Lack of influence of fetal hemoglobin levels or erythrocyte indices on the severity of sickle cell anemia

Neurological abnormalities among pediatric patients with sickle cell disease in Saudi Arabia: a single-center retrospective study

Introduction

Sickle cell disease (SCD) is a common inherited blood disorder characterized by the production of abnormal sickle-shaped red blood cells. SCD can lead to various complications including neurological issues. Early detection and treatment are crucial for preventing these complications. This study aimed to describe the neurological manifestations, radiological findings, and neurological diagnosis related to SCD in Saudi children with the aim of contributing to the formulation of population-based guidelines for screening and treating SCD-related neurological complications.

Methods

This descriptive retrospective study included pediatric patients aged < 14 years diagnosed with SCD who were regularly followed up at the hematology clinic in KAMC, Jeddah, Saudi Arabia, from January 2008 to January 2022. Demographic and clinical data were collected from the clinical charts of 101 participants.

Results

This study included 101 patients with SCD with a mean age of 23 months at diagnosis. Among these, 59% had SCD and high fetal hemoglobin (HbF) levels. Neurological sequelae, including seizures, stroke, and other abnormalities, were observed in 26.7% of patients. There were no significant differences in the onset of neurological issues between the patients with SCD-high HbF and those with other SCD phenotypes.

Discussion

This study highlights the increased risk of brain injury and neurocognitive deficits in children with SCD. The occurrence of neurological sequelae in many patients emphasizes the need for early detection and intervention. Some patients experience neurological complications despite having high HbF levels, suggesting that further interventions are needed. This study has some limitations, including its small sample size and retrospective nature.

Conclusion

Early detection and intervention are crucial for neurological complications in patients with SCD. This study emphasizes the need for further research and effective treatment strategies considering the presence of neurological complications despite the presence of high HbF levels. Large-scale studies and population-specific guidelines are warranted for better understanding and management of SCD-related neurological complications in the Saudi population.

Variation and impact of polygenic hematologic traits in monogenic sickle cell disease

Several of the complications observed in sickle cell disease (SCD) are influenced by variation in hematologic traits (HT), such as fetal hemoglobin (HbF) level and neutrophil count. Previous large-scale genome-wide association studies carried out in largely healthy individuals have identified thousands of variants associated with HT, which have then been used to develop multi-ancestry polygenic trait scores (PTS). Here, we tested whether these PTS associate with HT in SCD patients and if they can improve statistical models associated with SCD-related complications. In 2,056 SCD patients, we found that the PTS predicted less HT variance than in non-SCD individuals of African ancestry. This was particularly striking at the Duffy/DARC locus, where we observed an epistatic interaction between the SCD genotype and the Duffy null variant (rs2814778) that led to a two-fold weaker effect on neutrophil count. PTS for these HT which are measured as part of routine practice were not associated with complications in SCD. In contrast, we found that a simple PTS for HbF that includes only six variants explained a large fraction of the phenotypic variation (20.5-27.1%), associated with acute chest syndrome and stroke risk, and improved the statistical modeling of the vaso-occlusive crisis rate. Using Mendelian randomization, we found that increasing HbF by 4.8% reduces stroke risk by 39% (P=0.0006). Taken together, our results highlight the importance of validating PTS in large diseased populations before proposing their implementation in the context of precision medicine initiatives.

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.

Individual red blood cell fetal hemoglobin quantification allows to determine protective thresholds in sickle cell disease

Polymerization of the sickle hemoglobin (HbS) is a key determinant of sickle cell disease (SCD), an inherited blood disorder. Fetal hemoglobin (HbF) is a major modulator of the disease severity by both decreasing HbS intracellular concentration and inhibiting its polymerization. However, heterocellular distribution of HbF is common in SCD. For HbS polymerization inhibition, the hypothesis of an "HbF per red blood cell (HbF/RBC) threshold" requires accurate measurement of HbF in individual RBC. To date, HbF detection methods are limited to a qualitative measurement of RBC populations containing HbF - the F cells, which are variable. We developed an accurate method for HbF quantification in individual RBC. A linear association between mean HbF content and mean RBC fluorescence by flow cytometry, using an anti-Human-HbF antibody, was obtained from non-SCD subjects presenting homogeneous HbF distribution. This correlation was then used to measure HbF/RBC. Hydroxyurea (HU) improves SCD clinical manifestations, mainly through its ability to induce HbF synthesis. The HbF distribution was analyzed in 14 SCD patients before and during HU treatment. A significant decrease in RBC population containing less than 2 pg of HbF/RBC was observed. Therefore, we tested associations for %RBC above different HbF/RBC thresholds and showed a decrease in the pathognomonic vaso-occlusive crisis incidence from the threshold of 4 pg. This quantity was also correlated with the level of sickle RBC after in vitro deoxygenation. This new method allows the comparison of HbF/RBC distributions and could be a useful tool to characterize baseline patients HbF distribution and therapeutic response to HbF inducers.

Association of fetal hemoglobin level with frequency of acute pain episodes in sickle cell disease (HbS-only phenotype) patients

BACKGROUND

Sickle cell disease (SCD) is a Mendelian single gene disorder with highly variable phenotypic expression. In the present study, we analyzed the influence of HbF, alpha thalassemia and other hematological indices to determine their association with acute pain episodes.

METHOD

This case control study consisted of SCD subjects with HbS phenotype experiencing three or more acute pain episodes in last twelve months (cases) and without any episode of acute pain during last twelve months (controls). Hematological parameters, HbF, and presence of alpha thalassemia were assessed in all subjects.

