequencing and PCR-based assays in 913 patients with SCA. The mean of total and unconjugated bilirubin and the frequency of cholelithiasis in GS patients were higher when compared to those without this condition, regardless of age (P < 0.05). Cumulative analysis demonstrated an early age-at-onset for cholelithiasis in GS genotypes (P < 0.05). Low fetal hemoglobin (HbF) levels and normal alpha thalassemia genotype were related to cholelithiasis development (P > 0.05). However, not cholelithiasis but total and unconjugated bilirubin levels were associated with βS haplotype. These findings confirm in a large cohort that the UGT1A1 polymorphism influences cholelithiasis and hyperbilirubinemia in SCA. HbF and alpha thalassemia also appear as modulators for cholelithiasis risk.

Prevalence of β-S Globin Haplotypes in Jazan Region of Saudi Arabia.

Sickle cell disease (SCD) is a common hematological genetic disorder in Saudi Arabia, Africa, the Mediterranean region, and India. The present study aimed to characterize βS haplotypes found in the Jazan region, Saudi Arabia. One hundred sickle cell trait (SCT) individuals, diagnosed during their visit to the premarital screening clinic at King Fahad Central Hospital, were included in the study. Molecular analysis was carried out by polymerase chain reaction (PCR) and six polymorphic sites of the β-globin gene were analyzed using restriction endonucleases Hind II, Xmn-I, Hind III, and Ava II. The results of the current study revealed the presence of five typical haplotypes in which Benin, Bantu, and Senegal were found in homozygous state with 29%, 3% and 1% frequencies, respectively. Interestingly, 29% of the studied population showed atypical haplotypes in heterozygous state and 2% in homozygous state for the first time in Jazan region. In addition to the typical haplotypes, high frequency of atypical haplotypes in this study indicates a diverse genetic mechanism that might have a crucial effect on the severity of SCD in this region. Therefore, considering this study in a cohort population with SCD in Jazan region may provide more indepth details about the correlation between haplotypes and the clinical manifestation of the disease.

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.

Atypical β-S haplotypes: classification and genetic modulation in patients with sickle cell anemia.

β-S globin haplotype (βS haplotype) characterization in sickle cell anemia (SCA) patients is important because it assists individualized treatment. However, the patient with atypical haplotypes do not present detailed studies such as clinical and laboratory data. To understand the phenotypic expression of atypical haplotype patients in relation to typical haplotype ones, it may be necessary to assess the main clinical and laboratorial parameters and investigate transcription factors, as possible genetic modulators that can contribute to the improvement of the SCA patients' clinical condition. The study group was composed of 600 SCA Brazilian patients of both genders ranging in age from 1 to 68 years. The atypical haplotypes were the third most frequent (5.7%) with 11 patterns numerically ranked according to occurrence. We verified that patients with atypical 1 haplotype in combination with Bantu haplotype presented milder clinical outcomes in relation to Bantu/Bantu and Benin/Benin patients, according to improved values of hemoglobin and hematocrit. In clinical severity, we did not observe significant statistical differences between typical and atypical haplotype patients, and this result can be explained with reference to the action of transcription factors in β-globin cluster. Thus, we presented the atypical haplotype relationship with SCA pathophysiology, reinforcing the hypothesis that individual genetic factors may be responsible for phenotypic diversity of the disease.

Genetic Background of the Sickle Cell Disease Pediatric Population of Dakar, Senegal, and Characterization of a Novel Frameshift β-Thalassemia Mutation [HBB: c.265_266del; p.Leu89Glufs*2

Sickle cell disease is a genetic disorder with a large variability in the pattern and severity of clinical manifestations. Different genetic modulators have been identified but very few epidemiologic data are available on these modifier genes in Senegal. This study aimed to determine their prevalence in a Senegalese sickle cell disease pediatric population. The following genetic parameters were genotyped in 295 sickle cell disease children of the Dakar pediatric hospital: sickle cell disease genotype [βS/βS (HBB: c.20A>T), βS/βC (HBB: c.19G>A), βS/β0-thalassemia (β0-thal)], XmnI polymorphism, the five most common α-thalassemia (α-thal) deletions and the A(–) and Betica glucose-6-phosphate-dehydrogenase (G6PD) deficient variants. Despite very few βS/βC and βS/β0-thal children (1.0% each), a novel frameshift β0-thal mutation was characterized: HBB: c.265_266del; p.Leu89Glufs*2. The –α3.7 (rightward) deletion was the only α-thal deletion identified in this cohort (12.0% allelic frequency). Most of βS/βS patients (61.9%) were homozygous for the XmnI polymorphism and assumed to carry a Senegal/Senegal βS haplotype. The remaining haplotypes were predominantly of the Benin type. While the Betica G6PD variant was quite frequent (13.0%), a low frequency of the A(–) variant was detected (1.0–2.0%). The systematic genotyping of the –α3.7 deletion and of the G6PD Betica variant in sickle cell disease patients from Senegal could be useful to identify patients at risk for several complications, such as cerebral vasculopathy, where it has been demonstrated that a normal α-globin genotype and G6PD deficiency are predisposing factors. These patients should be eligible for a transcranial Doppler examination that is not routinely offered in Senegal.

