Feasibility trial for primary stroke prevention in children with sickle cell anemia in Nigeria (SPIN trial)

The vast majority of children with sickle cell anemia (SCA) live in Africa, where evidence‐based guidelines for primary stroke prevention are lacking. In Kano, Nigeria, we conducted a feasibility trial to determine the acceptability of hydroxyurea therapy for primary stroke prevention in children with abnormal transcranial Doppler (TCD) measurements. Children with SCA and abnormal non‐imaging TCD measurements (≥200 cm/s) received moderate fixed‐dose hydroxyurea therapy (～20 mg/kg/day). A comparison group of children with TCD measurements <200 cm/s was followed prospectively. Approximately 88% (330 of 375) of families agreed to be screened, while 87% (29 of 33) of those with abnormal TCD measurements, enrolled in the trial. No participant elected to withdraw from the trial. The average mean corpuscular volume increased from 85.7 fl at baseline to 95.5 fl at 24 months (not all of the children who crossed over had a 24 month visit), demonstrating adherence to hydroxyurea. The comparison group consisted of initially 210 children, of which four developed abnormal TCD measurements, and were started on hydroxyurea. None of the monthly research visits were missed (n = total 603 visits). Two and 10 deaths occurred in the treatment and comparison groups, with mortality rates of 2.69 and 1.81 per 100 patient‐years, respectively (P = .67). Our results provide strong evidence, for high family recruitment, retention, and adherence rates, to undertake the first randomized controlled trial with hydroxyurea therapy for primary stroke prevention in children with SCA living in Africa.     

Prospects for primary stroke prevention in children with sickle cell anaemia

This review will focus on the strengths and limitations associated with the current standard of care for primary prevention of ischaemic strokes in children with sickle cell anaemia (SCA) ‐ transcranial Doppler ultrasound (TCD) screening followed by regular blood transfusion therapy when TCD measurement is above a threshold defined by a randomized clinical trial (RCT). The theoretical basis for potential alternative strategies for primary prevention of neurological injury in SCA is also discussed. These strategies will include, but will not be limited to: immunizations to prevent bacterial infections, particularly in low income countries; management of elevated blood pressure; and targeted strategies to increase baseline haemoglobin levels with therapies such as hyroxycarbamide or potentially definitive haematopoietic stem cell transplant.     

Genetic predictors for stroke in children with sickle cell anemia

Stroke is a devastating complication of sickle cell anemia (SCA), affecting 5% to 10% of patients before adulthood. Several candidate genetic polymorphisms have been proposed to affect stroke risk, but few have been validated, mainly because previous studies were hampered by relatively small sample sizes and the absence of additional patient cohorts for validation testing. To verify the accuracy of proposed genetic modifiers influencing stroke risk in SCA, we performed genotyping for 38 published single nucleotide polymorphisms (SNPs), as well as α-thalassemia, G6PD A(-) variant deficiency, and β-globin haplotype in 2 cohorts of children with well-defined stroke phenotypes (130 stroke, 103 nonstroke). Five polymorphisms had significant influence (P < .05): SNPs in the ANXA2, TGFBR3, and TEK genes were associated with increased stroke risk, whereas α-thalassemia and a SNP in the ADCY9 gene were linked with decreased stroke risk. Further investigation at these genetic regions may help define mutations that confer stroke risk or protection in children with SCA.     

