SPINT3 (serine peptidase inhibitor, Kunitz type 3) is a reproductive tract-specific gene located on chromosome 20.1 that encodes a secreted 7.6 kDa protein containing a Kunitz protease inhibitor domain 1. The gene is predominantly expressed in the epididymis 1, a male reproductive tissue critical for sperm maturation. SPINT3 belongs to a conserved syntenic gene cluster with WFDC and other SPINT family members that have been preserved across 96 million years of mammalian evolution, suggesting functional importance 2. However, CRISPR/Cas9 knockout studies demonstrate that SPINT3 is individually dispensable for male mouse fertility, as Spint3 single-gene knockouts display normal reproductive function 32. The recombinantly produced SPINT3 protein lacks inhibitory activity against eight common proteases (trypsin, chymotrypsin, plasmin, thrombin, factor Xa, elastase, urokinase, and PSA) tested in vitro, suggesting either a narrow substrate specificity or alternative non-inhibitory functions 1. Genetically predicted circulating SPINT3 levels were associated with decreased ovarian cancer risk in Mendelian randomization analysis 4, though the mechanistic basis requires further investigation. Additional research is needed to clarify SPINT3's specific biological role in reproductive physiology.