Fetal Haemoglobin in Homozygous Sickle Cell Disease

Phenotypic variation in sickle cell disease: the role of beta globin haplotype, alpha thalassaemia and fetal haemoglobin in HbSS

INTRODUCTION

The haematological and clinical feature vary markedly between the different genotypes of sickle cell disease. Even within the single genotype of homozygous sickle cell disease (HbSS), there is marked variability which is presumed to result from interacting genetic and environmental factors.

AREAS COVERED

The classification of the different genotypes of sickle cell disease with approximate prevalence at birth in different communities and some of the major clinical and haematological differences. This assessment includes three potential genetic factors influencing haematology and clinical outcome in HbSS, the beta globin haplotype, alpha thalassaemia and persistence of fetal haemoglobin (HbF).

EXPERT OPINION

The author is a clinician with experience of sickle cell disease primarily in Jamaica but also in Greece, Uganda, Saudi Arabia and India. It is therefore necessarily an account of clinical data and does not address current debates on molecular mechanisms. Most data derive from Jamaica where efforts have been made to reduce any symptomatic bias by long term follow-up of patients all over the island and further reduced by a cohort study based on newborn screening which has been in operation for over 48 years.

Fetal Hemoglobin Modulators May Be Associated With Symptomology of Football Players with Sickle Cell Trait

OBJECTIVES

This study investigates whether genetic modifiers previously shown to influence adult fetal hemoglobin (HbF) levels and glucose-6-phosphate dehydrogenase deficiency were associated with variable symptomology in a small sample of collegiate football players with sickle cell trait.

METHODS

Survey data on self-assessed symptoms and genotype data from five single nucleotide polymorphisms (SNPs) related to HbF production and two SNPs that cause glucose-6-phosphate dehydrogenase deficiency were collected from current and former college football players.

RESULTS

In this sample, SNPs found within the β-globin gene cluster were found to be associated with a previous diagnosis of exertional sickling and experience of extreme heat during and after training. rs10189857 in the BCL11A gene was associated with body mass index and weight and with experiencing extreme thirst during and after training. No significant correlations were found between the other SNPs and symptoms within this sample.

CONCLUSIONS

These findings show that genetic variation known to affect sickle cell disease symptomology may partly explain why some football players with sickle cell trait experience adverse clinical outcomes during periods of extreme physical exertion and others do not.

Sickle cell dehydration: Pathophysiology and therapeutic applications

Cell dehydration is a distinguishing characteristic of sickle cell disease and an important contributor to disease pathophysiology. Due to the unique dependence of Hb S polymerization on cellular Hb S concentration, cell dehydration promotes polymerization and sickling. In double heterozygosis for Hb S and C (SC disease) dehydration is the determining factor in disease pathophysiology. Three major ion transport pathways are involved in sickle cell dehydration: the K-Cl cotransport (KCC), the Gardos channel (KCNN4) and Psickle, the polymerization induced membrane permeability, most likely mediated by the mechano-sensitive ion channel PIEZO1. Each of these pathways exhibit unique characteristics in regulation by oxygen tension, intracellular and extracellular environment, and functional expression in reticulocytes and mature red cells. The unique dependence of K-Cl cotransport on intracellular Mg and the abnormal reduction of erythrocyte Mg content in SS and SC cells had led to clinical studies assessing the effect of oral Mg supplementation. Inhibition of Gardos channel by clotrimazole and senicapoc has led to Phase 1,2,3 trials in patients with sickle cell disease. While none of these studies has resulted in the approval of a novel therapy for SS disease, they have highlighted the key role played by these pathways in disease pathophysiology.

The orphan nuclear receptor TR4 regulates erythroid cell proliferation and maturation

The orphan nuclear receptors TR4 (NR2C2) and TR2 (NR2C1) are the DNA-binding subunits of the macromolecular complex, direct repeat erythroid-definitive, which has been shown to repress ε- and γ-globin transcription during adult definitive erythropoiesis. Previous studies implied that TR2 and TR4 act largely in a redundant manner during erythroid differentiation; however, during the course of routine genetic studies, we observed multiple variably penetrant phenotypes in the Tr4 mutants, suggesting that indirect effects of the mutation might be masked by multiple modifying genes. To test this hypothesis, Tr4^+/- mutant mice were bred into a congenic C57BL/6 background and their phenotypes were reexamined. Surprisingly, we found that homozygous Tr4 null mutant mice expired early during embryogenesis, around embryonic day 7.0, and well before erythropoiesis commences. We further found that Tr4^+/- erythroid cells failed to fully differentiate and exhibited diminished proliferative capacity. Analysis of Tr4^+/- mutant erythroid cells revealed that reduced TR4 abundance resulted in decreased expression of genes required for heme biosynthesis and erythroid differentiation (Alad and Alas2), but led to significantly increased expression of the proliferation inhibitory factor, cyclin dependent kinase inhibitor (Cdkn1c) These studies support a vital role for TR4 in promoting erythroid maturation and proliferation, and demonstrate that TR4 and TR2 execute distinct, individual functions during embryogenesis and erythroid differentiation.

