Estimated pulmonary artery systolic pressure and sickle cell disease: a meta-analysis and systematic review

Global prevalence of elevated estimated pulmonary artery systolic pressure in clinically stable children and adults with sickle cell disease: A systematic review and meta-analysis

BACKGROUND

The current study sought to determine the prevalence of elevated estimated pulmonary artery systolic pressure (ePASP) in clinically stable children and adults with sickle cell disease)SCD(worldwide.

METHODS

The studies included were identified through a search of databases such as PubMed, Scopus, Science Direct, Web of Science, and Embase, as well as Google Scholar engine, adhering to specific inclusion and exclusion criteria. Heterogeneity among the primary study results was assessed using the I-squared index, while publication bias was evaluated through funnel plots, Egger's test, and trim and fill analysis. All statistical analyses were conducted using R software, version 4.3.0.

RESULTS

79 primary studies were included, comprising 6,256 children (<18 years old) and 6,582 adults (≥18 years old) with SCD from 22 countries. The prevalence of elevated ePASP was found to be 21.8% (95% confidence interval [CI]: 18.46 to 25.07) in children and 30.6% (95% CI: 27.1 to 34.1) in adults. The prevalence of elevated ePASP among studies with severe SCD genotypes including HbSS and HbS/β0 was found to be 19.45% (95% CI: 14.95 to 23.95) in children and 29.55% (95% CI: 24.21 to 34.89) in adults. Furthermore, sex-specific prevalence among SCD patients with elevated ePASP indicated the highest prevalence in male children at 60.35% (95% CI: 54.82 to 65.88) and adult female patients at 54.41% (95% CI: 47.3 to 61.5). A comparative analysis of the mean values of clinical and laboratory results revealed significant differences in several characteristics, including age, oxygen saturation, hemoglobin levels, fetal hemoglobin, white blood cell counts, platelet counts, and reticulocyte counts between patients with elevated ePASP and those without, in both children and adult SCD populations.

CONCLUSION

Our findings regarding clinically stable SCD patients highlight a high prevalence of elevated ePASP.

Respiratory manifestations of sickle cell disease in children: a comprehensive review for the pediatrician

INTRODUCTION

Sickle cell disease (SCD) is an inherited hemoglobinopathy characterized by the production of sickle hemoglobin, leading to red blood cells sickling and hemolysis in hypoxic conditions. The resulting acute and chronic endothelial inflammation leads to chronic organ damage. Respiratory manifestations in SCD usually start from childhood and represent the leading causes of morbidity and mortality. Nevertheless, they are generally poorly addressed or recognized later in life, often contributing to a more severe course and complications.

AREAS COVERED

This narrative review aims to outline the significant acute and chronic respiratory manifestations in children with SCD, focusing on prevention and clinical management. Compelling issues that need to be addressed in the future are also discussed. We searched the PubMed database for original papers written in English. Age restrictions were set for children (birth to 18 years). No limitations were set for the date and study country.

EXPERT OPINION

Early detection and treatment of respiratory manifestations in SCD should be central to follow-up with patients affected by SCD. Nonetheless, studies are lacking, especially in pediatric age, and there is still no consensus on their management. Further research is strongly needed to accomplish universally accepted guidelines to guarantee patients the best care possible.

Pulmonary Hypertension and Left Ventricular Geometric Types in Sickle Cell Anemia

