The effect of prolonged administration of hydroxyurea on morbidity and mortality in adult patients with sickle cell syndromes: results of a 17-year, single-center trial (LaSHS). Blood. 2010;115:2354-2363. [PMID: 19903897 DOI: 10.1182/blood-2009-05-221333]

Clinical and hematological effects of hydroxyurea therapy in sickle cell patients: a single-center experience in Brazil

CONTEXT AND OBJECTIVES Sickle cell disease (SCD) is the most common genetic disorder among people of African descent, affecting approximately 3,500 newborns each year in Brazil. Hydroxyurea (HU) is the only effective drug to treating patients with SCD, thereby reducing morbidity and mortality. The objective was to analyze the effects of HU on SCD patients at our institution. DESIGN AND SETTING Retrospective study conducted at a sickle cell centre in Ribeirão Preto, São Paulo, Brazil. METHODS We analyzed clinical and laboratory data on 37 patients. The hematological parameters and clinical events that occurred during the year before and the first year of treatment with HU were analyzed. The mean dose of HU was 24.5 ± 5.5 mg/kg/day. RESULTS There were rises in three parameters: hemoglobin (8.3 g/dl to 9.0 g/dl, P = 0.0003), fetal hemoglobin (HbF) (2.6% to 19.8%, P < 0.0001) and mean cell volume MCV (89 to 105 fl, P = 0.001); and reductions in the numbers of leukocytes (10,050/µl to 5,700/µl, P < 0.0001), neutrophils (6,200/µl to 3,400/µl, P = 0.001), platelets (459,000/µl to 373,000/µl, P = 0.0002), painful crises (1.86 to 0.81, P = 0.0014), acute chest syndromes (0.35 to 0.08, P = 0.0045), infections (1.03 to 0.5, P = 0.047), hospitalizations (1.63 to 0.53, P = 0.0013) and transfusions (1.23 to 0.1, P = 0.0051). CONCLUSION The patients presented clinical and hematological improvements, with an increase in HbF and a reduction in the infection rate, which had not been addressed in most previous studies.

Hydroxycarbamide: clinical aspects

Due to its oral route of administration and mild toxicity profile, as well as its potent laboratory and clinical effects, hydroxyurea (or hydroxycarbamide) has been the primary focus of fetal hemoglobin (HbF) induction strategies for the treatment of children with sickle cell anemia (SCA). When administered orally once a day, hydroxyurea treatment is very well tolerated with little short-term toxicity. Hydroxyurea has documented laboratory efficacy with increases in Hb and HbF; treatment also significantly reduces the number of painful episodes, acute chest syndrome, transfusions, and hospitalizations. Most young patients reach a maximum tolerated dose of hydroxyurea at 25-30 mg/kg/d, where they will achieve key laboratory thresholds (Hb ≥ 9 g/dL and HbF ≥ 20%) without excessive myelosuppression. Potential long-term toxicities continue to be of great concern and should be monitored in all patients with SCA who receive hydroxyurea therapy. To date, however, no increases in stroke, myelodysplasia, or carcinogenicity have been detected in SCA patient cohorts, with drug exposure now reaching 15 years for some treated children. Taken together, available evidence suggests that hydroxyurea represents an inexpensive and effective treatment option that should be offered to most, if not all, patients with SCA. As countries in Africa develop newborn screening programs to identify SCA, the widespread use of hydroxyurea may prove to be a useful treatment to help ameliorate the disease in resource-limited settings. Hydroxyurea is the only currently available disease-modifying therapy for SCA, and is emerging as a safe and effective treatment for all patients with SCA, in both developed and developing countries.

Novel approaches to the treatment of sickle cell disease: the potential of histone deacetylase inhibitors

Sickle cell disease (SCD) is a severe genetic disorder of hemoglobin causing vaso-occlusion. Patients suffer severe anemia, strokes, renal failure, pulmonary compromise and shortened life expectancy. Over 90,000 people in the USA have SCD, and the options for therapy are limited and only partially effective. With the available therapies - hydroxyurea, blood transfusion, hydration and pain medicines - patients continue to suffer the long-term complications of the disease. This review focuses on the pathogenesis of SCD and the role of fetal hemoglobin in disrupting the polymerization of sickle hemoglobin. The authors review the compounds that induce fetal hemoglobin: hydroxyurea, which is currently US FDA approved, and the histone deacetylase inhibitors and discuss their role in the treatment of SCD and other β-hemoglobinopathies.

Influence of severity of anemia on clinical findings in infants with sickle cell anemia: analyses from the BABY HUG study

BACKGROUND

Clinical complications of sickle cell anemia begin in infancy. BABY HUG (ClinicalTrials.gov, NCT00006400) was a NHLBI-NICHD supported randomized phase III placebo-controlled trial of hydroxyurea (HU) in infants (recruited at 9-18 months) unselected for clinical severity with sickle cell anemia. This secondary analysis of data from BABY HUG examines the influence of anemia on the incidence of sickle cell related complications, and the impact of hydroxyurea therapy in altering these events by comparing children with lower (<25th percentile) and higher (>75th percentile) hemoglobin concentrations at study entry.

PROCEDURE

Infants were categorized by: (1) age-adjusted hemoglobin quartiles as determined by higher (Hi) and lower (Lo) hemoglobin concentrations at study entry (9-12 months old: <8.0 and >10.0 gm/dL; 12-18 months old: <8.1 and >9.9 gm/dL) and (2) treatment arm (hydroxyurea or placebo). Four subgroups were created: placebo (PL) LoHb (n = 25), PL HiHb (n = 27), hydroxyurea (HU) LoHb (n = 21), and HU HiHb (n = 18). The primary and secondary endpoints of BABY HUG were analyzed by subgroup.

RESULTS

Infants with lower hemoglobin at baseline were more likely to have a higher incidence of clinical events (acute chest syndrome, pain crisis, fever) as well as higher TCD velocities and lower neuropsychological scores at study exit. Hydroxyurea reduced the incidence of these findings.

CONCLUSION

Infants with more severe anemia are at risk for increased clinical events that may be prevented by early initiation of hydroxyurea.

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.

