On the nature of sickle-cell disease in the Arabian Peninsula

Summary The sickle-cell gene contributes substantially to the presentation of anaemia in certain areas of the Arabian Peninsula. However, the clinical presentation of the homozygous state of Hb S is less severe than that observed in other ethnic groups, such as American negroes. In the present paper, biosynthesis studies performed on reticulocytes from heterozygotes and homozygotes for the Hb S give further indications of the mild nature of sickle-cell disease in Arabia. Comparison of two affected families, from Saudi Arabia and Jordan, showed that clinical manifestation of the disease is mirrored by the biochemical and haematological findings in affected individuals. The results are discussed in terms of the effect of co-existing thalassaemia and/or iron deficiency with Hb S. It is suggested that both genetic and acquired conditions play a role in the clinical features of the disease. The mechanisms responsible for regulation of -chain synthesis by iron (haem) deficiency are discussed.     

Sickle beta 0 thalassemia in Eastern Saudi Arabia

The sickle cell (beta s) gene occurs at a high frequency in the oasis populations of Eastern Saudi Arabia. However, as compared with the disorder in Africans, sickle cell anemia runs an unusually benign clinical course in this populations; this has been attributed in part to the relatively high levels of fetal hemoglobin (Hb F) which characterize Saudi Arabians with this condition [1, 2]. As yet, there is no satisfactory explanation for this remarkable phenomenon. To learn more about the expression of the beta s gene in Eastern Saudi Arabia, we examined its interaction with beta 0 thalassemia. We found that remarkably high levels of Hb F in this population are not restricted to individuals with sickle cell anemia but also occur in compound heterozygotes for the beta s and beta 0 thalassemia (beta 0 thal) genes. Additionally, this study has characterized sickle cell-beta 0 thalassemia (S-beta 0 thal) in Eastern Saudi Arabia for the first time.     

Iodination-Coupled Tetrazonium and Ferric Ferricya-Nide Reduction Stains for Differentiating Red Blood Cells Containing Fetal or Adult Hemoglobin

Either the iodination-coupled tetrazonium reaction or the ferric ferricyanide reduction procedure can be used to differentiate red blood cells containing fetal hemoglobin (hemoglobin F) from those containing adult hemoglobin (hemoglobin A) in blood smears. Oxalated blood is diluted with 3 parts of physiological saline, and smears are made on slides. The air-dried slides are treated with absolute ethanol for 2 min, dried, and placed in phosphate-citrate buffer of pH 3.2-3.6 for 1 min at 37°C. They are then rinsed in distilled water, and dried for storage or stained at once by either the iodination-coupled tetrazonium or the ferric ferricyanide reduction procedure. Adult hemoglobin is extracted by the buffer, so that red blood cells containing fetal hemoglobin give a much darker stain than those containing adult hemoglobin. The hemoglobin S of patients with sickle-cell anemia behaves like adult hemoglobin.     

Detection of hemoglobin variants in erythrocytes by flow cytometry

BACKGROUND: With the emergence of fetal hemoglobin (Hb F)stimulating agents as potential treatments for sickle-cell disease and thalassemias, procedures to monitor the effect of these agents on Hb F levels in individuals will be needed. We developed a rapid procedure that detects fetal hemoglobin in erythrocytes (F cells) using a fluorescein isothiocyanate (FITC) conjugated monoclonal antibody against Hb F. METHODS: Ten microliters of washed blood was fixed in formaldehyde and glutaraldehyde, then permeabilized in a Triton X-100/PBS solution containing a FITC-labeled monoclonal antibody to Hb F. The blood was analyzed by flow cytometry to determine the percentage of F cells. RESULTS: Nearly 200 Hb F-containing samples were analyzed by this protocol and demonstrated good correlation to percent Hb F results determined by high pressure liquid chromatography (HPLC). In addition, a number of samples were fixed and permeabilized using this method as well as a previously-described method that uses dimethyl 3,3'dithiobispropionimadate (DTBP) as a fixative as well as a different anti-Hb F monoclonal. Good correlation (r = 0.96, r2 = 0.93, P<0.001) was observed between the two protocols. CONCLUSIONS: This procedure is easy, reproducible, and gives accurate F cell results. It can be used to measure a wide range of F cell percentages and may also be used to dual-stain Hb F along with other hemoglobin variants and erythrocyte surface antigens.     