Pulmonary hypertension (PHT) is multifactorial in origin and a major cause of morbidity and mortality in the sickle cell populace. Its correlation with abnormal left ventricular geometric patterns has not been established. Subjects were sickle cell anemic patients of the hematology clinic of a tertiary hospital who gave informed consent. A modified Medical Research Council questionnaire was used to obtain the demographic, anthropometric, and clinical variables of the subjects. Blood samples were taken for hematologic and biochemical analysis. Spirometry, electrocardiography, and echocardiography were done for all subjects. SPSS version 25 was used for analysis. A p ≤0.05 was used for significance. In total 111 subjects with sickle cell anemia were recruited. Male:female ratio was 1:1.4. The prevalence of PHT was 8.1%. Those with PHT were older and had higher blood pressure, lower respiratory rate, higher body mass index, lower estimated glomerular filtration rate, and a higher prevalence of avascular necrosis of the head of femur, stroke, and chest pain. About 2/3 (66.7%) of those with PHT had concentric left ventricular hypertrophy (LVH) whereas none of those with eccentric LVH had PHT. Age, body mass index, systolic blood pressure, aortic root diameter, concentric LVH, serum creatinine, history of stroke, chest pain, and avascular necrosis of the head of femur correlated directly whereas eccentric LVH correlated inversely with PHT. Concentric LVH, relative systemic hypertension, history of chest pain, and respiratory rate were the independent correlates of PHT in subjects with sickle cell anemia. PHT is known to be of poor prognostic significance. Its association with relative systemic hypertension and concentric LVH suggests the need to initiate early treatment to reduce morbidity and mortality in this group.

Characterising the prevalence of overweight and obese status among adults with sickle cell disease

Individuals with sickle cell disease (SCD) have historically been considered underweight. Despite increasing body mass index (BMI) in the general population, the prevalence of overweight and obese status remains unclear in the adult SCD population. Our primary aim was to determine the prevalence of overweight and obese status and to identify associations between BMI, demographic, and clinical characteristics. We conducted an analysis of abstracted electronic health record data and patient-reported outcomes from the Sickle Cell Disease Implementation Consortium registry; individuals aged 20-45 years were included. The median (interquartile range) BMI for the 1664 adults in this analysis was 23.9 (21.1-28) kg/m2 . In this cohort, 42.9% had a BMI of >25 kg/m2 (Centers for Disease Control and Prevention definition of overweight/obese). In multivariable analysis, higher odds of being overweight or obese were associated with female gender, older age, college education, private insurance, and hypertension diagnosis. Higher odds of a BMI of >25 kg/m2 were observed in individuals with HbSC or HbSβ+ thalassaemia regardless of hydroxycarbamide (hydroxyurea) exposure (odds ratio [OR] 3.4, p < 0.0001) and HbSS or HbSβ0 thalassaemia exposed to hydroxycarbamide (OR 1.6, p = 0.0003) compared to those with HbSS or HbSβ0 thalassaemia with no hydroxycarbamide exposure. These data highlight the importance of early identification, prevention, and intervention for increasing BMI to reduce obesity-related complications that may impact SCD-related complications.

Pulmonary hypertension screening in children with sickle cell disease

BACKGROUND

Screening for pulmonary hypertension (PHT) is recommended in children with sickle cell disease (SCD). However, best approaches are poorly described. We examined the utility of PHT symptoms, echocardiogram (ECHO), N-terminal-pro hormone brain natriuretic peptide (NT-proBNP), and BNP to screen for PHT in the SCD pediatric population.

METHODS

Children (8-18 years old) with SCD-HbSS and HbSthal° were prospectively included and underwent PHT screening. The screening consisted of a comprehensive PHT symptoms evaluation, ECHO measurement, and NT-proBNP and BNP levels.

RESULTS

A total of 73 patients were included (mean age 12 ± 5.7 years; >80% on hydroxyurea), of which 37% had a symptom consistent with PHT, including exertional dyspnea (26.5%), fatigue (17.6%), palpitation (14.7%), and chest pain (10.3%). ECHO was obtained in 53 (72.6%) patients, with only ECHO of 48 patients included in the final analysis. Elevated ECHO peak tricuspid regurgitant jet velocity (TRV) >2.5 m/s or indirect findings to suggest PHT were seen in only two of 48 (4.2%). No significant differences were seen between those with and without PHT symptoms when compared for NT-proBNP, BNP, hemoglobin, pulmonary function testing, fractional exhaled nitric oxide, asthma, oxygen saturation, and sleep apnea.

CONCLUSION

PHT symptoms are not consistent with ECHO, NT-proBNP nor BNP findings in children with SCD. PHT prevalence based on TRV was low in children on hydroxyurea, therefore screening may not be warranted for this group.