Differences in the clinical and genotypic presentation of sickle cell disease around the world

Sickle cell disease (SCD), caused by a mutation in the β-globin gene HBB, is widely distributed in malaria endemic regions. Cardiopulmonary complications are major causes of morbidity and mortality. Hemoglobin SS (Hb SS) represents a large proportion of SCD in the Americas, United Kingdom, and certain regions of Africa while higher proportions of hemoglobin SC are observed in Burkina Faso and hemoglobin Sβ-thalassemia in Greece and India. Coinheritance of α-thalassemia and persistence of hemoglobin F production are observed in highest frequency in certain regions of India and the Middle East. As confirmed in the PUSH and Walk-PHaSST studies, Hb SS, absence of co-inheriting alpha-thalassemia, and low hemoglobin F levels tend to be associated with more hemolysis, lower hemoglobin oxygen saturations, greater proportions of elevated tricuspid regurgitant jet velocity and brain natriuretic peptide, and increased left ventricular mass index. Identification of additional genetic modifiers will improve prediction of cardiopulmonary complications in SCD.

Association of G6PD with lower haemoglobin concentration but not increased haemolysis in patients with sickle cell anaemia

The genetic bases of the highly variable degrees of anaemia and haemolysis in persons with Hb SS are not fully known, but several studies have indicated that G6PD deficiency is not a factor. The G6PD(202A) and G6PD(376G) alleles and alpha-thalassaemia were determined by molecular genetic testing in 261 children and adolescents with Hb SS in a multicentre study. G6PD(202A,376G) (G6PD A-) was defined as hemizygosity for both alleles in males and homozygosity in females. Among the participants 41% were receiving hydroxycarbamide. The prevalence of G6PD(202A,376G) was 13.6% in males and 3.3% in females with an overall prevalence of 8.7%. G6PD(202A,376G) was associated with a 10 g/l decrease in haemoglobin concentration (P = 0.008) but not with increased haemolysis as measured by lactate dehydrogenase, bilirubin, aspartate-aminotransferase, reticulocyte count or a haemolytic component derived from these markers (P > 0.09). Similar results were found within a sub-group of children who were not receiving hydroxycarbamide. By comparison, single and double alpha-globin deletions were associated with progressively higher haemoglobin concentrations (P = 0.005 for trend), progressively lower values for haemolytic component (P = 0.007), and increased severe pain episodes (P < 0.001). In conclusion, G6PD(202A,376G) may be associated with lower haemoglobin concentration in sickle cell anaemia by a mechanism other than increased haemolysis.

Hydroxyurea for children with sickle cell disease

Hydroxyurea therapy offers promise for ameliorating the clinical course of children with sickle cell disease (SCD). Hydroxyurea is a prototypic therapeutic option; it can be administered with minimal side effects, has a relatively wide therapeutic window, and has mechanisms of action that address pathophysiologic pathways of sickling, vaso-occlusion, hemolysis, and organ damage. There are limited data regarding hydroxyurea's ability to prevent or diminish organ dysfunction, and the long-term risks of hydroxyurea therapy remain incompletely defined. Although clinical trials are underway to address long-term issues, hydroxyurea remains an effective but underutilized therapy for SCD.

Vasculopathy in sickle cell disease: Biology, pathophysiology, genetics, translational medicine, and new research directions

Sickle cell disease has been very well characterized as a single amino acid molecular disorder of hemoglobin leading to its pathological polymerization, with resulting red cell rigidity that causes poor microvascular blood flow, with consequent tissue ischemia and infarction. More recently, an independent spectrum of pathophysiology of blood vessel function has been demonstrated, involving abnormal vascular tone and activated, adhesive endothelium. These vasculopathic abnormalities are attributable to pathways involving hemolysis-associated defects in nitric oxide bioavailability, oxidative stress, ischemia-reperfusion injury, hemostatic activation, leukocytes and platelets. Vasculopathy of sickle cell disease has been implicated in the development of pulmonary hypertension, stroke, leg ulceration and priapism, particularly associated with hemolytic severity, and reported also in other severe hemolytic disorders. This vasculopathy might also play a role in other chronic organ dysfunction in patients with sickle cell disease. These pathways present novel targets for pharmacologic intervention, and several clinical trials are already under way. The authors present their perspectives of a workshop held at the National Institutes of Health in August 2008 on vasculopathy in sickle cell disease, along with meritorious future scientific questions on the topic of vascular complications of sickle cell disease.