Genetic modulators of sickle cell disease in French Guiana: Markers of the slave trade.

Sickle cell disease (SCD) is the leading genetic disease in French Guiana, reflecting the predominantly African ancestry of the Guianese population. Our purpose was to characterize the genetic modulators of SCD in order to retrace the origin of the population in light of the slave trade. We have studied the sickle cell genotype, the βS haplotypes, the alpha and beta thalassemia and the UGT1A1 promoter polymorphisms in 224 Guianese patients with SCD. The genotypes of SCD were HbSS 65.6%, HbSC 24.5%, and HbS-beta thalassemia 9.4%. The most frequent βS haplotypes were the Benin haplotype (65.9% of the chromosomes) and the Bantu (20.5%). Alpha thalassemic deletions were present in 37% of the patients and homozygosity for the (TA)7 allele of the UGT1A1 promoter in 21.4%. When the patients' origins were considered, 3 groups, Noir Marron, Haitians and Creoles, displayed distinctive characteristics. The HbSC genotype, the Benin haplotype, and the homozygous UGT1A1 genotype TA7/TA7 were significantly more frequent in Noir Marron. The Haitian patients were characterized by the occurrence of alpha-thalassemia and beta-thalassemia and by a higher prevalence of the Bantu haplotype. In the group of Creole patients, the genotype HbSS was predominant but the other modulators of SCD were associated with intermediate risk. The results highlight the genetic diversity of the Guianese population and are concordant with historical data on the slave trade showing a West African origin for Noir Marron and a Central African origin for Haitians, while Guianese Creoles are highly admixed. Am. J. Hum. Biol. 28:811-816, 2016. © 2016Wiley Periodicals, Inc.

Influence ofβS-Globin Haplotypes and Hydroxyurea on Arginase I Levels in Sickle Cell Disease

Introduction. Sickle cell disease (SCD) is characterized by hemoglobin S homozygosity, leading to hemolysis and vasoocclusion. The hemolysis releases arginase I, an enzyme that decreases the bioavailability of nitric oxide, worsening the symptoms. The different SCD haplotypes are related to clinical symptoms and varied hemoglobin F (HbF) concentration. The aim of this study was to evaluate the impact of the βS gene haplotypes and HbF concentration on arginase I levels in SCD patients. Methods. Fifty SCD adult patients were enrolled in the study and 20 blood donors composed the control group. Arginase I was measured by ELISA. The βS haplotypes were identified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Statistical analyses were performed with GraphPad Prism program and the significance level was p < 0.05. Results. Significant increase was observed in the arginase I levels in SCD patients compared to the control group (p < 0.0001). The comparison between the levels of arginase I in three haplotypes groups showed a difference between the Bantu/Bantu × Bantu/Benin groups; Bantu/Bantu × Benin/Benin, independent of HU dosage. An inverse correlation with the arginase I levels and HbF concentration was observed. Conclusion. The results support the hypothesis that arginase I is associated with HbF concentration, also measured indirectly by the association with haplotypes.

The effects of old and recent migration waves in the distribution of HBB*S globin gene haplotypes

Sickle cell hemoglobin is the result of a mutation at the sixth amino acid position of the beta (β) globin chain. The HBB*S gene is in linkage disequilibrium with five main haplotypes in the β-globin-like gene cluster named according to their ethnic and geographic origins: Bantu (CAR), Benin (BEN), Senegal (SEN), Cameroon (CAM) and Arabian-Indian (ARAB). These haplotypes demonstrated that the sickle cell mutation arose independently at least five times in human history. The distribution of βS haplotypes among Brazilian populations showed a predominance of the CAR haplotype. American populations were clustered in two groups defined by CAR or BEN haplotype frequencies. This scenario is compatible with historical records about the slave trade in the Americas. When all world populations where the sickle cell gene occurs were analyzed, three clusters were disclosed based on CAR, BEN or ARAB haplotype predominance. These patterns may change in the next decades due to recent migrations waves. Since these haplotypes show different clinical characteristics, these recent migrations events raise the necessity to develop optimized public health programs for sickle cell disease screening and management.

