Pathophysiology and treatment of stroke in sickle-cell disease: present and future

Sickle cell detection using a smartphone

Sickle cell disease affects 25% of people living in Central and West Africa and, if left undiagnosed, can cause life threatening "silent" strokes and lifelong damage. However, ubiquitous testing procedures have yet to be implemented in these areas, necessitating a simple, rapid, and accurate testing platform to diagnose sickle cell disease. Here, we present a label-free, sensitive, and specific testing platform using only a small blood sample (<1 μl) based on the higher density of sickle red blood cells under deoxygenated conditions. Testing is performed with a lightweight and compact 3D-printed attachment installed on a commercial smartphone. This attachment includes an LED to illuminate the sample, an optical lens to magnify the image, and two permanent magnets for magnetic levitation of red blood cells. The sample is suspended in a paramagnetic medium with sodium metabisulfite and loaded in a microcapillary tube that is inserted between the magnets. Red blood cells are levitated in the magnetic field based on equilibrium between the magnetic and buoyancy forces acting on the cells. Using this approach, we were able to distinguish between the levitation patterns of sickle versus control red blood cells based on their degree of confinement.

Brain venular pattern by 7T MRI correlates with memory and haemoglobin in sickle cell anaemia

Sickle cell anaemia (SCA) is a hereditary hemoglobinopathy characterised by extensive vascular dysfunction that stems from inflammation, thrombosis and occlusion of post-capillary venules. Cognitive impairment is a neurological complication of SCA whose pathogenesis is unknown. We hypothesised that cerebral venular abnormalities are linked to cognitive impairment in SCA. Thus, we employed 7T magnetic resonance imaging (MRI) to examine the association between venular density and cognitive function in homozygous SCA. We quantified the density of total, long, and short venules in pre-defined regions of interest between the frontal and occipital cornu on each hemisphere. Cognitive function was assessed using the Hopkins Verbal Learning Test - Revised (HVLT-R) test of learning and memory. Patients (n=11) were compared with race, age and gender-equated controls (n=7). Compared to controls, patients had an overall venular rarefaction, with significantly lower density of long venules and greater density of short venules which was inversely related to HVLT-R performance and haemoglobin. To our knowledge, this is the first 7T MRI study in SCA and first report of associations between cerebral venular patterns and cognitive performance and haemoglobin. Future studies should examine whether these novel neuroimaging markers predict cognitive impairment longitudinally and are mechanistically linked to severity of anaemia.

First Ischemic Stroke in Sickle-Cell Disease: Are There Any Adult Specificities?

BACKGROUND AND PURPOSE

There is little evidence about characteristics of ischemic stroke (IS) occurring in adults with sickle-cell disease (SCD). The objective of this study was to assess characteristics of first-ever IS in adults with SCD and to assess whether they differ from those occurring in child patients with SCD.

METHODS

Adult and child individuals with SCD who had a first-ever IS were identified from cohorts of patients followed up in an adult and a child sickle cell referral center. Mechanisms of IS were determined by consensus meeting from all available explorations using the following predefined classification: Vasculopathy, cardioembolism, other defined cause, and undetermined. Treatment and stroke recurrences were recorded from prospective follow-up performed in the referral centers.

RESULTS

Twenty-nine adults and 26 children had a first-ever IS; mean age (SD) was 7.1 (4.3) and 32.3 (11.6), respectively. With regard to IS mechanism, vasculopathy was less often the cause of IS in adults (12/29, 41%) than in children (24/26, 92%; P<0.001). Other causes of IS in adults were cardioembolism in 7, antiphospholipid syndrome in 1, toxic (cocaine) in 1, and undetermined in 8. Adults with SCD had a higher risk of recurrent stroke (23.1% [7.0-39.2] at 5 years) compared with children (1 recurrence only; P log rank=0.046) despite exchange-blood transfusion in patients with vasculopathy.

CONCLUSIONS

First-ever IS occurring in adults with SCD has specificities that justify further studies conducted in adults with SCD to improve understanding and management.

Microfluidic study of enhanced deposition of sickle cells at acute corners

Sickle cell anemia is a blood disorder, known to affect the microcirculation and is characterized by painful vaso-occlusive crises in deep tissues. During the last three decades, many scenarios based on the enhanced adhesive properties of the membrane of sickle red blood cells have been proposed, all related to a final decrease in vessels lumen by cells accumulation on the vascular walls. Up to now, none of these scenarios considered the possible role played by the geometry of the flow on deposition. The question of the exact locations of occlusive events at the microcirculatory scale remains open. Here, using microfluidic devices where both geometry and oxygen levels can be controlled, we show that the flow of a suspension of sickle red blood cells around an acute corner of a triangular pillar or of a bifurcation, leads to the enhanced deposition and aggregation of cells. Thanks to our devices, we follow the growth of these aggregates in time and show that their length does not depend on oxygenation levels; instead, we find that their morphology changes dramatically to filamentous structures when using autologous plasma as a suspending fluid. We finally discuss the possible role played by such aggregates in vaso-occlusive events.

