Human mutations in SEC23B result in congenital dyserythropoietic anemia type II (CDAII) (17, 18), characterized by mild to moderate anemia, binucleated/multinucleated erythroblasts in the bone marrow, double membrane appearance in the red blood cell (RBC), and a faster shift and narrower band of RBC membrane protein band 3 on SDS-PAGE (19, 20). The gene discussed is SEC23B; the disease is congenital dyserythropoietic anemia type 2.