RESULTS

A statistically significant difference between HbF levels (P < 0.025, χ2 test) and alpha thalassemia (P < 0.008, χ2 test) was observed between controls and cases group. Univariate analysis indicated that increased HbF levels > 25% (OR: 0.37, 95% CI: 0.18-0.77, P < 0.008) and presence of alpha thalassemia (OR: 0.53, 95% CI: 0.33-0.85, P < 0.009) provided protection, while multivariate analysis revealed significant protection was attributable only by higher HbF levels (OR: 0.39, 95% CI: 0.17-0.88, P < 0.025). Significantly higher HbF levels were observed only in the 11-20 age group of cases in comparison to controls (Student's t-test, P < 0.001).

CONCLUSION

Higher concentrations of HbF are associated with protection against frequent episodes of acute pain crisis in SCD patients.

Neonatal Screening and the Clinical Outcome in Children with Sickle Cell Disease in Central India

BACKGROUND

Sickle cell disease (SCD) is a major health burden in India. The objective of the study was to establish a neonatal screening program and to understand the clinical course of children with SCD in central India.

METHODS AND FINDINGS

Pregnant mothers were screened for sickle hemoglobin using the solubility test. Babies were screened by high performance liquid chromatography if the mother was positive for sickle hemoglobin. The diagnosis was confirmed by molecular analysis. They received early prophylactic treatment and vaccination. Of 2134 newborns screened, 104 were sickle homozygous (SS), seven had sickle β-thalassemia (S-β thal) and 978 were sickle heterozygous (AS). The other hemoglobin abnormalities detected included HbS-δβ thalassemia-1, HbSD disease-2, HbE traits-5, β-thalassemia traits-4, alpha chain variants-3 and HbH disease-1.These babies were followed up regularly for hematological and clinical evaluation. Pain, severe anemia requiring blood transfusions and acute febrile illness were the major complications with 59.7, 45.1 and 42.6 cases per 100 person years. Fetal hemoglobin (HbF) levels were inversely associated with vaso-oclussive crisis (VOC) and severe anemia while presence of alpha thalassemia increased the rate of painful events and sepsis. Six early deaths occurred among the SS babies.

CONCLUSION

A systematic follow up of this first newborn SCD cohort in central India showed that 47% of babies presented within 1 year of age. In spite of the presence of the Arab-Indian haplotype many babies had severe manifestations.

Kinetics of sickle cell biorheology and implications for painful vasoocclusive crisis

We developed a microfluidics-based model to quantify cell-level processes modulating the pathophysiology of sickle cell disease (SCD). This in vitro model enabled quantitative investigations of the kinetics of cell sickling, unsickling, and cell rheology. We created short-term and long-term hypoxic conditions to simulate normal and retarded transit scenarios in microvasculature. Using blood samples from 25 SCD patients with sickle hemoglobin (HbS) levels varying from 64 to 90.1%, we investigated how cell biophysical alterations during blood flow correlated with hematological parameters, HbS level, and hydroxyurea (HU) therapy. From these measurements, we identified two severe cases of SCD that were also independently validated as severe from a genotype-based disease severity classification. These results point to the potential of this method as a diagnostic indicator of disease severity. In addition, we investigated the role of cell density in the kinetics of cell sickling. We observed an effect of HU therapy mainly in relatively dense cell populations, and that the sickled fraction increased with cell density. These results lend support to the possibility that the microfluidic platform developed here offers a unique and quantitative approach to assess the kinetic, rheological, and hematological factors involved in vasoocclusive events associated with SCD and to develop alternative diagnostic tools for disease severity to supplement other methods. Such insights may also lead to a better understanding of the pathogenic basis and mechanism of drug response in SCD.

Sickle cell disease in Saudi Arabia: the phenotype in adults with the Arab-Indian haplotype is not benign

Sickle cell disease (SCD) in Saudi patients from the Eastern Province is associated with the Arab-Indian (AI) HBB (β-globin gene) haplotype. The phenotype of AI SCD in children was described as benign and was attributed to their high fetal haemoglobin (HbF). We conducted a hospital-based study to assess the pattern of SCD complications in adults. A total of 104 patients with average age of 27 years were enrolled. Ninety-six per cent of these patients reported history of painful crisis; 47% had at least one episode of acute chest syndrome, however, only 15% had two or more episodes; symptomatic osteonecrosis was reported in 18%; priapism in 17%; overt stroke in 6%; none had leg ulcers. The majority of patients had persistent splenomegaly and 66% had gallstones. Half of the patients co-inherited α-thalassaemia and about one-third had glucose-6-phosphate dehydrogenase deficiency. Higher HbF correlated with higher rate of splenic sequestration but not with other phenotypes. The phenotype of adult patients with AI SCD is not benign despite their relatively high HbF level. This is probably due to the continued decline in HbF level in adults and the heterocellular and variable distribution of HbF amongst F-cells.

Polymorphism in the HMOX1 gene is associated with high levels of fetal hemoglobin in Brazilian patients with sickle cell anemia

The aim of this study was to investigate the association between three polymorphisms involved in the oxidative stress pathway and fetal hemoglobin (Hb F) levels in patients with sickle cell anemia in a Brazilian population. One hundred and seven patients with sickle cell anemia were recruited for genomic DNA extraction. The levels of Hb F, sex and age were evaluated. Three polymorphisms, rs4673:T>C and rs9932581:G>A in the CYBA gene and rs2071746:A>T in the HMOX1 gene, were identified through direct sequencing. Hb F levels were not associated with sex, age, or the polymorphisms rs4673:T>C and rs9932581:G>A. However, the TT genotype of the rs2071746:A>T polymorphism was associated with increased levels of Hb F (p value = 0.0131). We observed an association between the TT genotype of the rs2071746:A>T polymorphism, present in the HMOX1 gene, and increased levels of Hb F, indicating the presence of a new marker related to Hb F levels in sickle cell anemia patients.