Exercise-induced changes of vital signs in adults with sickle cell disease

The six-minute walk test (6MWT) has been used in patients with sickle cell disease (SCD), in conjunction with tricuspid regurgitant velocity (TRV) and plasma N-terminal pro-brain natriuretic peptide (NT-pro BNP), to assess risk of having pulmonary hypertension. Exercise-induced vital sign changes (VSCs) are predictors of clinical outcomes in other diseases. In this study, we assess the predictors and prognostic value of 6MWT VSC in adult SCD patients. Data from a multinational study of SCD patients (Treatment of Pulmonary Hypertension with Sildenafil: walk-PHaSST) were used to calculate the 6MWT VSC. Predictors of VSC were identified by a multivariable analysis, and a survival analysis was conducted by the Cox proportional hazard method. An increase in heart rate was observed in 90% of the 630 SCD adults, 77% of patients had an increase in systolic blood pressure (SBP), and 50% of patients had a decrease in oxygen saturation. TRV (odds ratio [OR] = 1.82, p = .020), absolute reticulocyte count (OR = 1.03, p < .001), and hemoglobin (OR = 0.99, p = .035) predicted oxygen desaturation ≥ 3% during the 6MWT. In the adjusted analysis, SBP increase during the 6MWT was associated with improved survival (hazards ratio = 0.3, 95% confidence interval: 0.1-0.8). Increases in heart rate and blood pressure, as well as oxygen desaturation, are common in adults with SCD during the 6MWT. VSC is associated with markers of anemia and TRV and can be used for risk stratification. Any increase in SBP during the 6MWT was associated with improved survival and may be indicative of a patient's ability to increase stroke volume.

Stable to improved cardiac and pulmonary function in children with high-risk sickle cell disease following haploidentical stem cell transplantation

Children with sickle cell disease (SCD) are at high-risk of progressive, chronic pulmonary and cardiac dysfunction. In this prospective multicenter Phase II trial of myeloimmunoablative conditioning followed by haploidentical stem cell transplantation in children with high-risk SCD, 19 patients, 2.0-21.0 years of age, were enrolled with one or more of the following: history of (1) overt stroke; (2) silent stroke; (3) elevated transcranial Doppler velocity; (4) multiple vaso-occlusive crises; and/or (5) two or more acute chest syndromes and received haploidentical transplants from 18 parental donors. Cardiac and pulmonary centralized cores were established. Pulmonary function results were expressed as percent of the median of healthy reference cohorts, matched for age, sex, height and race. At 2 years, pulmonary functions including forced expiratory volume (FEV), FEV₁/ forced vital capacity (FVC), total lung capacity (TLC), diffusing capacity of lung for carbon monoxide (DLCO) were stable to improved compared to baseline values. Importantly, specific airway conductance was significantly improved at 2 years (p < 0.004). Left ventricular systolic function (fractional shortening) and tricuspid regurgitant velocity were stable at 2 years. These results demonstrate that haploidentical stem cell transplantation can stabilize or improve cardiopulmonary function in patients with SCD.

Biomarkers of clinical severity in treated and untreated sickle cell disease: a comparison by genotypes of a single center cohort and African Americans in the NHANES study

Haemolysis and vaso-occlusion underlie multi-organ system complications in sickle cell disease (SCD). We assessed real-world biomarkers in University of Illinois adult SCD patients, categorised as severe (HbSS/Sβ0 -thalassaemia; n = 342) or mild (HbSC/Sβ+ -thalassaemia; n = 100) genotypes and stratified according to treatment. African-American controls from the National Health and Nutrition Examination Survey (NHANES) were matched with each genotype category. Most measures of haemolysis, anaemia, inflammation and function of kidneys, liver and lungs differed markedly in untreated severe genotype patients compared to NHANES controls. These same biomarkers were significantly closer to the NHANES control range in untreated mild versus severe genotype patients, but they were not improved in severe genotype patients receiving treatment with hydroxycarbamide or blood transfusions, except that haemoglobin and HbF were higher with hydroxycarbamide. Systolic blood pressures did not differ among the SCD and NHANES groups, but diastolic pressures were higher in mild genotype patients. Ferritin in severe genotype patients on chronic transfusions was 50-fold higher than NHANES controls. The cross-sectional real-world biomarkers of patients on hydroxycarbamide or transfusions were not markedly improved compared to untreated patients. This may be due partly to poor compliance or more severe disease. Our findings highlight the need for more effective treatments.