Changes in cerebral blood flow in children with sickle cell disease after splenectomy

The study assessed changes in cerebral blood flow and need for chronic blood transfusions in sickle cell disease children after splenectomy. A retrospective chart review of 40 children splenectomized between 1999 and 2014 was performed. The mean time-average maximum velocity before splenectomy was 129 cm/sec; which increased to 157 cm/sec and then decreased to 137 cm/sec, 2 and 5 years postsplenectomy, respectively. There was a persistent and statistically significant elevation in platelet count noted after splenectomy. The mean cerebral blood flow velocity seemed to increase transiently after splenectomy. Close monitoring and screening for stroke risk should be continued postsplenectomy.

Hematopoietic stem cell transplantation in thalassemia major and sickle cell disease: indications and management recommendations from an international expert panel

Thalassemia major and sickle cell disease are the two most widely disseminated hereditary hemoglobinopathies in the world. The outlook for affected individuals has improved in recent years due to advances in medical management in the prevention and treatment of complications. However, hematopoietic stem cell transplantation is still the only available curative option. The use of hematopoietic stem cell transplantation has been increasing, and outcomes today have substantially improved compared with the past three decades. Current experience world-wide is that more than 90% of patients now survive hematopoietic stem cell transplantation and disease-free survival is around 80%. However, only a few controlled trials have been reported, and decisions on patient selection for hematopoietic stem cell transplantation and transplant management remain principally dependent on data from retrospective analyses and on the clinical experience of the transplant centers. This consensus document from the European Blood and Marrow Transplantation Inborn Error Working Party and the Paediatric Diseases Working Party aims to report new data and provide consensus-based recommendations on indications for hematopoietic stem cell transplantation and transplant management.

Sensory and Thermal Quantitative Testing in Children With Sickle Cell Disease

Very little is known about pain processing in sickle cell disease (SCD). We examined the mechanical and thermal sensory patterns in children with SCD. Children ages 10 to 17 years (n = 48; mean 13.7 ± 2.0 y; 22 females) participated in quantitative sensory testing (QST) procedures and completed a quality of life (PedsQL) and anxiety and depression scale (RCADS). Thirteen children showed evidence of abnormal pain processing, indicated by decreased sensitivity to heat or cold sensations (hypoesthesia), and pain experienced with nonpainful stimuli (allodynia). Pain ratings associated with cold and warm sensations were significantly higher in the subgroup with abnormal QST compared with the 35 SCD children with normal QST (P = 0.01 and P < 0.0001, respectively). The presence of hypoesthesia and allodynia in children with SCD may represent abnormal changes in the peripheral and central nervous system. Clinicians need to be aware that sickle cell pain may not only be inflammatory or ischemic secondary to vasoocclusion and hypoxia, but may also be neuropathic secondary to nerve injury or nerve dysfunction. Neuropathic pain in SCD may be the result of tissue damage after vaso-occlusion in neural tissues, whether peripherally or centrally. Future studies are needed to determine the presence of neuropathic pain in children with SCD.

Transfusional iron overload and iron chelation therapy in thalassemia major and sickle cell disease

Iron overload is an inevitable consequence of blood transfusions and is often accompanied by increased iron absorption from the gut. Chelation therapy is necessary to prevent the consequences of hemosiderosis. Three chelators, deferoxamine, deferiprone, and deferasirox, are presently available and a fourth is undergoing clinical trials. The efficacy of all 3 available chelators has been demonstrated. Also, many studies have shown the efficacy of the combination of deferoxamine plus deferiprone as an intensive treatment of severe iron overload. Alternating chelators can reduce adverse effects and improve compliance. Adherence to therapy is crucial for good results.

Moyamoya disease and syndromes: from genetics to clinical management

Moyamoya angiopathy is characterized by a progressive stenosis of the terminal portion of the internal carotid arteries and the development of a network of abnormal collateral vessels. This chronic cerebral angiopathy is observed in children and adults. It mainly leads to brain ischemic events in children, and to ischemic and hemorrhagic events in adults. This is a rare condition, with a marked prevalence gradient between Asian countries and Western countries. Two main nosological entities are identified. On the one hand, moyamoya disease corresponds to isolated moyamoya angiopathy, defined as being “idiopathic” according to the Guidelines of the Research Committee on the Pathology and Treatment of Spontaneous Occlusion of the Circle of Willis. This entity is probably multifactorial and polygenic in most patients. On the other hand, moyamoya syndrome is a moyamoya angiopathy associated with an underlying condition and forms a very heterogeneous group with various clinical presentations, various modes of inheritance, and a variable penetrance of the cerebrovascular phenotype. Diagnostic and evaluation techniques rely on magnetic resonance imaging (MRI), magnetic resonance angiography (MRA) conventional angiography, and cerebral hemodynamics measurements. Revascularization surgery can be indicated, with several techniques. Characteristics of genetic moyamoya syndromes are presented, with a focus on recently reported mutations in BRCC3/MTCP1 and GUCY1A3 genes. Identification of the genes involved in moyamoya disease and several monogenic moyamoya syndromes unraveled different pathways involved in the development of this angiopathy. Studying genes and pathways involved in monogenic moyamoya syndromes may help to give insights into pathophysiological models and discover potential candidates for medical treatment strategies.

