In vivo blood flow abnormalities in the transgenic knockout sickle cell mouse

The accepted importance of circulatory impairment to sickle cell anemia remains to be verified by in vivo experimentation. Intravital microscopy studies of blood flow in patients are limited to circulations that can be viewed noninvasively and are restricted from deliberate perturbations of the circulation. Further knowledge of sickle blood flow abnormalities has awaited an animal model of human sickle cell disease. We compared blood flow in the mucosal-intestinal microvessels of normal mice with that in transgenic knockout sickle cell mice that have erythrocytes containing only human hemoglobin S and that exhibit a degree of hemolytic anemia and pathological complications similar to the human disease. In sickle cell mice, in addition to seeing blood flow abnormalities such as sludging in all microvessels, we detected decreased blood flow velocity in venules of all diameters. Flow responses to hyperoxia in both normal and sickle cell mice were dramatic, but opposite: Hyperoxia promptly slowed or halted flow in normal mice but markedly enhanced flow in sickle cell mice. Intravital microscopic studies of this murine model provide important insights into sickle cell blood flow abnormalities and suggest that this model can be used to evaluate the causes of abnormal flow and new approaches to therapy of sickle cell disease.

Sickle cell-like crisis and bone marrow necrosis associated with parvovirus B19 infection and heterozygosity for haemoglobins S and E

In the literature, heterozygosity for haemoglobins S and E is known as a clinically benign condition. Nevertheless, we present a case of double heterozygosity manifesting as an infarctive sickle cell-like crisis with acute chest syndrome and reversible bone marrow necrosis. Importantly, these complications were associated with serologically documented parvovirus B19 infection. Reviewing the literature, this case emphasizes a specific role of parvovirus B19 as a precipitating cause. Furthermore, it demonstrates how important the consideration of haemoglobin disorders can be even outside of the historically known areas.

Molecular exclusion of haemoglobin SD disease by prenatal diagnosis

The most common Hb D variant, Haemoglobin D (Hb D) Los Angeles is caused by a glutamic acid to glutamine substitution at codon 121 of the beta globin gene. Although asymptomatic in the heterozygous form, inheritance together with an Hb S allele can result in a severe disease similar to sickle-cell anaemia that is referred to as Hb SD disease. Prenatal diagnosis for Hb SD disease was requested by an at-risk couple of Irish/English descent. Prenatal diagnosis was performed on DNA isolated from chorionic villi at 12 weeks' gestation using dot blot and allele-specific oligonucleotide hybridization for the HbS mutation, and two independent approaches, restriction fragment analysis and ARMS (amplification refractory mutation system) for the detection of the Hb D Los Angeles mutation. The fetus was found to be heterozygous for the HbS mutation, but did not inherit the HbD mutation. Thus, a reliable and rapid prenatal diagnosis for the Hb SD disease can be achieved by molecular diagnosis.

Transgenic knockout mice exclusively expressing human hemoglobin S after transfer of a 240-kb betas-globin yeast artificial chromosome: A mouse model of sickle cell anemia

Sickle cell anemia (SCA) and thalassemia are among the most common genetic diseases worldwide. Current approaches to the development of murine models of SCA involve the elimination of functional murine alpha- and beta-globin genes and substitution with human alpha and betas transgenes. Recently, two groups have produced mice that exclusively express human HbS. The transgenic lines used in these studies were produced by coinjection of human alpha-, gamma-, and beta-globin constructs. Thus, all of the transgenes are integrated at a single chromosomal site. Studies in transgenic mice have demonstrated that the normal gene order and spatial organization of the members of the human beta-globin gene family are required for appropriate developmental and stage-restricted expression of the genes. As the cis-acting sequences that participate in activation and silencing of the gamma- and beta-globin genes are not fully defined, murine models that preserve the normal structure of the locus are likely to have significant advantages for validating future therapies for SCA. To produce a model of SCA that recapitulates not only the phenotype, but also the genotype of patients with SCA, we have generated mice that exclusively express HbS after transfer of a 240-kb betas yeast artificial chromosome. These mice have hemolytic anemia, 10% irreversibly sickled cells in their peripheral blood, reticulocytosis, and other phenotypic features of SCA.