Hydroxyurea (HU) for prevention of recurrent stroke in sickle cell anemia (SCA)

Cerebrovascular accident (CVA) is a major cause of morbidity and death in sickle cell anemia (SCA). Transfusion of packed erythrocytes is widely used to prevent this complication. However, chronic transfusion may lead to iron overload, alloimmunization, or infections. Cost and compliance may compromise transfusion therapy. A possible alternative, the prophylactic use of hydroxyurea (HU), has not been tried to determine whether it may prevent recurrent stroke. We used HU in five children with SCA who had suffered stroke, in three of them after a first episode and in the other two after a second CVA. Four had infarctive stroke and one a transient ischemic attack (TIA). Four patients took HU at a dose of 40 mg/kg/d, one patient at 30 mg/kg/d. None of the patients had recurrent stroke during 42-112 months of observation. None experienced pain crises. In all, HbF increased significantly and was maintained above 14.7% during treatment. The total Hb concentration increased 19.5 g/L (median) above the value before treatment. HU was well tolerated. None of the five children had leukopenia or thrombocytopenia during therapy. HU appears to prevent recurrence of stroke in SCA without risk of major toxicity.     

Feasibility and efficacy of chronic transfusion for stroke prevention in children with sickle cell disease

Objectives: In children with sickle cell disease (SCD), chronic transfusion to maintain haemoglobin S (HbS) below 30% markedly decreases both the risk of a first stroke when transcranial Doppler (TCD) ultrasonography shows abnormal cerebral blood flow velocities and the risk of recurrent stroke. Maintaining HbS below 30% may be difficult, especially in countries where blood donors and recipients belong to different ethnic groups and where the availability of closely matched blood products is limited. We assessed the feasibility and efficacy of chronic transfusion with an HbS target of 30% in children with SCD living in the Paris area. Methods: We retrospectively studied 29 children aged 6.8 ± 3.0 yr (3–15 yr) at inclusion who received chronic transfusion either because of abnormal TCD findings (primary prevention group, PPG, n = 17) or because of a previous cerebrovascular event (secondary prevention group, SPG, n = 12 including nine with a history of stroke and three of transient ischaemic attacks). Results: Mean follow‐up was 3.5 ± 3.0 yr (0.5–12 yr). No cases of stroke occurred in the PPG. In the SPG, one patient with a history of stroke and severe cerebrovascular disease had a recurrence after 11 yr of chronic transfusion, when the HbS level was 20%. The stroke recurrence rate (SPG group) was 1.6/100 patient‐years. Mean HbS levels before and after transfusion were 30 ± 10% and 20.6 ± 7%, respectively. Two patients acquired red‐cell alloantibodies. Of the 29 patients, 22 required iron chelation. Conclusions: Regular transfusion maintaining HbS below 30% is feasible and safe in children with SCD in France and protects from overt stroke.     

Randomized control trial of oral arginine therapy for children with sickle cell anemia hospitalized for pain in Nigeria

Low arginine bioavailability is associated with vaso‐occlusive painful crisis (VOC) severity in sickle cell anemia (SCA) and predicts need for pediatric hospitalization. Intravenous arginine therapy has opioid‐sparing effects and was found to significantly decrease pain scores in children hospitalized with SCA‐VOC in a phase‐two randomized placebo‐controlled trial (RCT). Efficacy of oral arginine is unknown. Our objective was to determine the safety and efficacy of oral arginine therapy in Nigerian children with SCA. A double‐blind RCT of oral L‐arginine‐hydrochloride (100 mg/kg TID) was conducted in children with SCA‐VOC, aged 5‐17 years, hospitalized at two Nigerian sites. The primary outcome measure was analgesic usage, quantified by difference in the mean Analgesic Medication Quantification Scale (MQS). Secondary outcomes included daily pain scores, time‐to‐crisis‐resolution and length‐of‐hospital‐stay. An intention‐to‐treat analysis was performed. Sixty‐eight children (age 5‐17 years, mean 10.6 ± 0.4 years; 56% male), were randomized to receive L‐arginine (35 patients) or placebo (33 patients). The mean total MQS for the arginine group was 73.4 (95% CI, 62.4‐84.3) vs 120.0 (96.7‐143.3) for placebo (P < .001). The mean rate of decline in worst pain scores was faster in the arginine arm vs placebo (1.50 [1.23‐1.77] vs 1.09 [0.94‐1.24] point/d, P = .009). Children receiving arginine had a shorter time‐to‐crisis‐resolution (P = .02), shorter hospital‐stay (P = .002) and experienced no serious adverse event. Pain control was more rapid, total analgesic requirement was significantly reduced, and most notably, time‐to‐crisis‐resolution and length‐of‐hospital‐stay were shorter in children with SCA‐VOC receiving arginine vs placebo. Given the established safety and low cost, oral arginine is a promising adjuvant therapy for SCA‐VOC management.     