The current state of imaging pediatric hemoglobinopathies

The hemoglobinopathies are a group of genetic disorders with a broad spectrum of clinical manifestations and radiologic findings. The imaging of pediatric hemoglobinopathies, which is influenced by concomitant hemosiderosis and the sequela of chelation therapy, has evolved over the years along with ever-improving technology. This article reviews and illustrates the most common radiographic and cross-sectional imaging findings of the 2 best known and clinically relevant hemoglobinopathies in pediatric patients, sickle cell disease and β-thalassemia.

Current concepts and clinical applications of stroke genetics

Driven by innovative technologies, novel analytical methods, and collaborations unimaginable not long ago, our understanding of the role of genetic variation in stroke has advanced substantially in recent years. However, a vast amount of data have accumulated quickly, and increasingly complex methodologies used in studies make keeping up to date on relevant findings difficult. In addition to well known, highly penetrant rare mutations that cause mendelian disorders related to stroke, several common genetic variants have been associated with common stroke subtypes, some of which also affect disease severity and clinical outcome. Furthermore, common genetic variations in biological pathways that have an important role in the pathophysiology of cerebrovascular diseases-such as blood pressure and oxidative phosphorylation-have been implicated in stroke. Clinical and translational applications of these and future discoveries in stroke genetics include identification of novel targets for treatment and development of personalised approaches to stroke prevention and management.

Atherogenesis and iron: from epidemiology to cellular level

Iron accumulates in human atherosclerotic lesions but whether it is a cause or simply a downstream consequence of the atheroma formation has been an open question for decades. According to the so called "iron hypothesis," iron is believed to be detrimental for the cardiovascular system, thus promoting atherosclerosis development and progression. Iron, in its catalytically active form, can participate in the generation of reactive oxygen species and induce lipid-peroxidation, triggering endothelial activation, smooth muscle cell proliferation and macrophage activation; all of these processes are considered to be proatherogenic. On the other hand, the observation that hemochromatotic patients, affected by life-long iron overload, do not show any increased incidence of atherosclerosis is perceived as the most convincing evidence against the "iron hypothesis." Epidemiological studies and data from animal models provided conflicting evidences about the role of iron in atherogenesis. Therefore, more careful studies are needed in which issues like the source and the compartmentalization of iron will be addressed. This review article summarizes what we have learnt about iron and atherosclerosis from epidemiological studies, animal models and cellular systems and highlights the rather contributory than innocent role of iron in atherogenesis.

Extracranial carotid arteriopathy in stroke-free children with sickle cell anemia: detection by submandibular Doppler sonography

BACKGROUND

Cerebral vasculopathy is a serious complication of sickle cell anemia. Overt strokes are largely due to intracranial arteriopathy, detected by routine transcranial Doppler and largely prevented through chronic transfusions. As extracranial internal carotid artery arteriopathy was considered rare, it has not been routinely assessed in sickle cell anemia. Recent cases of overt strokes associated with stenosis/occlusion of the extracranial portion of the internal carotid artery prompted us to include extracranial internal carotid artery assessment to our transcranial Doppler sonography protocol.

OBJECTIVE

The aim of the study was to perform a cross-sectional study in children with sickle cell anemia to evaluate Doppler flow patterns of the extracranial internal carotid arteries and to assess potential associated factors.

MATERIALS AND METHODS

Between June 2011 and April 2012, 435 consecutive stroke-free children with sickle cell anemia (200/235 M/F, median age: 7.9 years) were assessed for extracranial internal carotid artery using a 2-MHz transcranial Doppler sonography probe via a submandibular window during routine transcranial Doppler sonography visits. The course of both extracranial internal carotid artery was assessed by color Doppler mapping, and the highest flow velocity was recorded after insonation of the entire length of the artery and analyzed. Intra- and extracranial MR angiographies were available in 104/435 subjects for comparison.