HbS-oman heterozygote: a new dominant sickle syndrome

Hemoglobin (Hb) S-Oman has two mutations in the beta-chains. In addition to the classic betaS mutation (beta6 Glu --> Val), it contains a second mutation in the same chain (beta121 Glu --> Lys) identical to that of HbOARAB. We have studied a pedigree of heterozygous carriers of HbS-Oman that segregates into two types of patients: those expressing about 20% HbS-Oman and concomitant -/ thalassemia and those with about 14% of HbS-Oman and concomitant -/- thalassemia. The higher expressors of S-Oman have a sickle cell anemia (SS) clinical syndrome of moderate intensity, while the lower expressors have no clinical syndrome, and are comparable to the solitary case first described in Oman. In addition, the higher expressors exhibit a unique form of irreversibly sickled cell reminiscent of a "yarn and knitting needle" shape, in addition to folded and target cells. The CSAT of S-Oman is identical to that of S-Antilles, another supersickling hemoglobin, whose carriers express the abnormal hemoglobin at 40% to 50%, with a very similar clinical picture to HbS-Oman. Because the level of expression is so different and the clinical picture so similar, and based on the hemolysates CSAT's, we conclude that HbS-Oman produces pathology beyond its sickling tendencies. A clue for this additional pathogenesis is found in the fact that homozygous HbOARAB, which has the same second substitution as S-Oman, has a moderately severe hemolytic anemia; when HbOARAB is combined with HbS, it makes the phenotype of this double heterozygote as severe as SS. Properties of HbS-Oman red blood cells (RBCs) include reticulocytes that are much denser than normal (similar to those of SC and CC disease), a decrease in the Km for Ca2+ needed to activate the Gardos' channel (making this transporter more sensitive to Ca2+), increased association of HbS-Oman with the RBC membrane, the presence of dense cells by isopycnic gradient, the presence of folded cells, and abundant nidus of polymerization under the membrane. Other properties include a clear increase in volume and N-ethylmaleimide-stimulated K:Cl cotransport in RBCs expressing more than 20% HbS-Oman. We conclude that the pathology of heterozygous S-Oman is the product of the sickling properties of the beta6 Val mutation which are enhanced by the second mutation at beta121. In addition, the syndrome is further enhanced by a hemolytic anemia induced by the mutation at beta121. We speculate that this pathology results from the abnormal association of the highly positively charged HbS-Oman (3 charges different from normal hemoglobin) with the RBC membrane.

A new sickle cell disease phenotype associating Hb S trait, severe pyruvate kinase deficiency (PK Conakry), and an alpha2 globin gene variant (Hb Conakry)

A Guinean woman, heterozygous for haemoglobin (Hb) S, was studied because of episodes of marked anaemia, repeated typical metaphyseal painful crises and haemosiderosis. Her sickling syndrome resulted from the association of Hb S trait with a severe pyruvate kinase deficiency leading to a 2,3-DPG concentration of twice normal levels. Sequence of the PK-R gene revealed an undescribed mutation in the homozygous or hemizygous state within exon 5 (nucleotide 2670 C-->A), leading to the interchange of Ser 130 into Tyr (PK Conakry). In addition, the patient carried a new haemoglobin variant, Hb Conakry [alpha80(F1) Leu-->Val], which seemed to have a mild effect. The high intraerythrocytic 2,3-DPG concentration induced by the PK deficiency resulted in a decreased oxygen affinity which favoured sickling to a level almost similar to that of Hb S/C compound heterozygous patients. This was confirmed by oxygen binding measurements of Hb A/Hb S erythrocytes in which 2,3-DPG content was modified in vitro. Hysteresis between deoxy- and reoxygenation curves, as well as increase in the n(max) value, demonstrated that the extent of HbS polymerization in the propositus was almost the same as that of RBCs from a homozygous sickle cell patient or those of an A/S heterozygous patient with an artificial in vitro increase of 2,3-DPG concentration.