Fluid overload due to intravenous fluid therapy for vaso-occlusive crisis in sickle cell disease: incidence and risk factors

Intravenous fluid therapy (IV‐FT) is routinely used in the treatment of vaso‐occlusive crises (VOCs), as dehydration possibly promotes and sustains erythrocyte sickling. Patients with sickle cell disease (SCD) are at risk of developing diastolic dysfunction and fluid overload due to IV‐FT. However, data on the adverse effects of IV‐FT for VOC is sparse. We aimed to evaluate the incidence and risk factors of fluid overload due to IV‐FT in patients with SCD. Consecutive hospitalisations for VOC treated with IV‐FT between September 2016 and September 2018 were retrospectively analysed. The median (interquartile range) age was 25·0 (18·3–33·8) years and 65% had a severe genotype (HbSS/HbSβ⁰‐thal). Fluid overload occurred in 21% of 100 patients. Hospital stay was longer in patients with fluid overload (6·0 vs. 4·0 days, P = 0·037). A positive history of fluid overload (P = 0·017), lactate dehydrogenase level (P = 0·011), and top‐up transfusion during admission (P = 0·005) were independently associated with fluid overload occurrence. IV‐FT was not reduced in 86% of patients despite a previous history of fluid overload. Fluid overload is frequently encountered during IV‐FT for VOC. IV‐FT is often not adjusted despite a positive history of fluid overload or when top‐up transfusion is indicated, emphasising the need for more awareness of this complication and a personalised approach.

Chronic organ injuries in children with sickle cell disease

Median life expectancy of patients with sickle cell disease has increased to up to 55 years but there are still frequent cases of premature death, mostly in patients with pre-existing organ failure such as pulmonary hypertension, kidney injury, and cerebral vasculopathy. Most organ injuries remain asymptomatic for a long time and can only be detected through early systematic screening. Protocols combining assessment of velocities on transcranial Doppler and regular transfusions in patients with abnormal velocities have been demonstrated to dramatically reduce the risk of stroke. In contrast, no consensus has been reached on systematic screening or therapy for silent cerebral infarcts. The prognostic significance of increased tricuspid regurgitant jet velocity on echocardiography has not yet been identified in children, whereas increased albuminuria is a good predictor of kidney injury. Finally, screening for hip and eye disorder is recommended; however, different countries adopt different screening strategies. Hydroxyurea is probably of potential benefit in preventing chronic organ damage but this requires further study in order to be fully demonstrated. Efficacy and safety of the other new drugs available are also under investigation.

End points for sickle cell disease clinical trials: renal and cardiopulmonary, cure, and low-resource settings

To address the global burden of sickle cell disease and the need for novel therapies, the American Society of Hematology partnered with the US Food and Drug Administration to engage the work of 7 panels of clinicians, investigators, and patients to develop consensus recommendations for clinical trial end points. The panels conducted their work through literature reviews, assessment of available evidence, and expert judgment focusing on end points related to patient-reported outcome, pain (non-patient-reported outcomes), the brain, end-organ considerations, biomarkers, measurement of cure, and low-resource settings. This article presents the findings and recommendations of the end-organ considerations, measurement of cure, and low-resource settings panels as well as relevant findings and recommendations from the biomarkers panel.

Cardiovascular complications of sickle cell disease

Sickle cell disease (SCD) is the most common inherited blood disorder in the United States, and a global health problem. Pathological features of the abnormal hemoglobin (HbS) result in 2 hallmarks of the disease - recurrent episodes of acute microvascular occlusion and chronic hemolytic anemia - that inflict continuous and insidious damage to multiple organs. With improved childhood survival, SCD in adults has evolved into a chronic degenerative disease with underlying damage to multiple organs including the heart and lungs. Cardiopulmonary complications, including cardiomyopathy, diastolic dysfunction, pulmonary hypertension (PH), and sudden cardiac death are the most common causes of morbidity and mortality. Awareness of the sickle-related cardiovascular phenotypes is important for screening, early diagnosis, and intervention of cardiac complications in this disorder.

