Clinical diversity of sickle cell anemia: genetic and cellular modulation of disease severity

Tripartite collaboration of blood-derived endothelial cells, next generation RNA sequencing and bioengineered vessel-chip may distinguish vasculopathy and thrombosis among sickle cell disease patients

Sickle cell disease (SCD) is the most prevalent inherited blood disorder in the world. But the clinical manifestations of the disease are highly variable. In particular, it is currently difficult to predict the adverse outcomes within patients with SCD, such as, vasculopathy, thrombosis, and stroke. Therefore, for most effective and timely interventions, a predictive analytic strategy is desirable. In this study, we evaluate the endothelial and prothrombotic characteristics of blood outgrowth endothelial cells (BOECs) generated from blood samples of SCD patients with known differences in clinical severity of the disease. We present a method to evaluate patient-specific vaso-occlusive risk by combining novel RNA-seq and organ-on-chip approaches. Through differential gene expression (DGE) and pathway analysis we find that BOECs from SCD patients exhibit an activated state through cell adhesion molecule (CAM) and cytokine signaling pathways among many others. In agreement with clinical symptoms of patients, DGE analyses reveal that patient with severe SCD had a greater extent of endothelial activation compared to patient with milder symptoms. This difference is confirmed by performing qRT-PCR of endothelial adhesion markers like E-selectin, P-selectin, tissue factor, and Von Willebrand factor. Finally, the differential regulation of the proinflammatory phenotype is confirmed through platelet adhesion readouts in our BOEC vessel-chip. Taken together, we hypothesize that these easily blood-derived endothelial cells evaluated through RNA-seq and organ-on-chips may serve as a biotechnique to predict vaso-occlusive episodes in SCD patients and will ultimately allow better therapeutic interventions.

An Experimental-Computational Approach to Quantify Blood Rheology in Sickle Cell Disease

In sickle cell disease, aberrant blood flow due to oxygen-dependent changes in red cell biomechanics is a key driver of pathology. Most studies to date have focused on the potential role of altered red cell deformability and blood rheology in precipitating vaso-occlusive crises. Numerous studies, however, have shown that sickle blood flow is affected even at high oxygen tensions, suggesting a potentially systemic role for altered blood flow in driving pathologies, including endothelial dysfunction, ischemia, and stroke. In this study, we applied a combined experimental-computation approach that leveraged an experimental platform that quantifies sickle blood velocity fields under a range of oxygen tensions and shear rates. We computationally fitted a continuum model to our experimental data to generate physics-based parameters that capture patient-specific rheological alterations. Our results suggest that sickle blood flow is altered systemically, from the arterial to the venous circulation. We also demonstrated the application of this approach as a tool to design patient-specific transfusion regimens. Finally, we demonstrated that patient-specific rheological parameters can be combined with patient-derived vascular models to identify patients who are at higher risk for cerebrovascular complications such as aneurysm and stroke. Overall, this study highlights that sickle blood flow is altered systemically, which can drive numerous pathologies, and this study demonstrates the potential utility of an experimentally parameterized continuum model as a predictive tool for patient-specific care.

A microfluidic platform for simultaneous quantification of oxygen-dependent viscosity and shear thinning in sickle cell blood

The pathology of sickle cell disease begins with the polymerization of intracellular hemoglobin under low oxygen tension, which leads to increased blood effective viscosity and vaso-occlusion. However, it has remained unclear how single-cell changes propagate up to the scale of bulk blood effective viscosity. Here, we use a custom microfluidic system to investigate how the increase in the stiffness of individual cells leads to an increase in the shear stress required for the same fluid strain in a suspension of softer cells. We characterize both the shear-rate dependence and the oxygen-tension dependence of the effective viscosity of sickle cell blood, and we assess the effect of the addition of increasing fractions of normal cells whose material properties are independent of oxygen tension, a scenario relevant to the treatment of sickle patients with blood transfusion. For untransfused sickle cell blood, we find an overall increase in effective viscosity at all oxygen tensions and shear rates along with an attenuation in the degree of shear-thinning achieved at the lowest oxygen tensions. We also find that in some cases, even a small fraction of transfused blood cells restores the shape of the shear-thinning relationship, though not the overall baseline effective viscosity. These results suggest that untransfused sickle cell blood will show the most extreme relative rheologic impairment in regions of high shear and that introducing even small fractions of normal blood cells may help retain some shear-thinning capability though without addressing a baseline relative increase in effective viscosity independent of shear.

