Cytidine deaminase is an enzyme that in humans is encoded by the CDA gene.
This gene encodes an enzyme involved in pyrimidine salvaging. The encoded protein forms a homotetramer that catalyzes the irreversible hydrolytic deamination of cytidine and deoxycytidine to uridine and deoxyuridine, respectively. It is one of several deaminases responsible for maintaining the cellular pyrimidine pool. Mutations in this gene are associated with decreased sensitivity to the cytosine nucleoside analogue cytosine arabinoside used in the treatment of certain childhood leukemias.
A related activation-induced (cytidine) deaminase (AID) regulates antibody diversification, especially the process of somatic hypermutation.