Gene interactions and stroke risk in children with sickle cell anemia

Stroke is a devastating complication of sickle cell anemia (SCA), affecting up to 30% of children with the disease. Despite the relative frequency of stroke in SCA, few predictors of risk exist. Because stroke in SCA is likely a multifactorial disease, analysis of the combined effect of multiple genetic variants may prove more successful than evaluation of individual candidate genes. We genotyped 230 children with SCA for 104 polymorphisms among 65 candidate vascular genes to identify risk associations with stroke. Patients were phenotyped based on magnetic resonance imaging/angiography (MRI/MRA) findings into large-vessel (LV) versus small-vessel (SV) disease stroke subgroups. Specific polymorphisms in the IL4R 503, TNF (-308), and ADRB2 27 genes were independently associated with stroke susceptibility in the LV stroke subgroup, while variants in the VCAM1 (-1594) and LDLR NcoI genes were associated with SV stroke risk. The combination of TNF (-308)GG homozygosity and the IL4R 503P variant carrier status was associated with a particularly strong predisposition to LV stroke (odds ratio [OR] = 5.5; 95% confidence interval [CI] = 2.3-13.1). We show that several candidate genes may play a role in predisposition to specific stroke subtypes in children with SCA. If confirmed, these results provide a basis for population screening and targeted intervention to prevent stroke in SCA.     

Distinct HLA associations by stroke subtype in children with sickle cell anemia

Children with sickle cell anemia (SCA) carry a 200-fold increased risk for cerebral infarction. Stroke can be the result of small-vessel (SV) or large-vessel (LV) disease. However, it is unknown whether these subtypes result from the same pathophysiologic processes. Complete HLA genotyping was performed on 231 eligible children previously enrolled in the Cooperative Study of Sickle Cell Disease (CSSCD). Cerebral infarction on magnetic resonance imaging (MRI) was documented in 71 patients, and 160 patients had negative findings on MRI. Based on MRI/magnetic resonance angiography (MRA) findings, infarct size, and location, 36 patients were classified as having LV stroke and 35 as having SV stroke. When comparing the total MRI+ group with the MRI- group, HLA DPB1*0401 was associated with increased stroke risk (P =.01), whereas DPB1*1701 (P =.02) conferred protection from stroke. These DPB1 associations with stroke were attributed to the SV stroke group, in whom DPB1*0401 was associated with susceptibility (P =.003) and DPB1*1701 with protection from stroke (P =.06). In the LV stroke subgroup, HLA-A*0102 (P =.02) and -A*2612 (P =.007) conferred susceptibility, whereas -A*3301(P =.04) protected from stroke. These results suggest that specific HLA alleles influence stroke risk and appear to contribute differently to SV and LV stroke subtypes. The distinct HLA associations with SV and LV stroke suggest that different pathologic processes may be involved in the development of stroke in children with SCA. If these results are confirmed in a larger study, HLA type may serve as a useful marker for the early identification of SCA patients at high risk for stroke.     

