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      Sickle-cell disease.

      Lancet
      Acute Chest Syndrome, etiology, therapy, Africa, Anemia, Sickle Cell, blood, classification, complications, diagnosis, epidemiology, Antisickling Agents, therapeutic use, Blood Transfusion, Disease Susceptibility, Erythrocytes, pathology, Gene Transfer Techniques, Haplotypes, Heart Diseases, Hematopoietic Stem Cell Transplantation, Hematopoietic Stem Cells, Hemolysis, Humans, Hydroxyurea, Hypertension, Pulmonary, Iron Chelating Agents, Kidney Diseases, Mass Screening, Nervous System Diseases, Pain, Pain Management, Polymerization, Severity of Illness Index

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          Abstract

          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. Copyright © 2010 Elsevier Ltd. All rights reserved.

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          Vascular endothelial cells synthesize nitric oxide from L-arginine.

          Nitric oxide (NO) released by vascular endothelial cells accounts for the relaxation of strips of vascular tissue and for the inhibition of platelet aggregation and platelet adhesion attributed to endothelium-derived relaxing factor. We now demonstrate that NO can be synthesized from L-arginine by porcine aortic endothelial cells in culture. Nitric oxide was detected by bioassay, chemiluminescence or by mass spectrometry. Release of NO from the endothelial cells induced by bradykinin and the calcium ionophore A23187 was reversibly enhanced by infusions of L-arginine and L-citrulline, but not D-arginine or other close structural analogues. Mass spectrometry studies using 15N-labelled L-arginine indicated that this enhancement was due to the formation of NO from the terminal guanidino nitrogen atom(s) of L-arginine. The strict substrate specificity of this reaction suggests that L-arginine is the precursor for NO synthesis in vascular endothelial cells.
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            The clinical sequelae of intravascular hemolysis and extracellular plasma hemoglobin: a novel mechanism of human disease.

            The efficient sequestration of hemoglobin by the red blood cell membrane and the presence of multiple hemoglobin clearance mechanisms suggest a critical need to prevent the buildup of this molecule in the plasma. A growing list of clinical manifestations attributed to hemoglobin release in a variety of acquired and iatrogenic hemolytic disorders suggests that hemolysis and hemoglobinemia should be considered as a novel mechanism of human disease. Pertinent scientific literature databases and references were searched through October 2004 using terms that encompassed various aspects of hemolysis, hemoglobin preparations, clinical symptoms associated with plasma hemoglobin, nitric oxide in hemolysis, anemia, pulmonary hypertension, paroxysmal nocturnal hemoglobinuria, and sickle-cell disease. Hemoglobin is released into the plasma from the erythrocyte during intravascular hemolysis in hereditary, acquired, and iatrogenic hemolytic conditions. When the capacity of protective hemoglobin-scavenging mechanisms has been saturated, levels of cell-free hemoglobin increase in the plasma, resulting in the consumption of nitric oxide and clinical sequelae. Nitric oxide plays a major role in vascular homeostasis and has been shown to be a critical regulator of basal and stress-mediated smooth muscle relaxation and vasomotor tone, endothelial adhesion molecule expression, and platelet activation and aggregation. Thus, clinical consequences of excessive cell-free plasma hemoglobin levels during intravascular hemolysis or the administration of hemoglobin preparations include dystonias involving the gastrointestinal, cardiovascular, pulmonary, and urogenital systems, as well as clotting disorders. Many of the clinical sequelae of intravascular hemolysis in a prototypic hemolytic disease, paroxysmal nocturnal hemoglobinuria, are readily explained by hemoglobin-mediated nitric oxide scavenging. A growing body of evidence supports the existence of a novel mechanism of human disease, namely, hemolysis-associated smooth muscle dystonia, vasculopathy, and endothelial dysfunction.
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              Mortality in sickle cell disease. Life expectancy and risk factors for early death.

              Information on life expectancy and risk factors for early death among patients with sickle cell disease (sickle cell anemia, sickle cell-hemoglobin C disease, and the sickle cell-beta-thalassemias) is needed to counsel patients, target therapy, and design clinical trials. We followed 3764 patients who ranged from birth to 66 years of age at enrollment to determine the life expectancy and calculate the median age at death. In addition, we investigated the circumstances of death for all 209 adult patients who died during the study, and used proportional-hazards regression analysis to identify risk factors for early death among 964 adults with sickle cell anemia who were followed for at least two years. Among children and adults with sickle cell anemia (homozygous for sickle hemoglobin), the median age at death was 42 years for males and 48 years for females. Among those with sickle cell-hemoglobin C disease, the median age at death was 60 years for males and 68 years for females. Among adults with sickle cell disease, 18 percent of the deaths occurred in patients with overt organ failure, predominantly renal. Thirty-three percent were clinically free of organ failure but died during an acute sickle crisis (78 percent had pain, the chest syndrome, or both; 22 percent had stroke). Modeling revealed that in patients with sickle cell anemia, the acute chest syndrome, renal failure, seizures, a base-line white-cell count above 15,000 cells per cubic millimeter, and a low level of fetal hemoglobin were associated with an increased risk of early death. Fifty percent of patients with sickle cell anemia survived beyond the fifth decade. A large proportion of those who died had no overt chronic organ failure but died during an acute episode of pain, chest syndrome, or stroke. Early mortality was highest among patients whose disease was symptomatic. A high level of fetal hemoglobin predicted improved survival and is probably a reliable childhood forecaster of adult life expectancy.
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