Trimodal distribution of HbS levels in sickle heterozygotes--an useful predictor of the alpha-genotype for population screening

The trimodal distribution of HbS levels in sickle heterozygotes has been used as an indirect approach to determine the prevalence of alpha-thalassaemia in different population groups. We used this approach to predict the alpha-genotypes of 124 sickle cell heterozygotes where the HbS concentration varied from 20 to 46 per cent with antimodes at 28.0 and 33.0. The alpha-genotypes in these individuals were also determined by Southern blot hybridization. We predicted homozygous (-alpha/-alpha) or heterozygous (-alpha/alpha alpha) alpha-thalassaemia-2 in 78 subjects by the trimodal distribution of HbS. However, actual genotyping showed that 75 patients had alpha-thalassaemia. Forty six of the 47 subjects with a normal alpha-globin genotype (alpha alpha/alpha alpha) could be predicted indirectly. The overall sensitivity was 100 per cent and specificity was 94.2 per cent with a positive predictive value of 96.2 per cent and negative predictive value of 100 per cent. As alpha-genotyping is very expensive and not feasible in most laboratories in India, we conclude that the trimodal distribution of HbS levels is a suitable method for screening for alpha-thalassaemia in population studies.

Hemoglobins in Togolese newborns: Hb S, Hb C, Hb Bart's, and alpha-globin gene status

The gene frequency of the most important hemoglobin (Hb) abnormalities is reported in a population of 171 Togolese newborns. Hb phenotypes, hematological parameters, and the more frequently described alpha-gene deletions were analyzed. Structural abnormalities of beta-globin were observed in 35.7% of the children with a gene frequency of 0.105 for beta(S) and 0.091 for beta(C). The frequency of the different alpha-globin genotypes was alpha alpha/ = 0.71, -alpha/ = 0.28, and alpha alpha alpha/ = 0.01. All of the individuals homozygous for the -alpha genotypes, and most of the heterozygous individuals, carried Hb Bart's. Within the alpha alpha/alpha alpha and the -alpha/alpha alpha groups, several individuals with or without Hb Bart's were found; they did not differ from the others by their red blood cell (RBC) parameters but by their levels of fetal hemoglobin (Hb F). The African alpha2 polymorphism marker, characterized by the replacement of G by TCGGCCC at position 7238 (EMBL HSHBA4, 1993) and of T 7174 by G, was found in 21 newborns. The mean value of Hb F was calculated for each genotype, the mean (G)gamma percentage was 69.4 +/- 4.0%, and the gene frequency of the AgammaT marker was 0.10; this marker was linked to the normal beta-globin cluster.

[Splenic infarct in heterozygote sickle cell trait (Hb AS)]

We present a carrier of the sickle cell trait who developed a serious splenic infarction. An antecedent hypoxaemic event and a blood coagulation disorder were ruled out. The observation shows that the sickle cell trait can represent a risk factor for a life-threatening thrombotic event, even in the absence of a predisposing condition.

Inhibition of gene expression by the Ggamma 5' flanking region of the Bantu beta(s) chromosome

Beta(s)-chromosome haplotypes are peculiar to specific regions of Africa and Asia and are associated with the occurrence of different fetal hemoglobin (Hb) levels in sickle cell patients. Among these haplotypes, beta(s)-chromosomes found in the Senegal and the Arab-India regions are associated with relatively high levels of HbF expression, whereas those around the Benin, Bantu, and the Cameroon regions show low levels of HbF expression. The roles of 5'HS2 and the 5' flanking (promoter region) region in the expression of globin genes are well documented. Haplotype specific variations are found in these regions and have been postulated to be involved in the regulation of HbF expression. In this study, we have analyzed the effect of sequence variations in regulatory regions of the Bantu 5'HS2 and 5' flanking region of the Ggamma gene on CAT expression. A diminution was observed in K562 cells when the promoter originated from the Bantu beta(s) chromosome. The decreased expression was independent of the origin of the 5'HS2 sequence--combinations of the Bantu promoter were measured with the Benin, Bantu, or Senegal 5'HS2 sequences in K562 cells. However, expression of the same plasmids in murine erythroleukemic (MEL) cells showed no difference in CAT expression among the various sequence combinations studied.