Sickle cell disease: at the crossroads of pulmonary hypertension and diastolic heart failure

Sickle cell disease (SCD) is caused by a single point mutation in the gene that codes for beta globin synthesis, causing haemoglobin polymerisation, red blood cell stiffening and haemolysis under low oxygen and pH conditions. Downstream effects include widespread vasculopathy due to recurring vaso-occlusive events and haemolytic anaemia, affecting all organ systems. Cardiopulmonary complications are the leading cause of death in patients with SCD, primarily resulting from diastolic heart failure (HF) and/or pulmonary hypertension (PH). HF in SCD often features biventricular cardiac hypertrophy and left ventricular (LV) diastolic dysfunction. Among HF cases in the general population, approximately half occur with preserved ejection fraction (HFpEF). The insidious evolution of HFpEF differs from the relatively acute evolution of HF with reduced ejection fraction. The PH of SCD has diverse origins, which can be pulmonary arterial (precapillary), pulmonary venous (postcapillary) or pulmonary thromboembolic. It is also appreciated that patients with SCD can develop both precapillary and postcapillary PH, with elevations in LV diastolic pressures, as well as elevations in transpulmonary pressure gradient and pulmonary vascular resistance. Regardless of the cause of PH in SCD, its presence significantly reduces functional capacity and increases mortality. PH that occurs in the presence of HFpEF is usually of postcapillary origin. This review aims to assemble what has been learnt from clinical and animal studies about the manifestation of PH-HFpEF in SCD, specifically the contributions of LV diastolic dysfunction and myocardial fibrosis, in an attempt to gain an understanding of its evolution.

Splenectomy is not associated with a higher tricuspid regurgitant jet velocity in people with sickle cell anemia

BACKGROUND

Vascular complications such as pulmonary hypertension (PH) occur at an increased rate following splenectomy in patients with various hemolytic blood disorders including thalassemia. The goal of this retrospective cross-sectional analysis was to assess the independent association of splenectomy with an elevated tricuspid regurgitation velocity (TRV) in people with homozygous sickle cell disease (HbSS). TRV is a noninvasive screening test for PH and a surrogate marker of prognosis in sickle cell disease (SCD).

PROCEDURE

Data were obtained from the multicenter Walk-PHaSST (treatment of pulmonary hypertension and sickle cell disease with sildenafil therapy) study of PH (NCT00492531). We compared TRV in the cohort of patients with HbSS who were surgically splenectomized with patients who were not surgically splenectomized.

RESULTS

We found no significant differences in TRV between the two groups.

CONCLUSIONS

The lack of difference in TRV between the two groups is most likely because members of the comparator nonsurgical group in many cases experienced autoinfarction of the spleen in childhood. Splenectomy does not seem to confer additional risk for the development of a higher TRV in HbSS, unlike in patients with thalassemia or other hemolytic anemias. This could be an important consideration when weighing the risks and benefits of splenectomy in patients with HbSS.

Pathophysiology of Sickle Cell Disease

Since the discovery of sickle cell disease (SCD) in 1910, enormous strides have been made in the elucidation of the pathogenesis of its protean complications, which has inspired recent advances in targeted molecular therapies. In SCD, a single amino acid substitution in the β-globin chain leads to polymerization of mutant hemoglobin S, impairing erythrocyte rheology and survival. Clinically, erythrocyte abnormalities in SCD manifest in hemolytic anemia and cycles of microvascular vaso-occlusion leading to end-organ ischemia-reperfusion injury and infarction. Vaso-occlusive events and intravascular hemolysis promote inflammation and redox instability that lead to progressive small- and large-vessel vasculopathy. Based on current evidence, the pathobiology of SCD is considered to be a vicious cycle of four major processes, all the subject of active study and novel therapeutic targeting: ( a) hemoglobin S polymerization, ( b) impaired biorheology and increased adhesion-mediated vaso-occlusion, ( c) hemolysis-mediated endothelial dysfunction, and ( d) concerted activation of sterile inflammation (Toll-like receptor 4- and inflammasome-dependent innate immune pathways). These molecular, cellular, and biophysical processes synergize to promote acute and chronic pain and end-organ injury and failure in SCD. This review provides an exhaustive overview of the current understanding of the molecular pathophysiology of SCD, how this pathophysiology contributes to complications of the central nervous and cardiopulmonary systems, and how this knowledge is being harnessed to develop current and potential therapies.

