Mortality in sickle cell disease. Life expectancy and risk factors for early death

BACKGROUND

Information on life expectancy and risk factors for early death among patients with sickle cell disease (sickle cell anemia, sickle cell-hemoglobin C disease, and the sickle cell-beta-thalassemias) is needed to counsel patients, target therapy, and design clinical trials.

METHODS

We followed 3764 patients who ranged from birth to 66 years of age at enrollment to determine the life expectancy and calculate the median age at death. In addition, we investigated the circumstances of death for all 209 adult patients who died during the study, and used proportional-hazards regression analysis to identify risk factors for early death among 964 adults with sickle cell anemia who were followed for at least two years.

RESULTS

Among children and adults with sickle cell anemia (homozygous for sickle hemoglobin), the median age at death was 42 years for males and 48 years for females. Among those with sickle cell-hemoglobin C disease, the median age at death was 60 years for males and 68 years for females. Among adults with sickle cell disease, 18 percent of the deaths occurred in patients with overt organ failure, predominantly renal. Thirty-three percent were clinically free of organ failure but died during an acute sickle crisis (78 percent had pain, the chest syndrome, or both; 22 percent had stroke). Modeling revealed that in patients with sickle cell anemia, the acute chest syndrome, renal failure, seizures, a base-line white-cell count above 15,000 cells per cubic millimeter, and a low level of fetal hemoglobin were associated with an increased risk of early death.

CONCLUSIONS

Fifty percent of patients with sickle cell anemia survived beyond the fifth decade. A large proportion of those who died had no overt chronic organ failure but died during an acute episode of pain, chest syndrome, or stroke. Early mortality was highest among patients whose disease was symptomatic. A high level of fetal hemoglobin predicted improved survival and is probably a reliable childhood forecaster of adult life expectancy.

CRISPR-Cas9 Gene Editing for Sickle Cell Disease and β-Thalassemia

Transfusion-dependent β-thalassemia (TDT) and sickle cell disease (SCD) are severe monogenic diseases with severe and potentially life-threatening manifestations. BCL11A is a transcription factor that represses γ-globin expression and fetal hemoglobin in erythroid cells. We performed electroporation of CD34+ hematopoietic stem and progenitor cells obtained from healthy donors, with CRISPR-Cas9 targeting the BCL11A erythroid-specific enhancer. Approximately 80% of the alleles at this locus were modified, with no evidence of off-target editing. After undergoing myeloablation, two patients - one with TDT and the other with SCD - received autologous CD34+ cells edited with CRISPR-Cas9 targeting the same BCL11A enhancer. More than a year later, both patients had high levels of allelic editing in bone marrow and blood, increases in fetal hemoglobin that were distributed pancellularly, transfusion independence, and (in the patient with SCD) elimination of vaso-occlusive episodes. (Funded by CRISPR Therapeutics and Vertex Pharmaceuticals; ClinicalTrials.gov numbers, NCT03655678 for CLIMB THAL-111 and NCT03745287 for CLIMB SCD-121.).

Effect of hydroxyurea on mortality and morbidity in adult sickle cell anemia: risks and benefits up to 9 years of treatment

CONTEXT

Hydroxyurea increases levels of fetal hemoglobin (HbF) and decreases morbidity from vaso-occlusive complications in patients with sickle cell anemia (SCA). High HbF levels reduce morbidity and mortality.

OBJECTIVE

To determine whether hydroxyurea attenuates mortality in patients with SCA.

DESIGN

Long-term observational follow-up study of mortality in patients with SCA who originally participated in the randomized, double-blind, placebo-controlled Multicenter Study of Hydroxyurea in Sickle Cell Anemia (MSH), conducted in 1992-1995, to determine if hydroxyurea reduces vaso-occlusive events. In the MSH Patients' Follow-up, conducted in 1996-2001, patients could continue, stop, or start hydroxyurea. Data were collected during the trial and in the follow-up period.

SETTING

Inpatients and outpatients in 21 sickle cell referral centers in the United States and Canada.

PATIENTS

Two-hundred ninety-nine adult patients with frequent painful episodes enrolled in the follow-up. Follow-up data through May 2001 were complete for 233 patients.

INTERVENTION

In the MSH, patients were randomly assigned to receive hydroxyurea (n = 152) or placebo (n = 147).