Sickle cell anemia and α-thalassemia: A modulating factor in homozygous HbS/S patients in Oman

We report the general phenotype severity and the hematological presentation in a cohort of 125 sickle cell anemia (SCA) patients with identical homozygous HbS/S genotype and categorized by identical βS haplotype, both with and without alpha thalassemia. No clear general phenotype correlation was found when patients were compared regardless of the haplotype but overall, patients with homozygous alpha thalassemia (α−/α−) had the highest Hb, HCT, RBC and the lowest MCV, MCH and MCHC levels. When patients with identical haplotype were compared, the mildest hematological and clinical conditions were observed in patients of the Asian/Asian haplotype, also known as Arab-Indian haplotype, and carriers of α-thalassemia, suggesting an additional ameliorating effect of alpha thalassemia. In conclusion, our results show that alpha thalassemia improves the hematological conditions but amelioration of the general disease severity is only noticed when compared in cohorts of the same haplotype.

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BackgroundSickle cell anemia is a chronic inflammatory disease characterized by an increased production of proinflammatory cytokines including tumor necrosis factor-alpha. Hydroxyurea, by decreasing the polymerization of hemoglobin, reduces inflammatory states. The effect of the genetic polymorphisms of sickle cell patients on tumor necrosis factor-alpha levels remains unknown.ObjectiveThe aim of this study was to investigate the association of tumor necrosis factor-alpha levels with β-globin haplotypes and the use of hydroxyurea.MethodsA cross-sectional study was performed of 67 patients with sickle cell anemia diagnosed at steady-state in a referral hospital in Fortaleza, Ceará, Brazil. A group of 26 healthy individuals was used as control. βS haplotype analysis was performed by restriction fragment length polymorphism-polymerase chain reaction. The tumor necrosis factor- alpha levels were measured by the enzyme-linked immunosorbent assay test. Laboratory data (complete blood count and fetal hemoglobin) and information regarding the use of hydroxyurea were obtained from medical records. Statistical analysis was performed using R software with the Kruskal-Wallis and Mann–Whitney tests. Statistical significance was established for p-values < 0.05 for all analyses.ResultsThe mean age of the participants was 35.48 years. Patients with sickle cell anemia had significantly higher tumor necrosis factor-alpha levels than controls (p-values < 0.0001). Tumor necrosis factor-alpha levels were lower in sickle cell anemia patients who were receiving hydroxyurea treatment than those who were not (p-value = 0.1249). Sickle cell anemia patients with Bantu/n genotype had significantly higher levels than patients with the Bantu/Benin genotype (p-value = 0.0021).ConclusionIn summary, βS-globin haplotypes, but not hydroxyurea therapy, have a role in modulating tumor necrosis factor-alpha levels in sickle cell anemia adults at steady-state. Many previous studies have investigated prognosis and inflammatory states in sickle cell anemia patients, but the discovery that tumor necrosis factor-alpha levels vary according to the genetic polymorphism of the patient is a new finding. © 2014 Associação Brasileira de Hematologia, Hemoterapia e Terapia Celular. All rights reserved.

Influence of the βs haplotype and α-thalassemia on stroke development in a Brazilian population with sickle cell anaemia

Stroke is a catastrophic complication of sickle cell anaemia (SCA) and is one of the leading causes of death in both adults and children with SCA. Evidence suggests that some genetic polymorphisms could be related to stroke development, but their association remains controversial. Here, we performed genotyping of five published single nucleotide polymorphisms, the α-thalassemia genotype, the G6PD A (-) variant deficiency, and the β(S) haplotype in a large series of SCA patients with well-defined stroke phenotypes. Of 261 unrelated SCA patients included in the study, 67 (9.5%) presented a documented, primary stroke event. Markers of haemolysis (red blood cell (RBC) counts, p = 0.023; reticulocyte counts, p = 0.003; haemoglobin (Hb) levels, p < 0.001; indirect bilirubin levels, p = 0.006; lactate dehydrogenase (LDH) levels, p = 0.001) were associated with stroke susceptibility. Genetically, only the β(S) haplotype (odds ratio (OR) 2.9, 95% confidence interval (CI) 1.56 to 4.31; p = 0.003) and the α(3.7kb)-thalassemia genotype (OR 0.31, 95% CI 0.11 to 0. 83; p = 0.02) were associated with increased and decreased stroke risk, respectively. In multivariate analysis, the β(S) haplotype was independently associated with stroke development (OR 2.26, 95% CI 1.16 to 4.4; p = 0.016). Our findings suggest that only the β(S) haplotypes and the α(3.7kb)-thalassemia genotype modulate the prevalence of stroke in our SCA population. Genetic heterogeneity among different populations may account for the irreproducibility amongst different studies.