What is the role of screening for pulmonary hypertension in adults and children with sickle cell disease?

Patient case: An 18-year-old male patient with homozygous hemoglobin SS disease was evaluated for progressive dyspnea and elevated tricuspid regurgitant jet velocity (TRV) on echocardiography. The patient's case is described in detail in Lancet¹ He had been treated with regular transfusions since childhood for stroke, had rare episodes of vaso-occlusive pain episodes, and did not take narcotic pain medications. He presented with progressive severe dyspnea on exertion and lower extremity edema. His laboratory tests were notable for a total hemoglobin level of 11.8 g/dL and hemoglobin S levels <30% but with 18% reticulocytes and elevated markers of hemolysis, such as high plasma levels of lactate dehydrogenase, aspartate amino transferase, and indirect bilirubin. The computed tomography scan of his chest in Figure 1A-B shows a large pulmonary artery, which has a greater diameter than his aorta, and a mosaic perfusion pattern, typical for severe pulmonary arterial hypertension. His Doppler echocardiographic study (Figure 1C) showed an unusually high TRV of 5.93 m/s, consistent with a calculated pulmonary artery systolic pressure of >140 mm Hg (4 times the TRV squared = 4V²). Additional images in Figure 1D show a dilated right ventricle and right atrium with a compressed left ventricle. The patient's right heart catheterization revealed a pulmonary artery systolic pressure of 147 mm Hg and diastolic pressure of 49 mm Hg; note that the normal values are ∼25/10 mm Hg.

A reappraisal of the mechanisms underlying the cardiac complications of sickle cell anemia

Anemia, hemolysis-driven vasculopathy, and intrinsic myocardial injury have been proposed as predisposing factors to cardiac disease in sickle cell anemia (SCA). The individual impact of these mechanisms on the cardiac features of SCA and the way they influence complications such as sudden death and dysrhythmias have been unclear. Recent findings of an acquired restrictive SCA-related cardiomyopathy, driven by myocardial fibrosis, may explain some of these cardiac features. Given the complexity of cardiac pathology in SCA, using additional parameters to tricuspid regurgitant jet velocity (left atrial volume, diastolic parameters, NT-proBNP) may improve the accuracy of noninvasive screening for cardiopulmonary complications in SCA.

Sickle cell disease

Sickle cell disease is a common and life-threatening haematological disorder that affects millions of people worldwide. Abnormal sickle-shaped erythrocytes disrupt blood flow in small vessels, and this vaso-occlusion leads to distal tissue ischaemia and inflammation, with symptoms defining the acute painful sickle-cell crisis. Repeated sickling and ongoing haemolytic anaemia, even when subclinical, lead to parenchymal injury and chronic organ damage, causing substantial morbidity and early mortality. Currently available treatments are limited to transfusions and hydroxycarbamide, although stem cell transplantation might be a potentially curative therapy. Several new therapeutic options are in development, including gene therapy and gene editing. Recent advances include systematic universal screening for stroke risk, improved management of iron overload using oral chelators and non-invasive MRI measurements, and point-of-care diagnostic devices. Controversies include the role of haemolysis in sickle cell disease pathophysiology, optimal management of pregnancy, and strategies to prevent cerebrovascular disease.