MAIN OUTCOME MEASURE

Mortality, HbF levels, painful episodes, acute chest syndrome, and blood cell counts. The randomized trial was not designed to detect specified differences in mortality.

RESULTS

Seventy-five of the original 299 patients died, 28% from pulmonary disease. Patients with reticulocyte counts less than 250 000/mm3 and hemoglobin levels lower than 9 g/dL had increased mortality (P =.002). Cumulative mortality at 9 years was 28% when HbF levels were lower than 0.5 g/dL after the trial was completed compared with 15% when HbF levels were 0.5 g/dL or higher (P =.03 ). Individuals who had acute chest syndrome during the trial had 32% mortality compared with 18% of individuals without acute chest syndrome (P =.02). Patients with 3 or more painful episodes per year during the trial had 27% mortality compared with 17% of patients with less frequent episodes (P =.06). Taking hydroxyurea was associated with a 40% reduction in mortality (P =.04) in this observational follow-up with self-selected treatment. There were 3 cases of cancer, 1 fatal.

CONCLUSIONS

Adult patients taking hydroxyurea for frequent painful sickle cell episodes appear to have reduced mortality after 9 of years follow-up. Survival was related to HbF levels and frequency of vaso-occlusive events. Whether indications for hydroxyurea treatment should be expanded is unknown.

Deconstructing sickle cell disease: reappraisal of the role of hemolysis in the development of clinical subphenotypes

Hemolysis, long discounted as a critical measure of sickle cell disease severity when compared with sickle vaso-occlusion, may be the proximate cause of some disease complications. New mechanistic information about hemolysis and its effects on nitric oxide (NO) biology and further examination of the subphenotypes of disease requires a reappraisal and deconstruction of the clinical features of sickle cell disease. The biology underlying clinical phenotypes linked to hemolysis may increase our understanding of the pathogenesis of other chronic hemolytic diseases while providing new insights into treating sickle cell disease. The pathophysiological roles of dysregulated NO homeostasis and sickle reticulocyte adherence have linked hemolysis and hemolytic rate to sickle vasculopathy. Nitric oxide binds soluble guanylate cyclase which converts GTP to cGMP, relaxing vascular smooth muscle and causing vasodilatation. When plasma hemoglobin liberated from intravascularly hemolyzed sickle erythrocytes consumes NO, the normal balance of vasoconstriction:vasodilation is skewed toward vasoconstriction. Pulmonary hypertension, priapism, leg ulceration and stroke, all subphenotypes of sickle cell disease, can be linked to the intensity of hemolysis. Hemolysis plays less of a role in the vaso-occlusive-viscosity complications of disease like the acute painful episode, osteonecrosis of bone and the acute chest syndrome. Agents that decrease hemolysis or restore NO bioavailability or responsiveness may have potential to reduce the incidence and severity of the hemolytic subphenotypes of sickle cell disease. Some of these drugs are now being studied in clinical trials.

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.

Erythrocyte adherence to endothelium in sickle-cell anemia. A possible determinant of disease severity

We studied 33 patients with sickle-cell anemia to examine the possible relation between the severity of their disease (frequency of microvascular occlusions) and the abnormal adherence of sickle erythrocytes to cultured human endothelium. Neither clinical severity nor erythrocyte adherence correlates significantly with red-cell indexes, hemoglobin concentration, percentage of irreversibly sickled red cells, level of fetal hemoglobin, or reticulocyte count. However, clinical severity and erythrocyte adherence are strongly correlated (rank correlation coefficient = +0.666; P less than 0.001). These findings are consistent with the hypothesis that abnormal interactions between erythrocytes and endothelium may be the initiating factor in the development of microvascular occlusions in sickle-cell anemia.