Haemorheological changes and fibrinolytic activity in adult asthmatic patients with sickle cell trait (HbAS)

Haemorheological parameters and euglobulin lysis time (ELT) were assessed in eighty-one adult asthmatic patients, 27 in stable state (19 with genotype AA and 8 heterozygous AS), 27 during attack (13 homozygous AA and 13 heterozygous AS) and 27 normal healthy individuals as control group (16 homozygous AA and 11 heterozygous AS). Packed cell volume (PCV), plasma fibrinogen concentration (PFC) and plasma viscosity (PV) were significantly higher in asthmatic patients during attack and stable state (p < 0.001), respectively, than controls. ELT was higher in controls (p < 0.001) than in asthmatic patients during attack. Asthmatic patients during attack have higher PCV, PV, PFC and ELT (p < 0.001), respectively, than patients in stable state. The female have significantly higher PCV (p < 0.001) than male in the control group. Male asthmatic patients have higher PCV and PFC during attack (p < 0.001). Controls with haemoglobin AA have higher PCV (p < 0.001) and lower PFC (p < 0.001) and ELT (p < 0.001) than the control group with haemoglobin AS. Asthmatic patients in stable state have lower PFC (p < 0.001) and plasma viscosity (PV) than AS. The disturbances of fibrinolysis and haemorheology may be a contributory factor in the pathology and aetiology of intermittent bronchospasm episodes during attack.

Effects of sickle cell trait and hemoglobin C trait on determinations of HbA1c by an immunoassay method

OBJECTIVE

A number of studies, including the Diabetes Control and Complications Trial (DCCT), have shown that good glycemic control, as assessed by GHb measurements, can reduce the chronic complications of diabetes. The National Glycohemoglobin Standardization Program (NGSP) was established to insure that GHb measurements by different methods were comparable and could be related to the candidate reference method used in the DCCT. The measurement of HbA1c in patients with Hb variants is one area not directly addressed by the NGSP. Therefore, we assessed the comparability of two DCCT-traceable methods in samples with Hb variants.

RESEARCH DESIGN AND METHODS

Samples containing HbAA, HbAC, and HbAS were collected from diabetic and nondiabetic patients. HbA1c concentrations were measured by a high-performance liquid chromatography method (Bio-Rad Diamat) and an immunoassay that is suitable for use in a physician's office (Bayer DCA 2000).

RESULTS

The two methods compared well for samples with HbAA and HbAS. However, for samples containing HbAC the immunoassay method showed relative positive biases of 8.4 and 10.4% at HbA1c levels of 7 and 9%, respectively, such that the two methods would not be judged comparable according to NGSP guidelines.

CONCLUSIONS

The DCA 2000 HbA1c immunoassay method showed significant positive bias in patients with HbC trait. One possible clinical implication of this overestimation is overly rigorous glycemic control with a concomitant increase in hypoglycemia. This may be especially important in certain ethnic populations, such as African-Americans, who have a relatively high prevalence of HbC trait.

Compound heterozygosity Hb S/Hb Hope (beta 136 Gly-->Asp): a pitfall in the newborn screening for sickle cell disease

The presence of Hb Hope associated with Hb S may represent a pitfall (false positive) in the neonatal detection of sickle cell disease by two of the most widely used analytical methods in screening programmes-isoelectric focusing (IEF) and high performance liquid chromatography (HPLC). This example illustrates the need to improve analytical strategies to avoid unnecessary anxiety and summoning of families often from a cultural background in which testing of the father is difficult to obtain. It is suggested that using two independent HPLC procedures might improve the specificity of the screening strategies. Additionally, simple procedures for detection of the most common mutations of the beta globin gene of DNA extracted from dried blood specimens could be easily developed for the control of abnormal samples. These procedures could be introduced into the analytical strategy.

[Hemoglobin beta S haplotype in the Kebili region (southern Tunisia)]

Sickle cell anemia is a monogenic hereditary disease characterized by a mutation in the beta globin gene. Five major haplotypes associated with the beta S mutation have been defined: Benin, Bantu, Senegalian, Camerounian, and Arabo-Indian. Previous studies in northern Tunisia showed that sickle cell anemia was of Benin origin in this region. Patients from the south of Tunisia, mainly from the Kebili region, were not previously concerned. In this study, we have determined the beta S haplotype and evaluated phenotypical expression of the disease in 14 patients from this latter region. The use of four restriction endonucleases having polymorphic sites in the beta globin gene showed that all patients had the Benin haplotype, confirming the Benin origin of sickle cell anemia in Tunisia. This haplotype is associated with an heterogeneous expression of fetal hemoglobin (HbF) with extremes varying from 2.4 to 16.3% and a mean expression rate of 8.16%, which is in accordance with literature data. In spite of the haplotype homogeneity in our patients, clinical heterogeneity was noted. A unique case of alpha-thalassemia could not explain this heterogeneity. In contrast, we found a certain correlation between fetal hemoglobin expression and clinical severity.

