Congenital dyserythropoietic anemia type I: report of a pair of siblings in Japan.

This is the first case of two siblings with congenital dyserythropoietic anemia (CDA) type I to be reported from a Japanese family. Both of these cases showed characteristic morphological aberrations of erythroid precursors, ineffective erythropoiesis, and negative acidified serum test. The ultrastructural study of erythroblasts also revealed characteristics quite compatible with CDA type I.