Intravascular hemolysis and the pathophysiology of sickle cell disease

Hemolysis is a fundamental feature of sickle cell anemia that contributes to its pathophysiology and phenotypic variability. Decompartmentalized hemoglobin, arginase 1, asymmetric dimethylarginine, and adenine nucleotides are all products of hemolysis that promote vasomotor dysfunction, proliferative vasculopathy, and a multitude of clinical complications of pulmonary and systemic vasculopathy, including pulmonary hypertension, leg ulcers, priapism, chronic kidney disease, and large-artery ischemic stroke. Nitric oxide (NO) is inactivated by cell-free hemoglobin in a dioxygenation reaction that also oxidizes hemoglobin to methemoglobin, a non-oxygen-binding form of hemoglobin that readily loses heme. Circulating hemoglobin and heme represent erythrocytic danger-associated molecular pattern (eDAMP) molecules, which activate the innate immune system and endothelium to an inflammatory, proadhesive state that promotes sickle vaso-occlusion and acute lung injury in murine models of sickle cell disease. Intravascular hemolysis can impair NO bioavailability and cause oxidative stress, altering redox balance and amplifying physiological processes that govern blood flow, hemostasis, inflammation, and angiogenesis. These pathological responses promote regional vasoconstriction and subsequent blood vessel remodeling. Thus, intravascular hemolysis represents an intrinsic mechanism for human vascular disease that manifests clinical complications in sickle cell disease and other chronic hereditary or acquired hemolytic anemias.

New insights into sickle cell disease: mechanisms and investigational therapies

PURPOSE OF REVIEW

Sickle cell disease (SCD) afflicts millions worldwide. The simplicity of its single nucleotide mutation belies the biological and psychosocial complexity of the disease. Despite only a single approved drug specifically for the treatment of SCD, new findings reviewed from 2015 provide the direction forward.

RECENT FINDINGS

The last year has provided a wealth of support for mechanisms affecting the red cell, hemolysis and vasculopathy, the innate immune system activation, blood cell and endothelial adhesiveness, central sensitization to pain, and chronic brain injury. The evidence supporting expanded use of hydroxyurea continues to mount. Many promising therapies are reaching clinical trial, including curative therapies, with more on the horizon.

SUMMARY

Evidence is compelling that the use of hydroxyurea must be expanded by clinicians to gain the full pleiotropic benefits of this approved drug. Clinicians must become aware that severe acute and chronic pain has a biological and neurologic basis, and the understanding of this basis is growing. Researchers are testing investigational therapies at an unprecedented pace in SCD, and partnership between patients, researchers, and the private sector provides the most rapid and productive way forward.

[Pulmonary complications of sickle cell disease in children]

Acute and chronic pulmonary complications are frequent in sickle cell disease (SCD), with different spectrum and characteristics in children and adults. Chronic hypoxia is frequent and plays a role in several respiratory complications in SCD. Furthermore, hypoxia has been associated with a higher risk of cerebral ischemia. Despite differing oxygen affinity between hemoglobin A and S, standard pulse oximetry was shown to be accurate in diagnosing hypoxia in SCD patients. Whereas acute hypoxia management is similar to non-SCD patients, chronic hypoxia treatment is mainly based on a transfusion program rather than long-term oxygen therapy. Acute chest syndrome (ACS) is the foremost reason for admission to the intensive care unit and the leading cause of premature death. Guidelines on its management have recently been published. Asthma appears to be a different comorbidity and may increase the risk of vaso-occlusive crisis, ACS, and early death. Its management is not specific in SCD, but systemic steroids must be used carefully. Pulmonary hypertension (PH) is a major risk factor of death in adult patients. In children, no association between PH and death has been shown. Elevated tricuspid regurgitant velocity was associated with lower performance on the 6-min walk test (6MWT) but its long-term consequences are still unknown. These differences could be due to different pathophysiology mechanisms. Systematic screening is recommended in children. Regarding lung functions, although obstructive syndrome appears to be rare, restrictive pattern prevalence increases with age in SCD patients. Adaptation to physical exercise is altered in SCD children: they have a lower walking distance at the 6MWT than controls and can experience desaturation during effort, but muscular blood flow regulation maintains normal muscular strength. Sleeping disorders are frequent in SCD children, notably Obstructive sleep apnea syndrome (OSAS). Because of the neurological burden of nocturnal hypoxia, OSAS care is primordial and mainly based on adenotonsillectomy, which has been shown to reduce ischemic events. The high morbidity and mortality related to pulmonary impairments in SCD require a careful pulmonary assessment and follow-up. Mainly based on clinical examination, follow-up aims to the diagnosis of SCD-related respiratory complications early in these children.