Spontaneous oxygen radical generation by sickle erythrocytes

Since the various membrane abnormalities of sickle erythrocytes might result from excessive accumulation of oxidant damage, we have measured the generation of superoxide, peroxide, and hydroxyl radical by normal and sickle erythrocytes using assays involving reduction of cytochrome c, aminotriazole inhibition of catalase, and methane evolution from dimethyl sulfoxide, respectively. Compared with normal erythrocytes, sickle erythrocytes spontaneously generate approximately twice as much superoxide, peroxide, and hydroxyl radical. One possible source of hydroxyl radical generation was identified as hemichrome, excessive amounts of which are bound to sickle erythrocyte membranes. Hemichrome did not generate hydroxyl radical when exposed to superoxide alone or peroxide alone. However, in the presence of both superoxide and peroxide, hemichrome greatly facilitated hydroxyl radical generation. Supporting this, normal erythrocyte membranes induced to acquire sickle hemichrome concomitantly acquired an enhanced ability to mediate hydroxyl radical generation. Finally, sickle erythrocyte membranes greatly enhanced superoxide/peroxide-driven hydroxyl radical generation as compared with normal erythrocyte membranes. These data suggest that an excessive accumulation of oxidant damage in sickle erythrocyte membranes might contribute to the accelerated membrane senescence of these cells. They further indicate that accumulation of oxidant damage could be a determinant of normal erythrocyte membrane senescence.

Differential modulation of endotoxin responsiveness by human caspase-12 polymorphisms

Caspases mediate essential key proteolytic events in inflammatory cascades and the apoptotic cell death pathway. Human caspases functionally segregate into two distinct subfamilies: those involved in cytokine maturation (caspase-1, -4 and -5) and those involved in cellular apoptosis (caspase-2, -3, -6, -7, -8, -9 and -10). Although caspase-12 is phylogenetically related to the cytokine maturation caspases, in mice it has been proposed as a mediator of apoptosis induced by endoplasmic reticulum stress including amyloid-beta cytotoxicity, suggesting that it might contribute to the pathogenesis of Alzheimer's disease. Here we show that a single nucleotide polymorphism in caspase-12 in humans results in the synthesis of either a truncated protein (Csp12-S) or a full-length caspase proenzyme (Csp12-L). The read-through single nucleotide polymorphism encoding Csp12-L is confined to populations of African descent and confers hypo-responsiveness to lipopolysaccharide-stimulated cytokine production in ex vivo whole blood, but has no significant effect on apoptotic sensitivity. In a preliminary study, we find that the frequency of the Csp12-L allele is increased in African American individuals with severe sepsis. Thus, Csp12-L attenuates the inflammatory and innate immune response to endotoxins and in doing so may constitute a risk factor for developing sepsis.

Hydroxyurea and sickle cell anemia. Clinical utility of a myelosuppressive "switching" agent. The Multicenter Study of Hydroxyurea in Sickle Cell Anemia

Painful crises in patients with sickle cell anemia are caused by vaso-occlusion and infarction. Occlusion of blood vessels depends on (at least) their diameter, the deformability of red cells, and the adhesion of blood cells to endothelium. Deoxygenated sickle cells are rigid because they contain linear polymers of hemoglobin S (Hb S); polymerization is highly concentration dependent, and dilution of Hb S by a nonsickling hemoglobin such as fetal hemoglobin (Hb F) would be expected to lead ultimately to a decrease in the frequency of painful crises. It might also be expected to decrease the severity of anemia, although the pathogenesis of anemia in sickle cell anemia (SS disease) is not clearly understood. Reversion to production of fetal rather than adult hemoglobin became practical with the discovery that HU was an orally effective and relatively safe "switching agent." Preliminary dose-ranging studies led to a double-blind randomized controlled clinical trial, the Multicenter Study of Hydroxyurea in Sickle Cell Anemia (MSH), designed to test whether patients treated with HU would have fewer crises than patients treated with placebo. The MSH was not designed to assess the mechanism(s) by which a beneficial effect might be achieved, but it was hoped that observations made during the study might illuminate that question. The 2 MSH treatment groups were similar to each other and were representative of African-American patients with relatively severe disease. The trial was closed earlier than expected, after demonstration that median crisis rate was reduced by almost 50% (2.5 versus 4.5 crises per year) in patients assigned to HU therapy. Hospitalizations, episodes of chest syndrome, and numbers of transfusions were also lower in patients treated with HU. Eight patients died during the trial, and treatment was stopped in 53. There were no instances of alarming toxicity. Patients varied widely in their maximum tolerated doses, but it was not clear that all were taking their prescribed treatments. When crisis frequency was compared with various clinical and laboratory measurements, pretreatment crisis rate and treatment with HU were clearly related to crisis rate during treatment. Pretreatment laboratory measurements were not associated with crisis rates during the study in either treatment group. It was not clear that clinical improvement was associated with an increase in Hb F. Crisis rates of the 2 treatment groups became different within 3 months. Mean corpuscular volumes (MCVs) and the proportion of Hb F containing red cells (F cells) rose, and neutrophil and reticulocyte counts fell, within 7 weeks. When patients were compared on the basis of 2-year crisis rates, those with lower crisis rates had higher F-cell counts and MCVs and lower neutrophil counts. Neutrophil, monocyte, reticulocyte, and platelet counts were directly associated, and F cells and MCV were inversely associated, with crisis rates in 3-month periods. In multivariable analyses, there was strong evidence of independent association of lower neutrophil counts with lower crisis rates. F-cell counts were associated with crisis rate only in the first 3 months of treatment; MCV showed an association over longer periods of time. Overall, the evidence that decreased neutrophil counts played a role in reducing crisis rates was strong. Increased F cells or MCV and evidence of cytoreduction by HU were also associated with decreased crisis rates, but no definitive statement can be made regarding the mechanism of action of HU because the study was not designed to address that question. Future studies should be designed to explore the mechanism of action of HU, to identify the optimal dosage regimen, and to study the effect of HU when combined with other antisickling agents.

