The variability of sickle-cell rates in the tribes of Kenya and the Southern Sudan

Malaria is a cause of iron deficiency in African children

Malaria and iron deficiency (ID) are common and interrelated public health problems in African children. Observational data suggest that interrupting malaria transmission reduces the prevalence of ID1. To test the hypothesis that malaria might cause ID, we used sickle cell trait (HbAS, rs334 ), a genetic variant that confers specific protection against malaria2, as an instrumental variable in Mendelian randomization analyses. HbAS was associated with a 30% reduction in ID among children living in malaria-endemic countries in Africa (n = 7,453), but not among individuals living in malaria-free areas (n = 3,818). Genetically predicted malaria risk was associated with an odds ratio of 2.65 for ID per unit increase in the log incidence rate of malaria. This suggests that an intervention that halves the risk of malaria episodes would reduce the prevalence of ID in African children by 49%.

Prevalence of sickle cell disease and sickle cell trait among children admitted to Al Fashir Teaching Hospital North Darfur State, Sudan

Objective

It is estimated that 50% to 90% of infants born with (SCA) in sub-Saharan Africa die before 5 years old. Northern Darfur State at western Sudan region has a multiethnic population with a high frequency of sickle cell anaemia, but little about it is published. This study aimed to determine the prevalence of sickle cell anaemia among children admitted to Al Fashir Teaching Hospital in Al Fashir, Northern Darfur State, Sudan.

Results

The prevalence of sickle cell disease by haemoglobin electrophoresis among these 400 children patients was 59 (14.8%). Sickle cell trait patients were 11.3% and Sickle cell disease positive patients were 3.5%. Individuals with SCA have consistently low blood Hb concentration, normal MCV and high mean WBC’s. Individuals with sickle cell trait had haematological parameters near to those of normal individuals.

Micronutrient status differs among Maasai and Kamba preschoolers in a supplementary feeding programme in Kenya

Since 2001, ChildFund Kenya has supplied micronutrient fortified school meals to preschoolers from two tribes (Kamba and Maasai) attending early childhood development (ECD) centres in Emali, S.E. Kenya. Lack of information on the micronutrient status of the preschoolers prompted a cross-sectional assessment of micronutrient (iron, zinc, selenium, vitamin A, vitamin D) status and prevalence of deficiencies among the two tribes. Data on sociodemographic, health, anthropometric status, and micronutrient supply from preschool meals were collected from 287 Kamba and 213 Maasai children aged 3 to 5 years attending 23 ECD centres. Nonfasting blood samples were collected for haemoglobin and plasma biomarkers of iron, zinc, selenium, vitamin A, vitamin D, C-reactive protein (CRP), α₁ -acid glycoprotein, and immunoglobin G. The prevalence of anaemia was significantly higher in Maasai children than Kamba (38%, 95% CI [31%, 45%], vs. 5%, [3%, 9%]), as well as iron deficiency and its various stages (P < 0.001). No differences were seen in the prevalence of zinc, selenium, vitamin A, or vitamin D deficiencies (all P > 0.05). Body iron, CRP, and age were significant predictors of haemoglobin concentrations for both tribes (all P < 0.006) and plasma 25-OHD for Maasai children only. The higher prevalence of iron deficiency among Maasai than Kamba children was possibly attributed to the high consumption of cow's milk (low in bioavailable iron) in place of micronutrient fortified meals together with a higher prevalence of chronic inflammation and intestinal damage.

Effect of Previous Exposure to Malaria on Blood Pressure in Kilifi, Kenya: A Mendelian Randomization Study