Geographical survey of βS-globin gene haplotypes: Evidence for an independent Asian origin of the sickle-cell mutation

The haplotypes of 152 beta S-chromosomes were characterized in six different population groups. The chromosomes of individuals from Nigeria and from the southwest of the Arabian peninsula have the haplotype - - - - + + - + previously found in west African, Jamaican, and U.S. American blacks, whereas those from the eastern oases of Saudi Arabia and from the west and the east coast of India showed a different haplotype not found in Africa (+ + - + + + + -). These data are most consistent with an independent Asian origin of the sickle-cell mutation and provide further information about the geographic distribution of beta S-haplotypes in the Old World. The distribution of the Asian beta S-haplotype corresponds to the reported geographic distribution of a mild clinical phenotype of homozygous SS disease.     

A thermodynamic model for gelation of sickle-cell hemoglobin

The two-step concept of gelation of sickle-cell hemoglobin (Minton, 1973) provides the basis for a thermodynamic model to account for the macroscopic solution properties of sickle-cell hemoglobin in terms of microscopic structure and interactions. Step 1, the formation of a rod-like microtubular array, is treated as thermodynamically equivalent to a precipitation. Step 2, the alignment of microtubules to form a nematic phase, is treated as an isotropic-nematic transition in a suspension of interacting rod-like particles. Upon combination of these two steps a qualitative temperature-composition phase diagram is obtained.The results of several experimental studies on sickle-cell hemoglobin solutions, including measurements of solubility, sedimentation equilibrium and viscosity, are reviewed and it is shown that the proposed model provides a unified interpretation of many of the observed physical properties of these solutions.     

Imbalanced distribution of Plasmodium falciparum MSP-1 genotypes related to sickle-cell trait.

BACKGROUND: The sickle-cell trait protects against severe Plasmodium falciparum malaria and reduces susceptibility to mild malaria but does not prevent infection. The exact mechanism of this protection remains unclear. We have hypothesized that AS individuals are protected by virtue of being less susceptible to a subset of parasite strains; thus we compared some genetic characteristics of parasites infecting AS and AA subjects. MATERIALS AND METHODS: Blood was collected from asymptomatic individuals living in two different regions of Africa. The polymorphic MSP-1 and MSP-2 loci were genotyped using a PCR-based methodology. Individual alleles were identified by size polymorphism, amplification using family-specific primers, and hybridization using family-specific probes. Multivariate logistic regression was used to analyze allele distribution. RESULTS: In Senegalese carriers, age and hemoglobin type influenced differently the distribution of the three MSP-1 families and had an impact on distinct individual alleles, whereas the distribution of MSP-2 alleles was marginally affected. There was no influence of other genetic traits, including the HLA Bw53 genotype, or factors such as place of residence within the village. In a cohort of Gabonese schoolchildren in which the influence of age was abrogated, a similar imbalance in the MSP-1 allelic distribution but not of MSP-2 allelic distribution by hemoglobin type was observed. CONCLUSIONS: The influence of the host's hemoglobin type on P. falciparum genotypes suggests that parasite fitness for a specific host is strain-dependent, which is consistent with our hypothesis that innate resistance might result from reduced fitness of some parasite strains for individuals with sickle-cell traits.     

Genetic correction of sickle cell disease: insights using transgenic mouse models

Sickle cell disease is a hereditary disorder characterized by erythrocyte deformity due to hemoglobin polymerization. We assessed in vivo the potential curative threshold of fetal hemoglobin in the SAD transgenic mouse model of sickle cell disease using mating with mice expressing the human fetal Agamma-globin gene. With increasing levels of HbF, AgammaSAD mice showed considerable improvement in all hematologic parameters, morphopathologic features and life span/survival. We established the direct therapeutic effect of fetal hemoglobin on sickle cell disease and demonstrated correction by increasing fetal hemoglobin to about 9-16% in this mouse model. This in vivo study emphasizes the potential of the SAD mouse models for quantitative analysis of gene therapy approaches.     