Genetic dissection and prognostic modeling of overt stroke in sickle cell anemia

Sickle cell anemia (SCA) is a paradigmatic single gene disorder caused by homozygosity with respect to a unique mutation at the beta-globin locus. SCA is phenotypically complex, with different clinical courses ranging from early childhood mortality to a virtually unrecognized condition. Overt stroke is a severe complication affecting 6-8% of individuals with SCA. Modifier genes might interact to determine the susceptibility to stroke, but such genes have not yet been identified. Using Bayesian networks, we analyzed 108 SNPs in 39 candidate genes in 1,398 individuals with SCA. We found that 31 SNPs in 12 genes interact with fetal hemoglobin to modulate the risk of stroke. This network of interactions includes three genes in the TGF-beta pathway and SELP, which is associated with stroke in the general population. We validated this model in a different population by predicting the occurrence of stroke in 114 individuals with 98.2% accuracy.

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

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

The risks and benefits of long-term use of hydroxyurea in sickle cell anemia: A 17.5 year follow-up

A randomized, controlled clinical trial established the efficacy and safety of short-term use of hydroxyurea in adult sickle cell anemia. To examine the risks and benefits of long-term hydroxyurea usage, patients in this trial were followed for 17.5 years during which they could start or stop hydroxyurea. The purpose of this follow-up was to search for adverse outcomes and estimate mortality. For each outcome and for mortality, exact 95% confidence intervals were calculated, or tests were conducted at alpha = 0.05 level (P-value <0.05 for statistical significance). Although the death rate in the overall study cohort was high (43.1%; 4.4 per 100 person-years), mortality was reduced in individuals with long-term exposure to hydroxyurea. Survival curves demonstrated a significant reduction in deaths with long-term exposure. Twenty-four percent of deaths were due to pulmonary complications; 87.1% occurred in patients who never took hydroxyurea or took it for <5 years. Stroke, organ dysfunction, infection, and malignancy were similar in all groups. Our results, while no longer the product of a randomized study because of the ethical concerns of withholding an efficacious treatment, suggest that long-term use of hydroxyurea is safe and might decrease mortality.

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.

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.

An official American Thoracic Society clinical practice guideline: diagnosis, risk stratification, and management of pulmonary hypertension of sickle cell disease

BACKGROUND

In adults with sickle cell disease (SCD), an increased tricuspid regurgitant velocity (TRV) measured by Doppler echocardiography, an increased serum N-terminal pro-brain natriuretic peptide (NT-pro-BNP) level, and pulmonary hypertension (PH) diagnosed by right heart catheterization (RHC) are independent risk factors for mortality.

METHODS

A multidisciplinary committee was formed by clinician-investigators experienced in the management of patients with PH and/or SCD. Clinically important questions were posed, related evidence was appraised, and questions were answered with evidence-based recommendations. Target audiences include all clinicians who take care of patients with SCD.