&amp;lt;i&amp;gt;&amp;#223;&amp;lt;/i&amp;gt;-Globin Gene Cluster Haplotypes and Clinical Severity in Sickle Cell Anemia Patients in Southern Brazil

Hematopoietic stem cell transplantation(HSCT)has emerged as a curative strategy for sickle cell anemia(SCA); it is necessary to find markers of SCA clinical severity to spare those SCA patients whose clinical course is mild from the morbidity and mortality associated with HSCT. Haplotypes have been correlated with the severity of clinical manifestations in SCA patients, and fetal hemoglobin(HbF)and socioeconomic status(SeS)have also been described as negative factors. We studied these factors and their impact on clinical manifestations in a population of Southern Brazilian patients attending the Center for Sickle Cell Anemia at Hospital de Clinicas de Porto Alegre/RS, Brazil. Clinical severity was defined as two or more veno-occlusive episodes per year. The βS haplotypes were determined by PCR in 75 SCA patients. Among the 150 βS chromosomes analyzed, 99(66%)were identified as Bantu(Ban), 41(27%)asBenin(Ben), and 10(7%)as other haplotypes. Most patients in our sample(62.7%)belonged to lower SeS groups, precluding meaningful statistical analysis of SeS impact on clinical severity. There was no correlation between haplotypes or HbF level and SCA clinical severity. Gene polymorphisms and environmental issues have to be taken into consideration.

Beta-S globin haplotypes in patients with sickle cell anemia: one approach to understand the diversity in Brazil

Sickle cell anemia (SCA) is defined as a monogenic disease that characterizes thehomozygous state of hemoglobin S (Hb S). Hemoglobin S polymerizes under adverse conditionssuch as deoxygenation, acidosis or dehydration. Its polymers deform erythrocytes and leadto a diverse and complex pathophysiology(1,2). Beta-S globin haplotypes (βS haplotypes) areimportant in the comprehension of the clinical diversity of SCA patients. Five haplotypes havebeen associated with different ethnic groups. They are identified at specific restriction sites andnamed according to their region of origin and prevalence: Bantu, Benin, Senegal, Arabic-Indian(Saudi) and Cameroon(3). This study aimed to assess the frequencies of βS haplotypes in patientswith SCA from Rio de Janeiro State, Brazil. We analyzed DNA samples from 790 patients withsickle cell disease (SCD) and classified them according to their haplotypes through an analysisof six polymorphic sites reported by Sutton et al.(4). According to these authors, haplotypes thatdo not exhibit known digestion patterns should be classified as atypical. The polymorphic sites were evaluated by polymerase chain reaction (PCR) followed by restriction fragment lengthpolymorphism (RFLP)(4,5). Of the 790 patients, 527 had SCA with the following frequencies of genotyped βS haplotypes: 295 (56.0%) Bantu/Bantu; 128 (24.3%) Bantu/Benin; 44 (8.3%)Bantu/Atypical; 36 (6.84%) Benin/Benin; 10 (1.9%) Benin/Atypical; three (0.57%) Bantu/Cameroon; three (0.57%) Benin/Cameroon; three (0.57%) Atypical/Atypical; two (0.38%)Bantu/Saudi; two (0.38%) Bantu/Senegal and one (0.19%) Benin/Saudi. From the totalnumber of 1054 chromosomes analyzed, 769 (72.96%) were identified with the Bantu allele according to the allelic frequency evaluation; 214 (20.3%) Benin; 60 (5.7%) Atypical; six(0.57%) Cameroon; three (0.28%) Saudi and two (0.19%) Senegal. Data from genotype and allele frequencies are shown in Table 1. The high frequencies of Bantu and Benin haplotypesdemonstrate the influence of Western and South-Central African on the evolution of the Brazilian population(6). We identified atypical haplotypes which may have originated due togenetic mechanisms such as gene conversions and the intense miscegenation between ethnicgroups that inhabit Rio de Janeiro State and Brazil. We emphasize the need of identifying and characterizing these genetic variations in order to better understand the clinical aspects and phenotypic diversity found in Brazilian SCD patients. Table 1 Allelic and genotypic frequency of beta-S globin haplotypes

