The heterogeneous disorder, CDA, is characterized by ineffective erythropoiesis and ultrastructural alterations of late erythroblasts. Three major types have been described: Type I with macrocytosis, Type II (HEMPAS) with abnormal RBC antigens,and Type III with gigantoblasts. Studies of RBC antigens, metabolism, lipids, ferrokinetics, in vitro erythroid colony formation, and globinchain synthesis were performed in a 15 year old male with atypical CDA. Ferrokinetics showed ineffective erythropoiesis, chromium survival was shortened, bone marrow revealed 25-35% 2-3 lobed late normoblasts, and electron microscopy showed dyserythropoiesis but no “double membranes” or internuclear bridges. Acidhemolysis tests with 20 ABO compatible sera were negative and hemolysis by anti-I, anti-i, or hemolytic anti-B was not increased. Activity of i matched that of fetal cells. Increased membrane phosphatidyl choline (36%, normal 29%) and decreased sphingomyelin (19%, normal 27%) were noted. The ratio of α and β chain synthesized by peripheral blood and BM RBC was normal; glycolytic intermediates and enzymes were normal except for pyruvatekinase. Erythroid colony formation in vitro was normal; dyserythropoiesis was not observed. The findings are compatible with CDA Type IV, a rare disorder with morphologic features of Type II but lacking abnormal serology. Attempts to apply distinctive ultrastructural features to CDA may be misleading.

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Miller, D., Sitarz, A., Lieberman, P. et al. CONGENITAL DYSERYTHROPOIETIC ANEMIA (CDA) TYPE IV. Pediatr Res 11, 477 (1977).

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