Hydroxyurea for children with sickle cell disease

Hydroxyurea therapy offers promise for ameliorating the clinical course of children with sickle cell disease (SCD). Hydroxyurea is a prototypic therapeutic option; it can be administered with minimal side effects, has a relatively wide therapeutic window, and has mechanisms of action that address pathophysiologic pathways of sickling, vaso-occlusion, hemolysis, and organ damage. There are limited data regarding hydroxyurea's ability to prevent or diminish organ dysfunction, and the long-term risks of hydroxyurea therapy remain incompletely defined. Although clinical trials are underway to address long-term issues, hydroxyurea remains an effective but underutilized therapy for SCD.

Hematological profile of sickle cell disease in central India

Hematological profile of homozygous sickle cell disease patients attending RHDMC from Central India is presented. Central India has a huge population of sickle cell disease patients. Though predicted SS in the region is 22-44 %, 81 homozygous of sickle cell patients reported during study period of Jan 2003-Dec 2005. The clinical course of these patients is characterized in most of the cases by relatively long period without any symptoms punctuated by acute clinical events. Hematological profile of these 81 patients with age ranging from 6 month to 64 years is presented. There are 44 males and 37 females with an average age of 14.55yrs in males and 18.13 yrs females. Males out number females in pediatric age group where as females with SCD are attending hospital more in reproductive age group. Very few patients are reported after the age of 30 yrs. Average hemoglobin in males is 7.11 ± 2.13 gms/dl and in females 6.75 ± 1.85 gms/dl with parallel low RBC count.Hemoglobin rise is seen after 14 years of age in males and females. Age related rise in MCV is more noted in females after the age of 5 as compared to males. No age or sex related difference was seen in MCHC values. Hb A(2) levels for males is 2.13 ± 0.95% and for females 2.04 ± 0.91 %.Hb F in males is 19.58 + 5.86% and in females is 20.99 + 4.9%. There is no age and sex related difference in Hb F levels. Moderate to severe anemia with high Hb F dominate Central Indian sickle cell disease patient's hematological profile. The hematological profile in Central India is similar to the profile in other parts of India and Saudi Arabia but different from Jamaica and Africa.

High oxygen environment during pregnancy rescues sickle cell anemia mice from prenatal death

Several mouse models of sickle cell disease have been developed for the study of the pathophysiology of sickle cell disease and the investigation of drug and gene therapies. In previous years, we produced a sickle cell anemia mouse model in which the endogenous mouse alpha- and beta-globin genes were knocked out and replaced by the human alpha- and beta(s)-globin transgenes. The beta(s)-globin gene was contained in a 240 kb YAC that preserved the entire native genomic context of the beta-globin locus. These mice have hemolytic anemia, reticulocytosis and irreversible sickle cells in the peripheral blood, as well as other pathological features of sickle cell disease. However, in the embryo, the gamma-globin, like the mouse embryonic globin, declined quickly, and was replaced by beta(s)-globin expression from 12 days of gestation. The low level of fetal hemoglobin expression in utero led to intrauterine sickling and fetal death so that very few live-born sickle cell anemia mice could be obtained. To rescue these mice from intrauterine death, we investigated the effect of placing the pregnant mothers in a high O(2) environment. From the tenth day of gestation onwards, we placed the mothers into a chamber containing 50% O(2) and kept them with the newborn pups in it for another 10 days after birth. The frequency of sickle cell anemia mice we obtained was increased from less than 2% to 35%. The survived sickle cell anemia mice develop congestion, atrophy, and infarcts in multiple organs similar to those found in patients with sickle cell disease. We conclude that a high oxygen environment can be used to obtain more sickle cell anemia mice in those models that have a high perinatal mortality. The higher yield of these mice has facilitated physiological and therapeutic studies of sickle cell anemia.

Risk factors and prediction of outcomes in children and adolescents who have sickle cell anemia

This article discusses risk factors and prediction in children and adolescents who have sickle cell anemia.

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, alpha genotype, beta(s) haplotype, plasma 59Fe clearance, plasma iron turnover, erythron transferrin uptake), RBC Fe utilization, reticulocyte count, and erythropoietin levels. The alpha genotype was the most significant determinant of RBC survival followed, to a lesser extent, by the beta(s) 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 alpha genotype, and not independent determinants in themselves. The data suggest that the alpha genotype and, and to a lesser extent, the beta(s) 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.