Genetic modifiers of sickle cell disease

Sickle cell anemia is associated with unusual clinical heterogeneity for a Mendelian disorder. Fetal hemoglobin concentration and coincident α thalassemia, both which directly affect the sickle erythrocyte, are the major modulators of the phenotype of disease. Understanding the genetics underlying the heritable subphenotypes of sickle cell anemia would be prognostically useful, could inform personalized therapeutics, and might help the discovery of new "druggable" pathophysiologic targets. Genotype-phenotype association studies have been used to identify novel genetic modifiers. In the future, whole genome sequencing with its promise of discovering hitherto unsuspected variants could add to our understanding of the genetic modifiers of this disease.

The association between hydroxyurea treatment and pain intensity, analgesic use, and utilization in ambulatory sickle cell anemia patients

BACKGROUND

We compared daily pain, home analgesic use, and utilization among ambulatory adults in the randomized multicenter study of hydroxyurea in sickle cell anemia (MSH). We related the fetal hemoglobin (HbF) hydroxyurea response to these response variables.

METHODS

Patients rated their sickle cell pain intensity (0-9), use of analgesics, and visits for pain daily. Diaries were collected biweekly, and intensity was collapsed into single interval ratings. The interval proportions of days of analgesic use and medical visits for pain were also calculated. Group comparisons were made by intention to treat as well as by HbF change levels from baseline to 2 years of treatment (placebo and low, medium, high, or very high response).

RESULTS

A total of 134 (44.8%) enrollees completed 2 years of follow-up. Pain intensity correlated with analgesic use (r = 0.83, P > 0.0001) and utilization (r = 0.50, P < 0.0001). Pain intensity was lower for patients on hydroxyurea (2.51 ± 0.062 vs 2.82 ± 0.063 placebo, F(1270) = 11.65, P = 0.0007). The difference, though small, appeared early and was sustained. Analgesic use and utilization were also slightly lower (analgesic use: F (1270) = 11.97, P = 0.0006; utilization: F(1270) = 32.0, P < 0.0001). Each was statistically significantly lower among hydroxyurea patients with higher HbF treatment responses to hydroxyurea.

CONCLUSIONS

Hydroxyurea usage led to a small, statistically significant reduction in daily pain, analgesic use, and utilization in adults in MSH, corroborating previously shown larger reductions in crises and mortality. The degree of daily symptomatic reduction was related to the size of the HbF treatment response, further confirming HbF response as a useful laboratory correlate.

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.

Day hospital versus inpatient management of uncomplicated vaso-occlusive crises in children with sickle cell disease

BACKGROUND

Day hospital (DH) management for patients with sickle cell disease (SCD) experiencing uncomplicated vaso-occlusive pain crises has been utilized as an alternative care delivery system to inpatient hospitalization. The objective of this study was to determine whether DH management results in shorter length of stay compared to inpatient care.

PROCEDURE

We conducted a retrospective cohort study with 35 DH admissions and 35 inpatient admissions for children with SCD presenting with uncomplicated vaso-occlusive crises (VOCs). A DH admission was defined as a minimum of two consecutive days of aggressive pain management as an outpatient, including intravenous hydration and analgesics, supported by home treatment over night with oral analgesic and anti-inflammatory agents. We gathered data on demographics, pain scores, length of stay, admission charges, and needs for persistent care.

RESULTS

DH care resulted in a 39% reduction of the average length of stay compared to inpatient admissions. Multivariate linear regression demonstrated that the location of patient care for VOCs was a significant predictor of length of stay (P < 0.0006) after controlling for patient characteristics, severity of illness, and disease history.

CONCLUSIONS

We conclude that a dedicated DH facility has the potential to provide efficient and timely management of uncomplicated VOCs through reduction of length of stay. This delivery care system may be particularly relevant for children who are significantly impacted by inpatient hospitalization.

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.

Predicting clinical severity in sickle cell anaemia

The ability to predict the phenotype of an individual with sickle cell anaemia would allow a reliable prognosis and could guide therapeutic decision making. Some risk factors for individual disease complications are known but are insufficiently precise to use for prognostic purposes; predicting the global disease severity is not yet possible. Genetic association studies, which attempt to link gene polymorphisms with selected disease subphenotypes, may eventually provide useful methods of foretelling the likelihood of certain complications and allow better individualized treatment.

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.

Variation in hospitalizations and hospital length of stay in children with vaso-occlusive crises in sickle cell disease

OBJECTIVE

As a measure of morbidity of vaso-occlusive crises (VOC) in sickle cell disease, we used a national hospital discharge database, the Kids' Inpatient Database (KID), to determine the number of hospitalizations and hospital length of stay (LOS) by age.

PROCEDURE

Nationally weighted hospital discharges for VOC in children with sickle cell disease were analyzed using data from 2,500 hospitals in the Healthcare Cost and Utilization Project (HCUP) KID. Number of discharges and hospital LOS by age group were analyzed. Multiple linear regression was performed to analyze the effect of age on hospital LOS.

RESULTS

There were 20,271 hospital discharges for children with sickle cell disease and VOC. Mean age (SD) at time of admission was 10.6 (5.38) years with 49% being males. The overall average LOS was 4.4 days. There were differences in the number of hospital discharges by age group (P < 0.001). In addition, there was a difference in LOS by age group (P < 0.0001). After controlling for potential confounders, older age was associated with a longer LOS (P < 0.0001).