Innovations in Targeted Anti-Adhesion Treatment for Sickle Cell Disease

Sickle cell disease (SCD) is an inherited hemoglobinopathy that leads to significant lifetime morbidity and early mortality. An enhanced understanding of the complex pathophysiology of the disease has elucidated novel therapeutic targets for which new therapies are in development. In order to increase the therapeutic landscape, it has been important to identify the blood vessel and more specifically the endothelium as the target organ in this complex disease. Through this lens, we present a review of new anti-adhesion therapies for SCD in development. The long-term promise of multimodal therapies for SCD is finally on the horizon.

Genetic modifiers of severity in sickle cell disease

Sickle cell disease (SCD) is one of the most common single disease disorders world-wide. It is remarkable for its clinical heterogeneity, even among individuals with identical genotypes. Some individuals experience morbidity and mortality in early childhood, while others have a relatively mild course, and normal or near normal life expectancy. Many clinical complications are associated with SCD; most notably frequent pain episodes, stroke, acute chest syndrome, avascular necrosis, nephropathy, retinopathy and pulmonary hypertension. While the effects of higher fetal hemoglobin (HbF) levels, UGTA1A polymorphisms, alpha-thalassemia and G6PD deficiency on SCD has been extensively studied, these variables do not explain all of the clinical heterogeneity of SCD. It is not known why some patients develop certain complications, and it is difficult to predict which complications a particular patient will experience. Much work has been done to identify genetic variants associated with these disease complications; many associations remain unvalidated. As the field continues to move beyond small sample collections and candidate gene approaches into whole genome sequencing and merging of samples from all over the world, we will identify more genetic variants associated with development of specific SCD related complications, and hopefully leverage this knowledge into targeted therapies.

Cellular normoxic biophysical markers of hydroxyurea treatment in sickle cell disease

Hydroxyurea (HU) has been used clinically to reduce the frequency of painful crisis and the need for blood transfusion in sickle cell disease (SCD) patients. However, the mechanisms underlying such beneficial effects of HU treatment are still not fully understood. Studies have indicated a weak correlation between clinical outcome and molecular markers, and the scientific quest to develop companion biophysical markers have mostly targeted studies of blood properties under hypoxia. Using a common-path interferometric technique, we measure biomechanical and morphological properties of individual red blood cells in SCD patients as a function of cell density, and investigate the correlation of these biophysical properties with drug intake as well as other clinically measured parameters. Our results show that patient-specific HU effects on the cellular biophysical properties are detectable at normoxia, and that these properties are strongly correlated with the clinically measured mean cellular volume rather than fetal hemoglobin level.

Haematological determinants of cardiac involvement in adults with sickle cell disease

AIMS

Cardiac involvement is common in sickle cell disease (SCD). Studies are needed to establish haematological determinants of this involvement and prognostic markers. The aim of the study was to identify haematological factors associated with cardiac involvement in SCD and their impact on prognosis.

METHODS AND RESULTS

This longitudinal observational study was performed on 1780 SCD patients with SS or S-β(0)-thalassemia referred to our centre. Six hundred fifty-six met our inclusion criteria (availability of a blood-workup and echocardiogram obtained <1 year apart, no heart valve surgery and no current pregnancy). Median age was 31 (interquartile range, 25-40) years, and median haemoglobin (Hb) was 87 (80-95)g/L. Left ventricular (LV) dilation, left atrial dilation, cardiac index (CI) >4 L/min/m(2), LV ejection fraction <55%, and tricuspid regurgitant velocity (TRV) ≥2.5 m/s were found in 35, 78, 23, 8.5, and 17% of patients, respectively. Compared with other patients, those in the fourth quartiles (Q4) of LV end-diastolic dimension index (LVEDDind) and left atrial dimension index (LADind) and those with high CI had significantly lower Hb, % foetal Hb (HbF), and red blood cell (RBC) counts; and significantly higher lactate dehydrogenase, bilirubin, and %dense RBCs. Independent haematologic determinants of Q4 LVEDDind and LADind were low RBC count and %HbF; high %dense RBCs were associated with LADind. Low %HbF and RBC count were associated with high CI. High %dense RBCs or no α-thalassemia gene deletion was associated with greater severity of anaemia and cardiac dilation and with higher CI. During the median follow-up of 48 (32-59) months, 50 (7.6%) patients died. Tricuspid regurgitant velocity ≥ 2.5 m/s was a predictor of mortality. The risk of death increased four-fold when left ventricular ejection fraction <55% was present also (P = 0.0001).