A global perspective on sickle cell disease

The global burden of sickle cell disease (SCD) is now being increasingly realized. SCD poses a significant public health problem in sub-Saharan Africa, the Middle East, some regions of India, the Caribbean, and Brazil. In many of these regions, progress in the management of SCD has been slow. Long-term North-South and South-South partnerships between SCD professionals, funding agencies, governments, and industry are needed to help reduce the high disease burden in developing countries, through widespread SCD education, relevant research and implementation of evidence-based cost-effective interventions. A group of SCD professionals have responded with action by forming a global network.

Hydroxyurea for the treatment of sickle cell disease: efficacy, barriers, toxicity, and management in children

Hydroxyurea is the only approved medication in the United States for the treatment of sickle cell anemia (HbSS) and is widely used in children despite an indication limited to adults. We review the evidence of efficacy and safety in children with reference to pivotal adult studies. This evidence and expert opinion form the basis for recommended guidelines for the use of hydroxyurea in children including indications, dosing, therapeutic and safety monitoring, and interventions to improve adherence. However, there are substantial gaps in our knowledge to be addressed by on-going and planned studies in children.

Genotoxicity associated with hydroxyurea exposure in infants with sickle cell anemia: results from the BABY-HUG Phase III Clinical Trial

BACKGROUND

The laboratory and clinical benefits of hydroxyurea therapy for children with sickle cell anemia (SCA) are well recognized, but treatment in young patients is limited in part by concerns about long-term genotoxicity, and specifically possible carcinogenicity.

PROCEDURE

The Pediatric Hydroxyurea Phase III Clinical Trial (BABY HUG) was a multicenter double-blinded placebo-controlled randomized clinical trial (NCT00006400) testing whether hydroxyurea could prevent chronic organ damage in very young patients with SCA. An important secondary objective was the measurement of acquired genotoxicity using three laboratory assays: chromosomal karyotype, illegitimate VDJ recombination events, and micronucleated reticulocyte formation.

RESULTS

Our data indicate that hydroxyurea treatment was not associated with any significant increases in genotoxicity compared to placebo treatment.

CONCLUSIONS

These data provide additional support to the safety profile of hydroxyurea for young patients with SCA, and suggest that genotoxicity in this patient population is low.

Cardiovascular abnormalities in sickle cell disease

Sickle cell disease is characterized by recurrent episodes of ischemia-reperfusion injury to multiple vital organ systems and a chronic hemolytic anemia, both contributing to progressive organ dysfunction. The introduction of treatments that induce protective fetal hemoglobin and reduce infectious complications has greatly prolonged survival. However, with increased longevity, cardiovascular complications are increasingly evident, with the notable development of a progressive proliferative systemic vasculopathy, pulmonary hypertension (PH), and left ventricular diastolic dysfunction. Pulmonary hypertension is reported in autopsy studies, and numerous clinical studies have shown that increased pulmonary pressures are an important risk marker for mortality in these patients. In epidemiological studies, the development of PH is associated with intravascular hemolysis, cutaneous leg ulceration, renal insufficiency, iron overload, and liver dysfunction. Chronic anemia in sickle cell disease results in cardiac chamber dilation and a compensatory increase in left ventricular mass. This is often accompanied by left ventricular diastolic dysfunction that has also been a strong independent predictor of mortality in patients with sickle cell disease. Both PH and diastolic dysfunction are associated with marked abnormalities in exercise capacity in these patients. Sudden death is an increasingly recognized problem, and further cardiac investigations are necessary to recognize and treat high-risk patients.

Stem cell transplant for children with sickle cell anemia: parent and patient interest

We describe adolescents' and parents' interest in hematopoietic stem cell transplant (HSCT) as a cure for sickle cell disease (SCD) and factors associated with increased interest. We administered a 40 question survey to assess the interest in HSCT in parents and adolescents with HBSS or HBSβ(0) thalassemia. The survey tool assessed factors that may influence interest in HSCT including demographic data, disease severity, views on prognosis, and health-related quality of life (HRQOL). All participants were given a handout on the risks and benefits of an HSCT before completing the survey. One hundred twenty-nine parents and 59 adolescents completed the survey. Forty-five percent of parents (54 of 119) would likely have their child undergo HSCT, and 35% of adolescents (19 of 55) would likely undergo HSCT if it was recommended by their hematologist. Parents of adolescents, as well as adolescent patients with better HRQOL, were more interested in HSCT. Prior exchange transfusion was associated with increased interest in HSCT (62% [23 of 37] versus 38% [29 of 76]; P = .02). The majority of parents believe their child's SCD will get better (66%; [80 of 122]), will not likely prevent their child from achieving life goals (83%; [100 of 121]), and will not shorten their child's lifespan (86%; [102 of 119]). There is strong parent and adolescent interest in HSCT as a cure for SCD. It is concerning that few parents and adolescents believe SCD will negatively impact their prognosis. Education on the potential long-term sequelae of SCD is needed when considering the role for HSCT.

A national registry of haemoglobinopathies in Greece: deducted demographics, trends in mortality and affected births

Haemoglobinopathies are the most common hereditary disorders in Greece. Although there is a successful national prevention program, established 35 years ago, there is lack of an official registry and collection of epidemiological data for haemoglobinopathies. This paper reports the results of the first National Registry for Haemoglobinopathies in Greece (NRHG), recently organized by the Greek Society of Haematology. NRHG records all patients affected by thalassaemia major (TM), thalassaemia intermedia (TI), "H" Haemoglobinopathy (HH) and sickle cell disease (SCD). Moreover, data about the annual rate of new affected births along with deaths, between 2000 and 2010, are reported. A total of 4,506 patients are registered all over the country while the number of affected newborns was significantly decreased during the last 3 years. Main causes for still having affected births are: (1) lack of medical care due to financial reasons or low educational level; (2) unawareness of time limitations for prenatal diagnosis (PD); due either to obstetricians' malpractice or to delayed demand of medical care of couples at risk; and (3) religious, social or bioethical reasons. Cardiac and liver disorders consist main causes for deaths while life expectancy of patients lengthened after 2005 (p < 0.01). The NRHG of patients affected by haemoglobinopathies in Greece provides useful data about the haemoglobinopathies in the Greek population and confirms the efficacy of the National Thalassaemia Prevention Program on impressively decreasing the incidence of TM and sickle cell syndromes.