Fetal hemoglobin synthesis in sickle cell anemia: some molecular considerations

An ability to maintain high levels of fetal hemoglobin (Hb F) has been associated with the amelioration of the clinical severity of the sickle cell disease (SS). Clinical efforts to increase the Hb F level of the patients have, however, yielded variable therapeutic response. In an attempt to further elucidate the underlying molecular basis, in vitro Hb F synthesis was studied in erythroid progenitor (BFU-E) cells obtained from SS patients and their heterozygous (AS) relatives with varying genetic backgrounds. This allows us to study the Hb F biosynthesis pattern uncomplicated by the influence of the preferential survival of "F cells" in vivo. The Hb F levels and the relative concentrations of its constituent gamma globin chains, G gamma and A gamma, were assayed using the reversed phase HPLC method. A percentage increase in the fetal hemoglobin content was observed in the lysates of the erythroid progenitor cells relative to the circulating peripheral blood erythrocyte values in SS patients and their AS relatives with different beta S haplotypes reflecting the intrinsic capacity of fetal hemoglobin synthesis in these subjects. No such increase was observed in the patient with the Mor haplotype. Furthermore, the Hb F synthesized in the BFU-E colonies was more of the adult type, as evidenced by the decrease in the percent G gamma level relative to the corresponding peripheral blood values of the subjects in all the haplotype groups studied. The Mor haplotype was again an exception, synthesizing fetal hemoglobin more of the fetal type.

Increased HbF in adult life

Considerable advances have been made recently in our understanding of globin gene expression, its developmental regulation and the altered patterns in various inherited and acquired disorders. Each advance has revealed a new layer of complexity and as many questions remain as have been answered. Adult levels of HbF are clearly under genetic control but the number and nature of these genetic factors, either within or outside of the beta-globin gene cluster, remain to be determined. Many of the conditions resulting in increased HbF in adult life appear to involve an increased erythropoietic drive which results in a higher proportion of erythroid progenitor cells activating their inherent ability to synthesise low amounts of HbF. The mechanism by which this is achieved remains unknown but these observations have been confirmed in a number of experimental systems and have led to the use of mildly cytotoxic drugs to increase the HbF levels in sickle cell anaemia. Similarly, the clinical observation that infants of diabetic mothers show delayed fetal to adult haemoglobin switching has led to the development of butyrate derivatives to increase adult HbF levels. Analysis of the HPFH mutations has so far been largely limited to the deletion conditions and the gamma-gene promoter base substitutions. In neither case is there a complete explanation which can account for the raised adult HbF level characteristic of these conditions. Rather, they seem to demonstrate the complexity, and perhaps redundancy, of the mechanisms which control haemoglobin production. Both conditions show features which are consistent with competition between the gamma- and beta-genes in adult life, an interpretation which is apparently at odds with the 'autonomous' regulation of the gamma-genes in adult transgenic mice. Analysis of further transgenic mice, including ones bearing HPFH mutations, may help resolve this apparent contradiction and may provide suitable material to examine the in vivo protein-DNA interactions in this region.

Hb F in sickle cell anemia

We have reviewed the methodology for an accurate quantitation of Hb F in the blood of patients with sickle cell anemia, values observed in hundreds of patients of different (racial or ethnic) backgrounds and with differences in severity of the disease, and the various factors that affect the level of Hb F. The latter include sex, age, genetic background or chromosomal haplotypes, variations in the sequences of the locus control region(s) 5' to the epsilon-globin gene, and the presence of an alpha chain deficiency or alpha-thalassemia. Finally, a few remarks about agents effective in increasing the in vivo Hb F synthesis are also included.

Fetal haemoglobin and early manifestations of homozygous sickle cell disease

The relevance of fetal haemoglobin (HbF) concentration to the development of early clinical manifestations of homozygous sickle (SS) disease has been investigated by examining the time to first occurrence and the proportional hazard of these complications in three groups of the HbF distribution at age 5 years. HbF was significantly related to dactylitis, painful crises, acute chest syndrome, and acute splenic sequestration. The relationship suggested that a critically low HbF concentration increased the risk, little difference in risk occurring between the medium and high HbF groups. The abdominal painful crisis and hypersplenism were not related to HbF concentration suggesting that the degree of sickling may not be important in their genesis. Parental education on acute splenic sequestration should be focused on children with HbF concentrations in the lowest part of the HbF distribution for age.

