NYD-SP15 (testis development protein NYD-SP15), also known as CDADC1 (cytidine and dCMP deaminase domain containing 1), is a widely expressed protein with predominant expression in the testis, liver, spleen, kidney, thymus and placenta. NYD-SP15 is 514 amino acids in length and belongs to the cytidine and deoxycytidylate deaminase family. It is developmentally regulated with higher expression in adult testis than fetal testis and is believed to participate in spermatogenesis and testicular development. This suggests that NYD-SP15 may be a determining factor in male infertility. Due to alternative splicing events, four transcript variants exist for NYD-SP15.