Doppler-Defined Pulmonary Hypertension in Sickle Cell Anemia in Kurdistan, Iraq

To determine the frequency, clinical and laboratory associations of pulmonary hypertension in Iraqi Kurds with sickle cell anemia, a total of ninety four such patients attending a major hemoglobinopathy center in Iraqi Kurdistan were enrolled. All patients were re-evaluated clinically and had their blood counts, HbF, serum ferritin, LDH, renal and liver function assessed. Transthoracic Doppler echocardiography with measurement of tricuspid valve regurgitant jet velocity (TRV) was performed. A TRV in excess of 2.8 m/s was considered for the purposes of this study as indicative of pulmonary hypertension (PH). The prevalence of TRV in excess of 2.8m/s was 10.6%. By univariate analysis: significantly higher reticulocyte count, more frequent blood transfusions and pain episodes were encountered in the PH group as compared to the non-PH group (p = 0.001, 0.045 and 0.02 respectively). Moreover, PH patients had significantly higher mean right atrial area, left atrial size, E wave/A wave ratio and ejection fraction by echocardiography (p = 0.027, 0.037, <0.001 and 0.008 respectively). Except for reticulocyte count none of the other parameters remained significant by multivariate analysis (p = 0.024). In conclusion the current study revealed that pulmonary hypertension is rather frequent among Iraqi Kurds with sickle cell anemia, and identified reticulocyte count as an independently associated parameter with PH in this population. Future prospective studies including right heart catheterization and appropriate medical intervention are warranted.

Cardiovascular complications and risk of death in sickle-cell disease

In sickle-cell disease, a point mutation in the β-globin chain causes haemoglobin to polymerise within erythrocytes during deoxygenation, altering red blood cell rheology and causing haemolysis. Improvements in health infrastructure, preventive care, and clinical treatments have reduced the morbidity and mortality of sickle-cell disease in developed countries. However, as these patients live longer, the chronic effects of sustained haemolytic anaemia and episodic vaso-occlusive events drive the development of end-organ complications. Cardiopulmonary organ dysfunction and chronic kidney injury have a large effect on morbidity and premature mortality, and typically accelerate in the second decade of life. These processes culminate in the development of pulmonary hypertension, left ventricular diastolic heart disease, dysrhythmia, and sudden death. In this Series paper, we review the mechanisms, clinical features, and epidemiology of major cardiovascular complications in patients with sickle-cell disease and discuss how screening and intervention could reduce their incidence.

Minireview: Genetic basis of heterogeneity and severity in sickle cell disease

Sickle cell disease, a common single gene disorder, has a complex pathophysiology that at its root is initiated by the polymerization of deoxy sickle hemoglobin. Sickle vasoocclusion and hemolytic anemia drive the development of disease complications. In this review, we focus on the genetic modifiers of disease heterogeneity. The phenotypic heterogeneity of disease is only partially explained by genetic variability of fetal hemoglobin gene expression and co-inheritance of α thalassemia. Given the complexity of pathophysiology, many different definitions of severity are possible complicating a full understanding of its genetic foundation. The pathophysiological complexity and the interlocking nature of the biological processes underpinning disease severity are becoming better understood. Nevertheless, useful genetic signatures of severity, regardless of how this is defined, are insufficiently developed to be used for treatment decisions and for counseling.

Revisiting the hyperhemolysis paradigm

In this issue of Blood, 2 articles test fundamental hypotheses relating intravascular hemolysis to sickle cell disease (SCD) pathogenesis. Detterich et al confirm a role for hemolysis and cell-free plasma hemoglobin (Hb) in pulmonary and systemic endothelial dysfunction in humans. Almeida et al show in mice that hemolysis induces inflammation that is caused by nitric oxide (NO) scavenging and ameliorated by NO donors and the NO-donor properties of hydroxyurea (HU).