Development of myelodysplastic syndrome and acute myeloid leukemia 15 years after hydroxyurea use in a patient with sickle cell anemia

We report a 41 year old male with sickle cell disease who developed a myelodysplastic syndrome and acute myeloid leukemia with complex karyotype involving chromosomes 5, 7 and 17 after 15 years of hydroxyurea treatment. He responded poorly to induction chemotherapy with cytarabine/idarubicin followed by high dose cytarabine and succumbed to neutropenic sepsis. Multiple systematic reviews, observational studies and clinical trials were conducted to identify the toxicity profile of hydroxurea. Only six cases of leukemia/myelodysplastic syndrome were identified in patients with sickle cell anemia treated with hydroxyurea. Subsequently, it was concluded that hydroxyurea is not leukemogenic. However, it was noted that most of the published studies had only up to 9 years of follow-up. Our patient was started on hydroxyurea in 1990, before the widespread use of the drug and took hydroxyurea for 15 years. His presentation may reflect an outcome otherwise not yet observed because of the short follow-up of prior studies. We believe that the leukemogenic risk of hydroxyurea should be discussed with the patients and their families. Studies evaluating the adverse effects of hydroxyurea should have longer follow-up before definitive conclusions are drawn.

Polycythemia vera and essential thrombocythemia: 2012 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms primarily characterized by erythrocytosis and thrombocytosis, respectively. Other disease features include leukocytosis, splenomegaly, thrombohemorrhagic complications, vasomotor disturbances, pruritus, and a small risk of disease progression into acute myeloid leukemia or myelofibrosis.

DIAGNOSIS

Almost all patients with PV harbor a JAK2 mutation. When PV is suspected, the presence of a JAK2 mutation confirms the diagnosis and its absence, combined with normal or increased serum erythropoietin level, excludes the diagnosis. Differential diagnosis of ET had to include chronic myelogenous leukemia and prefibrotic myelofibrosis. A JAK2 mutation is found in approximately 60% of patients with ET.

RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of thrombotic complications: high-risk is defined by the presence of age >60 years or presence of thrombosis history; low-risk is defined by the absence of both of these two risk factors. Presence of extreme thrombocytosis (platelet count >1,000 × 10(9)/L) might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding. Risk factors for shortened survival in both PV and ET include advanced age, leukocytosis, and history of thrombosis.

RISK-ADAPTED THERAPY

Survival is near-normal in ET and reasonably long in PV. The 10-year risk of leukemic/fibrotic transformation is <1%/1% in ET and <3%/10% in PV. In contrast, the risk of thrombosis exceeds 20%. The main goal of therapy is therefore to prevent thrombohemorrhagic complications and this is effectively and safely accomplished by the use of low-dose aspirin (PV and ET), phlebotomy (PV) and hydroxyurea (high risk PV and ET). Treatment with busulfan or interferon-α is usually effective in hydroxyurea failures. Screening for clinically significant AvWS is recommended before administrating aspirin in the presence of extreme thrombocytosis.

Hydroxycarbamide alters erythroid gene expression in children with sickle cell anaemia

Sickle cell anaemia (SCA) is a severe debilitating haematological disorder associated with a high degree of morbidity and mortality. The level of fetal haemoglobin (HbF) is well-recognized as a critical laboratory parameter: lower HbF is associated with a higher risk of vaso-occlusive complications, organ damage, and early death. Hydroxycarbamide treatment can induce HbF, improve laboratory parameters, and ameliorate clinical complications of SCA but its mechanisms of action remain incompletely defined and the HbF response is highly variable. To identify pathways of hydroxycarbamide activity, we performed microarray expression analyses of early reticulocyte RNA obtained from children with SCA enrolled in the HydroxyUrea Study of Long-term Effects (NCT00305175) and examined the effects of hydroxycarbamide exposure in vivo. Hydroxycarbamide affected a large number of erythroid genes, with significant decreases in the expression of genes involved in translation, ribosome assembly and chromosome organization, presumably reflecting the daily cytotoxic pulses of hydroxycarbamide. Hydroxycarbamide also affected expression of numerous genes associated with HbF including BCL11A, a key regulator of baseline HbF levels. Together, these data indicate that hydroxycarbamide treatment for SCA leads to substantial changes in erythroid gene expression, including BCL11A and other potential signalling pathways associated with HbF induction.

Low micromolar intravascular cell-free hemoglobin concentration affects vascular NO bioavailability in sickle cell disease: a computational analysis

In sickle cell disease, the changes in RBC morphology destabilize the red blood cell (RBC) membrane and lead to hemolysis. Several experimental and clinical studies have associated intravascular hemolysis with pulmonary hypertension in sickle cell disease. Cell-free hemoglobin (Hb) from intravascular hemolysis has high affinity for nitrixc oxide (NO) and can affect the NO bioavailability in the sickle cell disease, which may eventually lead to pulmonary hypertension. To study the effects of intravascular hemolysis related cell-free Hb concentrations on NO bioavailability, we developed a two-dimensional mathematical model of NO biotransport in 50-μm arteriole under steady-state sickle cell disease conditions. We analyzed the effects of flow-dependent NO production and axial and radial transport of NO, a recently reported much lower NO-RBC reaction rate constant, and cell-free layer thickness on NO biotransport. Our results show that the presence of cell-free Hb concentrations as low as 0.5 μM results in an approximately three- to sevenfold reduction in the predicted smooth muscle cell NO concentrations compared with those under physiological conditions. In addition, increasing the diffusional resistance for NO in vascular lumen from cell-free layer or reducing NO-RBC reaction rate did not improve the NO bioavailability at the smooth muscle cell layer significantly for cell-free Hb concentrations ≥1 μM. These results suggest that lower NO bioavailability due to low micromolar cell-free Hb can disturb NO homeostasis and cause insufficient bioavailability at the smooth muscle cell layer. Our results supports the hypothesis that hemolysis-associated reduction in NO bioavailability may play a role in the development of pathophysiological complications like pulmonary hypertension in sickle cell disease that are observed in several clinical and experimental studies.

Hematological differences between patients with different subtypes of sickle cell disease on hydroxyurea treatment

OBJECTIVE

Sickle cell anemia and the interaction S/Beta thalassemia differ in hematological values due to microcytosis and hypochromia caused by the thalassemic mutation. The clinical benefit of long-term hydroxyurea treatment is undeniable in sickle cell disease with monitoring of the biological action of the drug being by the complete blood count. The objective of this work is to compare changes in some of the erythrocytic indexes between S/Beta thalassemia and sickle cell anemia patients on long-term hydroxyurea treatment.