CONCLUSIONS

Older children with sickle cell disease and VOC have increased hospitalizations and longer LOS. This age effect should be considered when measuring the effect of an intervention on hospital utilization in these children.

Mechanism of monocyte activation and expression of proinflammatory cytochemokines by placenta growth factor

Monocytes from patients with sickle cell disease (SCD) are in an activated state. However, the mechanism of activation of monocytes in SCD is not known. Our studies showed that placenta growth factor (PlGF) activated monocytes and increased mRNA levels of cytokines (tumor necrosis factor-alpha [TNF-alpha] and interleukin-1beta [IL-1beta]) and chemokines (monocyte chemotactic protein-1 [MCP-1], IL-8, and macrophage inflammatory protein-1beta [MIP-1beta]) in both normal monocytes and in the THP-1 monocytic cell line. This increase in mRNA expression of cytochemokines was also reflected in monocytes derived from subjects with SCD. We studied the PlGF-mediated downstream cellular signaling events that caused increased transcription of inflammatory cytochemokines and chemotaxis of THP-1 monocytes. PlGF-mediated cytochemokine mRNA and protein expression was inhibited by PD98059 and wortmannin, inhibitors of mitogen-activated protein kinase kinase (MAPK/MEK) kinase and phosphatidylinositol-3 (PI3) kinase, respectively, but not by SB203580, a p38 kinase inhibitor. PlGF caused a time-dependent transient increase in phosphorylation of extracellular signal-regulated kinase-1/2 (ERK-1/2), which was completely inhibited by wortmannin, indicating that activation of PI3 kinase preceded MEK activation. PlGF also induced transient phosphorylation of AKT. MEK and PI3 kinase inhibitors and antibody to Flt-1 abrogated PlGF-induced chemotaxis of THP-1 monocytes. Overexpression of a dominant-negative AKT or a dominant-negative PI3 kinase p85 subunit in THP-1 monocytes attenuated the PlGF-mediated phosphorylation of ERK-1/2, cytochemokine secretion, and chemotaxis. Taken together, these data show that activation of monocytes by PlGF occurs via activation of Flt-1, which results in activation of PI3 kinase/AKT and ERK-1/2 pathways. Therefore, we propose that increased levels of PlGF in circulation play an important role in the inflammation observed in SCD via its effects on monocytes.

Sickle cell disease: the neurological complications

The genetic cause of sickle cell disease has been known for decades, yet the reasons for its clinical variability are not fully understood. The neurological complications result from one point mutation that causes vasculopathy of both large and small vessels. Anemia and the resultant cerebral hyperemia produce conditions of hemodynamic insufficiency. Sickled cells adhere to the endothelium, contributing to a cascade of activated inflammatory cells and clotting factors, which result in a nidus for thrombus formation. Because the cerebrovascular reserve becomes exhausted, the capacity for compensatory cerebral mechanisms is severely limited. There is evidence of small-vessel sludging, and a relative deficiency of nitric oxide in these vessels further reduces compensatory vasodilatation. Both clinical strokes and silent infarcts occur, affecting motor and cognitive function. New data suggest that, in addition to sickle cell disease, other factors, both environmental (eg, hypoxia and inflammation) and genetic (eg, mutations resulting in thrombogenesis), may contribute to a patient's stroke risk. The stroke risk is polygenic, and sickle cell disease can be considered a model for all cerebrovascular disease. This complex disease underscores the potential intellectual and practical distance between the determination of molecular genetics and effective clinical application and therapeutics.

Foetal haemoglobin in homozygous sickle cell disease: a study of patients with low HBF levels

High foetal haemoglobin (HbF) levels are believed to ameliorate the manifestations of homozygous sickle cell (SS) disease. The corollary implies that patients with low HbF levels should have more severe clinical courses. We investigated this in a retrospective study of 50 Jamaican patients with steady-state HbF levels below 1% compared with a control group (A) of 54 subjects with steady-state HbF levels between 2.5 and 3.4% (around the 25th centile for our population), and a second control group (B) of 60 patients with steady-state HbF levels between 4.6 and 5.2% (around the 50th centile). Comparisons across the groups indicated significantly fewer females in the study group (16, 50 and 57%, respectively). Examination for haematological trends across the groups showed positive linear trends for haemoglobin (Hb) (P=0.004), packed cell volume (PCV) (P=0.01), mean cell volume (MCV) (P= < 0.001), mean cell haemoglobin (MCH) (P= < 0.001) and a negative trend for haemoglobin A2 (P=0.03). Clinically, there were no differences in the incidence of painful crises, abdominal crises and the acute chest syndrome, but leg ulcers were significantly less frequent in the study group (P=0.04). Therefore low HbF levels do not appear to increase the clinical severity of SS disease and may be protective against leg ulceration.

Cerebrovascular complications and parvovirus infection in homozygous sickle cell disease

Human parvovirus B19 infection causes most clinically defined aplastic crises in homozygous sickle cell (SS) disease. With transfusion support, the outcome is generally benign; however, cerebrovascular complications in close temporal association with B19-induced aplastic crises have been described. We carried out a retrospective review, between 1978 and 1999, of 346 aplastic crises in patients with SS disease attending the Sickle Cell Clinic of the University Hospital of the West Indies, Kingston, Jamaica. Six cerebrovascular episodes, 5 with hemiplegia, occurred within 2 days of aplastic crises; and 4, all with features of encephalitis, occurred within 2 to 5 weeks. Hemiplegia in 2 children resolved completely, one is improving, and one persists 20 years later; one patient died from recurrent strokes. Of the 4 children whose events occurred later, all had seizure disorders and 2 had transient cortical blindness. The crude risk of cerebrovascular episodes in the 5-week interval after B19 infection was calculated as 58 times greater than expected, which is suggestive of a causal association.