Molecular analysis of the high-hemoglobin-F phenotype in Saudi Arabian sickle cell anemia

Patients from the eastern province of Saudi Arabia who have sickle cell anemia have high circulating levels of fetal hemoglobin (hemoglobin F, 17 percent), and they therefore have a mild form of the disease. To examine the molecular basis of the elevated production of hemoglobin F, we searched for mutations in the promoter regions of the two hemoglobin F gamma-globin genes (G gamma and A gamma). The DNA sequences 450 bp (base pairs) upstream of both the G gamma and A gamma globin genes were normal except for a single-base cytosine-to-thymidine (C----T) substitution at -158 bp 5' to the cap (preinitiation) site of the G gamma-globin gene of the high-hemoglobin-F chromosome. We searched for an association between this -158 C----T substitution and the production of hemoglobin F and G gamma in normal Saudis and Saudis with sickle cell disease or trait. The substitution was present in nearly 100 percent of the patients with sickle cell disease or trait, and in 22 percent of the normal Saudis. Homozygosity for this mutation had no demonstrable effect on hemoglobin F production in the normal Saudi population. We conclude that this mutation is not uniquely responsible for the increase in hemoglobin F in Saudi patients. It may nevertheless have an important role in regulating hemoglobin F production, but its expression is complex and requires interaction with additional factors, such as hemolytic stress or other molecular determinants, possibly linked to the sickle cell gene.

Sickle cell anemia associated with alpha-thalassemia in Malaysian Indians

The Indian rubber estate workers in Negri Sembilan, Malaysia, who originated from Orissa in India were found to have a high frequency of Hb S (Joishy SK, Hassan K: Clin Res 28:280, 1980). Unlike the usually severe clinical picture of sickle cell anemia seen in African and American blacks, the clinical picture of the disease in this population was mild and many have reached old age. We studied the leukocyte DNA of 12 patients with sickle cell anemia, ranging in age from 4 to 61 years and 30 sickle cell trait carriers, ranging in age from 7 to 63 years, for the presence of alpha-globin gene deletions by gene mapping according to Southern (Southern EM: J Mol Biol 98:503, 1975), using alpha- and zeta-globin gene probes obtained by nick translation of the alpha- and zeta-globin genes cloned into plasmid. All 12 sickle cell anemia patients were found to have alpha-thalassemia2 (alpha-thal2), either in the homozygous or heterozygous condition. Of the Hb S trait carriers, six did not have alpha-thal2 or alpha-thal1 and 24 had alpha-thal2 (15 heterozygous, 9 homozygous). Seven of these Hb S trait carriers with alpha-thal2 had an additional gene abnormality. Five of them had a fast-moving Eco RI fragment 5.6 kb long that hybridized with zeta-specific probe but not with alpha-specific probe. An unusual DNA pattern of a different type was further found in the other two. Bgl II restriction analysis showed that the alpha-thal2 was mostly of the rightward deletion alpha-thal1 genotype. None of the sickle cell anemia patients and Hb S trait carriers had deletion type alpha-thal1. The sickle cell anemia patients had very high levels of Hb F and low levels of Hb A2. The Hb S trait carriers with alpha-thal2 had relatively low levels of Hb S.

Hematologically and genetically distinct forms of sickle cell anemia in Africa. The Senegal type and the Benin type

Patients with sickle cell anemia vary in the hematologic and clinical features of their disease, in part because of variability in the presence of linked and unlinked genes that modify the expression of the disease. The hemoglobin S gene is strongly linked to three different haplotypes of polymorphic endonuclease-restriction sites of the beta-like gene cluster (genes in the vicinity of the beta-globin gene)--one prevalent in Atlantic West Africa, another in central West Africa, and yet another in Bantu-speaking Africa (equatorial, East, and southern Africa). We have studied the differences in the hematologic characteristics of patients with sickle cell anemia from the first two geographical areas. We find that the Senegalese (Atlantic West Africa) patients have higher levels of hemoglobin F, a preponderance of G gamma chains in hemoglobin F, a lower proportion of very dense red cells, and a lower percentage of irreversibly sickled cells than those from Benin (central West Africa). We interpret these data to mean that the gamma-chain composition and the hemoglobin F level are haplotype linked and that the decrease in the percentage of dense cells and irreversibly sickled cells is secondary to the elevation in the hemoglobin F level. Patients with sickle cell anemia in the New World probably correspond to various combinations of these types, in addition to the still hematologically undefined haplotype associated with sickle cell anemia in the Bantu-speaking areas of Africa.