CONCLUSION

Cardiac dilation and CI elevation in patients with SCD are associated with haematologic variables reflecting haemolysis, RBC rigidity, and blood viscosity. Tricuspid regurgitant velocity ≥ 2.5 and LV dysfunction (even mild) predict mortality.

Addition of multimodal therapy to standard management of steady state sickle cell disease

Most people on folic acid to boost erythropoiesis and prophylactic antimicrobials, the standard management of steady state sickle cell disease (SCD), have unacceptable numbers of crises. The objective of this study was to evaluate the effects of adding multimodal therapy with potassium thiocyanate and omega-3 fatty acids to the standard management of steady state SCD. Pre- and post-treatment numbers of crises and other disease indices were compared in 16 HbSS individuals on folic acid and paludrine after 12 months of adding eicosapentaenoic acid 15 mg/kg/day, docosahexaenoic acid 10 mg/kg/day, and potassium thiocyanate 1-2 mL/day, each milliliter of which contained 250 mg of thiocyanate and 100 micrograms of iodine to prevent hypothyroidism: a possible side-effect due to competitive inhibition of the transport of iodide into the thyroid gland by thiocyanate. Median number of crises reduced from 3/yr to 1/yr (P < 0.0001). There was no evidence of impaired thyroid function. Plasma level of tri-iodothyronine improved (P < 0.0001). Steady state full blood count and bilirubin level did not change significantly. The findings suggest that addition of potassium thiocyanate and eicosapentaenoic and docosahexaenoic acids to standard management of steady state SCD reduces the number of crises. This observation needs to be evaluated in larger studies.

Acute chest syndrome is associated with single nucleotide polymorphism-defined beta globin cluster haplotype in children with sickle cell anaemia

Genetic diversity at the human β-globin locus has been implicated as a modifier of sickle cell anaemia (SCA) severity. However, haplotypes defined by restriction fragment length polymorphism sites across the β-globin locus have not been consistently associated with clinical phenotypes. To define the genetic structure at the β-globin locus more thoroughly, we performed high-density single nucleotide polymorphism (SNP) mapping in 820 children who were homozygous for the sickle cell mutation (HbSS). Genotyping results revealed very high linkage disequilibrium across a large region spanning the locus control region and the HBB (β-globin gene) cluster. We identified three predominant haplotypes accounting for 96% of the β(S) -carrying chromosomes in this population that could be distinguished using a minimal set of common SNPs. Consistent with previous studies, fetal haemoglobin level was significantly associated with β(S) -haplotypes. After controlling for covariates, an association was detected between haplotype and rate of hospitalization for acute chest syndrome (ACS) (incidence rate ratio 0·51, 95% confidence interval 0·29-0·89) but not incidence rate of vaso-occlusive pain or presence of silent cerebral infarct (SCI). Our results suggest that these SNP-defined β(S) -haplotypes may be associated with ACS, but not pain or SCI in a study population of children with SCA.

Erythrocyte density in sickle cell syndromes is associated with specific clinical manifestations and hemolysis

Dense, dehydrated red blood cells (DRBCs) are a characteristic feature of sickle-cell disease (SCD). DRBCs play a role in the pathophysiology of SCD acute and chronic organ damage because of heightened tendency to undergo polymerization and sickling because of their higher hemoglobin S concentration. Relations between red cell density (assessed with phthalate density-distribution profile method) and several hematologic, biochemical, genetic parameters, and clinical manifestations were studied in a large cohort of homozygous patients. The percentage of DRBCs was significantly higher in patients who experienced skin ulcers, priapism, or renal dysfunction. Presence of α-thalassemia deletions was associated with fewer DRBCs. A multivariable analysis model showed DRBCs to be positively associated with hemolytic parameters such as lactate dehydrogenase and bilirubin and negatively with fetal hemoglobin. The percentage of DRBCs decreased by 34% at 6 months of hydroxycarbamide (xydroxyurea) therapy. Thus, DRBCs are associated with specific clinical manifestations and biologic markers and may be a useful addition to the biologic and clinical evaluation of patients with SCD, because they can easily be measured in a hematocrit tube.

