Congenital dyserythropoietic anemia type IIIb (CDAN3B) is an autosomal recessive disorder characterized macrocytic anemia, aberrant giant multinucleated erythroblasts in the bone marrow, and skull defects secondary to severe anemia with ineffective erythropoiesis (summary by Hernandez et al., 2023). For a general description and a discussion of genetic heterogeneity of CDA, see CDAN1 (224120). [from OMIM]