From OMIM
CDA type I is a rare inherited red blood cell disorder characterized by macrocytic anemia, ineffective erythropoiesis, and secondary hemochromatosis. It is occasionally associated with bone abnormalities, especially of the hands and feet (acrodysostosis), nail hypoplasia, and scoliosis (Tamary et al., 2005). Striking morphologic abnormalities of erythroblasts, reviewed by Wickramasinghe and Wood (2005), include the 'Swiss-cheese' abnormality of erythroblasts on electron microscopy. Four types of CDA, all of which show show ineffective erythropoiesis and multinuclear erythroblasts, have been characterized by clinical and hematopoietic findings. The classification of the first 3 types is based on that described by Wendt and Heimpel (1967). Type I is characterized by megaloblastic changes. Type II (224100), which is more common, is characterized by normocytic binuclear or multinuclear red cells, which on electron microscopy contain double cytoplasmic membranes. Type III (see, e.g., 105600) has prominent erythroblastic multinuclearity forming 'gigantoblasts' with up to 12 nuclei. Type IV (see 613673) is the designation given to a form of CDA with characteristics different from those of types I, II, and III (Wickramasinghe et al., 1991; Arnaud et al., 2010). Genetic Heterogeneity of Congenital Dyserythropoietic Anemia CDAN1B (615631) is caused by mutation in the CDIN1 gene (615626) on chromosome 15q14; CDAN2 (224100) is caused by mutation in the SEC23B gene (610512) on chromosome 20p11; CDAN3A (105600) is caused by mutation in the KIF23 gene (605064) on chromosome 15q23; CDAN3B (619789) is caused by mutation in the RACGAP1 gene (604980) on chromosome 12q13; and CDAN4A (613673) and CDAN4B (620969) are both caused by mutation in the KLF1 gene (600599) on chromosome 19p13. For a possible additional form of CDA type I, see 603529.  http://www.omim.org/entry/224120