RESULTS

Mean (SD) extracranial internal carotid artery time-averaged mean of maximum velocity was 96 (40) cm/s. Extracranial internal carotid artery tortuosities were echo-detected in 25% cases and were more frequent in boys (33% vs.18%; P < 0.001). Velocity ≥160 cm/s in at least one extracranial internal carotid artery was found in 45 out of 435 patients with sickle cell anemia (10.3%) and was highly predictive of MR angiography stenosis. Simultaneous abnormal intracranial velocity (≥200 cm/s) was recorded in 5/45 patients, while 40 patients had isolated extracranial internal carotid artery velocity ≥160 cm/s. Low hemoglobin (odds ratio: 1.9/g/dL, 95% confidence interval (CI): 1.3-2.9; P = 0.001) and tortuosities (odds ratio: 19.2, 95% CI: 7.1-52.6; P < 0.001) were significant and independent associated factors for isolated extracranial internal carotid artery velocities ≥160 cm/s.

CONCLUSION

Adding extracranial internal carotid artery evaluation via the submandibular window to transcranial Doppler sonograpy allowed us to detect 10.3% patients at risk for extracranial internal carotid arteriopathy. Further studies are needed to evaluate the prognosis of these anomalies.

Cerebrovascular complications in children with sickle cell disease

Cerebrovascular accidents were until recently responsible for much mortality and morbidity in children with sickle cell disease; the likelihood of a child with HbSS having a stroke was 11% before age 20 years, with a peak incidence of ischemic stroke between 2 and 5 years of age, and of hemorrhagic strokes between 20 and 29 years of age. Vessels occlusion is likely initiated by intimal proliferation and amplified by inflammation, excessive adhesion of cells to activated endothelium, hypercoagulable state, and vascular tone dysregulation. Silent infarcts may occur and are associated with decreased cognitive functions. Transcranial Doppler ultrasonography (TCD) was more recently demonstrated able to achieve early detection of the children at high risk for clinical strokes. A randomized study demonstrated that a first stroke may be prevented by monthly transfusion in children with abnormal TCD, leading to a recommendation for annual TCD screening of children aged between 2 and 16 years and monthly transfusion for those with abnormal results. In children who have had a first stroke, the risk of recurrence is more than 50% and is greatly reduced by chronic transfusion, although not completely abolished. Hematopoietic stem cell transplant is indicated in children with cerebral vasculopathy who have an HLA-identical sibling.

Sickle cell disease and posterior reversible leukoencephalopathy

Sickle cell disease can present with neurological manifestations. One such presentation is with posterior reversible leukoencephalopathy also known as reversible posterior leukoencephalopathy. The condition is classically described as reversible over time; it commonly presents with oedematous changes involving the white matter of the occipital and parietal regions. Only a few patients with the association between sickle cell disease and posterior reversible leukoencephalopathy have been described in the adult literature. We present two patients from our institutions to emphasise the association between the two conditions and summarise the published cases in the literature.

Profound morphological changes in the erythrocytes and fibrin networks of patients with hemochromatosis or with hyperferritinemia, and their normalization by iron chelators and other agents

It is well-known that individuals with increased iron levels are more prone to thrombotic diseases, mainly due to the presence of unliganded iron, and thereby the increased production of hydroxyl radicals. It is also known that erythrocytes (RBCs) may play an important role during thrombotic events. Therefore the purpose of the current study was to assess whether RBCs had an altered morphology in individuals with hereditary hemochromatosis (HH), as well as some who displayed hyperferritinemia (HF). Using scanning electron microscopy, we also assessed means by which the RBC and fibrin morphology might be normalized. An important objective was to test the hypothesis that the altered RBC morphology was due to the presence of excess unliganded iron by removing it through chelation. Very striking differences were observed, in that the erythrocytes from HH and HF individuals were distorted and had a much greater axial ratio compared to that accompanying the discoid appearance seen in the normal samples. The response to thrombin, and the appearance of a platelet-rich plasma smear, were also markedly different. These differences could largely be reversed by the iron chelator desferal and to some degree by the iron chelator clioquinol, or by the free radical trapping agents salicylate or selenite (that may themselves also be iron chelators). These findings are consistent with the view that the aberrant morphology of the HH and HF erythrocytes is caused, at least in part, by unliganded (‘free’) iron, whether derived directly via raised ferritin levels or otherwise, and that lowering it or affecting the consequences of its action may be of therapeutic benefit. The findings also bear on the question of the extent to which accepting blood donations from HH individuals may be desirable or otherwise.

Genetics of ischaemic stroke

Recent advances in genomics and statistical computation have allowed us to begin addressing the genetic basis of stroke at a molecular level. These advances are at the cusp of making important changes to clinical practice of some monogenic forms of stroke and, in the future, are likely to revolutionise the care provided to these patients. In this review we summarise the state of knowledge in ischaemic stroke genetics particularly in the context of how a practicing clinician can best use this knowledge.

Stroke with intracranial stenosis is associated with increased platelet activation in sickle cell anemia

BACKGROUND

Overt stroke in sickle cell anemia (SCA) is associated with intracranial stenosis and thrombus formation. Platelet activation is critical for thrombus formation.