Physiologic decline in fetal hemoglobin parameters in infants with sickle cell disease: implications for pharmacological intervention

PURPOSE

Fetal hemoglobin (HbF) is an important determinant in the clinical severity of patients with sickle cell disease. The physiologic decline in HbF parameters in a cohort of infants with sickle cell disease was investigated.

PATIENTS AND METHODS

The percent HbF and F cells were quantitated, and the HbF per F cell was then calculated. One hundred thirty-eight blood samples from 44 infants with homozygous sickle cell anemia (HbSS) and 56 samples from 24 infants with sickle cell hemoglobin (HbSC) were studied.

RESULTS

Infants with HbSS had a logarithmic decline in HbF parameters; at 24 months, the average HbF was 14.6%+/-7.3% and the % F cells was 64.7%+/-16.9%. The amount of HbF in each F cell (HbF per F cell) was <15 pg/cell, a suggested threshold for intracellular sickle polymerization, by age 12 months. Infants with HbSC had a more rapid decline: at 12 months the average % HbF was 12.2%+/-9.3%, the % F cells was 60.5%+/-18.7%, and the HbF per F cell was <10 pg/cell.

CONCLUSIONS

By age 2 years, HbF parameters including the % HbF, % F cells, and the HbF per F cell decrease to levels insufficient to inhibit sickling. Pharmacologic intervention designed to enhance HbF production and prevent chronic organ damage should be considered during infancy.

The costs of children with sickle cell anemia: preparing for managed care

PURPOSE

To anticipate the clinical challenges and financial risks facing physicians and managed care organizations who care for children with chronic illnesses, such as sickle cell anemia (SCA), under capitated managed care arrangements.

PATIENTS AND METHODS

A cross-sectional study based on claims data from the Washington State Medicaid Program (WSMP) and the Federal Employees Health Benefits Program (FEP). Expenditure patterns were compared for children 18 years of age or younger for whom a claim with a diagnosis of SCA was submitted and paid in the State of Washington during fiscal year 1993 (FY1993) or by the FEP during FY1992 to expenditure patterns for all children.

RESULTS

Children with SCA had mean expenditures 8.8 times the mean expenditures for all children in WSMP. There was wide variation in the annual expenditures among children with SCA; the most expensive 10% of children accounted for 56% of total expenditures. Ninety-seven percent of the expenditures were concentrated in four broad categories: 72% for inpatient care, 11% for outpatient care, 11% for physician payments, and 3% for prescription drugs. Examination of expenditure and utilization patterns for children with sickle cell anemia enrolled in the FEP yielded similar results.

CONCLUSIONS

Unless managed care organizations and capitated pediatricians receive payment rates that reflect the higher expected expenditures of caring for these children, access to and quality of care may suffer. Analyses of practice guidelines and utilization patterns suggest that newborn screening, regular access to specialty facilities, and comprehensive education programs are critical areas that are vulnerable to reductions under capitation.

Intracellular Hemoglobin S Polymerization and the Clinical Severity of Sickle Cell Anemia

Recent work has enabled us to quantitate the four variables (2,3-DPG concentration, pHi, non-S hemoglobin composition, and O2 saturation) that modulate the equilibrium solubility (csat) of Hb S inside sickle erythrocytes (SS RBCs). Using measured values of mean corpuscular hemoglobin concentration (MCHC), 2,3-DPG concentration, and %Hb (F+A2), along with estimates of pHiand the Δcsat due to partial oxygenation of SS RBCs in the microcirculation, we calculated the mean polymer fraction (fp) in erythrocytes from 46 SS homozygotes. Values of fp derived from the conservation of mass equation ranged from 0.30 to 0.59. MCHC and %Hb F were major determinants of the magnitude of fp; 2,3-DPG concentration and pHialso contributed, but to a lesser extent. A clinical severity score (CSS) was assigned to each patient based on mean hospitalization rate. There was a weak, but statistically significant, negative correlation between fp and steady state hematocrit (P = .017), but none between fp and whole blood hemoglobin concentration (P = .218). Although there was no correlation between fp and mean number of hospitalization days per year, patients with the greatest number of admissions and hospitalization days were found only among those who had an fp > 0.45. All five patients who died during the follow-up period (median, 7 years; range, 3 to 10 years) had fp values ≥0.48. However, patients with few admissions, low hospitalization days, and long survivals occurred at all fp levels. These results suggest that the clinical course of homozygous SS disease cannot be predicted by mean fpcalculations, which assume a homogeneous distribution of the five variables that modulate intraerythrocytic polymerization. A heterogeneous distribution is more likely; so the amount of polymerized Hb S could vary considerably among cell populations. Factors such as membrane abnormalities and endothelial cell interactions may also contribute to clinical severity.