A biophysical indicator of vaso-occlusive risk in sickle cell disease

The search for predictive indicators of disease has largely focused on molecular markers. However, biophysical markers, which can integrate multiple pathways, may provide a more global picture of pathophysiology. Sickle cell disease affects millions of people worldwide and has been studied intensely at the molecular, cellular, tissue, and organismal level for a century, but there are still few, if any, markers quantifying the severity of this disease. Because the complications of sickle cell disease are largely due to vaso-occlusive events, we hypothesized that a physical metric characterizing the vaso-occlusive process could serve as an indicator of disease severity. Here, we use a microfluidic device to characterize the dynamics of "jamming," or vaso-occlusion, in physiologically relevant conditions, by measuring a biophysical parameter that quantifies the rate of change of the resistance to flow after a sudden deoxygenation event. Our studies show that this single biophysical parameter could be used to distinguish patients with poor outcomes from those with good outcomes, unlike existing laboratory tests. This biophysical indicator could therefore be used to guide the timing of clinical interventions, to monitor the progression of the disease, and to measure the efficacy of drugs, transfusion, and novel small molecules in an ex vivo setting.

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.

Multiple complications in a sickle cell disease patient: a case report

Summary

This case report illustrates the multiple complications experienced by a sickle cell anaemia patient. Although he enjoyed fairly good health till age 16 years; he subsequently suffered grade four bilateral femoral head necrosis, cerebella infarct and cerebral atrophy from cumulative effect of repetitive vasoocclussion, recurrent overwhelming septicaemia, fixed flexion deformities and decubitous ulcer as a sequelae of earlier complications. He eventually became bed ridden. Financial constraint seriously compounded these problems. The determinants, of which type of the wide-ranging complications of SCD a particular patient will eventually develop, remain elusive.

Exposure of blood from patients with sickle cell disease to air changes the morphological, oxygen-binding, and sickling properties of sickled erythrocytes

We collected venous blood samples from 7 steady-state patients with homozygous sickle cell disease under venous oxygen pressure without exposure to air (UnExp-blood) and compared the morphological, oxygen-binding, and sickling properties with those of SS cells in aliquots of the same venous blood samples that were oxygenated in room air or at a PO2 near 180 mmHg (Exp-blood). Results showed that (1) upon deoxygenation under nitrogen, UnExp-blood generated a significantly higher percentage of elongated reversibly sickled cells (RSCs) than did Exp-blood; (2) upon gradual oxygenation of completely deoxygenated sickled cells, RSCs in UnExp-blood converted to discocytes at a higher oxygen pressure than did those in Exp-blood; (3) the degree of hysteresis between the sickling/desickling curves of UnExp-blood was greater than that of Exp-blood; and (4) deoxy-Hb S in hemolysate prepared from SS cells in UnExp-blood polymerized without a delay time, while those from Exp-blood polymerized with a distinct delay time. The in vivo properties of RSCs significantly changed upon oxygenation. We also found that the various properties of blood samples collected from patients with SCD by the ordinary method were similar to those of Exp-blood, probably because such blood samples are exposed to oxygen through air in the needle, syringe, and Vacutainer. Once SS cells were oxygenated, the in vivo properties of RSCs could not be recovered by partial deoxygenation to venous oxygen pressure.

Blood samples collected under venous oxygen pressure from patients with sickle cell disease contain a significant number of a new type of reversibly sickled cells: constancy of the percentage of sickled cells in individual patients during steady state

We found various levels of a new type of reversibly sickled cell (RSC) with blunt edges in 44 blood samples obtained from 32 steady-state patients with sickle cell disease (SCD) without exposure to air (UnExp-blood). Because these RSCs could be generated in vitro by partial oxygenation of once-deoxygenated SS cells to venous oxygen pressure, we named them "partially oxygenated sickled cells" (POSCs). These RSCs were classified into elongated and non-elongated RSCs, depending on the ratio of the short axis to long axis. The presence of these cells was previously unknown because the standard blood collection method oxygenates most of the POSCs to discocytes due to oxygen in the air space in the needle, syringe, and blood collection tube (Exp-blood). Although the shape of elongated POSCs is similar to that of irreversibly sickled cells (ISCs), POSCs revert to discocytes upon exposure to air. We found the following: (1) the percentage of total sickled cells (total POSCs + ISCs) in UnExp-blood (29.0 +/- 14.5%) was significantly higher than the percentage of sickled cells (mainly ISCs) in Exp-blood (7.3 +/- 5.7%); (2) the percentage of sickled cells in UnExp-blood was specific to individual patients during steady state, while it decreased at the onset of a vaso-occlusive event; and (3) the percentage of sickled cells in UnExp-blood varied widely among steady-state patients (4-56%). This new type of RSC may be used as an internal biomarker to evaluate the disease state of individual patients.