The haematology of steady state homozygous sickle cell disease: frequency distributions, variation with age and sex, longitudinal observations

The steady state haematological characteristics observed in 1071 patients with homozygous sickle cell (SS) disease aged 5-66 years are presented. Cross sectional studies indicated that HbA2 levels were consistently higher in males but no age related change was apparent. Fetal haemoglobin levels were consistently higher in females and fell significantly in males between the 5-9 and 10-14 year age groups. Total haemoglobin was significantly higher in females before age 15 and higher in males after 20 years, a dramatic age related rise occurring in males between the 10-14 and 25-29 year age groups, and a fall in patients aged 40 years and over. The mean cell volume was consistently greater in females after 15 years and a marked age related rise occurred in both sexes between the 5-9 and 25-29 year age groups. Counts of irreversibly sickled cells were consistently higher in males. Reticulocytes fell significantly with age, while platelets and total bilirubin fell significantly after the age of 15 years. Longitudinal studies confirmed the increase in total haemoglobin levels in males over the ages 10-14 years, and a significant fall in males after the age of 30 years. Such studies also confirmed the fall in HbF in males aged 5-14 years, the increase in MCV in both sexes aged 5-29 years, and the fall in platelet counts in both sexes over the age of 20 years. These observations provide 'normal' values for patients seen elsewhere and also contribute to an understanding of factors determining the haemoglobin indices in SS disease.

Osteoarticular manifestations in sickle-cell disorders

The osteoarticular manifestations of the main sickling disorders (homozygous sickle cell-HbSS anaemia-, double heterozygous-HbS-beta thalassaemia, double heterozygous HbS-C disease and sickle cell-trait) are reviewed; They may be grouped into 3 main categories: vaso-occlusive, infective and metabolic. The pathophysiology and pathogenesis as well as the treatment are discussed.

Stability over time of hematological variables in 197 children with sickle cell anemia

One hundred ninety-seven children with sickle cell anemia were followed for 4 years at the Wayne State Comprehensive Sickle Cell Center to evaluate the stability of the hematological variables (Hb, Hct, RBC count, MCV, %HbF and %HBA2) over time. The mean values of the hematological measurements taken during three separate 16-month intervals were used to represent an individual's values. The correlations of the hematological variables between intervals ranged from a low of 0.46 for %HBA2 to a high of 0.91 for %HbF. Correlations that spanned two intervals (an average of 32 months) were of the same magnitude as those that spanned only one interval (an average of 16 months), suggesting that there was no decrease in the degree of stability of these variables as the time between measurements increased. The stability of the correlations between variables within intervals, and the stability of the coefficients of the first two principal components of the six hematological variables over time suggested that the relationships among variables were also stable. In a recent report [Odenheimer et al, 1983], we used the values of the six hematological variables collected at an individual's first visit to the sickle cell center to identify four hematologically distinct subgroups of children. In the current report, we found that as many as 83% of the individuals remained in the same subgroup in at least two of the three follow-up intervals, suggesting that the factors that contributed to this classification were the result of stable, rather than transient phenomena.

Blood rheology and proliferative retinopathy in sickle cell-haemoglobin C disease

Haematological and rheological (plasma and serum viscosity, whole blood viscosity, and erythrocyte filterability) factors were studied in 31 age-sex matched pairs of patients with sickle cell haemoglobin C disease with and without proliferative sickle retinopathy (PSR). Patients with PSR had significantly higher mean cell haemoglobin and lower Hb F levels on average than the matched controls, but the viscosity and erythrocyte filtration indices did not differ between the 2 groups. There was, therefore, no evidence of rheological differences between patients with and without PSR at the time of the study, although transient rheological abnormalities at the time of development of PSR could not be excluded. Prospective longitudinal studies of rheology before, during, and after the development of PSR would be necessary to detect such changes.

Hb F levels, longevity of homozygotes and clinical course of sickle cell anemia in Brazil

A sample of 354 individuals with sickle cell anemia ascertained in the city of Rio de Janeiro was studied to investigate the relationships between Hb F level, morbidity, and mortality. The mean Hb F level was 6.41 +/- 5.21%. The relationship between age and the proportion of Hb F can be described as a quadratic polynomial distribution, the level falling from approximately 11% in the first year to 4% at 25 years and then rising proportionally after 30 years. The correlations between Hb F level and 140 variables, including hematological values, signs and symptoms of the disease, as well as therapeutic requirements, showed that the patients with high Hb F levels are less anemic and have a more benign course. Several significant correlations (between amount of Hb F and the following clinical signs: pallor of mucous membranes, jaundice, cholelithiasis, leg ulcers, bronchial asthma, increased pulmonary vascularity, left ventricular hypertrophy, and osteomyelitis) are being reported here for the first time.

