Congenital dyserythropoietic anemia (CDA)

Three classical types were defined by marrow morphology, and all three show marrow hypercellularity with distinct erythropoietic hyperplasia.
CDA type I can be diagnosed when >20% of the erythroblasts have an abnormal chromatin structure (general appearance of a spongy nucleus), 2% to 5% are binucleated erythroid precursor cells and fine chromatin bridges involving polychromatic erythroblasts are present. Peripheral blood RBC morphology is characterized by anisocytosis and poikilocytosis, and occasionally Cabot rings are seen (unique to type I, not seen in type II & III)
In CDA type II, usually 10% to 40% of the late normoblasts are binucleated with equal size of the two nucleithe fraction. Karyorrhexis is seen in >2% of the erythroblasts.
In CDA Type III macrocytosis and megaloblastic erythroid maturation and giant multinucleated erythroid precursors with up to 12 nuclei per cell is observed in 10% to 40% of erythroid precursors cells.