Combined use of nonmyelosuppressive nitrosourea analogues with hydroxyurea in the induction of F-cell production in a human erythroleukemic cell line

OBJECTIVE

Although hydroxyurea (HU) has been used clinically to treat patients with sickle cell disease (SCD), not all patients benefit from HU treatment due to its toxicity. The objective of this study was to investigate the effectiveness of the use of two new Hb F-inducing nitrosourea analogues, 2-[3-(2-methyl, 2-nitroso) ureido]-2-deoxy-D-glucopyranose (MNGU) and 2-[3-(2-chloroethyl) ureido]-2-deoxy-D-glucopyranose (CGU), in combination with HU in K562 cells or erythroid progenitors.

MATERIALS AND METHODS

After K562 cells were cultured with different concentrations of HU with CGU or MNGU, aliquots of the cells were obtained to determine the total (benzidine-positive) hemoglobin level, number of F cells, and Hb F level. Erythroid progenitor cells of SCD patients and healthy donors were cultured with the optimal drug concentrations, and the number of BFU-E and Hb F level were determined.

RESULTS

Our results showed that the combined use of HU with CGU or MNGU increased the number of both benzidine-positive normoblasts and F cells in a synergistic manner. Further, a lower concentration of HU was required to induce a significant level of Hb F synthesis when combined with either of the two compounds in comparison with treatment with HU alone. On day 4, the number of benzidine-positive cells was 4.5- to 6.5-fold and the number of F cells was 5.0- to 8.0-fold higher than the respective numbers in the untreated K562 cells. Similarly, a 3.2- to 14.3-fold induction of Hb F was obtained when human erythroid progenitors from SCD patients were treated with the same drug combinations.

CONCLUSION

Based on these results, the use of CGU or MNGU in combination with HU might offer substantial benefits to patients with SCD and other hemoglobinopathies.

Relationship between the clinical manifestations of sickle cell disease and the expression of adhesion molecules on white blood cells

BACKGROUND

The severity of sickle cell disease (SCD) increases with leukocyte count. The biological basis could be that leukocyte adherence to vascular endothelium mediated by adhesion molecules (AMs) facilitates vaso-occlusion, the basic pathological process in SCD.

OBJECTIVE

To find out if there is a relationship between expression of AMs by leukocytes and the clinical manifestations of SCD.

METHODS

Flow cytometry was used to study the relationship between leukocyte AM expression and disease manifestations in 100 patients with homozygous (HbSS) sickle cell disease and 34 genotype HbAA controls. The effect of hydroxyurea therapy on AM expression was also examined. We excluded HbSS patients with any other disease, pregnancy in the previous 3 months, or Haemogloben F (HbF) > or = 10%.

RESULTS

Patients with complications of SCD showed high expression of alphaMbeta integrin by the neutrophils; and l-selectin by lymphocytes and neutrophils (P < 0.03). CD18 was highly expressed by neutrophils in patients with sickle nephropathy (P = 0.018), and l-selectin by lymphocytes in those with stroke (P = 0.03). Monocyte l-selectin increased in sickle cell crisis relative to steady state (P = 0.04). Expression of alphaLbeta2 integrin by neutrophils, monocytes, and lymphocytes decreased within a month of hydroxyurea therapy (P < 0.05), with symptomatic improvement in the patients and no more than 3.3% rise in HbF level.

CONCLUSIONS

The findings suggest that in SCD (1): High steady-state expression of alphaMbeta2 integrin and l-selectin by leukocytes predisposes to severe manifestations. (2) Increased leukocyte AM expression above steady-state levels could be important in the genesis of crisis. (3) The early symptomatic improvement that follows hydroxyurea therapy is mediated via mechanisms independent of increased HbF, and may involve reduced AM expression in leukocytes. (4) Other treatment modalities that reduce leukocyte AM expression might also confer clinical benefit.