Hb S [β6(A3)Glu→Val, GAG>GTG] and β-Globin Gene Cluster Haplotype Distribution in Mauritania

Of 1050 Mauritanian blood donors screened from the two main racial groups, i.e., the Moors and Black Africans, 60 were found to carry Hb S [β6(A3)Glu→Val, GAG >GTG], giving a global frequency of 5.71%. The prevalence observed in the Black African Mauritanians (10.69%) is almost five times that found in the Moor group (2.25%). Four of the five main βS haplotypes were detected in this study: Senegal (77.8%), Benin (8.8%), Arab-Indian (5.5%) and Bantu (4.4%). These data showed that Hb S is a serious public health problem in Mauritania. They also confirm the ethnic heterogeneity of the Mauritanian population.

Determination of βS haplotypes in patients with sickle-cell anemia in the state of Rio Grande do Norte, Brazil

βS haplotypes were studied in 47 non-related patients with sickle-cell anemia from the state of Rio Grande do Norte, Brazil. Molecular analysis was conducted by PCR/RFLP using restriction endonucleases XmnI, HindIII, HincII and HinfI to analyze six polymorphic sites from the beta cluster. Twenty-seven patients (57.5%) were identified with genotype CAR/CAR, 9 (19.1%) CAR/BEN, 6 (12.8%) CAR/CAM, 1 (2.1%) BEN/BEN, 2 (4.3%) CAR/Atp, 1 (2.1%) BEN/Atp and 1 (2.1%) with genotype Atp/Atp. The greater frequency of Cameroon haplotypes compared to other Brazilian states suggests the existence of a peculiarity of African origin in the state of Rio Grande do Norte.

Mortality in Sickle Cell Patients on Hydroxyurea Therapy

Mortality in Sickle Cell Patients on Hydroxyurea Therapy

Determinants of Red Cell Survival and Erythropoietic Activity in Patients with Sickle Cell Anemia in the Steady State

We have studied 26 patients with sickle cell anemia to determine the factors that affect red blood cell (RBC) survival and other parameters of erythropoietic activity in the steady state. Determinants of erythropoietic activity included RBC survival by the 51Cr method, RBC production/destruction rate, a genotype, βs haplotype, plasma 59Fe clearance, plasma iron turnover, eryth-ron transferrin uptake), RBC Fe utilization, reticulocyte count, and erythro-poietin levels. The α genotype was the most significant determinant of RBC survival followed, to a lesser extent, by the βs haplotype. Hb F showed no correlation with RBC survival due to patient selection bias - the patients studied had comparable Hb F levels to start with. Other determinants of erythropoietic activity (hemoglobin level, mean corpuscular volume, reticulocyte count, RBC mass, RBC production/destruction rate, and erythropoietin level) were most likely secondary determinants associated with the α genotype, and not independent determinants in themselves. The data suggest that the α genotype and, and to a lesser extent, the βs haplotype, might be determinants of the severity of the anemia of sickle cell disease, and should be considered in genetic counseling and patient selection for aggressive therapeutic interventions.

Diverse Genetic Mechanisms Operate to Generate Atypical βs Haplotypes in the Population of Guadeloupe

In a survey of the chromosomal background associated with the sickle cell gene in Guadeloupe, a French Caribbean island, we identified 37 unrelated patients with sickle cell disease (27 SS, nine SC, and one S-β-thalassemia) of 477 unrelated sickle cell patients where the βs gene was linked to 20 different atypical haplotypes. These atypical chromosomes account for about 5% of the overall βs chromosomes in this population. To investigate the origin of these atypical βs haplotypes, we performed extensive typing of βs and βAchromosomes. Twenty-two different 5' subhaplotypes were identified among the βs chromosomes. Fifteen of 20 different atypical haplotypes are likely to be the product of recombination by a single crossover around the <<hot-spot>> 5' to the β-globin gene, or between a major βs haplotype and one of the βs haplotypes present in the population. The remaining casm require genetic mechanisms (gene conversions, additional substitutions in a given haplotype) other than crossovers to generate these atypical haplotypes.

Historical and Anthropological Correlates of βS Haplotypes and α- and β-Thalassemia Alleles in the Arabian Peninsula

(1997). Historical and Anthropological Correlates of βS Haplotypes and α- and β-Thalassemia Alleles in the Arabian Peninsula. Hemoglobin: Vol. 21, No. 3, pp. 281-296.