Mutations in the SEC23B gene (Sec23 homolog B; MIM# 610512, 20p11.23) cause the vast majority of the congenital dyserythropoietic anemia Type II (CDA II MIM# %224100), an autosomal recessive disorder that represents the most common form of CDAs. The gene discussed is SEC23B; the disease is Congenital dyserythropoietic anemia type II.