Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0039730 (thalassemia)
 10,305 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hereditary pyropoikilocytosis (HPP) is a recessively inherited hemolytic anemia characterized by severe poikilocytosis and red blood cell fragmentation. HPP red blood cells are partially deficient in spectrin and contain a mutant alpha or beta-spectrin that is defective in terms of spectrin self-association. Although the nature of the latter defect has been studied in considerable detail and many mutations of alpha-spectrin and beta spectrin have been identified, the molecular basis of spectrin deficiency is unknown. Here we report two mechanisms underlying spectrin deficiency in HPP. The first mechanism involves a thalassemia-like defect characterized by a reduced synthesis of alpha-spectrin as shown by studies involving synthesis of spectrin in two unrelated HPP probands and their parents: One parent carries the elliptocytogenic spectrin mutation, whereas the other parent is fully asymptomatic. Peripheral blood mononuclear cells as a source of erythroid burst-forming unit (BFUe) were cultured in a two-phase liquid culture system that gives rise to terminally differentiated erythroblasts. Pulse-labeling studies of an equal number of erythroblasts or morphologically identical maturity showed that the synthesis of alpha-spectrin as well as the mRNA levels as measured by the competitive polymerase chain reaction (PCR) method are markedly reduced in the presumed asymptomatic carriers and the HPP probands. In contrast, the synthesis and mRNA levels of beta-spectrin were normal. These results constitute a direct demonstration of an alpha-spectrin synthetic defect in a subset of asymptomatic carriers of HPP and HPP probands. The second mechanism underlying spectrin deficiency involves increased degradation of mutant spectrin before its assembly on the membrane. This is evidenced by pulse labeling studies of erythroblasts from a patient with HPP associated with a homozygous state for spectrin alpha I/46 mutation (leu-pro mutation at AA 207 of alpha-spectrin). These studies showed that although spectrin is synthesized in the cytosol in normal amounts, the rate of turnover of alpha-spectrin is faster resulting in about 40% to 50% reduced assembly of alpha-spectrin and beta-spectrin on the membrane. Thus, spectrin deficiency in this case is at least in part caused by increased susceptibility of the mutant spectrin to degradation before its assembly on the membrane. We conclude that at least two separate mechanisms underlie the molecular basis of spectrin deficiency in HPP.
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PMID:Molecular basis of spectrin deficiency in hereditary pyropoikilocytosis. 836 14

Thrombosis is a major complication of human hemolytic anemias such as sickle cell disease, thalassemia, and severe hereditary spherocytosis (HS). Mice with severe HS and severe hereditary elliptocytosis (HE) also suffer from thrombosis, with incidences ranging from 15 and 22% in beta-spectrin- and ankyrin-deficient mice, respectively, to 85 to 100% in alpha-spectrin-deficient and band 3 knockout mice. A contributing factor to thrombosis could be loss of phospholipid asymmetry of the mutant red blood cells (RBCs), with concomitant exposure of the aminophospholipid phosphatidylserine (PS). Increased PS exposure occurs in RBCs from sickle cell and thalassemia patients and in RBCs from band 3-deficient mice. To determine if increased PS exposure correlates with thrombotic risk in HS and HE mice with ankyrin, beta-spectrin, and alpha-spectrin deficiencies, measurements of FITC-labeled annexin V binding to externalized PS on RBCs were performed. PS exposure is elevated in all mice with HS and HE, but the percentage of RBCs with exposed PS does not correlate with thrombotic risk in these mice.
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PMID:Erythroid phosphatidyl serine exposure is not predictive of thrombotic risk in mice with hemolytic anemia. 1077 78