Mutations in SEC23B have been identified in several familial cases of congenital dyserythropoietic anemia (CDA) type II, a form of anemia due to ineffective erythropoiesis that is characterized by phenotypic variability, although interestingly, these patients do not have evident abnormalities in the MCV or MCH (Schwarz et al. 2009). The gene discussed is SEC23B; the disease is anemia.