Hydroxyurea and sodium phenylbutyrate therapy in thalassemia intermedia

Hydroxyurea (HU) and sodium phenylbutyrate (SPB) have been shown to increase fetal hemoglobin (Hb F) levels in patients with thalassemia intermedia. The reported effects of these agents in increasing total Hb, however, have been inconsistent and there have been no studies on the combination of these medications. We describe the clinical response, as determined by increases in total Hb and decreased transfusion needs, in five patients with thalassemia intermedia treated with HU alone or in combination with SPB. All of the patients responded with increased levels of Hb F, but the responses in total Hb varied. Of the five patients, two had a marked response in total Hb in excess of 3 g/dl, two responded modestly with an increase in total Hb of 1-2 g/dl, and one did not respond. Prolonged responses were achieved with low doses of HU (3-10 mg/kg/day) and higher doses were associated with mild reversible hematologic or hepatic toxicity and no further increases in Hb. Sodium phenylbutyrate was added to treatment with HU in two patients, but failed to produce an increase in total Hb despite increasing Hb F levels. Of the four patients who responded to HU with an increase in total Hb, all reported symptomatic improvement and three have not required further transfusions. We conclude that low-dose HU therapy in patients with thalassemia intermedia may increase total Hb levels sufficiently to eliminate the need for transfusions. We, therefore, recommend a trial of HU for thalassemia intermedia patients in whom chronic transfusion therapy is being contemplated.

Complement haemolytic activity, circulating immune complexes and the morbidity of sickle cell anaemia

The aim of this study was to find out if the number of crises and complications of sickle cell anaemia (SCA) relate to complement function, or the levels of circulating immune complexes (CIC), complement factor B (Bf), C3 and C4. In 73 steady-state HbSS patients and 50 HbAA control subjects, we determined the haemolytic activity of the alternative pathway of complement (AP50), of the classical pathway (CH50); and the serum concentrations of Bf, C3, C4 and CIC. By clinical examination of each patient and review of the medical records, we determined the number of complications of SCA which had occurred and the mean number of crises per year over a minimum period of 3 years. The mean+/-SD AP50 for the patients (14+/-2 U/ml) was significantly lower than the control value of 16+/-3 U/ml (p<0.001). AP50 had a significant inverse correlation with the number of crises (r=-0.30, p<0.02). Mean+/-SD CIC in patients (0.45+/-0.38 g/l) was significantly higher than in controls: 0.24+/-0.15 g/l (p<0.002). CIC showed a significant direct correlation with the number of complications of SCA (r=+/-0.28, p<0.02). Mean+/-SD Bf in SCA patients (0.19+/-0.09) was higher than in controls (0.17+/-0.05). The difference reached marginal statistical significance (p=0.049). SCA patients and controls had no significant differences in CH50, C3 and C4. These parameters and Bf did not correlate with either the number of crises or complications. The mechanisms underlying the correlations observed in this study are yet to be fully elucidated.

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.

Advances in the prenatal and molecular diagnosis of the hemoglobinopathies and thalassemias

Prenatal diagnosis is available for pregnancies at risk for virtually all inherited disorders of hemoglobin production. The field of reproductive genetics must confront many ethical, legal, and social concerns regarding its use, many of which derive from a woman's desire to bear children but legal right to abortion. The goal of more widespread utilization of prenatal diagnosis is sought in the context of questioning the ethical control to be exerted over the biological makeup of future generations. Its appropriate application would be facilitated greatly by the availability of reliable DNA markers of disease severity. Advances in fetal sampling and in detecting mutant globin genes have provided the safe, accurate methodology required for prenatal diagnosis. Chorionic villus sampling in the first trimester has become standard practice, but second trimester amniocentesis also is used for sampling fetal DNA. The use of preimplantation diagnosis and testing fetal cells from the maternal circulation will soon be practical. DNA-based detection of globin gene mutations has been facilitated greatly by the polymerase chain reaction revolution, and several reliable diagnostic methods are available. Polymerase chain reaction-based methods rely on restriction analysis, allele-specific hybridization or amplification, DNA sequence analysis, and new non-polymerase chain reaction methods for DNA amplification in vitro. These methods are available for detecting hemoglobinopathy, thalassemia, and thalassemic-hemoglobinopathy genes that affect alpha- or beta-globin loci.

Sickle cell anemia and fetal hemoglobin

Fetal hemoglobin, the predominant hemoglobin of the fetus, is good for sickle cell anemia. This hemoglobin inhibits the polymerization of sickle hemoglobin. Clinical studies have shown that at any level of fetal hemoglobin, the more that is present, the better off is the patient. We are now able to increase fetal hemoglobin levels by pharmacologic means. We should know shortly if this is associated with clinical benefit.

Genetic dissection of complex traits

Medical genetics was revolutionized during the 1980s by the application of genetic mapping to locate the genes responsible for simple Mendelian diseases. Most diseases and traits, however, do not follow simple inheritance patterns. Genetics have thus begun taking up the even greater challenge of the genetic dissection of complex traits. Four major approaches have been developed: linkage analysis, allele-sharing methods, association studies, and polygenic analysis of experimental crosses. This article synthesizes the current state of the genetic dissection of complex traits--describing the methods, limitations, and recent applications to biological problems.