Sickle-cell Anaemia,Sickle-cell Thalassaemia,Sickle-cell Haemoglobin C Disease,and Asymptomatic Haemoglobin C Thalassaemia in one Ghanaian Family

A Ghanaian family is described in which a sickle-cell haemoglobin C man married to a sickle-cell thalassaemia woman produced 12 children (eight alive). Four children have sickle-cell anaemia, two sickle-cell haemoglobin C disease, one has sickle-cell thalassaemia, and one is asymptomatic haemoglobin C thalassaemia.It is emphasized that the contribution that adult sickle-cell disease patients make, through procreation, to the persistence of the S gene may be greater than is normally supposed, and that this contribution may soon outstrip that made by balanced polymorphism through falciparum malaria. Widespread haemoglobin genotyping in schools leading to genetic counselling is advocated to decrease the incidence of sickle-cell disease.     

Cell-free hemoglobin limits nitric oxide bioavailability in sickle-cell disease

Although the deleterious vasoconstrictive effects of cell-free, hemoglobin-based blood substitutes have been appreciated, the systemic effects of chronic hemolysis on nitric oxide bioavailability have not been considered or quantified. Central to this investigation is the understanding that nitric oxide reacts at least 1,000 times more rapidly with free hemoglobin solutions than with erythrocytes. We hypothesized that decompartmentalization of hemoglobin into plasma would divert nitric oxide from homeostatic vascular function. We demonstrate here that plasma from patients with sickle-cell disease contains cell-free ferrous hemoglobin, which stoichiometrically consumes micromolar quantities of nitric oxide and abrogates forearm blood flow responses to nitric oxide donor infusions. Therapies that inactivate plasma hemoglobin by oxidation or nitric oxide ligation restore nitric oxide bioavailability. Decompartmentalization of hemoglobin and subsequent dioxygenation of nitric oxide may explain the vascular complications shared by acute and chronic hemolytic disorders.     

Sickle-cell disease in a British urban community.

Seventy cases of sickle-cell disease were identified in the London Borough of Brent from records dating back to 1962. All but three were still alive and, with one exception, were recalled for confirmation of the diagnosis and to provide personal and family histories. The group consisted of 22 individuals with homozygous sickle-cell anaemia (Hb SS), 12 with sickle-cell/beta-thalassaemia double heterozygosity, 34 with sickle-cell/haemoglobin C disease (Hb SC), and two with the combination of haemoglobin S and hereditary persistence of fetal haemoglobin. They were predominantly of West Indian origin, more than half had been born in Britain, and most were aged under 25. The records for 304 patient admissions between 1962 and 1979 were analysed. There were 199 sickle-cell-disease-related admissions, 61 unrelated to sickle-cell disease, and 44 for pregnancy or its complications. Admissions per patient-year averaged less than one, except for children with Hb SS under the age of 5 years, who were admitted more frequently. The commonest reasons for admission were painful crises (74% of all admissions) and the "chest syndrome" (21%). There were four pneumococcal infections, all in children with Hb SS under the age of 8 years; all recovered. Three patients, aged 10, 15, and 50 years, died. The two children with Hb SS died in their sleep without gross evidence of sickling at necropsy. Multiple brain infarcts were found at necropsy in the 50-year-old woman with Hb SC who, having survived nine uneventful pregnancies, succumbed to an infection after cryosurgery to the cervix. Obstetric records were available for 18 term pregnancies in 11 women. Three antenatal sickling crises and three postpartum thromboembolic complications were encountered. There were no maternal or perinatal deaths. Fifteen asymptomatic individuals with sickle-cell disease were diagnosed as a result of routine screening procedures. There are likely to be many such individuals currently undiagnosed in the community. They urgently need identification because of their increased risks from pregnancy, surgery, and infection.     