METHODS

The values of erythrocyte indexes (mean corpuscular volume and mean corpuscular hemoglobin) were compared in a retrospective study of two groups of patients (Sickle cell anemia and S/Beta thalassemia) on hydroxyurea treatment over a mean of six years.

RESULTS

The quantitative values of the two parameters differed between the groups. Increases in mean corpuscular volume and reductions in mean corpuscular hemoglobin delay longer in S/Beta thalassemia patients (p-value = 0.018).

CONCLUSION

Hematological changes are some of the beneficial effects of hydroxyurea in sickle cell disease as cellular hydration increases and the hemoglobin S concentration is reduced. The complete blood count is the best test to monitor changes, but the interpretation of the results in S/Beta thalassemia should be different.

Management of children with sickle cell disease: a comprehensive review of the literature

OBJECTIVE

Sickle cell disease (SCD) affects 70 000 to 100 000 people in the United States, and 2000 infants are born with the disease each year. The purpose of this study was to review the quality of the literature for preventive interventions and treatment of complications for children with SCD to facilitate the use of evidence-based medicine in clinical practice and identify areas in need of additional research.

METHODS

We searched the Ovid Medline database and the Cochrane Library for articles published between January 1995 and April 2010 for English-language abstracts on 28 topics thought to be important for the care of children with SCD. We also added pertinent references cited by studies identified in our search. Each abstract was reviewed independently by 2 authors. Data from articles retrieved for full review were abstracted by using a common form.

RESULTS

There were 3188 abstracts screened, and 321 articles underwent full review. Twenty-six articles (<1% of abstracts initially screened), which consisted of 25 randomized controlled trials and 1 meta-analysis, were rated as having level I evidence. Eighteen of the 28 topics selected for this review did not have level I evidence studies published. The management and prevention of pain episodes accounted for more than one-third of the level I studies.

CONCLUSIONS

Although significant strides have been made in the care of children with SCD in the past 2 decades, more research needs to be performed, especially for acute events associated with SCD, to ensure that the health and well-being of children with SCD continues to improve.

Hydroxyurea therapy of a murine model of sickle cell anemia inhibits the progression of pneumococcal disease by down-modulating E-selectin

Sickle cell anemia is characterized by chronic hemolysis coupled with extensive vascular inflammation. This inflammatory state also mechanistically promotes a high risk of lethal, invasive pneumococcal infection. Current treatments to reduce vaso-occlusive complications include chronic hydroxyurea therapy to induce fetal hemoglobin. Because hydroxyurea also reduces leukocytosis, an understanding of the impact of this treatment on pneumococcal pathogenesis is needed. Using a sickle cell mouse model of pneumococcal pneumonia and sepsis, administration of hydroxyurea was found to significantly improve survival. Hydroxyurea treatment decreased neutrophil extravasation into the infected lung coincident with significantly reduced levels of E-selectin in serum and on pulmonary epithelia. The protective effect of hydroxyurea was abrogated in mice deficient in E-selectin. The decrease in E-selectin levels was also evident in human sickle cell patients receiving hydroxyurea therapy. These data indicate that in addition to induction of fetal hemoglobin, hydroxyurea attenuates leukocyte-endothelial interactions in sickle cell anemia, resulting in protection against lethal pneumococcal sepsis.

Epigenetic and molecular profiles of erythroid cells after hydroxyurea treatment in sickle cell anemia

Hydroxyurea has been shown to be efficacious for the treatment of sickle cell anemia (SCA), primarily through the induction of fetal hemoglobin (HbF). However, the exact mechanisms by which hydroxyurea can induce HbF remain incompletely defined, although direct transcriptional effects and altered cell cycle kinetics have been proposed. In this study, we investigated potential epigenetic and alternative molecular mechanisms of hydroxyurea-mediated HbF induction by examining methylation patterns within the (G)γ-globin promoter and miRNA expression within primary CD71(+) erythrocytes of patients with SCA, both at baseline before beginning hydroxyurea therapy and after reaching maximum tolerated dose (MTD). Using both cross-sectional analysis and paired-sample analysis, we found that the highly methylated (G)γ-globin promoter was inversely correlated to baseline HbF levels, but only slightly altered by hydroxyurea treatment. Conversely, expression of several specific miRNAs was significantly increased after hydroxyurea treatment, and expression of miR-26b and miR-151-3p were both associated with HbF levels at MTD. The significant associations identified in these studies suggest that methylation may be important for regulation of baseline HbF, but not after hydroxyurea treatment, whereas changes in miRNA expression may be associated with hydroxyurea-mediated HbF induction. This study was registered at ClinicalTrials.gov (NCT00305175).

Sickle cell nephropathy - a practical approach

Despite its apparently simple molecular aetiology, sickle cell disease (SCD) has long been known to have a remarkably variable clinical course, with complications involving many organs including the kidneys. Whilst many affected individuals show no evidence of renal involvement into late adulthood, others develop renal dysfunction in childhood or early adult life with a significant proportion eventually requiring renal replacement therapy. This review explores the pathophysiology and clinical manifestations of sickle cell nephropathy (SCN) and discusses how each complication can be investigated, monitored and managed in the outpatient setting. We summarize current knowledge of genetic modulation of sickle-related renal dysfunction. We outline the evidence for various treatment options and discuss others for which little evidence currently exists.

Pharmacokinetics, pharmacodynamics, and pharmacogenetics of hydroxyurea treatment for children with sickle cell anemia

Hydroxyurea therapy has proven laboratory and clinical efficacies for children with sickle cell anemia (SCA). When administered at maximum tolerated dose (MTD), hydroxyurea increases fetal hemoglobin (HbF) to levels ranging from 10% to 40%. However, interpatient variability of percentage of HbF (%HbF) response is high, MTD itself is variable, and accurate predictors of hydroxyurea responses do not currently exist. HUSTLE (NCT00305175) was designed to provide first-dose pharmacokinetics (PK) data for children with SCA initiating hydroxyurea therapy, to investigate pharmacodynamics (PD) parameters, including HbF response and MTD after standardized dose escalation, and to evaluate pharmacogenetics influences on PK and PD parameters. For 87 children with first-dose PK studies, substantial interpatient variability was observed, plus a novel oral absorption phenotype (rapid or slow) that influenced serum hydroxyurea levels and total hydroxyurea exposure. PD responses in 174 subjects were robust and similar to previous cohorts; %HbF at MTD was best predicted by 5 variables, including baseline %HbF, whereas MTD was best predicted by 5 variables, including serum creatinine. Pharmacogenetics analysis showed single nucleotide polymorphisms influencing baseline %HbF, including 5 within BCL11A, but none influencing MTD %HbF or dose. Accurate prediction of hydroxyurea treatment responses for SCA remains a worthy but elusive goal.