PROCEDURE

Platelet activation studies were performed in 50 subjects: 18 SCA patients with history of stroke or abnormal transcranial Doppler (TCD) and intracranial stenosis seen by magnetic resonance angiogram (MRA), 7 SCA patients with history of stroke or abnormal TCD but no intracranial stenosis, 13 SCA patients with no history of stroke or abnormal TCD, and 12 healthy African-Americans.

RESULTS

Of the 18 patients with intracranial stenosis, 11 (61%) had evidence of the moyo-moya phenomenon on MRA. SCA children with intracranial stenosis had a significantly greater total white cell count compared to both healthy African-American controls and SCA patients in the steady-state (P < 0.001). In addition, SCA patients with history of stroke or abnormal TCD had a significantly higher platelet count compared to healthy African-American controls (P < 0.002). The percentage of platelet surface P-selectin expression was significantly greater in patients with intracranial stenosis compared to the other groups (P < 0.05), particularly in individuals that did not have the moya-moya phenomenon seen on MRA.

CONCLUSION

Stroke with intracranial stenosis is associated with increased platelet activation in sickle cell anemia, and further investigation is needed on the role of anti-platelet agents in this high-risk population.

Stroke in sickle cell anemia patients: a need for multidisciplinary approaches

Sickle cell anemia (SCA) is an autosomal recessive disorder, with Mendelian inheritance pattern, caused by a missense mutation in the β-polypeptide chain of the hemoglobin B. SCA preferentially affects populations in countries where malaria was/is present (e.g. Africa, USA, Brazil). Thereby, in USA, the incidence of SCA is relatively high, around 1/500, and the prevalence is about 1/1000. In Brazil, SCA represents a major public health problem with an incidence ranging from 1/2000 to 1/600 depending on the regions. Homozygotic patients present more severe medical conditions and reduced life expectancy than heterozygous individuals who generally are asymptomatic. Eventually, this life-threatening disease displays a complex etiology owing to heterogeneous phenotypes and clinical outcomes, subsequently affecting the management of the patients. One of the most critical complications associated with SCA is stroke, a leading neurologic cause of death and disability. About 24% of SCA patients have a stroke by the age of 45 and 11% by the age of 20. From the general population, twin and familial aggregation studies as well as genome-wide association studies (GWAS), mostly in pediatric populations with ischemic stroke, showed that the risk of stroke has a substantial genetic component. Nevertheless, to fully characterize genomic contributors of stroke and permit reliable personalized medicine, multidisciplinary studies incorporating knowledge from clinical medicine, epidemiology, genetics, and molecular biology, are required. In this manuscript, stroke in SCA patients is extensively reviewed with emphasis to the US and Brazilian populations. Recent advances in genomics analysis of stroke in SCA patients are highlighted.

Doppler ultrasound velocimetry of middle cerebral arteries of patients with sickle cell disease at Aminu Kano Teaching Hospital: a preliminary report

Transcranial Doppler ultrasound scan is a noninvasive method of evaluating the major intracranial vessels. It is becoming an important screening tool for predicting high-risk sickle cell patients for developing cerebrovascular disease. This study evaluates the patients' characteristics, common indications, and findings on Doppler ultrasound of the middle cerebral arteries of sickle cell patients performed at Aminu Kano Teaching Hospital, Kano, Nigeria.This is a preliminary report of an ongoing review of the transcranial Doppler scans done at Aminu Kano Teaching Hospital. The records of all patients, the indications for Doppler examination, and major findings on the middle cerebral arteries were documented.There are 60 patients, consisting of 22 males and 38 females. Their ages ranged from 1.0 to 41.0 years, with mean of 11.58 ± 7.30 years. About a third of the patients were asymptomatic (38.3%). Those with headache constituted 20.0%, whereas those with past cerebral syndrome constituted 8.3%. Other indications include stroke (11.67%) and transient ischemic attack (3.3%).The mean peak systolic velocity of the middle cerebral artery measured 204.8 cm/s (±80 cm/s) and 208.8 (±79 cm/s) on the respective right and left side. This right-to-left difference was statistically significant (P = 0.046). Symptomatic and female patients showed higher mean peak systolic velocity values when compared with males, although the difference was not statistically significant.