Cardiac abnormalities in children with sickle cell anemia

Sickle cell anemia (SCA) results in chronic volume overload of the heart due to hemodilution. Previous echocardiographic studies of cardiac function in children with SCA have not accounted for these abnormal loading conditions. The objectives of this study were to (1) determine how the degree of anemia and transfusion status relate to cardiac findings and (2) evaluate cardiac function using load-independent parameters of function. We evaluated 77 patients with SCA, ages 2 to 22 years (mean +/- SD = 11.7 +/- 4.7), using physical examination, electrocardiography, and echocardiography. We compared two groups of patients. Group 1 consisted of 57 non-transfused patients, and Group 2 consisted of 20 patients on a chronic transfusion protocol. Group 1 patients exhibited a significantly lower hemoglobin, higher cardiac output, and larger left ventricular (LV) end-diastolic dimension and LV mass than groups 2 (P < 0.05). However, the velocity of circumferential fiber shortening-wall stress index (a load-independent measure of systolic function) was normal and not statistically different between the two groups. Conversely, the LV myocardial performance index (a measure of combined systolic and diastolic function) was significantly higher in Group 2 (P < 0.001), possibly indicating impaired myocardial diastolic function. SCA in children results in a volume-overloaded heart with a significant increase in LV dimensions and mass, both proportional to the degree of anemia. Despite these abnormal loading conditions, systolic function is preserved. Patients on a chronic transfusion protocol may develop diastolic dysfunction despite iron chelation therapy.     

Cardiac abnormalities in children with sickle cell anemia

The cardiac status of 64 children (ages 0.2 to 18 yr) with sickle cell anemia documented by hemoglobin electrophoresis was evaluated by echocardiography. Left atrial, left ventricular and aortic root dimensions were significantly increased in over 60 percent of these children at all ages compared to values for 99 normal black (non-SCA) control subjects. Left ventricular wall thickness was increased in only 20 percent of older children with sickle cell anemia. Estimated LV mass/m2 and left ventricular cardiac index were increased compared to control subjects (p less than 0.001). Left heart abnormalities expressed as a single composite function, derived from multivariate regression analysis, correlated well with severity of anemia expressed as grams of hemoglobin (r = -0.52, p = less than 0.001) and with percentage of hemoglobin S (r = 0.51, p less than 0.001), but not to the same extent with age. Echocardiographically assessed left ventricular function at rest was comparable to that of control subjects. These data suggest that the major cardiac abnormalities in children are related to the volume overload effects of chronic anemia, and that in this age group, there is no evidence for a distinct "sickle cell cardiomyopathy" or cardiac dysfunction.     

Lung function in children with sickle cell anemia.

Lung volumes and expiratory flows were measured in 12 children with sickle cell anemia and 12 height-matched black control subjects. Diffusing capacity of the lung for CO, pulmonary capillary blood volume, the membrane component of diffusing capacity, arterial blood gases on breathing room air and 100 per cent O2 were measured in the subjects with sickle cell anemia. The lung volumes and expiratory flows of subjects with sickle cell anemia were no different from those of the control subjects. Diffusing capacity for CO was maintined in the noraml range despite the severe anemia by increases in pulmonary capillary blood volume and the membrane component of diffusing capacity. All subjects with sickle cell anemia had mild hypoxemia and abnormal increases in calculated shunt. Pulmonary function in children with sickle cell anemia appears to be determined by their race and anemia.     

Alpha thalassemia and stroke risk in sickle cell anemia

In an effort to identify possible risk factors for stroke in Sickle Cell Anemia (Hb SS), we analyzed the distribution of alpha-globin gene deletions in a group of Hb SS patients with and without stroke. The group with stroke consisted of 44 patients, (27 male, 17 female) with a mean of 7.5 years at time of stroke. The control group (non-stroke) had 256 Hb SS patients (126 male, 130 female) with a mean age of 7.7 years. There were 9 patients with heterozygous α-thalassemia in the stroke group (20.5%). In the control group, there were 93 patients with heterozygous α-thalassemia and 5 with homozygous α-thalassemia. The incidence of α-thalassemia in Hb SS patients without stroke (38%) was comparable to that reported for the African-American population in general. The incidence in the stroke population (20.5%) was significantly lower (P = 0.02) These results indicate that α-thalassemia is associated with a lower risk of stroke in Hb SS. This observation should be confirmed in studies involving larger numbers of patients. Possible protective effects of α-thaiassemia are unknown but may be related to decreased hemolysis and more favorable rheologlc properties of red blood cells. © 1994 Wiley-Liss, Inc.     