NT-pro brain natriuretic peptide levels and the risk of death in the cooperative study of sickle cell disease

Epidemiological studies support a hypothesis that pulmonary hypertension (PH) is a common complication of sickle cell disease (SCD) that is associated with a high risk of death and evolves as a complication of haemolytic anaemia. This fundamental hypothesis has been recently challenged and remains controversial. In order to further test this hypothesis in a large and independent cohort of SCD patients we obtained plasma samples from the Cooperative Study of Sickle Cell Disease (CSSCD) for analysis of a biomarker, N-terminal-pro brain natriuretic peptide (NT-proBNP), which is elevated in the setting of pulmonary arterial and venous hypertension. A NT-pro-BNP value previously identified to predict PH in adults with SCD was used to determine the association between the risk of mortality in 758 CSSCD participants (428 children and 330 adults). An abnormally high NT-proBNP level ≥160ng/l was present in 27·6% of adult SCD patients. High levels were associated with markers of haemolytic anaemia, such as low haemoglobin level (P<0·001), high lactate dehydrogenase (P<0·001), and high total bilirubin levels (P<0·007). A NT-proBNP level ≥160ng/l was an independent predictor of mortality (RR 6·24, 95% CI 2·9-13·3, P<0·0001). These findings provide further support for an association between haemolytic anaemia and cardiovascular complications in this patient population.

Hydroxycarbamide in very young children with sickle-cell anaemia: a multicentre, randomised, controlled trial (BABY HUG)

BACKGROUND

Sickle-cell anaemia is associated with substantial morbidity from acute complications and organ dysfunction beginning in the first year of life. Hydroxycarbamide substantially reduces episodes of pain and acute chest syndrome, admissions to hospital, and transfusions in adults with sickle-cell anaemia. We assessed the effect of hydroxycarbamide therapy on organ dysfunction and clinical complications, and examined laboratory findings and toxic effects.

METHODS

This randomised trial was undertaken in 13 centres in the USA between October, 2003, and September, 2009. Eligible participants had haemoglobin SS (HbSS) or haemoglobin Sβ(0)thalassaemia, were aged 9-18 months at randomisation, and were not selected for clinical severity. Participants received liquid hydroxycarbamide, 20 mg/kg per day, or placebo for 2 years. Randomisation assignments were generated by the medical coordinating centre by a pre-decided schedule. Identical appearing and tasting formulations were used for hydroxycarbamide and placebo. Patients, caregivers, and coordinating centre staff were masked to treatment allocation. Primary study endpoints were splenic function (qualitative uptake on (99)Tc spleen scan) and renal function (glomerular filtration rate by (99m)Tc-DTPA clearance). Additional assessments included blood counts, fetal haemoglobin concentration, chemistry profiles, spleen function biomarkers, urine osmolality, neurodevelopment, transcranial Doppler ultrasonography, growth, and mutagenicity. Study visits occurred every 2-4 weeks. Analysis was by intention to treat. The trial is registered with ClinicalTrials.gov, number NCT00006400.

FINDINGS

96 patients received hydroxycarbamide and 97 placebo, of whom 83 patients in the hydroxycarbamide group and 84 in the placebo group completed the study. Significant differences were not seen between groups for the primary endpoints (19 of 70 patients with decreased spleen function at exit in the hydroxycarbamide group vs 28 of 74 patients in the placebo group, p=0·21; and a difference in the mean increase in DTPA glomerular filtration rate in the hydroxycarbamide group versus the placebo group of 2 mL/min per 1·73 m(2), p=0·84). Hydroxycarbamide significantly decreased pain (177 events in 62 patients vs 375 events in 75 patients in the placebo group, p=0·002) and dactylitis (24 events in 14 patients vs 123 events in 42 patients in the placebo group, p<0·0001), with some evidence for decreased acute chest syndrome, hospitalisation rates, and transfusion. Hydroxyurea increased haemoglobin and fetal haemoglobin, and decreased white blood-cell count. Toxicity was limited to mild-to-moderate neutropenia.

INTERPRETATION

On the basis of the safety and efficacy data from this trial, hydroxycarbamide can now be considered for all very young children with sickle-cell anaemia.

FUNDING

The US National Heart, Lung, and Blood Institute; and the National Institute of Child Health and Human Development.

Hydroxyurea for sickle cell anemia: what have we learned and what questions still remain?

PURPOSE OF REVIEW

Sickle cell anemia (SCA) is a well characterized severe hematological disorder with substantial morbidity and early mortality. Hydroxyurea is a potent inducer of fetal hemoglobin, and evidence over the past 25 years has documented its laboratory and clinical efficacy for both adults and children with SCA.

RECENT FINDINGS

The phase III study of hydroxyurea in infants (BABY HUG) has just been completed and preliminary results indicate equivocal benefits for organ protection during the 2-year treatment period, but significant benefits for pain, acute chest syndrome, hospitalizations, and transfusions. Three new reports document the benefits of hydroxyurea on reducing mortality in SCA: two adult trials (LaSHS and MSH) and one pediatric study (Brazilian cohort). Recent results from the HUSTLE protocol suggest minimal genotoxicity or carcinogenicity with long-term hydroxyurea exposure.

SUMMARY

The potential utility of hydroxyurea for all patients with SCA is clear and indisputable. With decades of accumulated evidence and documented efficacy with an acceptable long-term safety profile, it is time to consider hydroxyurea treatment the standard of care for all young patients with SCA. Exporting our knowledge and experience with hydroxyurea to developing nations with large medical burdens from SCA can help relieve global suffering from this condition.

Fetal hemoglobin in sickle cell anemia

Fetal hemoglobin (HbF) is the major genetic modulator of the hematologic and clinical features of sickle cell disease, an effect mediated by its exclusion from the sickle hemoglobin polymer. Fetal hemoglobin genes are genetically regulated, and the level of HbF and its distribution among sickle erythrocytes is highly variable. Some patients with sickle cell disease have exceptionally high levels of HbF that are associated with the Senegal and Saudi-Indian haplotype of the HBB-like gene cluster; some patients with different haplotypes can have similarly high HbF. In these patients, high HbF is associated with generally milder but not asymptomatic disease. Studying these persons might provide additional insights into HbF gene regulation. HbF appears to benefit some complications of disease more than others. This might be related to the premature destruction of erythrocytes that do not contain HbF, even though the total HbF concentration is high. Recent insights into HbF regulation have spurred new efforts to induce high HbF levels in sickle cell disease beyond those achievable with the current limited repertory of HbF inducers.