Background Malaria exposure in childhood may contribute to high blood pressure ( BP ) in adults. We used sickle cell trait ( SCT ) and α+thalassemia, genetic variants conferring partial protection against malaria, as tools to test this hypothesis. Methods and Results Study sites were Kilifi, Kenya, which has malaria transmission, and Nairobi, Kenya, and Jackson, Mississippi, where there is no malaria transmission. The primary outcome was 24-hour systolic BP. Prevalent hypertension, diagnosed using European Society of Hypertension thresholds was a secondary outcome. We performed regression analyses adjusting for age, sex, and estimated glomerular filtration rate. We studied 1127 participants in Kilifi, 516 in Nairobi, and 651 in Jackson. SCT frequency was 21% in Kilifi, 16% in Nairobi, and 9% in Jackson. SCT was associated with -2.4 (95% CI , -4.7 to -0.2) mm Hg lower 24-hour systolic BP in Kilifi but had no effect in Nairobi/Jackson. The effect of SCT in Kilifi was limited to 30- to 59-year-old participants, among whom it was associated with -6.1 mm Hg ( CI , -10.5 to -1.8) lower 24-hour systolic BP. In pooled analysis allowing interaction by site, the effect of SCT on 24-hour systolic BP in Kilifi was -3.5 mm Hg ( CI , -6.9 to -0.1), increasing to -5.2 mm Hg ( CI , -9.5 to -0.9) when replacing estimated glomerular filtration rate with urine albumin to creatinine ratio as a covariate. In Kilifi, the prevalence ratio for hypertension was 0.86 ( CI , 0.76-0.98) for SCT and 0.89 ( CI , 0.80-0.99) for α+thalassemia. Conclusions Lifelong malaria protection is associated with lower BP in Kilifi. Confirmation of this finding at other sites and elucidating the mechanisms involved may yield new preventive and therapeutic targets.

Blood Pressure and Arterial Stiffness in Kenyan Adolescents With the Sickle Cell Trait

The potential association between sickle cell trait (SCT) and increased arterial stiffness/blood pressure (BP) has not been evaluated in detail despite its association with stroke, sudden death, and renal disease. We performed 24-hour ambulatory BP monitoring and arterial stiffness measurements in adolescents raised in a malaria-free environment in Kenya. Between December 2015 and June 2016, 938 randomly selected adolescents (ages 11–17 years) who had been continuous residents of Nairobi from birth were invited to participate in the study. Standard clinic BP measurement was performed, followed by 24-hour ambulatory BP monitoring and arterial stiffness measurement using an Arteriograph24 (TensioMed Ltd., Budapest, Hungary) device. SCT status was determined using DNA genotyping in contemporaneously collected blood samples. Of the 938 adolescents invited to participate, 609 (65%) provided complete data for analysis. SCT was present in 103 (15%). Mean 24-hour systolic and diastolic BPs were 116 (standard deviation (SD), 11.5) mm Hg and 64 (SD, 7) mm Hg, respectively, in children with SCT and 117 (SD, 11.4) mm Hg and 64 (SD, 6.8) mm Hg, respectively, in non-SCT children. Mean pulse wave velocity (PWV) was 7.1 (SD, 0.8) m/second and 7.0 (SD, 0.8) m/second in SCT and non-SCT children, respectively. We observed no differences in PWV or in any clinic or ambulatory BP-derived measures between adolescents with and without SCT. These data suggest that SCT does not independently influence BP or PWV.

Environmental Correlation Analysis for Genes Associated with Protection against Malaria

Genome-wide searches for loci involved in human resistance to malaria are currently being conducted on a large scale in Africa using case-control studies. Here, we explore the utility of an alternative approach-"environmental correlation analysis, ECA," which tests for clines in allele frequencies across a gradient of an environmental selection pressure-to identify genes that have historically protected against death from malaria. We collected genotype data from 12,425 newborns on 57 candidate malaria resistance loci and 9,756 single nucleotide polymorphisms (SNPs) selected at random from across the genome, and examined their allele frequencies for geographic correlations with long-term malaria prevalence data based on 84,042 individuals living under different historical selection pressures from malaria in coastal Kenya. None of the 57 candidate SNPs showed significant (P < 0.05) correlations in allele frequency with local malaria transmission intensity after adjusting for population structure and multiple testing. In contrast, two of the random SNPs that had highly significant correlations (P < 0.01) were in genes previously linked to malaria resistance, namely, CDH13, encoding cadherin 13, and HS3ST3B1, encoding heparan sulfate 3-O-sulfotransferase 3B1. Both proteins play a role in glycoprotein-mediated cell-cell adhesion which has been widely implicated in cerebral malaria, the most life-threatening form of this disease. Other top genes, including CTNND2 which encodes δ-catenin, a molecular partner to cadherin, were significantly enriched in cadherin-mediated pathways affecting inflammation of the brain vascular endothelium. These results demonstrate the utility of ECA in the discovery of novel genes and pathways affecting infectious disease.

