Patient iPSC-derived erythroblasts recapitulate CDA I pathology. Light microscopy and transmission electron microscopy (TEM) of normal and CDA I iPSC-derived erythroblasts generated in ∼30 day differentiation cultures. Inserts show higher magnification of the marked areas. CDA I cells exhibit occasional internuclear bridges on light microscopy (third panel). TEM showed abnormal spongy chromatin structure in most CDA I erythroid precursors (fourth panel).