Transplantation for liver failure in patients with sickle cell disease: challenging but feasible

Sickle cell disease (SCD) frequently affects the liver; if acute liver failure (ALF) develops, the only potentially effective therapeutic option is liver transplantation (LT). Only 12 patients for whom LT was performed for SCD-related ALF have been described so far. We report a retrospective series of 6 adult patients with SCD (3 men and 3 women, median age = 40.1 years) who underwent emergency LT. The indication for LT was ALF complicating cirrhosis in 5 patients (hepatitis C/iron overload-induced cirrhosis in 3 and iron overload-induced cirrhosis in 2); one patient had autoimmune hepatitis. The median follow-up was 52.7 months (0.5-123 months). The 1-, 3-, 5-, and 10-year survival rates were 83.3%, 66.7%, 44.4%, and 44.4%, respectively. One patient died of hepatocellular failure precipitated by hyperacute allograft rejection on post-LT day 10. Soon after LT, 2 patients developed seizures; in 1 case, the seizures were a complication of early calcineurin inhibitor-induced leukoencephalopathy. Four long-term survivors benefited from specific management of SCD; specifically, the hemoglobin S fraction was maintained below 30% and the total hemoglobin level was maintained between 8 and 10 g/dL. Two patients had mild vaso-occlusive crises. Three patients experienced a recurrence of hepatitis C virus (HCV) infection; 2 of these patients experienced reversible neurological complications while they were receiving antiviral treatment. Carefully selected patients with SCD may benefit from emergency LT. However, such patients seem to be particularly susceptible to neurological complications after LT. In contrast, severe SCD-related crises do not seem to recur if specific management is provided. Outcomes may be improved if the neurological complications can be minimized; for example, the administration of a calcineurin inhibitor can be delayed, and the management of HCV infection recurrence can be improved.

Long-term results using hydroxyurea/phlebotomy for reducing secondary stroke risk in children with sickle cell anemia and iron overload

Children with sickle cell anemia (SCA) and a primary overt stroke are at high risk of recurrent (secondary) stroke. Chronic transfusion therapy dramatically reduces but does not eliminate this high risk, and inevitably results in transfusion-related hemosiderosis. We previously reported the use of hydroxyurea/phlebotomy as an alternative to transfusions to reduce the risk of secondary stroke and improve management of iron overload in 35 children with SCA. To report long-term results, we retrospectively reviewed clinical and laboratory data through October 2008. With a median of 5.6 years and total of 219 patient-years of follow-up, 10 of 35 patients (29%) had recurrent stroke after switching to hydroxyurea; seven were previously reported and three new strokes occurred during extended follow-up. The overall secondary stroke event rate was 4.6 per 100 patient-years. Children on hydroxyurea received serial phlebotomy and had lower mean serum ferritin values than children on transfusions (591 ng/mL vs. 3410 ng/mL, P = 0.02). In this cohort, long-term hydroxyurea treatment reduced but did not eliminate the risk of stroke recurrence and, uniquely, allowed phlebotomy to reduce iron overload. Long-term assessments of this therapy should evaluate risk factors for secondary stroke and assessments of hemosiderosis, neurocognitive outcome, and health-related quality of life.

Annual Clinical Updates in Hematological Malignancies: a continuing medical education series: polycythemia vera and essential thrombocythemia: 2011 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms primarily characterized by erythrocytosis and thrombocytosis, respectively. Other disease features include leukocytosis, splenomegaly, thrombohemorrhagic complications, vasomotor disturbances, pruritus, and a small risk of disease progression into acute leukemia or myelofibrosis.

DIAGNOSIS

Diagnosis is based on JAK2 mutation status (PV and ET), serum erythropoietin (Epo) level (PV), and bone marrow histopathology (ET). The presence of a JAK2 mutation and subnormal serum Epo level confirm a diagnosis of PV. Differential diagnosis in ET should include chronic myelogenous leukemia and prefibrotic myelofibrosis.

RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of thrombotic complications: high-risk-age > 60 years or presence of thrombosis history; low-risk-absence of both of these two risk factors. Presence of extreme thrombocytosis (platelet count > 1,000 x 10⁹/L) might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding. Risk factors for shortened survival in both PV and ET include age > 60 years, leukocytosis, history of thrombosis, and anemia.

RISK-ADAPTED THERAPY

Survival is near-normal in ET and reasonably long in PV. The 10-year risk of leukemic/fibrotic transformation is < 1%/1% in ET and < 5%/10% in PV. In contrast, the risk of thrombosis exceeds 20%. The main goal of therapy is therefore to prevent thrombohemorrhagic complications and this is effectively and safely accomplished by the use of low-dose aspirin (PV and ET), phlebotomy (PV), and hydroxyurea (high risk PV and ET). Treatment with busulfan or interferon-a is usually effective in hydroxyurea failures.

Hydroxyurea adherence and associated outcomes among Medicaid enrollees with sickle cell disease

While laboratory and clinical benefits of hydroxyurea for patients with sickle cell disease (SCD) are well-established, few data describe the extent and implications of non-adherence. We sought to assess adherence to hydroxyurea among patients with SCD and investigate associations between adherence and clinical and economic outcomes. Insurance claims of North Carolina Medicaid enrollees (6/2000-8/2008) with SCD were analyzed. Inclusion criteria included age < 65 years, continuous Medicaid enrollment ≥ 12 months before and following hydroxyurea initiation, and ≥ 2 hydroxyurea prescriptions. Three hundred twelve patients, mean age 21 (± 12.2) years, met inclusion criteria and 35% were adherent, defined as a medication possession ration (MPR) ≥ 0.80; mean MPR was 0.60. In the 12 months following hydroxyurea initiation, adherence was associated with reduced risk of SCD-related hospitalization (hazard ratio [HR] = 0.65, p = .0351), all-cause and SCD-related emergency department visit (HR = 0.72, p = .0388; HR = 0.58, p =.0079, respectively), and vaso-occlusive event (HR = 0.66, p = .0130). Adherence was associated with reductions in health care costs such as all-cause and SCD-related inpatient (-$5,286, p < .0001; -$4,403, p < .0001, respectively), ancillary care (-$1,336, p < .0001; -$836, p < .0001, respectively), vaso-occlusive event-related (-$5,793, p < .0001), and total costs (-$6,529, p < .0001; -$5,329, p <.0001, respectively). Adherence to hydroxyurea among SCD patients appears suboptimal and better adherence is associated with improved clinical and economic outcomes.