RESULTS

Mortality risk stratification guides decision making. An increased risk for mortality is defined as a TRV equal to or greater than 2.5 m/second, an NT-pro-BNP level equal to or greater than 160 pg/ml, or RHC-confirmed PH. For patients identified as having increased mortality risk, we make a strong recommendation for hydroxyurea as first-line therapy and a weak recommendation for chronic transfusions as an alternative therapy. For all patients with SCD with elevated TRV alone or elevated NT-pro-BNP alone, and for patients with SCD with RHC-confirmed PH with elevated pulmonary artery wedge pressure and low pulmonary vascular resistance, we make a strong recommendation against PAH-specific therapy. However, for select patients with SCD with RHC-confirmed PH who have elevated pulmonary vascular resistance and normal pulmonary capillary wedge pressure, we make a weak recommendation for either prostacyclin agonist or endothelin receptor antagonist therapy and a strong recommendation against phosphodiesterase-5 inhibitor therapy.

CONCLUSIONS

Evidence-based recommendations for the management of patients with SCD with increased mortality risk are provided, but will require frequent reassessment and updating.

Sickle cell anemia, the first molecular disease: overview of molecular etiology, pathophysiology, and therapeutic approaches

The root cause of sickle cell disease is a single beta-globin gene mutation coding for the sickle beta-hemoglobin chain. Sickle hemoglobin tetramers polymerize when deoxygenated, damaging the sickle erythrocyte. A multifaceted pathophysiology, triggered by erythrocyte injury induced by the sickle hemoglobin polymer, and encompassing more general cellular and tissue damage caused by hypoxia, oxidant damage, inflammation, abnormal intracellular interactions, and reduced nitric oxide bioavailability, sets off the events recognized clinically as sickle cell disease. This disease is a group of related disorders where sickle hemoglobin is the principal hemoglobin species. All have varying degrees of chronic hemolytic anemia, vasculopathy, vasoocclusive disease, acute and chronic organ damage, and shortened life span. Its complex pathophysiology, of which we have a reasonable understanding, provides multiple loci for potential therapeutic intervention.

The paradox of hemoglobin SC disease

Homozygous HbC gene results only in mild hemolytic anemia. In HbSC disease red cells contain equal levels of HbS and HbC. It is a paradox that HbSC exhibit a moderately severe phenotype in spite of being a mixture of HbS trait and HbC trait, neither of which has significant pathology. Why does the combination of these two Hbs result in a serious disease? The short answer is that HbC enhances, by dehydrating the SC red cell, the pathogenic properties of HbS, resulting in a clinically significant disorder, but somewhat milder that sickle cell anemia (SCA). Nevertheless, retinnitis proliferans, osteonecrosis, and acute chest syndrome have equal or higher incidence in HbSC disease compared to SCA. This pathogenic trick is accomplished by HbC inducing, by mechanisms not fully understood, an increase in the activity of K:Cl cotransport that induces the lost of K(+) and consequently of intracellular water. This event creates a sufficient increase of MCHC, so that the lower levels of HbS found in SC red cells can polymerize rapidly and effectively. This situation offers a unique opportunity: if we could inhibit the effect of HbC on K(+) transport we can cure the disease.

N-terminal pro-brain natriuretic peptide levels and risk of death in sickle cell disease

CONTEXT

Thirty percent of patients with sickle cell disease (SCD) develop pulmonary hypertension, a major risk factor for death in this population. A validated blood biomarker of pulmonary hypertension in SCD could provide important prognostic and diagnostic information and allow the exploration of the prevalence of pulmonary hypertension in participants in the 1996 Multicenter Study of Hydroxyurea in Sickle Cell Anemia (MSH) Patients' Follow-up Study. Levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) provide such information in patients with idiopathic pulmonary arterial hypertension.

OBJECTIVE

To determine the relationship between NT-proBNP levels and severity of pulmonary hypertension and prospective mortality in patients with SCD.

DESIGN, SETTING, AND PARTICIPANTS

NT-proBNP levels were measured in 230 participants in the National Institutes of Health (NIH) Sickle Cell Disease-Pulmonary Hypertension Screening Study (enrollment between February 2001 and March 2005) and in 121 samples from patients enrolled starting in 1996 in the MSH Patients' Follow-up Study. A threshold level predictive of high pulmonary artery pressure and mortality was identified in the NIH Sickle Cell Disease-Pulmonary Hypertension Screening Study and used to define an a priori analytical plan to determine the prevalence and associated mortality of pulmonary hypertension in the MSH follow-up study.

