Bone marrow erythroblasts from a patient with congenital dyserythropoietic anemia type I: chromatin bridges between two adjacent nuclear lobes (arrow-head), spongy appearance of the chromatin (stars), and widening of nuclear pores with nucleus invasion by the cytoplasm (arrow) are characteristic ultrastructural features of the disease. Original magnification × 10,400. (Courtesy of Elisabeth M. Cramer and Josette Guichard, INSERM U.91, Hopital Henri Mondor, 94010 Creteil, France.)