Fetal hemoglobin reactivation and cell engineering in the treatment of sickle cell anemia

The natural history of severe hemoglobinopathies like sickle cell disease (SCD) is rather variable, depending on the circumstances, but the main influence on such variability is the level of fetal hemoglobin (HbF) in the patient's red cells. It is well known that a significant HbF level is associated with a milder course of disease and fewer complications. Therefore, attempts have been made to reactivate using various means the HbF production, which is normally switched off perinatally. A pharmacological approach has been attempted since the 1980s, ranging from drugs like 5-azacytidine and its derivative, decitabine, to a series of compounds like hydroxyurea and a number of histone deacetylase inhibitors like butyrate, which seem to act as epigenetic modifiers. Many other disparate agents have been tried with mixed results, but hydroxyurea remains the most effective compound so far available. Combinations of different compounds have also been tried with some success. Established treatments like bone marrow or cord blood transplantation are so far the only real cure for a limited number of patients with severe hemoglobinopathies. Improved chemotherapy regimens of milder toxicity than those employed in the past have made it possible recently to obtain a stable, mixed donor-recipient chimerism, with reversal of the SCD phenotype. However, great effort is directed to cell engineering, searching for an effective gene vector by which a desired gene can be transferred into new classes of vectors for autologous hemopoietic stem cells. Recent studies are also aiming at targeted insertion of the therapeutic gene into hemopoietic cells, which can also be "induced" human stem cells, obtained from somatic dedifferentiated cells. Attention in this area must be paid to the possibility of undesired effects, like the emergence of potentially oncogenic cell populations. Finally, an update is presented on improved HbF determination methods, because common international standards are becoming mandatory.

Iron in sickle-cell disease: what have we learned over the years?

Over the last four decades, monumental advances have been made in the understanding, assessment, and management of transfusion-dependent patients, which have translated into significant improvements in patient morbidity and mortality. Important lessons have been learned from extensive clinical experience of iron management in the thalassemias, but greater knowledge of key differences in the sickle-cell disease (SCD) population may impact on our approach to patient assessment and management. The unique pathophysiology of SCD is reflected in a distinct pattern of iron loading with minimal organ-specific injury. An appreciation and understanding of these differences should allow us to develop tailored management approaches that optimize patient outcomes.

Genetic modifiers of HbF and response to hydroxyurea in sickle cell disease

Fetal hemoglobin (HbF) levels are generally inversely proportional to severity of sickle cell disease (SCD) for given sickle phenotypes. Molecular regulation of HbF occurs through complex interactions cis and trans to the beta globin gene locus. Novel insights made through population-based genetic epidemiologic studies of non-anemic populations were replicated in SCD groups, despite large differences in HbF levels. Identification of the lymphoid transcription factor BCL11A as a key suppressor of HbF expression validates approaches using population genetics to study HbF expression. We review these methods and findings, and speculate on applying pharmaco-genetics to optimize hydroxyurea therapy aimed at increasing HbF.

A combined top-down and bottom-up MS approach for the characterization of hemoglobin variants in Rhesus monkeys

Sickle cell disease is caused by one of the 1200 known hemoglobin variations. A single-point mutation β6(A3)Glu→Val leads to sickling of red blood cells, which in turn causes a lack of oxygen supply to tissue and organs. Although sickle cell disease is well understood, treatment options are currently underdeveloped. The only Food and Drug Administration-approved drug is hydroxyurea, an inducer of fetal γ-hemoglobin, which is known to have a higher oxygen affinity than adult hemoglobins and thus alleviates symptoms. In the search for better cures, Rhesus monkeys (Macaca mulatta) serve as models for monitoring success of induction of fetal γ-hemoglobins and with recent advances in proteomics, MS has become the leading technique to determine globin expression. Similar to humans, Rhesus monkeys possess hemoglobin variants that have not been sufficiently characterized to initiate such a study. Therefore, we developed a combined bottom-up and top-down approach to identify and characterize novel hemoglobin variants of the umbilical cord blood of Rhesus monkeys. A total of four different variants were studied: α, β, γ1 and γ2. A new α- and β-hemoglobin variant was identified, and the two previously hypothesized γ-hemoglobins were identified. In addition, glutathionylation of both γ-hemoglobin variants at their cysteines has been characterized. The combined approach outperformed either bottom-up or top-down alone and can be used for characterization of unknown hemoglobin variants and their PTMs.

Effect of hydroxyurea on physical fitness indices in children with sickle cell anemia

The current studies aimed at determining physical fitness indices and anthropometrics profiles of children with sickle cell anemia (SCA) after the use of hydroxyurea (HU). Ninety-three male schoolchildren--who participated previously in a similar study before the introduction of HU--comprising 2 groups participated in the studies. Group 1 was 41 children who were suffering from sickle cell disease (SCD) and were on HU for a minimum of 2 years, whereas group 2 was 50 normal healthy controls. Anthropometrics measurement and parameters of physical fitness were assessed in all subjects. All children were also subjected to a minimum of 6-minute running exercise test on a flat motorized treadmill at speed corresponding to 5 km/h. Throughout the test heart rate was monitored and recorded during exercise and for 10 minutes during recovery. Blood hemoglobin (Hb) and HbF% were measured after the use of HU. The mean values of weight, height, and lean body mass were still lower in the SCD children (P < .05) compared with the healthy subjects. However, they had significant decrease in the mean heart rate values and they spent longer time on the treadmill before they got tired compared to their previous performance and were just below the normal controls. Hydroxyurea treatment improved the aerobic exercise tolerance and most of the physical fitness parameters in children with SCD.