The pathophysiology of the sickle hemoglobinopathies and implications for perioperative management

Patients with sickle hemoglobinopathies are at risk for unique postoperative complications and increased mortality. Understanding the pathophysiology of these disorders is important for safe perioperative management. Because there is no animal model for sickle cell disease, understanding has progressed through in vitro studies and clinical observations. This review describes the clinical manifestations of the sickle hemoglobinopathies with special emphasis on current knowledge of pathophysiology. It also discusses issues of preoperative screening, transfusion, and postoperative care.

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.

Acute phase reactants and severity of homozygous sickle cell disease

Serum concentrations of seven acute-phase reactants: albumin, transferrin (Tf), alpha-1-antitrypsin (AIAT), caeruloplasmin (Cp), alpha 2-macroglobulin (alpha 2-MG), haptoglobin (hp) and C-reactive protein (CRP) were determined in 73 subjects with varying severities of homozygous sickle cell (HbSS) disease. Fifty healthy subjects of comparable sex, age and socio-economic class distributions as the HbSS subjects served as controls. Albumin and alpha 2-MG were comparable in all the subject groups. Tf and hp levels were significantly reduced in the HbSS groups relative to the control group. Conversely, AIAT, CRP and CP were significantly elevated. However only Tf and CRP manifested significant correlations with any of the indices of disease severity employed. Transferrin and CRP are suggested as plasma proteins worthy of further evaluation as indicators of severity in homozygous sickle cell disease.

Pharmacological modification of hemoglobin F expression in sickle cell anemia: an update on hydroxyurea studies

The most studied pharmacological intervention in sickle cell anemia aiming at elevating HbF expression is the use of hydroxyurea. At the present time the experience has been that after 1 year of treatment with maximum tolerated doses (MTD) all patients showed increases of percent HbF, with a mean of 15% HbF, without apparent side effects besides the reversible ones observed during the process of attaining the MTD. The question of efficacy is presently being investigated by a multicenter placebo controlled double blind clinical trial that involves more than 20 sites. The goal of the study is to determine if hydroxyurea can decrease the incidence of painful crises by 50%. Results of this study are not expected before the end of 1993.

Hb S/beta zero-thalassemia due to the approximately 1.4-kb deletion is associated with a relatively mild phenotype

We report a relatively mild phenotype associated with two siblings who are compound heterozygotes for Hb S and a beta zero-thalassemia mutation due to a approximately 1.4-kb deletion of the 5' region of the beta-globin gene. Each is found to have unusually high levels of Hb A2 and Hb F, accounting for more than 20% of the total hemoglobin. These may interfere with intracellular Hb S polymerization, thus leading to a mild clinical course.

Potential of descriptive linear discriminant analysis for studying clinical chemical and haematological data from persons with heterozygous sickle cell disease

To study the potential of multivariate classification methods in order to obtain more insight into abnormal laboratory data from patients with sickle cell disease, we investigated standard haematological and clinical chemical variables of 18 controls and 37 apparently healthy persons with heterozygous sickle cell disease (Hb AS), all women, using both univariate and multivariate classification methods. In the univariate method, those with Hb AS showed decreased serum log aspartate aminotransferase (log AST) activity, mean corpuscular volume and mean corpuscular haemoglobin (MCH) and increased sodium concentration. The multivariate method identified sodium, potassium, urea, uric acid, log AST, alanine aminotransferase and MCH as the variables that produced maximal separation between persons with Hb As and controls. It increased the 'non-error rate' for classification of persons with Hb AS by 16.4% compared with classification based on the variable, MCH, that produced maximal separation by the univariate method. The frequency distribution of percentage Hb S in the Hb AS group proved bimodal with maximal separation at 37.0% Hb S. The subgroup with 37.0% or less (n = 16) was considered to have concomitant heterozygous alpha-thalassaemia-2. In the univariate method the subgroup characterized by greater than 37.0% Hb S (n = 21) had increased serum sodium and uric acid concentrations, perhaps related to sickle cell nephropathy, whereas the subgroup with less than or equal to 37% Hb S did not. The multivariate method added information to the univariate method by additionally identifying abnormalities in serum potassium and urea concentrations in the former subgroup.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrogen metabolism in sickle cell anemia: free amino acids in plasma and urine

