Congenital dyserythropoietic anemia type IIIa (CDAN3A) is a rare autosomal dominant hematologic disorder characterized by nonprogressive mild to moderate hemolytic anemia, macrocytosis in the peripheral blood, intravascular hemolysis, and giant multinucleated erythroblasts in the bone marrow. The disorder results from ineffective erythropoiesis. Laboratory studies show evidence of intravascular hemolysis, including increased thymidine kinase, lactate dehydrogenase, and/or undetectable haptoglobin (summary by Lind et al., 1995; Liljeholm et al., 2013). For a discussion of genetic heterogeneity of congenital dyserythropoietic anemia, see 224120.