New considerations in the treatment of sickle cell disease

The familial pattern of recurring pain and early death seen so often among those affected by sickle cell disease has been long recognized within African cultures, though its first clear description in Western medical literature did not appear until 1910 (1). Although most common in persons of African ancestry, the mutation giving rise to the sickle gene arose independently in several locations where malaria was prevalent (2), traveled with migrating populations, and is now widely distributed among regions and ethnic groups. Recognizing the qualitative abnormality of sickle hemoglobin as a prototype, Pauling & Castle established the notion of a molecular disease (3). Ironically, while the biochemistry and molecular biology of sickle cell disease has been intensively investigated, research into patient care has been limited in scope until recently. Prospective study of large patient groups diagnosed at birth is now providing insight into the disease's natural history and facilitating investigational treatments. Newborn diagnosis, combined with study of new drugs, cytokines, surgical procedures, and a more proactive utilization of transfusion is leading to greatly improved care and survival. Life expectancy is increasing (4) but adults are experiencing more complications of chronic organ dysfunction. A few patients have been cured by stem-cell transplantation, but difficult problems will continue to limit its application.

Pathophysiology of sickle cell disease

Sickle cell disease is caused by a mutation in the beta-globin chain of the haemoglobin molecule. Sickle haemoglobin, the result of this mutation, has the singular property of polymerizing when deoxygenated. Exactly how normal tissue perfusion is interrupted by abnormal sickle cells is complex and poorly understood. Despite genetic identity at the site of the sickle haemoglobin mutation, all patients with sickle cell anaemia are not affected equally by this disease. Secondary genetic determinants and acquired erythrocyte and vascular damage are likely to be central components of the pathophysiology of sickle cell anaemia.

Molecular basis of beta-thalassemia in the Maldives

We have systematically analyzed beta-thalassemia genes using polymerase chain reaction-related techniques, dot-blot hybridization with oligonucleotide probes, allele specific-polymerase chain reaction, and sequencing of amplified DNA fragments from 41 unrelated patients, including 37 beta-thalassemia homozygotes, three with beta-thalassemia/Hb E, and one with beta-thalassemia/Hb S. Four different beta-thalassemia mutations were detected in 78 alleles. These are the IVS-I-5 (G-->C), codon 30 (AGG-->ACG) [also indicated as IVS-I (-1)], IVS-I-1 (G-->A), and codons 41/42 (-TTCT) mutations. The distribution of the beta-thalassemia mutations in the Maldives is 58 alleles (74.3%) with the IVS-I-5 (G-->C) mutation, 12 (15.4%) with the codon 30 (AGG-->ACG) mutation, seven (9%) with the IVS-I-1 (G-->A) mutation, and one with the codons 41/42 (-TTCT) mutation. The first three mutations account for 98.7% of the total number of beta-thalassemia chromosomes studied. These mutations are clustered in the region spanning 6 bp around the junction of exon 1 and the first intervening sequence of the beta-globin gene. These observations have significant implications for setting up a thalassemia prevention and control program in the Maldives. Analysis of haplotypes and frameworks of chromosomes bearing each beta-thalassemia mutation suggested that the origin and spread of these mutations were reflected by the historical record.

Molecular and population genetic analyses of beta-thalassemia in Turkey

In this report we describe the molecular analysis of 795 chromosomes derived from unrelated Turkish beta-thalassemia and sickle cell anemia carriers identified in hematology clinics in Istanbul, Ankara, Izmir, Adana, and Antalya. The determination of the molecular pathology of 754 beta-thalassemia and 42 abnormal hemoglobin genes and analysis of the frequency distribution in six distinct regions of Turkey was accomplished. The experimental strategy, based on PCR amplification of the beta-globin gene, included dot-blot hybridization with 18 probes specific for the Mediterranean populations, denaturing gradient gel electrophoresis, and genomic sequencing. When the regional results are compared with the overall frequency of mutations in the country, it is observed that the frequencies in the western and southern parts of Turkey are in good accordance with the overall distribution, whereas the northern and eastern parts have a more region/population-specific profile with some rare mutations having a significantly high occurrence in these regions. Further evaluation of the data with respect to region- or population-dependent differences will contribute to a better understanding of the mechanisms leading to the marked genetic heterogeneity in Turkey, but could also be extremely valuable in facilitating rapid identification of mutations in families at risk for different hemoglobinopathies.