Post-natal decline of fetal haemoglobin in homozygous sickle cell disease: relationship to parenteral Hb F levels

The decline of fetal haemoglobin (Hb F) from birth to 6 years has been compared in a cohort of 266 Jamaican children with homozygous sickle cel (SS) disease and in 243 matched controls with a normal haemoglobin (AA) genotype. Hb F levels were significantly higher in the SS cases from 1 month onward but, unlike the normal controls, no sex difference was apparent. The Hb F levels in SS disease were significantly correlated with parental Hb F levels, suggesting that genetic factors regulating adult Hb F levels are active at earlier stages in development. Furthermore, some of these genetic determinants of Hb F production may be linked to the beta-like globin gene complex and be in linkage disequilibrium with the beta s allele.

The interaction of alpha-thalassemia and homozygous sickle-cell disease

Patients with homozygous sickle-cell disease may be homozygous for alpha-thalassemia 2 (alpha-/alpha-), may be heterozygous for alpha-thalassemia 2 (alpha-/alpha alpha), or may have a normal alpha-globin-gene complement (alpha alpha/alpha alpha). We compared the clinical and hematologic features of 44 patients who had sickle-cell disease and homozygous alpha-thalassemia 2 with those of controls with the two hematologic conditions. The patients with homozygous alpha-thalassemia 2 had significantly higher red-cell counts and levels of hemoglobin and hemoglobin A2, as well as significantly lower hemoglobin F, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, mean corpuscular volume, reticulocyte counts, irreversibly-sickled cell counts, and serum total bilirubin levels, than those with a normal alpha-globin-gene complement. Heterozygotes (alpha-/alpha alpha) had intermediate values. In the group with homozygous alpha-thalassemia 2, fewer patients had episodes of acute chest syndrome and chronic leg ulceration and more patients had splenomegaly, as compared with patients in other two subgroups. These data confirm previous suggestions that alpha-thalassemia inhibits in vivo sickling in homozygous sickle-cell disease and may be an important genetic determinant of its hematologic severity.

Concurrent sickle-cell anemia and alpha-thalassemia: effect on severity of anemia

We studied 47 patients with sickle-cell anemia to determine the effect of alpha-thalassemia on the severity of their hemolytic anemia. We diagnosed alpha-thalassemia objectively by using alpha-globin-gene mapping to detect alpha-globin-gene deletions, studying 25 subjects with the normal four alpha-globin-genes, 18 with three, and four with two. The mean hemoglobin, hematocrit, and absolute reticulocyte levels (+/- S.D.) were 7.9 +/- 0.9 g per deciliter (4.9 +/- 0.6 mmol per liter), 22.9 +/- 2.9 per cent, and 501,000 +/- 126,000 per cubic millimeter, respectively, in the non-thalassemic group; 9.8 +/- 1.6 g per deciliter (6.1 +/- 1.0 mmol per liter), 29.0 +/- 5.0 per cent, and 361,000 +/- 51,000 per cubic millimeter in the group with three alpha-globin genes; and 9.2 +/- 1.0 g per deciliter (5.7 +/- 0.6 mmol per liter), 27.5 +/- 3.0 per cent, and 100,000 +/- 15,000 per cubic millimeter in the group with two alpha-globin genes. Deletion of alpha-globin genes was also accompanied by a decreased mean corpuscular hemoglobin concentration (MCHC) in post-reticulocyte erythrocytes and by increased hemoglobin F levels. The decreased intraerythrocytic hemoglobin S concentration and elevated hemoglobin F levels associated with alpha-thalassemia appear to diminish the degree of hemolytic anemia found in sickle-cell disease.

The laboratory evaluation of microcytic red blood cells

Microcytic red blood cell states are common clinical problems in both adult and pediatric age groups. The recent widespread availability of electronic blood cell counters for performing routine blood counts has increased the detection of microcytic red blood cells. Physicians must workup both symptomatic and asymptomatic patients with microcytic red blood cells before they can initiate proper therapy and/or counseling. The purpose of this review is threefold: (1) to discuss the causes of microcytic red blood cells in terms of disorders of decreased heme production vs. disorders of decreased globin production, (2) to review the clinical laboratory tests useful in differentiating microcytic red blood cell states, and (3) to present a practical approach for the laboratory workup of microcytic red blood cells.

Observations on the natural history of dactylitis in homozygous sickle cell disease

The incidence of the hand-foot syndrome (dactylitis) has been studied in a group of 233 children with homozygous sickle cell (SS) disease followed prospectively from birth. Dactylitis affected 45% of the children by the age of 2 years, with most cases occurring before this age. Episodes were significantly more common during colder months of the year, similar to the seasonal relationship previously noted in painful crises. Comparison of hematologic indices at age 6 months in patients with and without development of dactylitis indicated a lower fetal hemoglobin and higher reticulocyte counts in affected patients. The occurrence of dactylitis in combination with low fetal hemoglobin may serve to identify high-risk patients with SS disease.