Nutritional status of young children with inherited blood disorders in western Kenya

To determine the association between a range of inherited blood disorders and indicators of poor nutrition, we analyzed data from a population-based, cross-sectional survey of 882 children 6–35 months of age in western Kenya. Of children with valid measurements, 71.7% were anemic (hemoglobin < 11 g/dL), 19.1% had ferritin levels < 12 μg/L, and 30.9% had retinol binding protein (RBP) levels < 0.7 μmol/L. Unadjusted analyses showed that compared with normal children, homozygous α⁺-thalassemia individuals had a higher prevalence of anemia (82.3% versus 66.8%, P = 0.001), but a lower prevalence of low RBP (20.5% versus 31.4%, P = 0.024). In multivariable analysis, homozygous α⁺-thalassemia remained associated with anemia (adjusted odds ratio [aOR] = 1.8, P = 0.004) but not with low RBP (aOR = 0.6, P = 0.065). Among young Kenyan children, α⁺-thalassemia is associated with anemia, whereas G6PD deficiency, haptoglobin 2-2, and HbS are not; none of these blood disorders are associated with iron deficiency, vitamin A deficiency, or poor growth.

Sickle cell trait is not associated with endemic Burkitt lymphoma: an ethnicity and malaria endemicity-matched case-control study suggests factors controlling EBV may serve as a predictive biomarker for this pediatric cancer

Endemic Burkitt lymphoma (eBL) is associated with Epstein–Barr virus (EBV) and Plasmodium falciparum coinfections. Malaria appears to dysregulate immunity that would otherwise control EBV, thereby contributing to eBL etiology. Juxtaposed to human genetic variants associated with protection from malaria, it has been hypothesized that such variants could decrease eBL susceptibility, historically referred to as “the protective hypothesis.” Past studies attempting to link sickle cell trait (HbAS), which is known to be protective against malaria, with protection from eBL were contradictory and underpowered. Therefore, using a case–control study design, we examined HbAS frequency in 306 Kenyan children diagnosed with eBL compared to 537 geographically defined and ethnically matched controls. We found 23.8% HbAS for eBL patients, which was not significantly different compared to 27.0% HbAS for controls [odds ratio (OR) = 0.85; 95% confidence interval (CI) 0.61–1.17; p-value = 0.33]. Even though cellular EBV titers, indicative of the number of latently infected B cells, were significantly higher (p-value < 0.0003) in children residing in malaria holoendemic compared to hypoendemic areas, levels were not associated with HbAS genotype. Combined, this suggests that although HbAS protects against severe malaria and hyperparasitemia, it is not associated with viral control or eBL protection. However, based on receiver operating characteristic curves factors that enable the establishment of EBV persistence, in contrast to those involved in EBV lytic reactivation, may have utility as an eBL precursor biomarker. This has implications for future human genetic association studies to consider variants influencing control over EBV in addition to malaria as risk factors for eBL.

World distribution, population genetics, and health burden of the hemoglobinopathies

Although information about the precise world distribution and frequency of the inherited hemoglobin disorders is still limited, there is no doubt that they are going to pose an increasing burden on global health resources in the future. Their high frequency is a reflection of natural selection combined with a high frequency of consanguineous marriages in many countries, together with an epidemiological transition; whereby, as public health measures improve in the poorer countries of the world, more babies with these disorders are surviving to present for treatment.

Sickle cell disease in Middle East Arab countries

The sickle cell (HbS) gene occurs at a variable frequency in the Middle Eastern Arab countries, with characteristic distribution patterns and representing an overall picture of blood genetic disorders in the region. The origin of the gene has been debated, but studies using β-globin gene haplotypes have ascertained that there were multiple origins for HbS. In some regions the HbS gene is common and exhibits polymorphism, while the reverse is true in others. A common causative factor for the high prevalence and maintenance of HbS and thalassaemia genes is malaria endemicity. The HbS gene also co-exists with other haemoglobin variants and thalassaemia genes and the resulting clinical state is referred to as sickle cell disease (SCD). In the Middle Eastern Arab countries, the clinical picture of SCD expresses two distinct forms, the benign and the severe forms, which are related to two distinct β-globin gene haplotypes. These are referred to as the Saudi-Indian and the Benin haplotypes, respectively. In a majority of the Middle Eastern Arab countries the HbS is linked to the Saudi-Indian haplotype, while in others it is linked to the Benin haplotype. This review outlines the frequency, distribution, clinical feature, management and prevention as well as gene interactions of the HbS genes with other haemoglobin disorders in the Middle Eastern Arab countries.

