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

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

Transfusion and alloimmunization in sickle cell disease. The Cooperative Study of Sickle Cell Disease

The abnormal shape and poor deformability of the sickled erythrocyte (RBC) have generally been held responsible for the microvascular occlusions of sickle cell disease. However, there is no correlation between the clinical severity of this disease and the presence of sickled RBC. In searching for additional factors that might contribute to the pathophysiology of sickle cell disease, we have investigated the possibility that sickle RBC might be less than normally repulsive of the vascular endothelium. After RBC suspensions are allowed to settle onto plates of cultured human endothelial cells, normal RBC are completely removed by as few as six washes. In contrast, sickle RBC remain adherent despite multiple washes. On subconfluent culture plates, normal RBC are distributed randomly, whereas sickle RBC cluster around endothelial cells. Sickle RBC adherence is not enhanced by deoxygenation but does increase with increasing RBC density. The enzymatic removal of membrane sialic acid greatly diminishes the adherence of sickle RBC to endothelial cells, suggesting that sialic acid participates in this abnormal cell-cell interaction. Although net negative charge appears normal, sickle RBC mainfest an abnormal clumping of negative surface charge as demonstrated by localization of cationized ferritin. These abnormalities are reproduced in normal RBC loaded with nonechinocytogenic amounts of calcium. We conclude that sickle RBC adhere to vascular endothelial cells in vitro, perhaps caused by a calcium-induced aberration of membrane topography. This adherence may be a pathogenetic factor in the microvascular occlusions characteristic of sickle cell disease.

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Abnormal Adherence of Sickle Erythrocytes to Cultured Vascular Endothelium: POSSIBLE MECHANISM FOR MICROVASCULAR OCCLUSION IN SICKLE CELL DISEASE

It has long been recognized that certain ordinarily salutary drugs may produce an acute hemolytic anemia in some susceptible individuals. The 8-aminoquinoline antimalarial, pamaquine (plasmoquine), was such a medication. It was the investigation of the hemolytic effect of pamaquine and its derivatives which led to the recognition that hereditary red cell enzyme deficiencies could produce hemolytic disease.

Glucose-6-phosphate dehydrogenase deficiency.

The ability to predict the phenotype of an individual with sickle cell anaemia would allow a reliable prognosis and could guide therapeutic decision making. Some risk factors for individual disease complications are known but are insufficiently precise to use for prognostic purposes; predicting the global disease severity is not yet possible. Genetic association studies, which attempt to link gene polymorphisms with selected disease subphenotypes, may eventually provide useful methods of foretelling the likelihood of certain complications and allow better individualized treatment.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2141.2005.05411.x

Predicting clinical severity in sickle cell anaemia.

Twenty-one patients with mild sickle cell disease (MSD) between 18 and 56 years of age had mild, infrequent, or no pain crises, were active or employed, and led relatively normal lives. Mean hemoglobin concentration, reticulocyte count, and hemoglobin A2and F levels did not distinguish this group from a smaller group of patients with typical sickle cell anemia (SSA). On the basis of electrophoresis, hemoglobin H preparations, and distribution of hemoglobin F in erythrocytes, there was no evidence for thalassemia, hereditary persistence of hemoglobin F, or other hemoglobinopathies that might modify the course of SSA. There may be many host or environmental factors that protect individuals with MSD. Knowledge of these may suggest new therapeutic strategies for the control of SSA.

https://jamanetwork.com/HttpHandlers/ArticlePdfHandler.ashx?journal=jama&articleId=347814&pdfFileName=jama_224_3_005.pdf