Fetal hemoglobin and clinical severity of homozygous sickle cell disease in early childhood

The relationship of the clinical features of homozygous sickle cell disease in the first two years of life to the level of fetal hemoglobin at age 6 months was investigated. Mean HgbF levels were significantly lower in children manifesting early palpable splenomegaly, dactylitis, acute splenic sequestration, and in those who died. The risks of dactylitis and ASS were significantly greater in patients with lower HgbF levels. Since early splenomegaly itself may increase the risks of ASS, infection, and death, the relationship of HgbF to these features was further analyzed within the early splenomegaly group. The results suggest that a low HgbF may have a direct effect on the etiology of ASS, but any effect on infection or death is probably mediated via its relationship with the appearance of a palpable spleen. A protective effect of a high HgbF on the risk of dactylitis was demonstrated coincident with the accepted theory of its pathogenesis. Early HgbF determinations may be of value in identifying patients at high risk of serious complications during infancy.

Hb F synthesis in sickle cell anaemia: a comparison of Saudi Arab cases with those of African origin

Fetal haemoglobin (Hb F) synthesis has been studied in 22 cases of sickle cell anemia (SS) from Saudi Arabia and compared with an equal number of cases of African origin. Among the Saudi Arabs gamma chain synthesis ranged from 4.0% to 19.9% of the total non-alpha chain synthesis (mean 8.1%) while the corresponding range for the Negro cases was < 0.3% to 4.6% (mean 1.7%). In both groups the peripheral blood Hb F level was on average 3--4 times higher than the proportion synthesized, indicating that the selective survival of Hb F containing cells (F cells) was an important factor in determining the final Hb F levels. Among the Saudi Arab cases there was a significant negative correlation between the degree of F cell enrichment and either the Hb F level of the percentage gamma chain synthesis. No such correlation was observed among the Negro cases. A high proportion of the cases in both groups were carriers of alpha thalassaemia in addition to SS, but no effect of alpha thalassaemia on Hb F production was observed.

Hematological and clinical features of sickle cell diseases: a review

The differentiation, hematologic features and clinical manifestations of patients with the various sickling disorders are reviewed. The deficiencies in our current knowledge about the spectrum of the clinical course of patients with these conditions is discussed. The interaction of alpha thalassemia with sickle cell anemia and its possible effect upon the severity of the disease is summarized. The apparent milder disease in certain groups of patients with sickle cell anemia in whom there is an associated elevation of hemoglobin F is contrasted with the controversy surrounding the effects of hemoglobin F levels in the patients of African origin.

Sickle cell anemia and trait in southern India: further studies

Population surveys and family studies among 568 members of nine ethnic groups in southern India identified 15 homozygotes for sickle hemoglobin (HbS)who had mild clinical and hematological manifestations with high levels of fetal hemoglobin (mean=20%, range 8-36%) in a heterogeneous red cell distribution. In one family, the heterozygous mother had a hemoglobin pattern consistent with a form of the heterocellular hereditary persistence of fetal hemoglobin. Sickle cell trait was found in 153(27%) of those studied. Chromatographic quantitation of the hemoglobin fractions in these heterozygotes showed a trimodal distribution of the proportion of HB Sexplicable by a genetic model postulating the presence of genotypes with two (-alpha/-alpha), three (-alpha/alpha alpha) and four (alpha alpha/alpha alpha) active alpha-globin genes. Globin synthesis studies in four heterozygotes believed to have two active alpha-globin genes demonstrated an alpha/non-alpha total activity ratio (0.57) consistent with this model.

Individual variation in the production and survival of F cells in sickle-cell disease

The protective role and underlying sources of the elevated levels of fetal hemoglobin associated with sickle-cell anemia were reassessed by microscopical immunodiffusion assays. Three variables that contribute to levels of fetal hemoglobin were examined: the percentage of fetal-hemoglobin-containing reticulocytes produced; the quantity of fetal hemoglobin synthesized within such cells; and the extent to which the fraction of fetal-hemoglobin-bearing erythrocytes is enriched beyond the level produced. Four general findings emerged from analysis of 29 patients: each variable is separately regulated; the expression of each is often distinctly different between individual patients; contrary to prior speculation, production of fetal hemoglobin may be as great in the absence of heterocellular hereditary persistence of the hemoglobin as in its presence; and fetal hemoglobin does not, as often supposed, guarantee preferential cell survival. We conclude that the differences encountered among patients must reflect heterogeneity among factors that modify production and survival of cells bearing fetal hemoglobin.