Characteristics of sickle cell anemia in Yemen

We studied 136 males and 105 females with sickle cell anemia to determine the characteristics of the disease in Yemen. Their mean age [± SD (standard deviation)] was 12.8 ± 9.5 years (range: 9 months-40 years). Taiz, Hudaydah and Hajjah governorates, in the South-Central and the Northwestern provinces, showed the highest prevalence. Eighty percent of the patients had family history of the disease, 73.0% patients had history of parental consanguinity and 20.7% of death of relative(s) due to the disease; 5.4% patients were older than 30 years of age. Pain, jaundice and infection were the most frequent features. Splenomegaly, cholelithiasis, osteomyelitis, acute chest syndrome (ACS), osteonecrosis and stroke occurred in 12.0, 9.5, 8.7, 6.6, 6.6 and 2.9%, respectively. Priapism and leg ulcers were rare. The mean laboratory values (obtained in the steady state) were: hemoglobin (Hb) 7.9 g/dL, WBC 14.08 × 10(9)/L, platelet 460 × 10(9)/L, reticulocytes 14.5%, lactate dehydrogenase (LDH) 597 U/L, Hb F (α2γ2) 16.69%, Hb S [β6(A3)Glu→Val, GAG>GTG] 77.31% and Hb A(2) (α2δ2) 1.47%, respectively. There was no significant difference between South-Central and Northwestern provinces regarding clinical events and hematological parameters.

To SWiTCH or not to SWiTCH?

In this issue of Blood, Ware and Helms report results from the Stroke With Transfusions Changing To Hydroxyurea (SWiTCH) study designed to determine whether hydroxyurea is as effective as transfusions in preventing recurrent strokes in children with sickle cell anemia. The finding of strokes in 7 of 67 children receiving hydroxyurea but none in 66 children who received transfusions led the authors to conclude that hydroxyurea is not effective in mitigating strokes.1

Sickle cell disease activates peripheral blood mononuclear cells to induce cathepsins k and v activity in endothelial cells

Sickle cell disease is a genetic disease that increases systemic inflammation as well as the risk of pediatric strokes, but links between sickle-induced inflammation and arterial remodeling are not clear. Cathepsins are powerful elastases and collagenases secreted by endothelial cells and monocyte-derived macrophages in atherosclerosis, but their involvement in sickle cell disease has not been studied. Here, we investigated how tumor necrosis alpha (TNFα) and circulating mononuclear cell adhesion to human aortic endothelial cells (ECs) increase active cathepsins K and V as a model of inflammation occurring in the arterial wall. ECs were stimulated with TNFα and cultured with peripheral blood mononuclear cells (PBMCs) from persons homozygous for sickle (SS) or normal (AA) hemoglobin. TNFα was necessary to induce cathepsin K activity, but either PBMC binding or TNFα increased cathepsin V activity. SS PBMCs were unique; they induced cathepsin K in ECs without exogenous TNFα (n = 4, P < 0.05). Inhibition of c-Jun N-terminal kinase (JNK) significantly reduced cathepsins K and V activation by 60% and 51%, respectively. Together, the inflammation and activated circulating mononuclear cells upregulate cathepsin activity through JNK signaling, identifying new pharmaceutical targets to block the accelerated pathology observed in arteries of children with sickle cell disease.

Brain magnetic resonance angiography in splenectomized adults with β-thalassemia intermedia

BACKGROUND

 Hypercoagulability and venous thromboembolism are common in patients with β-thalassemia intermedia (TI), especially in the splenectomized adult. Although arterial involvement is not commonly reported, we have recently observed a high prevalence (60%) of silent brain infarction on brain MRI in 30 splenectomized adults with TI. The pathophysiology of these white matter lesions remains unknown.

METHODS

In this prospective work, we evaluated magnetic resonance angiography (MRA) scans of the same cohort of 30 patients. Data collected were the presence or absence of vascular lesions, their locations, and severity. Correlations between MRA abnormality and patients/disease characteristics were evaluated. Comparisons between MRA and previous MRI findings were made.

RESULTS

Of 29 evaluable patients, 8 (27.6%) had evidence of arterial stenosis on MRA. The majority of lesions had mild narrowing and mostly involved the internal carotid artery. Five patients (17.2%) had evidence of aneurysms. Low total hemoglobin and high non-transferrin-bound iron levels independently characterized patients with evidence of stenosis on MRA. Among the 18 patients with silent brain infarction on MRI, three had evidence of stenosis on MRA with only one patient having lesions that could explain the silent infarcts.

CONCLUSIONS

Cerebral vasculopathy is common in splenectomized adults with TI. However, large-vessel disease does not explain the occurrence of silent brain infarction. The combined use of MRA and MRI better identifies splenectomized TI adults with neuroimaging abnormalities.

Primary Prophylaxis in Sickle Cell Disease: Is It Feasible? Is It Effective?

Consideration of primary prophylaxis to prevent complications of sickle cell disease (SCD) requires a clear understanding of the earliest manifestations of SCD-related organ injury, a reliable clinical or laboratory tool to detect organ dysfunction, and evidence that an intervention instituted in the presymptomatic state can mitigate disease progression. This review examines the pathophysiology of SCD in organs that may be potential targets for intervention, our current capacity to evaluate early SCD manifestations, results of clinical trials, and opportunities for future interventions.