Between black and miscegenated population groups: sickle cell anemia and sickle cell trait in Brazil in the 1930s and 1940s

The article examines medical and scientific studies of sickle cell anemia published in Brazil in the 1930s and 1940s, when the vast majority of physicians and scientists believed that miscegenation played a significant role in the epidemiology of the disease in the country. Special focus is placed on hematologist Ernani Martins da Silva, of the Oswaldo Cruz Institute, who conducted blood analyses around the interior of Brazil with the purpose of classifying miscegenated and pure population groups based on the presence of sickle cells and the racial distribution of blood groups. The article explores the ambivalences stemming from associations between sickle cell anemia and the 'black race' during this period.

Reference ranges for the clinical laboratory derived from a rural population in Kericho, Kenya

The conduct of Phase I/II HIV vaccine trials internationally necessitates the development of region-specific clinical reference ranges for trial enrollment and participant monitoring. A population based cohort of adults in Kericho, Kenya, a potential vaccine trial site, allowed development of clinical laboratory reference ranges. Lymphocyte immunophenotyping was performed on 1293 HIV seronegative study participants. Hematology and clinical chemistry were performed on up to 1541 cohort enrollees. The ratio of males to females was 1.9:1. Means, medians and 95% reference ranges were calculated and compared with those from other nations. The median CD4+ T cell count for the group was 810 cells/microl. There were significant gender differences for both red and white blood cell parameters. Kenyan subjects had lower median hemoglobin concentrations (9.5 g/dL; range 6.7-11.1) and neutrophil counts (1850 cells/microl; range 914-4715) compared to North Americans. Kenyan clinical chemistry reference ranges were comparable to those from the USA, with the exception of the upper limits for bilirubin and blood urea nitrogen, which were 2.3-fold higher and 1.5-fold lower, respectively. This study is the first to assess clinical reference ranges for a highland community in Kenya and highlights the need to define clinical laboratory ranges from the national community not only for clinical research but also care and treatment.

Reference ranges for the clinical laboratory derived from a rural population in Kericho, Kenya

The conduct of Phase I/II HIV vaccine trials internationally necessitates the development of region-specific clinical reference ranges for trial enrolment and participant monitoring. A population based cohort of adults in Kericho, Kenya, a potential vaccine trial site, allowed development of clinical laboratory reference ranges. Lymphocyte immunophenotyping was performed on 1293 HIV seronegative study participants. Hematology and clinical chemistry were performed on up to 1541 cohort enrollees. The ratio of males to females was 1.9∶1. Means, medians and 95% reference ranges were calculated and compared with those from other nations. The median CD4+ T cell count for the group was 810 cells/µl. There were significant gender differences for both red and white blood cell parameters. Kenyan subjects had lower median hemoglobin concentrations (9.5 g/dL; range 6.7–11.1) and neutrophil counts (1850 cells/µl; range 914–4715) compared to North Americans. Kenyan clinical chemistry reference ranges were comparable to those from the USA, with the exception of the upper limits for bilirubin and blood urea nitrogen, which were 2.3-fold higher and 1.5-fold lower, respectively. This study is the first to assess clinical reference ranges for a highland community in Kenya and highlights the need to define clinical laboratory ranges from the national community not only for clinical research but also care and treatment.

Relationship of the sickle cell gene to the ethnic and geographic groups populating the Sudan

The presence of a geographical pattern in the distribution of the sickle cell gene (S gene) and its association with malaria is well documented. To study the distribution of the S gene among various ethnic and linguistic groups in the Sudan we analyzed a hospital-based sample of 189 sickle cell anemia (SCA) patients who reported to the Khartoum Teaching Hospital between June 1996 and March 2000 and 118 controls with other complaints, against their ethnic and linguistic affiliations and geographic origin. Electrophoresis for hemoglobin S and sickling tests were carried out on all patients and controls as a prerequisite for inclusion. The majority of patients (93.7%) belonged to families of single ethnic descent, indicating the high degree of within-group marriages and thus the higher risk of augmenting the gene. SCA was found to be predominant among the Afro-Asiatic-speaking groups (68.4%) including nomadic groups of Arab and non- Arab descent that migrated to the Sudan in various historical epochs. Those patients clustered in western Sudan (Kordofan and Darfur) from where 73% of all cases originate. The proportion of patients reporting from other geographic areas like the south (3.1%), which is primarily inhabited by Nilo-Saharan-speaking groups (19% of the whole sample) who populated the country in previous times, is disproportionate to their total population in the country (chi(2) = 71.6; p = 0.0001). Analysis of the haplotypes associated with the S gene indicated that the most abundant haplotypes are the Cameroon, Benin, Bantu and Senegal haplotypes, respectively. No relationship was seen between haplotypes and the various hematological parameters in the sub-sample analyzed for such association. These results provide an insight into the distribution of the sickle cell gene in the Sudan, and highlight the strong link of the middle Nile Valley with West Africa through the open plateau of the Sahel and the nomadic cattle herders and also probably the relatively young age of the S gene.