Intracellular Hemoglobin S Polymerization and the Clinical Severity of Sickle Cell Anemia

Recent work has enabled us to quantitate the four variables (2,3-DPG concentration, pHi, non-S hemoglobin composition, and O2 saturation) that modulate the equilibrium solubility (csat) of Hb S inside sickle erythrocytes (SS RBCs). Using measured values of mean corpuscular hemoglobin concentration (MCHC), 2,3-DPG concentration, and %Hb (F+A2), along with estimates of pHiand the Δcsat due to partial oxygenation of SS RBCs in the microcirculation, we calculated the mean polymer fraction (fp) in erythrocytes from 46 SS homozygotes. Values of fp derived from the conservation of mass equation ranged from 0.30 to 0.59. MCHC and %Hb F were major determinants of the magnitude of fp; 2,3-DPG concentration and pHialso contributed, but to a lesser extent. A clinical severity score (CSS) was assigned to each patient based on mean hospitalization rate. There was a weak, but statistically significant, negative correlation between fp and steady state hematocrit (P = .017), but none between fp and whole blood hemoglobin concentration (P = .218). Although there was no correlation between fp and mean number of hospitalization days per year, patients with the greatest number of admissions and hospitalization days were found only among those who had an fp > 0.45. All five patients who died during the follow-up period (median, 7 years; range, 3 to 10 years) had fp values ≥0.48. However, patients with few admissions, low hospitalization days, and long survivals occurred at all fp levels. These results suggest that the clinical course of homozygous SS disease cannot be predicted by mean fpcalculations, which assume a homogeneous distribution of the five variables that modulate intraerythrocytic polymerization. A heterogeneous distribution is more likely; so the amount of polymerized Hb S could vary considerably among cell populations. Factors such as membrane abnormalities and endothelial cell interactions may also contribute to clinical severity.

Is Hb A2 elevated in adults with sickle-alpha-thalassemia (beta(S)/beta(S); -alpha/-alpha)?

Thirteen patients with sickle cell anemia (SS) were found to have two alpha gene deletions with a presumptive genotype of beta(S)/beta(S); -alpha/-alpha. Hematological data showed that this group of patients had elevated Hb A2 level. In order to determine whether the elevation of Hb A2 is typical of SS with a two alpha gene deletion or is due to undiagnosed S-beta(O)-thalassemia with a two alpha gene deletion we looked for the presence or absence of beta(O)-thalassemia by molecular techniques. The latter included reverse dot-blot hybridization to rule out a beta-thalassemia mutation, digestion with CvnI endonuclease followed by Southern blotting and hybridization with a beta genomic probe, and, in selected patients, determination of the synthetic alpha/beta ratio. One of the 13 patients had S-beta(O)-thalassemia with a G-->A mutation at IVS-II-1 indicating that her genotype was beta(S)/beta(O) thalassemia; -alpha/-alpha. The remaining 12 patients were homozygous for the sickle gene, had relatively elevated Hb levels, increased Hb A2 values, and Hb F levels similar to those in patients with SS and four or three alpha genes. At the clinical level, the 12 patients with SS and a two alpha gene deletion had increased prevalence of avascular necrosis, retinopathy, and splenomegaly, but decreased prevalence of leg ulcers and cerebrovascular accidents. Together, the data indicate that SS with a two alpha gene deletion (beta(S)/beta(S); -alpha/-alpha) is a unique subset of patients with SS characterised by distinct hematological and clinical features.

Benign clinical course in homozygous sickle cell disease: a search for predictors

AIMS

(1) To estimate the proportion of subjects with homozygous sickle cell disease who have a benign clinical course, and (2) to assess factors that may be predictive of benign disease.

MATERIAL

Subjects (n = 280) were participants in a longitudinal cohort study of sickle cell disease. They were classified as benign or control based on clinical history from birth to age 13 years old. Associations with growth, hematology, and an index of social status were investigated.

RESULTS

Benign disease occurred in 43 (15%) patients. Neither growth nor social status were related to benign disease. There were only two statistically independent associations: alpha thalassemia status and average steady state fetal hemoglobin (HbF). Patients with a normal complement of alpha globin genes were 2.2 (1.0, 4.9) times more likely to have benign disease than those with gene deletion, and were less likely to have frequent painful crises, dactylitis, and bone necrosis. The odds of having benign disease were 1.09 (1.02, 1.17) times higher for each unit increase in HbF, and 44% of subjects with HbF in the top decile (HbF > 13.8%) of the distribution had benign disease. There was no evidence for a threshold effect of high HbF on benign disease.

CONCLUSION

A benign clinical course of sickle cell disease may occur in Jamaica and is associated with a normal alpha globin gene complement, and high levels of HhF. Ability to predict benign disease at birth is limited.

Quantitative analysis of erythrocytes containing fetal hemoglobin (F cells) in children with sickle cell disease

Variation in the level of fetal hemoglobin (HbF) accounts for much of the clinical heterogeneity observed in patients with sickle cell disease (SCD). The HbF level has emerged as an important prognostic factor in both sickle cell pain and mortality, and a % HbF of 10-20% has been suggested as a threshold level for diminished clinical severity. The number of erythrocytes that contain HbF (termed F cells) may also be critically important, as F cells resist intravascular sickling and have preferential in vivo survival. Since F cells can be enumerated with high accuracy using flow cytometry methods, we prospectively studied a cohort of 242 children with SCD. Children with HbS and hereditary persistence of fetal hemoglobin (S/HPFH) had essentially 100% F cells. In contrast, children with homozygous sickle cell anemia (HbSS), HbS/beta0 thalassemia, or HbS/beta+ thalassemia had significantly lower mean % F cell values (55.9, 61.6, and 51.3%, respectively; P < 0.001), and children with HbSC had even fewer F cells (27.0%; P < 0.001). There was a highly significant correlation between the % F cells and the log (% HbF), which was observed for the total population of children (r = 0.95, P < 0.001), as well as for each of the individual subgroups of children with HbSS (r = 0.94, P < 0.001), HbSC (r = 0.89, P < 0.001), or HbS/beta0 thalassemia and HbS/beta+ thalassemia (r = 0.95, P <0.001). This logarithmic correlation between % F cells and % HbF has not been previously described and has important implications for the pharmacologic manipulation of HbF in patients with SCD.