Cerebral infarction in children with sickle cell disease: a concise overview

Cerebral infarction is a common complication in sickle cell disease. Both overt and silent infarcts evident on neuroimaging have been described. In this article we overview the current knowledge of cerebral infarction in this patient population and discuss recent updates on the role of preventive intervention.

Current concepts in the management of stroke in children with sickle cell disease

Stroke is the most significant complication of sickle cell disease (SCD) in children with the potential for major morbidity and mortality. The recent two decades have witnessed tremendous advancements in understanding the pathophysiology of stroke, risk stratification of children and the role of timely preventative interventions. The aetiopathogenesis, types of stroke and specific risk factors are reviewed here with special emphasis on the role of transcranial Doppler ultrasonogram in the early identification of at-risk children. Published studies on primary and secondary prevention of stroke in children with SCD are analysed with respect to the levels of evidence, in favour of preventative and therapeutic strategies. The roles of the neurologist and the neurosurgeon are highlighted.

Discontinuing prophylactic transfusions increases the risk of silent brain infarction in children with sickle cell disease: data from STOP II

In the STOP II trial, discontinuation of prophylactic transfusions in high risk children with sickle cell disease (SCD) resulted in a high rate of reversion to abnormal blood-flow velocities on transcranial Doppler (TCD) ultrasonography and strokes. We analyzed data from STOP II to determine the effect of discontinuing transfusions on the development or progression of silent brain infarcts on magnetic resonance imaging (MRI). At study entry, 21 of 79 (27%) patients had evidence of silent infarcts. There were no statistically significant differences in baseline characteristics between patients with normal brain MRI or silent infarcts at study entry. At study end, 3 of 37 (8.1%) patients in the continued-transfusion group developed new brain MRI lesions compared with 11 of 40 (27.5%) in the transfusion-halted group (P = .03). The total number of lesions remained essentially unchanged decreasing from 25 to 24 in the continued-transfusion group while increasing from 27 to 45 in transfusion-halted patients. Thus, discontinuation of transfusions in children with SCD and abnormal TCD who revert to low-risk increases the risk of silent brain infarction. Together with data from STOP, these findings demonstrate that transfusions prevent the development of silent infarcts in patients with SCD and abnormal TCD but normal MRA.

Upper airway genioglossal activity in children with sickle cell disease

STUDY OBJECTIVES

The prevalence of obstructive sleep apnea syndrome (OSAS) in sickle cell disease (SCD) has been reported to be higher than that in the general pediatric population. However, not all subjects with SCD develop OSAS. We hypothesized that SCD patients with OSAS have a blunted neuromuscular response to subatmospheric pressure loads during sleep, making them more likely to develop upper airway collapse.

DESIGN

Subjects with SCD with and without OSAS underwent pressure-flow measurements during sleep using intraoral surface electrodes to measure genioglossal EMG (EMGgg). Two techniques were applied to decrease the nasal pressure (P(N)) to subatmospheric levels, resulting in an activated and relatively hypotonic upper airway. The area under the curve of the inspiratory EMGgg moving time average was analyzed. EMGgg activity was expressed as a percentage of baseline. Changes in EMGgg in response to decrements in nasal pressure were expressed as the slope of the EMGgg vs. nasal pressure (slope of EMGgg-P(N)).

SETTING

Sleep laboratory.

PARTICIPANTS

4 children with SCD and OSAS and 18 children with SCD but without OSAS.

RESULTS

THE MAJOR FINDINGS OF THIS STUDY WERE: (1) using the activated but not the hypotonic technique, the slope of EMGgg-P(N) was more negative in SCD controls than SCD OSAS; (2) the slope of EMGgg-P(N) was significantly lower using the activated technique compared to the hypotonic technique in SCD controls only; (3) similarly, the critical closing pressure, Pcrit, was more negative using the activated technique than the hypotonic technique in SCD controls but not in SCD OSAS.

CONCLUSION

This preliminary study has shown that children with SCD but without OSAS have more prominent upper airway reflexes than children with SCD and OSAS.

Current strategies for the management of children with sickle cell disease

Children with sickle cell disease may present to doctors anywhere in the world. In developed countries, neonatal screening allows early identification and management of the disease, mostly through daily antibioprophylaxis, immunizations and education of the parents. Stroke prevention relies on the detection of high-risk patients by annual transcranial Doppler ultrasonography from 2 to 16 years of age. Annual check-ups aim to detect early organ deficiencies. The most frequent complications are pain, infections and acute anemia; they may occur in combination. Approximately 10% of children have severe sickle cell disease that may require chronic blood transfusion, hydroxyurea or hematopoietic stem cell transplantation. Comprehensive management programs have dramatically increased survival, and most patients now reach adulthood.

Genetic risk factors for stroke in the genome-wide association era

IMPORTANCE OF THE FIELD

Recent genome-wide association studies (GWASs) have renewed interest in genetic determinants of a wide range of complex traits and disorders, including stroke.