Defining stroke risk in children with sickle cell anaemia

Sickle cell anaemia (SCA) is the most common cause of childhood stroke, occurring with the highest frequency before the age of 6 years. Despite the relative frequency of stroke in SCA, few predictors of risk exist. Anaemia, leucocytosis, hypertension, silent infarction, and history of acute chest syndrome are well-documented risk factors for ischaemic stroke in SCA. Recent data suggest that other environmental and genetic factors, many unrelated to SCA, influence the development of cerebrovascular disease. Non-invasive assessment of individual stroke risk using transcranial Doppler ultrasonography has provided a means of selecting and prophylactically treating SCA children at highest risk. With the ultimate goal of preventing stroke, the information gained from the studies reviewed here may lead to improved prediction of stroke so that clinical trials to assess risk-based therapy may be carried out on selected children with SCA.     

Growth of lung function in children with sickle cell anemia

Lung disease is a common cause of morbidity among children with sickle cell disease (SCD). Although cross-sectional studies of children with SCD describe abnormal pulmonary function, the pattern of lung function growth in these children compared to children in the general population is not known. To provide preliminary evidence that growth of lung function is attenuated in children with SCD, we conducted a retrospective cohort study of children with hemoglobin SS (HbSS) ages 6-19 years who received at least two spirometry assessments for clinical care. The growth of lung function in these cases was compared to age, gender, and race-specific children without SCD or respiratory complaints from the Harvard Six Cities Study (H6CS). Seventy-nine children with HbSS contributed 363 spirometry measurements (mean per child = 4.6, median = 4.0, range = 2-17) and 255 controls contributed 1,543 spirometry measurements (mean per child = 6.1, median = 6.0, range = 2-13). Longitudinal forced expiratory volume in 1 sec (FEV(1)) was lower for boys and girls with HbSS compared to children in the general population, P = 0.031 and P = 0.002, respectively. When compared to the H6CS cohort, girls with HbSS showed lower longitudinal forced vital capacity (FVC) (P < 0.001) and FEV(1)/FVC (0.038); there was no difference in FVC or FEV(1)/FVC between boys in the HbSS and H6CS cohort. We conclude that growth of lung function is reduced in children with HbSS compared to children in the general population. Gender may influence the risk of developing abnormal lung function and airway obstruction in children with HbSS.     

Evidence for HLA-related susceptibility for stroke in children with sickle cell disease

Cerebral infarction occurs in one quarter of all children with sickle cell anemia (SCA). There is an increased risk of stroke in siblings with SCA, suggesting genetic factors may influence risk of stroke. The authors investigated whether HLA type was associated with risk of stroke in children with SCA. Fifty-three patients with SCA underwent complete HLA typing at both HLA class I (HLA-A, B) and HLA class II (HLA-DR, DQ, DP) loci. Of the 53 patients, 22 had magnetic resonance imagining (MRI)-documented evidence of cerebral infarction, and the remaining 31 patients had negative MRI scans. Comparison of the results of HLA typing between the SCA patients with a positive and those with a negative MRI documented that the 2 groups differed with respect to the class I HLA-B (P =.012), and the class II HLA-DRB1 (P =.0008) and DQB1 (P =.029). Susceptibility associations at the HLA-DRB1 locus included both DR3 alleles, where DRB1*0301 and *0302 were both associated with an increased risk of stroke. Protective associations were found in the DR2 group, where DRB1*1501 was protective for stroke. DQB1*0201, which is in linkage disequilibrium with DRB1*0301, was also associated with stroke. Similarly, DQB1*0602, in linkage disequilibrium with DRB1*1501, was protective. Specific HLA alleles may influence the risk of stroke in children with SCA. HLA typing may prove useful in identifying SCA patients at higher risk for stroke.