MAIN OUTCOME MEASURES

Severity of pulmonary hypertension and risk of all-cause mortality.

RESULTS

NT-proBNP levels were higher in patients with sickle cell pulmonary hypertension and correlated directly with tricuspid regurgitant jet velocity in the NIH cohort (R = 0.50, P<.001). An NT-proBNP level of 160 pg/mL or greater had a 78% positive predictive value for the diagnosis of pulmonary hypertension and was an independent predictor of mortality (21 deaths at 31 months' median follow-up; risk ratio, 5.1; 95% confidence interval, 2.1-12.5; P<.001; 19.5% absolute increase in risk of death). In the MSH cohort, 30% of patients had an NT-proBNP level of 160 pg/mL or greater. An NT-proBNP level of 160 pg/mL or greater in the MSH cohort was independently associated with mortality by Cox proportional hazards regression analysis (24 deaths at 47 months' median follow-up; risk ratio, 2.87; 95% confidence interval, 1.2-6.6; P = .02; 11.9% absolute increase in risk of death).

CONCLUSIONS

Pulmonary hypertension, as indicated by an NT-proBNP level of 160 pg/mL or greater, was very common in patients in the NIH study and in the MSH cohort. The MSH analysis suggests that rates of vaso-occlusive pain episodes in these patients were unrelated to risk of death; this risk was largely determined by occult hemolytic anemia-associated pulmonary hypertension.

Abnormal pulmonary function in adults with sickle cell anemia

RATIONALE

Pulmonary complications of sickle cell anemia (Hb-SS) commonly cause morbidity, yet few large studies of pulmonary function tests (PFTs) in this population have been reported.

OBJECTIVES

PFTs (spirometry, lung volumes, and diffusion capacity for carbon monoxide [DLCO]) from 310 adults with Hb-SS were analyzed to determine the pattern of pulmonary dysfunction and their association with other systemic complications of sickle cell disease.

METHODS

Raw PFT data were compared with predicted values. Each subject was subclassified into one of five groups: obstructive physiology, restrictive physiology, mixed obstructive/restrictive physiology, isolated low DLCO, or normal. The association between laboratory data of patients with decreased DLCO or restrictive physiology and those of normal subjects was assessed by multivariate linear regression.

MEASUREMENTS AND MAIN RESULTS

Normal PFTs were present in only 31 of 310 (10%) patients. Overall, adults with Hb-SS were characterized by decreased total lung capacities (70.2 +/- 14.7% predicted) and DLCO (64.5 +/- 19.9%). The most common PFT patterns were restrictive physiology (74%) and isolated low DLCO (13%). Decreased DLCO was associated with thrombocytosis (p = 0.05), with hepatic dysfunction (elevated alanine aminotransferase; p = 0.07), and a trend toward renal dysfunction (elevated blood urea nitrogen and creatinine; p = 0.05 and 0.07, respectively).

CONCLUSIONS

Pulmonary function is abnormal in 90% of adult patients with Hb-SS. Common abnormalities include restrictive physiology and decreased DLCO. Decreased DLCO may indicate more severe sickle vasculopathy characterized by impaired hepatic and renal function.

Hemolysis-associated priapism in sickle cell disease

Priapism, although uncommon in the general population, is one of the many serious complications associated with sickle cell disease (SCD). Few studies have described the clinical and hematologic characteristics of individuals with priapism and SCD. Using data from the Cooperative Study for Sickle Cell Disease, we assembled 273 case subjects with priapism and 979 control subjects. Case subjects, compared with control subjects, had significantly lower levels of hemoglobin; higher levels of lactate dehydrogenase, bilirubin, and aspartate aminotransferase; and higher reticulocyte, white blood cell, and platelet counts. These findings suggest an association of priapism with increased hemolysis. Hemolysis decreases the availability of circulating nitric oxide, which plays an important role in erectile function.

Chronic hyper-hemolysis in sickle cell anemia: association of vascular complications and mortality with less frequent vasoocclusive pain

Background

Intravascular hemolysis in sickle cell anemia could contribute to complications associated with nitric oxide deficiency, advancing age, and increased mortality. We have previously reported that intense hemolysis is associated with increased risk of vascular complications in a small cohort of adults with sickle cell disease. These observations have not been validated in other populations.