Surface properties of irreversibly sickled cells differ from those of the bulk of sickle cells. Studies by partitioning in aqueous phase systems

Counter-current distribution (CCD) of red blood cells (RBC) from individuals with homozygous sickle cell (HbSS) disease in a charge-sensitive aqueous dextran-poly(ethylene glycol) phase system, which fractionates cells on the basis of surface properties, indicates that the percentage of irreversibly sickled cells (ISC) increases and the percentage of reticulocytes decreases with increasing cell partition ratios. The high partition ratios of ISC correspond to those of older RBC when RBC from normal individuals are subjected to CCD. Our results thus indicate that ISC differ in surface properties from those of the bulk of sickle RBC (including reticulocytes) in the population and that the difference is, most likely, charge-related. While the question as to whether ISC are indeed old cells has not yet been unequivocally answered, this view finds support in the fact that the independent parameters of ISC surface properties, as reflected by partition ratios, and densities correlate as they do in older RBC from normal individuals.

Effects of alpha thalassaemia and haemoglobin F (HbF) level on the clinical severity of sickle-cell anaemia

Three clinical parameters - average steady-state haematocrit (ASSH), number of crises per year (Cr/Y), and number of transfusions per year (Tx/Y) - were evaluated in 52 patients with sickle-cell anaemia in relation to their foetal haemoglobin (HbF) levels. No correlation was observed between HbF and any of these parameters. A comparison of these three clinical parameters and the alpha globin gene status was also made in 28 of these patients. The relationships between (ASSH) or (Cr/Y) and alpha globin gene status were not significantly different (p > 0.05) but a significantly different value (p < 0.05) was observed between (Tx/Y) and the alpha globin gene status in these patients. It is concluded that, although HbF levels did not affect any of these parameters, alpha thalassaemia deletion significantly reduces the transfusion requirements of these patients.

The clinical features of sickle cell disease

Evidence from structural studies of DNA suggest that the sickle cell mutation has arisen on at least three separate occasions in Africa and as a fourth independent mutation in the Eastern Province of Saudi Arabia or India. The pathophysiology of sickle cell disease is essentially similar in these different areas although the frequency and severity of complications may vary between areas. Generally, the chronic haemolysis and resulting anaemia is well tolerated, although serious morbidity and occasionally mortality may be associated with the aplastic crisis or cholelithiasis. Exacerbation of anaemia below steady state levels occurs with chronic glomerular damage and renal failure, especially in older patients. Most of the morbidity of the disease arises from bone marrow necrosis in the painful crisis or from vaso-occlusive manifestations. Changes in the splenic circulation result in life-threatening episodes of acute splenic sequestration, the chronic morbidity of hypersplenism, and splenic dysfunction renders children prone to pneumococcal septicaemia. Chronic organ damage contributes to chronic leg ulceration in adolescence and progressive renal, pulmonary, and occasionally cardiovascular impairment in later life. The clinical spectrum of homozygous sickle cell disease varies widely between patients. Factors contributing to this variability include alpha-thalassaemia, persistence of high HbF levels, haematology, social circumstances, and geographical and climatic variation. Many of the causes of mortality may be prevented or more effectively treated, leading to increased survival and an increased quality of life in affected subjects.

Sickle cell vasoocclusion: many issues and some answers

The pathophysiology of sickle (SS) cell vasoocclusion is derived from the presence of hemoglobin S (HbS) which forms polymeric fibers in the deoxygenated state. Nevertheless, phenotypic expression of sickle cell disease (i.e., clinical severity) shows marked individual variations and is influenced by genetic modifiers such as epistatic effects of linked and unlinked genes. Furthermore, the polymerization of HbS is central but not the only event, and is more likely a consequence of disruptions of the steady state of flow. The available evidence indicates that the vasoocclusive crisis is a microcirculatory event in which multiple factors could be involved. We present a model of vasoocclusion as a two step process in which adhesion of deformable cells occurs first, followed by obstruction induced by less deformable SS cells. This review discusses, in addition, rheologic and microcirculatory behavior of SS erythrocytes and the interacting role of vascular factors, red cell heterogeneity, deoxygenation rates, and red cell-endothelial interactions in the pathophysiology of SS cell vasoocclusion.

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.

Stroke in a cohort of patients with homozygous sickle cell disease

Strokes occurred in 17 of 310 children with homozygous sickle cell disease who were followed from birth, representing an incidence of 7.8% by the age of 14 years. Two children had subarachnoid hemorrhage, one having resolution of symptoms after aneurysm surgery and another dying of a presumed second hemorrhage 14 days later. The remaining 15 strokes were presumed to be cerebral infarction, although autopsy, angiographic, or computed tomographic evidence was available in only 8 children. There were 6 deaths, 2 in the acute event and 4 after recurrence, which occurred in 6 (46%) of 13 patients who survived the initial episode. There were 10 recurrent episodes at a median interval of 9 months after the initial event. Steady-state hematologic data revealed significantly higher leukocyte counts than in control subjects without strokes at age 1 year and in the last study preceding the stroke. The initial stroke coincided with an acutely lowered hemoglobin value in 5 patients (3 aplastic crises, 1 acute splenic sequestration, 1 probable pulmonary sequestration) and with painful crises in another 7 patients. We conclude that a high leukocyte count and an acute decrease of hemoglobin are risk factors for stroke in patients with homozygous sickle cell disease.