The population genetics of the haemoglobinopathies

The haemoglobinopathies are the commonest single-gene disorders known, almost certainly because of the protection they provide against malaria, as attested by a number of observations. The geographical distributions of malaria and haemoglobinopathies largely overlap, and microepidemiological surveys confirm the close relationship between them. For two of the commonest disorders, haemoglobin S and alpha(+)-thalassaemia, there is also good clinical evidence for protection against malaria morbidity. However, not all the evidence appears to support this view. In some parts of the world malaria and haemoglobinopathies are not, and never have been, coexistent. It is also difficult to explain why the majority of haemoglobinopathies appear to be recent mutations and are regionally specific. Here we argue that these apparent inconsistencies in the malaria hypothesis are the result of processes such as genetic drift and migration and of demographic changes that have occurred during the past 10,000 years. When these factors are taken into account, selection by malaria remains the force responsible for the prevalence of the haemoglobinopathies.

Assessment of diagnostic quantitative fluorescent multiplex polymerase chain reaction assays performed on single cells

We have refined polymerase chain reaction (PCR) assays for the detection of sickle cell anaemia, the delta F 508 deletion causing cystic fibrosis, and the IVS1-110 mutation leading to beta thalassaemia, allowing them to be successfully performed upon single cells using fluorescent primers. We have also assessed the possibility of detecting aneuploidies of chromosomes 13, 18 and 21 using a quantitative fluorescent polymerase chain reaction (QF-PCR) with primers flanking polymorphic short tandem repeat (STR) markers. Trisomies were readily diagnosed by the detection of tri-allelic patterns. However some heterozygote normal and trisomic diallelic patterns did not produce the expected ratios of amplified PCR products due to preferential DNA sequence amplification. Total allelic drop out (ADO) did not occur with any of the cells tested. Multiplex QF-PCR assays can be performed on a single cell in under 6 h and simultaneously provide diagnosis of single gene defects, sex determination and an indication of selected chromosome aneuploidy.

[Influence of the sickle cell trait heterozygote on energy abilities]

The sickle cell trait (SCT) is a genetic abnormality of the red blood cell which mainly affects people of African descent. It is due to the mutation of only one parental gene (one glutamic acid of the chain beta of the globin is substituted by one valin). The prevalence of SCT in the black US population is within the range of 8-9%. It is increasing in Europe and in Africa where it may reach up to 40% in some regions. The rate of prevalence of SCT in athletic populations was found to be similar to that of the general sedentary population in west African countries. SCT is usually asymptomatic. However, SCT has been associated with a higher risk of sudden death during exercise. In fact, the substitution of one amino-acid modifies the properties of haemoglobin and produces physiological disorders such as sickling, less solubility of the deoxidized form and the reduction of affinity for oxygen. The sickling phenomenon (formation of sickle cells) mainly occurs in some conditions related to the practise of sport (intense and/or prolonged exercise, exercise in hypoxic conditions, exercise in heat conditions). These sickled red blood cells reduce the speed of capillary flow or obstruct the blood vessels which, because of the lack of oxygen, become altered. The physical ability of sickle cell trait carriers (HbAS) who practise sport should be different from the physical ability of subjects with normal haemoglobin (HbAA) because of: 1) potential risks due to their haemoglobinopathy and 2) the eventual modification of their performance ability. These two aspects have caused controversies among many researchers particularly in line with their investigation methods. Nevertheless, the following results seem to be established: 1) the ability to perform sprint exercises is not altered in the HbAS subjects. Their performances in these events are similar to those of HbAA subjects; 2) The ability of HbAS subjects to perform intense and prolonged exercise is decreased. Our former results have shown that prolonged aerobic efforts in hypobaric hypoxic conditions may be associated with a deleterious effect on the performance of HbAS subjects. The damaging consequences on their performance in these conditions could be due to tissue oxygen delivery limitations.