Sickle cell trait and the risk of Plasmodium falciparum malaria and other childhood diseases

BACKGROUND

The gene for sickle hemoglobin (HbS) is a prime example of natural selection. It is generally believed that its current prevalence in many tropical populations reflects selection for the carrier form (sickle cell trait [HbAS]) through a survival advantage against death from malaria. Nevertheless, >50 years after this hypothesis was first proposed, the epidemiological description of the relationships between HbAS, malaria, and other common causes of child mortality remains incomplete.

METHODS

We studied the incidence of falciparum malaria and other childhood diseases in 2 cohorts of children living on the coast of Kenya.

RESULTS

The protective effect of HbAS was remarkably specific for falciparum malaria, having no significant impact on any other disease. HbAS had no effect on the prevalence of symptomless parasitemia but was 50% protective against mild clinical malaria, 75% protective against admission to the hospital for malaria, and almost 90% protective against severe or complicated malaria. The effect of HbAS on episodes of clinical malaria was mirrored in its effect on parasite densities during such episodes.

CONCLUSIONS

The present data are useful in that they confirm the mechanisms by which HbAS confers protection against malaria and shed light on the relationships between HbAS, malaria, and other childhood diseases.

Serum transferrin receptor concentration indicates increased erythropoiesis in Kenyan children with asymptomatic malaria

BACKGROUND

Serum transferrin receptor concentrations indicate both erythropoietic activity and the deficit of functional iron in the erythron. In contrast with serum ferritin concentrations, serum transferrin receptor concentrations are not or are only marginally influenced by the inflammatory response to infection.

OBJECTIVE

We assessed iron status and examined the relation between serum transferrin receptor concentrations and malaria in children aged 2-36 mo who were asymptomatic for malaria.

DESIGN

This was a community-based cluster survey (n = 318).

RESULTS

Prevalences of malaria, anemia (hemoglobin concentration <110 g/L), iron deficiency (serum ferritin concentration <12 microg/L), and iron deficiency anemia were 18%, 69%, 53%, and 46%, respectively. Malaria was associated with lower mean hemoglobin concentrations (92.7 compared with 104.1 g/L; P = 0.0001) and higher geometric mean serum concentrations of transferrin receptor (11.4 compared with 7.8 mg/L; P = 0.005), ferritin (21.6 compared with 11.9 microg/L; P = 0.05), and C-reactive protein (12.5 compared with 6.8 mg/L; P = 0.004). There was no evidence for an association between serum concentrations of C-reactive protein and transferrin receptor. Children with malaria had higher serum transferrin receptor concentrations than expected for the degree of anemia, even after adjustment for inflammation indicated by serum C-reactive protein concentration quartiles (P = 0.02).

CONCLUSIONS

Our findings are consistent with the notion that malaria-induced hemolysis is accompanied by increased erythropoiesis. Serum transferrin receptor concentration is not useful for detecting iron deficiency in individuals with malaria. Individuals with high concentrations of serum C-reactive protein or similar acute phase reactants should be excluded from analysis if serum ferritin concentrations <12 microg/L are to be used to measure iron deficiency in malaria-endemic areas.

Sickle cell anaemia in Sudan: clinical findings, haematological and serum variables

Ninety homozygous patients with Hb S haemoglobinopathy from Sudan were reported with respect to clinical findings, haematological and serum parameters. For comparison, 27 Hb AS heterozygous subjects and 28 Hb AA controls were investigated also. The patients showed an extreme type of illness presenting with severe clinical signs such as dactylitis, liver enlargement and cardiac complications. There was marked haemolytic anaemia (mean haemoglobin 66 g/l). Some patients also presented with low serum (S)-iron levels, indicating iron deficiency. S-bilirubin, S-ASAT, S-ALAT, S-GT and S-urate were notably raised, most probably as a consequence of haemolysis with liver involvement. The patients had lower S-calcium levels when compared with the AS and AA subjects. This may suggest a possible role of HB S in the production of this feature.