Twenty-four hour urinary levels and fasting plasma concentrations of free amino acids (AA) were evaluated in adult sickle cell anemia (HbSS) and age-matched HbAA subjects with comparable daily energy (E) and protein (N) intake. HbSS elicited significant reduction in the sum of plasma indispensable (EAA) with no change in the dispensable (NAA) amino acids, resulting in a prominent (P less than 0.01) reduction in the EAA/NAA ratio from 71% to 55%. Arg (-38%), Leu (-32%), Val (-28%) and His (-32%) were among the AA most severely affected. Despite a twofold increase in 24-hour urine volume in HbSS compared with HbAA subjects, total urinary losses of EAA and NAA were markedly reduced in the former group, with Arg (-53%) and Gly (-56%) levels most prominently affected. Compared with HbAA controls, HbSS subjects showed a three-fourfold increase in 24-hour urinary orotate excretion that had no relationship to amount of N intake. The results indicated that adult subjects with HbSS, who consumed adequate N and E as per the RDA for healthy individuals, behaved like normal HbAA controls on a low protein diet. There was evidence that the HbSS subject might be in a precarious state with respect to sufficiency of several amino acids, particularly L-Arg, which is now classified as conditionally indispensable for the human.

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.

Sickle cell disease in Sudan

The clinical, haematological and biochemical features of 50 Sudanese patients with sickle cell disease (SCD) were determined. Of 23 patients with complete family data, 21 had sickle cell anaemia (homozygous HbSS), 2 had sickle-cell/beta+thalassaemia but none had sickle cell/beta Othalassaemia. The remaining 27 patients had HbSS phenotype. 84% of patients were from the Baggara tribe in western Sudan, where HbS is a natural extension of the west African HbS belt. 21 patients were children under 2 years old; 19 were 3-10 years old; and the remaining 10 were over 10 years old. Young patients presented mainly with painful vaso-occlusive crisis, severe anaemia, hand and foot syndrome, fever, underweight, malnutrition and various infectious diseases. All patients had mild to moderate cardiac enlargment; 42% had a moderately enlarged spleen but only 10% had an enlarged liver; 20% had infarctive lesions of long bones and another 8% had Salmonella osteomyelitis. Leg ulcers, priapism, enuresis and cholelithiasis were not observed. Patients had a mean haemoglobin concentration of 7.3 g/dl; reticulocyte count of 15.1%; serum bilirubin of 2.1 mg/dl; HbA2 level of 2.8% and HbF of 7%. Thus, the observed pattern of SCD in Sudan is comparable to the severe type described for Africans and not comparable to the benign form found in Shiite Moslem Arabs of Saudi Arabia. 6 adults with mild SCD had HbF levels below 5%. Amelioration of the disease, therefore, does not seem to be related to HbF levels; nor was it possible to relate it to high levels of erythrocyte 2,3-diphosphoglycerate.

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.

Review: the sickle hemoglobinopathies--genetic analyses of common phenocopies and new molecular approaches to treatment

Within the very large group of sickle cell hemoglobinopathies several phenocopy clusters exist. These can be conveniently classified as: 1) conditions in which HbA and S are present, 2) disorders where HbS is the predominant hemoglobin, and 3) the HbSF phenotype. This review will focus on distinguishing the genotype of these common phenocopies as well as new potential approaches to therapy.

Lipids, fatty acids and trace elements in plasma and erythrocytes of pediatric patients with homozygous sickle cell disease

Plasma and erythrocyte levels of zinc, copper, fatty acids, total cholesterol and cholesterol sulfate, and plasma vitamin E and free cholesterol were measured in six pediatric patients with HbSS sickle cell anemia, one adult patient in crisis and six age-, sex- and race-matched pediatric controls. Patient plasma zinc levels were significantly decreased, while erythrocyte zinc levels were normal. Although subject to a large range, plasma vitamin E levels were not significantly altered. For patients an increased plasma percentage of free cholesterol, increased levels of oleic acid and vaccenic acid, and decreased values for total cholesterol were found. Erythrocyte fatty acid analyses revealed a significant decrease in total polyunsaturated fatty acids which was 'compensated' for by increased total monounsaturated and saturated fatty acids. The low amounts of total polyunsaturated fatty acids could completely be ascribed to decreased levels of linoleic acid. Erythrocyte cholesterol levels were significantly increased, while the total fatty acid/cholesterol molar ratio was found to be subject to a relatively large range. Cholesterol sulfate determinations showed that patients had relatively low plasma or erythrocyte levels, or both. The present results are suggestive of a lipid peroxidation mediated, and hepatic and/or splenic dysfunction mediated lipid component in the rigidification of the sickle cell membrane.