CDIN1 (CDAN1 interacting nuclease 1) is an essential protein required for normal erythroid cell differentiation and red blood cell production. CDIN1 physically interacts with CDAN1 (Codanin-1) to form cytosolic complexes that engage histone H3-H4 chaperones ASF1A and ASF1B 1. This interaction is critical for regulating histone chaperoning during erythropoiesis, as CDAN1 sequesters ASF1A/B by occupying their functional binding sites 1. Mutations in CDIN1 cause Congenital Dyserythropoietic Anemia type 1B (CDA-1B), a rare hereditary disorder characterized by ineffective erythropoiesis and abnormal red blood cell development 2. CDIN1 variants impair erythroid differentiation with disruptions in transcription, cell proliferation, and histone regulation 2. At the cellular level, CDIN1 dysfunction causes delays in terminal erythroid differentiation, increased erythroblast proliferation, widespread chr15 accessibility changes, and abnormal nucleolar structure and function 3. Both CDAN1 and CDIN1 proteins localize to nucleoli, suggesting roles in ribosomal biogenesis or nucleolar function 3. CDA-1B presents clinically with macrocytic/normocytic anemia, splenomegaly, and iron overload; approximately 41.7% of CDA-1B patients require transfusion support 2. Understanding CDIN1 function has advanced diagnosis and illuminated pathogenic mechanisms underlying ineffective erythropoiesis.