Relationship of foetal haemoglobin levels and beta s haplotypes in homozygous sickle cell disease

The foetal haemoglobin (HbF) levels and the haplotypes of beta s chromosomes in sickle cell anaemia patients in Nigeria were evaluated. The mean HbF level was 5.9 +/- 3.8% with a range of 0.9-16.7%. 80% of the patients had HbF values below 8% and 94% had HbF levels below 10%. No significant difference in haematological parameters was seen between those with less than 2% HbF and those with greater than 8% HbF. The presence (+) or absence (-) of eight restriction endonuclease enzyme sites within the beta s globin gene cluster (haplotype) on chromosome 11 were mapped. The common haplotype (- - - - + + - +) in 97% of the chromosomes examined closely correlates with the low levels of foetal haemoglobin generally observed in sickle cell patients in the same population.

The influence of fetal hemoglobin on the clinical expression of sickle cell anemia

The variable levels of HbF in sickle cell anemia reflect the heterogeneous genetic mix of the beta s-gene-cluster haplotypes and coinheritance of alpha-thalassemia-2 in American SS patients. Clinical severity is less when the level of HbF reaches 20% or 1.2 g/dl or more. The coinheritance of alpha-thalassemia-2 not only increases the intracellular red cell water but modifies the HbF level in accordance with the beta-cluster haplotype. In general, the SS patient with at least one Senegalese haplotype who does not have a CAR haplotype in trans, has a significantly greater probability of maintaining HbF above 20%. This is in part related to the genetic control of the G gamma HbF locus. Such a patient is protected from arteriolar vasculopathy and subsequent major organ destruction. Much of this but perhaps not all of the better health of patients with a Senegalese haplotype can be attributed to the elevation of G gamma HbF. The coinheritance of alpha-thalassemia-2 further decreases the risk of major morbidity of the soft tissues but increases the risk of avascular necrosis of the bony skeleton. Although these heterozygous Senegal patients are healthier, eventually most, in time, will show the deleterious effect of HbS as retinopathy and avascular necrosis usually beginning after age 30 and sickle nephropathy after age 40. Because of the age-specific effect, the onset of the sickle vasculopathy is delayed by nearly 20 years in the Sen/Ben patient with increased G gamma HbF as compared to those with a CAR haplotype or the homozygous Benin. Lifetime elevation of HbF above 20% modifies the severity of disease expression and provides relative protection to the patient with sickle cell anemia.

Effect of polymerization tendency on haematological, rheological and clinical parameters in sickle cell anaemia

The polymerization tendency of sickle haemoglobin was estimated as a function of oxygen saturation in 30 patients with homozygous sickle cell anaemia. The deformability of their erythrocytes was also measured, by initial-flow-rate filtration at 37 degrees C through pores of 5 microns diameter, and clinical severity was assessed using a visual analogue scale. By means of partial correlation analysis, it was found that correlations between haematological, rheological, and clinical parameters in sickle cell anaemia could be explained on the basis of an association of each variable with polymerization tendency. Patients with the greatest tendency to form polymer had the least deformable erythrocytes and perceived their disease to be more severe as judged by the visual analogue scale. Polymer formation also appeared to be a determinant of the number of dense cells which, in turn, determine haemolytic rate and erythrocyte deformability.

The relationship between fetal hemoglobin and disease severity in children with sickle cell anemia

A study was conducted in a sample of 140 children with sickle cell anemia to evaluate the relationship between hematological variables (%HbF, %HbA2, %Hb, and mean cell volume) and disease severity. A patient's severity status was determined by whether he/she was hospitalized, had a transfusion, and/or had a pain crisis at 2 evaluation periods; the first was based on a patient's history taken at the initial assessment visit to the Wayne State Comprehensive Sickle Cell Center, and the second was based on a 1-3 year follow-up at the center. Fetal hemoglobin was a strong predictor of a patient's hospitalization and transfusion status. A decrease in %HbF of 4.76% (one SD of %HbF) was associated with a 3.58 fold (95% confidence interval, 1.18-7.28) greater odds of being hospitalized both prior to initial assessment and on follow-up, compared to not being hospitalized at either evaluation. Similarly, a decrease in %HbF of 4.76% was associated with a 5.56 fold (95% confidence interval, 1.67-18.96) greater odds of having a transfusion both prior to initial assessment and on follow-up compared to not having a transfusion at either evaluation. Patients who were both hospitalized and transfused at initial assessment and on follow-up (n = 12) had a mean %HbF of 7.59%, while patients who were not hospitalized or transfused at either evaluation (n = 19) had a mean %HbF of 13.61%. Fetal hemoglobin was not a significant predictor of pain crises in this sample of patients. None of the other hematological variables were significant predictors of disease severity in this study. The strong relationship between %HbF and disease severity identified in this study suggests that a single %HbF measurement may be useful in predicting important aspects of the clinical course of children with sickle cell anemia.

Sickle cell anemia and central nervous system infarction: a neuropathological study

CNS infarcts were demonstrated in 12 of 24 autopsied patients with sickle cell anemia. The infarcts occurred most extensively in the territory supplied by the distal branches of the internal carotid artery, especially the anterior-middle cerebral artery boundary zone. They were regularly associated with organizing and recanalizing thrombi involving the distal cervical and proximal intracranial divisions of the internal carotid system. On the basis of these findings, we infer that the pathogenesis of the infarction involves perfusion failure or intraarterial embolization in addition to intravascular sickling.

Five adults with mild sickle cell anemia share a beta S chromosome with the same haplotype

Five adult SS patients from Qatar, Turkey, and South Africa with mild disease, had greatly elevated Hb F and specific patterns of polymorphic sites on their beta S chromosomes. One subject had an alpha-thalassemia (-alpha/-alpha). The haplotypes were the common type #19, associated with severe disease, and type #31, not seen thus far in an SS patient (numbering system of Antonarakis et al). The data suggest that modifications in the DNA of the beta S #31 chromosome promotes the synthesis of gamma chains.