Thermodynamic analysis of the chemical inhibition of sickle-cell hemoglobin gelation.

When added to a solution of deoxygenated sickle-cell hemoglobin, a variety of compounds are known to increase the minimum gelling concentration. In the present analysis, this increase is attributed to a corresponding increase in the solubility of non-aggregated hemoglobin, which in turn is attributed to preferential interaction of additive with the isolated hemoglobin molecule in solution relative to that in the aggregate. An equilibrium thermodynamic model for chemical inhibition of gelation, based on these concepts, is presented. Using the model, experimental data in the literature are interpreted in terms of the hemoglobin-binding properties of the various additive species.     

Candidate Sequence Variants and Fetal Hemoglobin in Children with Sickle Cell Disease Treated with Hydroxyurea

Background

Fetal hemoglobin level is a heritable complex trait that strongly correlates swith the clinical severity of sickle cell disease. Only few genetic loci have been identified as robustly associated with fetal hemoglobin in patients with sickle cell disease, primarily adults. The sole approved pharmacologic therapy for this disease is hydroxyurea, with effects largely attributable to induction of fetal hemoglobin.

Methodology/Principal Findings

In a multi-site observational analysis of children with sickle cell disease, candidate single nucleotide polymorphisms associated with baseline fetal hemoglobin levels in adult sickle cell disease were examined in children at baseline and induced by hydroxyurea therapy. For baseline levels, single marker analysis demonstrated significant association with BCL11A and the beta and epsilon globin loci (HBB and HBE, respectively), with an additive attributable variance from these loci of 23%. Among a subset of children on hydroxyurea, baseline fetal hemoglobin levels explained 33% of the variance in induced levels. The variant in HBE accounted for an additional 13% of the variance in induced levels, while variants in the HBB and BCL11A loci did not contribute beyond baseline levels.

Conclusions/Significance

These findings clarify the overlap between baseline and hydroxyurea-induced fetal hemoglobin levels in pediatric disease. Studies assessing influences of specific sequence variants in these and other genetic loci in larger populations and in unusual hydroxyurea responders are needed to further understand the maintenance and therapeutic induction of fetal hemoglobin in pediatric sickle cell disease.     

Orthopaedic manifestations of sickle-cell disease

Sickle-cell disease is a well-recognized clinical entity. The pathophysiology of this hemoglobinopathy has been described in detail by numerous investigators since the first case report appeared in 1910. Orthopaedic manifestations of sickle-cell disease account for much of the morbidity associated with this disorder, including pain, osteonecrosis, arthritis, and sepsis. Effective management of these bone and joint sequelae reflect accurate diagnosis, understanding of this disorder's pathophysiology, and knowledge of available medical and surgical treatment alternatives. In this review, the authors summarize the major orthopaedic manifestations of sickle-cell disease with special emphasis placed upon osteonecrosis and osteomyelitis, since these conditions are the most disabling and serious complications in patients with sickle-cell disease.     

Coupling ecology and evolution: malaria and the S-gene across time scales

Malaria has long been a scourge to humans. The exceptionally high mortality in some regions has led to strong selection for resistance, even at the cost of increased risk of potentially fatal red blood cell deformities in some offspring. In particular, genes that confers resistance to malaria when they appear in heterozygous individuals are known to lead to sickle-cell anemia, or other blood diseases, when they appear in homozygous form. Thus, there is balancing selection against the evolution of resistance, with the strength of that selection dependent upon malaria prevalence. Over longer time scales, the increased frequency of resistance in a population might be expected to decrease the frequency of malaria and reduce selection for resistance. However, possession of the sickle-cell gene leads to longer-lasting parasitaemia in heterozygote individuals, and therefore the presence of resistance may actually increase infection prevalence. In this paper, we explore the interplay among these processes, operating over very different time scales. In particular, we show that on the fast time scale of malarial dynamics, the disease level reaches an equilibrium; on the slower, evolutionary time scale, this equilibrium tracks gene frequency. We analyze the slow time scale dynamics to investigate the impact of malaria on the evolution of resistance.     