Mild Sickle Cell Disease: Clinical and Laboratory Studies

Mild forms of alpha thalassaemia are difficult to detect in adults. Since alpha thalassaemia existing with structural defects of the beta chain of haemoglobin may lead to decreased levels of the abnormal haemoglobin, we examined individuals having sickle-cell trait for the possible coexistence of alpha thalassaemia. Patients with sickle-cell trait having haemoglobin-S (Hb-S) levels less than commonly expected were compared to two control groups--one with sickle-cell trait and the usual levels of Hg S and one with normal haemoglobin. Twenty-one patients with sickle-cell trait having Hb-S concentrations below 35% had 65.8% Hb A, 31.8% Hb S, and a mean corpuscular volume of 81.6 fl. Studies of the relative rates of alpha-, betaS- and betaA-chain synthesis in 14 of these individuals showed a mean alpha:beta ratio of 0.76. In patients with normal haemoglobin as well as in sickle-cell trait with Hb-S levels above 35%, this ratio was unity. These findings are consistent with the presence of alpha thalassaemia in patients with sickle-cell trait who have lower than usual levels of Hb S and microcytosis.

Alpha thalassaemia in adults with sickle-cell trait.

The variability in the clinical expression of sickle cell anemia led us to study factors which might influence the course of this disease. We examined erythrokinetics, blood volumes, and variables which influence hemoglobin function in a group of adults with sickle cell anemia of varying degrees of clinical severity. We were unable to correlate any single measurement with the clinical course; however, our patient sample was small and the data suggested areas for further study. An expansion of plasma volume noted in all patients. This made it difficult to predict red cell mass from the hemoglobin level, which consistently underestimated its magnitude. The red cell production index and iron turnover values indicated that there is often a suboptimal erythropoietic response to anemia in sickle cell disease.

Sickle cell anemia: erythrokinetics, blood volumes, and a study of possible determinants of severity.

The diseases commonly confused with sickle cell anemia include sickle cell beta-thalassemia in which synthesis of betaA-chains are completely suppressed (HbS-betao-thalassemia). We obtained hematologic measurements and studied globin biosynthesis in five patients with this disorder and compared the results with those obtained in five patients with "mild" sickle cell anemia and seven individuals with sickle cell-beta-thalassemia having hemoglobin A levels of 20-30% (HbS-beta+-thalassemia). A distinction between HbS-betao-thalassemia and sickle cell anemia was not always possible on clinical, hematologic, or electrophoretic grounds. Thalassemia heterozygotes had hypochromia and microcytosis, not generally a feature of sickle cell anemia, although overlap of values did exist. The ratio of alpha to non-alpha, or alpha to betaS-chains in sickle cell anemia approximated unity, whereas patients with HbS-betao-thalassemia had a deficit of beta-chain production relative to that of the alpha-chain. The differentiation of HbS-betao-thalassemia and sickle cell anemia can be best made on the basis of family or biosynthetic study. We estimated the regional prevalence of HbS-betao-thalassemia to be 1:23,000 of the black population.

Clinical, hematologic and biosynthetic studies in sickle cell-betao-thalassemia: a comparison with sickle cell anemia.

Hemoglobin electrophoresis on polyacrylamide gels is a technique applicable in the clinical laboratory that processes moderately large numbers of specimens. Rapid and precise, it yields reproducible quantitative data when the hemoglobins are eluted from the gel and their concentrations determined spectrophotometrically. Hemoglobin A2 measurements were reproducible and did not differ from those measured by column chromatography on DEAE-cellulose. Concentrations of hemoglobin A2 in the blood of patients with sickle cell anemia were significantly higher than in normal individuals and individuals with sickle trait, but significantly lower than is the case for patients with beta-thalassemia minor.

Bernard J. Dreiling

Papers

Mild Sickle Cell Disease: Clinical and Laboratory Studies

Alpha thalassaemia in adults with sickle-cell trait.

Sickle cell anemia: erythrokinetics, blood volumes, and a study of possible determinants of severity.

Clinical, hematologic and biosynthetic studies in sickle cell-betao-thalassemia: a comparison with sickle cell anemia.

Electrophoresis of Hemoglobin on Polyacrylamide Gels: Precise Method for Measurement of Hemoglobin A2