AREAS COVERED IN THIS REVIEW

This paper reviews the current knowledge of genes that contribute to rare monogenic forms of stroke as well as more common 'garden variety' forms, focusing on the results of GWASs. Potential clinical pharmacogenetic and diagnostic applications of this information are considered. Publications from 1990 to September 2010 were identified through a Medline search using terms 'human stroke' and 'genetics', 'monogenic', 'familial', 'mutation', 'genome-wide association study', 'polymorphism', or 'genotype'.

WHAT THE READER WILL GAIN

The review synthesizes and collates the current understanding of genes that are involved across a range of stroke subphenotypes.

TAKE HOME MESSAGE

The complexity of stroke will make translation of genetic findings into new diagnostic or therapeutic tools relatively more challenging than for some other conditions and tempers the authors' enthusiasm for the eventual clinical utility of this information.

High reticulocyte count is an independent risk factor for cerebrovascular disease in children with sickle cell anemia

BACKGROUND

Transcranial Doppler ultrasonography (TCD) is an important way of detecting risk of ischemic stroke in children with sickle cell anemia.

PROCEDURE

A random sample of 262 FS-hemoglobin children from a newborn screening inception cohort in Brazil (1998-2005) was followed up to May 2009. Pulsed TCD followed STOP protocol. Children with mean blood flow velocity < 170 cm/sec in cerebral arteries were classified as low risk; between 170 and 184, low conditional risk; between 185 and 199, high conditional risk; and ≥ 200, high risk.

RESULTS

Median age, 6.2 years (2-11.2 years); 147 female; 13 children (5%) had ischemic stroke prior to TCD; 186/249 (74.7%) were classified as low risk; 19 (7.6%) as low conditional; 7 (2.8%) as high conditional; and 8 (3.2%) as high risk; inadequate tests, 11.6%. The probability of ischemic stroke at 10 years was 8.3% (SEM 2.3%); of stroke or high-risk TCD 15.6% (3.5%). Children with stroke or altered TCD (conditional and high risk) were compared to children with normal examinations. They were younger (P = 0.03), with lower hemoglobin (P = 0.003), higher leukocytosis (P = 0.015), and higher reticulocytosis (P < 0.001). Episodes per year of acute chest syndrome were also higher in that group, but not significantly (P = 0.09). Reticulocytosis remained the only significant variable upon multivariate analysis (P = 0.004). Basilar and middle cerebral artery velocities were significantly correlated (R = 0.55; P < 0.001).

CONCLUSIONS

Probability of stroke was similar to international reports; of belonging to high-risk group, lower. High-reticulocyte count was the most important factor associated with cerebrovascular disease. Basilar artery velocity > 130 cm/sec seems to be an indirect sign of an underlying cerebrovascular disease.

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.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Sickle cell biomechanics

As the predominant cell type in blood, red blood cells (RBCs) and their biomechanical properties largely determine the rheological and hemodynamic behavior of blood in normal and disease states. In sickle cell disease (SCD), mechanically fragile, poorly deformable RBCs contribute to impaired blood flow and other pathophysiological aspects of the disease. The major underlying cause of this altered blood rheology and hemodynamics is hemoglobin S (HbS) polymerization and RBC sickling under deoxygenated conditions. This review discusses the characterization of the biomechanical properties of sickle RBCs and sickle blood as well as their implications toward a better understanding of the pathophysiology of the disease.

Pediatric stroke: the importance of cerebral arteriopathy and vascular malformations

PURPOSE

Population-based estimates of the annual incidence of childhood stroke range from 2 to 13 per 100,000 person-years. More than half of children who have had a stroke have long-term neurological sequelae. The goal of this article is to review recent literature on both hemorrhagic and ischemic stroke in children with a focus on cerebral arteriopathy and vascular malformations as stroke risk factors. Additionally, we review diagnostic studies for childhood stroke, outcome data, and regional and geographic practice differences.

METHODS

PubMed was searched using the terms child, childhood, pediatric, stroke, ischemic, intracerebral hemorrhage, vasculopathy, and vascular malformation. Reference lists of these articles were reviewed for additional key publications. Preference was given to articles published since the year 2000; however, seminal articles in the field were also reviewed.

RESULTS

Pediatric stroke is a heterogeneous disorder and a major cause of morbidity in the pediatric population. Five-year recurrence risk is estimated to be 5-19%. Children with cerebrovascular abnormalities are at the highest risk of recurrence (66% at 5 years for ischemic stroke in one study). Furthermore, cerebral arteriopathy including arterial dissection may account for up to 80% of childhood stroke in otherwise healthy children.

CONCLUSION

In many cases, evaluation and treatment of pediatric stroke is not evidence-based, and regional and geographic variations in practice patterns exist. Ultimately multicenter cohort studies and dedicated pediatric clinical trials are essential to establish comprehensive evidence-based guidelines for pediatric stroke care.