Analysis of the recombination zone in hereditary persistence of fetal hemoglobin with fetal gene rearrangement of the G gamma-G gamma-A gamma type

An increased synthesis of fetal hemoglobin in adult life is a common feature of the genetically determined severe disorders like beta thalassemia and sickle cell anemia. A continued synthesis of fetal hemoglobin in adults is also characteristic of clinical or subclinical syndromes like respectively delta beta thalassemia or hereditary persistence of fetal hemoglobin (HPFH). These disorders are highly heterogeneous with respect to their molecular defects as well as to the composition of Hb F. We report here a novel case of hereditary persistence of fetal hemoglobin in heterozygous state discovered by chance, in a young perfectly healthy french man. The gamma chain of his fetal hemoglobin was almost entirely composed of G gamma chains. Molecular analysis of the DNA revealed the existence of triplicated gamma genes on one chromosome with the genotype arrangement of G gamma-G gamma-A gamma. A polymorphic Xmn I restriction site (at position -158 5' to the cap site) was present in 5' of both of these G gamma genes. The presence of this site in front of G gamma gene had previously been shown to be associated both with high G gamma phenotype constitutively and also with high fetal hemoglobin level only in case of anemic stress. In the absence of any anemic stress in this individual, the constitutive increase of both fetal hemoglobin and G gamma chains could be due to the presence of a chromosome with triplicated arrangement of gamma genes. The classical triplication (G gamma-A gamma-G gamma-A gamma) does not result in HPFH phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential control of the synthesis of two hemoglobin beta chains in normal mice

A fetal-to-adult switch in the proportion of the mouse minor hemoglobin is described. Although mice have no fetal hemoglobin per se, the timing of this switch in the mouse suggests that the mechanism of its control may directly parallel that of the human switch from fetal to adult hemoglobin expression. The mouse minor hemoglobin is expressed only in strains with the "diffuse" allele for the beta chain complex locus. Fetal liver cells of these mice synthesize a much greater proportion of the betaminor globin chain that do adult hematopoietic cells. Consequently, circulating fetal erythrocytes carry a high level of the minor hemoglobin containing it. By the time of birth, a lowered proportion of betaminor is synthesized in the liver. This low proportion continues to be expressed during early erythroid maturation in the adult. The fetal-to-adult switch is the first indication that in normal mice, the two beta chain loci can be expressed noncoordinately. The similarity between the patterns of the decline of the minor hemoglobin in mice and of the disappearance of fetal hemoglobin in humans suggests that the minor hemoglobin in the "diffuse" mouse may function to some degree as a fetal hemoglobin in the period between the disappearance of the embryonic hemoglobins and the time of birth.     

The Sickle-cell and Altitude

High altitude seemed to be responsible for seven recent cases of sickling crisis. People with sickle-cell trait are at risk if they fly in unpressurized aircraft, which are used for many local air services. Those with sickle-cell haemoglobin C disease should avoid air travel even in pressurized aircraft. Possibly as a result of “autosplenectomy,” patients with sickle-cell anaemia seem to be able to fly in pressurized aircraft with little risk. All passengers and aircrew who might have some form of sickle-cell disease should be screened before flight.     

胎儿血红蛋白数量性状相关基因的研究进展

胎儿血红蛋白(HbF)是一种主要在胎儿期间大量存在的血红蛋白, 但成年后含量极少, 然而少量人群及部分镰刀型贫血和地中海贫血患者体内仍保留一定量的HbF, 其存在对缓解贫血临床并发症具有重要益处。以往研究已经确定影响HbF数量性状的基因座定位于6q23和2p15, 而最新的一系列研究表明, 定位于6q23的HBS1L-MYB和2p15的BCL11A与HbF含量关联最高。这些研究一方面有助于理解HbF表达机理, 另一方面也为镰刀型贫血的治疗提供了潜在的药物靶点。文章对HbF表达的数量性状相关基因的研究现状及潜在应用进行了综述