Some blood genetic markers of the Nuba and Hawazma tribes of western Sudan

Two hundred eighty subjects comprising 112 Nuba and 168 Hawazma of the Sudan were tested for the distribution of hemoglobins, eight red cell enzymes, and four serum proteins. The Nuba, the indigenous negroid tribe, had no HbS, HbO-Arab, or GdB(Khartoum) compared to the Hawazma tribe of Negro-Arab descent. The gene frequencies of the above polymorphic systems in the latter were as follows: HbS, 0.13; HbO-Arab, 0.01; GdB(Khartoum), 0.03. The frequency of GdA was higher in the Hawazma than in the Nuba. A high frequency of glucose 6-phosphate dehydrogenase (G6PD) deficiency and HpO was present in both the tribes. Essentially similar gene frequencies of Hp1, TfD, PGDC, pC, and PGM1 were observed in both Nuba and Hawazma. The average heterozygosity at five polymorphic loci was the same (0.23) in both the tribes. The above results agree with the social practice whereby people of mixed Hawazma and Nuba descent are considered members of the Hawazma tribe and confirm that racial admixture between the two groups can be seen as a process of gene flow from the Nuba to the Hawazma, even though the Nuba are the indigenous group, while the Hawazma are the new settlers.

Some blood genetic characteristics of several Sudanese tribes

The distribution of ABO and Rhesus blood groups, serum haptoglobin, and transferrin; red cell glucose-6-phosphate dehydrogenase and acid phosphatase; and hemoglobin was studied among the two aboriginal negroid tribes (Nuba and Fur); the Nilotic tribe; five tribes of Arab ancestory; and a mixed group of other minor tribes of Arab origin. The Nilotic and Nuba tribes were genetically quite distinct from the rest, with lower R1, R2, and r in the Rhesus system and low HbS and Gd-. The Arab tribes had a genetic structure which was intermediate between that of the original negroid population of the Sudan and the Arabs to the north. However, some of the Arab tribes had special genetical characteristics, e.g., Messeria had high TfD1; both Messeria and Hawazma had high HbS and Gd-, while GdA was higher only in the Hawazma. The Gaalin had very low HbS, Ro, GdA, and Gd-, suggestive of less negroid admixture compared to Messeria and Hawazma. The Fur, though an aboriginal negroid tribe, had genetic characteristics similar to Arabs.

Haplotypes and alpha globin gene analyses in sickle cell anaemia patients from Kenya

Over 60 patients from the Luo and Luhya tribes of Western Kenya, aged 1-23 years, with severe sickle cell anaemia were evaluated through haematological and gene mapping analyses. Nearly all (56 of 58 tested) were homozygous for haplotype 20 (Antonarakis et al, 1984) which is also frequently present in SS patients of the Central African Republic. All patients had a severe haemolytic anaemia with low Hb F levels and low levels of G gamma chains. An alpha-thalassaemia-2 heterozygosity (-alpha/alpha alpha; -3.7 kb deletion) was present in 26 of 53 patients tested; one patient was a homozygote [f(-alpha) = 0.255]. The alpha-thal-2 was type I in all but one subject with this deficiency; the one exception had an alpha-thal-2 heterozygosity, type II. Heterozygosity for the alpha-thal-2 did not affect the clinical condition nor the haematology; Hb F levels were somewhat lower in SS patients with -alpha/alpha alpha than in those with alpha alpha/alpha alpha. A high frequency was observed for the absence of an Xba I restriction site 5' to the zeta globin gene; the frequency of this anomaly [f(Xba I-)] was estimated at 0.39 for the chromosome with two alpha globin genes and at 0.74 for that with the alpha-thal-2 deletion. An Apa I restriction site polymorphism was observed in the IVS-II of the alpha 2 globin gene; 13 alpha 2 genes of 53 normal (alpha alpha/) chromosomes had this restriction site which was absent in the hybrid alpha globin gene of the -alpha/chromosome.

Sickling and malaria

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