Reconstructing sickle cell disease: a data-based analysis of the "hyperhemolysis paradigm" for pulmonary hypertension from the perspective of evidence-based medicine

The "hyperhemolytic paradigm" (HHP) posits that hemolysis in sickle disease sequentially and causally establishes increased cell-free plasma Hb, consumption of NO, a state of NO biodeficiency, endothelial dysfunction, and a high prevalence of pulmonary hypertension. The basic science underpinning this concept has added an important facet to the complexity of vascular pathobiology in sickle disease, and clinical research has identified worrisome clinical issues. However, this critique identifies and explains a number of significant concerns about the various HHP component tenets. In addressing these issues, this report presents: a very brief history of the HHP, an integrated synthesis of mechanisms underlying sickle hemolysis, a review of the evidentiary value of hemolysis biomarkers, an examination of evidence bearing on existence of a hyperhemolytic subgroup, and a series of questions that should naturally be applied to the HHP if it is examined using critical thinking skills, the fundamental basis of evidence-based medicine. The veracity of different HHP tenets is found to vary from true, to weakly supported, to demonstrably false. The thesis is developed that the HHP has misidentified the mechanism and clinical significance of its findings. The extant research questions identified by these analyses are delineated, and a conservative, evidence-based approach is suggested for application in clinical medicine.

Umbilical cord blood transplantation for children with thalassemia and sickle cell disease

We examined the efficacy of unrelated cord blood (CB) transplantation in children with thalassemia (n = 35) and sickle cell disease (n = 16), using data reported to 3 registries. Donor-recipient pairs were matched at HLA-A and -B (antigen level) and DRB1 (allele level) in 7 or HLA mismatched at 1 (n = 18), 2 (n = 25), or 3 loci (n = 1). Transplant conditioning was myeloablative (n = 39) or reduced intensity (n = 12). Neutrophil recovery with donor chimerism was documented in 24 patients; 11 patients developed grade II-IV acute graft-versus-host disease (aGVHD) and 10 patients, chronic GVHD (cGVHD). Overall survival (OS) and disease-free survival (DFS) were 62% and 21% for thalassemia and 94% and 50% for sickle cell disease (SCD), respectively. In multivariate analysis, engraftment rate (hazard ratio [HR] 2.2, P = .05) and DFS (HR 0.4, P = .01) were higher with cell dose >5 × 10(7)/kg. The 2-year probability of DFS was 45% in patients who received grafts with cell dose >5 × 10(7)/kg and 13% with lower cell dose. Primary graft failure was the predominant cause of treatment failure occurring in 20 patients with thalassemia and 7 patients with SCD. Primary graft failure was fatal in 5 patients with thalassemia. These results suggest that only CB units containing an expected infused cell dose >5 × 10(7)/kg should be considered for transplantation for hemoglobinopathy.

Myeloproliferative neoplasms: molecular pathophysiology, essential clinical understanding, and treatment strategies

To update oncologists on pathogenesis, contemporary diagnosis, risk stratification, and treatment strategies in BCR-ABL1-negative myeloproliferative neoplasms, including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Recent literature was reviewed and interpreted in the context of the authors' own experience and expertise. Pathogenetic mechanisms in PV, ET, and PMF include stem cell-derived clonal myeloproliferation and secondary stromal changes in the bone marrow and spleen. Most patients carry an activating JAK2 or MPL mutation and a smaller subset also harbors LNK, CBL, TET2, ASXL1, IDH, IKZF1, or EZH2 mutations; the precise pathogenetic contribution of these mutations is under investigation. JAK2 mutation analysis is now a formal component of diagnostic criteria for PV, ET, and PMF, but its prognostic utility is limited. Life expectancy in the majority of patients with PV or ET is near-normal and disease complications are effectively (and safely) managed by treatment with low-dose aspirin, phlebotomy, or hydroxyurea. In PMF, survival and quality of life are significantly worse and current therapy is inadequate. In ET and PV, controlled studies are needed to show added value and justify the risk of unknown long-term health effects associated with nonconventional therapeutic approaches (eg, interferon-alfa). The unmet need for treatment in PMF dictates a different approach for assessing the therapeutic value of new drugs (eg, JAK inhibitors, pomalidomide) or allogeneic stem-cell transplantation.

Sickle-cell disease

Sickle-cell disease is one of the most common severe monogenic disorders in the world. Haemoglobin polymerisation, leading to erythrocyte rigidity and vaso-occlusion, is central to the pathophysiology of this disease, although the importance of chronic anaemia, haemolysis, and vasculopathy has been established. Clinical management is basic and few treatments have a robust evidence base. One of the main problems of sickle-cell disease in children is the development of cerebrovascular disease and cognitive impairment, and the role of blood transfusion and hydroxycarbamide for prevention of these complications is starting to be understood. Recurrent episodes of vaso-occlusion and inflammation result in progressive damage to most organs, including the brain, kidneys, lungs, bones, and cardiovascular system, which becomes apparent with increasing age. Most people with sickle-cell disease live in Africa, where little is known about this disease; however, we do know that the disorder follows a more severe clinical course in Africa than for the rest of the world and that infectious diseases have a role in causing this increased severity of sickle-cell disease. More work is needed to develop effective treatments that specifically target pathophysiological changes and clinical complications of sickle-cell disease.

How I use hydroxyurea to treat young patients with sickle cell anemia

Hydroxyurea has many characteristics of an ideal drug for sickle cell anemia (SCA) and provides therapeutic benefit through multiple mechanisms of action. Over the past 25 years, substantial experience has accumulated regarding its safety and efficacy for patients with SCA. Early proof-of-principle studies were followed by prospective phase 1/2 trials demonstrating efficacy in affected adults, then adolescents and children, and more recently infants and toddlers. The phase 3 National Heart, Lung and Blood Institute-sponsored Multicenter Study of Hydroxyurea trial proved clinical efficacy for preventing acute vaso-occlusive events in severely affected adults. Based on this cumulative experience, hydroxyurea has emerged as an important therapeutic option for children and adolescents with recurrent vaso-occlusive events; recent evidence documents sustained long-term benefits with prevention or reversal of chronic organ damage. Despite abundant evidence for its efficacy, however, hydroxyurea has not yet translated into effective therapy for SCA. Because many healthcare providers have inadequate knowledge about hydroxyurea, patients and families are not offered treatment or decline because of unrealistic fears. Limited support for hydroxyurea by lay organizations and inconsistent medical delivery systems also contribute to underuse. Although questions remain regarding its long-term risks and benefits, current evidence suggests that many young patients with SCA should receive hydroxyurea treatment.