Methods

The distribution of serum lactic dehydrogenase (LDH) values was used as a surrogate measure of intravascular hemolysis in a contemporaneous patient group and an historical adult population from the Cooperative Study of Sickle Cell Disease (CSSCD), all with sickle cell anemia. Chronic hyper-hemolysis was defined by the top LDH quartile and was compared to the lowest LDH quartile.

Results

Hyper-hemolysis subjects had higher systolic blood pressure, higher prevalence of leg ulcers (OR 3.27, 95% CI 1.92-5.53, P<0.0001), priapism (OR 2.62, 95% CI 1.13-6.90, P = 0.03) and pulmonary hypertension (OR 4.32, 95% CI 2.12-8.60, P<0.0001), while osteonecrosis (OR 0.32, 95% CI 0.19-0.54, P<0.0001) and pain (OR 0.23, 95% CI 0.09-0.55, P = 0.0004) were less prevalent. Hyper-hemolysis was influenced by fetal hemoglobin and α thalassemia, and was a risk factor for early death in the CSSCD population (Hazard Ratio = 1.97, P = 0.02).

Conclusions

Steady state LDH measurements can identify a chronic hyper-hemolysis phenotype which includes less frequent vasooclusive pain and earlier mortality. Clinicians should consider sickle cell specific therapies for these patients, as is done for those with more frequent acute pain. The findings also suggest that an important class of disease modifiers in sickle cell anemia affect the rate of hemolysis.

Erythrocyte glutamine depletion, altered redox environment, and pulmonary hypertension in sickle cell disease

Erythrocyte glutathione depletion has been linked to hemolysis and oxidative stress. Glutamine plays an additional antioxidant role through preservation of intracellular nicotinamide adenine dinucleotide phosphate (NADPH) levels, required for glutathione recycling. Decreased nitric oxide (NO) bioavailability, which occurs in the setting of increased hemolysis and oxidative stress, contributes to the pathogenesis of pulmonary hypertension (PH) in sickle cell disease (SCD). We hypothesized that altered glutathione and glutamine metabolism play a role in this process. Total glutathione (and its precursors) and glutamine were assayed in plasma and erythrocytes of 40 SCD patients and 9 healthy volunteers. Erythrocyte total glutathione and glutamine levels were significantly lower in SCD patients than in healthy volunteers. Glutamine depletion was independently associated with PH, defined as a tricuspid regurgitant jet velocity (TRV) of at least 2.5 m/s. The ratio of erythrocyte glutamine:glutamate correlated inversely to TRV (r = -0.62, P < .001), plasma arginase concentration (r = -0.45, P = .002), and plasma-free hemoglobin level (r = -0.41, P = .01), linking erythrocyte glutamine depletion to dysregulation of the arginine-NO pathway and increased hemolytic rate. Decreased erythrocyte glutathione and glutamine levels contribute to alterations in the erythrocyte redox environment, which may compromise erythrocyte integrity, contribute to hemolysis, and play a role in the pathogenesis of PH of SCD.

Sickle cell leg ulcers: associations with haemolysis and SNPs in Klotho, TEK and genes of the TGF-beta/BMP pathway

Cutaneous leg ulcers are common in sickle cell anaemia and their risk might be genetically determined. Sickle cell anaemia patients were studied to examine the relationship of leg ulcers with haemolysis and with single nucleotide polymorphisms (SNPs) in candidate genes that could affect sickle vasoocclusion. Leg ulcer patients had lower haemoglobin levels and higher levels of lactate dehydrogenase, bilirubin, aspartate transaminase and reticulocytes than did control patients with sickle cell anaemia but without leg ulcers. Age-adjusted comparisons showed that sickle cell anaemia-alpha thalassaemia was more frequent among controls than cases. These results strongly suggested that the likelihood of having leg ulcers was related to the intensity of haemolysis. 215 SNPs in more than 100 candidate genes were studied. Associations were found with SNPs in Klotho, TEK and several genes in the TGF-beta/BMP signalling pathway by genotypic association analyses. KL directly or indirectly promotes endothelial nitric oxide (NO) production and the TEK receptor tyrosine kinase is involved in angiogenesis. The TGF-beta/BMP signalling pathway modulates wound healing and angiogenesis, among its other functions. Haemolysis-driven phenotypes, such as leg ulcers, could be improved by agents that reduce sickle erythrocyte density or increase NO bioavailability.